REVIEW
Fungicide impacts on photosynthesis in crop plants
Anne-Noe
¨lle Petit ?Florence Fontaine ?
Parul Vatsa ?Christophe Cle
′ment ?Nathalie Vaillant-Gaveau
Received:27March 2011/Accepted:12January 2012/Published online:1February 2012óSpringer Science+Business Media B.V.2012
Abstract Fungicides are widely used to control pests in crop plants.However,it has been reported that these pes-ticides may have negative effects on crop physiology,especially on photosynthesis.An alteration in photosyn-thesis might lead to a reduction in photoassimilate pro-duction,resulting in a decrease in both growth and yield of crop plants.For example,a contact fungicide such as copper inhibits photosynthesis by destroying chloroplasts,affecting photosystem II activity and chlorophyll biosyn-thesis.Systemic fungicides such as benzimidazoles,ani-lides,and pyrimidine are also phytotoxic,whereas azoles stimulate photosynthesis.This article focuses on the available information about toxic effects of fungicides on photosynthesis in crop plants,highlighting the mechanisms of perturbation,interaction,and the target sites of different classes of fungicides.
Keywords Chlorophyll áCrop plants áFungicides áPhotosynthesis áPhotosystems áPhysiology áPhytotoxicity áStomatal closure áStress
Introduction
Fungicides remain a vital solution to the effective control of plant diseases,which are estimated to cause yield reductions of almost 20percent in major food and cash
crops worldwide.The great variety of known fungicides can be classi?ed into two main categories:contact and systemic.Contact fungicides,such as copper or sulfur have a preventive action by killing fungi as their spores germi-nate,before mycelia can grow and develop within plant tissues (Yuste and Gostincar 1999).Since their introduc-tion in the 1960’s,systemic fungicides have gradually replaced older non-systemic products,establishing higher levels of disease control and developing new fungicide markets.Systemic fungicides,known as curative or eradi-cation fungicides,can also kill the fungus when mycelia have penetrated into the parenchyma,stopping the dis-persal or infection within the plant (Table 1,Yuste and Gostincar 1999).Among systemic fungicides,benzimi-dazoles are a group of organic fungicides that are exten-sively used in agriculture along with the other classes of fungicides.
All these types of compounds control a broad range of fungi at relatively low application rates.However,the effects of fungicides on crop growth depend on various factors.Application of fungicides may affect crop physi-ology by various disruptions such as growth reduction,perturbation in the development of reproductive organs,alteration of nitrogen,and/or carbon metabolism leading to a lower nutrient availability for plant growth.The sensi-tivity of some plant species may depend on the develop-mental stage (i.e.more sensitive to the treatments at young stages or during critical events such as reproduction)or the type of pesticides used.
It has been previously reported that in response to a stress,plants often mobilize nutrients and metabolite pro-duction to develop defense mechanisms in detriment to growth (Smith and Moser 1985).Under stress conditions,plants ?rstly trigger their defence response for their sur-vival because of the energetic cost of resistance and
A.-N.Petit áF.Fontaine áP.Vatsa áC.Cle
′ment áN.Vaillant-Gaveau (&)
Laboratoire de Stress,De
′fenses et Reproduction des Plantes,URVVC EA 2069,Universite
′de Reims Champagne-Ardenne,UFR Sciences Exactes et Naturelles,Ba
?timent 18,Moulin de la Housse,BP 1039,51687Reims Cedex 2,France e-mail:nathalie.vaillant-gaveau@univ-reims.fr
Photosynth Res (2012)111:315–326DOI 10.1007/s11120-012-9719-8
Table1Basic chemical characteristics of fungicides(data from International Union of Pure Applied Chemistry) Fungicides,
Formules
Structures Primary mode of action in fungus
Copper and/or sulfate
Bordeaux mixture CuSO4á3Cu(OH)2 3CaSO4Inhibit several enzymes involved in respiration and this multi-site action (Leroux2003)
Kumulus S x Inhibit several enzymes involved in respiration and this multi-site action (Leroux2003)
Cuproxat
3Cu(OH)2CuSO4Inhibit several enzymes involved in respiration and this multi-site action (Leroux2003)
Strobilurine
Kresoxim-methyl C18H19NO
4Inhibits spore germination and mycelial growth(Leroux et al.2002) QoI inhibitors,which act to inhibit the respiratory chain at the level of Complex III(Grossmann et al.1999)
Azoxystrobin C22H17N3O
5
Inhibits spore germination and mycelial growth(Zhang et al.2010) Pyrrole
Fludioxonil C12H6F2N2O
2Perturbe the osmo-regulatory signal transmission pathway(Pillonel and Meyer1997)
Inhibits spore germination and mycelial growth(Leroux et al.2002)
Anilides
Fenhexamid C19H15FN2O
4Inhibits germ-tube elongation and mycelial growth(Ha¨n b ler and Pontzen 1999)
A sterol biosynthesis inhibitor:inhibits the3-keto reductase involved in the enzymatic complex of the sterol C-4demethylation(Debieu et al.2001)
Phthalimide
Folpet
C9H4Cl3NO2
S Inhibits spore germination and mycelial growth Multi-site action(Teisseire et al.1999)
Azoles
Cyazofamid C13H13ClN4O2
S Inhibit mycelial growth
Indirect effect against germination of zoosporangia,zoospore motility, cystospore germination,and oospore formation
Impairment of the ATP energy generation system
Inhibit several enzymes involved in respiration(Mitani et al.2001)
Paclobutrazol C15H20ClN3
O Inhibition of sterol biosynthesis at the14a-demethylation step(Haughan et al.1988)
Triadimefon C14H16ClN3O
2
Sterol C-14demethylation inhibitor(Debieu et al.1995)
growth.The intensity of the stress induced by pesticide application and the intensity of plant response will thus have a subsequent impact on the growth process if the crops overcome the stress.According to the growth reductions observed after agrochemical exposures,plants may react by developing this kind of metabolite reorien-tation.Therefore,the plant carbon and/or nitrogen primary metabolism,which regulates the plant growth rate,appears necessary to be investigated in order to understand more precisely how pesticides can affect the crops(Saladin and Cle′ment2005).
Carbon metabolism is of particular importance for crop culture and is re?ected by both crop’s photosynthetic rate and its management of carbohydrate reserves.Indeed, photosynthesis alteration may lead to a decrease in pho-toassimilate production and thus to plant yield and vigour.
A negative effect of sulfur-containing fungicides(particu-larly lime sulfur)was revealed on apple production by a loss of fruits and a delay in harvest(Palmer et al.2003). However,spray treatments did not in?uence shoot growth, leaf area development or increment in trunk cross-sectional area.Fungicide application programme containing Kocide or slaked lime or use of both together,demonstrated that Black spot incidence(caused by Venturia inaequalis),on fruit at harvest was signi?cantly higher on trees treated with either Kocide or slaked lime compared to the controls.When used together,however,control of Black spot was as good as in the control.Dry eye rot incidence(caused by Botrytis cinerea)was signi?cantly higher on the trees treated with lime sulfur(Palmer et al.2003).Another study about the effect of lime sulfur applied at different stages to apple trees reported leaf phytotoxicity,revealed as necro-sis,and a reduction of yield in terms of?rst class fruits (Holb et al.2003).
As stress increases,various photosynthetic processes may be impaired,leading to a decrease in net photosyn-thesis(Pn),equivalent to CO2assimilation(Fig.1). Stomatal closure,caused by a reduction in stomatal con-ductance(gs),is often considered as an early physiological response to stress,resulting in decreased Pn through lim-ited CO2availability(Ci)in the mesophyll(Krause and Weis1991).Photosynthesis is one of the most studied and best understood physiological process.Detailed biochem-ical models of photosynthesis,including light reactions, electron and proton transport,enzymatic reactions,and regulatory functions have been recently developed(Laisk et al.2006).Life on earth is driven essentially by photo-synthetic solar energy conversion.Photosynthetic organ-isms use light energy for the synthesis of organic molecules.In the case of plants,algae,and cyanobacteria, oxygen is emitted into the atmosphere as a by-product of photosynthesis.Fundamental to the photosynthetic process
Table1continued
Fungicides,
Formules
Structures Primary mode of action in fungus
Hexaconazole C14H17Cl2N3
O
Sterol C-14demethylation inhibitor(Debieu et al.1995)
Propiconazole C15H17Cl2N3O
2
Sterol C-14demethylation inhibitor(Gaita′n et al.2005)
Epoxiconazole C17H13ClFN3
O
Sterol C-14demethylation inhibitor(Debieu et al.1995) Benzimidazoles
Carbendazim C9H9N3O
2Inhibition of microtubule assembly which is due to their binding to tubulin,the main protein of microtubules(Leroux and Descotes1996)
Benomyl C14H18N4O
3Inhibition of microtubule assembly which is due to their binding to tubulin,the main protein of microtubules(Leroux and Descotes1996)
Pyrimethanil C12H13N
3Inhibits germ tube elongation and initial mycelial
Inhibit biosynthesis of methionine affecting cystathionine-b-lyase Prevention of fungal secretion of hydrolytic enzymes(Fritz et al.1997)
is the ability of plants to absorb light energy that is then converted into chemical energy.Light energy is captured by pigments in the light-harvesting complex (LHC)pro-teins and transferred to the reaction centers of the chloro-plast thylakoid membrane.LHC proteins bind to chlorophyll a,chlorophyll b,and carotenoids with weak non-covalent bonds.LHC are assembled into two separate yet biophysically linked photosystems:photosystem I (PSI)and photosystem II (PSII)(Hillier and Babcock 2001).PSII catalyzes light-induced electron transfer from water to plastoquinone.The oxygen-evolving complex,located on the luminal side of PSII is responsible for water oxidation and produces protons,electrons,and molecular oxygen as a by-product (Krause and Weis 1991).The protons are involved in the formation of adenosine triphosphate (ATP),the plant stock of energy,through the ATPase.The elec-trons run along a complex transfer chain ending with the formation of another energetic molecule,nicotinamide adenine dinucleotide phosphate (NADP).Then ferredoxin is reduced by a photochemical reaction at the level of PSI,and the ferredoxin–NADP ?reductase enzyme mediates electron transfer from this reduced protein to NADP with the formation of NADPH necessary for CO 2?xation.An alteration of any one of these processes can lead to
Pn
Fig.1Schematic representation showing the interactions of the main processes in C3photosynthesis in higher plants (according to Baker and Rosenqvist 2004)and impacts of fungicides (North east increase and South east decrease).Photophosphorylation starts with the absorption of light by the light-harvesting antenna complexes (LHCI and LHCII)associated with photosystem II (PSII)and photosystem I (PSI)in the chloroplast thylakoid membrane.This drives electron transport from water via a series of electron carriers to NADP,producing reducing power (NADPH)and a H ?electrochemical potential difference across the membrane.Dissipation of this proton motive force by the passage of H ?back across the membrane through the ATPase drives the production of ATP.Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco)catalyses the assimilation of CO 2with ribulose 1,5-bisphosphate (RubP)in the carboxylation reaction of the Calvin–Benson cycle in the stroma of the chloroplast.The
diffusion of atmospheric CO 2into the leaf is regulated by the stomata in the epidermis.Other reactions of the Calvin–Benson cycle utilize NADPH and ATP to produce triose phosphates,which are required for the synthesis of carbohydrates.NADPH and ATP are also used in a range of other metabolic activities (e.g.nitrogen and sulfur metabolism,lipid and pigment synthesis)in the chloroplast.Rubisco can also catalyse the photorespiratory oxygenation of RubP,which involves consumption of NADPH and ATP by the Calvin–Benson cycle.O 2can also be directly photoreduced by electron transfer from PSI to produce superoxide,which is then rapidly dismutated to hydrogen peroxide,which in turn is detoxi?ed to water;this process is often termed the Mehler-peroxidase reaction or the water–water cycle.Cyt b/f cytochrome b6/f complex;PC plastocyanin;PQ plastoquinone;PQH 2plastoquinol
inhibition.ATP and NADPH are then necessary for the second step,i.e.,the energy-consuming reductive conver-sion of CO2into carbohydrates.These latter reactions follow a cyclic sequence called the Calvin cycle.The key enzyme of the cycle,Ribulose1,5-bisphosphate carboxyl-ase/oxygenase(Rubisco),is a prerequisite for CO2?xation and catalyzes the carboxylation of ribulose1,5-bisphos-phate(RuBP).There is a strong evidence that Pn might thus be limited by other biochemical processes occurring in the mesophyll,such as Rubisco activity and RuBP regen-eration(Krause and Weis1991).
Apart from affecting wide variety of crop plants,fungi-cides have also been reported to be toxic to nitrogen-?xing cyanobacteria(blue-green algae).The effect of pesticides on cyanobacterial populations has been considered to be stim-ulatory at low concentrations and inhibitory at high doses. The rates of photosynthesis and respiration along with chlorophyll content have been shown to decline in the presence of Bavistin,a broad spectrum fungicide,containing 50%WP carbendazim(Rajendran et al.2007).Previously,it has been demonstrated that carbendazim50%WP is effec-tive against a wide range of pathogenic fungi and is highly speci?c in its control of important plant pathogens on a variety of crops,ornamental plants and plantation crops. Dewez et al.(2005)demonstrated that when alga Scenedes-mus obliquus was exposed to different copper concentrations signi?cant inhibition on the growth rate and chlorophyll synthesis was noticed.Phytoremediation with microalgae has been utilized for areas polluted with nutrients or heavy metals (Perales-Vela et al.2006);however,increasing environ-mental pollution by pesticides might lead to consider mic-roalgae as good candidates to remove these contaminants from water at low cost(Dosnon-Olette et al.2010).
The aim of this review is to make a thorough account of the current available information about impacts of fungi-cides on different crop varieties in relation to the photo-synthetic process,relating different families of fungicides, crop varieties,and photosynthetic parameters that are affected.A large number of papers on the topic covered by this review have been published since1978.This review summarizes the main?ndings in the?eld of agriculture, photosynthesis,and fungicides.Furthermore,many articles have reported negative effects of these products,but it does not mean that all fungicides have negative effects.
Effect of contact fungicides on photosynthesis Application of fungicides alters the crop physiology,in terms of growth and development along with nitrogen,and/ or carbon metabolism(Saladin and Cle′ment2005).This former physiological trait is fundamental for crop culture and is re?ected by both photosynthetic rate and mobilization of carbohydrate reserves.Indeed,as plants rely on their ability to assimilate carbon through photo-synthesis for their growth and overall vigor,photosynthesis disruption may decrease both the yield and the vigor. Several works on photosynthesis?uctuations after fungi-cide application on various crops report modi?cations of both photosynthetic activity and chlorophyll?uorescence (Krugh and Miles1996;van Iersel and Bugbee1996; Untiedt and Blanke2004;Xia et al.2006).
Several chemical compounds,based mainly on copper, sulphur or?udioxonil,are used to prevent crop plant dis-ease through non-systemic control programs.Copper is commonly used both as a pesticide(e.g.Bordeaux mixture) and as an algicide in agriculture.Copper is also an essential plant micronutrient as a component of various proteins, particularly those involved in both photosynthetic(plasto-cyanin)and the respiratory(cytochrome oxidase)electron transport chain(Baro′n et al.1995).However,an excess is strongly phytotoxic for crops.Toxicity symptoms were observed in cucumber leaves by a pronounced inhibition of Pn in mature leaves exposed to20l g g-1in soil for5days (Table2).Although Pn decline which is associated with a parallel decrease in gs,stomatal closure does not account for Pn inhibition(Vinit-Dunant et al.2002).
Inhibition of photosynthesis in the leaves of stressed plants is most likely a consequence of an altered source-sink relationship.Indeed,growth inhibition decreases car-bohydrate export from leaves,causes both starch and sucrose accumulations,and?nally leads to a feedback inhibition of photosynthesis(Vinit-Dunant et al.2002). However,Pn inhibition after copper exposure may be due to a disturbance of other processes in photosynthesis. Copper has a pronounced effect on chloroplast ultrastruc-ture(Baszynski et al.1988).In addition,chloroplast destruction was observed in green algae exposed to copper with enhanced peroxidative processes(Sandmann and Bo¨ger1980).Copper alters the lipid chloroplast membrane (Szalontai et al.1999),affecting light reaction processes, especially those associated with PSII(Baro′n et al.1995). Copper inhibits pigment accumulation and retards chloro-phyll integration into the photosystems of barley(Caspi et al.1999).It inhibits both the synthesis of the chlorophyll precursor,delta aminolevulinic acid and the activity of protochlorophyllide reductase,an enzyme that catalyzes the reductive formation of chlorophyllide from protochlo-rophyllide during chlorophyll biosynthesis(Stiborova′et al. 1986).Most of the in vitro studies using isolated chloro-plasts or excised leaves have reported an inhibition of the photosynthetic electron transport both at the reducing side of PSI and at the oxidizing side of PSII(Sandmann and Bo¨ger1980).Another effect of copper-based fungicides used in the treatment of plant disease is the suppression of oxygen evolution,inducing a decrease in photosynthetic
capacity(Caspi et al.1999).Sensitivity of PSII was con-?rmed with increased PSII inactivation under photoinhib-itory conditions(Pa¨tsikka¨et al.1998).Action has also been localized within the compounds of the thylakoid membrane such as PSI(Samuelsson and Oquist1980),the coupling factor(Uribe and Stark1982)and the ferredoxin-dependent reactions(Shioi et al.1978).Finally,a direct inhibition of Rubisco by Mg2?substitution or by interaction with SH-groups of the ATPase may also account for the inhibition of photosynthesis following exposure(van Assche and Clijsters1990).
A decrease in the disease severity and improvement in the foliage colour and retention has been observed by treatment with sulfur,which acts both as a plant nutrient and a fungicide(Stone et al.2004).Despite its ef?ciency, treatments containing sulfur also cause phytotoxicity on crops(Holb and Schnabel2005).In his review,Ferree (1979)summarized works in the1930’s and1940’s reporting that sulfur and lime sulfur reduce leaf Pn.Ferree et al.(1999)later found that a single spray of sulfur results in a signi?cant decrease in Pn of greenhouse grown apple trees.Similarly,Palmer et al.(2003)reported that leaf photosynthesis of Braeburn apple trees was signi?cantly reduced by almost50%following sulfur treatments(lime sulfur or Kumulus i.e.800g kg-1).The reduction in Pn is always accompanied by reduced stomatal conductance. The phytotoxicity of cuproxat(copper sulfate at0.54g l-1) on photosynthesis was investigated in a cucumber crop after using it as a pesticide treatment;the result was a decreased Pn accompanied by a decreased stomatal con-ductance and Ci,indicating that Pn inhibition is mostly attributed to stomatal factors.However,cuproxat had no signi?cant effects on PSII activity(Xia et al.2006).
The fungicide?udioxonil(fdx)[4-(2,2-di?uoro-1,3-benzodioxol-4-yl)-1H-pyrrole-3-carbonitrile],a phenyl-pyrrole compound,is commonly used as a botryticide in the vineyards(Rosslenbroich and Stuebler2000).Fdx is a non-systemic molecule and acts by inhibiting spore ger-mination,germ-tube elongation,and the mycelium growth of Botrytis cinerea(Table1).It increases the glycerol content in the fungus,leading to a perturbation of the osmoregulation potential(Pillonel and Meyer1997).Fdx applied during?ower and berry development,may thus have signi?cant consequences on yield.In grapevine,a decrease in Pn was noticed8days after treatment although fdx is not associated with a reduction in gs at6mM,the recommended concentration(Saladin et al.2003,Petit et al.2008a).In parallel studies,decrease in chlorophyll contents and carotenoids after fungicide treatments appeared to be dose-dependent(Saladin et al.2003).It was shown that fdx effects on Pn,were related neither to inactivation of both Rubisco and other key enzymes of the Calvin cycle,nor,to modi?cation of CO2diffusion to Rubisco.Pn recovered10days post-treatment,which would mean that either fdx had only a slight deleterious effect on plant photosynthesis or that grapevine has greater capacity to overcome this temporary stress(Saladin et al. 2003;Petit et al.2008a,b).Petit et al.(2009)suggest a relationship between the application of the fungicide fdx and the circadian rhythm of a plant’s photosynthesis. Interpreting the effect of fdx spraying on grapevine pho-tosynthesis,these authors showed a phenomenon of gating
Table2Effects of contact fungicides on crop physiology
Affected parameters Molecules References
Inhibition of Pn Copper Vinit-Dunant et al.(2002)
Sulfur(kumulus)Ferree(1979),Ferree et al.(1999),Palmer et al.(2003)
Copper sulfate(cuproxat)Xia et al.(2006)
Fludioxonil Saladin et al.(2003),Petit et al.(2008a,b)
Stomatal closure Copper Vinit-Dunant et al.(2002)
Sulfur(kumulus)Palmer et al.(2003)
Copper sulfate(cuproxat)Xia et al.(2006)
Inhibition of Ci Copper sulfate(cuproxat)Xia et al.(2006)
Inhibition of Rubisco Copper van Assche and Clijsters(1990)
Decreased of chlorophyll (synthesis or content)Copper Stiborova′et al.(1986) Fludioxonil Saladin et al.(2003)
Modi?cation on chloroplast ultrastructure Copper Sandmann and Bo¨ger(1980),Baszynski et al.(1988),
Caspi et al.(1999),Szalontai et al.(1999)
PSII inactivation Copper Baro′n et al.(1995),Caspi et al.(1999),Vinit-Dunant et al.(2002) PSI inactivation Copper Samuelsson and Oquist1980
Inhibition of other sites of electron transport chain Copper Shioi et al.(1978),Sandmann and Bo¨ger(1980),Uribe and Stark
(1982),van Assche and Clijsters(1990),Baro′n et al.(1995)
for the?rst time,i.e.external stimuli of equal strength applied at different times of the day can result in different intensities of response.The time period for spraying also was an important parameter in stress response.These data suggest that a morning treatment results in a non-stomatal limitation of Pn,while a midday treatment is more suitable to treat grapevine because it is the time period that least disrupts photosynthesis.
Folpet,used to control mildew and other fungal diseases in grape(Table1),is an uncoupling fungicide(uncouple oxidative phosphorylation in mitochondria).The folpet phytotoxicity was only investigated on duckweed(Lemna minor L.),an aquatic macrophyte regularly used as a model for non-target species in ecotoxicological studies(Teisseire et al.1999).Within the range of tested folpet concentra-tions(0–30mg l-1),no signi?cant effect of total chloro-phyll content was observed.No data is available on the cultivated plants.
Systemic fungicides:for better or for worse
A group of organic fungicides called benzimidazoles is widely used in agriculture for pre-and post-harvest pro-tection of crops against many fungal diseases,such as anthracnose,fruit rot,or grey mould.Its key compound, benomyl,is especially effective because it penetrates into plants faster than carbendazim(methyl2-benzimidazolec-arbamate),its active metabolite(Upham and Delp1973). Benomyl is a broad spectrum fungicide currently employed in agriculture,and many studies on the interaction between fungi and vascular plants(for example mycorrhizae)use benomyl as a systemic fungicide in order to get uninfected plants(Carey et al.1992;Merryweather and Fitter1996).It is possible that these fungicides may be phytotoxic to crops (Table3).Moreover,benomyl breaks down to n-butyl isocyanate which may subsequently react to produce n-butylamine or N-N0-dibutylurea(DBU).Products of degradation of benomyl also contribute to the phytotoxicity of the fungicide(van Iersel and Bugbee1996).It was also demonstrated that at a rate of2.8kg ha-1,DBU reduces cucumber biomass3weeks after treatment and inhibits Pn of hydrilla1day after treatment(Shilling et al.1994). Benlate(50%benomyl)caused a seven-to-ten day decrease in Pn of petunia and impatiens(van Iersel and Bugbee 1997)and DBU may be partly responsible for byside benomyl deleterious effects on plant growth.Crops have various sensitivities to DBU.Greenhouse studies revealed that corn is unaffected by DBU,whereas DBU is phyto-toxic when applied as a soil drench to cucumber(Shilling et al.1994).Indeed,physical symptoms in cucumber begin with chlorosis at the leaf margins then extend to the whole leaf and?nally lead to necrosis(Shilling et al.1994).Similarly,Mihuta-Grimm et al.(1990)noted chlorosis and stunting in tomato plants following applications of high benomyl concentrations.Ultra structural examination of cucumber chloroplasts10days after treatment with 5.6kg ha-1DBU showed dilation and a disorganization of granal membranes(Shilling et al.1994).Moreover,DBU affects PSII;it causes elevated chlorophyll?uorescence in cucumber leaf discs and inhibits photosynthetic oxygen evolution in hydrilla.In isolated spinach chloroplasts,DBU also reduces oxygen production and causes photo-induced, ferricyanide reduction by PSII alone as well as NADP reduction from a site in the electron transport chain prior to oxidation of plastohydroquinone,explaining Pn reduction (Querns et al.1998).
Carbendazim applications result in changes to foliar pigment concentrations(Garcia et al.2002).The applica-tion of doses lower than the recommended 2.6mM increases carotenoid concentrations,whereas a higher rate ([2.6mM)of carbendazim causes a decrease in all foliar pigments2weeks after treatment.These treatments with carbendazim may trigger a photoprotection mechanism in plants via carotenoids,which would interact with light to alleviate damages caused by the fungicide application (Garcia et al.2002;Skillman and Osmond1998).
Strobilurins,are another class of fungicides which are considered as a very valuable tool for managing diseases. Strobilurin fungicides are beta-methoxyacrylate com-pounds that inhibit respiration in fungi by binding to the Qo site of the cytochrome bc1complex located in the inner mitochondrial membrane(Bartlett et al.2002;Wiggins and Jager1993).This blocks electron transport and so reduces ATP synthesis.Strobilurin fungicides inhibit respiration in cytochrome bc1isolated from yeast,?y,rat,and corn (Roehl and Sauter1993)and wheat(Ko¨hle et al.1997). They also inhibit respiration in intact wheat plants and in spinach(Spinacia oleracea L.)leaf discs(Glaab and Kaiser 1999).When a fungicide preparation containing the stro-bilurin kresoxim-methyl is applied to the wheat plants,a reduction in the stomatal aperture is observed along with an increase in Pn rate(Fig.2;Grossmann et al.1999;Ko¨hle et al.1997).This result was quite surprising,because a direct relationship between Pn and gs is well established where the stomatal aperture increases Pn by increasing diffusive transport of carbon dioxide(Yu et al.2001).In an interesting work,Nason et al.(2007)demonstrated that strobilurin fungicides reduced the rate of gs to water in the leaves of wheat,barley and soya plants.Coincidently, plants treated with strobilurin fungicides have a lower rate of transpiration(T),a lower Ci and a lower Pn compared with control plants or plants treated with a epoxiconazole which is a triazole fungicide.Azoxystrobin is an uncou-pling strobilurin fungicide.The only data concerning impact of azoxystrobin on photosynthesis showed that
azoxystrobin does not affect the chlorophyll content in winter wheat,however its application delayed the increase of AOS,thus delaying the senescence of wheat and pro-longing the duration of?ag leaf photosynthesis(Zhang et al.2010).
Triazole compounds such as triadimefon(TDM),prop-iconazole,hexaconazole,and paclobutrazol are the largest and most important group of systemic compounds devel-oped for control of crop fungal diseases caused by Fusarium sp and Erysiphe necator.These fungicides may present phytotoxicity for crops as well as stimulant effects on plant physiology.Pn increased after triazole applica-tions in rice seedlings and bhendi(Guirong et al.1995; Sujatha et al.1999),after paclobutrazol applications in apple(Hong et al.1995)and after TDM(15–20g m-3) applications in radish crops(Panneerselvam et al.1997) and elephant foot yam(Gopi et al.2005).By contrast, cyazofamid(0.22g l-1)inhibits Pn in cucumber crops,but no effect was measured with?usilazole on the same plants (Xia et al.2006)(Table3).Gas exchange analysis dem-onstrated that the suppression of Pn induced by cyazofamid is associated with an increase of Ci,suggesting that Pn alteration is mostly attributed to non-stomatal factors(Xia et al.2006).TDM also increases Pn along with Ci and gs in maize(Kasele et al.1995).To contrast,TDM treatments induce stomatal closure in bean(Fletcher and Hofstra 1988),wheat(Sairam et al.1989),elephant foot yam(Gopi et al.2005),radish(Panneerselvam et al.1997),and mul-berry plants(Sreedhar1991).TDM treatments increased the level of abscisic acid content in various plants,inducing stomatal closure(Fletcher and Hofstra1988;Panneersel-vam et al.1997;Gopi et al.2005).
In the mesophyll,the number of cells per unit area in both palisade and spongy layers and chloroplast number per cell in the leaves of Chinese potato increased with hexaconazole and paclobutrazol treatments(Kishorekumar et al.2006).The use of triazoles enhanced chlorophyll and carotenoid contents in rice seedlings(Guirong et al.1995)
Table3Effects of systemic fungicides on crop physiology
Family Affected parameter Active ingredient References
Anilides Inhibition of Pn Fenhexamid Petit et al.(2008b)
Repression of Rubisco genes Fenhexamid Petit et al.(2008b)
Azoles Inhibition of Pn Cyazofamid Xia et al.(2006)
Stimulation of Pn Paclobutrazol Hong et al.(1995)
Triadimefon Kasele et al.(1995),Panneerselvam et al.(1997),
Gopi et al.(2005)
Stomatal operture Triadimefon Kasele et al.(1995)
Stomatal closure Triadimefon Fletcher and Hofstra(1988),Sairam et al.(1989),
Sreedhar(1991),Panneerselvam et al.(1997),
Gopi et al.(2005)
Increased Ci Cyazofamid Xia et al.(2006)
Triadimefon Kasele et al.(1995)
Increased chlorophyll and chloroplast contents Paclobutrazol Kishorekumar et al.(2006)
Triadimefon Buchenauer and Rohner(1981),Gao et al.(1988),
Muthukumarasamy and Panneerselvam(1997),
Gopi et al.(1999)
Hexaconazole Kishorekumar et al.(2006)
Reduced oxygen evolution
and electron transport
Epoxiconazole Benton and Cobb(1997)
Benzimidazoles Inhibition of Pn Dibutylurea Shilling et al.(1994),Querns et al.(1998) Chlorophyll declined Carbendazim Mihuta-Grimm et al.(1990),Garcia et al.(2002)
Carotenoids increased Carbendazim Garcia et al.(2002)
Disorganization of chloroplasts Dibutylurea Shilling et al.(1994)
PSII inactivation Dibutylurea Shilling et al.(1994)
Inhibition of electron transport Dibutylurea Querns et al.(1998)
Pyrimidines Inhibition of Pn Pyrimethanil Saladin et al.(2003)
Modi?cations of pigment concentrations Pyrimethanil Saladin et al.(2003)
Strobilurine Stomatal closure Kresoxim-methyl Grossmann et al.(1999)
Increased chlorophyll Kresoxim-methyl Grossmann et al.(1999)
and bhendi(Sujatha et al.1999).TDM treatments increased chlorophyll content in the leaves of the tomato (Buchenauer and Rohner1981),radish(Muthukumarasamy and Panneerselvam1997),cowpea(Gopi et al.1999),and wheat(Gao et al.1988).Triazole compounds increase the level of cytokinin,which might stimulate chlorophyll biosynthesis(Jaleel et al.2008).Triazoles accelerate chloroplast differentiation,and chlorophyll production, enlarged chloroplasts while also protecting the integrity of chlorophyll(Fletcher et al.2000;Jaleel et al.2008).By contrast,foliar application of epoxiconazole retards the growth of cleavers(Benton and Cobb1997).In addition, 7days after treatment,epoxiconazole clearly reduces oxygen evolution,determined as electron?ow from water to ferricyanide,and thus the associated electron transport capability of isolated thylakoids(Benton and Cobb1997).
Use of fungicides in the vineyards leads to an effective protection against a wide variety of pathogens but at the same time,generates long term residues in food and the environment.Photosynthesis alteration was revealed by reduction in Pn accompanied by changes in gs and Ci including modi?cations of dark respiration after fungicide treatment(van Iersel and Bugbee1996;Untiedt and Blanke 2004;Xia et al.2006).Considering?uorescence,the rel-ative quantum yield of PSII(U PSII)and the maximal quantum ef?ciency of PSII(Fv/Fm)were reduced by some fungicides and were attributed to decrease in photochemi-cal quenching(qP)(Krugh and Miles1996).Fungicides of the anilide family(pyrimethanil)and pyrimidine family (fenhexamid)are newly synthesized pesticides used for chemical control of Botrytis cinerea in viticulture. Regarding pyrimethanil,the effects differ according to the studied https://www.doczj.com/doc/f52367274.html,ing in vitro grown plantlets of grapevine, 6mM pyrimethanil causes a decline in Pn and in photo-synthetic pigment concentrations7days after application (Saladin et al.2003).In cuttings,pyrimethanil also inhibits Pn but without reduction in chlorophyll concentrations. In the vineyard,differences have been observed according to cultivars.Pyrimethanil increases Pn and pigment con-centrations in Chardonnay,whereas a decrease of these parameters is observed in Pinot noir and Pinot Meunier (Saladin et al.2003).Petit et al.(2008b)demonstrated a decrease in Pn following fenhexamid(1.5kg ha-1)7days after treatment in the vineyard.Pn modi?cation is mostly attributed to non-stomatal limitation since the reduction of photosynthesis is associated with few changes in Ci despite gs decline.However,PSII activity is not affected.Addi-tionally,decreased Pn is coupled with repression of genes encoding Rubisco small and large subunits. Conclusions and prospects
Fungicides constitute one of the most effective and inte-grative method to control diseases against phytopathogenic fungus in agriculture.However,the toxicity and the
pollution generated by fungicides cannot be neglected.The toxic effect of a given pesticide on seeds depends on its distribution,persistence,metabolism,its active form,and its concentration.Some pesticides interfere with the met-abolic pathways of plants and some interfere speci?cally with the photosynthetic process.
This review examines the toxic effects of a number of different classes of fungicides on photosynthesis.They are of importance in modern agriculture and in crop protection but the modes of action are still not known indeed.How-ever,this review does refer to the relevant literature and illustrates the need for further research in this area to mitigate against the deleterious effects.This is particularly important for some of the older treatments such as copper. Many?ndings indicate that some fungicides may affect the photosynthetic process.Some pesticides lead to Pn alter-ation through stomatal closure,while others affect the structure and the functioning of chloroplasts.Certain molecular compounds have no effect,whereas a few of them,such as the azoles,stimulate Pn.Triadimefon and hexaconazole could be used as a potential tool to manip-ulate carbohydrate metabolism(Gomathinayagam et al. 2007).Photosynthesis is a complex physiological process. More research highlighting and decoding each component of the photosynthetic electron transport chain for example PSI,PSII,Cyt b/f,and ATP synthase would be necessary.
In addition to damages caused by pesticides to crops,all pesticides are potentially harmful to human health and environment.Therefore taking into consideration the nega-tive effects due to the use of chemicals for disease control,it is of great importance to develop new active ingredients, which could be used at such a dose where it shows high speci?c toxicity to the target fungi and low toxicity to rest of the species and have a curative effect.Among other desired properties,having a low runoff potential and a rapid bio-degradation potential might be good from an environmental perspective.In addition to this,designing and testing active ingredients that are less exposed to the risk of pathogen resistance development and that do not present a risk during experimental process would be very useful for the human health and environment as well.New axes of research in this area require attention.It would be indispensible to look for new targets for example functional genomics.The diversi-?cation of chemical structures,along with combinatorial chemistry and screening systems are some approaches that will confer their bene?ts in the coming times.
Moreover,pesticide applicability can be compromised by the emergence of resistant pathogen strains.Thus,the need exists to curtail pesticide use,which will reduce the environmental impact of this cultural practice.To this purpose,there is an increasing demand to develop alter-native methods for plant disease control.Another alterna-tive strategy commonly used to control fungi is the activation of plant defence mechanisms using a variety of biotic and abiotic inducers.
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in，on，at的时间用法和地点用法 一、in, on, at的时间用法 ①固定短语： in the morning/afternoon/evening在早晨/下午/傍晚, at noon/night在中午/夜晚, （不强调范围，强调的话用during the night） early in the morning=in the early morning在大清早， late at night在深夜 on the weekend在周末（英式用at the weekend在周末，at weekends每逢周末） on weekdays/weekends在工作日/周末， on school days/nights在上学日/上学的当天晚上， ②不加介词 this, that, last, next, every, one, yesterday, today, tomorrow, tonight，all，most等之前一般不加介词。如， this morning 今天早晨 （on）that day在那天（that day更常用些） last week上周 next year明年 the next month第二个月（以过去为起点的第二个月，next month以现在为起点的下个月） every day每天 one morning一天早晨 yesterday afternoon昨天下午 tomorrow morning明天早晨 all day/morning/night整天/整个早晨/整晚（等于the whole day/morning/night） most of the time （在）大多数时间 ③一般规则 除了前两点特殊用法之外，其他≤一天，用on，＞一天用in，在具体时刻或在某时用at（不强调时间范围） 关于on 生日、on my ninth birthday在我九岁生日那天 节日、on Teachers’Day在教师节 （注意：节日里有表人的词汇先复数再加s’所有格，如on Children’s Day, on Women’s Day, on Teachers Day有四个节日强调单数之意思，on Mother’s Day, on Father’s Day, on April Fool’s Day, on Valenti Day） 星期、on Sunday在周日，on Sunday morning在周日早晨 on the last Friday of each month 在每个月的最后一个星期五 日期、on June 2nd在六月二日 on the second (of June 2nd) 在六月的第二天即在六月二日 on the morning of June 2nd在六月二日的早晨，on a rainy morning在一个多雨的早晨 on a certain day 在某天 on the second day在第二天（以过去某天为参照） 注意：on Sunday在周日，on Sundays每逢周日（用复数表每逢之意），every Sunday每个周日，基本一个意思。 on a school day 在某个上学日，on school days每逢上学日。on the weekend在周末，on weekends每逢 周末。 关于in in June在六月 in June, 2010在2010年六月
慕课、翻转课堂、微课的介绍和特点 所谓“慕课”(MOOC)，顾名思义，“M”代表Massive(大规模)，与传统课程只有几十个或几百个学生不同，一门MOOCs课程动辄上万人，最多达16万人；第二个字母“O”代表Open(开放)，以兴趣导向，凡是想学习的，都可以进来学，不分国籍，只需一个邮箱，就可注册参与；第三个字母“O”代表Online(在线)，学习在网上完成，无需旅行，不受时空限制；第四个字母“C”代表Course，就是课程的意思。[1] MOOC是新近涌现出来的一种在线课程开发模式，它发端于过去的那种发布资源、学习管理系统以及将学习管理系统与更多的开放网络资源综合起来的旧的课程开发模式。通俗地说，慕课是大规模的网络开放课程，它是为了增强知识传播而由具有分享和协作精神的个人组织发布的、散布于互联网上的开放课程。 这一大规模在线课程掀起的风暴始于2011年秋天，被誉为“印刷术发明以来教育最大的革新”，呈现“未来教育”的曙光。2012年，被《纽约时报》称为“慕课元年”。[2]多家专门提供慕课平台的供应商纷起竞争，Coursera、edX和Udacity是其中最有影响力的“三巨头”，前两个均进入中国。 主要特点: 1)、大规模的：不是个人发布的一两门课程：“大规模网络开放课程”(MOOC)是指那些由参与者发布的课程，只有这些课程是大型的或者叫大规模的，它才是典型的的MOOC。 2)、开放课程：尊崇创用共享（CC）协议；只有当课程是开放的，它才可以成之为MOOC。 3)、网络课程：不是面对面的课程；这些课程材料散布于互联网上。人们上课地点不受局限。无论你身在何处，都可以花最少的钱享受美国大学的一流课程，只需要一台电脑和网络联接即可。
常用标点符号用法简表 标点符号栏目对每一种汉语标点符号都有详细分析，下表中未完全添加链接，请需要的同学或朋友到该栏目查询。名称符号用法说明举例句号。表示一句话完了之后的停顿。中国共产党是全中国人民的领导核心。逗号，表示一句话中间的停顿。全世界各国人民的正义斗争，都是互相支持的。顿号、表示句中并列的词或词组之间的停顿。能源是发展农业、工业、国防、科学技术和提高人民生活的重要物质基础。分号；表示一句话中并列分句之间的停顿。不批判唯心论，就不能发展唯物论；不批判形而上学，就不能发展唯物辩证法。冒号：用以提示下文。马克思主义哲学告诉我们：正确的认识来源于社会实践。问号？用在问句之后。是谁创造了人类？是我们劳动群众。感情号①！1.表示强烈的感情。2.表示感叹句末尾的停顿。战无不胜的马克思主义、列宁主义、毛泽东思想万岁！引号 ②“ ” ‘ ’ ╗╚ ┐└1.表示引用的部分。毛泽东同志在《论十大关系》一文中说：“我们要调动一切直接的和间接的力量，为把我国建设成为一个强大的社会主义国家而奋斗。”2.表示特定的称谓或需要着重指出的部分。他们当中许多人是身体好、学习好、工作好的“三好”学生。 3.表示讽刺或否定的意思。这伙政治骗子恬不知耻地自封为“理论家”。括号③（）表示文中注释的部分。这篇小说环境描写十分出色，它的描写（无论是野外，或是室内）处处与故事的发展扣得很紧。省略号④……表示文中省略的部分。这个县办工厂现在可以生产车床、电机、变压器、水泵、电线……上百种产品。破折号⑤——1.表示底下是解释、说明的部
分，有括号的作用。知识的问题是一个科学问题，来不得半点的虚伪和骄 傲，决定地需要的倒是其反面——诚实和谦逊的态度。2.表示意思的递进。 团结——批评和自我批评——团结3.表示意思的转折。很白很亮的一堆洋 钱！而且是他的——现在不见了！连接号⑥—1.表示时间、地点、数目等 的起止。抗日战争时期（1937-1945年）“北京—上海”直达快车2.表 示相关的人或事物的联系。亚洲—太平洋地区书名号⑦《》〈〉表示 书籍、文件、报刊、文章等的名称。《矛盾论》《中华人民共和国宪法》《人 民日报》《红旗》杂志《学习〈为人民服务〉》间隔号·1.表示月份和日期 之间的分界。一二·九运动2.表示某些民族人名中的音界。诺尔曼·白求 恩着重号.表示文中需要强调的部分。学习马克思列宁主义，要按照毛泽 东同志倡导的方法，理论联系实际。······
In\ on\ at (time) at 用在具体某一时刻eg at 11:00 at 4:30 在节假日的全部日子里at Christmas 习惯用法at noon at weekends\ at the weekend at night at breakfast\lunch\supper on 具体到某一天；某一天的早晨，中午或晚上on May the first on Sunday morning 对具体某一天的早晨，中午，晚上进行详细的描述on a sunny morning on a windy night 节日的当天；星期on Women?s Day on Monday In 用在年；月；季节in spring in 2012 in August 后面+一段时间表示将来时in two days 习惯用法in the morning\in the afternoon\in the evening “\”以this, that, last, next, some, every, one, any,all开始的时间副词之前的at\on\in 省略在today, tomorrow, yesterday, the day after tomorrow, tomorrow morning，yesterday afternoon，the day before yesterday 之前的介词必须省略 Practice ___ summer ____ 2012 ____ supper ___ 4:00 ___ June the first ___yesterday morning ____ New Year?s Day ___ Women?s Day ___ the morning ____ the morning of July the first ____ 2014 ___ tomorrow morning ____ midnight 1.—What are you doing ____ Sunday? And what is your wife doing ___ the weekend? 2. He?ll see you ____ Monday. And he…ll see your brother ____next Monday. 3. They often go out ___ the evenings. But they don?t go out ____ Sunday evenings. 4. Do you work ____ Fridays? Does she work _____ every Friday? 5. They usually have a long holiday ___ summer. But their son can only have a short holiday ___ Christmas. 6. Paul got married ___ 2010, He got married ___ 9 o?clock ___ 19 May 2010. His brother got married ___ May, 2011. His sister is getting married ___ this year. 1.—When will Mr Black come to Beijing? ---_______ September 5 A. on B. to C. at D. in 2. The twins were born ____ a Friday evening. A. on B. of C. at D. in 3. It?s the best time to plant ____ spring. A. on B. in C. at D.\ 4. ____ the age of twelve, Edison began selling newspaper on train. A. On B. At C. In D.By 5. She has been an English teacher ____ 2000. A. for B. since C. in D.on 6.I have studied English _____ 2003. A. since B. for C. from D.in
一、基本定义 句子，前后都有停顿，并带有一定的句调，表示相对完整的意义。句子前后或中间的停顿，在口头语言中，表现出来就是时间间隔，在书面语言中，就用标点符号来表示。一般来说，汉语中的句子分以下几种： 陈述句： 用来说明事实的句子。 祈使句： 用来要求听话人做某件事情的句子。 疑问句： 用来提出问题的句子。 感叹句： 用来抒发某种强烈感情的句子。 复句、分句： 意思上有密切联系的小句子组织在一起构成一个大句子。这样的大句子叫复句，复句中的每个小句子叫分句。 构成句子的语言单位是词语，即词和短语（词组）。词即最小的能独立运用的语言单位。短语，即由两个或两个以上的词按一定的语法规则组成的表达一定意义的语言单位，也叫词组。 标点符号是书面语言的有机组成部分，是书面语言不可缺少的辅助工具。它帮助人们确切地表达思想感情和理解书面语言。 二、用法简表 名称
句号① 问号符号用法说明。？1．用于陈述句的末尾。 2．用于语气舒缓的祈使句末尾。 1．用于疑问句的末尾。 2．用于反问句的末尾。 1．用于感叹句的末尾。 叹号！ 2．用于语气强烈的祈使句末尾。 3．用于语气强烈的反问句末尾。举例 xx是xx的首都。 请您稍等一下。 他叫什么名字？ 难道你不了解我吗？为祖国的繁荣昌盛而奋斗！停止射击！ 我哪里比得上他呀！ 1．句子内部主语与谓语之间如需停顿，用逗号。我们看得见的星星，绝大多数是恒星。 2．句子内部动词与宾语之间如需停顿，用逗号。应该看到，科学需要一个人贡献出毕生的精力。 3．句子内部状语后边如需停顿，用逗号。对于这个城市，他并不陌生。 4．复句内各分句之间的停顿，除了有时要用分号据说苏州园林有一百多处，我到过的不外，都要用逗号。过十多处。 顿号、用于句子内部并列词语之间的停顿。
介词in on at 表示时间的用法及区别 Step1 Teaching Aims 教学生掌握时间介词in,on和at的区别及用法。 Step2 Teaching Key and Difficult Points 教学生掌握时间介词in,on和at的区别及用法。 Step3 Teaching Procedures 1.用in的场合后所接的都是较长时间 (1)表示“在某世纪/某年代/特定世纪某年代/年/季节/月”这个含义时，须用介词in Eg: This machine was invented in the eighteenth century. 这台机器是在18世纪发明的。 、 She came to this city in 1980. 他于1980年来到这个城市。 It often rains here in summer. 夏天这里常常下雨。 (2)表示“从现在起一段时间以后”时，须用介词in。(in+段时间表将来) Eg: They will go to see you in a week. 他们将在一周后去看望你。
I will be back in a month. 我将在一个月后回来。 (3)泛指一般意义的上、下午、晚上用in, in the morning / evening / afternoon Eg: They sometimes play games in the afternoon. 他们有时在下午做游戏。 Don't watch TV too much in the evening. 晚上看电视不要太多。（4）A. 当morning, evening, afternoon被of短语修饰，习惯上应用on, 而不用in. Eg: on the afternoon of August 1st & B. 但若前面的修饰词是early, late时，虽有of短语修饰，习惯上应用in, 而不用on. Eg: in the early morning of September 10th 在9月10的清晨； Early in the morning of National Day, I got up to catch the first bus to the zoo. 国庆节一清早，我便起床去赶到动物园的第一班公共汽车。 2.用on的场合后所接的时间多与日期有关 （1）表示“在具体的某一天”或（在具体的某一天的）早上、中午、晚上”，或“在某一天或某一天的上午，下午，晚上”等，须用介
介词in, on, at在表示时间时的用法区别 ①in时间范围大（一天以上）如：in Tanuary, in winter, in 1999;泛指在上午，下午，晚上，如：in the morning(afternoon, evening). 习惯用法：in the daytime 在白天。 ②on指在某一天或某一天的上午，下午，晚上，如：on Monday, on Sunday afternoon, on July 1, 1999 ③at时间最短，一般表示点时间，如at six o’clock, at three thirty.习惯用法：at night, at noon, at this time of year. in, on和at在表达时间方面的区别 in 表示在某年、某季节、某月、某周、某天和某段时间 in a year在一年中 in spring 在春季 in September 在九月 in a week 在一周中 in the morning/afternoon/evening 在上午/下午/傍晚 但在中午，在夜晚则用at noon/night on 表示某一天或某一天的某段时间 on Monday 在周一 on Monday afternoon 在周一下午 on March 7th 在3月7日 on March 7th, 1998. 在1998年3月7日 on the morning of March 7th, 1998. 在1998年3月7日上午
at 表示某个具体时刻。 at eight o’clock 在8点钟 at this time of the year 在一年中的这个时候 at the moment 在那一时刻 at that time 在那时 注意：在英语中，如果时间名词前用this, last, next 等修饰时，像这样的表示，“在某时”的时间短语前，并不需要任何介词。 例如：last month, last week, this year, this week, next year, the next day, the next year 等。 1．What’s the weather like in spring/summer/autumn/winter in your country? 你们国家春天/夏天/秋天/冬天的天气怎么样？ in 在年、月、周较长时间内 in a week 在里面 in the room 用某种语言 in English 穿着 in red on 某日、某日的上下午on Sunday afternoon 在……上面 on the desk 靠吃……为生live on rice 关于 a book on Physics 〔误〕We got to the top of the mountain in daybreak. 〔正〕We got to the top of the mountain at day break. 〔析〕at用于具体时刻之前，如：sunrise, midday, noon, sunset, midnight, night。〔误〕Don't sleep at daytime 〔正〕Don't sleep in daytime. 〔析〕in 要用于较长的一段时间之内，如：in the morning / afternoon, 或in the week / month / year. 或in spring / supper /autumn / winter等等。 〔误〕We visited the old man in Sunday afternoon. 〔正〕We visited the old man on Sunday afternoon. 〔析〕in the morning, in the afternoon 如果在这两个短语中加入任何修饰词其前面的介
作品简介 本微课视频的教学内容为牛津小学英语5B Unit8 At the weekends (B)部分的单词教学。本部分的教学内容和教学重点是掌握6个昆虫类单词及insects的发音。教学目标是让学生通过微视频的学习，能够正确、流利地朗读6种昆虫类的单词以及单词insects，并能够熟练运用。教学难点是让学生读准单词发音，掌握发音规律，掌握以字母y结尾的可数名词变为复数时的变化规则。情感态度方面，需要学生具有通过微视频学习知识的兴趣，能够积极、主动的参与到教学活动中来，通过微视频学习的方式，掌握语言技能；能够根据自己对知识的掌握程度和实际需要借助视频学习的优势，反复观看，解决自己的难点问题，积极参与到视频教学中的操练项目，巩固和运用知识。 作品的创作说明： 教学设计 教学内容：牛津小学英语5B Unit8 At the weekends (B) 教学目标：让学生通过微视频学习，能够正确、流利地朗读6种昆虫类的单词以及单词insects，并能够熟练运用。 教学重点：熟练掌握6个昆虫类单词及insects的发音 教学难点：让学生读准6个昆虫类单词及insects的发音，掌握发音规律，知道以y结尾的可数名词变为复数时的变化规律。 教学过程：
Step 1借助情境图，激发兴趣，揭示课题 1.出示情境图，公园的一角 T: Here’s a picture. Is it nice? What can you see in the picture? T: Today, let’s learn some words about insects. 2.揭示课题，读2遍 Step2利用猜谜的游戏，呈现新单词，学习新单词 1.边听边猜，激发兴趣，学习新单词a grasshopper , a bee 教师讲两个昆虫的特点，让学生猜他们是什么？学生猜对后，教师呈现昆虫的图和单词，带领学生跟读，并指导单词grasshopper中a 和o的发音以及字母组合ee的发音。利用已知的单词学习新单词的发音。 2.自主阅读，猜一猜，他们是哪些昆虫 （1）学生自己读文本，猜文本中所指的是哪些昆虫。学生抓住昆虫的特点，思考。 （2）核对答案，并学习他们的发音，同时学习他们的复数形式及发音。 （3）引导学生观察发现，掌握以辅音字母+y 结尾的可数名词复数形式的变化规律。 3．整体呈现单词，齐读 整体呈现新单词，播放录音让学生整体跟读一遍，加以巩固。Step3 巩固操练 1.仔细阅读，根据歌谣内容，选择正确的图，填空。
精心整理in，on，at的时间用法和地点用法 一、in,on,at的时间用法 1、固定短语： inthemorning/afternoon/evening在早晨/下午/傍晚, 2 （on thenextmonth第二个月（以过去为起点的第二个月，nextmonth以现在为起点的下个月） everyday每天 onemorning一天早晨 yesterdayafternoon昨天下午
tomorrowmorning明天早晨 allday/morning/night整天/整个早晨/整晚（等于thewholeday/morning/night）mostofthetime（在）大多数时间 3、一般规则 除了前两点特殊用法之外，其他≤一天，用on，＞一天用in，在具体时刻或在某时用at（不强调时间范围） 关于 On 1 2) 3) （注意：节日里有表人的词汇先复数再加s’所有格，如 onChildren’sDay,onWomen’sDay,onTeachers’Day有四个节日强调单数之意思，onMother’sDay,onFather’sDay,onAprilFool’sDay,onValentine’sDay） 星期、onSunday在周日，onSundaymorning在周日早晨onthelastFridayofeachmonth在每个月的最后一个星期五
日期、onJune2nd在六月二日 onthesecond(ofJune2nd)在六月的第二天即在六月二日onthemorningofJune2nd在六月二日的早晨，onarainymorning在一个多雨的早晨 onacertainday在某天 onthesecondday在第二天（以过去某天为参照） 关于 In 1 2) InJune在六月 inJune,2010在2010年六月 in2010在2010年 inamonth/year在一个月/年里（在将来时里翻译成一个月/年之后） inspring在春天
创作编号：BG7531400019813488897SX 创作者：别如克* 微课的类型介绍 按照不同的划分方法，微课可以被分为许多种类型，其中按照教学方法来分类，微课大致可以划分为分别为五类，分别为：讲授类、讨论类、启发类、演示类、练习类等。那么今天我们就为大家介绍几种常见的微课类型，以便于大家在今后的微课制作中有更好设计思路和创意。 一、讲授类 讲授类微课适用于教师运用口头语言向学生传授知识,如描绘情境、叙述事实、解释概念、论证原理和阐明规律。这是中小学最常见、最主要的一种微课类型。 1.课堂实录微缩版 这种类型的微课中有教师、有学生、有活动、有交互……然而学生不是教研员，也不是评课专家。他不需要观看师生活动过程，学生需要的仅仅是学习内容本身。 2.画中画版 这种方式的优点在于，老师的头像出现在视频局部，仿佛老师就在自己身边一对一讲解，亲切而自然，更易于被学生接受从而愿意去学习。 二、讨论类 讨论类微课适用于在教师指导下，由全班或小组围绕某一种中心问题通过发表各自意见和看法，共同研讨，相互启发，集思广益地进行学习。 三、演示类 1.幻灯片动画式 演示类微课适用于教师在课堂教学时，把实物或直观教具展示给学生看，或者作示范性的实验，或通过现代教学手段，通过实际观察获得感性知识以说明和印证所传授知识。 PPT类微课是指教师借助PPT的视频录制功能将嵌入有课程讲解配音的PPT直接录制成流媒体视频。这类微课视频的制作门槛低，要求老师必须具备一定的动画设计制作能力。 2.手机+白纸 工具随手可得，技术难度低，操作快捷方便，画面真实亲切，并且易于分享
结语： 但在实际微课的设计与拍摄时，老师还得根据课程的性质、教学的要求、学校的实际硬件条件及自身的技术能力来选择微课的类型，只有这样，微课才能真正与课堂教学相结合，并能通过翻转课堂教学来提升课程教学的质量。 创作编号：BG7531400019813488897SX 创作者：别如克*
常用标点符号主要用法 问号 1、用在特指问句后。如：(7)你今年多大了？ 2、用在反问句后。如：(8)为什么我们不能刻苦一点呢？ ?提示：反问句若语气缓和，末尾可用句号；若语气重可用感叹号。如：(9)国家 主席可以活活被整死；堂堂大元帅受辱骂；……这哪里还有什么尊重可言！ 3、用在设问句后。如：(10)我们能让你计划实现吗？不会的。 4、用在选择问句中。如：(11)我们是革命呢，还是要现大洋？ ( 12)你到底是去，还是不去？ 5、用在表疑问的独词句后。如：(13)我？不可能吧。 ?提示：若疑问句为倒装句，问号应放在句末。如：(14)到底出了什么问题，你的 车？(若说成：“到底出了什么问题？你的车。”则错误。) ?特别提示： 句号、问号均表示句末停顿。句号用于陈述句末尾，问号用于疑问句末尾。有些句 中虽有疑问词，但全句并不是疑问句，句末只能用句号，不能用问号。 例如：(17)……最后应求出铜块的体积是多少？ (18)面对千姿百态、纷繁芜杂的期刊世界，有哪位期刊编辑不想通过期刊版面设 计为刊物分朱布白、添花增色呢？ (19)关于什么是智力？国内外争论多年也没有定论。 (17) (18) ( 19)三句都是非疑问句，(17) (18)句中问号均应改为句号，(19)句中的问号应改为逗号。 感叹号 ?特别提示： 1、在表感叹或祈使语气的主谓倒装句中，感叹号要放在句末。 如：(20)多么雄伟壮观啊，万里长城！ 2、句前有叹词，后是感叹句，叹号放在句末。 如：(21)啊，这儿多么美丽！ 下面介绍句中点号的用法。句中点号包括逗号、分号、顿号、和冒号四种。 逗号 提示：复句内各分句之间的停顿，除了有时用分号外，都要用逗号。 顿号 用于句中并列的词、词组之间较小的停顿。 如：(22)邓颖超的品德、人格、风范为中华民族树立了一座精神丰碑。 (23)从1918年起，鲁迅陆续发表了《狂人日记》、《药》、《祝福》等短篇小说。 ?特别提示：以下九种情况不用顿号。 1、不定数的两个数字间不用顿号。 如：(24)你的年龄大概是十六七岁。(不能写成“十六、七岁”) ?【注意】相邻的两个数字而非约数之间要用顿号。
i n o n a t的时间用法和 地点用法版 集团档案编码：[YTTR-YTPT28-YTNTL98-UYTYNN08]
i n，o n，a t的时间用法和地点用法 一、in,on,at的时间用法 1、固定短语： inthemorning/afternoon/evening在早晨/下午/傍晚, atnoon/night在中午/夜晚,（不强调范围，强调的话用duringthenight）earlyinthemorning=intheearlymorning在大清早， lateatnight在深夜 ontheweekend在周末（英式用attheweekend在周末，atweekends每逢周末）onweekdays/weekends在工作日/周末， onschooldays/nights在上学日/上学的当天晚上， 2、不加介词 this,that,last,next,every,one,yesterday,today,tomorrow,tonight，all，most等之前一般不加介词。如， thismorning今天早晨 （on）thatday在那天（thatday更常用些） lastweek上周 nextyear明年 thenextmonth第二个月（以过去为起点的第二个月，nextmonth以现在为起点的下个月） everyday每天 onemorning一天早晨 yesterdayafternoon昨天下午 tomorrowmorning明天早晨
allday/morning/night整天/整个早晨/整晚（等于 thewholeday/morning/night） mostofthetime（在）大多数时间 3、一般规则 除了前两点特殊用法之外，其他≤一天，用on，＞一天用in，在具体时刻或在某时用at（不强调时间范围） 关于on On指时间表示： 1）具体的时日和一个特定的时间，如某日，某节日，星期几等。Hewillcometomeetusonourarrival. OnMay4th(OnSunday,OnNewYear’sday,OnChristmasDay),therewillbeacelebra tion. 2)在某个特定的早晨，下午或晚上。 Hearrivedat10o’clocko nthenightofthe5th. Hediedontheeveofvictory. 3)准时，按时。 Iftherainshouldbeontime,Ishouldreachhomebeforedark. 生日、onmyninthbirthday在我九岁生日那天 节日、onTeachers’Day在教师节 （注意：节日里有表人的词汇先复数再加s’所有格，如 onChildren’sDay,onWomen’sDay,onTeachers’Day有四个节日强调单数之意思， onMother’sDay,onFather’sDay,onAprilFool’sDay,onValentine’sDay）星期、onSunday在周日，onSundaymorning在周日早晨
本微课视频有以下几个优点： 1、通过本节课的教学，让学生进一步体会，数学来源于生活，又用于生活，提供学生生活中熟悉的材料作背景，学生学习兴趣很高。 2、教学设施中，我非常重视开头的引入教学，激发学生学习的兴趣。注意鼓励学生大胆发言，注意从生活中的两幅图片出发，展现知识的形成过程，使学生能够利用已有的生活知识和数学知识，通过知识迁移、类比的方法归纳得出同类项的概念以及合并同类项的法则。使他们不会觉得数学概念学习的单调乏味，逐步提高学生抽象概括的能力。 3、教学的设计主要是体现以“学生为主体，教师为主导”的教学理念。整个教学过程都是学生在思考、交流，相互比赛，并解决问题，老师只是进行适当的点拨，从而真正体现了以学生为主体，教师为主导的教学理念。学生通过自学，再小组讨论，把不懂的问题都在组内消化完成。全班交流展示时，所举同类项的例子，能检验该学生是否真正掌握了同类项的概念，突出了合作交流的重要性。 4、通过议一议，汇报学习成果，培养了学生的数学语言表达能力，促使学生对合并同类项的法则理解记忆。通过比一比，看谁反应快；填一填，看谁写得最快；全班分为两组进行比赛能检验学生对同类项的概念及合并同类项的法则是否掌握，学生通过两组比赛活动，也能发扬学生合作学习的精神，进一步培养学生团结协助、严谨求实的学习精神。从而激发了学生探究数学的兴趣，更能发挥学生解决问题的主动性，使每个学生在比赛活动中都有收获。 5、通过学生谈收获，教师做补充，培养学生的数学语言表达能力和自我整理的学习习惯。因此整堂课主要突出了以下三个方面：贯穿了一个原则——以学生为主体的原则；培养了一种意识——合作交流的意识；锻炼了一种能力——数学语言表达能力。
介词in,on与at表时间的用法 at < 天(eg. noon, dawn, night, one’ clock) on = 天(Monday, 30th June, New Year’s Day, Mother’s Day) in > 天(2008, summer, April, 还有早午晚) 用in的场合后所接的都是较长时间 (1)表示“在某世纪/某年代/特定世纪某年代/年/季节/月”这个含义时,须用介词in Eg: This machine was invented in the eighteenth century. 这台机器是在18世纪发明的。 This incident happened in the 1970s. 该事件发生在20世纪70年代。 She came to this city in 1980. 他于1980年来到这个城市。 It often rains here in summer. 夏天这里常常下雨。 (2)表示“从现在起一段时间以后”时,须用介词in。(in+段时间表将来) Eg: They will go to see you in a week. 他们将在一周后去看望你。 I will be back in a month. 我将在一个月后回来。 (3)泛指一般意义的上、下午、晚上用in, in the morning / evening / afternoon Eg: They sometimes play games in the afternoon. 他们有时在下午做游戏。
Don't watch TV too much in the evening. 晚上看电视不要太多。 (4)A. 当morning, evening, afternoon被of短语修饰,习惯上应用on, 而不用in. Eg: on the afternoon of August 1st (5)B. 但若前面的修饰词是early, late时,虽有of短语修饰,习惯上应用in, 而不用on. Eg: in the early morning of September 10th 在9月10的清晨; in the late afternoon of September 12th 在9月12日的傍晚。 Early in the morning of National Day, I got up to catch the first bus to the zoo. 国庆节一清早,我便起床去赶到动物园的第一班公共汽车。 用on的场合后所接的时间多与日期有关 (1)表示“在具体的某一天”或(在具体的某一天的)早上、中午、晚上”,或“在某一天或 某一天的上午,下午,晚上”等,须用介词on。 Eg: Jack was born on May 10th, 1982. 杰克生于1982年5月10日。 They left on a rainy morning. 他们是在一个雨天的早上离开的。 He went back to America on a summer afternoon. 他于一个夏天的下午返回了美国。
公文写作中标点符号的使用规范 《中华人民共和国国家标准》（GB|T15834—1995）中有《标点符号用法》，其中对标点符号的使用作了明确的规定： 标点符号是辅助文字记录语言的符号，是书面语的有机组成部分，用来表示停顿、语气以及词语的性质和作用。 常用的标点符号有16种，分点号和标号两大类。 点号的作用在于点断，主要表示说话时的停顿和语气。点号又分为句末点号和句内点号——句末点号用在句末，有句号、问号、叹号3种，表示句末的停顿，同时表示句子的语气；句内点号用在句内，有逗号、顿号、分号、冒号4种，表示句内的各种不同性质的停顿。 标号的作用在于标明，主要标明语句的性质和作用。常用的标号有9种，即：引号、括号、破折号、省略号、着重号、连接号、间隔号、书名号和专名号。 一、常用标点符号用法简表 名称符号用法说明举例 句号。表示一句话完了之后的停 顿。 中国共产党是全中国人民的领导核心。 逗号，表示一句话中间的停顿。全世界各国人民的正义斗争，都是互相支持的。 顿号、表示句中并列的词或词组 之间的停顿。 能源是发展农业、工业、国防、科学技术和提高人 民生活的重要物质基础。 分号；表示一句话中并列分句之 间的停顿。 不批判唯心论，就不能发展唯物论；不批判形而上 学，就不能发展唯物辩证法。 冒号：用以提示下文。马克思主义哲学告诉我们：正确的认识来源于社会实践。 问号？用在问句之后。是谁创造了人类？是我们劳动群众。 感情号！1.表示强烈的感情。 2.表示感叹句末尾的停 顿。 战无不胜的马克思主义、列宁主义、毛泽东思想万 岁！ 引号“”1.表示引用的部分。毛泽东同志在《论十大关系》一文中说：“我们要
七年级语文常用标点符号用法简表 七年级常用标点符号用法简表 一、基本定义 句子，前后都有停顿，并带有一定的句调，表示相对完整的意义。句子前后或中间的停顿，在口头语言中，表现出来就是时间间隔，在书面语言中，就用标点符号来表示。 二、复习标点符号的写法，明确标点符号的书写位置。 常用的标点符号有16种，分为点号和标号。 点号 句号 。 问号 ？ 感叹号 ！ 逗号 顿号 分号 ； 冒号 标号
引号“”‘’括号[] 破折号——省略号……书名号 着重号· 间隔号· 连接号— 专名号____ 备注占两格左上角
右上角 各占 一格 各占 一格 占两格 每格 三个点 占两格 标字下 标字间 占一格 标字下点号表示语言中的停顿，一般用在句中或句末。标号主要标明语句的性质和作用。 标点符号的书写位置。 在横行书写的文稿中，句号、问号、叹号、逗号、顿号、分号和冒号都占一个字的位置，放在句末的左下角。这七种符号通常不能放在一行的开头，因为这些符号表示语气的停顿，应该紧跟在一句话的末尾。如果一行的最后的一个格正好被文字占用了，那么这个标点就必须点标在紧靠文字的右下角。 引号、括号、书名号的前一半和后一半都各占一个字的
位置，它们的前一半可以放在一行的开头，但不出现在一行的末尾，后一半不出现在一行的开头。 破折号和省略号都占两个字的位置，可以放在一行的开头，也可以放在一行的末尾，但不可以把一个符号分成两段。这两种符号的位置都写在行次中间。） 引用之语未独立，标点符号引号外；引用之语能独立，标点符号引号里。 注意事项： 冒号 表示提示性话语之后的停顿，用来提引下文。 ①同志们，朋友们：现在开会了。 ②他十分惊讶地说：“啊，原来是你！” ③北京紫禁城有四座城门：午门、神武门、东华门和西华门。 注意：“某某说”在引语前，用冒号；在引语中或引语后，则不用冒号。如： ⑴老师说：“李白是唐代的大诗人，中学课本有不少李白的诗。” ⑵“李白是唐代的大诗人，”老师说，“中学课本里有不少李白的诗。” ⑶“李白是唐代的大诗人，中学课本里有不少李白的诗。”老师说。
时间介词(at, in ,on) 的用法 1. at （1）时间的一点、时刻等。如： They came home at seven o’clock. (at night, at noon, at midnight, at ten o’clock, at daybreak, at dawn）. （2）后面接表示岁数的词。 Children in China start school at 6 years old. （3）较短暂的一段时间。可指某个节日或被认为是一年中标志大事的日子。如： He went home at Christmas （at New Year, at the Spring Festival）. 2. in （1）在某个较长的时间（如世纪、朝代、年、月、季节以及泛指的上午、下午或傍晚等） 内。如： in 2004, in March, in spring, in the morning, in the evening, etc （2）在一段时间之后,常用于将来时。 He will arrive in two hours. These products will be produced in a month. 3. on （1）具体的时日和一个特定的时间，如某日、某节日、星期几等。如： On Christmas Day（On May 4th）, there will be a celebration. （2）在某个特定的早晨、下午或晚上。如： He arrived at 10 o’clock on the night of the 5th. （3）准时，按时。如： If the train should be on time, I should reach home before dark. 表示频率的副词用法详解 一、常见的频率副词 always，usually，often，sometimes， seldom，never. 1) always表示的频率为100%，意思是"总是、一直、始终"。 I always do my cleaning on Sundays. 我总是在星期天搞卫生。 2）usually与always相比，表示的频率要低些，约为70%-80%。意思是"通常"。 Plants are usually green. 植物通常是绿色的。 Usually she goes to work by bus. 她通常乘公共汽车去上班。 3）often的频率比usually又略低些，约为60%-70%，意思是"经常"、"常常"。 Do you often write to them? 你常给他们写信吗？ Does Fred come here often? 弗雷德常来这儿吗？ 4）sometimes的频率比often又低些，约为50%＞sometimes＞30%，意思是“有时、不时”。(window.cproArray = window.cproArray || []).push({ id: "u3054369" }); 3