Effect Of Drought On Corn Photosynthetic Physiology And Related Enzyme Gene Expression Of Photosynthetic

Objective: Photosynthesis is the primary gateway for the growth and metabolism of maize underdrought, which can cause many other second effects on physiology and agronomy traits. Photosynthesisinvolved in two procedures, the light and dark phases. This experiment aims to study the effects of PEG(Polyethylene glycol) and drought stress in the field on the photosynthetic characteristics of maize. Thepaper will provide some theoretical mechanism and practical instruction for maize drought resistancebreeding.Methods: Maize seedling were cultivated after germination, PEG6000with four concentrations wasstressed maize seedling at3leaves stage. And the photosynthetic characters, such as photosynthetic gasexchange parameters, chlorophyll fluorescence parameters and photosynthetic enzymes activities, wereinvestigated, and expression of gene related with photosynthetic were tested by real quantitative PCRtechnology at24h,48h,72h under PEG6000stress at3leaf stage maize seedings. The same traits andcharacters were invested at the huge bellbottom stage, silking stage,10days after silking stage with maizeleaves under drought stress in field.Result and conclusion: The net photosynthetic rate (Pn), stomatal conductance (Gs) and transpirationrate (Tr) of maize seedling were significantly lower under10%and15%PEG6000than the control. Theactivities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and content ofmalondialdehyde (MDA) were significantly higher than the control. The expression levels of genephosphoenolpyruvate carboxykinase (PEPC), Pyruvate orthophosphate dikinase (PPDK), carbonicanhydrase (CA) and NADP-Malic enzyme (NADP-ME) were all higher under stress than the control. Thechlorophyll fluorescence parameters were no significantly different under10%and15%PEG stress, WhilePn, Gsand Trat72h were significantly higher than that at24h and48h. The protective enzyme activityand chlorophyll fluorescence parameters have no significantly different with the stress time extension. Itcould be concluded that maize has some mechanisms to alleviate the drought damage. The Gs and Trreduction leads to Pn decreasing significantly, which blocked the exchange of CO2and water in maize.The activities of SOD, POD and CAT significantly increased under20%polyethylene glycol stress,and the activities and expression levels of PPDK, NADP-ME gene significantly reduced, and the activitiesand expression levels of PEPC, CA gene were significantly increased under20%polyethylene glycol stress,The content of MDA increased significantly and the minimal fluorescence(Fo), non-photochemicalquenching (NPQ) increased, and maximum fluorescence (Fm), Fv, maximum photochemical efficiency(Fv/Fm), φPSⅡdecreased under the stress of20%PEG. The Pn, Gsand Trdecreased significantly andintercellular CO2concentration (Ci) decreased significantly under the stress. The photosynthetic activityreduced significantly, and heat dissipation increased significantly under the stress. It could be concludedthat the photosynthesis of maize seedling were restrained, and PSⅡ photochemical activity, PSⅡ originallight energy conversion efficiency, PSⅡ potential activity and photochemical activity all are restrainedunder the drought stress, and the photosynthesis decreased significantly when maise was stressed by drought. Photosynthetic rate decreasing is caused by porosity and non stomatal factors.The activities of SOD, POD, CAT, and MDA contents increased significantly at maize big bell stage,silking stage and10days after silking stage under drought stress. It could be concluded that SOD, POD andCAT protective enzyme help to remove active oxygen to reduce or avoid its harm to the cell under droughtstress. The Pn, Tr, Gs, Ciwere significantly lower than control. The chlorophyll fluorescence parameters Foand NPQ increased, and Fm, Fv, Fv/Fm, Fv/Fo, φPSⅡdecreased under the stress. The photosynthetic activitydecreased significantly, and the heat dissipation significantly increased, PSⅡphotochemical activity, theoriginal light energy conversion efficiency of PSⅡ, PSⅡ photochemical energy potential all is restrainedunder drought stress. The activities of PEPC, PPDK, NADP-ME, and expressions of these genes weresignificantly higher than control. The result shows that higher PEPC, PPDK, NADP-ME enzyme activitiesand higher expression of these genes expressed mitigates the effects of drought on maize photosynthesis.