Physiological Mechanism Of Weak-light Stress During Grain Filling On Grain Yield Formation In Maize

The experiments were conducted to study the effect of weak-light stress(moderate shading:30%light deprivation,severe shading:50%light deprivation,and taken plants without shading as control)after pollination on maize yield,dry matter accumulation and translocation,leaf senescence and grain filling using Zhengdan 958,Jiangyu 877,Suyu 29 and Suyu 30 as materials.The main results were as follows.1.Grain yield,and dry matter accumulation and translocationWeak-light stress during grain-filling significantly reduced the grain number and weights,which led to the loss of grain yield.The grain yields of Zhengdan 958,Jiangyu 877,Suyu 29,and Suyu 30 were reduced by 52.1%,52.3%,48.1%and 37.4%under moderate shading and 72.2%,69.4%,69.0%,and 67.8%under severe shading stress,respectively.Among the four varieties,the grain yield reduction of Suyu30 under moderate and severe weak light stresses was lowest than the other three varieties.The correlation analysis results indicated that the grain yield loss under shading stress was mainly due to the decrease of grain number,followed by the reduction of grain weight.Weak-light stress reduced the accumulation of dry matter and nitrogen after pollination.The reduction was severe when more light was deprived,though the translocation of the stored carbohydrate pre-flowering was increased,it was not meet the grain filling demand,as a results,led to grain yield loss.2.Leaf senescent propertyWeak-light stress during grain filling reduced the leaf SPAD value,chlorophyll and carotenoid content,leaf water content and soluble protein content.Additionally,the activities of enzymes that involved in nitrogen metabolism(NR,GS,GOGAT),photosynthetic property(PEPCase?RuBPCase),and anti-oxidants(SOD,CAT,POD,APX)were weakened.With the plant development,the MDA and ROS content gradually increased and the production of those two parameters were more pronounced under shading stress.The IAA content was decreased and ABA content was increased under shading,respectively.Those changes of content and activities of enzymes induced a reduction in photosynthetic rate,transpiration rate,stomatal conductance,PSII potential photochemical efficiency(Fv/Fo),and initial maximum light use efficiency(Fv/Fm),accelerated leaf senescence,and effects were serious under severe weak-light stress condition.3.Grain filling propertyWith grain filling proceeding,starch content increased,and soluble sugar and protein content decreased gradually.Weak-light stress during grain filling significantly reduced the starch and amylose content,increased the relative content of soluble sugar and protein,and the changing was more obvious under severe weak-light stress.Weak-light stress during grain-filling reduced the activities of sucrose synthase(SS,synthetic and cleavage),sucrose phosphate synthase(SPS),adenosine diphosphate glucose(ADPG),soluble starch synthase enzyme(SSS),starch debranching enzyme(DBE),glutamine synthase(GS),and glutamate synthase(GOGAT),while the activity of enzyme of starch branching enzyme(SBE)was increased by weak-light stress.The contents of IAA,GA3 and Z+ZR in grains were decreased,while the ABA content was increased under weak-light stress,and effects were serious under severe weak-light stress.Generally,weak-light stress in the grain-filling stage reduced the activities of enzymes involved in synthesis of starch,protein,and sucrose,and the dynamic balance was endogenous hormones was disrupted,which led to the changes of proportion of starch,protein,and sugar,and the starch deposition was restrained,resulting in the reduction of grain dry weight,and fresh weight and volume,and the reduction were severe when more light was deprived.