| High temperature and drought are two of the most important abiotic adversities during maize growth in southern China.The pot trials were conducted to study the effects of heat and heat/drought stress during grain filling on the physiological mechanism that affects waxy maize grain yield formation using Suyunuo 5 and Yunuo 7(Control varieties of national waxy maize regional test in southern China)as materials.The parameters include dry matter accumulation and translocation,leaf photosynthetic and senescent characteristics and activities of anti-oxidant enzymes,grain filling property,soluble sugar,starch and protein accumulation and activities of enzymes involved in grain components synthesis,and contents of endogenous hormone.The main results were as follows.1.Dry matter accumulation and translocation and grain fillingHigh temperature and high temperature/drought after pollination decreased the grain numbers and weights,which led to the grain yield loss.The grain numbers,weights and yields were decreased by 15.0%,19.4%and 40.1%for Suyunuo 5 and 15.9%,8.2%and 26.8%for Yunuo 7 under high temperature stress conditions,respectively.Those three parameters were decreased by 29.8%,30.7%and 53.0%for Suyunuo 5 and 28.2%,23.0%and 47.4%for Yunuo 7 under high temperature/drought stress conditions,respectively,indicated that Suyunuo 5 was more susceptible to high temperature/drought than Yunuo 7.High temperature during grain filling decreased the dry matter accumulation after pollination,translocation amount and contribution rate of vegetative organs photosynthate after pollination to grain yield,while translocation amount,translocation rate,and contribution rate of vegetative organ photosynthate before pollination to grain yield were enhanced.The influences of high temperature on dry matter accumulation and translocation were aggravated by water deficit.High temperature and high temperature/drought after pollination reduced the grain dry weight,fresh weight,fresh grain volume and water content,indicated that grain filling was suppressed and duration was shortened by stress,especially under high temperature/drought conditions.2.Leaf photosynthetic propertiesHigh temperature during grain filling decreased the leaf SPAD value,water content,activities of phosphoenolpyruvate carboxylase and ribulose-bisphosphate carboxylase,which induced the reduction of leaf photosynthetic rate,stomatal conductance,transpiration rate,Fv/Fo,and Fv/Fm,and the increase of inter-cellular CO2 concentration and Fo.The influence of high temperature on leaf photosynthesis was aggravated by the interaction of high temperature and drought.3.Leaf senescenceThe contents of soluble protein and pigment(chlorophyll and carotenoid)and activities of antioxidases(catalase,peroxidase and superoxide dismutase)in leaf rose first and fall later,while malondialdehyde content gradually increased with the proceeding of leaf senescence.The leaf soluble protein,chlorophyll and carotenoid contents were reduced and the activities of catalase,peroxidase and superoxide dismutase were weakened,while malondialdehyde content was increased by heat stress during grain filling.The influences of high temperature on those parameters were exacerbated when drought and high temperature occurred simultaneously.4.Accumulation of grain components and activities of participant enzymesUnder heat stress conditions,the soluble sugar content was increased at 5-15 DAP,decreased at 20 DAP,and the value was similar to ambient temperature at 25-30 DAP,while the content under heat/drought stress conditions was suppressed during whole grain developmental stages.The starch content was higher before 15 DAP under heat stress and before 10 DAP under heat/drought stress and the accumulation was suppressed thereafter.The protein content before 10-15 DAP was decreased by stress,while the value was increased,especially under high temperature/drought conditions thereafter.High temperature and high temperature/drought changed the activities of enzymes involved in the synthesis of grain components.The activities of sucrose phosphate synthetase(SPS)and sucrose synthetase(SS)(synthetic)were reduced by stress and the reduction was serious under heat/drought stress conditions.The activity of SS(cleavage)was increased by stress before 15 DAP and the increase was higher under heat/drought conditions for Yunuo 7 and under high temperature conditions for Suyunuo 5,respectively,and the difference was disappeared after 20 DAP.The activities of ADP-glucose pyrophosphorylase(AGP),soluble starch synthase enzyme(SSS),and starch branching enzyme(SBE)that involved in starch synthesis were decreased by stress and the decrease were serious under high temperature/drought conditions.The activity of glutamine synthetase(GS)was suppressed by stress and the suppression was aggravated by high temperature/drought.The activities of glutamate synthase(GOGAT)under different stages were increased by heat stress.The value was also increased by heat/drought stress at 5-10 DAP and the increase was higher than high temperature,while the value in response to heat/drought stress after 15 DAP was dependent on variety and year.5.Grain endogenous hormones contentsIndole acetic acid(IAA),cytokinin(CTK)and zeatin(Z)contents under high temperature and high temperature/drought conditions were increased early and decreased thereafter during grain filling.The increases of IAA content at early grain development stages were higher under high temperature conditions in 2014 and under high temperature/drought conditions in 2015,respectively.The reduction of it under later grain filling stages was higher under high temperature/drought conditions in both varieties in both years.The increase of CTK contents at early grain development stages was higher under heat stress,while the decrease of it at later grain filling stages was large under high temperature conditions for Yunuo 7 and under high temperature/drought conditions for Suyunuo 5,respectively.The Z content was increased early and decreased thereafter by stress and the increase was higher under heat stress conditions and the decrease was higher under heat/drought stress conditions,respectively.The ABA content was increased by stress and the increase was higher under high temperature/drought conditions.The gibberellin content(GA3)was also increased by stress,and the value for Yunuo 7 was higher under high temperature conditions at early grain development stages and higher under high temperature/drought conditions at later grain filling stages.The value for Suyunuo 5 in response to stress was different between two years.The ethylene content(ETH)was decreased by high temperature/drought stress,while the value was increased by high temperature at 15-25DAP for both varieties.In conclusion,high temperature and high temperature/drought after pollination increased the aborted grain numbers,suppressed grain development and shortened filling duration and reduced grain weight,which led to the grain yield loss.Heat and heat/drought stress during grain filling reduced the leaf water content,SPAD value and activities of photosynthetic and antioxidant enzymes,which restrained the leaf photosynthesis,accelerated leaf senescence,and reduced photoassimlate supply.High temperature and high temperature/drought during grain filling decreased the activities of AGP,SSS,SBE,GS,SPS and SS(synthetic),and increased the activities of SS(cleavage)and GOGAT.The IAA,CTK and Z contents were increased by stress at early grain development stages and decreased by stress thereafter,GA3 and ABA contents was increased by stress during grain filling,while ETH content was decreased by heat/drought stress and the value was increased by heat stress.The lower grain starch accumulation under stress was due to the changes of activities of enzymes involved in grain components accumulation and content of endogenous hormones.Generally,leaf photosynthesis and senescence,dry matter accumulation,grain filling and components accumulation was serious affected by high temperature/drought. |
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