Physiological Mechanism Of Post-Silking High Temperature And Drought Stress Affecting Leaf Senescence Of Waxy Maize

The experiment was conducted at Agricultural College of Yangzhou University in 2017 and 2018.Suyunuo 5(SYN5)and Yunuo 7(YN7)(control varieties of national waxy maize regional test in Southern China)were used as materials.The temperature was controlled by intelligent greenhouse and soil moisture content was controlled by weighing method.The effects of post-silking heat(HS)and/or drought stress(DS)after silking on dry matter accumulation and translocation,leaf photosynthetic and senescent characteristics,activities of anti-oxidant enzymes and contents of endogenous hormone of waxy maize were studied.The main results were as follows:1.Grain yield and dry matter accumulation and translocationPost-silking HS and/or DS reduced the grain numbers and weights,which led to the loss of grain yield.The decreased grain yield under HS,DS and heat and drought stress(HDS)for SYN5 were 30.5%,15.9%and 47.2%in 2017,and were 39.0%,39.4%and 48.0%in 2018,respectively.The decreased grain yield under HS,DS and HDS for YN7 were 27.6%,12.8%and 45.1%in 2017,and were 27.0%,34.2%and 51.4%in 2018,respectively.Post-silking HS and/or DS decreased the post-silking dry matter accumulation,translocation amount after silking and its contribution rate to grain yield,and those values present as CK>HS>DS>HDS.Post-silkiing HS and/or DS increased the translocation amount and ratio of pre-silking stored assimilates in vegetative organs and its contribution ratio to grain yield,and present as CK<HS<DS<HDS among different treatments.2.Leaf photosynthetic properties and N metabolismPost-silking HS and/or DS decreased the ear-leaf water content,photosynthetic rate,transpiration rate,stomatal conductance but increased the inter-cellular CO2 concentration.The activities of PEPCase,RuBPCase,NR and GS,the SPAD value,contents of soluble protein and pigment in apical,forth,and ear leaf were decreased by HS and/or DS,and showed tends of CK>HS>DS>HDS.The results of correlation analysis indicated that contents of pigments in leaves had slight effect on grain yield.The higher SPAD value,soluble protein content,and activities of PEPCase,RuBPCase and NR were beneficial to enhance leaf photosynthesis and nitrogen metabolism,and results in high grain yield.The high correlation coefficients between apical leaf and grain yield indicated its large influence on grain yield formation.3.Leaf senescence and endogenous Hormones contentsPost-silking HS and/or DS accelerated the leaf senescence significantly.The contents of ROS and MDA significantly increased by stresses,and showed tends of HDS>HS>DS>CK among different treatments.With the proceeding of plant development,the activities of SOD,POD,CAT in leaves increased initially and decreased thereafter,while the activity of APX gradually decreased,and the activities of those enzymes were weakened by stresses,especially when HS and DS occurred simultaneously.Under stress conditions,leaf IAA content decreased whereas ABA content increased,and the influence were severe under interaction of HS and DS.The results of correlation analysis indicated that high SOD and APX activity,low MDA and ROS content,and higher IAA content in leaves were beneficial to achieve high yield,and the effect was most significant in the apical leaves.