Responses Of Maize Leaf And Kernel To Heat Stress

In recent years,with global climate change,high temperature process occurred frequently,the research of high temperature on crop physiological ecology has become a hot topic.Maize requires a higher temperature in its whole growth period,but abnormal high temperature often lead to heat injury for maize that resulting in decreased production.In order to explore the response characteristics of the vegetative and reproductive growth of maize on heat stress,We conducted a field experiment using two maize hybrids Zhengdan958(ZD958)and Xianyu335(XY335)as they have large planting acreage in China,ZD958 on behalf of Chinese maize varieties and XY335 representative America Maize Varieties.From the 10 th leaf fully expanded to tasseling stage,in an artificial simulation heat device,plants were given a high temperature treatment(T)from 8:30 to 17:30 daily,and the other grown under natural temperature as controls(CK),study the response characteristics of maize’s Leaf and kernel to heat stress.The main results were as follows: showed that:(1)Under high temperature,Compared with the control,The plant height of ZD958 increased while increased first and decreased afterwards for XY335,and it became more significant with the stress continue;The leaf area index,stem diameter,specific leaf weight and dry matter of ZD958 and XY335 decreased,and the decreased of on leaf area index and leaf weight of ZD958 were higher than XY335 while the dry matter accumulation and stem diameter of ZD958 was less than XY335.(2)The relative electrical conductivity and MDA of mature leaves is higher than the young leaves and increasing during high temperature stress,the increase extent was higher in mature leaves than in young leaves of ZD958 while it is opposite for XY335.The superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)show different trends among maize varieties and leaves under heat stress.In the early stage of high temperature stress,compared with control,the activities of SOD,POD and CAT increased in mature leaves of ZD958,and then decreased even lower than control.Contrary to the mature leaves,the three enzymes activities increased in the later stage in young leaves under high temperature.In mature leaves of XY335,theactivities of SOD and POD decreased while increased for CAT,and the three enzymes activities increased or increased significantly in young leaves of XY335.Under high temperature stress Compared with control,there were no significant changes of soluble protein in leaves,the contents of soluble sugar increased first and decreased afterwards in leaves of ZD958,increased in mature leaves of XY335,and showed a change of increased-decreased-increased-decreased in young leaves of XY335.The content of free proline present a trend of decreased-increased-decreased in mature leaves,and increased first and decreased afterwards in young leaves of ZD958 while increased in XY335.(3)Compared with the control,the light intensity range of photosynthesis was shortened as the light compensation point(LCP)increased and the light saturation point(LSP)decreased under high temeperature.The apparent quantum efficiency(a)and dark respiration rate(Rd)increased.The maximum net photosynthetic rate(Pmax)of ZD958 increased while decreased for XY335.In ZD958,Net photosynthetic rate(Pn),light energy utilization(LUE)at low light intensity,stomatal conductance(Gs)and instantaneous water use efficiency(WUE)decreased,but intercellular CO2concentration(Ci)at low light intensity and transpiration rate(Tr)increased;In XY335,instantaneous WUE at low light intensity,Pn and LUE decreased,but Tr at low light intensity,Ci under high Light Intensity and Gs increased.The enzymes of Photosynthesis show different trends among maize varieties and leaves under heat stress,and different enzymes have different sensitivity to heat stress.Under high temperature stress,compared with control,the activities of PEPCase were decreased while decreased for Ru BPCase in mature leaves of ZD958;The activities of PEPCase showed a change of decreased-increased-decreased while showed a change of increased-decreased-increased-decreased for Ru BPCase in young leaves of ZD958;And the activities of AGPase showed a change of increased-decreased-increased and UGPase decreased first and increased afterwards in mature leaves and young leaves of ZD958.The activities of PEPCase increased first and decreased afterwards in mature leaves and young leaves of XY335;in mature leaves of XY335,Ru BPCase showed a change of decreased-increased-decreased-increased,AGPase decreased first and increased afterwards,UGPase showed a change of increased-decreased-increased;In young leaves of XY335,Ru BPCase showed a change of increased-decreased-increased,AGPase showed a change of decreased-increased-decreased-increased,UGPase showed a change of increased-decreased-increased-decreased.(4)Under high temperature stress,compared with control,in mature leaves of ZD958,the content of ABA and GA increased while decreased for ZR,and decreased first and increased afterwards for IAA;In young leaves of ZD958,the content of GA,ZR and IAA decreased while increased first and decreased afterwards for ABA.In mature leaves of XY335,the content of ABA,GA,ZR,IAA is decreased;In young leaves of XY335,the content of ABA is decreased,while changed repeatedly for GA,ZR and IAA.(5)After high temperature stress,compared with control,the content of ABA,GA,ZR,IAA increased first and decreased afterwards in kernel of ZD958;The content of ABA and ZR increased first and decreased afterwards in kernel of XY335,GA keep increasing,and there were no significant changes of IAA in the early stage of kernel grouting and increased afterwards.(6)With ongoing of grouting,the activity of GBSS,SSS,SS,SPS were higher in kernel of ZD958 and XY335 after high temperature.The period of the vegetative and reproductive growth under high temperature wes beneficial to synthesis of kernel starch.(7)Compared with control,after high temperature,the number of leaf mesophyll cells decreased,intercellular space greatens and loosely arranged,structure of the garland smaller,and the leaves and the upper and lower epidermis thinner.Chloroplast deformed and drifted from the cell wall to the center,and the Chloroplast of mature leaves became slender while the young leaves became swollen and rounded;The number of starch granules in the chloroplast increased and the volume was larger.Grana reduced or even disappear,grana layer and substrate were blurred,lamella loosely arranged and disorder.(8)Compared with control,after high temperature,the dry weight of kernel decreased in the early and middle stage of Grain filling and increased afterwards,the curve of grouting rate presented a characteristic of parabolic.The maximum grain filling rate decreased by 8.08% and 14.91% and the time was delayed for 6 days and 2days respectively of ZD958 and XY335.Compared with control,the grain filling rate was lower in the early stage of grain filling and higher afterwards.Compared with control,High temperature reduced the spike ear diameter,grains per row,kernels per spike,dry matter weight and yield,and the inhibition effect of XY335 was greater than ZD958;the bald tip length increased,and there was nosignificant changes of ear rows;The spike length and hundred-grain weight of ZD958 were lower than control while it was opposite for XY335.