Responses Of Reproductive Organs Development In Maize(Zea Mays L.) To High Temperature Stress

Global warming is the main characteristic of global climate change.The impact of high temperature on crops has become a hot topic.As an important food crop originated in the tropical regions of Central and South America,maize requires a higher temperature in its whole growth period,but abnormal high temperature often lead to heat injury for maize,which resulting in decreased production and quality.Heat stress affects plant growth throughout its ontogeny,though heat-threshold level varies considerably at different developmental stages.In order to reveal the mechanism of high temperature stress on maize,this study was to investigate effects of high temperature stress on tassel and ear development and yield in maize.We conducted a field experiment using two maize hybrids Zhengdan 958(ZD958)and Xianyu 335(XY335),because they have large planting acreage in China.ZD 958 on behalf of Chinese maize varieties,XY 335 representative America Maize Varieties.From the 9th leaf fully expanded stage 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).The main results were as follows:showed that:(1)Under high temperature stress,the anthesis silking interval(ASI)of two maize hybrids were prolonged,the rates of pollination and fertility were decreased,and the kernel number per ear were reduced markedly,which resulted in significant yield reduction,but the relative value of yield reduction was less for ZD958 than XY335.(2)Under high temperature stress,the tassel development was inhibited significantly,which mainly manifested as delayed in tassel differentiation,the number and the length of tassel branch,the number of flowers and pollen grain of tassel were decreased.The viability and germination of pollen grain were declined.The anther epidermal cells appeared irregular shape and loosely arranged,and the connectivum vascular tissue damaged.The above events showed a significant difference between two hybrids,and the effects were less for ZD958 than XY335.(3)Under high temperature stress,the ear development was inhibited significantly,which mainly manifested as delayed in silk differentiation,reduced in fluff number per silk in ear,and declined in the viability of silk.(4)Under high temperature the trend of antioxidant enzyme activities change,osmoregulation substances content,relative conductivity,the amounts of MDA and souble protein accumulation both in ear and anther are the same.The superoxide dismutase(SOD)activity increased obviously in maize anther at early stage under high temperature stress,then decreased rapidly,the peroxidase(POD)and catalase(CAT)activity continue to rise.Compared with heat sensitive lines,higher souble proline content and souble sugar content,lower malondial dehyde(MDA)content,relative conductivity and souble protein content were found in anther of heat tolerant lines.(5)Under high temperature stress,the IAA content and dry matter wight in tassel has a similar trend.With high temperature stress continues,the IAA content of tassel in two maize varieties decreased significantly,and ZD958 have a smaller decline.Under high temperature stress,the ZR content of tassel in ZD958 was rise significantly in the top,and decreased in the base.Both top and base of XY335 reduced obviously.The GA3 content of tassel in XY335 have reduced obviously under heat.The ration of IAA to ABA were reduced under heat,XY335 have a larger decline.The effect of high temperature on the content of endogenous hormones in maize male spike is the direct cause why the growth and development of spike was blocked under heat.