Physiological And Molecular Mechanisms Of High Temperature Damage At Rice Spike Stage

Rice is more sensitive to the ambient temperature and vulnerable during panicledevelopment period. This study used indica hybrid rice as material to discuss the impact ofhigh temperature stress on photosynthetic physiology of rice leaf, endogenous hormonescontents, gene expression of key enzymes which control endogenous hormone synthesis inrice, and regulation effect of methyl jasmonate on rice flowering under high temperature.Main results are as follows:1、Artificial climate box was used to control temperature, Provided with a hightemperature (8:00～18:00,38℃;18:00～8:00，30℃) and optimum temperature control(8:00～18:00,32℃;18:00～8:00,25℃) treatment during rice booting stage. The resultsshowed: under high temperature stress, the rice leaf chlorophyll content and chlorophylla/b ratio decline. High temperature make the rice leaf net photosynthetic rate, stomatalconductance and transpiration rate decreased, intercellular CO2concentration increased;Fv/Fm and qP decline, NPQ with the Fo rise. High temperature stress acceleratedproduction rate of O2-· in rice leaf, H2O2content increased, decreased activity of protectiveenzymes SOD and POD, which led to rice antioxidant capacity decreased significantly.Under the high temperature rice leaf free proline, soluble sugar and soluble protein contentdecreased while MDA content increased.2、The content changes of IAA, GA, CTK and ABA in rice leaves was measured byenzyme-linked immunosorbent assay (ELISA) under high temperature stress. The resultsshowed: in rice leaf, IAA, GA and CTK content significantly decreased, while ABAcontent increased significantly under high temperature stress. This result is consistent withGA20ox, ipt and NCED gene relative expression levels in rice leaf.3、Using RT-PCR technique and the rice plant stable expression18SRNA as aninternal reference, to study relative expression levels of GA20ox gene which control thekey enzyme GA20-oxidase of gibberellin biosynthetic, ipt gene which control the keyenzyme isopentenyl transferase of cytokinin synthesis and NCED gene which control thekey enzyme9-cis-epoxycarotenoid dioxygenase biosynthetic in rice leaves under hightemperature stress. The results showed: relative expression levels of GA20ox gene and iptgene reduce while NCED gene increase in rice leaves under high temperature stress.4、Spraying exogenous methyl jasmonate could increase the number of openingspikelets, Concentrate spikelet opening time, improve the rate of spikelet flowering before noonday during rice flowering under high temperature; Moreover, exogenous methyljasmonate could increase pollen vigor under high temperature. Therefore, in praticaloperation, we can try to spray exogenous methyl jasmonate to reduce heart damage ofplants, and achieve high and stable yield of rice.