Studies On Physiological Characteristics And Formation Of Grain Quality During Grain-filling Period Under High Temperature Stress In Rice Plants

Rice grain is used as the main food by half of the world's population including nearly whole East Asia and Southeast Asia.The Chinese cultivation land area of rice accounts for about 25%of the world,and 33%of the whole cultivation land in China.In recent years,heat injury of rice plants caused by "effects of green house" happens with increasingly frequency,which may bring hidden dangers of food security.In this research,rice plants with heat tolerance were used as material,high temperature stress were set during filling period,the aim was to systematically study the physiological mechanism and effects on grain quality under high temperature.The main results are as follows:1.Effects of high temperature stress on photosynthesis and transpiration during filling periodUnder high temperature,the chlorophyll content was lower than control in Xinongyou 30 and Fuyou 1,and decreased during filling period.The net photosynthetic rate(Pn) also dropped under both high and optimal temperature in two cultivars K30 and 21.Compared with 21,Pn was nearly same in K30 during the first filling period,but obviously higher during the mid and late filling period(20-30 d).Under high temperature,stomatal conductance(Gs),CO₂ concentration inside leaf (Ci) and transpiration rate(Tr) were above the control.Change of water use efficiency(WUE) in two cultivars was different,the range of WUE was small in K30 treated under high temperature(the range was 21.6%between the maximum and minimum),while larger in K30 control(the range was 49.4%);WUE of K30 treatment was below control during the first filling-period(5-15d),while above the control during the late period(20-30 d).Under high and optimal temperature,the change scope of WUE of 21 was great during the late filling period(20-30 d),and WUE of control was lower than treatment in 21 during the whole filling period;Under optimal temperature,Carbon dioxide use efficiency(CUE) increased during the first filling period in both two cultivars,then gradually decreased during the mid filling period,CUE of 21 was higher than K30.Under high temperature,CUE of K30 dropped during first filling period(5-10 d),then gradually rised(5-25 d),and last dropped to the lowest;CUE of 21 showed downtrend during filling period.The trend of apparent quantum yield(AQY) was identical in both two cultivars under high and optimal temperature:AQY was higher during first filling period,then gradually declined.Compared with control,AQY of 21 treatment was similar during first and mid filling period(5-20 d),but obviously lowered during the late filling period(25-30 d);AQY of K30 treatment was below the control under high temperature during the whole filling period.2.Effects of high temperature stress on chlorophyll fluorescence kinetics during filling periodUsing Xinongyou 30 and Fuyou 1 as material,the characteristics of chlorophyll fluorescence kinetics were studied.The results showed that F_o increased during filling period,compared with control,F_o increased 8.61%and 26.43%during mid and late filling period in Xinongyou 30,also 5.02%and 12.21%in Fuyou 1.Compared with control,both F_v/F_o and F_v/F_m was low in two cultivars and declined during the whole filling period;F_v/F_o and F_v/F_m dropped 20.76%and 5.35% from 7 d to 28 d in Xinongyou 30 treatment,while 6.05%and 1.23%in Xinongyou 30 control,and the same trend showed in Fuyou 1,qP was lowest in the first filling period,highest in 14 d,then gradually decreased.The two cultivars differed,compared with control,qP was beyond during the whole filling period in Fuyou 1,while below during the first three stages in Xinongyou 30.3.Effects of high temperature stress on antioxidant system during filling periodUsing K30 and 21 as material,effects of high temperature on antioxidant system during filling period were studied.The results showed that activity of superoxide dismutase(SOD) declined in K30,especially in the late filling period under high temperature,compared with 21,activity of SOD increased in K30.Activity of peroxidase(POD) of K30 also showed higher under high temperature, but the variety of POD activity was not observed in 21 under high and optimal temperature.In K30, catalase(CAT) activity increased most obviously among the three enzymes under high temperature: the CAT activity of treatment was 6.7 times as great as the control.In K30,soluble sugar content declined under high temperature,in 21,soluble sugar content rised during the first filling period(5-15 d),falled during the late filling period(15-30 d) compared with the control.In the late filling period,soluble sugar content of two cultivars had rising trend.In K30,proline content of treatment was lower than control during the filling period of 5-20 d,but higher during the filling period of 20 -30 d.Malondialdehyde(MDA) content increased in two cultivars under high temperature,the change scope of MDA content in K30 treatment was narrow,while MDA content in K30 control ascended markedly.Under high temperature,soluble protein content descended in K30 leaf,first ascended in 21 leaf during filling period of 5-20d,then dropped during the filling period of 20-30d. Compared with 21,soluble protein content had high level in K30 leaf.The dynamic change of thermostability protein content was identical with soluble protein,the thermostability protein content in K30 was higher than 21.Using Xinongyou 30 and Fuyou 1 as material,the dynamic change characteristics of active oxygen resistance reactivity units(AORRU) and total antioxidant reactivity units(TARU) were studied.AORRU of treatment was lower than the control during the whole filling period;in the late filling period,AORRU decreased to 45.16%and 35.99%in Xinongyou 30 and Fuyou 1 respectively contrast with the control.TARU increased in first filling period in Xinongyou 30 under high temperature,while decreased in the late filling period.TARU descended in Fuyou 1 in mid and late filling period(14-28d),and TARU of treatment was lower than control during the whole filling period.4.Dynamic variation of endogenous hormones in leaf and grain during filling period under high temperature stressUsing K30 and 21 as material,dynamic change of endogenous hormones in leaf and grain during filling period was studied.In leaf,abscisic acid(ABA) content increased in K30,but no change of ABA content appeared in 21 under high temperature.In grain,ABA content of treatment was much higher than control in K30.During the late filling period,ABA content of grain was lower in 21 than K30.Indole-3-acetic acid(IAA) content of grain declined in both cultivars during the late filling period.In leaf,the effect of high temperature on gibberellic acid(GA₃) content of two cultivars was opposite:increased in K30,while decreased in 21.In grain,GA₃ content dropped in the late filling period.Compared with 21,the period of zeatin nucleotide(ZR) highest content was long under high temperature in leaf in K30,and higher content of ZR of treatment was found in K30 grain.Under high temperature,ABA ratio of leaf to grain in K30 was much higher than 21 during the first filling period of 5 and 10 d(4.3 and 4.5 times respectively).5.Effects of high temperature stress on the metabolism of starch and grain quality during filling periodUsing K30 and 21 as material,effects of high temperature on the metabolism of starch and grain quality during filling period was studied.In two cultivars,activities of sucrose-phosphate synthase(SPS) and sucrose synthase(SS) declined under high temperature.The change process of starch branch enzyme(SBE or Q enzyme) was from rising to falling,the highest activity appeared in the filling period of 10 to 15 d in 21,and 10 to 15 d in K30.The content of soluble,thermostability protein and lysine m grain increased under high temperature.The results of mature grain analysis showed that chalkiness accrued,protein content increased, 1 000 grain,total starch and amylose content decreased in four cultivars.Comparing the two cultivars of Xmongyou 30 and Fuyou 1 under optimal temperature,protein content was approximate. Protein content ascended 15.1%1 after high temperature stress in Fuyou,while 51.3%in Xinongyou 30.Total starch content dropped 14.1%after high temperature stress in Fuyou 1,while 20.5%in Xinongyou 30.