Physiological And Biochemical Mechanisms Of Starch Accumulation In High-starch Maize

To explain the profound mechanism,the two high-starch maize and two common maize have been used as experiment materials,we studied the dynamic accumulation of starch,amylose and amylopectin, the proliferation of endosperm cell,the changes of endogenous plant hormones in kernels and the activity changes of key enzymes involved in starch synthesis and the relationship to the accumulation speed of starch,amylose and amylopectin during grain filling period.The main results shows as followed:1 The changing of the accumulation content of starch (tatal starch,amylose,amylopectin)during grain filling of the 4 types maize increased in"S"curve fashion until reaching a stationary phase of max- imal content.Amylose accumulation rate of maize were not significantly different in early grain filling stage,the differences of amylose content appeared at the middle to later stage of grain filling but the beginning stage of grain filling.The difference in amylopectin content appeared at the beginning stage of grain filling,amylopectin content of the two high-starch maize were constant higher than the two common maize during grain filling.The accumulation of amylopectin content depends on the rate of amylopectin,s accumulating and the maximal accumulating rate.In the total starch content,the difference between the amylopectin content was distinct, however,the difference of amylose content was not.2 Endosperm cell number was counted and simulated by Richards equation.The results indicated the endosperm cell number of the two high-starch maize were higher than the two common maize during grain filling and the endosperm cell number depends on the proliferation rate include the maximum proliferation rate.Endosperm cell proliferation was primary at early age of endosperm develop- ment,and starch accumulation was primary at late age of endosperm development. Improve the rate of proliferation at the early age and the rate of starch accumulation at the late age was more beneficial for the improvement of starch accumulation .3 According to the correlation analyse,changes in activities of SS,ADPGPPase,UDPGPPase,SSS,GBSS,SBE and DBE of 4 types of maize lines grains appeared a single-peak curves. The two high-starch maize had higer peaks of SS,ADPGPPase activities than the two common maize at the grain filling stage,but the SS's activities had no correlation to the starch accumulation of the 4 types maize,and the ADPGPPase's activities had a significantly positive correlation to the total starch and amylose's accumulating rate of the two high-starch maize.Compared with the two common maize,the two high-starch maize had higher peaks of SSS and GBSS's activities at the early grain filling stage,SSS's had a significant positive corelation to amylopectin's accumulating rates of the 4 types maize,expecially had a extreme significant positive correlation to the high-starch maize,however,the GBSS's activities only had a significantly positive correlation to the amylose's accumulating rate of the two high-starch maize.The two high-starch maize had higher peak values of SBE and DBE than the two common maize,and the activity of SBE was significantly positively correlated with the amylopectin accumulating rate,but the DBE's activities had a little relationship or a negative correlation to the starch accumulation. The results indicates that the activities of ADPGPPase,SSS and GBSS control the starch accumulation of the high-starch maize,and the SS,ADPGPPase, SSS,GBSS and SBE are the key enzymes to the synthesis of maize starch.4 Endogenous hormones plays an important role in grain filling.The content of IAA,GA and CTK(ZR+DHZR)in different maize had a trend of single-peak curve during the grain filling period and their peak value all appeared on 20 days after pollination. The content of ABA was high in the early grain filling and low in the late grain filling. According to the correlation analyse,IAAcontent had a negative correlation to the starch accumulation,GA and ZR's content had a significant positive correlation to the starch accumulation.ABA and DHZR's contenth and a little relationship or a negative correlation to the starch accumulation.IAA content was not beneficial for the starch accumulating,but the GA and ZR content were more beneficial for the improvement of starch synthesis ability.