Studies On The Relationship Between The Metabolism Of Sucrose And Starch And Grain Yield In Hybrid Rice

Effective earing tillers, seed-setting percentage, thousand kernel and filled-grain percentage are key factors which comprise yield. The factors have relation to carbohydrate metabolism. Materials of this study are five varieties and combinations of. hybridized rice, which are different in effective earing tillers, thousand kernel and grain yield. The carbon metabolism and physiological chemical property, such as sucrose and starch cintent and key enzymes of flag leaf, stem-shealth, and kernel are dynamically measured from anthesis to maturity. The expressions of sucrose phosphate synthetase (SPS) gene are compared by using RT-PCR method, Correlations of activities of key enzymes at early filling stage and during whole filling period with seed-setting percentage, thousand kernel weight and grain yield are compared. The influence of metabolism of sucrose and starch in grain yield are studied. The reference view is suggested in physiology, biochemistry and molecular biology for super-yield of hybrid rice.The main results are followings:1. The net photosynthetic rates of the flag leaf reach peak (come to a climax) eight days after blossom for different varieties and combinations, which appear single mode curve. High yield combination 683/527 has the highest rate, and the longest duration of the high rate; The stomatal conductance of flag leaf is positive correlated with the net photosynthetic rate; The content of sucrose, and the activity of the SPS of flag leaf are also high, and they are highly correlated; Moreover, the activity of the sucrose synthetase of flag leaf obviously increases from middle to later grain-filling period. Therefore, the net photosynthetic rate, the activity of the SPS and the sucrose synthetase can be an indicator of high energy.2. During the early and middle grain-filling period, high yield combination 683/527 has high content of sucrose and starch in the stem-shealth, which appears single mode curve. It is of benefit to transfer material from stem-shealth to kernel; The changes of activity of a-amylases, the content of sucrose and starch of other combinations are two mode curve, which illustrates that the material can not be immediately transferred from stem-shealth to kernel during the later grain-filling period. The dynamic change of thesucrose content in the stem-shealth is correlated with the activity of the SPS and the sucrose synthetase. During the early filling period, the activities of a-amylases are relative low for all combinations; they quickly got high after the middle term. The degradation of starch is correlated with the activity of a-amylases. High yield combination 683/527 has the highest activity, which is of benefit to decompose and transfer starch from stem-shealth to kernel. Oppositely, II-32A/ Lianhui 9 has relative low activity, which is unfavorable to decompose and transfer starch from stem-shealth to kernel.3. The superior grain and inferior grain trend to fill with the same pattern for 683/527 and Xianyou 63 with good grain plumpness, while the superior grain and inferior grain trend to fill with different pattern for II-32A/ Lianhui 9 with poorer grain plumpness; The initial filling rate of a kernel, the maximum filling rate of a kernel, and the growth capacity of a kernel of superior grain are obviously larger than these of inferior grain. The time reaching the maximum filling rate of superior grain is obviously smaller than that of inferior grain.4. During the early grain-filling period, the activities of sucrose synthetase, ADP-glucose phrophosphorylase, and starch synthetase increase quickly. Therefore, the starch content of superior grain is higher than that of inferior grain; The activity of sucrose synthetase of inferior grain displays later than that of superior grain, which is unfavorable to decompose the sucrose transferred to the kernel, it makes inferior grain to have higher percentage of solvable sugar than superior grain to do. The activity of the kernel sink (ADP-glucose phrophosphorylase and sucrose synthetase) is positive correlated with the initial filling rate of a kernel, the maximum filling rate of a kernel, and the filled-grain percentage.5. High yield combination 683/527 has the highest seed-setting percentage, filled-grain percentage, and theoretical yield, while the lowest for II-32A/ Lianhui 9. The combination has high filled-grain percentage because of high percentage for both superior grain and inferior grain, the difference of them is small; oppositely, the combination has low filled-grain percentage, which is mainly due to inferior grain. The difference of seed-setting percentage among the varieties and combinations is mainly due to the difference of shriveled grains. The net photosynthetic rates, the activity of the SPS,sucrose synthetase, a-amylases, ADP-glucose phrophosphorylase, and starch synthetase are correlated with with seed-setting percentage.thousand kernel weight and grain yield.6. The expression of SPS gene is different between parent and varieties and combinations after blossom. The expression of SPS gene of hybridized combination results in the complementarity of parents' expression.