Study On Physiobiochemical Characteristics Of Grain-filling In Rice (Oryza Sativa L.)

Three different rice cultivars, characterized by a larger panicle type, such as Eryou86,peiai64s/E32 and new plant type rice NPT-22, were used for the experiment to investigate the physiochemical mechanism on the difference in grain-filling of the three rice cultivars through analyzing the relationships among 搒ource~~ 搒ink?and 搕ransportation?per Se. The main results were summarized as follows:l.As far as the source capability was concerned,NPT-22 had the higher source capability among the three cultivars under consideration, showing its highest net photosynthetic rate which was attributed to its highest contents of chlorophyll and soluble carbonhydrate , but lower soluble protein content in the leaves compared with the other cultivars Eryou86 and peiai64s/E32.2.According to the results obtained from analyzing the physiochemical activity in grain-sink of rice, it indicated that the strong grain of rice in each entry had higher initial growth power than the weak grains, in turn leading to entering active grain-filling stage earlier. The strong grain also performed higher activities of ADP-glucose pyrophosphorylase and starch synthase, higher contents of IAA and ABA, higher ratios of ABAIIAA,ABAIGA1+3~ABAI (IAA+GA1 +3+ZR5+ABA) and (ABA盳R5) / (IAA+GA1 +3+ZR5?ABA) than the weak grain in each entry during the early stage ofgrain-filling. It was helpful to promote the transportation of dry matter into the strong grains, resulting in increased filled grains in this case. The weak grain in each entry showed its higher activities of the key enzymes, higher contents of the phytohormone and its ratios as mentioned above only after mid-stage of grain-filling. However at this moment, carbonhydrate produced by synthesis gradually reduced, especially at the late grain-filling stage. It therefore resulted in decreased filling rate of the weak grains. The result also showed that there were differences in genotypes in the case of the physiochemical activities. Among the three rice cultivars concerned, NPT-22 exhibited its poor physiochemical activities, in turn led to lower ability to promote transportation of dry matter into the weak grains, consequently decreased percentage of filled grains and yield.3.Regarding the status of dry matter transportation from stem-sheath parts to grain-sink, it showed that translocation of stem-sheath reserves in peiai64s/E32 and Eryou86 to grains took place within 20 days after heading. The rate of the transportation still kept higher in ripening stage. However the reverse was true in case of NPT-22, showing its lower translocation rate within 10 days after heading, then negative rate of the translocation was found, especially at late stage of heading. This implied that NPT-22 was poor in transportation of dry matter which was considered an obstacle to realize the yield potential of the rice cultivars...