Grain Filling Characteristics of Rice and Their Relationships to Physiological Activities of Grains

The grain filling Characteristics of 6 rice cultivars (combinations) and their relationships to the physiological activities of grains were studied. For the cultivars with good grain plumpness of Wuyujing 3 and 9516, the filling processes of superior and inferior grains were synchronous. The difference between superior and inferior grains was small in terms of the initial filling power (R 0), the maximum filling rate (G max ), the mean filling rate (G) and the time reaching the maximum filling rate (T max ). For the cultivars (combinations) with poorer grain plumpness of Yangdao 4, Shanyou 63, PC311/Zaoxian dang 18 and PC311/IR36, the filling processes of superior and inferior grains were asynchronous, and R 0, G max and G of superior grains were larger than those of inferior ones. The content of soluble sugars was obviously higher and starch content was much lower in inferior grains than in superior ones at early grain filling stage. The physiological activities of grains (PAOGs) (content of zeatin + zeatin riboside and spermidine, starch synthase activity) were higher in superior grains and for the cultivars with good grain plumpness than in inferior grains and for the cultivars (combinations) with poorer grain plumpness. PAOGs at early grain filling stage were very significantly correlated with R 0, G max , G, filled grain percentage and grain weight. PAOGs at early filling stage and grain weight were increased after spraying N 6 (benzyl) adenine at the initial heading, and the results were reversed when cycloheximide was applied. The results suggest that PAOGs manipulate the grain filling rate and grain plumpness.