| With several typical rice varieties (including a hybrid combination) as materials, the characteristics of growth and development, remobilization of carbohydrate, and grain filling under dry-cultivated conditions were studied. The main results are as follows:1. Compared to moist-cultivated rice (conventional cultivation, the control), dry-cultivated (plastic film mulching cultivation) rice had slower tillering; smaller leaf area index and less accumulation of dry matter before the critical stage of productive tillers, and the results were reversed at the jointing. The percentage of productive tillers, grain-leaf ratio of dry-cultivated rice were smaller or lower than those of moist-cultivated rice, but the former was larger or higher than the later, in terms of the root dry weight at heading, and root-shoot ratio at heading. Dry-cultivated rice had fewer spikelets per panicle but more panicles per unit area than moist-cultivated rice. There was no significant difference between the two cultivated patterns in the percentage of ripened grains. The differences in grain weight and yield between dry- and moist-cultivated rice were significant for Zhendao 88 but not significant for indica hybrid rice of Shanyou 63.2. The re-allocation of pre-fixed 14C from stems to grains, the transfer radio of nonstructural carbohydrate (NSC) pre-stored in the stems and its contribution to grains from heading to maturity in dry-cultivated rice were very significantly greater than those in moist-cultivated rice. The dry-cultivation enhanced the activities of sucrose synthase and acid invertase in grains and a , -amylase in stems, with the activities of sucrose synthase and a -amylase enhanced more. Activities of a -glucosidase and starch phosphorylase were no significant differences between the dry-cultivation and moist-cultivation. The remobilization of starch and 14C transferred from stems to grains were very significantly and positively correlated with the activities of sucrose synthase in grains and a , 3 -amylase in stems, but not significantly correlated with a - glucosidase and acid invertase activities, and negatively correlated with activity of starch phosphotylase. The results indicate that the dry-cultivation in rice promotes carbon remobilization from stems to grains during grain filling and enhanced activities of sucrose synthase in grains and a , -amylase in stems play an important role.3. Compared to moist-cultivated rice, dry-cultivated rice had lighter grain weight, greatergrain-filling rate, earlier time to reach the maximum grain-filling rate and shorter active grain-filling period, which was more obvious for inferior grains than for superior ones. The contents of indole-3-acetic acid (IAA), zeatin riboside (ZR) and abscisic acid (ABA) were higher in superior grains than in inferior ones at early grain-filling stage. The peak of IAA and ZR contents appeared just before, and that of ABA content simultaneously with the maximum grain-filling rate. The grains of dry-cultivated rice contained less IAA and ZR but more ABA than those of moist-cultivated rice at early and mid grain filling stages, and the differences were mainly in inferior grains. When 20 x 10-5 mol/1 IAA was applied to plants at the initial grain filling stage, IAA and ZR were increased and ABA was decreased in inferior grains, and active grain-filing period was prolonged and grain-filling rate was decreased. The grain weight of dry-cultivated rice was increased and that of moist-cultivated rice was decreased to a different degree by application of IAA. When 25 10-6 mol/1 ABA was applied, the contents of hormones in grains, active grain-filling period and grain-filling rate were reversed with those of application of IAA, and the grain weight in dry-cultivated rice was significantly reduced. The results suggest that shortened grain filling period and reduced grain weight in dry-cultivated rice are attributed to an increase in ABA or decreases in IAA and ZR in the grains. Regulation of the ratio of ABA to IAA in grains would increase the grain wei...
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