Effects Of Temperature And Light On Quality Of Grains On Different Positions Of A Panicle And Its Physiological Mechanisms

With typical Indica and Japonica rice cultivars as materials, the effects of temperature and light on the quality of grains at different positions within a rice panicle were studied. The main results were as follows.1. Effects of temperature on the quality of different grains within a rice panicle: (1) High temperatures imposed at early and middle grain filling stages reduced brown rice rate(BRR), head rice rate(HRR) and head milled rice rate(HMRR), the later-flowered grains was affected more greatly,but influences of temperature on two materials had some difference.(2) Both high and low temperature imposed at early grain filling stage significantly increased chalkiness degree (CD) and chalky grain percentage (CGP) of Yangdao 6, while high temperature treatment at early grain filling stage and low temperature treatment at middle grain filling stage significantly increased CD and CGP of Yangjing 9538; the effects of high temperature treatment was more greatly than that of low temperature treatment, and grains on a primary branch, in general, was more greatly affected than that on a secondary branch, and that of the earlier-flowered spikelets was greater than that of later-flowered spikelets on the same branch. (3) Amylose content (AC) was reduced under different temperature at early filling stage, the influences of temperature on grains on primary branches were more greatly than those of secondary branches; low temperature treatment at middle grain filling stage increased AC , but reduced gel consistence (GC). (4) Both high and low temperature imposed at early grain filling stage increased crude protein content(CPC)of Yangdao 6, while all temperature treatments increased CPC of Yangjing 9538. Influences of low temperature treatment was more serious than that of high temperature treatment and grains on secondary branches were affected more serious than those on primary branches, and that of later-flowered spikelets more serious than that of the earlier-flowered spikelets. (5) Both high and low temperature treatments reduced breakdown value (BDV) and increased setback value (SBV), grains on primary branches were affected more greatly than those on secondary branches.2. Effects of light on the quality of different grains within a rice panicle:(1) With the reduction in light intensity, milling quality became poor, and HMRR was affected most seriously. The effect of weak light treatment on the quality of later-flowered grains was greater than those of earlier-flowered on the same branch, and grains on primary branches more than those on secondary branches. (2) With the weakness of light intensity, CD and CGP increased, the effect on Yangjing 9538 was greater than Yangdao 6, the effect on grains on primary branches greater than those on secondary branches. Different light intensity differently affected earlier or later flowered grains that. (3) With the reduction of light intensity, AC reduced, the effect on Yangdao 6 was greater than that on Yangjing 9538, and the effect on grains on primary branches were greater than those on secondary branches. GC of grains on both primary branches and secondary branches reduced with the reduction in light intensity, but GC of grains on secondary branches would increase when light intensity reduced to a weakest point. (4) The reduction in light intensity made quality of cooking and eating became poor, but increased CPG.3. Physiological mechanisms for the variation in the quality of grains at different positions within a panicle :1)The contents of zeatin(Z)+zeatin riboside(ZR), indole-3-acetic acid (IAA) and ABA and activities of starch synthase (SSase), starch branching enzyme (Q-enzyme) in earlier-flowered grains were obviously greater than those in later-flowered grains at early filling stage, but it was reversed at late filling stage. The earlier the spikelets flowered, the shorter the duration of reaching the maximum grain-filling rate (Vmax) was, the higher the contents and activities were. The contents of Z+ZR, IAA and ABA, the ratio of ABA to IAA+Z+ZR, and activities of SSase and Q-enzyme at early grain filling stage were positively and significantly or very significantly correlated with 1000-grain weight (KGW), amylose accumulation rate and AC, but negatively and significantly or very significantly correlated with CD.The results were reversed at late grain filling stage. Activities of SSase and Q-enzyme at early grain filling stage were negatively correlated with GC, whereas positively correlated with GC at middle and late grain-filling stages. The correlation of the hormones and enzymatic activities with CPC varied with cultivars, and the correlation with head milled rice rate (HMRR) was insignificant.