Effects Of Temperature And Light On Carbohydrate Metabolism And Quality In Rice Grain

Using such rice varieties as Koshihikari (Japonica), Sasanishiki (Japonica), Mirukikuin (japonica), Hoshiyutaka (indica), IR72 (Indica) and Nipponbare (Japonica), Gang-you26(Indica hybrid rice) and Nipponbare(Japonica), the effects of temperature and light on carbohydrate metabolism, enzyme activity and quality of rice grain were researched in this paper. Based on the changes of carbohydrate metabolism and enzyme activity, the mechanism of changes of rice quality was revealed. Relations between temperature and light in different latitude situation and amylose content and protein content of rice grains were analysed. The regularity of rice quality changes under the different temperature and light was quested.1. Effect of high temperature on carbohydrate metabolism and enzyme activities of rice grain1.1 Effect of high temperature on sucrose cleaving and enzyme activities involving in sucrose cleavingSucrose content in the grain of two varieties increased significantly, but the fructose and glucose content did not increase alternatively, namely sucrose cleaving decelerated; the activity of sucrose synthase (SS), vacuolar invertase (VCI) and cell wall bound invertase (CW1) decreased in high temperature, compared with the control group. The treatment profited sucrose accumulation and disadvantaged sucrose cleaving in grains. Correlation analysis showed that SS activity and CWI activity were positively and significantly correlated with starch filling rate in grains. The results demonstrated that SS and CWI played an important role in sucrose cleaving and starch synthesis.1.2 Effect of high temperature on starch synthesis and enzyme activity involving in starch synthesisStarch and amylose content in the grain decreased, adenosine diphosphate glucose pyrophosphorylase(ADPGPPase) activity decreased, soluble starch synthase(SSS) activity and granule bound starch synthase(GBSS) activity decreased, soluble starch branching enzyme(SSBE, Q-enzyme) activity increased, and granule bound starch branching enzyme(GBSBE, Q-enzyme) activity had only a little change, starch debranching enzyme (DBE, R-enzyme) activity decreased in the high temperature, compared with the control group. Correlation analysis showed that the activities of ADPGPPase, SSS, SSBE and DBE were positively and significantly correlated with starch accumulation rate.The changes of carbohydrate metabolism of rice grain had an important impact on quality formation under the high temperature. The analysis showed that the decrease of starch was relevant to decline of the activities of sucrose synthase, invertase, ADPGPPase and starch synthase. While the decrease of ratio of amylose to total starch was related to increase of the activity of soluble starch branching enzyme under the high temperature.2. Effect of temperature on rice quality2.1 Effect of daily average temperature on rice qualityThe distinction of the brown rice rate, milled rice rate and length of grain were insignificant under the different daily average temperature, but head rice rate decreased and chalky rate increased, amylose content decreased, protein content increased as lift of daily average temperature. The results of high temperature experiment were as same.2.2 Effect of temperature difference on rice qualityThe distinction of the brown rice rate, milled rice rate and length of grain were non-significant under the different temperature difference, but head rice rate decreased, chalky rate increased, amylose content decreased, protein content increased as falling of temperature difference.3. Effect of weak light on carbohydrate metabolism and enzyme activities of rice grain3.1 Effect of weak light on sucrose cleaving and enzyme activities involving in sucrose cleavingSucrose contents in the grain of two varieties decreased, sucrose cleaving accelerated. SS activity decreased while both VC1 and CWI activity increased under the weak light, compared with the control group. The treatment was favorable to sucrose cleaving by invertase pathway and the increase of invertase activity accelerated sucrose cleaving. Correlation analysis showed thatSS and CWI activity were positively and significantly correlated with starch filling rate in grains.The results demonstrated that SS and CWI played an important role in sucrose cleaving andstarch synthesis.3.2 Effect of weak light on starch synthesis and enzyme activities involving in starchsynthesisStarch and amylose content in the grain of two varieties decreased, while ADPGPPase activity had only a little change, SSS and GBSS activities decreased, SSBE (Q-enzyme) and GBSBE (Q-enzyme) activities increased, DBE (R-enzyme) activity in IR72 decreased. DBE in Nipponbare increased under the weak light, compared with the control group. Correlation analysis showed that the change of starch content was positively and significantly correlated with the change of sucrose content under the weak light. Both ADPGPPase and SSBE activities were positively and significantly correlated with starch accumulation rate.The changes of carbohydrate metabolism of rice grain had an important impact on quality formation under the weak light. The analysis showed that the decrease of starch content was relevant to decline of the activity of sucrose synthase. While the decrease of ratio of amylose to total starch was related to increase of the activity of soluble starch branching enzyme under the weak light. 4. Effect of light on rice quality4.1 Effect of light intensity on rice qualityUnder the weak light, the grain filling rate was even lower than the control. And the grain filling rate reduced sharply with the reduction of the light intensity; correspondingly, the time of filling was much longer than the control. The distinction of the brown rice rate, milled rice rate and length of grain were non-significant, but head rice rate decreased and chalky rate increased. Amylose content decreased and gel consistency decreased, length of gel became shortening, alkali spreading value had not change regularly, protein content increased.4.2 Effect of light length on rice qualityShortening the light length, the weight of the grain decreased and the maximum time of filling delayed, while brown rice rate, milled rice rate and head rice rate increased significantly: the distinction of grain shape was non-significant, but kernel chalkiness decreased, amylose content, gel consistency and alkali spreading value had falling tendency, protein content increased.4.3 Effect of shading in different period of filling stage on rice qualityShading in the earlier stage of filling had more effects than that in the later stage of filling. The rate of brown rice, milled rice, head rice dropped under shading in different filling period, the distinction of length, width and length/width of grain was non-significant but kernel chalkiness upswing in different shading period. Amylose content, gel consistency and alkali spreading value had falling tendency.