Tuesday, November 14, 2006 - 10:30 AM

Rice enzymes related to grain filling.

Paul Counce1, Terry J. Siebenmorgen2, and Nora T. Watson Cooper2. (1) Rice Research & Extension Cntr, 2900 Highway 130E, 2900 Highway 130E, Stuttgart, AR 72160, United States of America, (2) Department of Food Science, University of Arkansas, Fayetteville, AR 72701

High night temperatures have been shown to lower head rice yields.  A study was conducted to more fully understand the underlying reasons for this. Soluble starch synthase (SSS) is partially deactivated at high temperatures in wheat and maize; the objective of this study was to determine if this was true in rice.  Significant responses to night temperature and cultivar were found for four of the enzymes but the most dramatic responses were for SSS.  The SSS activities were significantly affected by temperature and cultivar and by a cultivar by temperature interactions.  The enzyme activity response to nighttime temperature can be characterized as (1) an expected temperature optimum for enzyme activity for LaGrue, Cypress and M204 at 22oC, (2) an optimum response to temperature for Bengal at 26º C, and (3) little change between 18 and 22ºC for XL8 and XP710 and a decrease as night temperatures increased between 22 and 30ºC.  Others   have found similar quadratic responses for maize and wheat to those we found for LaGrue, Cypress, M204 and Bengal.  The SSS builds the amylopectin molecules glucose unit by glucose unit.  This enzyme has been reported to have a lower temperature optimum than other enzymes in the grain filling process.  The significant temperature by variety interaction is promising for development of varieties that are less sensitive to high night temperature stress.  Of particular interest in this regard, is the higher temperature optimum for Bengal relative to the other cultivars.  The responses of the hybrids were also noteworthy, in that both XL8 and XP710 responded to night temperature differently from the other cultivars in the test.  It would appear that selection for improved rice yield and quality could result from effectively manipulating SSS in the rice grain.