Purification of Endosperm Sucrose Synthase From Guichao

Sucrose synthase activity in rice is potentially yield limiting. Earlier research indicated that endosperm sucrose synthase activity during grain filling was higher in ‘Guichao’ rice than in U.S. rice cultivars. We set about to purify sucrose synthase from Guichao endosperm as part of an overall research effort to understand the physiological reasons for the high yields of Guichao compared to U.S. rice cultivars. In 2002 and early 2003 we made substantial progress toward the purification of sucrose synthase from Guichao endosperm. We used several novel separation techniques including successful partial purification of the enzyme using ammonium sulfate precipitation. We have resolved the enzyme electrophoretically to one large band and four small bands. The small electrophoretic bands may be either other proteins or degradation products of sucrose synthase. We continued to conduct field experiments with F2 derived lines from reciprocal crosses of Guichao and ‘Lemont’ for further analysis of this project. In addition, F2 selections from a cross of two of the most promising of the Guichao/ Lemont lines with ‘LaGrue’ were made. These selections are being incorporated into the rice breeding effort. In conclusion, progress was made in 2002 toward a better understanding of the physiological basis of Guichao’s high yields and to incorporating Guichao into Arkansas rice cultivars.