Multiple Isoforms of Endosperm Sucrose Synthase from Guichao Rice

Sucrose synthase activity in rice is potentially yield limiting. This is because the carbon that forms starch enters the developing rice grain as sucrose and that sucrose must be broken down to form the precursors of starch. The enzyme that breaks down sucrose in the filling rice grain is sucrose synthase. Earlier research efforts on rice physiology 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. We used several novel separation techniques including utilization of hydrophobic interaction and an improved ion exchange column. The successful procedure yielded four isoforms of the enzyme.