Transgenic rice with low sucrose-phosphate synthase activities retain moresoluble protein and chlorophyll during flag leaf senescence

We investigated whether changes in sucrose-phosphate synthase (EC 2.4.1.14, SPS) activity could alter N remobilization during leaf senescence. Transge nic rice (Oryza sativa L. cv. Nipponbare) with low SPS activities and wild- type rice plants were grown with basal N (1.0 mM NH4NO3) until the late veg etative stage. Subsequently, half of the plants were transferred to a low N (0.1 mM NH4NO3) condition to accelerate leaf senescence, and the others we re continuously grown with basal N. With low N supply, the amounts of chlor ophyll and soluble protein in flag leaf blades decreased after anthesis in both the low SPS plants and wild-type plants, although the decrease was les s in the low SPS plants. Panicle weights were significantly lower in the lo w SPS plant than in the wild-type plant. These results suggest that the rem obilization of N from flag leaves was diminished by suppressing the develop ment of reproductive sinks in the low SPS plant. (C) 1999 Editions scientif iques et medicales Elsevier SAS.