EFFECTS OF PANICLE REMOVAL ON THE PHOTOSYNTHETIC CHARACTERISTICS OF THE FLAG LEAF OF RICE PLANTS DURING THE RIPENING STAGE

All panicles were removed from rice plants (Oryza saliva L.) at anthes is and the effects of this treatment on photosynthetic gas-exchange ra tes and the underlying biochemical properties of the blade of the flag leaf were examined during senescence. Panicle removal retarded the de crease in photosynthesis in the flag leaf during senescence. Similarly , the levels of ribulose-1,5-bisphosphate carboxylase (Rubisco), chlor ophyll and Cyt f, and the activities of sucrose-phosphate synthase (SP S) and ADP-glucose pyrophosphorylase in panicle-free plants remained r elatively high during leaf senescence and decreased more slowly than t hose in the control plants. Regression analysis showed no difference b etween the treated and untreated plants in the relationship between CO 2-limited photosynthesis (measured at an intercellular CO2 pressure of 15 Pa) and Rubisco content, or in the relationships between CO2-satur ated photosynthesis (measured at an intercellular CO2 pressure above 6 0 Pa), Cyt f content and SPS activity. These results indicated that th e change in photosynthesis caused by panicle removal at anthesis could be explained by the changes in the amounts and/or activities of the m ajor biochemical participants in photosynthesis. The temporary accumul ation of starch and sucrose in the flag leaf was observed in the panic le-free plants, but the accumulation was not significant. However, in the panicle-free plants, the weight of shoots, excluding panicles, inc reased by 200% and that of roots increased by 150% at the harvesting s tage. Thus, it appears that, since the effective translocation of phot osynthate to other organs, such as late tillers and roots, can occur, the removal of panicles has no effect on the relationship between the rate of photosynthesis and the levels of the major biochemical partici pants in photosynthesis.