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 sativa L.)at anthesis and the effects of this treatment on photosyntheticgas-exchange rates and the underlying biochemical propertiesof the blade of the flag leaf were examined during senescence.Panicle removal retarded the decrease in photosynthesis in theflag leaf during senescence. Similarly, the levels of ribulose-l,5-bisphosphatecarboxylase (Rubisco), chlorophyll and Cyt f, and the activitiesof sucrose-phosphate synthase (SPS) and ADP-glucose pyrophosphorylasein panicle-free plants remained relatively high during leafsenescence and decreased more slowly than those in the controlplants. Regression analysis showed no difference between thetreated and untreated plants in the relationship between CO₂-limitedphotosynthesis (measured at an intercellular CO₂ pressure of15 Pa) and Rubisco content, or in the relationships betweenCO₂-saturated photosynthesis (measured at an intercellular CO₂pressure above 60 Pa), Cytf content and SPS activity. Theseresults indicated that the change in photosynthesis caused bypanicle removal at anthesis could be explained by the changesin the amounts and/or activities of the major biochemical participantsin photosynthesis. The temporary accumulation of starch and sucrose in the flagleaf was observed in the panicle-free plants, but the accumulationwas not significant. However, in the panicle-free plants, theweight of shoots, excluding panicles, increased by 200% andthat of roots increased by 150% at the harvesting stage. Thus,it appears that, since the effective translocation of photosynthateto other organs, such as late tillers and roots, can occur,the removal of panicles has no effect on the relationship betweenthe rate of photosynthesis and the levels of the major biochemicalparticipants in photosynthesis. (Received January 7, 1995; Accepted March 15, 1995)