ANALYSIS OF THE PHOTOSYNTHETIC CHARACTERI STICS OF THE HIGH-YIELDING RICE CULTIVAR TAKANARI

It was clarified in a previous paper that higher dry matter production for a newly bred high-yielding rice cultivar, Takanari was mainly due to the higher net assimilation rate (NAR) owing to better light-inter cepting characteristics after the panicle formation stage. The CO2 exc hange rare, which affects the NAR, was studied using cultivars, Takana ri and Nipponbare in this paper. Observations showed that Takanari was remarkably higher in CO2 exchange rate than Nipponbare during diurnal courses, during leaf senescence or at different leaf positions. These results indicate that the higher NAR for Takanari was due to not only better light-intercepting characteristics but also a higher CO2 excha nge rate. Furthermore, the cause why these differences in photosynthes is existed between the two varieties was examined. It was found that t he CO2 exchange rates for Takanari maintained a higher level owing to its higher diffusive conductance during diurnal courses, and owing to both its higher diffusive conductance and higher photosynthetic capaci ty during leaf senescence. Further investigation indicated that the hi gher photosynthetic capacity for Takanari was mainly owing to a higher apparent carboxylation efficiency and Rubisco content during leaf sen escence.