Difference of Photosynthetic Rates among the Leaves at the Equivalent Positions on the Main Stem and Its Tillers in Rice Plants

Abstract

The photosynthetic rates of the leaves at the equivalent positions on the main stem and its tillers, that is, the photosynthetic rates among the synchronously expanded leaves on the main stem and tillers in Nipponbare (short culm and ear number type rice cultivar) were compared. Immediately after the leaves fully expanded, little difference was noticed between the photosynthetic rates of the leaf on the main stem and the synchronously expanded leaves on the primary tillers except with those on the 5th tiller which emerged just after transplanting. Two or three weeks after expansion, the photosynthetic rate of the leaf on the main stem was higher than that of the synchronously expanded leaves on the primary tillers. The extent of the decrease in the photosynthetic rates with leaf aging was larger in the leaves on the primary tillers than those on the main stems, and also larger in the leaves in those tillers that emerged from the higher node of the main stem. The photosynthetic rates at 2 or 3 weeks after leaf expansion highly correlated with the diffusive conductance, chlorophyll content and RuBPCase content in the leaves on the main stems and the primary tillers. These results indicate that one of the factors responsible for the difference in the photosynthetic rates of the leaves at the equivalent positions on the stems in a hill was the difference between the periods of senescence of the leaves on the main stem and those on the primary tillers. The extent of the decrease in the photosynthetic rates with leaf aging in the primary tillers was different between Nipponbare and Tainung 67, a high yielding cultivar (long culm and ear weight type) in Taiwan, when the extents were compared with those in the main stem. However the extent of the decrease in the photosynthetic rates with leaf aging was not different between the leaves on the main stem and those on the primary tillers in Tainung 67. These results suggest that the photosynthetic rates of the leaves at the equivalent positions on the stems in a hill were almost the same between the main stem and their primary tillers in Tainung 67. © 1991, CROP SCIENCE SOCIETY OF JAPAN. All rights reserved.