Studies on CO₂ Exchange in Crop Plants : IV. Roles played by the various parts of the photosynthetic organd of rice plant in producing grains during the ripening period.

Abstract

Experiments were made on rice plants in order fo analyse the roles of the leaves and ears in assimilation and grain production during the ripening period, indirectly by means of artificial defoliation and shading of leaves or ears. Photosynthetic rate and respiration rate of various organs were measured by the apparatus described in the authors' previous paper. The results obtained may be summarized as follows : (1) Shading of ears and both the shading and defoliation of leaves starting from the heading stage, gave remarkable effects on the yield, while the effects were negligible when the treatment was started 20 days. after heading, and they were intermediate when it was started 10 days after heading and was continued upto ripening period. From this results, it was elucidated that the translocation of carbohydrates to grains had nearly finished 20 days after heading in rice plant. (2) About 1/3 of the grain yield quantity seemed to be contributed by translocated assimilates synthesized before heading. (3) From the results of shading the ear, it was found that the ear itself had acted as an assimilating organ, as shading of it induced a decrease of 8 % of yield. On the other hand, the apparent photosynthesis of ear, measured by gas analysis, was found very low or sometimes even negative. It might be due to the fact that the amount of respiration in that part was very large as compared with that of assimilation. (4) The flag leaf did not seem to be a mere storage organ of assimilates synthesized before heading, but had proved itself to be a photosynthetic organ after heading. On the other hand the 2nd, 3rd and 4th leaves played more important roles as storage organs than as photosynthetic one. (5) After heading, the photosynthetic activity of the 4th leaf decreased remarkably with the progress of maturation, followed by depression in the activitiy of the 3rd and then by that of the 2nd leaf. The flag leaf, however, kept its photosynthetic activity till late through the ripening period. (Received March 31st, 1955)