Studies on CO<SUB>2</SUB> Uptake and CO<SUB>2</SUB> Evolution in Each Part of Crop Plants : II. Photosynthetic activity in the leaf sheath and ear of rice plant

Abstract

Leaf sheaths and ears of rice plants have been classified as non-photosynthetic organs on the growth analysis method, but their tissues have chlorophyll as photosynthetic element. The purpose of this paper is to evaluate the activity of CO2 uptake of their parts in more detail on dry matter production. Furthermore, one has to point out the physiological factors related to that photosynthetic activity. Using an open system of gas analysis (air flow method), it was found that CO2 uptake and CO2 evolution in light and in darkness from the upper and lower parts of leaf sheaths and ears for potted rice have a different response to light intensities. I. Maximum rate of net photosynthesis per exposed surface of the leaf sheath and the rear were 3 and 1∼2mgCO2/dm2(100 spikelets)/hr respectively, and the light saturation point was about 40 Klux on vigorous organs. Gross photosynthetic rate and saturation point were decreased along with the discoloring of green on their organs. 2. Changes of the gross photosyntheis of ears with elapsed time showed the trend of a close parallel to that of the respiratory rate in darkness and to that of chrolophyll content in their parts, also the net photosynthetic rate of ears was related to water content in their parts. It is suggested that the ability of photosynthesis of ears may be less contributive to dry matter production, and have a net photosynthesis for a short time from heading to the milky stage. The gross photosynthetic rate of leaf sheaths had an intimate possitive correlation to the respiratory rate and the chrolophyll content in their organs through all growth stages. 3. The leaf sheaths and the ears of rice plats have an ability of net photosynthesis, however, the maximum rate is as small as 10 per cent and below 5 per cent of that of vigorous leaves. It is considered that the leaf sheaths and the ears of rice plants might be classified as non-photosynthetic organs on growth analysis studies, and light penetration within rice plant populations depresses the CO2 evolution from the leaf sheaths at daytime according to the relation of light intensity to photosynthesis of it.