作物の葉における光合成機能の発達と衰退に関する研究 : 第2報 イネ葉の老化過程に及ぼず窒素欠乏の影響

抄録

Photosynthetic activity measured by O₂ evolution and other physiological characteristics such as the content of total nitrogen, soluble protein, fraction I protein and chlorophyll (a+b) were investigated in the senescing 5th, 7th, 8th and flag leaf of rice grown under different nitrogen supply. The results obtained are as follows: 1. Nitrogen deficiency given during leaf senescence immediately decreased photosynthetic activity as well as the content of soluble protein, fraction I protein and chlorophyll (a+b). The older 5th leaf was affected more severely as compared with the upper and younger leaves (Table 1). 2. Photosynthetic activity, which was affected heavily by nitrogen deficiency, declined with age of the leaf more rapidly in its value measured under a high light intensity (70 klx) than in that measured under a low light intensity (10 klx) (Fig. 1). 3. The content of fraction I protein which was influenced most severely by nitrogen deficiency among various leaf constituents, decreased most rapidly with the progress of leaf senescence (Table 1, Fig. 1). 4. A close, curvilinear correlation was observed between the photosynthetic activity and the content of fraction I protein of rice leaves at vegetative stage (Fig. 2). Thus, the content of fraction I protein which declined most rapidly during leaf senescence, seems to be the most important limiting factor for the photosynthetic activity of senescing rice leaves at vegetative stage. 5. The regression curve for the control plant differed from that for the no nitrogen supplied plant, although a fairly close correlation was found in both cases between the photosynthetic activity and the content of fraction I protein (Fig. 3). This disagreement suggests the existence of other limiting factors than the content of fraction I protein for the photosynthetic activity of a flag leaf.