Abstract
A physiological function of culm-node-parts of the culm of rice plant at grain maturing stage was investigated. The term, culm-node-part represents the complex of basements of a leaf-sheath and of an elongated internode, as shown in Fig. 1. This culm-node-part can readily be distinguished in a longitudinal section by staining with ninhydrin, TTC, or iodine. The form of each culm-node-part in a culm varies apparently with the positions of the node. The proportion of internode basement to leaf-sheath basement in an uppermost culm-node-part was 85.0%, while that of the third node from top was 45.5% in dry weight with the variety Manryo (Table 1). In other words, the nearer to the panicle, the greater the proportion of internode basement is. Amylase activity of culm-node-parts was determined as shown in Table 2. The activity in an internode basement was greater at upper node, but that of leaf-sheath basement was conversely decreased at upper node. Such high amylase activity in the uppermost internode basement seems to favor sugar translocation from the culm to the panicle. On other hand, the low activity in the terminal leaf-sheath basement seems to be due to the decreasing leaf area in the upper leaf. Changes in form and amylase activity in culm nodes as described above might have some bearing on the translocation of carbohydrates to the maturing grains. As is generally known, the cutting of leaf-blade at or ten days before heading results in the decreased yield, the removal of flag leaf being most deteriorating. Thus the terminal leaf-blade must have an important function to grains yield. Thereupon, the effect of removing leaf blade on the amylase activity in the culm-node-parts was investigated. The activity was clearly decreased in the culm-node-part with treated leaf as shown in Table 3 and starch content in the internodes just above the culm-node-part with treated leaf was also clearly decreased (Table 4). Hitherto, it has been though that the main reason for the decreased grain yield caused by the leaf-blade cutting is the decrease of leaf area during the maturing stage. However, the results obtained in this experiment suggest that the yield decrease caused by leaf cutting is not only due to the decreased leafarea but to the decrease in translocation of assimilates resulting from the lowering in amylase activity in the culm-node-parts. To prevent a decline of a physiological activity in the culm-node-part will be important for better grains maturing.
