抄録
It was reported in previous paper that water absorption could not catch transpiration up in the day time of a fine day even though the rice plant was grown under submerged soil condition, and consequently stomata closed considerably. Moreover, it was considered that there was a relationship between the decreasing of stomatal aperture of leaf blade in a day time and potential of root water absorption which was related to age and activity of the roots. In this paper, we investigated root activity which related to potential of root water absorption by measuring the exudation rate from the base of the leaf blade in paying attention to the leaf position and plant growth stages. 1. Except the flag leaf the higher the leaf position, the higher the exudation rate; the older the leaf age, the lesser the exudation rate regardless of growth stages (Fig. 1, 2 and 3). 2. The exudation rate from the base of the flag leaf increased if the culm was kept horizontally (Fig. 2D). Also rooting from the upper nodes by molding promoted the exudation rate of the flag leaf (Fig. 4 and Table 1). Thus we assumed that the exudation rate of the flag leaf was affected by both factors; water pressure related to the position of the flag leaf and abscence of roots on the upper nodes. 3. After the heading stage the exudation rate of upper four or five leaves decreased conspicuously (Fig. 3). The root pressure estimated from water potential of culture solution in which exudation was ceased was 2.1-2.4 bar before the booting stage, but it decreased to 0.7 bar in the early ripening stage (Fig. 5 and 6, and Table 2). From both the results mentioned above and the fact that treating roots with NaN3 inhibited exudation (Fig. 7), it was assumed that the decreasing rate of exudation due to leaf age may be related to the decrease of activity in roots physiologically connected with the leaf, and that the decreasing rate after the heading stage may be due to aging of all roots. Furthermore, it was presumed that root activity which related to potential of root water absorption participated in leaf water maintenance during intensive transpiration.
