Abstract
In previous papers, it was clarified that in adult plants the lamina joint participates to the bending movement of laminae to their abaxial side and that an increment of cell length of the adaxial side is induced favourably in the regions because vascular bundles are here centrally placed. In this paper the effects of gibberellin and auxin on the extension of adaxial side of lamina joint in rice seedlings were demonstrated. They were cultivated in controlled condition of temperature and moisture, in Phytotron at Nagoya University, under sunlight in summer. The effects on the angles between laminae and sheaths were observed (Table 1), indicating an increment of the angular degrees by gibberellin treatment in all of the varieties used (Table 3). Further an attention was devoted to the nature of interaction between gibberellin and auxins. The gibberellin was applied to root medium and NAA, at various concentrations, was sprayed daily to their shoots. NAA alone was effective to increase the angular degrees at higher concentrations. But in combination with gibberellin NAA did not induce any additive effect in the angles between laminae and sheaths (Table 4). These results on the interaction of gibberellin and auxins in the experiment with intact plants were contradictory with those in excised leaves. This fact would be very interesting when considered the mode of action of growth substances on the extension of the lamina joint. Some experiments were also performed on the combined action of red light and gibberellin upon the lamina-joint extension (Table 6).
