Effects of Gibberellin on the Morphogensis in Rice Plants : 1. Effects of gibberellin applied at different stages of growth.

Abstract

The morghogenetic effects of gibberellin on rice plants were studied, providing several plots according to the time of gibberellin application. Gibberellin was applied at the concentration of 100 ppm and 500 ppm as foliar spray or soil treatment. Available results are as followings. 1) When gibberellin is applied at the stage of early vegetative growth, the number of tillers is increased and the leaf blade, leaf sheath and internode which are under the rapid elongation stages at that time, show marked elongation. 2) In the case of application at the stage of late vegetative growth, the date of young panicle differentiation is hastened distinctly, while the number of leaves is increased on the other hand. 3) When gibberellin is applied at the stage of young panicle differentiation, branches, especially the secondary ones and pedicels of the panicle show striking increments in number and consequently the number of spikelets is increased conspicuously, while the ratio of unfertilized spikelets grows larger than that of the control. 4) The date of heading is slightly promoted by the application at the just before heading time due to a rapid elongation of the upper internodes. 5) More cells and mitotic figures are observed in shoot apices and internodes of the treated plants than in those of the control. 6) Various abnormalities as shown in photograph No. 4 are caused by gibberellin application. From the results above mentioned followings are considered. The effect of gibberellin is not specific to the growth or differentiation of organs and tissues, but varies according to the physiological state of them at the moment of application. Referring to the growth of cell, the effect of gibberellin appears not only in cell elongation but also in cell multiplication and accelerates the meristematic activity. From the fact that branches and spikelets of the panicle treated show marked increases in number, gibberellin is thought to have some effect to advance the differentiation of vascular bundles in the panicle. Phenomena of the frequent appearance of bract leaf and well development of the primary branch at the first bract, suggest that gibberellin may have some physiological act in revelation and development of degenerate organs or tissues, though sometimes induces morphogenetic disorders.