Studies on the Effects of IAA, TIBA and X-ray Irradiation on the Appearance of Abnormal Spikelets in a Special Variety of Paddy Rice "Akaho"

Abstract

The effects of IAA (3-indoleacetic acid), TIBA (2, 3, 5-triiodobenzoic acid) and x-ray irradiation on the appearance of abnormal spikelets, especially regarding the changes in sex expression, were investigated with a special variety of paddy rice "Akaho". "Akaho" is known to have very unstable characters in regard to the morphogenic regulation of spikelet genetically and to express various abnormalities of spikelet even under usual cultivating conditions. Since this experiment was carried out in phytotron at 25-30°C, in the winter of 1965-1966, the short-day condition promoted female and depressed male sex expression remarkably as seen in other short-day or day-neutral plants grown under the short day condition. With external application of IAA, the femaleness was promoted further and the maleness was suppressed, decreasing the number of stamens and increasing the organs of intermediate structure that were partially transformed stamens to pistil and the pistils of multi-ovary. On the contrary, the application of TIBA and x-ray irradiation showed clear cut inhibitory effects on the shifting tendency of the control plants toward femaleness, increasing stamens and decreasing the pistils of multi-ovary in number, particularly in the plots of x-ray treatment. In these plots, the morphological abnormalities in glumes and the development of additional glumes became to appear more frequently than in the control, on the other hand. From the results above mentioned, it is clarified that an elevation of auxin level promotes the female and depresses the male sex expression in rice plants. Based upon the results obtained in this study and the writers' other obsevations regarding to the effects of gibberellin on the spikelet morphogenesis, it is considered that the endogenous level of gibberellin-like substances may be high at the early stage of spikelet development and afterwards that of auxin-like substances may become dominant absolutely or relatively, in the regions of organogenesis, and the unbalance of these substances in spikelt development seems to induce various kinds of abnormalities in the spikelet morphogenesis.