Abstract
The study was carried out to compare the effects of gibberellin with those of auxins on the morphogenesis of spikelets in rice plants. Gibberellin, α-indoleacetic acid, β-naphthaleneacetic acid and 2, 4-dichlorophenoxyacetic acid were applied just after the time of young panicle differentiation, in the nutrient solution at various concentrations as seen in table 1. It was reconfirmed that gibberellin had some important effects on the spikelet morphogenesis, as had been reported previously by the writers and not only induced various malformed spikelets but also tended to increase the number of glumes, stamens, stigmata and pistils, causing several kinds of abnormal sexual organs and multi-floral spikelets. On the other hand, as shown in table 2, since such phenemena as found in the plots of gibberellin treatment have not been caused by the application of auxins at all, it is considered that the modes of action of the exogenous gibberellin and auxins on the spikelet morphogenesis are different or contrastic with in many faces especially on the differentiation of lateral organs, among all the staminate one in the spikelet. With regard to sex expression, it is said that auxin level at the differentiating apex determines the sex balance and the concentration promoting maximal stamen growth is lower than promoting maximal pistil growth. In this case of rice plants, exogenous auxin is considered to elevate the auxin level at the spikelet apex up over the maximal concentration, and to suppress the maleness, following no marked promotion in the development of female organ. Recently, gibberellin has been reported by a number of investigators to have promotive effects on the staminate organ, suppressing the pistilate one, but the results obtained in this study are not necessarily agree with them completely, the development of both male and female organs having been promoted by gibberellin application. It was indicated that further extensive studies should be done in order to clarify the real relationship between gibberellin or auxins and sex expression, using various methods of application or concentrations of them, followed by the more critical observations on the effects, not only from the quantitative or morphological but also qualitative or functional standpoints of view, analysing them on differentiation and on growth of primordia.
