Abstract
The study was performed to investigate the effects of X-ray irradiation or/and gibberellin on the spikelet morphogenesis in rice plants. X-ray irradiation was carried out at the differetiating stage of spikelet at the dosages of 1kr, 5kr, 10kr and 20kr, and gibberellin was applied in the nutrient solution at the concentration of 100 ppm on the day after the X-ray treatment. Various abnormalities, these are, appearance of malformed spikelets, development of additional glumes, variation in stamen initiation, increase of stigmata in number, development of multiple pistils in a spikelet etc., have been induced by X-ray irradiation. These phenomena are closely similar to those induced by gibberellin in many faces. When gibberellin application was added to X-ray treatment, it was found that the morphogenetic effects of gibberellin had been promoted strongly by the pre-treatment of X-ray and every abnormality caused by gibberellin had been strengthened remarkably. Based on the results above mentioned, it is considered that the physiological changes as influenced by X-ray may not be inhibitory to exhibition of gibberellin activity but strongly promotive ones. A few considerations were tried on the relationship between gebberellin and auxin, regarding to the spikelet morphogenesis from the standpoint of auxin economy, since a level down of auxin had been reported by a number of investigators to be caused by X-ray irradiation.
