Internode Elongation of Rice Plant : I. Effects of light and gibberellic acid on the second interode elongation

Abstract

The present study was undertaken to clarify the physiological basis of the interaction between light and gibberellic acid (GA₃) on the elongation of the second internode of rice seedlings. After two days immersion of rice seeds (Oryza sativa L.) in water, germinated seeds were placed on the agar medium in tubes, five seeds to a tube under green safe light. Then they were incubated in the dark growth chamber at 30°C. Various concentrations of GA₃ were given to the medium at several seedling stages, and the seedlings were irradiated with light of various intensities, time of irradiation, and light of different wave length at several seedling stages. At 14 days after immersion, the length of organs were measured. Results obtained were summarized as follows. 1. The elongation of the second internode in darkness was repressed by irradiation of light and stimulated by GA₃ application. The maximum effects of light and GA₃ were obtained when they were given on the 2∼5 day before the apparent elongation started. 2. The light inhibition on the second internode growth became greater with an increase of the irradiation time, and the elongation was almost completely inhibited when irradiated for several hours. 3. Light inhibition due to the longer irradiation time was reversed by the higher level of GA₃ pretreatment, resulting that the internode elongated about 10-60 mm length even under continuos light by the pretreatment of 1000-2000 ppm of GA₃. 4. From these results, it may be suggested that the internode elongation is under the control of photosensitive reactions, the action of which is interfered with exogenous GA₃ and act in the most effectiveness before the apparent internode growth starts.