Internode Elongation of Rice Plant : II. Effects of light and gibberellic acid on the anatomical characters of the second internode

Abstract

Studies were conducted on the changes in cell division, cell elongation, and vascular system formation of the second internode of dark-grown rice seedlings due to light and gibberellic acid (GA₃) treatments. After two days immersion in water in darkness at 30°C, germinated rice seeds (Oryza sativa L.) were placed on the agar medium, each five seeds to a tube under green safe light. The total 90 tubes were transferred into a dark growth chamber where the seedlings were grown at 30°C till sampling. One third of them were applied with 10 ppm of GA₃ at the planting, and the other third were interrupted with light (white fluorescent lamp, 500 1x) for 4 hours on the second day after planting. The rest tubes were kept in darkness without GA₃ application. 1. In darkness, the number of parenchyma cells of the second internode in the longitudinal direction increased rapidly from the 5th day after immersion, and it almost reached the final numbers on the 7th day when the prominent elongation of the internode started, being followed by the enlargement of the cells formed. 2. The meristematic activity of the internode was severely affected by light and GA₃ given on the 4th and 2nd day after immersion, respectively. The cell division in the longitudinal direction was retarded by light irradiation, while that in the transverse direction and vascular bundle formation were stimulated by light. In contrast, the added GA₃ accelerated the former and repressed the latter. 3. These results may suggest that light and GA₃ counteract each other on the balance of meristematic activity in longitudinal and transverse directions, and on the vascular bundle formation in the internodes.