Abstract
We investigated the role of each plant hormone in the internodal elongation of rice seedlings using japonica rice cultivar 'Sasanishiki', and deepwater rice cultivar 'Leb Mue Nahng 111, and 'Habiganj Aman VIII'. Rice seedlings were grown in the light conditions at 30°C and applied with various plant growth regulators : abscisic acid (ABA), benzyl-adenine (BA), brassinolide (BR), ethylene (ET), gibberellin-A3 (GA3), indole-3-acetic acid (IAA) and triazinone (TA). (1) Among the seven growth regulators, only GA3 induced internode elongation when applied alone. In japonica rice, the elogation was not induced when applied with low level of GA3 (10-5M∼10-6M). The elongation, however, was induced by GA3 (10-5M∼10-6M) in the presence of polyethylene glycol (PEG) or TA (gibberellin synergist). In the deepwater rice, low level of GA3 (10-5M∼10-6M) induced the elongation. (2) GA3 or BR stimulated the coleptile growth. GA3, BR or IAA promoted the mesocotyl growth. GA3 promoted the leaf growth. GA3 and ET stimulated the internode elongation but the BR or BA inhibited the internode growth. ABA produced both an inhibition and a promotion of the internode growth. This may be due to the stage dependent response of the internode to ABA. These results may suggest that the regulation mechanism of the internode growth may include both organ-specific steps and the common process to other organs.
