Abstract
1. A possibility whether plants react differently to an exogenous growth regulator applied at different times in a day was examined adopting rice plant (Oryza sativa L., cultivar Nipponbare), gibberellic acid (GA3) and abscisic acid (ABA) as materials. Solutions of the regulators were poured onto the soil surface close to the plant base every mornlng or evening. 2. In the later stage of growth, a difference between morning and evening applications was detected. Applications of GA3 every evening (GA-E), and ABA every morning (ABA-M) made the flag leaf longer than GA-M or ABA-E respectively. A less conspicuous difference was also observed in the number of expanded leaves. 3. The two growth regulators caused different effects on the final leaf number and the days required from seeding to heading. GA3 treatments made the final number of leaves less and the days to heading shorter than the water control, while ABA treatments did those slightly more and longer than the control. 4. The present report expects further experiments with more precise methods especially for the applications of plant growth regulators.
