Abstract: GA₃ had little effects in dark condition and an obvious effect in light on retarding the decrease of chlorophyll content in barley (Hordeum vulgare L.) leaf segments.GA₃ had little effect either in light when it was mixed with ABA and applied to the segments.The free ABA content determined by RIA in the segments was obviously lower in light than in dark conditions in the experiment.It was inferred that the different effects of GA₃ on delaying the decrease of chlorophyll content in dark and light conditions was due to the different content of endogenous ABA in the segments in dark and light conditions.

Key words: GA₃, Light, Chlorophyll