IAA-induced elongation of light-grown cucumber hypocotyl sections was examined with respect to the osmotic relationship of the cell. Sucrose suppression of IAA-induced elongation in the light occurred at a lower sucrose concentration than in the dark, but there was no difference in the mannitol concentration which suppressed elongation. This differential sucrose suppression could be explained by the difference in the osmotic potential of the cells between light and darkness. It was lower in the dark than in light, and the difference was more distinct in the presence of sucrose. Treatment of sections with a photosynthetic inhibitor, CMU, also resulted in the maintenance of a low osmotic potential. Under the experimental conditions where a larger IAA-induced elongation was obtained, a lower osmotic potential was also obtained. The results are discussed with respect to the role of the osmotic potential of the cell in the enhancement of IAAinduced elongation.
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