Light growth inhibition and growth inhibitors in Sakurajima radish seedlings

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Abstract
Growth of Sakurajima radish seedlings (Raphanus sativus var. hortensis f. gigantissimus Makino) was studied in relation to the effects of light, the effectiveness of plant hormones, and the variation in endogenous growth inhibitor content Externally applied GAs and IAA had no effect on the elongation of the hypocotyl in the light as well as in the dark. BA was slightly promotive in the light, but was not so effective as to nullify the light-induced inhibition of elongation. ABA was strongly suppressive in the light as well as in the dark. Growth inhibitors in seedlings were extracted, analyzed by thin-layer chromatography and the Sakurajima radish hypocotyl elongation test, and 3 acidic and 3 neutral inhibitors were detected. Among them all of the acidic and one of the neutral inhibitors increased with the time period of illumination, whereas the other 2 neutral substances remained almost unchanged in the light but decreased in the dark. Thus the levels of all 6 inhibitors was higher in light-grown seedlings than in dark-grown ones. This suggests that light inhibition in Sakurajima radish hypocotyls may be controlled by the variation in the inhibitor levels in the seedlings.