Interaction of Growth Substances in Growth and Organ Initiation in the Embryos of Capsella

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Abstract
When embryos of Capsella bursa-pastoris (251-450 [mu] long) were grown in media containing low concentrations of indoleacetic acid and an optimum concentration of gibberellic acid, the root, hypocotyl and cotyledons of the embryos were longer than in corresponding treatments with the same concentrations of indoleacetic acid alone. The presence of gibberellic acid in the medium, however, suppressed initiation of embryonic leaves and formation of callus induced by indoleacetic acid. Low concentrations of indole-acetic acid overcame the inhibition of kinetin on the growth of the hypocotyl and cotyledons, but the presence of kinetin itself was inhibitory to indoleacetic acid-induced growth of the primary root system of the embryos. Kinetin prevented auxin-induced callus formation in the embryos, but at high concentrations of kinetin and low concentrations of indoleacetic acid, kinetin -induced callus was formed. In media containing both gibberellic acid and kinetin, the latter did not appreciably affect the growth of the embryonic organs induced by gibberellic acid. The primary effects of gibberellic acid and kinetin on the morphogenesis of the embryos were not mutually altered by a combination of both substances at physiological levels.