On the Nature of the Physiological Responses of Avena Stem Segments to Gibberellic Acid Treatment

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Abstract
Gibberellic acid was found to cause elongation in Avena sativa (oat) stem segments whether it was applied continuously or as a short pulse. The shorter the pulse time became, the higher was the gibberellic acid concentration needed to cause elongation; the segmental growth apparently depends upon the amount of gibberellic acid taken up by the segments. Avena segments showed a decreased growth response to gibberellic acid if the treatments were initiated at increasingly later times after excision from the plant. This decreased responsiveness to gibberellic acid was inhibited by low temperature (0-4 C), but accelerated by anaerobiosis. On the other hand, growth stimulation by a gibberellic acid pulse at the start of incubation was not altered by cold treatment but was nullified by a nitrogen atmosphere. Both the readiness of the segments for growth stimulation by gibberellic acid and its action in promoting growth clearly involve temperature-dependent, aerobic metabolism.