Changes in growth‐substance contents during growth of wheat grains

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Abstract
SUMMARY: Samples of developing wheat grains were extracted at weekly intervals from ear emergence until maturity and the growth substances estimated by bioassay. Immature grains contained two cytokinins; one was similar to zeatin and another, with more cytokinin activity, had different properties. Ovules contained only small amounts of growth substances but at the end of anthesis the grains had a maximum content of cytokinin. The gibberellin content increased until 3 wk after anthesis then decreased; their auxin content increased until 4 wk after anthesis but decreased as the grains ripened and lost fresh weight. The husks contained smaller amounts of growth substances than the grains they surrounded. Exudates from young stems contained cytokinins and these may originate in the roots and move to the ears through the stems. The auxin in the grains was identified as indole‐3yl‐acetic acid and may be derived from the phenols present reacting with tryptophan.