Auxin-Gibberellin Interaction in Rice Coleoptile Elongation

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Abstract
Coleoptile elongation on Oryza aativa L. seedlings was inhibited by growth in varying depths of water or in solutions of P.-chlorophenozy-isobutyric acid. The inhibitions were reversed by 3-indolelacetic acid (IAA). The 2 inhibitory treatments are considered to change the auxin status of the coleoptile. The elongation of coleoptiles in red or far-red light or darkness and with or without added IAA or gibberellic acid (GA), suggested that relative to far-red grown coleoptiles, dark grown coleoptiles were gibberellin dificient, and red grown coleoptiles were auxin and gibberellin deficient. The effect of GA upon coleoptile elongation under all conditions showed the length increase with added GA to be dependent on elongation without GA. The contribution of exogenous gibberellin to elongation is thus dependent on the auxin status of the coleoptile. The results support hypotheses requiring an interaction between auxin and gibberellin in the control of coleptile elongation but not those hypotheses requiring independent roles for auxin and gibberellin or an influence of gibberellin upon elongation through an effect upon the IAA-oxidase system.