Interaction of Growth-retarding Compounds and Gibberellin on Indoleacetic Acid Oxidase and Peroxidase of Cucumber Seedlings

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Abstract
Cucumber seedlings were grown in darkness on filter paper saturated with water, potassium gibberellate (GA), 5 growth-retarding chemicals (2-isopropyl-4-dimethyl-amino-5-methylphenyl-1-piperidine-carboxylate methyl chloride (Amo-1618); 3-isopropyl-4-dimethylamino-6-methylphenyl-1-piperidine-carboxylate methyl chloride (Carvadan); 2,4-dichlorobenzyltributyl-phosphonium chloride (Phosfon); 2-chloroethyl trimethylammonium chloride (CCC); andn-dimethylaminosuccinnamic acid(B-995)maleic hydrazide), or both GA and Amo-1618. Theeffects of the chemicals on the activity of peroxidase and indoleacetic acid oxidase were studied in cotyle -dons, radicles and hypocotyl tips. GA inhibited and Amo-1618 stimulated the activity of peroxidase and IAA oxidase in hypocotyl tips and cotyledons. The effect was inversely correlated with the effect of the various concentrations of the chemicals on hypocotyl elongation. The same relation was apparent with the effect of Amo-1618 on radicles. GA did not affect peroxidase activity in radicles, and slightly decreased their IAA-oxidase activity. The inverse effects of GA and Amo-1618 on peroxidase and IAA-oxidase activity were mutually antagonized when both chemicals were applied at concentrations nullifying their opposite effects on hypocotyl growth. Stimulation of peroxidase and IAA-oxidase activity was found with all 5 growth-retarding compounds tested, but not with maleic hydrazide. It is proposed that the growth-retarding chemicals exert their effect on plant growth by interacting with gibberellin in IAA oxidase or its cofactors and inhibitors, and thus affect the auxin level of tissues.