The hormonal control of amaranthin synthesis in Amaranthus caudatus seedlings.

Exogenous gibberellic acid, A3 (GA3) inhibits phytochrome mediated betacyanin synthesis in seedlings of Amaranthus caudatus. The growth retardants, β-chloroethyl-trimethylammonium chloride (CCC), 'isopropyl-4'-(triethylammonium chloride)-5'-methylphenyl piperidine carboxylate (AMO 1618) and tributyl-2,4,-dichlorobenzylphosphonium chloride (phosphon D) enhance pigment synthesis. Retardant stimulation of pigment synthesis is overcome by GA3 application. Besides lowering endogenous GA levels the retardants inhibit protein synthesis by as much as 25%. Retardant inhibition of protein synthesis is not overcome by GA3. The results suggest that amaranthin synthesis in Amaranthus caudatus can be directly controlled by endogenous GA. GA3 has no effect on kinin induced dark pigment synthesis. Kinins, however, do not overcome GA3 inhibition of pigment synthesis in the light.