Abstract
Gibberellic acid (GA 3) inhibits amaranthin synthesis whereas the growth retardant, phosphon D, enhances pigment levels in A. caudatus seedlings exposed to light. No effect was observed on chlorophyll and carotenoid synthesis. Radioactive tyrosine and DOPA were incorporated into amaranthin. The specific activity of amaranthin synthesised in the presence of 14C-tyrosine or 14C-DOPA in seedlings treated with GA 3 is higher than water controls. The specific activity of pigment from phosphon D treated tissue is relatively low. GA 3 treated tissue has lower active tyrosine and DOPA pools compared to phosphon treated seedlings. Tyrosine and DOPA-oxidase activity increases in GA 3 treated and H 2O control seedlings exposed to light. Kinetin stimulates the synthesis of amaranthin in dark-grown seedlings and this is not overcome by simultaneous GA 3 application. Dark-grown seedlings treated with different kinetin concentrations and incubated in 14C-tyrosine synthesise radioactive amaranthin of similar specific activity. Kinetin treatment of dark-grown seedlings brings about an increased tyrosine and DOPA-oxidase activity. The results indicate that GA 3 controls the production and/or availability of tyrosine whereas kinetin can mimic light treatment and controls the utilisation of tyrosine probably by bringing about the synthesis or activation of tyrosine and DOPA-oxidase protein.
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