Effect of light and exogenously applied precursors on amaranthin synthesis in Amaranthus caudatus

Light stimulates the synthesis of amaranthin in Amaranthus caudatus var. viridis. Evidence suggests that this stimulation is markedly dependent on seedling age. Synthesis is controlled by both a “low-energy” red/far-red reversible phytochrome system and an HER at least partially under phytochrome control. In seedlings exposed to light, synthesis is promoted by exogenously applied DOPA and tyrosine. It is suggested that at least two light-promoted reactions occur in the biosynthetic pathway; one between tyrosine and DOPA and a second between DOPA and amaranthin.     

Effect of exogenous dopa and tyrosine on amaranthin synthesis and pigment type in Amaranthus

The efrects of exogenously applied DOPA (l-3,4-dihydroxy-phenylalanine) and tyrosine on amaranthin synthesis under a variety of light conditions are described. A possible explanation for the light-sensitive period in development is suggested to be limitation of substrate in the less sensitive stages of development. A yellow pigment tentatively identified as a betaxanthin becomes apparent under exogenous DOPA feeding.