Phytochrome effect on free amino acid metabolism of higher plants.

Activated phytochrome lowers the free amino acid pools of all plants investigated by about 15%. The action of red light is preferentially directed to Asp, Glu and Phe. Exogenously supplied Leu-U-(14)C is incorporated more quickly into protein of red-light-treated samples compared with dark controls. In contrast, red light decreases the amount of Asp-U-(14)C incorporated into protein, but increases the amount of (14)CO2 respired after feeding with Asp-U-(14)C. Red light has no effect on the amount of (14)CO2 respired after feeding with Leu-U-(14)C. Red-light-mediated stimulation of incorporation of Leu-U-(14)C into protein occurred within 15 min, well before the red-light-mediated increase in (14)CO2 production following feeding with Asp-U-(14)C could be detected.