Difference in zeaxanthin formation in nitrate‐ and ammonium‐grown <i>Phaseolus vulgaris</i>

Abstract

Absorption at 505 nm and high‐performance liquid chromatography showed that light‐induced conversion of violaxanthin to antheraxanthin and zeaxanthin was much stronger in leaves of nitrate‐ than in leaves of ammonium‐grown Phaseolus vulgaris . Feeding ascorbate via the petiole increased zeaxanthin formation in ammonium‐grown plants. However, there was no difference in energy quenching, qE, or photoinhibition (measured as FV/FM), as determined by chlorophyll fluorescence in nitrate‐ and ammonium‐grown plants. Dithiothreitol decreased the light‐induced stimulation of zeaxanthin formation and increased photoinhibition in nitrate‐grown plants, suggesting that these plants utilize zeaxanthin for the protection of photosystem II (PSII). Ammonium‐grown plants seem to have established an alternative way to protect PSII.