Zeaxanthin Synthesis, Energy Dissipation, and Photoprotection of Photosystem II at Chilling Temperatures

When leaves of a mangrove, Rhizophora mangle, were exposed to an excess of light at chilling temperatures, synthesis of zeaxanthin through violaxanthin de-epoxidation as well as nonphotochemical fluorescence quenching were markedly reduced. The results suggest a protective role of energy dissipation against the adverse effects of high light and chilling temperatures: leaves of R. mangle that had been preilluminated in 2% O₂, 0% CO₂ at low photon flux density and showed a high level of zeaxanthin, and leaves that had been kept in the dark and contained no zeaxanthin, were both exposed to high light and chilling temperatures (5°C leaf temperature) in air and then held under control conditions in low light in air at 25°C. Measurements of chlorophyll a fluorescence at room temperature showed that the photochemical efficiency of PSII and the yield of maximum fluorescence of the preilluminated leaf recovered completely within 1 to 3 hours under the control conditions. In contrast, the fluorescence responses of the predarkened leaf in high light at 5°C did not recover at all. During a dark/light transient in 2% O₂, 0% CO₂ in low light at 5°C, nonphotochemical fluorescence quenching increased linearly with an increase in the zeaxanthin content in leaves of R. mangle. In soybean (Glycine max) leaves, which contained a background level of zeaxanthin in the dark, a similar treatment with excess light induced a level of nonphotochemical fluorescence quenching that was not paralleled by an increase in the zeaxanthin content.