Changes in chlorophyll a fluorescence parameters in leaves and stems of the CAM plant Cissus quinquangularis Chiov exposed to high irradiance

The effects of high irradiance (700 and 1400 mu mol photons m(-2) s(-1)) on the regulation of photochemistry in leaves and stems of the CAM plant Cissus quinquangularis Chiov. were investigated by chlorophyll a fluorescence parameters. Significant decreases in F-o, F-m and F-v were observed in the leaf and in the stem tissues with increasing light intensity and exposure time. F-v/F-m, the PSII photochemical efficiency, decreased at an higher extent in stems and leaves at 1400 mu mol photons m(-2) s(-1). Non-photochemical quenching increased with the intensity and duration of light exposure, being higher in leaves than in stems. Upon high-light stress, a slighter reduction in quantum yield of the PSII electron transport was observed in the stem than in the leaf tissue. A significant decrease of photochemical quenching was observed in leaves but not in stems, thus suggesting a different strategy in the regulation of photochemistry in leaves and stems of C. quinquangularis plants exposed to high-light stress.