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 we re observed in the leaf and in the stem tissues with increasing light intensity and exposure time. F-v/F-m, the PSII photochemical efficienc y, decreased at an higher extent in stems and leaves at 1400 mu mol ph otons m(-2) s(-1). Non-photochemical quenching increased with the inte nsity and duration of light exposure, being higher in leaves than in s tems. 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 observe d in leaves but not in stems, thus suggesting a different strategy in the regulation of photochemistry in leaves and stems of C. quinquangul aris plants exposed to high-light stress.