Effects of Deuterium Oxide and Free Radical Scavengers on Carotenoid Photobleaching in Spinach Chloroplasts

The effect of D₂O on carotenoid photobleaching was examinedin spinach chloroplasts poisoned by carbonylcyanide m-chlorophenylhydrazone.D₂O, which prolongs a life time of singlet molecular oxygen,stimulated carotenoid photobleaching under aerobic conditions,but not under anaerobic conditions. The stimulation became smalleras the intensity of actinic light was lowered. Propyl gallateand (+)-catechin, radical scavengers, suppressed photobleaching.The suppression was greater at a low actinic light intensity.These results suggest that cartoenoid is photobleached by singletmolecular oxygen and radical chain reactions. (Received July 17, 1982; Accepted January 13, 1983)