Suppression of Carotenoid Photobleaching by Kaempferol in Isolated Chloroplasts

The effects of kaempferol on carotenoid photobleaching wereexamined using chloroplasts poisoned by carbonylcyanide m-chlorophenylhydrazone(CCCP). Kaempferol suppressed carotenoid photobleaching withoutaffecting electron transfer reactions. Half-maximal suppressionwas observed at about 10 µM. Kaempferol was photooxidizedby CCCP-poisoned chloroplasts, as observed by its bleachingat 380 nm. Ascorbate inhibited the oxidation of kaempferol.Under anaerobic conditions, kaempferol did not affect the photobleachingof carotenoid. Other fiavonols, quercetin and its glycosides,also suppressed the carotenoid photobleaching. The results suggestthat flavonols act as antioxidants in illuminated chloroplastsunder aerobic conditions. (Received February 22, 1982; Accepted May 14, 1982)