Singlet oxygen, flavonols and photoinhibition in green and senescing silver birch leaves

Abstract Key message Decreased absorptance and increased singlet oxygen production may cause photoinhibition of both PSII PSI in birch leaves during autumn senescence; however, photosynthetic electron transfer stays functional until late senescence. During senescence, deciduous trees degrade chlorophyll synthesize flavonols. We measured parameters, epidermal flavonols, vivo the photosystems (PSII PSI) from green senescing silver ( Betula pendula ) leaves. Chlorophyll a fluorescence P 700 absorbance measurements showed that amounts decreased throughout but remaining units stayed ~ 90% leaf was degraded. An increase to b ratio, decrease > nm blue shift peak at 77 K suggest light-harvesting complex I first degraded followed by II finally photosystems. Senescing produced more than leaves, possibly because low light absorption allows high flux incident per photosystem. also induced less non-photochemical quenching, which contribute production. Faster under light, most probably caused rapid However, maintained capacity recover PSII. Amounts flavonols correlated neither nor birch. Moreover, Arabidopsis thaliana mutants, incapable synthesizing were not susceptible or wild type plants; screening was, small A. . These results do protect against chloroplasts.