Non-destructive optical detection of pigment changes during leaf senescence and fruit ripening

Reflectance spectra in the visible and near infra-red range of the spectrum, acquired for maple (Acer platanoides L.), chestnut (Aesculus hippocastanum L.), potato (Solanum tuberosum L.), coleus (Coleus blumei Benth.), leaves and lemon (Citrus limon L.) and apple (Malus domestica Borkh.) fruits were studied. An increase of reflectance between 550 and 740 nm accompanied senescence-induced degradation of chlorophyll (Chl), whereas in the range 400-500 nm it remained low, due to retention of carotenoids (Car). It was found that both leaf senescence and fruit ripening affect the difference between reflectance (R) near 670 and 500 nm (R(678) - R(500)), depending on pigment composition. The plant senescing reflectance index in the form (R(678) R(500))/R(750) was found to be sensitive to the Car/Chl ratio, and was used as a quantitative measure of leaf senescence and fruit ripening. The changes in the index were followed during leaf senescence, and natural and ethylene-induced fruit ripening. This novel index can be used for estimating the onset, the stage, relative rates and kinetics of senescence/ripening processes.