Light-induced pigment degradation in leaves and ripening fruits studied insitu with reflectance spectroscopy

Pigment breakdown mediated by activated oxygen species is a consequence and a general symptom of oxidative stress and injury to plants. We have attemp ted to estimate the patterns of pigment bleaching and follow pigment suscep tibility to irradiation as related to the process of senescence/ripening Li ght-induced pigment breakdown was studied in situ in the leaves of a shade- requiring plant, wax flower (Hoya carnosa R. Br.), as well as in apple (Mal us domestica Borlh. cv. Zhigulevskoe) and lemon (Citrus limon Burm. cv. Pav lovsky) fruits, using reflectance spectroscopy. It was found that the sensi tivity of plant pigments to photobleaching increases as ripening progresses in lemon fruit. Kinetic analysis showed that in all systems a rapid breakd own of the pigment occurs after a lag-phase. The signature analysis reveale d a common pattern of chlorophyll and carotenoid changes, but degradation o f the individual pigments was found to be inhomogeneous. Both in lemon and apple fruits a decrease in reflectance in the band of carotenoid absorption preceded pigment photodestruction. In the fruits, the bulk of chlorophyll b and the long-wavelength chlorophyll a forms were degraded at early stages of the process whereas the breakdown of both chlorophylls in H. carnosa le aves was more synchronous. Prolonged irradiation induced bleaching of the m ain chlorophyll a band with maximum at 678 nm in the difference spectra, as well as carotenoids. Some features of reflectance spectra in the bands of chlorophyll and carotenoid absorption were found to be suitable for the dif ferentiation of photo-induced pigment breakdown from the transformation of the pigments taking place during senescence.