Light-stress-induced pigment changes and evidence for anthocyanin photoprotection in apples

Fruit of two apple (Malus domestica Borkh.) cultivars, differing in their a bility to produce anthocyanin pigments when exposed to sunlight, have been studied using reflectance spectroscopy. Comparison of the spectra shows tha t apple anthocyanins in vivo possess a symmetric absorption band at 500-600 nm with a maximum near 550 nm. Anthocyanins considerably increase Light ab sorption by apples. In on-tree-ripening Zhigulevskoe apples, accumulating h igh amounts of anthocyanin pigments, chlorophyll contents in sunlit and sha ded sides of the fruits are found to be similar. In contrast, frequently co nsiderably lower chlorophyll content is estimated in sunlit compared with s haded sides of Antonovka apples exhibiting low potential for anthocyanin fo rmation. Sunlight also brings about an increase of carotenoid content over that of chlorophylls and accumulation of substances responsible for light a bsorption in the range 350-400 nm. The rates of high-light-induced chloroph yll bleaching in red zones of fruit containing anthocyanins are considerabl y lower than those in green zones and decrease with an increase in the pigm ent content. Anthocyanins show more stability to irradiation than chlorophy lls. A protective function of anthocyanins against both light-induced stres s in, and damage to, apples is suggested. It is proposed that anthocyanins function as an effective internal light trap filling the chlorophyll absorp tion gap in the green-orange part of the visible spectrum. (C) 2000 Elsevie r Science S.A. All rights reserved.