| Anthocyanin is one of the most important soluble pigments and antioxidants in plants.Red apple cultivars possess high content of anthocyanin, whereas non-red cultivars cannotsynthesize anthocyanin under natural conditions. The present study focuses on the mechanismof anthocyanin synthesis in non-red apple peels regulated by high light. The synthesis ofanthocyanin was compared between red and non-red apple cultivars. These studies mightprovide an insight for apple breeding.In present studies, non-red apple cultivar ‘Golden Delicious’ was used as the majormaterial. Anthocyanin synthesis, xanthophyll cycle, the antioxidant system, and active oxygenspecies （AOS） production in apple peels were studied under high light. The main results areas follows,1. During fruit development of ‘Golden Delicious’, the fraction of absorbed lightconsumed via photochemistry was no more than7%in the sun-exposed peel and no morethan5%in the shaded peel under high light conditions. The light dependent thermaldissipation in the sun-exposed peel mainly depended on the xanthophyll cycle whereas that inthe shaded peel depended on both the xanthophyll cycle and the reversible inactivation ofreaction centers. Compared with the sun-exposed peel, the shaded peel produced more excessexcitation energy which increased as fruit developed.2. Fruit bagging treatment significantly lowered the concentrations of phenoliccompounds, especially anthocyanin, in the peels of red and non-red apple cultivars. Undernatural sunlight (the maximum light intensity was1500-1800μmol m-2s-1) conditions duringfruit development of red and non-red apples, increases of the xanthophyll cycle and theantioxidant system capacities were much lower in red apple peel than in non red peel late infruit development, which induced an excess accumulation of AOS. To alleviating theoxidative damage, the synthesis of anthocyanin was accelerated in red apple peels. Whenbagged fruits were exposed to sunlight （the maximum light intensity was900-1200μmol m-2s-1） late in development, both red and non-red apples synthesized anthocyanin in their peels,but it was faster in red peels. As a result, the xanthophyll cycle and the antioxidant systemwere protected by anthocyanin from high light damage. 3. Under natural sunlight conditions, UV-B irradiation increased the activity of NADPHoxidase in ‘Golden Delicious’ fruit peel. As a result, excess superoxide anion was produced,which might up-regulate the gene expression of MdMYB10and MdUFGT and the synthesis ofanthocyanin in ‘Golden Delicious’ fruit peel. Exogenous application of hydrogen peroxidecould accerelate the synthesis of anthocyanin, but this depended on the irradiation of UV-Blight. |
