Differential dependence of apple (Malus domestica Borkh.) cultivars on the xanthophyll cycle for photoprotection
The dependence of fruit peel photosystems of ‘Granny Smith’, ‘Braeburn’, ‘Fuji’, ‘Golden Delicious’ and ‘Topred’ apple (Malus domestica Borkh.) peel on the xanthophyll cycle for photoprotection was studied under laboratory conditions. Mature fruit peel was either treated with 1 mm dithiothreitol (DTT) to inhibit the xanthophyll cycle or not treated. Fruit peel was subsequently exposed to photosynthetic active radiation stress of 1 500 μmol m−2 s−1 combined with heat stress of 45 °C for 3 h. Fruit peel photodamage was assessed by measuring the change in the maximum light use efficiency of photosystem II (Fv/Fm). The change in the concentration of the xanthophyll-cycle carotenoids zeaxanthin, antheraxanthin and violaxanthin plus lutein and β-carotene were analysed. The Fv/Fm of heatand light-stressed DTT-treated (+DTT) ‘Granny Smith’ and ‘Braeburn’ peel had a low recovery after stress compared with the recovery Fv/Fm of similarly stressed peel not treated with DTT (−DTT). However, there was no difference in the recovery Fv/Fm between +DTT and −DTT ‘Fuji’, ‘Golden Delicious’ and ‘Topred’ peel. The photosystem of ‘Granny Smith’ and ‘Braeburn’ fruit therefore appear to have a higher dependency on the xanthophyll cycle for photoprotection than ‘Fuji’, ‘Golden Delicious’ and ‘Topred’ fruit.
Keywords: light, Malus domestica, sunburn, temperature, xanthophyll cycle