Damage in old leaves of shade-treated tea trees induced by high light after shade removal and shoot harvest

High-quality green tea is produced from developing shoots (apical buds and young leaves) of tea plants (<i>Camellia sinensis</i> (L.) Kuntze) grown under shaded conditions. However, the removal of shade covers causes shaded tea plants to experience a sudden exposure to high light (HL). Since in ordinary tea plantation new shoots are cropped immediately following shade removal, the remaining leaves emerging from the canopy are exposed to HL. In this study, we investigated the HL response of old leaves on shaded tea plants to evaluate possible deleterious effects of HL illumination after shade removal and shoot harvesting in two years (2017 and 2018). Old leaves of both shade-grown and unshaded tea plants suffered from temporal photoinhibition caused by HL exposure after shoot harvesting but were able to recover within two weeks. Moreover, chlorophyll <i>a</i>/<i>b</i> ratios remained unchanged in old leaves experiencing shading treatment, suggesting that old leaves have a weakened capacity to respond to low light conditions. Furthermore, protein carbonyl content was elevated 3-7 days after shade removal in summer 2018. Shoot growth during the subsequent autumn season was inhibited in shaded plants relative to the control group. Taken together these results indicate that old leaves on shaded tea plants suffer from oxidative damage after shade removal in summer, and this may inhibit the growth of autumn shoots.