Role of xanthophyll cycle and D1 protein turnover in photoprotection of Phyllostachys edulis (Carr.) Lehaie leaves

To investigate the roles of the xanthophyll cycle and D1 protein turnover in photoprotection of bamboo, we applied chlorophyll fluorescence techniques to measure the characteristics of photoinhibition in moso bamboo (Phyllostachys edulis (Carr.) Lehaie) leaves under strong light and xanthophyll cycle inhibitor-dithiothreitol (DTT) and D1 protein synthesis inhibitor-streptomycin sulfate (SM) treatment, respectively. Results showed that the maximum photochemical efficiency (F_v/F_m) decreased significantly in leaves of Ph. edulis exposed to strong artificial light or strong natural noon light in summer. However, the F_v/F_m value could be restored under darkness or in the afternoon under decreased intensity of sunlight. Non-photochemical quenching (NPQ) in Ph. edulis leaves was inhibited by the DTT and SM treatments, with the inhibition effect of DTT significantly better than that of SM. In addition, the DTT and SM treatments increased the declining degree of chlorophyll fluorescence parameters in Ph. edulis leaves under strong light, including F_v/F_m, actual photochemical efficiency Y(Ⅱ), and photochemical quenching q_P. These results suggest that Ph. edulis leaves possess a complete photoprotection defense mechanism. NPQ is closely associated with the xanthophyll cycle and D1 protein turnover, which plays an important role in Ph. edulis photoprotection.