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To explore the plant active oxygen scavenging and photosynthesis function of 2-Cys Prx, a newly discovered member of the antioxidant protease family, the tobacco 2-Cys Prx gene was cloned into the plant expression vector prok Ⅱ. This vector, which is controlled by the constitutive strong promoter CaMV35S, was introduced into tobacco by Agrobacteria-mediated transformation. The 816-bp open reading frame of tobacco 2-Cys Prx encodes 271 amino acids and showed high homology with 2-Cys Prx genes from Solanum lycopersicum, Vitis vinifera, and Populus trichocarpa, indicating 2-Cys Prx gene is highly conserved. The active oxygen metabolism and chlorophyll fluorescence response to salt stress were also studied. Under salt stress, superoxide dismutase (SOD) activity in tobacco leaves increased, while ascorbate peroxidase (APX) activity decreased. Additionally, the donor- and acceptor-side function of photosystem Ⅱ (PSⅡ) were affected by salt stress to different degrees, with the latter significantly more affected than the former. The H2O2 and malondialdehyde content of 2-Cys Prx-overexpression tobacco leaves under salt stress were all significantly lower than those of wild-type (CK) leaves. The PSⅡ maximum photochemical efficiency (Fv/Fm) and the performance index on absorption basis (PIABS) of 2-Cys Prx-overexpression leaves were significantly lower than those of CK leaves under salt stress. Various relative fluorescence intensities of the 2-Cys Prx-overexpression plants exhibited significantly lower increases in amplitude than those of CK plants. Thus, 2-Cys Prx increased the salt tolerance of PSⅡ function and lowered the PSⅡ light inhibition effect in plants under salt stress, suggesting that 2-Cys Prx gene overexpression can alleviate H2O2 buildup and lower the peroxide levels of cytomembrane lipids under salt stress. Thus, 2-Cys Prx gene overexpression can protect oxygen-evolving complex function at the donor side of PSⅡ under salt stress and also improve electron transfer at the acceptor side of PSⅡ.