Recent studies have demonstrated melatonin protects various crops against abiotic stresses. However, the effects of melatonin on the photosynthetic apparatus of stressed plants is poorly characterized. We investigated the effects of melatonin pretreatment on photosynthesis and tolerance to salinity stress in Avena sativa (oat) plants. Oat plants were exposed to four treatments (three replicate pots per treatment): well-watered (WW; control); watered with 300 mM salt solution for 10 days (NaCl); pretreated with 100 µM melatonin solution for 7 days then watered normally for 10 days (Mel+W); or pretreated with 100 µM melatonin for 7 days then 300 mM salt for 10 days (Mel+NaCl). Considerable differences in growth parameters, chlorophyll content, stomatal conductance, proline accumulation, lipid peroxidation, electrolyte leakage, and growth parameters were observed between groups. Genes encoding three major antioxidant enzymes were upregulated in the Mel+NaCl group compared to the other groups. Chlorophyll-a fluorescence kinetic analyses revealed that almost all photosynthetic parameters were improved in Mel+NaCl plants compared to the other treatments. Analysis of genes encoding the major extrinsic proteins of photosystem II (PSII) revealed that PsbA, PsbB, PsbC, and PsbD (but not PsbO) were highly upregulated in Mel+NaCl plants compared to the other groups, indicating melatonin positively influenced photosynthesis under control conditions and salt stress. In addition, melatonin upregulated stress-responsive NAC transcription factor genes in plants exposed to salt stress. These findings suggest melatonin pretreatment improves photosynthesis and enhances salt tolerance in oat plants.

In this study, the effects of melatonin-induced enhancement on the principal photosynthetic parameters and antioxidant machinery were investigated in Avena sativa (oat) plants exposed to polyethylene glycol (PEG)-induced osmotic stress. The parameters of growth, chlorophyll content, stomatal conductance, proline accumulation, lipid peroxidation, and electrolyte leakage showed noteworthy improvements between the groups. Melatonin treatment caused upregulation of the genes that encode the three major antioxidant enzymes: ascorbate peroxidase (APX), superoxide dismutase (SOD) and catalase (CAT). Chlorophyll-a fluorescence kinetic analyses revealed that melatonin treatment improved performance indices (PIABS and PItotal), quantum yields, and efficiencies of photosystem II (PSII) in oat plants subjected to PEG-induced osmotic stress. Furthermore, upregulation of five genes (PsbA, PsbB, PsbC, PsbD, and PsbO) that encode the core proteins of PSII implied melatonin exerted a positive influence on photosynthesis under conditions of osmotic stress.

In this study, transgenic Arabidopsis lines expressing a potato gene (D43), encoding Glyceraldehyde 3phosphate dehydrogenase, were studied. The D43 plants exhibited improved morphological parameters and accumulation of photosynthetic pigments compared to wild-type (WT) plants under salinity stress conditions. In addition, the D43 transgenic plants showed significantly reduced electrolyte leakage, higher stomatal conductance, lower malondialdehyde (MDA) content, and higher proline content than the WT plants under salinity stress. The gene expression analysis showed that the D43 plants accumulated 1.7-fold, 2.2-fold, and 1.3-fold higher mRNA transcripts of genes encoding the antioxidant enzymes ascorbate peroxidase (APX), superoxide dismutase (SOD), and catalase (CAT), respectively under salt-stress conditions. Furthermore, they significantly altered the expression of seven major stress-responsive genes, which indicated that overexpression of the potato D43 gene gave salinity stress resistance to Arabidopsis. Chlorophyll-a fluorescence kinetics confirmed the efficient photon absorption, electron transport, and overall PSII efficiency that led to improved photosynthesis in the D43 plants subjected to NaCl-induced salinity stress. Overall, our findings have suggested that potato D43 is a potential candidate gene for developing salinity stress resistance in higher plants.