The present study was designed to highlight the effects of cold plasma (10 kV) treatment and priming with 2 mM salicylic acid (SA) and their combination (10 kV of plasma + 2 mM SA) on the physiological parameters and metabolism of two cultivars of Oryza sativa, i.e., Zhu Liang You 06 (ZY) and Qian You No. 1 (QY), under salinity stress (150 mM NaCl) and normal growth condition (0 mM NaCl). Seed germination and seedling growth were enhanced by SA priming and cold plasma treatment either alone or in combination under salinity stress. Photosynthetic pigments, photosynthetic gas exchange, and chlorophyll fluorescence were improved by cold plasma treatment and SA priming under salinity stress as compared to the untreated seeds. The activities of antioxidant enzymes were significantly improved by the combination of SA priming and cold plasma treatment in both cultivars under salinity stress. There were rapid changes in the cellular content of sodium (Na+) and calcium (Ca+), where the plants grown under saline conditions accumulate more Na+ and less Ca+ contents resulting in ionic imbalances. Interestingly, cold plasma and SA treatments diminished this action by reducing Na+ accumulation and increasing K+ and Ca+ contents in the plant cell under salinity stress. The activities of enzymes involved in secondary metabolism assimilation were up-regulated with cold plasma and SA priming either alone or combination under salinity stress. An increase in reactive oxygen species (ROS) accumulation and malondialdehyde (MDA) content was also observed under salinity stress condition. On contrast, seed treated with SA and plasma alone or combined resulted in a significant decrease in ROS and MDA contents under salinity stress. Our results indicated that SA priming and cold plasma treatment either alone or combined improved plant uptake of nutrients in both cultivars under stress conditions. The ultrastructural changes were observed to be more prominent in ZY than QY cultivar. Plants without SA priming or cold plasma treatments have a big vacuole due to the movement of ions into the vacuole directly from the apoplast into the vacuole through membrane vesiculation leading to membrane destabilization. However, SA priming and cold plasma treatment alone or combined helped the plants to recover their cell turgidity under salinity stress.
Keywords: Antioxidant; Cold plasma; Oryza sativa; SA; Salinity; Secondary metabolism; Ultrastructure.