Exogenous Zinc Forms Counteract NaCl-Induced Damage by Regulating the Antioxidant System, Osmotic Adjustment Substances, and Ions in Canola (Brassica napus L. cv. Pactol) Plants

Salinity is the principal natural obstacles for sustainable agriculture, adversely impacting 30% of the world's irrigated land, resulting in food insecurity, particularly in arid and semi-arid areas. Zinc has several functions in plants; nevertheless, the promising roles of nano-zinc oxide particle in plants under salinity stress are not clear. The current study aims to investigate the roles of zinc (water, 75 mg L-1 zinc sulfate (Zn), and 10 mg L-1 zinc oxide nanoparticle (ZNP)) on the mitigation of NaCl stress (6000 mg L-1) on morpho-physiological attributes and yield of canola plants. Salinity exhibited a substantial reduction in canola plant growth, enhanced photosynthetic pigment degradation, and decreased nutrient concentrations. A decrease in the overall yield and a decrease in various individual components were considerably stimulated by zinc application under non-salinized and salinized conditions. Salinity caused a visible increase in membrane permeability (MP%), malondialdehyde (MDA), and hydrogen peroxide (H2O2) concentrations. Interestingly, zinc application significantly decreased MP%, MDA, and H2O2 concentrations by the upregulation of antioxidant enzymes (superoxide dismutase, catalase, peroxidase) and levels of non-enzymatic antioxidants (ascorbic, carotenoids, and total soluble phenolic compounds). Furthermore, zinc application also enhanced osmoregulation by increasing proline and total soluble carbohydrates accumulation, as well as increased nitrogen, potassium, and phosphorus in the plant tissues in correlation with a decline in sodium and chloride contents. Zinc's, especially ZNP, role in the mitigation the negative effects of salinity on canola growth and yield may be connected with the upregulating oxidative defense system and osmolyte synthesis as well as ionic regulation.