Exogenous proline enhances salt tolerance in wheat: regulating osmolytes, hormonal balance, antioxidant defence, and yield performance

This study investigates the impacts of exogenously applied proline (Pro, 10 mmol/L) on the growth and productivity of wheat plants in saline environments. The findings indicated that increased NaCl concentrations, 60 and 120 mmol/L, further depressed the shoot and root growth parameters and flag leaf area. However, the Pro treatment ameliorated salt stress and improved all growth parameters, reducing the magnitude of such growth inhibitions compared to nontreated plants. It also enhanced the organic osmolyte accumulation, including Pro, total soluble sugars, and total soluble protein, implicated in osmotic balance and cell protection under stress. Furthermore, supplementing Pro improved ionic balance through a reduction in Na accumulation and an enhancement in the uptake of K, Ca, and Mg, thus mitigating the negative effects of salinity on nutrient availability. Pro treatment affected phytohormone levels, especially increasing auxin and gibberellins while decreasing abscisic acid under salt stress. Antioxidant enzymes such as catalase, superoxide dismutase, ascorbate peroxidase, and glutathione reductase, as well as nonenzymatic antioxidants like ascorbic acid and glutathione, were also enhanced by Pro, thereby protecting the plants against oxidative damage. Moreover, it was noticed that Pro treatment substantially improved all yield attributes of wheat plants, such as plant height, spike length, no. of spikelets/main spike, grain no./main spike, grain fresh and dry weights, and grain yield/plant through attenuation of the negative impact of NaCl. In this regard, Pro application appears to be a very promising approach toward mitigating the adversities of salinity in agriculture, especially in crop productivity in saline environments.