Proline and salicylic acid seed priming improves germination and early salt stress tolerance in wheat

Abstract

Abstract Salt stress is one of the major limiting factors affecting wheat germination and early seedling establishment throughout the world. There is a need to improve plant stress tolerance through physiological modifications. Exogenous application of proline and salicylic acid (SA) through seed priming was evaluated for its potential to ameliorate salinity-induced damage and improve early growth performance of wheat in salt-affected areas. Wheat seeds from two varieties (Akbar-2019 and Faisalabad − 2008) were primed with different concentrations of proline (1 (P 1 ), 5 (P 2 ), and 10 mM (P 3 )) and salicylic acid (1 (SA 1 ), 5 (SA 2 ), and 10 mM (SA 3 )) individually and in combination (P 1 SA 1 P 1 SA₂ P 1 SA 3 P₂SA 1 P₂SA₂, P₂SA 3 , P 3 SA 1 , P 3 SA₂, P 3 SA 3 ) to improve salinity tolerance of wheat under 0 mM NaCl (Non-Saline) and 160 mM NaCl (Saline) conditions, along with a hydroprimed control (P₀SA₀). The germination attributes including germination percentage, germination index, plumule and radicle length (cm), vigor index, stress tolerance index, plumule fresh and dry weight (g) were tested along with other physiological and biochemical attributes for assessment of relative growth improvement. Photosynthetic pigments (chlorophyll a, chlorophyll b, total chlorophyll and carotenoids) were assessed as indicators of growth and photosynthesis. Mineral nutrient concentrations (K, Ca, Na, Mg, Mn, Fe, Cu, and Zn) were determined to evaluate mineral accumulation, oxidative stress markers (MDA and H₂O₂) were assessed as indicators of oxidative damage, while antioxidant enzyme activities (CAT, POD, and SOD) were evaluated to assess antioxidant responses. It was observed that seed priming significantly reduced the negative impact of salinity stress on germination. Among all treatments, P 2 , SA 1 , and P 2 SA 2 were particularly effective, with P 2 SA 2 demonstrating the greatest overall improvement. Combined seed priming with P 2 SA 2 increased germination percentage from 37.14% in the corresponding salt-stressed control to 74.92% in Akbar-2019, representing a 101.7% relative increase, improved seedling traits by up to 3-fold, and increased stress tolerance index by up to 136.2% compared with salt-stressed controls. It also improved total chlorophyll by up to 51.5%, essential mineral accumulation by up to 50.1%, reduced MDA and H₂O₂ by up to 50.5% and 53.2%, and enhanced SOD, POD, and CAT activities by up to 43.5%, 48.4%, and 44.2%, respectively. Akbar-2019 showed a stronger response to salinity than Faisalabad-2008, with greater improvements in growth, mineral concentrations, and antioxidant responses. Results helped to establish a novel and comprehensive framework of physiology and biochemistry to demonstrate the combined effects of seed priming with P₂SA₂ in providing broad protection against NaCl salinity stress in wheat, resulting in simultaneous improvement of germination and seedling vigor, reduced Na⁺ accumulation, improved mineral accumulation, maintenance of photosynthetic pigments, and enhanced antioxidant responses with reduced oxidative damage. Overall, these findings support combined proline and salicylic acid seed priming as a feasible, resource-saving strategy to improve early-stage salt tolerance in wheat, although field trials and molecular-level studies are needed to translate these findings into practical agronomic recommendations.