Mitigation of salinity-induced oxidative damage in wheat (Triticum aestivum L.) seedlings by exogenous application of phenolic acids

In the present investigation, influence of exogenous phenolic acids on antioxidative defense system of salt stressed wheat seedlings was explored at the seventh day of growth. Electrical conductivity of 10 dS/m was used for imposing salt stress in two wheat cultivars showing contrasting behavior for salt tolerance. For observing stress mitigating effects of various phenolic acids, 20 ppm of ferulic, 10 ppm of caffeic, 10 ppm of p-coumaric, 5 ppm of salicylic, and 15 ppm of sinapic acids were selected for biochemical studies. Imposition of salinity stress reduced membrane stability as depicted by electrolyte leakage and reduction was more in sensitive cultivar HD2329 which was well correlated with its higher ROS accumulation in terms of H₂O₂ content and lipid peroxidation as MDA content. Exogenous application of phenolic acids reduced electrolyte leakage in NaCl-stressed seedlings of both the cultivars and maximum decrease was observed in the presence of sinapic acid, followed by caffeic, salicylic, ferulic, and p-coumaric acids. When phenolic acids were applied to salt stressed wheat seedlings, malondialdehyde content either decreased or remained unaffected in the shoots of both the cultivars, whereas hydrogen peroxide (H₂O₂) decreased in the roots and shoots of both cultivars maximally by caffeic and salicylic acids. Hydroxyl radical scavenging capacity of salt stressed seedlings increased to the maximum extent by the use of caffeic and sinapic acids. Catalase (CAT) and peroxidase activities were upregulated in the stressed shoots of salt-tolerant cultivar by the exogenous use of caffeic and sinapic acids. In comparison to stress, ascorbate peroxidase (APX) activity was also upregulated in stressed seedlings of both cultivars by exogenous use of caffeic and sinapic acids. In stressed seedlings of salt-sensitive cultivar, monodehydroascorbate reductase activity increased by exogenous use of caffeic, p-coumaric, salicylic, and sinapic acids. In roots of Kharchia local, use of ferulic, p-coumaric, and caffeic acids resulted into upregulation of glutathione reductase activity, whereas in salt-sensitive cultivar, only caffeic acid caused upregulation of this enzyme. Proline (Pro) content increased in HD2329 on addition of different exogenous phenolic acids in the medium, whereas in Kharchia local, addition of sinapic acid enhanced pro content. Glycine betaine (GB) content was increased by use of different phenolic acids in the stressed roots of Kharchia local. On the other hand, exogenous application of sinapic acid led to enhanced GB content in salt-sensitive cultivar. Based upon the fine regulation of CAT and APX activities and hydroxyl radical scavenging activity in relation to H₂O₂ content and electrolyte leakage, caffeic and sinapic acids may be regarded as the most efficient among the different phenolic acids in averting ROS-accrued oxidative damage in salt stressed wheat seedlings.