Exogenous Salicylic Acid and Trehalose Ameliorate Short Term Drought Stress in Wheat Cultivars by Up-regulating Membrane Characteristics and Antioxidant Defense System

Abstract

In this study, the protective role of salicylic acid (SA) and trehalose (Tre) in relation to lipid peroxidation, membrane leakage, membrane stability index, antioxidant defense system as well as non-enzymatic antioxidants were investigated in drought stressed wheat Gemmieza-7 (drought sensitive cultivar) and Sahel-1 (drought tolerant cultivar) plants. Water stress reduced bio-membranes stability through inducing its lipid peroxidation resulting in an increment in membrane leakage with marked decrease in membrane stability index of flag leaf of both wheat cultivars during grain-filling. Moreover, it was obvious that drought significantly increased the activity of ascorbic acid oxidase (AAO), peroxidase (POD) and phenylalanine ammonia lyase (PAL) activities and induced non-significant reduction in polyphenol oxidase (PPO) activity in flag leaves of both wheat cultivars during grain-filling in comparing with well watered plants. Among cultivars, tolerant one showed higher enzymes activity than the sensitive one. Application of SA and/or Tre markedly increased AAO, POD and PAL activities and non-significant decrease in PPO activity in flag leaf of water stressed wheat plants. Generally, SA and Tre treatment appeared to be the most effective treatment in counteracting the negative effects of water stress and Sahel-1 appeared to induce better results than Gemmieza-7 and proved to be more tolerant. Drought stress caused significant increase in the amount of total phenols and flavonoids in flag leaf of both cultivars during grain-filling where the sensitive plants accumulated more total phenols and flavonoids contents than the tolerant one. Furthermore, water stress increased the non-photosynthetic pigment content of the two wheat cultivars particularly drought sensitive one during grain filling. These results suggest that the exogenous application of SA and/or Tre assisted the plants to become more tolerant to drought stress-induced oxidative damage by upregulating the membrane characteristics and enhancing their antioxidant defense system as well as non- enzymatic antioxidants.