Ethylene- and Proline-Dependent Regulation of Antioxidant Enzymes to Mitigate Heat Stress and Boost Photosynthetic Efficacy in Wheat Plants

Abstract

Ethylene regulates the photosynthetic efficiency of plants grown under challenging environments by the regulation of the antioxidant system and other biomolecules, such as osmolytes (proline). The role of ethylene in modulating proline biosynthesis and subsequent changes in antioxidant system to protect wheat (Triticum aestivum L. cv. WH-711) against heat stress was studied. The effects of exogenously sourced ethylene (as 200 µL L−1 ethephon: 2-chloroethylphosphonic acid) and proline (50 mM) were studied in the protection of photosynthetic performance and heat stress tolerance by studying mechanisms of proline biosynthesis, activity and gene expression of antioxidants, and ethylene evolution. The cultivars WH-711, RAJ-3765, PBW-373, HD-2967, PBW-550, DBW-17, PBW-343, and UP-2338 were screened for their proline accumulation capacity and tolerance to heat stress. Plants of the cultivar WH-711 with higher proline accumulation and heat tolerance capacity were subjected to a temperature of 40 °C for 6 h per day over 15 days and then allowed to recover at 28 °C. These plants showed increased H2O2 and TBARS (thiobarbituric acid reactive substances), proline accumulation, and ethylene evolution, activity of antioxidant enzymes, and reduced photosynthetic characteristics. Ethephon plus proline supplementation under heat stress upregulated the antioxidant defense system, reduced oxidative stress, and upregulated psbA and psbB expression and photosynthesis. The study’s outcome may be taken to improve photosynthetic performance and heat stress tolerance through ethylene-enhanced proline accumulation and antioxidant defense system.