Ethylene and spermine attenuate chromium-inhibited photosynthetic functions by improving nitrogen and sulfur assimilation and antioxidant system in mustard

Abstract

Phytohormones signaling is known for the regulation of metabolites synthesis, photosynthetic performance and abiotic stress acclimation in plants. We investigated the influence of ethylene (sourced as ethephon; 2-chloroethyl phosohonic acid, ETH) and spermine (Spm; polyamine) in alleviating the chromium (Cr)-triggered oxidative stress in the mustard (Brassica juncea cv. Varuna). The individual additions of 200 µL L−1 ETH and 1 mM Spm improved photosynthetic and growth parameters in the absence of Cr, but the Cr presence increased oxidative stress and the formation of stress (excess) ethylene, inhibiting photosynthesis, and growth. The application of ETH and Spm together in the absence of Cr, improved photosynthesis conspicuously. In the presence of Cr, ETH and Spm application improved photosynthesis by upregulation of psbA and psbB genes expression, and reducing oxidative stress, stress ethylene formation, and increase in activity of antioxidant enzymes, upregulation of ascorbate peroxidase (APX) and glutathione reductase (GR) genes, and nitrogen (N) and sulfur (S) assimilation. The possible ways in which ethylene and Spm interact in the mitigation of Cr-triggered oxidative damage are discussed. The study will provide insight into the mechanisms of N and S assimilation, antioxidant system, and regulation of ethylene production under the influence of ETH and Spm, and the strategy may be adopted for the sustainability of mustard plants under Cr stress.