Plant-Derived Smoke Ameliorates Salt Stress in Wheat by Enhancing Expressions of Stress-Responsive Genes and Antioxidant Enzymatic Activity

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Abstract
Abiotic stresses are the biggest threat to the increasing population worldwide. Salt stress is one of the most significant abiotic stresses, affecting 20% of the crop production around the world. Plant-derived smoke (PDS) has been reported as a biologically active plant product in stimulating seed germination, seedling growth and physiological characteristics of crops under abiotic stress conditions. Nevertheless, studies showing how PDS alleviates salt stress are largely unknown. Here, we report the molecular mechanism of how PDS could alleviate salt stress in wheat. Initially, PDS at 2000 ppm enhanced seed germination, root/shoot length and seedling fresh weight. However, PDS at 1000 and 500 ppm did not show any significant effect. Salt stress at 150 and 200 mM significantly reduced seed germination rate, root/shoot length and fresh weight of the wheat seedlings. Interestingly, PDS supplementation at 2000 ppm concentration was sufficient to restore seed germination under salt stress condition. Moreover, PDS improved root/shoot length and seedling biomass under 150 and 200 mM salt stress, suggesting that PDS is a potent plant product, capable of abiotic stress alleviation in crops. In comparison to the control, PDS-treated seedlings displayed increased activity of major antioxidative enzymes such as superoxide dismutase, peroxidase and ascorbate peroxidase under salt stress, resulting in reduced levels of hydrogen peroxide and lipid peroxidase, showing that PDS can possibly help in salt stress amelioration by regulating redox homeostasis. Importantly, salt stress altered the expression of germination marker genes, such as TaSAM, TaPHY, TaBGU (germination positive effectors), TaLEA and TaGARS34 (germination negative effectors), suggesting the potential role of PDS in the germination pathway under salt stress. Further, PDS modulated the transcript levels of several salt stress stress-responsive genes, including TaSOS4, TaBADH and TaHKT2. In conclusion, this study provides a molecular and physiological basis for elucidating the mechanism of how PDS functions in stress induction in wheat, as well as demonstrates the importance of PDS in agricultural practices, laying the groundwork for future research into the role of PDS in the amelioration of abiotic stresses in various plants.

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