Salicylic acid-mediated alleviation of fluoride toxicity in rice by restricting fluoride bioaccumulation and strengthening the osmolyte, antioxidant and glyoxalase systems.

Abstract

The aim of the manuscript was to demonstrate the efficacy of salicylic acid (SA) in abrogating the fluoride-induced oxidative damages in the susceptible rice cultivar, MTU1010. Prolonged exposure of seedlings to sodium fluoride (25 mg L-1) severely impaired growth and overall physiological parameters like germination percentage, biomass and root and shoot length and incited the formation of hydrogen peroxide that enhanced electrolyte leakage, formation of cytotoxic products like malondialdehyde and methylglyoxal and lipoxygenase activity. Exogenous application of SA (0.5 mM) enhanced the endogenous level of SA that restored the chlorophyll content and catalase activity and further escalated the activity of other enzymatic antioxidants (superoxide dismutase, guaiacol peroxidase, ascorbate peroxidase, glutathione peroxidase and glutathione S-transferase), formation of non-enzymatic antioxidants (anthocyanins, carotenoids, flavonoids, phenolics, ascorbate and reduced glutathione) and osmolytes (proline, amino acids and glycine betaine) that cumulatively maintained the integrity of membrane structure and homeostatic balance of the cells by scavenging the accumulated hydrogen peroxide. SA-mediated formation of proline and flavonoids was linked with the enhanced activity of Δ1-pyrroline-5-carboxylate synthetase and phenylalanine ammonia lyase. Fluoride stress enhanced the activity of enzymes like glyoxalase I and glyoxalase II which were further aggravated in the seedlings upon treatment with SA, effectively detoxifying the methylglyoxal formed during stress. Overall, the manuscript depicts the pivotal role played by exogenous SA in ameliorating the effects of fluoride-induced damages in the seedlings and proves its potentiality as a protective chemical against fluoride stress when applied exogenously in rice.