Spermidine and Melatonin Attenuate Fluoride Toxicity by Regulating Gene Expression of Antioxidants in Cajanus cajan L.

Being regulators of growth, both spermidine (Spd) and melatonin (Mel) are involved actively in the modulation of abiotic stress responses of plants. Hence, the present study was aimed to scrutinize the possible involvements of Spd and Mel in alleviation of fluoride ion (F-)-induced injuries in Cajanus cajan L. Seeds of C. cajan L. were exposed to 1) control, 2) F-, 3) Spd, 4) Spd+F-, 5) Mel and 6) Mel+F- for five days. The results unveiled that F- treatment caused inhibited growth (radicle length and dry mass accumulation), protein content, genomic template stability, membrane stability index, and free radical scavenging capacity, but enhanced the levels of cell death, active oxygen species (AOS), malondialdehyde, lipase, protein carbonylation, and DNA polymorphism. Moreover, F- toxicity elevated the concentrations of endogenous proline, ascorbic acid, and glutathione, and altered the isoenzyme profiles and gene expressions of stress responsive enzymes (superoxide dismutase, catalase, ascorbate peroxidase, and glutathione-S-transferase). In contrast, exogenous supplementation of Spd and Mel alleviated the deleterious effects of F-, consequently improved growth, free radical scavenging capacity, and accumulations of protein, proline, ascorbic acid, and glutathione in C. cajan L. Additionally, application of Spd or Mel also improved the isoenzyme profiles and gene expressions of stress responsive enzymes, and genomic template stability, thereby reduced cell death, AOS, lipid peroxidation, lipase activity, and DNA polymorphism in stressed tissues. The present study concludes that Spd and Mel, particularly Mel, alleviated the adverse impacts of F- by improving antioxidant machinery and genomic template stability.