2-Hydroxymelatonin induced nutritional orchestration in Cucumis sativus under cadmium toxicity: modulation of non-enzymatic antioxidants and gene expression

Abstract

2-Hydroxymelatonin (2-OHMT) is an important metabolite produced through melatonin interaction with oxygenated compounds. 2-OHMT pretreated seeds (50 µM, 100 µM, and 150 µM) were grown in soil contaminated with 50 mg kg^-1 cadmium. Cadmium imposed stress reduced seed germination, growth, biomass production, and chlorophyll (Chl) content in Cucumis sativus seedlings. 2-OHMT application emphatically revamped germination, shoot length, root length, and plant biomass production. The 2-OHMT pretreatment modulated expression levels of plasma membrane H⁺-ATPase genes of C. sativus including CsHA2, CsHA3, CsHA4, CsHA8, and CsHA9. This biomolecule amplified the accumulation of antioxidants such as glutathione, proline, phenolics, and flavonoids. The reduced Cd-uptake in 2-OHMT treated C. sativus seedlings encouraged uptake of essential plant nutrients. Furthermore, conjugated increase of indole acetic acid contents and ethylene production rate were observed in 2-OHMT treated seedlings in a dose-dependent manner. The improved nutritional content in 2-OHMT applied seedlings was ascribed to enhanced expression of H⁺-ATPase regulating genes besides increased amount of non-enzymatic antioxidants in Cd-stressed plants. The present novel study elucidates the potential of 2-OHMT in improving nutritional content in cucumber plants by modulation of non-enzymatic antioxidants and gene expression.

Keywords: 2-hydroxymelatonin; Antioxidants; Cucumis sativus; cadmium; nutrients.