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Water deficit severely limits plant growth especially in arid and semi-arid regions. Sunflower is one of the economically important oil producing crops. It is usually grown in water limited environment due to its moderate biological tolerance towards water stress. Interestingly,sunflower growth was improved in water deficit conditions using a plant growth promoter i.e. melatonin. Seeds were primed for 12 hours with melatonin (0, 50, 75, 100 µM) and these plants were later exposed to water limited environment (100 and 50 %). Results showed that reduced water conditions negatively affected various parameters such as leaf area, plant height, leaf number, achene weight/plant, capitulum weight, leaf total soluble sugars, catalase activity, anthocyanin, quercetin, gallic acid, vanillic acid, chlorogenic acid and cinnamic acid. The seed oil content also showed reduction of unsaturated to saturated fatty acid ratio. Specifically, almost all levels of melatonin applications improved growth (leaf area, leaf fresh and dry weight, plant height), yield (achene weight/plant, number of achenes/capitulum) and leaf metabolites (total soluble proteins, total soluble sugars, proline, total phenolics, anthocyanins, quercetin, gallic acid, vanillic acid, benzoic acid, syringic acid, sinapic acid) of stressed plants. The primed sunflowers exhibited enhanced leaf catalase activity, metabolizable energy and tissue nutritive value. The following phenolic profiles were observed: caffeic acid 100, syringic acid 100, p-coumaric 100, m-coumaric 9.8 and ferulic acid 100 % increased under 100 % water irrigations. Whereas, quercetin (4.7), gallic acid (76.2), vanillic acid (34.0), benzoic acid (334.5), cinnamic (0.6), sinapic acid (22.5) exhibited proportional % reduction. The unsaturation to saturation ratio of fatty acids was also better in the melatonin (100 µM) primed plants. Unprimed plants gave 47.0, while the primed plant exhibited 58.1 unsaturated to saturated fatty acids ratio. Moving forward, the application of 100 µM melatonin delivered better antioxidant protection and nutraceutical value of sunflower plants under water deficit along with enhanced yield. |
