Exogenous melatonin promotes growth and sucrose metabolism of grape seedlings

Melatonin (MT) has many important functions in plants. In this study, different concentrations of MT (0, 50, 100, 150, and 200 μmol/L) were sprayed on grape seedlings, and its effects on plant growth and sucrose metabolism were determined. The results show that there was a mutual influence and promotional relationship between growth and sugar metabolism in grape seedlings. The MT treatments promoted the development and growth of grape seedlings by increasing their biomass and promoting the photosynthetic performance of leaves. This resulted in increased nutrient absorption and a greater ability to compete for resources. The increase in photosynthesis resulted in greater sucrose production. The MT treatments increased the activities of enzymes related to sucrose metabolism, so that a large amount of sucrose was hydrolysed into glucose and fructose to meet the rapid growth requirements of grape seedlings. The increased total soluble sugars contents and increased activities of antioxidant enzymes resulted in greater resistance of grape seedlings, and greater adaptability to environmental changes. In general, MT treatments had beneficial effects on grape seedling growth, glucose metabolism, and resistance. Under these conditions, foliar spraying with MT at 150 μmol/L had the best effects.