Melatonin Application at Different Doses Changes the Physiological Responses in Favor of Cabbage Seedlings (Brassica oleracea var. capitata) Against Flooding Stress

In recent physiology studies, the number of chemical-based agents applied to allow the recovery of plants under different stress conditions has greatly increased, and melatonin is one significant novel one among these agents. Extremely high and low precipitation regimes are two of the most important factors limiting agricultural production and resulting in drought and flooding stresses. The present study aimed to investigate the effects of melatonin on the physiological responses of early-growth stage seedlings to flooding stress. In this context, cabbage seedlings were subjected to excess water followed by measurement of the essential parameters, such as photosynthesis, antioxidant enzymes, chlorophyll fluorescence, and certain agronomic features. The results indicated that underground fresh mass (UFM) and dry mass (UDM), leaf area (LA), chlorophyll (Chl b) content, carotenoid (CT) content, relative water content (RWC), and protein (PT) content in cabbage seedlings were increased, while the levels of chlorophyll fluorescence (Fv/Fm) and superoxyde dismutase (SOD), peroxidase (POX), and catalase (CAT) levels were stable in flooding-stressed cabbage seedlings treated with 150 µM melatonin. Proline content was significantly reduced in the 150 µM melatonin treatment group. The photosynthetic parameters of cabbage seedlings under the flooding stress condition were not much affected by changes in the stoichiometry of the Chla and Chlb ratio. Consequently, improvements were observed at varying rates, and the effects of flooding stress were alleviated in the melatonin-treated cabbage seedlings. It was, accordingly, inferred that treatment with 150 mM melatonin exerted substantial effects in terms of suppressing the detrimental effects of flooding stress in cabbage seedlings.