Objective Effects of melatonin application on plant physiology and biochemistry as well as cell wall components of Bougainvillea plants under low temperature were studied.
Method Bougainvillea leaves were sprayed with melatonin solutions in the concentrations of 0, 50, 100, and 150 µmol·L–1 at 4 ℃. Leaf area, chlorophyll content, chlorophyll fluorescence parameters at the optimal/maximal quantum yield of PSⅡ (Fv/Fm), apparent electron transfer rate (ETR), photochemical quenching coefficient (qP), non-photochemical quenching coefficient (qN), activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), membrane lipid peroxidation products at the production rate of superoxide anion (O2−), hydrogen peroxide (H2O2) content, osmotic adjustment soluble sugar (SS) and soluble protein (SP) as well as cell wall components including chelate pectin (CSP), alkali-soluble pectin (SSP), hemicellulose (HC), and cellulose (CE) of the plants were monitored weekly for 3 consecutive weeks from the beginning of treatments (MT0).
Result At 4 ℃, the growth and development of Bougainvillea plants was hindered showing unbalanced chlorophyll fluorescence parameters, intensified membrane lipid peroxidation, and altered cell wall composition. The spray of 100 µmol·L−1 melatonin significantly enhanced the physiological activity, reduced wilting, Fv/Fm and ETR, increased activities of SOD, POD, and CAT (e.g., by 96.45%, 104.35%, and 73.11%, respectively, in Elizabeth Angus), decreased H2O2 content by 21.07% and O2− production rate by 26.85%, and raised CSP by 22.55% and SSP by 43.08% in the cell wall over those at MT0.
Conclusion Melatonin regulated the physiology of Bougainvillea plants and effectively mitigated the growth inhibition by cold stress. The spray reduced the damage to the photosystem, enhance the antioxidant enzyme activity, retard the membrane lipid oxidation, and stabilize the cell wall of the plant suggesting a potential treatment for preventing serious harms by temperature decline in winter.
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