外源褪黑素对低温胁迫下红树莓叶片生理特性的影响

Effects of exogenous melatonin on physiological characteristics of leaves under low-temperature stress in red raspberry

【目的】为缓解红树莓初冬低温冷害,通过研究外源褪黑素(melatonin,MT)处理对低温胁迫下红树莓抗性的影响,明确MT对红树莓耐冷能力的作用及适宜浓度。【方法】以盆栽双季红树莓波尔卡为供验试材,在初冬降温时期,对叶面喷施不同浓度MT(0、50、100、150、200μmol·L^(-1)),研究其对低温胁迫下波尔卡红树莓叶片相对电导率、叶绿素含量、抗氧化酶活性和渗透调节物质含量的影响。【结果】在褪黑素处理后的第5天时,150μmol·L^(-1) MT处理的叶片相对电导率、MDA含量和可溶性糖含量值最低;叶绿素a、总叶绿素、可溶性蛋白质、淀粉含量及SOD、POD、CAT活性最高。【结论】在低温胁迫下喷施150μmol·L^(-1) MT可增加红树莓叶片抗氧化酶活性,减轻膜脂过氧化反应并调节渗透物质含量,从而有助于缓解胁迫伤害,提高红树莓耐冷能力。

【Objective】Red raspberry, the third generation golden fruit, is rich in a variety of vitamins and mineral elements, and the root, stem and fruit can be used as medicine. Red raspberry not only owns nutritional and medicinal value, but also has high economic values. However, due to the falling temperature and leaf frostbite, most of the red raspberry cannot ripen in the northern regions of China,which seriously affects the yield of the red raspberries, thus reducing the economic return. To alleviate the chilling injury to red raspberry in early winter, the effects of exogenous melatonin(MT) treatment on cold hardiness of red raspberry under low-temperature stress were studied, and the effects of exogenous melatonin treatment on cold hardiness and the appropriate concentration of MT were determined.【Methods】The 2-year-old potted red raspberry cultivar Polka was used as experimental material. Potted Polka red raspberry seedlings with the same growth vigor were selected. The upper diameter of the pot was 44 cm, the lower diameter was 25 cm and the height was 30 cm. Routine management was applied before treatment to ensure normal growth. On October 20, 2020, the maximum temperature was 18 ℃, and the minimum temperature was 4 ℃. The treatments were designed as 50, 100, 150, and 200μmol·L^(-1) melatonin leaf spraying with an equal amount of distilled water as the control(CK), and each treatment was repeated for 3 times. At 5:30 p.m., the corresponding concentration of melatonin was fully sprayed on the front and back sides of each leaf, until the liquid drips off the leaves. It was treated once every other day for 4 times. On the first, third and fifth days after the last foliar spraying with melatonin, leaf samples were taken to determine the effects of relative electrical conductivity, chlorophyll content, antioxidant enzyme activity and osmotic regulatory substances in the leaves of red raspberry.【Results】MT treatment could significantly reduce the relative electrical conductivity and MDA content of leaves compared with CK. The contents of chlorophyll, soluble protein and soluble sugar increased. The activity of SOD(superoxide dismutase), POD(peroxidase) and CAT(catalase) increased significantly, and the effect of 150 μmol·L^(-1) MT treatment was the most obvious. The relative conductivity, MDA content and soluble sugar content in leaves increased with the extension of low-temperature stress, and the lowest values were 19.26%, 2.248 9 umol·g^(-1) and 50.22 mg·g^(-1) on the 5 th day with150 μmol·L^(-1) Mt treatment, respectively. POD and CAT activity increased with the extension of lowtemperature stress, and the highest values were 86.7833 U ·g^(-1)·min^(-1) and 82.044 4 U·g^(-1)·min^(-1) with 150μmol·L^(-1) MT on the 5 th day, respectively. The contents of starch, chlorophyll a and total chlorophyll decreased with the extension of low-temperature stress, and the highest values were 48.42 mg·g^(-1), 1.23 mg·g^(-1) and 1.6 mg·g^(-1) on the 5 th day with 150 μmol·L^(-1) MT treatment, respectively. The soluble protein content increased firstly and then decreased with the extension of low-temperature stress. On the5 th day, the value of 150 μmol·L^(-1) MT treatment was 2.973 2 mg·g^(-1), which was higher than that of other treatments. The SOD activity with 150 μmol·L^(-1) MT was 4.935 1 U·g^(-1)·min^(-1), which was higher than that with other treatments.【Conclusion】Low-temperature stress will cause the disorder of physiological and biochemical systems in plants, affect the normal growth and development of plants, and even lead to production reduction and inevitable economic loss. When plants are damaged by low-temperature stress, the plant cell membrane system will be impacted, resulting in the change or loss of the membrane integrity, and the rapid accumulation of reactive oxygen species and free radicals in cells.However, plants also have a self-preservation mechanism. At low-temperature, plants usually accumulate osmotic regulation substances to reduce the water potential in cells and promote the absorption of water by plant cells to maintain normal physiological functions. It can also mobilize the close connection among the three enzymes of SOD, CAT and POD in the antioxidant system within the body to form part of the defense system in the plant body, which plays an important role in maintaining ROS level. In this experiment, different concentrations of MT(0, 50, 100, 150, 200 μmol·L^(-1)) were sprayed on the leaves of red raspberry under low-temperature stress, which significantly reduced the membrane leakage and malondialdehyde content, and reduced the degree of membrane lipid peroxidation in red raspberry leaves under low-temperature stress. The total chlorophyll, soluble protein and soluble sugar contents in red raspberry leaves increased, and the intracellular osmotic balance was maintained. The antioxidant enzyme activity system of SOD, POD and CAT was activated to alleviate the oxidative damage caused by reactive oxygen species and free radicals. According to the effects of different concentrations, the 150 μmol·L^(-1) MT concentration was suggested to alleviate the low-temperature stress of red raspberry leaves.