Abstract: In order to study the effects of exogenous melatonin on tobacco seedlings under different drought stress levels, the growth, photosynthetic characteristics, antioxidant enzymes activities and osmotic regulatory substances contents of tobacco seedlings under drought stress were investigated after sprayed 100 μmol·L-1 melatonin. The results showed that plant growth was inhibited by drought stress; spraying melatonin alleviated the growth of tobacco plants inhibited by drought stress. Melatonin spraying improved the chlorophyll content and net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) of tobacco plant leaves, decreased the intercellular CO2 concentration (Ci). Moreover, melatonin application enhanced the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), reduced O-2 and malondialdehyde (MDA) content, and increased the accumulation of osmotic regulation substances significantly. Therefore melatonin application can improve drought stress resistance of tobacco seedling. The present research provided reference for studying the mechanism of effects of melatonin on drought resistance in tobacco seedlings.

Key words: melatonin, tobacco seedlings, drought stress, physiological mechanism

摘要： 为研究喷施外源褪黑素对烟草幼苗不同程度干旱胁迫条件下的影响效应。以烟草幼苗为试验材料，探究喷施100 μmol·L-1外源褪黑素对干旱胁迫下幼苗的生长、光合特性、抗氧化酶活性以及渗透调节物质含量的影响。结果表明，干旱严重影响植物生长，喷施褪黑素缓解了干旱胁迫造成的植株生长抑制，并通过提高叶片叶绿素含量和净光合速率（Pn）、气孔导度（Gs）、蒸腾速率（Tr），降低胞间CO2浓度（Ci），同时增强超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）的活性，减少O-2和丙二醛（MDA）的含量，显著增加渗透调节物质的积累，以提高烟草幼苗的抗干旱胁迫能力，结果为褪黑素对烟草幼苗的抗旱性影响机理提供依据。

关键词: 褪黑素, 烟草幼苗, 干旱胁迫, 生理机制