Abstract: This study was conducted to determine the effects of melatonin (MT) on growth and antioxidant system of perennial ryegrass (Pinnacle Ⅲ) seedlings under cold and drought stresses. The results showed that cold and drought stresses induced the increase of endogenous MT,indicating that MT might be involved in regulating the response of perennial ryegrass to cold and drought stresses. Under different cold or drought stresses,MT led to a change in the fresh biomass of the seedlings in a concentration-dependent manner. MT affected relative electrolyte leakage in a dose-dependent manner as plants were exposed to cold and drought stresses. Pretreatment with 100 μM MT resulted in lower electrolyte leakage in the plants under cold and drought stresses. Meanwhile,compared with the control,both cold and drought stresses changed the activities of peroxidase (POD),catalase (CAT),ascorbate peroxidase (APX) and glutathione reductase (GR),and declined reactive oxygen species and malondialdehyde (MDA) contents. Exogenous MT further increased the activities of CAT,APX,GR and proline contents,accompanied by alleviating plant growth inhibition and lower ROS and MDA levels compared with the control. In conclusion,endogenous levels of MT might act as a secondary signal to trigger downstream antioxidant defense responses,which was characterized by enhancing the activities of antioxidant system and proline accumulation,improving the scavenging capacity of reactive oxygen species,and maintaining the cell membrane stability under stress tolerances.

Key words: Melatonin, Low temperature stress, Drought stress, Perennial ryegrass, Antioxidant System

摘要： 本研究以‘顶峰Ⅲ’为供试多年生黑麦草（Lolium perenne）品种，研究了低温和干旱胁迫下内源褪黑素（melatonin，MT）的响应，并采用叶面喷施不同浓度MT （0，20，100，1 000 μM）的方法，探讨了MT对低温和干旱胁迫下黑麦草幼苗生长和抗氧化防御系统的影响。结果表明：低温和干旱胁迫下内源MT水平均显著增加（P<0.05）；在不同胁迫强度下，喷施一定浓度的MT会在一定程度上降低叶片相对电导率、使幼苗鲜重发生改变，其中100 μM的MT处理对提高幼苗鲜重和降低相对电导率的效果最佳；低温和干旱胁迫下，黑麦草叶片中O₂^·-，H₂O₂和丙二醛（malondialdehyde，MDA）含量显著增加；过氧化物酶（peroxidase，POD），过氧化氢酶（catalase，CAT），抗坏血酸过氧化物酶（ascorbate peroxidase，APX）和谷胱甘肽还原酶（glutathione reductase，GR）活性发生不同程度的改变；MT显著地降低了MDA和活性氧的积累，提高了CAT，APX和GR活性及脯氨酸含量。综上，低温和干旱胁迫下MT能够诱导植物体内抗氧化酶活性增强和脯氨酸积累，有效地清除活性氧，从而缓解了黑麦草的生长抑制，增强了其抗寒和抗旱性。

关键词: 褪黑素, 低温胁迫, 干旱胁迫, 多年生黑麦草, 抗氧化系统