外源MT和EBR对干旱胁迫下烤烟幼苗的缓解效应

  目的  为探明外源褪黑素（melatonin, MT）与2, 4-表油菜素内酯（2, 4-epibrassinolide, EBR）对干旱胁迫下植物的缓解作用。  方法  以烤烟（Nicotiana tabacum L.）品种‘豫烟6号’为试材，采用营养液水培法，研究了15%聚乙二醇(PEG-6000)模拟干旱胁迫下，单独和复配施用外源MT、EBR对烤烟幼苗生长、活性氧生成、抗氧化系统、光合特性和叶绿素荧光特性的影响。  结果  干旱胁迫下，MT、EBR单独和复配处理均能显著促进干旱胁迫下烤烟幼苗的生长，增强根系活力，降低超氧阴离子（O₂-）生成速率和丙二醛（MDA）含量，提高超氧化物歧化酶（SOD）、过氧化物酶（POD）和过氧化氢酶（CAT）活性，提高叶绿素相对含量（SPAD）、叶片净光合速率（P_n）、蒸腾速率（T_r）、水分利用率（WUE）、气孔导度（G_s）、气孔限制值（L_s）、光系统Ⅱ最大光化学效率（F_v/F_m）、光系统Ⅱ实际光化学效率（Φ_PSⅡ）和光化学猝灭系数（qP），降低胞间二氧化碳（C_i）和非光化学猝灭系数（NPQ），其中以MT和EBR复配处理效果最好。  结论  外源MT、EBR单独和复配处理均能通过提高烟苗的抗氧化酶活性，减少活性氧的积累，提高光合电子传递速率，增强光合作用能力，促进烤烟幼苗的生长，从而增强其对干旱胁迫的耐受性，且MT和EBR复配在提高烤烟幼苗抗旱方面具有协同增效的作用。 

Alleviation effects of exogenous melatonin and 2, 4-epibrassinolide on flue-cured tobacco seedlings under drought stress

In order to explore the alleviating effects of exogenous melatonin (MT) and 2, 4-epibrassinolide (EBR) on plants under drought stress, the effects of single and combined application of exogenous MT and EBR on the growth, antioxidant system, reactive oxygen generation, photosynthetic characteristics and chlorophyll fluorescence characteristics of flue-cured tobacco seedlings under drought stress(simulated by 15% polyethylene glycol (PEG-6000) were investigated by using the method of hydroponics nutrient solution with flue-cured tobacco variety'Yuyan6' as research objects.Results show that single and combined application of MT and EBR could significantly promote growth of flue-cured tobacco seedlings under drought stress, enhance root activity, decrease generation rate and content of MDA, increase activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), increase relative chlorophyll content(SPAD), leaf net photosynthetic rate (P_n), transpiration rate (T_r), water use efficiency (WUE), stomatal conductance (G_s), stomatal limitation(L_s), maximal photochemical efficiency of PSⅡ (F_v /F_m), actual photochemical efficiency of PSⅡ (Φ_PSⅡ) and photochemical quenching coefficient (qP), reduce intercellular carbon dioxide (C_i) and non-photochemical quenching coefficient (NPQ). Combined application of MT and EBR had better effect.These results indicated that single or combined applications of exogenous MT and EBR effectively improved activity of antioxidant enzymes, reduced accumulation of reactive oxygen species, reduced level of membrane lipid peroxidation, increased synthesis of chlorophyll, alleviated photoinhibition of PSⅡ damage, improved photosynthetic electron transport rate, enhanced the capacity of photosynthesis, increased root activity, promoted growth of flue-cured tobacco seedlings, and thus enhanced its tolerance to drought stress. Moreover, the combined application of MT and EBR had synergistic effects on drought resistance of flue-cured tobacco seedling.