Abstract: To investigate the alleviating effect of exogenous melatonin（MT）on sesame plants under high‐temperature stress and to enhance their thermotolerance，the cultivar Shangzhi 196 was used as the test material，with natural climate growth as the control（CK）.During the full‐bloom stage under high‐temperature stress，sesame leaves were sprayed with melatonin solution at concentrations of 0（MT0），100（MT100），150（MT150），200（MT200），and 250 mg/L（MT250）.The study examined the agronomic traits，photosynthetic and chlorophyll fluorescence characteristics，antioxidant enzyme activities，quality and yield‐related traits under different treatments.The results showed that high‐temperature stress during the full‐bloom stage（MT0）significantly reduced plant height and fruit axis length by 8.15% and 15.09%，respectively，compared with CK，while increased yellow tip length by 21.11%.The number of capsules per plant，seeds per capsule，1 000‐seed weight，and yield decreased significantly by 18.22%，24.93%，8.60%，and 12.53%，respectively. Leaf net photosynthetic rate（Pn），stomatal conductance（Gs），and transpiration rate（Tr）were significantly reduced，and the photosystem Ⅱ（PSⅡ）reaction center was damaged. Additionally，seed moisture content increased by 4.54%，while oil and protein contents decreased by 0.28% and 0.75%，respectively. Exogenous melatonin application significantly increased the number of capsules per plant and seeds per capsule，while reduced yellow tip length.Leaf SPAD value，Pn，Gs，and Tr were significantly enhanced，whereas intercellular CO_₂ concentration（Ci）decreased.The maximum quantum efficiency of PSⅡ（Fv/Fm），actual photochemical efficiency of PSⅡ（ΦPSⅡ），and photochemical quenching coefficient（qP） increased significantly，while minimal fluorescence（Fo）decreased. Additionally，exogenous MT application significantly enhanced the activities of peroxidase（POD），superoxide dismutase（SOD），and catalase（CAT）in sesame leaves，while markedly reduced the malondialdehyde（MDA） content. Concurrently，both the grain water content and protein content decreased，accompanied by a significant increase in yield.Principal component analysis revealed that the high‐temperature tolerance of sesame followed the order of MT200 > MT150 > MT250 > MT100 > MT0，indicating that exogenous melatonin alleviated growth inhibition under high‐temperature stress，with the 200 mg/L treatment（MT200）exhibiting the best mitigation effect.Under MT200 treatment，SOD，POD and CAT activities increased by 24.36%，22.72%，and 22.42%，respectively，compared to MT0.Oil content increased by 1.06%，while moisture and protein contents decreased by 3.47% and 1.30%，respectively.Yield improved by 11.75%.In conclusion，exogenous melatonin application positively enhanced thermotolerance of sesame during the full‐bloom stage by protecting chloroplast structural stability and regulating antioxidant pathways，thereby mitigating high‐temperature‐induced damage.The optimal concentration for foliar spraying was determined to be 200 mg/L.

Key words: Sesame, High‐temperature stress, Melatonin, Full‐bloom stage, Photosynthetic characteristics, Quality, Yield

摘要： 为探究外源褪黑素（MT）对高温胁迫下芝麻植株的缓解效应，提高芝麻植株的耐热性，以自然气候生长为对照（CK），在盛花期高温胁迫处理下采用0 mg/L（MT0）、100 mg/L（MT100）、150 mg/L（MT150）、200 mg/L（MT200）、250mg/L（MT250）MT溶液对芝麻品种商芝196叶片进行喷施，研究不同处理对芝麻农艺性状、叶片光合荧光特性、抗氧化酶活性、品质与产量构成的影响。结果表明，芝麻盛花期遭受高温胁迫（MT0）后，株高、果轴长分别较CK降低8.15%、15.09%，黄梢尖长较CK增加21.11%，单株蒴数、每蒴粒数、千粒质量、产量分别较CK显著下降18.22%、24.93%、8.60%、12.53%；叶片净光合速率（Pn）、气孔导度（Gs）和蒸腾速率（Tr）显著降低，光系统Ⅱ（PSⅡ）反应中心受损；芝麻籽粒含水量增加4.54%，含油量、蛋白质含量分别下降0.28%、0.75%。与MT0处理相比，外源喷施MT显著增加芝麻的单株蒴数和每蒴粒数，降低空梢尖长度，使叶片SPAD值、Pn、Gs和Tr显著增加，胞间二氧化碳浓度（Ci）显著降低，Fv/Fm、ΦPSⅡ、qP均显著上升，Fo显著下降，同时增加芝麻叶片超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）活性，显著降低丙二醛（MDA）含量，且芝麻籽粒含水量和蛋白质含量均有所下降，产量显著提升。主成分分析结果显示，各处理芝麻的耐高温能力依次为MT200>MT150>MT250>MT100>MT0，表明喷施不同质量浓度外源MT对高温胁迫下芝麻的生长抑制具有缓解作用，且以200 mg/L MT（MT200）处理的缓解效果最好，SOD、POD、CAT活性较MT0分别上升24.36%、22.72%、22.42%，含油量增加1.06%，含水量、蛋白质含量分别下降3.47%、1.30%，产量提升11.75%。综上，喷施外源MT对提高盛花期芝麻耐热性有积极作用，可通过保护叶绿体结构的稳定性、调节抗氧化途径来缓解高温胁迫对植株造成的伤害，提高盛花期芝麻对高温的耐受性，MT喷施质量浓度以200 mg/L为宜。

关键词: 芝麻, 高温胁迫, 褪黑素, 盛花期, 光合特性, 品质, 产量