Melatonin has recently emerged as a multifunctional biomolecule with promising aspects in plant stress tolerance. The present study examined the effects of foliar-sprayed melatonin (0, 100 and 200 μM) on growth and essential oil yield attributes of lemon verbena (Lippia citriodora) under water-shortage (mild, moderate and severe). Results revealed that melatonin minimized drought effects on lemon verbena, resulting in improved growth and essential oils yield. Drought impositions gradually and significantly reduced several growth parameters, such as plant height and biomass, whereas melatonin application revived the growth performance of lemon verbena. Melatonin protected the photosynthetic pigments and helped maintain the mineral balance at all levels of drought. Melatonin stimulated the accumulation of proline, soluble sugars and abscisic acid, which were positively correlated with a better preservation of leaf water status in drought-stressed plants. Melatonin also prevented oxidative damages by enhancing the superoxide dismutase, ascorbate peroxidase and catalase activities. Furthermore, increased levels of total phenolic compounds, chicoric acid, caffeic acid and chlorogenic acid, as well as ascorbate and total antioxidant capacity in melatonin-sprayed drought-stressed plants indicated that melatonin helped verbena plants to sustain antioxidant and medicinal properties during drought. Finally, melatonin treatments upheld the concentrations and yield of essential oils in the leaves of lemon verbena regardless of drought severities. These results provided new insights into melatonin-mediated drought tolerance in lemon verbena, and this strategy could be implemented for the successful cultivation of lemon verbena, and perhaps other medicinal plants, in drought-prone areas worldwide. This article is protected by copyright. All rights reserved.

中文翻译：

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褪黑激素通过增强抗氧化反应、矿物质平衡和脱落酸含量减轻干旱对柠檬马鞭草生长和精油产量的影响

褪黑激素最近已成为一种多功能生物分子，在植物胁迫耐受方面具有广阔的前景。本研究考察了叶面喷洒褪黑激素（0、100 和 200 μM）对缺水（轻度、中度和重度）下柠檬马鞭草（Lippia citriodora）的生长和精油产量属性的影响。结果表明，褪黑激素最大限度地减少了对柠檬马鞭草的干旱影响，从而改善了生长和精油产量。干旱逐渐显着降低了一些生长参数，例如植物高度和生物量，而褪黑激素的应用则恢复了柠檬马鞭草的生长性能。褪黑激素保护光合色素，并有助于在各种干旱水平下维持矿物质平衡。褪黑激素刺激脯氨酸、可溶性糖和脱落酸的积累，这与干旱胁迫植物更好地保存叶片水分状态呈正相关。褪黑激素还通过增强超氧化物歧化酶、抗坏血酸过氧化物酶和过氧化氢酶活性来防止氧化损伤。此外，喷洒褪黑激素的干旱胁迫植物中总酚类化合物、菊苣酸、咖啡酸和绿原酸以及抗坏血酸和总抗氧化能力的增加表明，褪黑激素有助于马鞭草植物在干旱期间保持抗氧化和药用特性。最后，无论干旱严重程度如何，褪黑激素处理都能维持柠檬马鞭草叶子中精油的浓度和产量。这些结果为柠檬马鞭草中褪黑激素介导的耐旱性提供了新的见解，并且可以实施该策略以在全球干旱多发地区成功种植柠檬马鞭草，或许还有其他药用植物。本文受版权保护。版权所有。