The popularity of lemon balm in conventional medicine is suggested by the existence of two groups of compounds, namely essential oil and phenylpropanoids pathway derivatives. One of the promising approaches to improve tolerance to drought stress induced oxidative damage in seedlings grown in greenhouses and plant growth chambers is replacing the traditional and high-cost light technologies by recently developed light emitting diodes (LED). In this experiment, we analyzed the role of various LED lights including red (R), blue (B), red (70%) + blue (30%) (RB), and white (W) as well as normal greenhouse light (as control) to stimulate defense mechanisms against drought stress in two genotypes of Melissa officinalis L. The present study demonstrates that pre-treatment with LEDs with high-intensity output for 4 weeks alleviated harmful effects of drought stress in the two genotypes. Under drought stress, RB LED pre-treated plantlets of the two genotypes exhibited the highest relative growth index of shoot and root and total phenolic and anthocyanin content compared to those irradiated with other LEDs and greenhouse lights. The highest amount of malondialdehyde level was detected in R LED exposed plants. In response to drought, LED-exposed plants especially RB light-irradiated plants of the two genotypes maintained significantly higher antioxidant and phenylalanine ammonia-lyase (PAL) enzyme activities and higher expression level of the PAL1 and 4CL-1 genes compared to those irradiated with greenhouse light. We concluded that RB LED light provides a better growth condition and resistance to drought stress for the two genotypes of lemon balm by the highest antioxidant activity and the least amount of damage to the cell membranes. Our data suggest that LED light pre-treatments as moderate stress activate antioxidant systems, enhance the scavenging of ROS and induce drought stress tolerance in the two genotypes of lemon balm plants.

中文翻译：

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LED 光介导干旱胁迫条件下香蜂草酚类积累并增强抗氧化活性

柠檬香脂在常规医学中的流行是由两组化合物的存在表明的，即精油和苯丙烷类途径衍生物。提高温室和植物生长室中生长的幼苗对干旱胁迫诱导的氧化损伤的耐受性的一种有前途的方法是用最近开发的发光二极管 (LED) 取代传统和高成本的光技术。在这个实验中，我们分析了各种 LED 灯的作用，包括红色 (R)、蓝色 (B)、红色 (70%) + 蓝色 (30%) (RB) 和白色 (W) 以及普通温室灯 (作为对照）以刺激 Melissa officinalis L. 的两种基因型对干旱胁迫的防御机制。本研究表明，用具有高强度输出的 LED 预处理 4 周可减轻干旱胁迫对两种基因型的有害影响。在干旱胁迫下，与其他 LED 和温室灯照射的植株相比，RB LED 预处理的两种基因型的幼苗表现出最高的地上部和根系相对生长指数以及总酚和花青素含量。在暴露于 R LED 的植物中检测到的丙二醛水平最高。为应对干旱，与受光照射的植物相比，两种基因型的 LED 暴露植物，尤其是 RB 光照射植物保持了显着更高的抗氧化和苯丙氨酸解氨酶 (PAL) 酶活性以及 PAL1 和 4CL-1 基因的更高表达水平。温室光。我们得出的结论是，RB LED 灯通过最高的抗氧化活性和对细胞膜的最小损伤为两种基因型的柠檬香脂提供了更好的生长条件和对干旱胁迫的抵抗力。我们的数据表明，LED 光预处理作为中等压力激活抗氧化系统，增强 ROS 的清除并诱导两种基因型柠檬香脂植物的干旱胁迫耐受性。