橙皮精油的主要成分是柠檬烯。柠檬烯是一种天然活性单萜，具有抗菌、防腐和抗肿瘤活性，在农业上具有重要的开发价值。本研究发现柠檬烯对烟草花叶病毒（TMV）具有出色的抗生物活性，结果显示其800 μg/mL的保护率、灭活率和治愈率分别为84.93%、59.28%和58.89%——显著高于壳寡糖。虽然未观察到柠檬烯对TMV颗粒的直接作用，但柠檬烯能在烟草中引发超敏反应（HR）。进一步测定柠檬烯对TMV的诱导活性，结果显示其在800 μg/mL下，诱导活性达到60.59%。生理生化实验的结果显示，在不同处理天数下，800 μg/mL柠檬烯诱导烟草中防御酶活性的提高，SOD、CAT、POD和PAL的活性分别比对照增加了3.2倍、4.67倍、4.12倍和2.33倍（POD和SOD活性以第七天最高，PAL和CAT活性以第五天最高）。柠檬烯还增强了与病理相关的(PR)基因的相对表达水平，包括NPR1、PR1和PR5，分别上调了3.84倍、1.86倍和1.71倍。柠檬烯诱导了水杨酸（SA）的积累，并增加了与SA合成（PAL）和活性氧（ROS）爆发（RBOHB）相关的基因的相对表达水平，分别比对照增加了2.76倍和4.23倍。系统性获得性抗性（SAR）是植物对病原体感染的重要免疫防御机制。观察到SA的积累、防御酶活性的增强和防御相关基因的高水平表达表明，柠檬烯可能通过激活受SA信号途径调节的SAR来诱导烟草对TMV的抗性。此外，实验结果还表明，在800 μg/mL柠檬烯处理的烟草中，叶绿素合成基因POR1的表达水平相比对照增加了1.72倍，这表明柠檬烯处理可能增加烟草的叶绿素含量。盆栽实验结果显示，800 μg/mL柠檬烯可诱导植物对好气孢菌（33.33%）、辣椒疫病菌（54.55%）和灰霉菌（50.00%）产生抗性。生物测定结果显示，柠檬烯提供了广谱和持久的抗病原体感染能力。因此，柠檬烯具有良好的开发和利用价值，预计可开发成为一种新型的植物源抗病毒剂和植物免疫激活剂，除了杀虫剂和杀菌剂之外。版权所有© 2023 Elsevier Inc. 保留所有权利。

The main component of orange peel essential oil is limonene. Limonene is a natural active monoterpene with multiple functions, such as antibacterial, antiseptic and antitumor activity, and has important development value in agriculture. This study found that limonene exhibited excellent anti-tobacco mosaic virus (TMV) bioactivity, with results showing that its protection activity, inactivation activity, and curative activity at 800 μg/mL were 84.93%, 59.28%, and 58.89%, respectively-significantly higher than those of chito-oligosaccharides. A direct effect of limonene on TMV particles was not observed, but limonene triggered the hypersensitive response (HR) in tobacco. Further determination of the induction activity of limonene against TMV demonstrated that it displayed good induction activity at 800 μg/mL, with a value of 60.59%. The results of physiological and biochemical experiments showed that at different treatment days, 800 μg/mL limonene induced the enhancement of defense enzymes activity in tobacco, including of SOD, CAT, POD, and PAL, which respectively increased by 3.2, 4.67, 4.12, and 2.33 times compared with the control (POD and SOD activities reached highest on the seventh day, and PAL and CAT activities reached highest on the fifth day). Limonene also enhanced the relative expression levels of pathogenesis related (PR) genes, including NPR1, PR1, and PR5, which were upregulated 3.84-fold, 1.86-fold and 1.71-fold, respectively. Limonene induced the accumulation of salicylic acid (SA), and increased the relative expression levels of genes related to SA biosynthesis (PAL) and reactive oxygen species (ROS) burst (RBOHB), which respectively increased by 2.76 times and 4.23 times higher than the control. Systemic acquired resistance (SAR) is an important plant immune defense against pathogen infection. The observed accumulation of SA, the enhancement of defense enzymes activity and the high-level expression of defense-related genes suggested that limonene may induce resistance to TMV in tobacco by activating SAR mediated by the SA signaling pathway. Furthermore, the experimental results demonstrated that the expression level of the chlorophyll biosynthesis gene POR1 was increased 1.72-fold compared to the control in tobacco treated with 800 μg/mL limonene, indicating that limonene treatment may increase chlorophyll content in tobacco. The results of pot experiment showed that 800 μg/mL limonene induced plant resistance against Sclerotinia sclerotiorum (33.33%), Phytophthora capsici (54.55%), Botrytis cinerea (50.00%). The bioassay results indicated that limonene provided broad-spectrum and long-lasting resistance to pathogen infection. Therefore, limonene has good development and utilization value, and is expected to be developed into a new botanical-derived anti-virus agent and plant immunity activator in addition to insecticides and fungicides.Copyright © 2023 Elsevier Inc. All rights reserved.