Coumarins from the Leaves of Nicotiana tabacum and Their Anti-Tobacco Mosaic Virus Activities

Toxicity of coumarins in plant defense against pathogens

Coumarins are a specific type of secondary metabolite that can be found in many plants. These compounds are predominantly produced through the phenylpropanoid pathway. Coumarins have been proven to possess a range of biological activities, including antimicrobial properties and antioxidant functions that aid in plant disease resistance response. The antimicrobial effect of coumarins is achieved through various mechanisms. They disrupt the cell membranes of pathogens, inhibit enzymatic activity, and hinder nucleic acid synthesis. Additionally, coumarins stimulate plant defense responses by triggering the production of reactive oxygen species (ROS) and activating the expression of immunity-related genes and signaling pathways such as the salicylic acid-dependent pathway. Due to their crucial role in defense mechanisms, coumarins can be effectively used in sustainable agriculture practices that emphasize environmentally friendly integrated pest management strategies. By providing a comprehensive overview of the biosynthetic pathways, mode of action, and application of coumarins in plant defense, this review aims to highlight the potential importance of coumarins in developing safe and sustainable crop protection strategies.

Coumarin Derivatives Containing Sulfonamide and Dithioacetal Moieties: Design, Synthesis, Antiviral Activity, and Mechanism

Cucumber mosaic virus (CMV) is currently a known plant virus with the most hosts, broadest distribution, and economic hazard. To develop new antiviral drugs against this serious virus, a new range of coumarin derivatives containing sulfonamide and dithioacetal structures were designed and synthesized, and their anti-CMV activities were detected by the half-leaf dead spot method. The results of the biological activity assay showed that most of the compounds exhibited outstanding anti-CMV activity. Especially, compound C23 displayed the optimal in vivo anti-CMV activity, with an EC50 value of 128 μg/mL, which was remarkably better than that of COS (781 μg/mL) and ningnanmycin (436 μg/mL). Excitingly, we found that compound C23 could be a promising plant activator that significantly increased defense-related enzyme activities and the tobacco chlorophyll content. Furthermore, compound C23 enhanced defense responses against viral infection by inducing the abscisic acid (ABA) pathway in tobacco. This work established a basis for multifunction pesticide discovery involving mechanism of action study and structure optimization.

Design, Synthesis, and Antiviral Activities of Coumarin Derivatives Containing Dithioacetal Structures

In this study, a series of coumarin derivatives containing dithioacetals were synthesized, characterized, and assessed for their anti-tobacco mosaic virus (TMV) activities. Biological tests showed that most of the title compounds exhibited significant anti-TMV biological activities; in particular, compound b21 showed good inactivating activity anti-TMV, with an EC₅₀ of 54.2 mg/L, superior to that of ribavirin (134.2 mg/L). Transmission electron microscopy analyses showed that compound 21 severely ruptured TMV particles. The interaction of compound b21 with TMV coat protein (TMV CP) was investigated using microscale thermophoresis and molecular docking. Compound b21 exhibited a strong binding ability to TMV CP, with a value of 2.9 μM, superior to ribavirin.

Ecological Roles and Biological Activities of Specialized Metabolites from the Genus Nicotiana

Species of Nicotiana grow naturally in different parts of the world and have long been used both medicinally and recreationally by human societies. More recently in our history, Nicotiana tabacum has attracted interest as one of the most economically important industrial crops. Nicotiana species are frequently investigated for their bioactive natural products, and the ecological role of their specialized metabolites in responses to abiotic stress or biotic stress factors like pathogens and herbivores. The interest of tobacco companies in genetic information as well as the success of a few wild tobacco species as experimental model organisms have resulted in growing knowledge about the molecular biology and ecology of these plants and functional studies of the plant's natural products. Although a large number of reviews and books on biologically active natural products already exists, mostly from N. tabacum, we focus our attention on the ecological roles and biological activity of natural products, versus products from cured and processed material, in this Review. The studied compounds include alkaloids, aromatic compounds, flavonoids, volatiles, sesquiterpenoids, diterpenes alcohols, and sugar esters from trichomes of the plants, and recently characterized acyclic hydroxygeranyllinalool diterpene glycosides (HGL-DTGs). In this Review (1800s-2017), we describe the above-mentioned classes of natural products, emphasizing their biological activities and functions as they have been determined either in bioassay-guided purification approaches or in bioassays with plants in which the expression of specific biosynthetic genes has been genetically manipulated. Additionally, a review on the history, taxonomy, ecology, and medicinal application of different Nicotiana species growing around the globe presented in this Review may be of interest for pharmacognosists, natural products, and ecological chemists.