Soliman Sameh, Mohammad Mohammad G, El-Keblawy Ali A, Omar Hany, Abouleish Mohamed, Madkour Mohamed, Elnaggar Attiat, Hosni Racha M
Sharjah Institute for Medical Research, University of Sharjah, Sharjah, United Arab Emirates.
College of Pharmacy, University of Sharjah, Sharjah, United Arab Emirates.
PLoS One. 2018 Feb 7;13(2):e0192576. doi: 10.1371/journal.pone.0192576. eCollection 2018.
Unlike animals, plants are sessile organisms, lacking circulating antibodies and specialized immune cells and are exposed to various harsh environmental conditions that make them at risk of being attacked by different pathogens and herbivores. Plants produce chemo-signals to respond to the surroundings and be able to distinguish between harmless and harmful signals. In this study, the production of phytochemicals as plant signaling mechanisms and their defensive roles in disease resistance and repelling herbivores are examined in Calligonum comosum. C. comosum is a leafless standalone perennial shrub widespread in sand dunes. The plant has the ability to survive the drastic environmental conditions of the arid/ hyperarid deserts of the Arabia. Structural anatomy and phytochemicals analyses were used to identify both mechanical and chemical defensive mechanisms in C. comosum. Microscopy-based investigations indicated that stems of this species developed hard structures in its outer layers including sclerenchyma and cluster crystals of calcium oxalate (CaOx). Sclerenchyma and CaOx are difficult to be eaten by herbivores and insects and can harm their mouthparts. On the other hand, the plant developed both short-distance (local) and long-distance (systematic over limited sphere) phytochemicals-producing cells located at its outer regions that is surrounding the inner nutrient-rich vascular system (VS). Local chemical was represented by phenolic idioblasts that were released in response to plant cutting. Systematic chemical was represented by toxic volatile oil containing ~50% benzaldehyde derivative (cuminaldehyde). The oil caused strong killing effect on both mammalian cells and microbial pathogens via either direct addition or indirect exposure to its vapor. The plants lost the oil content and allowed fungal growth once cut and dried. The localization of both defensive mechanisms to the outer region of the plant seemed to protect the inner nutrient-rich VS and hence maintained the plant survival. Surprisingly, in relation to traditional folklore use as medicine, local people use only green parts of the plant and only during the winter, where the plant found devoid of volatile oil and phenolic idioblasts. Moreover, it turns into recommendations for local people to avoid any health problems caused by the plant supply.
与动物不同，植物是固着生物，缺乏循环抗体和专门的免疫细胞，并且暴露于各种恶劣的环境条件下，这使它们有被不同病原体和食草动物攻击的风险。植物产生化学信号以响应周围环境，并能够区分无害和有害信号。在本研究中，在沙拐枣中研究了作为植物信号传导机制的植物化学物质的产生及其在抗病性和驱避食草动物方面的防御作用。沙拐枣是一种无叶的独立多年生灌木，广泛分布于沙丘中。该植物有能力在阿拉伯干旱/超干旱沙漠的恶劣环境条件下生存。采用结构解剖学和植物化学分析来确定沙拐枣的机械和化学防御机制。基于显微镜的研究表明，该物种的茎在其外层形成了坚硬的结构，包括厚壁组织和草酸钙（CaOx）簇晶。厚壁组织和草酸钙难以被食草动物和昆虫食用，并且会伤害它们的口器。另一方面，该植物在其围绕内部富含营养的维管系统（VS）的外部区域发育了产生短距离（局部）和长距离（有限范围内系统性）植物化学物质的细胞。局部化学物质由酚类异细胞代表，它们在植物被切割时释放。系统性化学物质由含有约50%苯甲醛衍生物（枯茗醛）的有毒挥发油代表。该油通过直接添加或间接暴露于其蒸汽对哺乳动物细胞和微生物病原体都有强烈的杀伤作用。一旦植物被切割和干燥，其油含量就会损失并允许真菌生长。两种防御机制都定位于植物的外部区域，这似乎保护了内部富含营养的维管系统，从而维持了植物的生存。令人惊讶的是，关于传统民俗医学用途，当地人只在冬季使用植物的绿色部分，此时发现植物不含挥发油和酚类异细胞。此外，这还转化为对当地人的建议，以避免因使用该植物而引起的任何健康问题。
