Plant-derived secondary metabolites as defensive chemicals in herbivorous insects: a case study in chemical ecology
Plant-derived secondary metabolites as defensive chemicals in herbivorous insects: a case study in chemical ecology
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DOI：
10.1007/s00425-004-1249-y
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发表时间：
2004-05-01
期刊：
影响因子：
4.3
通讯作者：
Hartmann, T
中科院分区：
文献类型：
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作者：
Hartmann, T
在陆地群落中，植物光合作用是营养关系链的第一步，涉及许多种食草动物、病原体和它们的敌人。在适应食草动物和病原体压力的进化过程中，植物发展出了各种各样的防御措施。在无根的陆生植物中，化学防御策略起着突出的作用，植物次生代谢的巨大多样性已经证明了这一点，已知的化合物约有20万种。其中一些防御显然是如此强大，以至于专门的食草昆虫采用它们来保护自己免受捕食者、寄生虫和病原体的侵害。这些例子不仅肯定了植物化学防御的重要性，而且还提供了一个机会，将植物衍生的防御化合物追踪到下一个营养水平并了解其影响。近年来的研究证实，特殊昆虫对植物次生代谢物的吸收与影响植物生理、形态和行为功能的特定机制有关。吡咯利西啶生物碱（PAs）就是一个例子，它被许多食草昆虫所利用（详细回顾，见Hartmann 1999； Hartmann and Ober 2000）。本进展报告重点介绍了PAs对生物化学、感觉和行为适应的影响，以北极蛾（鳞翅目）和金体叶甲虫（鞘翅目）为例。PAs对昆虫和脊椎动物有很强的威慑作用。它们可能以两种分子形式存在，即前毒性游离碱和无毒n-氧化物（图1a）。大多数植物以n -氧化物的形式产生和储存PAs。这些在食草动物的肠道中很容易减少，并作为亲脂性自由碱被扩散吸收到血液和血淋巴中。在昆虫和脊椎动物中，PA游离基作为外生代谢多底物细胞色素P450氧化酶的底物。PA生物活化的产物，即活性吡咯中间体，对脊椎动物具有肝毒性和致癌性，对昆虫具有诱变性。利用PAs的适应性昆虫必须发展出耐受PAs和防止自我中毒的策略。世纪60年代末，米里亚姆·罗斯柴尔德（Miriam Rothschild）首次观察到北极蛾对PAs的吸收。欧洲朱砂蛾（Tyria jacobaeae）的毛虫从它们的食物来源——植物“黄貂草”（transy ragwort; Asteraceae）中摄取和积累PAs，并在整个蜕变过程中保留生物碱，直至成虫阶段。这一现象已经在许多其他北极虫物种中得到证实，最近，已经确定了特定的机制，证明了植物获得性pa与北极虫生活的独特整合。Thomas Eisner和他的同事们证明，雌性Utetheisa ornatrix在交配过程中从成年雄性那里接收pa，并将这些生物碱连同它们自己的负载一起传递给卵（回顾，见Eisner et al. 2002）。交配行为受PAs的强烈影响。雄性通过PA衍生的求偶信息素羟胺酮向雌性宣传它们的PA负荷。这种信息素是由一对被称为核心的雄性刷子状器官发出的，这些器官在与雌性近距离交配前的互动中从腹部伸出。信息素的释放量与雄性体内的生物碱水平有关（Dussourd et al. 1991）。雌性具有对信息素高度敏感的触角化学感受器。信号传递PA负荷似乎是信息素的唯一功能（Iyengar et al. 2001）。这个迷人的序列
In terrestrial communities, plant photosynthesis is the first step in a chain of trophic relationships involving many species of herbivores, pathogens and their enemies. In the evolutionary course of their adaptations to the pressure of herbivores and pathogens, plants developed a diverse array of defenses. In sessile terrestrial plants, chemical defense strategies play an outstanding role, well documented by the immense diversity of plant secondary metabolism with some 200,000 known compounds. Some of these defenses are apparently so powerful that specialized herbivorous insects adopted them for their own protection against predators, parasitoids and pathogens. Such examples not only affirm the importance of plant chemical defenses but also provide an opportunity to trace a plantderived defensive compound to the next trophic level and realize its impact. Recent research confirmed that recruitment of plant secondary metabolites by specialized insects is associated with specific mechanisms affecting physiological, morphological and behavioral functions. An example is offered by the pyrrolizidine alkaloids (PAs), which are utilized by a number of herbivorous insects (for detailed review, see Hartmann 1999; Hartmann and Ober 2000). This Progress Report focuses on the impact of PAs on biochemical, sensory and behavioral adaptations, exemplified by arctiid moths (Lepidoptera) and chrysomelid leaf-beetles (Coleoptera).PAs are strong deterrents to insects and vertebrates. They may exist in two molecular forms, the pro-toxic free base and the non-toxic N-oxide (Fig. 1a). Most plants produce and store PAs as N-oxides. These are easily reduced in the gut of a herbivore and absorbed by diffusion as the lipophilic free base into the blood and the hemolymph. In insects and vertebrates the PA free base serves as a substrate of the multi-substrate cytochrome P450 oxidase of xenobiotic metabolism. The products of the PA bioactivation, ie reactive pyrrolic intermediates, are hepatotoxic and cancerogenic in vertebrates and mutagenic in insects. Adapted insects utilizing PAs must have developed strategies to tolerate PAs and prevent self-poisoning. Sequestration of PAs by arctiid moths was first observed by Miriam Rothschild in the late 1960s. Caterpillars of the European cinnabar moth Tyria jacobaeae ingest and accumulate PAs from their food source, the plant Senecio jacobaea (tansy ragwort; Asteraceae), and retain the alkaloids throughout metamorphosis into the adult stage. This phenomenon has been demonstrated for many other arctiid species and, more recently, specific mechanisms have been identified that demonstrate a unique integration of plant-acquired PAs into the arctiid’s life. Thomas Eisner and his colleagues demonstrated that females of Utetheisa ornatrix receive PAs from adult males during copulation and transmit these alkaloids together with their own load to the eggs (for review, see Eisner et al. 2002). The mating behavior is strongly influenced by PAs. Males advertise their PA load to the females by the PA-derived courtship pheromone, hydroxydanaidal. This pheromone is emitted from a pair of androconial brush-like organs called coremata, which are everted from the abdomen during close-range precopulatory interactions with the female. The amount of emitted pheromone correlates with the male’s systemic alkaloid level (Dussourd et al. 1991). The female possesses antennal chemoreceptors highly sensitive to the pheromone. Signaling the PA load appears to be the exclusive function of the pheromone (Iyengar et al. 2001). This fascinating sequence of