CAA: Analyses of Chemical Defenses in Young Leaves of Tropical Species

9407835 Coley在热带雨林中，食草动物对植物的捕食大多发生在嫩叶上。其危害率是成熟叶片的20倍，70%的终身危害发生在叶片膨大的短时间内。危害很大，因为嫩叶很嫩，富含蛋白质。韧性，最有效的防御，是不可能在叶片扩张。这表明其他防御，包括次生化学代谢物，可能在幼嫩叶片中特别重要。对化合物的固存、回收和周转率的理论考虑也表明，嫩叶应该包含多种化学防御。然而，以前的研究量化总酚或单宁浓度无法解释不同物种之间的食草率差异。因此，为了充分了解热带地区植物-食草动物的相互作用，需要更详细地了解幼嫩叶片中的化学防御。PI建议通过从每个物种中分离和鉴定尽可能多的化合物来检查幼嫩叶片中的次生代谢物。分离化合物的阻吓性或毒性活性将用一套从病毒、细菌、真菌到昆虫的天敌来测试。这些复杂的化学分析将使PI能够解决关于植物-食草动物相互作用的各种生态和进化问题，包括：1)目前的理论在预测幼叶中次生代谢物的多样性方面是否正确？2)为什么单一物种会有多种次生代谢物？这是对天敌多样性的适应性反应吗？3)次生代谢物的合成可能在生理上与幼叶的另一个主要防御措施——快速膨胀以缩短易损期——不相容。在这项研究中收集的数据将为所有这些有趣的生态问题提供更多的线索。

9407835 Coley In tropical rainforest, most predation on plants by herbivores occurs on young leaves. Rates of damage are 20 times higher than on mature leaves, and 70% of the lifetime damage takes place during the short period of leaf expansion. Damage is high because young leaves are tender and rich in protein. Toughness, the most effective defense, is not possible during leaf expansion. This suggests that other defenses, including secondary chemical metabolites, may be particularly important in young leaves. Theoretical considerations of sequestration, reclamation and turnover rates of compounds also suggest that young leaves should contain a diversity of chemical defenses. However, previous studies that quantified total phenolic or tannin concentrations were unable to explain variation among species in rates of herbivory. Thus a more detailed perspective of chemical defense in young leaves is needed in order fully to understand plant-herbivore interactions in the tropics. The PI proposes to examine the secondary metabolites in young leaves by isolating and identifying as many compounds as possible from each of a few species. The deterrent or toxic activity of isolated compounds will be tested using a suite of natural enemies ranging from viruses, bacteria and fungi to insects. These sophisticated chemical analyses will allow the PI to address a variety of ecological and evolutionary questions about plant-herbivore interactions, including: 1) are current theories correct in predicting a great diversity of secondary metabolites in young leaves? 2) Why does a single species have a variety of secondary metabolites? Is it an adaptive response to the occurrence of a diversity of natural enemies? 3) It has been argued that synthesis of secondary metabolites may be physiologically incompatible with another major defense of young leaves, namely rapid expansion to shorten the period of vulnerability. The data gathered in this study will shed much light on all these intriguing ecologi cal problems.