Berenbaum M R, Zangerl A R
Department of Entomology, University of Illinois, 320 Morrill Hall, 505 South Goodwin, 61801, Urbana, Il, USA.
Oecologia. 1993 Sep;95(3):370-375. doi: 10.1007/BF00320991.
The ubiquitous occurrence of series of biosynthetically related plant secondary compounds within individual species has given rise to the suggestion that such multiplicity is adaptive; one possible mechanism that would serve to maintain such within-plant diversity is analog synergism. In a series of experiments, we provide evidence that synergism may account for the presence of multiple structurally related furanocoumarins in apiaceous plants. The black swallowtail, Papilio polyxenes, feeds exclusively on plant species containing furanocoumarins. Growth of larvae fed parsley leaves treated with both xanthotoxin and angelicin, two furanocoumarins that co-occur widely in swallowtail hostplants, was significantly slower than that of larvae fed leaves with an equimolar concentration of either xanthotoxin or angelicin. A multivariate combination of growth, food consumption and frass excretion differed significantly between larvae fed leaves treated with both xanthotoxin and angelicin and larvae fed leaves treated with angelicin alone. In addition, we measured rates of in vitro cytochrome P450-mediated metabolism of three furanocoumarins - bergapten, xanthotoxin, and angelicin. While bergapten and xanthotoxin, both linear furanocoumarins, were metabolized at similar rates (8.07 and 9.86 nmoles/min/g fw caterpillar, respectively), angelicin, an angular furanocoumarin, was metabolized more slowly (2.76 nmoles/min/g fw caterpillar). When all three furanocoumarins were assayed together, overall rates of metabolism were significantly reduced, suggesting substrate inhibition. Thus, the pattern of growth of larvae is consistent with the pattern of in vitro metabolism and is evidence in support of analog synergism. In a separate experiment, metabolism of xanthotoxin and angelicin individually and together were compared in six maternal families. Again, angelicin was metabolized more slowly than xanthotoxin and each furanocoumarin inhibited metabolism of the other. That significant family effects were found for rates of metabolism and for the ratio of moles of angelicin metabolized for each mole of xanthotoxin metabolized raises the possibility that genetic variation exists for the rate and specificity of metabolism and suggests that insect herbivores may be able to adapt to analog synergism.
单个物种内一系列生物合成相关的植物次生化合物普遍存在，这引发了一种观点，即这种多样性具有适应性；一种可能用于维持植物内这种多样性的机制是类似物协同作用。在一系列实验中，我们提供了证据表明协同作用可能解释了伞形科植物中多种结构相关的呋喃香豆素的存在。黑凤蝶（Papilio polyxenes）仅以含有呋喃香豆素的植物物种为食。用黄樟素和白芷素处理过的欧芹叶喂养幼虫，这两种呋喃香豆素在凤蝶寄主植物中广泛共存，其生长速度明显慢于用等摩尔浓度的黄樟素或白芷素单独处理过的叶子喂养的幼虫。用黄樟素和白芷素共同处理过的叶子喂养的幼虫与仅用白芷素处理过的叶子喂养的幼虫相比，在生长、食物消耗和粪便排泄的多变量组合上存在显著差异。此外，我们测量了三种呋喃香豆素——补骨脂素、黄樟素和白芷素在体外由细胞色素P450介导的代谢速率。虽然补骨脂素和黄樟素这两种线性呋喃香豆素的代谢速率相似（分别为8.07和9.86纳摩尔/分钟/克鲜重毛虫），但白芷素这种角型呋喃香豆素的代谢速度较慢（2.76纳摩尔/分钟/克鲜重毛虫）。当同时检测这三种呋喃香豆素时，总体代谢速率显著降低，表明存在底物抑制。因此，幼虫的生长模式与体外代谢模式一致，这是支持类似物协同作用的证据。在另一个实验中，比较了六个母系家族中黄樟素和白芷素单独及共同的代谢情况。同样，白芷素的代谢速度比黄樟素慢，并且每种呋喃香豆素都会抑制另一种的代谢。在代谢速率以及每代谢一摩尔黄樟素所代谢的白芷素摩尔比方面发现了显著的家族效应，这增加了代谢速率和特异性存在遗传变异的可能性，并表明昆虫食草动物可能能够适应类似物协同作用。
