Neilson Elizabeth H, Goodger Jason Q D, Woodrow Ian E
School of Botany, The University of Melbourne, Parkville, Vic. 3010, Australia.
Funct Plant Biol. 2006 May;33(5):487-496. doi: 10.1071/FP05293.
Cyanogenesis is the release of cyanide from certain organisms upon tissue disruption. Tissue disruption, such as that caused by folivory, brings cyanogenic glycosides into contact with catabolic enzymes and toxic HCN is subsequently released. The process provides a measure of defence against generalist herbivores. Within the genus Eucalyptus, several species have been identified as cyanogenic and all of these store cyanide exclusively in the form of the cyanogenic glycoside prunasin. Here we report for the first time cyanogenesis in Eucalyptus camphora subsp. humeana L.A.S. Johnson & K.D. Hill. We found that foliage contains at least five different cyanogenic glycosides, three of which were purified and identified (prunasin, sambunigrin and amygdalin). Two natural populations of E. camphora trees were screened for cyanogenesis, and quantitative polymorphism was measured at both sites. Trees varied in their capacity for cyanogenesis from 0.014 to 0.543 mg CN g DW in one population and from 0.011 to 0.371 mg CN g DW in the other. A progeny trial, testing both cyanogenesis and carbon-based defence (namely total phenolics and condensed tannins), was performed with seed sourced from two cyanogenic, open-pollinated maternal trees. Interestingly, the seedlings exhibited markedly lower levels of cyanogenesis and condensed tannins than the adult population, with some individuals completely lacking one or both of the chemical defences. Total phenolic concentrations, however, were significantly higher in the seedlings than in the parental population from which the seed was sourced. Eucalyptus camphora is relatively unique among cyanogenic trees having multiple foliar cyanogenic glycosides and an apparently marked ontogenetic regulation of cyanogenic capacity.
氰化物生成是指某些生物体在组织受到破坏时释放出氰化物。组织破坏，如由食叶行为造成的破坏，会使含氰糖苷与分解代谢酶接触，随后释放出有毒的氢氰酸。这一过程为抵御广食性食草动物提供了一种防御手段。在桉属植物中，已鉴定出几种含氰物种，并且所有这些物种都仅以含氰糖苷苦杏仁苷的形式储存氰化物。在此，我们首次报道了樟脑桉亚种休姆桉（Eucalyptus camphora subsp. humeana L.A.S. Johnson & K.D. Hill）中的氰化物生成现象。我们发现其叶片中至少含有五种不同的含氰糖苷，其中三种已被纯化并鉴定（苦杏仁苷、黑芥子苷和扁桃苷）。对两个樟脑桉天然种群进行了氰化物生成筛选，并在两个地点测量了数量多态性。在一个种群中，树木的氰化物生成能力在0.014至0.543毫克氰/克干重之间变化，在另一个种群中则在0.011至0.371毫克氰/克干重之间变化。利用来自两棵开放授粉的含氰母树的种子进行了一项子代试验，测试了氰化物生成和基于碳的防御（即总酚和缩合单宁）。有趣的是，幼苗的氰化物生成水平和缩合单宁含量明显低于成年种群，有些个体完全缺乏一种或两种化学防御物质。然而，幼苗中的总酚浓度显著高于种子来源的亲代种群。樟脑桉在具有多种叶片含氰糖苷且氰化物生成能力具有明显个体发育调控的含氰树木中相对独特。
