Roitto Marja, Rautio Pasi, Markkola Annamari, Julkunen-Tiitto Riitta, Varama Martti, Saravesi Karita, Tuomi Juha
Department of Biology, University of Oulu, P.O. Box 3000, FIN-90014 Oulu, Finland.
Tree Physiol. 2009 Feb;29(2):207-16. doi: 10.1093/treephys/tpn017. Epub 2008 Dec 5.
Phenolic compounds often accumulate in foliar tissues of deciduous woody plants in response to previous insect defoliation, but similar responses have been observed infrequently in evergreen conifers. We studied the effects of defoliation on the foliar chemistry of Scots pine (Pinus sylvestris L.) and cocoon mass, and survival of the pine sawfly (Diprion pini L.). In two successive years, needles were excised early in the season leaving only the current-year shoot intact (defoliated trees); untreated entire shoots served as controls (control trees). A year after the second defoliation, pine sawfly larvae were transferred to the trees. Delayed induced resistance in Scots pine in response to defoliation was indicated by (1) reduced cocoon mass in defoliated trees and (2) increased concentrations of phenolics and soluble condensed tannins in the foliage of defoliated trees compared with controls. Myricetin-3-galactoside, which showed the strongest induced response (104% and 71% increase in current-year (C) and previous-year (C+1) needles) of the compounds analyzed, also entered the regression model explaining variation in sawfly performance. Other compounds that entered the model, e.g., (+)-catechin, showed weaker responses to defoliation than myricetin-3-galactoside. Hyperin, condensed tannins and quercitrin showed strong induced responses in C or C+1 needles, or both, but these compounds did not explain the variation in sawfly performance. Accumulation of phenolics is sometimes associated with the reduced foliage nitrogen (N) concentrations in deciduous trees, and our results suggest that this may also be the case in evergreen conifers. Based on the earlier findings that defoliation reduces needle N concentration and N deficiency results in the accumulation of the same phenolic compounds, i.e., myricetin and quercetin glycosides, and soluble condensed tannins, we suggest that the accumulation of phenolics in defoliated trees occurred in response to the reduced foliar N concentration.
酚类化合物通常会在落叶木本植物的叶片组织中积累，以应对先前的昆虫落叶，但在常绿针叶树中很少观察到类似的反应。我们研究了落叶对苏格兰松（Pinus sylvestris L.）叶片化学、茧质量以及松叶蜂（Diprion pini L.）存活的影响。在连续两年中，在季节早期切除针叶，仅保留当年新梢完整（落叶树）；未处理的整个新梢作为对照（对照树）。第二次落叶一年后，将松叶蜂幼虫转移到树上。落叶后苏格兰松的延迟诱导抗性表现为：（1）落叶树的茧质量降低；（2）与对照相比，落叶树叶片中的酚类和可溶性缩合单宁浓度增加。杨梅素-3-半乳糖苷在所分析的化合物中表现出最强的诱导反应（当年（C）和上一年（C+1）针叶分别增加104%和71%），该化合物也进入了解释叶蜂表现差异的回归模型。其他进入模型的化合物，如（+）-儿茶素，对落叶的反应比杨梅素-3-半乳糖苷弱。金丝桃苷、缩合单宁和槲皮苷在C或C+1针叶中或两者中均表现出强烈的诱导反应，但这些化合物无法解释叶蜂表现的差异。落叶树中酚类物质的积累有时与叶片氮（N）浓度降低有关，我们的结果表明常绿针叶树可能也是如此。基于早期的研究结果，即落叶会降低针叶氮浓度，而氮缺乏会导致相同酚类化合物（即杨梅素和槲皮素糖苷）以及可溶性缩合单宁的积累，我们认为落叶树中酚类物质的积累是对叶片氮浓度降低的响应。
