Goodger Jason Q D, Seneratne Samiddhi L, Nicolle Dean, Woodrow Ian E
School of BioSciences, The University of Melbourne, Melbourne, Victoria, Australia.
Currency Creek Arboretum, PO Box 808 Melrose Park, Currency Creek, SA, 5039, Australia.
PLoS One. 2016 Mar 15;11(3):e0151432. doi: 10.1371/journal.pone.0151432. eCollection 2016.
The sub-dermal secretory cavities (glands) embedded within the leaves of Eucalyptus (Myrtaceae) were once thought to be the exclusive repositories of monoterpene and sesquiterpene oils. Recent research has debunked this theory and shown that abundant non-volatile compounds also occur within foliar glands. In particular, glands of four species in subgenus Eucalyptus contain the biologically active flavanone pinocembrin. Pinocembrin shows great promise as a pharmaceutical and is predominantly plant-sourced, so Eucalyptus could be a potential commercial source of such compounds. To explore this we quantified and assessed the purity of pinocembrin in glands of 11 species of E. subg. Eucalyptus using Electro-Spray Ionisation Liquid Chromatography Mass Spectrometry of acetonitrile extracts and Gas Chromatography Mass Spectrometry analyses of hexane extracts of isolated glands which were free from other leaf tissues. Our results showed that the glands of subgenus Eucalyptus contain numerous flavanones that are structurally related to pinocembrin and often present in much greater abundance. The maximum concentration of pinocembrin was 2 mg g-1 dry leaf found in E. stellulata, whereas that of dimethylpinocembrin (5,7-dimethoxyflavanone) was 10 mg g-1 in E. oreades and that of pinostrobin (5-hydroxy-7-methoxyflavanone) was 12 mg g-1 in E. nitida. We also found that the flavanones are exclusively located within the foliar glands rather than distributed throughout leaf tissues. The flavanones differ from the non-methylated pinocembrin in the degree and positions of methylation. This finding is particularly important given the attractiveness of methylated flavonoids as pharmaceuticals and therapeutics. Another important finding was that glands of some members of the subgenus also contain flavanone O-glucosides and flavanone-β-triketone conjugates. In addition, glands contain free β-triketones, β-triketone heterodimers and chromone C-glucosides. Therefore, the foliar glands of this taxonomically distinct group of plants are a rich source of a range of flavonoids and other biologically active compounds with great commercial potential.
桉属植物（桃金娘科）叶片中嵌入的皮下分泌腔（腺体）曾被认为是单萜和倍半萜油的唯一储存库。最近的研究推翻了这一理论，并表明叶腺体中也存在大量非挥发性化合物。特别是，桉亚属的四个物种的腺体中含有具有生物活性的黄烷酮松属素。松属素作为一种药物显示出巨大的潜力，并且主要来源于植物，因此桉属植物可能是此类化合物的潜在商业来源。为了探究这一点，我们使用乙腈提取物的电喷雾电离液相色谱质谱法和分离出的不含其他叶片组织的腺体的己烷提取物的气相色谱质谱分析法，对11种桉亚属桉属植物腺体中的松属素进行了定量和纯度评估。我们的结果表明，桉亚属的腺体含有许多与松属素结构相关的黄烷酮，且含量往往更高。在星芒桉中发现松属素的最大浓度为2毫克/克干叶，而在奥瑞桉中二甲松属素（5,7 - 二甲氧基黄烷酮）的浓度为10毫克/克，在光亮桉中匹诺司曲（5 - 羟基 - 7 - 甲氧基黄烷酮）的浓度为12毫克/克。我们还发现黄烷酮仅存在于叶腺体中，而不是分布在整个叶片组织中。黄烷酮在甲基化程度和位置上与未甲基化的松属素不同。鉴于甲基化黄酮类化合物作为药物和治疗剂的吸引力，这一发现尤为重要。另一个重要发现是，该亚属一些成员的腺体还含有黄烷酮O - 葡萄糖苷和黄烷酮 - β - 三酮共轭物。此外，腺体中含有游离的β - 三酮、β - 三酮异二聚体和色酮C - 葡萄糖苷。因此，这一分类学上独特的植物群体的叶腺体是一系列具有巨大商业潜力的黄酮类化合物和其他生物活性化合物的丰富来源。
