Traumatic oil glands induced by pruning in the wound-associated phloem of Eucalyptus globulus: chemistry and histology

The natural occurrence of oil glands in various organs such as bark and leaves is well established as a characteristic of Eucalyptus, but this is the first reported case of traumatic oil glands induced in response to wounding. The new phloem enveloping the wound, which had developed within the 2 years following branch pruning in 5-year-old Eucalyptus globulus Labill., was morphologically distinct from healthy stem phloem. Histological examinations revealed this wound-associated phloem to be largely composed of secretory cavities similar in appearance to oil glands. Subsequent analysis of the wound-associated phloem extracts by GC-MS confirmed the presence of volatile terpenes and phenols. The total extracted oil content determined for wound-associated phloem extracts was significantly higher (>4 times) than for healthy stem phloem extracts. A comparison of the relative abundances of ten individual terpenoids from wound-associated phloem and healthy phloem revealed a number of significant differences in terpene composition. Implications of the role of terpenes as inducible secondary metabolites in tree wound responses are discussed.