The role of isoprenoid accumulation and oxidation in sealing wounded needles of Mediterranean pines

This study was carried out to investigate how the emission of isoprenoids that follows wounding of pine needles is restrained and how this can be associated to wound sealing processes and to defense mechanisms against pathogenic attacks. Needles of two Mediterranean pines (Pinus pined and Pinus halepensis) emitted a high amount of monoterpenes immediately after wounding but the emission became undetectable within 24 h. Histochemical analysis revealed that the purple stain coloring the isoprenoids in fresh needle sections turned black 24 h after wounding the needles. This suggests that isoprenoids accumulated at the wounding sites. Sections below the wounds showed that the ducts were still full of isoprenoids stained in purple. This excluded the possibility that the emission from wounded needles ceases because the ducts were empty. Chromatographic analysis of the resin covering the wounds indicated a high amount of sesquiterpenes 1 h after wounding and a considerable increase in oxygenated isoprenoids 24 h after wounding. Our results indicate that the emission from wounded needles may be rapidly limited and eventually stopped by the accumulation of oxidation products of the same emitted isoprenoids. This mechanism is similar to that used to seal trunk wounding and may constitute a physical and chemical barrier against pest attacks.