Emission and content of monoterpenes in intact and wounded needles of the Mediterranean Pine, Pinus pinea

Abstract

1. Biogenic emission of isoprenoids may be involved in protecting plants against pathogens and may interfere with the chemistry of atmosphere. Pinus pinea (L.) is one of the most widespread conifers in the Mediterranean area and is a potentially strong emitter of monoterpenes. 2. We demonstrated by gas-exchange studies that monoterpenes other than transβ-ocimene are not emitted significantly by intact primary and secondary needles of 3-year-old P. pinea plants. 3. Trans-β-ocimene emission is light- and CO2-dependent. Therefore this compound is probably formed from photosynthetic carbon in the chloroplasts and does not originate from the same biochemical route as other monoterpenes stored in resin ducts. 4. Trans-β-ocimene emission starts in spring, peaks in summer and ceases at the end of summer. This strong seasonality may mark a phase-shift in needle ontogeny, but is not related strictly to changes in photosynthesis. 5. Wounded needles, either illuminated or darkened, massively release monoterpenes contained in the ducts, primarily limonene and α-pinene. Monoterpene release from wounded needles rapidly decreases but does not cease altogether, even after 24 h. The amount of monoterpenes emitted from wounded needles in 24 h can be estimated at about 1200 and 120 μmol g-1 day-1 (dry mass) of limonene and α-pinene, respectively. Wounded needles are a main contributor to monoterpene emission by vegetation. 6. Monoterpene content is two to three times greater in primary than in secondary needles. In primary needles, typical only of young plants, the elevated content of monoterpenes may allow plant survival against pathogenic attacks.