BIOCHEMISTRY OF SHORT-CHAIN ALKANES - TISSUE-SPECIFIC BIOSYNTHESIS OFN-HEPTANE IN PINUS-JEFFREYI

Short-chain (C-7-C-11) alkanes accumulate as the volatile component of oleoresin (pitch) in several pine species native to western North Ame rica. To establish the tissue most amenable for use in detailed studie s of short-chain alkane biosynthesis, we examined the tissue specifici ty of alkane accumulation and biosynthesis in Pines jeffreyi Grev. & B alf. Short-chain alkane accumulation was highly tissue specific in bot h 2-year-old saplings and mature trees; heartwood xylem accumulated al kanes up to 7.1 mg g(-1) dry weight, whereas needles and other young g reen tissue contained oleoresin with monoterpenoid, rather than paraff inic, volatiles. These tissue-specific differences in oleoresin compos ition appear to be a result of tissue-specific rates of alkane and mon oterpene biosynthesis; incubation of xylem tissue with [C-14]sucrose r esulted in accumulation of radiolabel in alkanes but not monoterpenes, whereas incubation of foliar tissue with (CO2)-C-14 resulted in the a ccumulation of radiolabel in monoterpenes but not alkanes. Furthermore , incubation of xylem sections with [C-14]acetate resulted in incorpor ation of radiolabel into alkanes at rates up to 1.7 nmol h(-1) g(-1) f resh weight, a rate that exceeds most biosynthetic rates reported with other plant systems for the incorporation of this basic precursor int o natural products. This suggests that P. jeffreyi may provide a suita ble model for elucidating the enzymology and molecular biology of shor t-chain alkane biosynthesis.