© 2004 Heron Publishing—Victoria, Canada
Seasonal and within-stem variations of neutral lipids in silver birch (Betula pendula) wood
Riikka Piispanen (1, 2) and Pekka Saranpää (1)
1. Finnish Forest Research Institute, P.O. Box 18, FIN-01301 Vantaa, Finland / 2. Corresponding author (riikka.piispanen@metla.fi) / Received August 20, 2003; accepted January 10, 2004; published online July 1, 2004
Summary
Neutral lipids were analyzed in stem wood of a 7-year-old clone and in five 35–70-year-old mature trees of silver birch (Betula pendula Roth). In young trees and in mature wood of old trees, the free fatty acid fraction comprised less than 5% of the concentration
of triacylglycerols (TG). The concentration of free linoleic acid was lowest in March when the young trees were dormant and
highest during midsummer and September. In mature trees, the TG concentration increased toward the pith, indicating that living
parenchyma cells close to the pith have a large TG storage capacity. The TG concentration (mean 0.51 ± 0.02% of wood dry mass)
remained constant throughout the year in young trees, whereas the concentration of β-sitosterol, the dominant free sterol
(mean 82.5 ± 0.4% of total free sterols), decreased during spring and early summer when the temperature gradually increased,
and increased during autumn when the trees became dormant. In young trees, we detected a seasonal interconversion between
the free and esterified forms of β-sitosterol and campesterol, and within the steryl ester fraction between squalene and betulaprenol-7.
The concentration of esterified sterols/isoprenoids was exceptionally high, especially in the inner regions of mature stem
wood (mean 0.6 ± 0.03% of wood dry mass). No heartwood formation was detected.
Keywords:
deciduous, fatty acid, isoprenoid, sterol, xylem.
