Natur, Verteilung und Umsetzung von Reservesubstanzen in verholzten Achsen

2001

S. 91-108

23 Lit. Ang.

Unselbständiges Werk

200084581

Wood (=xylem) is a secondary plant tissue produced by a meristem, the vascular cambium. The xylem fulfills three major functions: support of the plant through mechanical strength, conduction of water and minerals, and storage. The main storage products are soluble sugars, fructosans, starch, fat (triacylglycerides), and proteins. These compounds are localized exclusively in parenchymatous cells. In general, soluble sugars, starch and triacylglycerides are found in the sapwood, while heartwood is free of reserves. Heartwood of Pinus sylvestris L. exhibits high amounts of free fatty acids. In Robinia pseudoaccacia L. and Pinus sylvestris L. there is a shift towards higher amounts of (1-4) glycosyl chains (amylose) at the expense of Alpha (1-6) glycosyl chains (amylopectin) with increasing depth of the sapwood. Reserve substances show annual fluctuations: in the cold period of the year (November to December) soluble sugars accumulate (Acer pseudoplatanus L.). The higher molecular storage materials starch and fat (triacylglycerides) show, compared to soluble sugars and free glycerol, an opposite behavior (Picea abies L. Karst). In Tilia cordata Mill. storage lipids in both trunk and roots undergo conspicuous changes long before budbreak and unfolding of the leaves. Rootwood contains considerable amounts of triacylglycerides. During cambial activity storage lipids seem to be converted into sugars via the glyoxylate pathway.