CHANGES IN CONTENT OF STARCH, PROTEIN, FAT AND SUGARS IN THE BRANCHWOOD OF BETULA-PENDULA ROTH DURING FALL

The deposition of storage material (starch, protein, fat, sugars) in 6- to 8-year-old branchwood of Betula pendula Roth was followed biochemically and microscopically during fall. At the time of leaf fall, 34.2 g of starch, ca. 12 g of sugars, 11.4 g of protein, and 0.22 g of fat-bound glycerol ( = ca. 2 g fat) have accumulated per kg dry weight (DW) of wood. Thereafter, starch decreases again while the sugar content increases parallel drastically to 19.5 g kg-1 DW. The increase is mainly in sucrose and its galactosides (16.2 g kg-1 DW). Fat and protein decrease at this stage. There is no significant starch-to-fat conversion when starch dissolves.The storage compounds differ also in their deposition behaviour. Their maximum content is reached at different periods in the branch wood. Starch is deposited continuously from summer until leaf fall. Fat increases mainly in late summer, i.e. until September. Protein accumulates only in fall concomitantly with the yellowing of leaves. In the apoplast, sugars also accumulate substantially in late fall reaching 0.15% (w/v) in xylem sap in early winter. Here, reducing sugars are dominating, in contrast to the living cells. The amount of parenchyma cells available for storage in the branch wood was determined to be 10.7 and 8.0% for the ray and the axial parenchyma, respectively. Evidence for protein body deposition was found in particular in axial parenchyma cells.