CARBON ALLOCATION IN DEVELOPING SPRUCE NEEDLES - ENZYMES AND INTERMEDIATES OF SUCROSE METABOLISM

In lyophilized needles of Norway spruce (Picea abies [L.] Karsten) and starting from bud break, we determined enzyme activities (sucrose phosphate synthase [SPS; EC 2.4.1.141, sucrose synthase [SS; EC 2.4.1.13], acid invertase [AI; EC 3.2.1.261) and intermediates (starch, sucrose, glucose, fructose; fructose 6-phosphate, fructose 2,6-bisphosphate [F26BP]) of carbohydrate metabolism together with needle weight, shoot length, chlorophyll and protein. For up to 110 days after bud break, samples were taken twice a week from about 25-year-old trees under field conditions. At least three periods can be distinguished during needle maturation. During the first period (up to 45 days after bud break) Al showed the highest extractable activity. This coincided with very high levels of F26BP (up to 11 pmol [mg dry weight]-1) and a transient increase of starch in parallel to a decrease of sucrose. The interval between 45 and 70 days after bud break was characterized by high SS activity (ratio of fructose/glucose >1), much decreased levels of F26BP (down to below 1 pmol [mg dry weight]-1), and a pronounced increase in the dry weight/fresh weight ratio. In parallel, starch declined and soluble carbohydrates increased. Finally, needle maturation was characterized by decreasing SS and continuously increasing SPS activities, so that the ratio of SPS/SS increased more than 6-fold. Al, however, did not decline with maturation. Changes in pool sizes of metabolites and enzyme activities (AI, SPS) are consistent with current concepts on sink/source transition. SS is obviously important with regard to the synthesis of structural polysaccharides.