CARBOHYDRATE-METABOLISM IN ONE- AND 2-YEAR-OLD SPRUCE NEEDLES, AND STEM CARBOHYDRATES FROM 3 MONTHS BEFORE UNTIL 3 MONTHS AFTER BUD BREAK

Starch and sucrose metabolism of one- and two-year-old needles of Norw ay spruce (Picea abies [L.] Karst., about 30 years old) was investigat ed from three months before until three months after bud break at a na tural site. We distinguish different metabolic states according to the extractable activities of enzymes (alpha-amylase [EC 3.2.1.1], ADP-gl ucose pyrophosphorylase [AGP, EC 2.7.7.27], D-enzyme [EC 2.4.1.25], st arch phosphorylase [STP, EC 2.4.1.1]), sucrose phosphate synthase [SPS , EC 2.4.1.14], sucrose synthase [SS, EC 2.4.1.13], acid invertase [AI , EC 3.2.1.26]) and pool sizes of related metabolites (starch, glucose , fructose, sucrose, raffinose, stachyose, fructose 6-phosphate [F6P], glucose 6-phosphate [G6P], fructose 2,6-bisphosphate [F26BP], and ino rganic phosphate [P-i]. The period ending with bud break was character ized by high rates of net photosynthesis, a pronounced decrease in the amount of soluble sugars, and a steep rise in starch (from the detect ion limit to approximately 600 nmol glycosyl units [mg dry weight](-1) ). In parallel, the extractable activity of AGP increased, while D-enz yme was on a relative high level when compared with the period after b ud break. With respect to sucrose metabolism, F26BP, an inhibitor of s ucrose synthesis, decreased from 1 to 0.4 pmol (mg dry weight)(-1). Th is was complemented by SPS activity, which was due to both increased p rotein levels shown by immunoblotting and activation under metabolite control (high levels of G6P and a low P-i/G6P ratio). This indicates a high capacity of synthesis of starch and sucrose in the period before bud break. These observations are in accordance with estimates of pho tosynthetic carbon gain, which indicate that in early spring large amo unts of carbon from current photosynthesis are exported out of the nee dles. In addition, the content of nonstructural carbohydrates (express ed as hexoses) increased in the bark of the stem. This could also be a consequence of an enhanced carbon export from the needles. After the onset of bud break, starch concentration decreased in all tissues unde r investigation. In contrast, the level of total nonstructural carbohy drates in the outermost sapwood nearly doubled from bud break until th e end of sampling. In the needles, net photosynthesis was reduced by a bout 75% and a decrease in SPS activity and protein level were found t ogether with lower G6P concentration, and an increased P-i/G6P ratio. These results suggest that during that period sucrose synthesis was re duced in the older needles. In addition, under conditions of reduced p hotosynthesis, carbon demand of current year needles was in part ensur ed by the mobilization of starch in the older needles. Taken together our data show that before bud break carbon metabolism of mature leaves is related with the sink demands of storage organs. After bud break t he accumulated assimilate pools in needles and stem, mainly the bark, are mobilized and support carbon supply to new tissues.