DEVELOPMENTAL-CHANGES OF SUCROSE SYNTHASE ACTIVITY AND ABUNDANCE IN ROOT AND LEAF TISSUES OF ZOSTERA-MARINA

The activity of sucrose synthase (EC 2.4.1.13) is correlated with tiss ue carbon (C) demand in vascular plants. The patterns of SS activity a nd abundance, and soluble protein abundance are described along age gr adients within leaf bundles and in roots along the subterranean rhizom e of the marine angiosperm Zostera marina L. (eelgrass). Soluble prote in content decreased exponentially with increasing age in root tissue (concentrations in oldest roots were 20% of those of the youngest root s), but decreased in a linear fashion and overall to a lesser extent i n leaves (to 62% of values in youngest shoots). Variation of SS activi ty with tissue age depended on the tissue and parameter to which measu rements were normalized. Biomass-specific root SS activity decreased e xponentially from 90-40 mu mol g(-1) fresh weight h(-1) in root bundle s numbers 1 (youngest) through 9, while protein-specific activity rema ined constant in the same tissue (approximately 16 mu mol mg(-1) prote in h(-1)). Roots 10-12 had elevated, but variable SS activities. In le aves numbers 1-5, the decreases in both biomass- (200 to 50 mu mol g(- 1) FW h(-1)) and protein-specific SS activity (23-12 mu mol mg(-1) pro tein h(-1)) were approximately linear. The abundance of SS protein in roots and leaves (determined by western analysis) also decreased with the increasing age, though not to the same extent (leaves), or with si milar pattern (roots) as for SS activity. The age-dependent changes in SS activity are consistent with other indices of C metabolism (e.g., respiratory rates, carbohydrate content), but not with an index of N m etabolism (glutamine synthetase activity) during development of Z mari na tissues. (C) 1998 Elsevier Science B.V. All rights reserved.