© 1989 Heron Publishing—Victoria, Canada
Sucrose metabolic pathways in sweetgum and pecan seedlings
S. S. Sung (1), P. P. Kormanik (2), D. P. Xu (1) and C. C. Black (1)
1. Biochemistry Department, School of Chemical Sciences, University of Georgia, Athens, GA 30602, USA / 2. Institute for Mycorrhizal Research and Development, USDA Forest Service, University of Georgia, Athens, GA 30602, USA / Received July 12, 1988
Summary
Sucrose metabolism and glycolysis were studied in one- to two-year-old seedlings of sweetgum (Liquidambar styraciflua L.) and pecan (Curya illinoinensis (Wangenh.) C. Koch). The sucrose synthase pathway was identified as the dominant sucrose metabolic activity in sucrose sink
tissues such as terminal buds and the root cambial zone. The sucrose synthase pathway was completely dependent on uridine
diphosphate and pyrophosphate and it was activated by fructose 2,6-bisphosphate. Both acid and neutral invertases were less
active than sucrose synthase in sucrose sink tissues. According to the magnitude of seasonal changes in activity, sucrose
synthase, the pyrophosphate-dependent phosphofructokinase, and fructokinase were identified as adaptive enzymes, whereas neutral
invertase, uridine diphosphate-glucopyrophosphorylase, phosphoglucomutase, and the nonspecific, nucleotide triphosphate-dependent
phosphofructokinase were identified as maintenance enzymes. The periodically high activities of pyrophosphate-dependent phosphofructokinase
indicate that pyrophosphate can serve as an energy source in trees. The observations support the hypothesis that sucrose glycolysis
and gluconeogenesis in plants proceed by a network of alternative enzymes and substrates.
