title: Sulfur assimilation in c(4) plants: intercellular compartmentation of adenosine 5'-triphosphate sulfurylase in crabgrass leaves.
abstract: The activity of adenosine 5' triphosphate sulfurylase was determined in crabgrass mesophyll cells, bundle sheath strands, and whole leaf extracts. The enzyme was assayed by following molybdate-dependent pyrophosphate release from ATP, (35)SO(4) (2-) incorporation into adenosine 5' phosphosulfate, and ATP synthesis dependent upon adenosine 5' phosphosulfate and inorganic pyrophosphate. With all assays, greater than 90% of the activity was found in extracts from bundle sheath strands. The activities in whole leaf extracts were consistently intermediate between the activities of mesophyll and bundle sheath extracts and extract-mixing experiments gave no indication of enzyme activation or inhibition in vitro. Whole leaf activities were several hundred-fold less than concurrent measurements of ribulose 1,5-bisphosphate and phosphoenolpyruvate carboxylase activities, which is interpreted as being consistent with the relative amounts of elemental carbon and sulfur found in higher plants. A hypothesis is presented for the intercellular compartmentation of sulfur assimilation in relationship to NO(3) (-) and CO(2) assimilation in leaves of C(4) plants.
authors: Biochemistry Department, University of Georgia, Athens, Georgia 30602.
authors: B C
authors: BC
authors: Gerwick
authors: C C
authors: CC
authors: Black