title: Developmental Control of Apiogalacturonan Biosynthesis and UDP-Apiose Production in a Duckweed.
abstract: Vegetative fronds of Spirodela polyrrhiza were induced to form dormant turions by the addition of 1 micromolar abscisic acid or by shading. The cell wall polymers of fronds contained a high proportion of the branched-chain pentose, d-apiose (about 20% of total noncellulosic wall sugar residues), whereas turion cell walls contained only trace amounts (about 0.2%). When the fronds were fed d-[(3)H]glucuronic acid for 30 minutes, the accumulated UDP-[(3)H]apiose pool accounted for about 27% of the total phosphorylated [(3)H]pentose derivatives; in turions, the UDP-[(3)H]apiose pool accounted for only about 4% of the total phosphorylated [(3)H]pentose derivatives. We conclude that the developmentally regulated decrease in the biosynthesis of a wall polysaccharide during turion formation involves a reduction in the supply of the relevant sugar nucleotide. One controlling enzyme activity is suggested to be UDP-apiose/UDP-xylose synthase. However, since there was a 100-fold decrease in the rate of polysaccharide synthesis and only a 9-fold decrease in UDP-apiose accumulation, there is probably also control of the activity of the relevant polysaccharide synthase.
authors: Department of Botany, University of Edinburgh, The King's Buildings, Mayfield Road, Edinburgh, EH9 3JH, United Kingdom.
authors: J M
authors: JM
authors: Longland
authors: S C
authors: SC
authors: Fry
authors: A J
authors: AJ
authors: Trewavas