PLANT PHYSIOLOGY , Vol 112, Issue 3 1261-1271, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Heterogeneity of Arabinogalactan-Proteins on the Plasma Membrane of Rose Cells
M. D. Serpe and E. A. Nothnagel
Department of Botany and Plant Sciences, University of California, Riverside, California 92521-0124
Arabinogalactan-proteins (AGPs) have been purified from the plasma membrane
of suspension-cultured Paul's Scarlet rose (Rosa sp.) cells. The two most
abundant and homogeneous plasma membrane AGP fractions were named plasma
membrane AGP1 (PM-AGP1) and plasma membrane AGP2 (PM-AGP2) and had apparent
molecular masses of 140 and 217 kD, respectively. Both PM-AGP1 and PM-AGP2
had [beta]-(1-3)-, [beta]-(1,6)-, and [beta]-(1,3,6)-galactopyranosyl
residues, predominantly terminal [alpha]-arabinofuranosyl residues, and
(1,4)- and terminal glucuronopyranosyl residues. The protein moieties of
PM-AGP1 and PM-AGP2 were both rich in hydroxyproline, alanine, and serine,
but differed in the abundance of hydroxyproline, which was 1.6 times higher
in PM-AGP2 than in PM-AGP1. Another difference was the overall protein
content, which was 3.7% (w/w) in PM-AGP1 and 15% in PM-AGP2. As judged by
their behavior on reverse-phase chromatography, PM-AGP1 and PM-AGP2 were
not more hydrophobic than AGPs from the cell wall or culture medium. In
contrast, a minor plasma membrane AGP fraction eluted later on
reverse-phase chromatography and was more negatively charged at pH 5 than
either PM-AGP1 or PM-AGP2. The more negatively charged fraction contained
molecules with a glycosyl composition characteristic of AGPs and included
at least two different macromolecules. The results of this investigation
indicate that Rosa plasma membrane contains at least four distinct AGPs or
AGP-like molecules. These molecules differed from each other in size,
charge, hydrophobicity, amino-acyl composition, and/or protein content.
