Arabinogalactan-Proteins in Different Layers of Cabbage Leaves

Abstract

This communication describes the distribution and chemical variations of water-soluble arabinogalactan-proteins in three layers of cabbage leaves. The inner and outer leaves contained two arabinogalactan-proteins (A-I and A-II) differing in molecular weight, whereas the green leaves and veins were devoid of high molecular weight A-I and contained a lower amount of lower molecular weight A-II. In addition, veins from green leaves were completely devoid of A-I and A-II. The ratio of galactose/arabinose and contents of glycine and arginine in arabinogalactan-proteins increased with leaf hardening, while hydroxyproline decreased with leaf hardening. It was also found that the amounts of arabinose, galactose and hydroxyproline in water extracts of cabbage leaves decreased with their concomitant increase in extraction residues as leaf hardening progressed. This suggested that water-soluble arabinogalactan-proteins are transformed into insoluble forms with leaf hardening.