Chemical composition of viscin, an adhesive involved in dispersal of the parasite Phoradendron californicum (Viscaceae)

Abstract

The seeds of nearly all mistletoes are covered with an adhesive mucilaginous tissue, viscin, which is of importance in the bird-mediated dispersal of these parasites and in the attachment of their seeds to the host surface. The present paper presents an examination of the chemical composition of the viscin of mature fruits of the California desert mistletoe, Phoradendron californicum Nutt. Mature viscin cells are highly clongated and consist of an inner microfibrillar cylinder and an outer mucilaginous one. The viscin mucilage was soluble in ethylenediamine tetraacetic acid and sodium carbonate/sodium borohydride and consisted primarily of highly-branched xylans containing an unusual 2,3-branch point in addition to 2,4 and 3,4-branches typically found in xylans of dicotyledonous species. Highly-branched arabinans, pectinaceous rhamnogalacturonans, and fragments of galactomannans and xyloglucans also comprised a portion of the mucilage. The thickened walls of the viscin cells comprised polymers whose linkages were typical of arabinans, arabinoxylans, galactomannans, and xyloglucans.