Structure and composition of the thick wall in hair root epidermal cells of Woollsia pungens.

Abstract

• Hair roots of Woollsia pungens are shown to have thick-walled epidermal cells, a feature found in a small number of other species within the Epacridaceae. Hair roots otherwise had a structure typical of the Ericales. • Ultrastructural, immunocytochemical and histochemical techniques were used to investigate the structure and composition of these thick-walled epidermal cells. • The thick walls were multilamellate with a helicoidal arrangement of microfibrils typical of a secondary cellulosic wall. Staining techniques revealed a relatively high abundance of β-glucans; these were not β 1-3 linked and there was no detectable protein. Galactose side-chains were abundant but not mannose or glucose side-chains. The wall contained a pH-dependent net negative charge. Although apparently rich in COOH groups the thick wall did not react, or only minimally, with the monoclonal antibodies JIM5 and JIM7, testing for nonesterified and methyl-esterified pectins, respectively; this contrasted with the strong positive reaction in the cortical and stelar cells. In epidermal cells colonized by mycorrhizal fungi the thick wall had additional layers of spongy appearance with many interconnected, irregular patches containing dispersed material. Colonized cells retained their integrity longer than noncolonized cells. • The thick wall might be important in long-term survival of infected cells and the low levels of pectin might control mycorrhizal endophyte infection.