Cell Wall Biosynthesis during Silicification of Grass Hairs

Abstract

Summary Cell walls of mature hairs from the lemma of Phalaris canariensis L. consisted of ≃ 40 % silica, 55% polysaccharides (containing 53% hexose, 45% pentose, and ⩽2% uronic acid residues) and ⩽ 5% protein. The ultrastructural form of the silica being deposited varied during development, the sequence being (1) sheet-like silica, (2) globular silica, (3) fibrillar silica. At the same time, a shift in the pattern of labelling of hair polysaccharides was detected in experiments where [ 14 C]glucose or [ 3 H]arabinose were fed to inflorescences of various ages for 32 h. At the early stages of secondary wall formation, when sheet-like silica was being deposited, arabinoxylan and cellulose were the major polymers being synthesised. Later, when globular silica was deposited, there was a dramatic increase in synthesis of «mixed-linked» β-(1→3, 1→4)- D -glucan relative to cellulose and arabinoxylan; some mannan was also labelled. In the final stages, during fibrillar silica deposition, little incorporation of sugars was occurring. It is argued that the changing composition of the organic phase of the cell wall may govern the size and ultrastructural arrangement of the silica particles being deposited.