Patterns of cellulose synthesis in maize root-tips: A chemical and autoradiographic study

Abstract

By analysis of mm segments of maize root-tip, it has been shown that pectic substances, which are relatively poor in uronic acid but rich in arabinose and galactose, provide only 13 per cent of the cell wall polysaccharides. Their contribution is highest in young cells. The hemicelluloses constituted over 50 per cent of all polysaccharides throughout the root. α-Cellulose increases during elongation from about 20 per cent of all polysaccharide in the younger region to about 35 per cent in cell walls of growing cells. Patterns of cellulose synthesis in excised and intact roots were also investigated by autoradiography. During short incubation periods with 14C-6- d-glucose, most of the label incorporated into the ethanol-insoluble fraction was recovered, after hydrolysis, in hexose. When this residue was extracted with alkali, the insoluble α-cellulose contained 4C in glucose units only. This incorporation was presumed to be related to the amount of cellulose synthesised during the incubation. Autoradiographs of sections extracted with alkali revealed, therefore, the incorporation pattern into cellulose within the root. Cellulose was synthesised only slowly in cell walls of the cap and meristematic region. As cells began to extend more rapidly, there was a sharp rise in incorporation, increasing to a maximum in the pith, inner and outer cortex and epidermis between the third and fourth mm behind the cap-junction. Cells at this stage had not completed their growth, and no direct relationship could be inferred to exist between deposition of cellulose and extension of the wall.