Chemical control of plant cell wall structure and of cell shape

It has been shown by Galston, Baker & King (1953) that, if sub-apical sections of pea epicotyl are floated on a sucrose solution containing an appropriate indole acetic acid ( IAA ) concentration, the sections will elongate considerably. If benzimidazole (BIA) is added in addition to the auxin there is a narrow concentration range of BIA over which elongation is strongly inhibited, while increase in section diameter is actually enhanced. This increase in diameter is due specifically to an increase in diameter of the cortical cells. It is shown in this paper that the cortical cells in tissues which have been induced to increase in diameter have a different wall structure from cortical cells in tissues which have increased mainly in length. In the latter case the cellulose microfibrils are arranged transversely to the longitudinal axis of the cell, but, in cells which have increased mainly in diameter, there are two distinct microfibrillar components: a transverse set of microfibrils, and organized bands of longitudinally oriented microfibrils on the outside of the cell wall. The structure of the wall and its plastic and elastic properties are discussed in relation to the way in which the wall may determine the shape of the cell. It is pointed out that changes in cell shape which result from alteration of the chemical environment of the cell could be explained by modification of the plastic and elastic properties of the wall due to change in wall structure. This hypothesis supports the idea that plasticity of the cell wall is an important factor in extension growth and also suggests that the arrangement of microfibrils plays an important part in determining the shape of the cell. If this hypothesis is correct it may have considerable bearing upon the mechanism of cell and tissue differentiation. The observed changes in cell wall structure favour the view that microfibril orientation is controlled through the agency of the protoplasm. The occurrence of bands of longitudinal microfibrils on the outside of the cell wall suggests that cellulose microfibrils can be laid down remote from the cytoplasm.