Cell Growth and the Structure and Mechanical Properties of the Wall in Internodal Cells ofNitella opaca: III. SPIRAL GROWTH AND CELL WALL STRUCTURE

Abstract

The internodal cells of the alga Nitella opaca L, which are in the form of long thin cylinders, exhibit the phenomenon of spiral growth, i.e. as the cells elongate they also twist about their longitudinal axis. It has been shown in an earlier paper (Probine and Preston, 1962) that the cell wall is mechanically anisotropic. In this paper the moduli necessary to describe the elastic behaviour of a material possessing this sort of symmetry are considered. It is pointed out that if the Nitella cell is regarded as a thin-walled cylinder built of a material possessing orthorhombic elastic symmetry, then there can be a coupling between shear and extension which will produce a torsional twist as the cylinder is pressurized. It is suggested that this is the basic mechanism of spiral growth. Experimental evidence is presented which supports this view.