A Mechanism for the Origin of Specifically Oriented Textures in Development with Special Reference to Nitella Wall Texture

Abstract

Many oriented growth phenomena, including the elongation of the Nitella internode, are based upon oriented or textured cell wall structure. In many cases the ordered textures are not present in the earliest stages of cell development but appear later. In Nitella lateral cell (leaf) development the first appearance of transverse wall texture (detected in polarized light) approximately coincides with a transverse stretching of the cell and its wall. This oriented stretching appears not to have its origin in a pre-existing texture but rather to be the result of a particular distribution of wall expansion rates. The relation between rates and oriented distortions is studied as a general phenomenon. The form these rate variations must take to provide longitudinal, transverse, or isotropic distortion is derived. Model devices made of rubber membranes, where expansion rate is varied by reinforcement of the rubber, generate distortions (textures in the rubber) of the type predicted. In the course of development it is possible that imbalances in expansion rate based on gradients (of metabolites, pH, light, etc.) bring on, through strain orientation, the initial alignment of originally randomly oriented fibrous ultrastructures, such as microfibrils of the cell wall or cytoplasmic microtubules.