Cell Growth and the Structure and Mechanical Properties of the Wall in Internodal Cells ofNitella opaca

Abstract

This is the first of two papers dealing with the relationship between growth and the mechanical properties of the wall in internodal cells of Nitella opaca L. The submicroscopic structure of the cell wall of this alga, as determined by chemical analysis, X-ray crystallography, polarizing microscopy, electron microscopy, swelling measurements, and infra-red spectrography, is described in detail and the changes during growth are recorded. It has been found that the wall contains cellulose in the form of cellulose I (type B). The constituent microfibrils are preferentially oriented, usually in slow helices with considerable angular dispersion about the common direction. They are arranged in discrete layers with pectic substances providing an amorphous matrix between microfibrillar-reinforced laminations. It is shown that, as the cell elongates, both the streaming direction in the cell and the mean microfibrillar orientation in the wall change in such a way as to allow the possibility of a causal connexion between streaming and microfibrillar orientation in a new wall lamella. The orientation in such a lamella is undoubtedly modified by subsequent passive extension much as implied in the multi-net growth hypothesis of Roelofsen.