Patterns of cellulose deposition within the cell wall directly affect the size and shape of plant cells, in turn affecting the overall structure of the plant. In the primary wall of Nitella, and in the walls of many other algae and higher plants, a correspondence has been observed between the organization of cellulose microfibrils and cortical microtubules, each lying on opposite sides of the plasma membrane. The present work examines the development of the secondary wall in maturing Nitella internodal cells in an attempt to determine whether a relationship exists between cellulose microfibril organization and the organization of cortical microtubules. Treatments that artificially rearrange or remove microtubules were used, and effects on cellulose organization in the cell wall were examined through the use of transmission electron microscopy in thin sections and by the replica technique. Removal of microtubules in very young cells had a randomizing effect on cellulose organization, but absence of microtubules or their rearrangement did not prevent the formation of secondary walls with characteristic helicoidal patterns. The findings on the timing of helicoidal development in Nitella and the appearance of the innermost surface of helicoidal layers are discussed in relation to models of helicoidal architecture.

Mechanical support is a required function of most biological materials. Skeletal helicoids are a structural motif often used in the construction of plant cell walls and arthropod exoskeletons. Nitella axillaris, a giant-celled freshwater alga has many characteristics which make it an ideal subject for helicoidal analysis. Earlier research had shown that the cell wall of mature Nitella internodes exhibit helicoidal layers. However, no previous work had concentrated on studying the relationship between the presence of helicoids and internodal age. The work presented here examines the relationships among growth rate, cell age, cell length, and presence of helicoidal layers. Internodes were categorized according to age, from their position along the shoot. In addition, by monitoring cell growth, the cultures were classified into three groups, slow, medium and fast. Cross sections of the various cells were examined for the presence of helicoidal layers. Once the presence of helicoidal layers was established, oblique, longitudinal and tangential sections were used to further study helicoidal structure. We showed that the transition state between the presence and lack of helicoidal layers is between cells III and IV. The timing of this transition was not exact but more or less coincided with the cessation of cell elongation. Also, no apparent correlation was found between the timing of helicoid deposition and growth rate for cells of equivalent age (internode number}.