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Date of Award

1992

Document Type

Thesis - Pacific Access Restricted

Degree Name

Master of Science (M.S.)

Department

Graduate Studies

First Advisor

Paul A. Richmond

First Committee Member

Steven C. Anderson

Second Committee Member

Dale McNeal

Abstract

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}.

Pages

76

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