Date of Award

1999

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

First Advisor

Marilyn Harlin

Abstract

While under investigation as a toxicity-testing organism, female gametophytes of the small marine red alga, Champia parvula (C. Agardh) Harvey exhibited a loss of diaphragm formation in indeterminately growing branch tips. Further study revealed that this change of morphology occurred when bromide was omitted from nutrient enriched, synthetic seawater (Thursby and Harlin 1984).

The goals of this project were to verify and further document the loss of .diaphragm formation in C. parvula under bromide minus and other culture conditions and to observe developmental events associated with the loss of diaphragm formation. The working hypothesis was that diaphragm formation is dependent on bromide. To test this hypothesis, diaphragm formation in C. parvula branch tips was morphometricly measured by monitoring first segment length (FSL ), the region from the apex to the first observable diaphragm. Overall growth of C. parvula branch tips was monitored by measuring tip length (TL), the distance from the apex to the base of the tip. FSL was selected as an appropriate measure of diaphragm formation by comparing FSL to the increase in segment number in branch tips over time. Tips in synthetic media lacking bromide showed an increase in FSL, but only a small increase in segment number indicating that formation of new diaphragms and, therefore, new segments had stopped. In contrast, branch tips in control treatments showed an increase in segment number but little change in FSLs over time indicating continuous, periodic formation of new diaphragms. The sensitivity of diaphragm formation to bromide availability was observed in both tetrasporophytes and female gametophytes in two versions of synthetic media. However, the two versions of synthetic media with bromide (used as controls) proved unsuccessful in maintaining diaphragm formation indefinitely. Toward the end of experiments, FSL was inconsistent among branch tips cultured in synthetic media, and by two weeks, branch tips from synthetic media were more similar in length to tips from the bromide free media than to tips from NSW. This finding undermined the hypothesis that loss of diaphragm formation depends on the availability of bromide.

Lack of bromide may induce stress in C. parvula and loss of diaphragm formation may be a generalized stress response. This possibility is supported in that C. parvula showed a reduced reproductive capability in synthetic media as compared to natural seawater, and that altering nitrogen sources led to loss of diaphragm formation. Features of C. parvula that were not significantly affected in synthetic media with and without bromide were growth (as measured by TL), branch formation, and the development of hyphal filaments and gland cells.

The effort to test whether bromide is required for diaphragm formation in C. parvula was not conclusive. However, the investigation did support previous research performed with C. parvula -- developmental work by Bigelow (1887) and culturing studies by Thursby and Harlin (1984). A staining technique was tried in the investigation that, if pursued, may provide the histological information that is needed to determine the role of bromide in diaphragm formation in C. parvula. Suggestions for pursuing this research in the future are provided.

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