Date of Award

2000

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

Russell L. Chapman

Abstract

Molecular, karyological, and nuclear genome quantification data from representatives of the order Trentepohliales (Chlorophyta) were used to infer evolutionary relationships with other green algal classes and orders. Phylogenetic analyses of the nuclear-encoded small subunit ribosomal DNA (18S rDNA) sequences from taxa representing all of the major lineages of green algae consistently indicated that the subaerial Trentepohliales are closely related to Ulvophycean marine green algae, particularly to the siphonous and hemisiphonous orders. The phylogenetic distribution of continuous and discontinuous types of mitochondrial large subunit ribosomal RNAs (mtLSU rRNA) in green algae has been shown to be consistent with phylogenetic relationships previously suggested by both ultrastructural data from the flagellar apparatus and nuclear rRNA sequence analysis. Our studies indicated the presence of a continuous mtLSU rRNA in Cephaleuros parasiticus ; continuous mtLSU rRNA have been reported in all the investigated zoosporic green algae with a counterclockwise orientation of the flagellar apparatus and their autosporic descendants; a result that is consistent with an ulvophycean affinity. Microspectrophotometry with the DNA-localizing fluorochrome DAPI was used to quantify nuclear DNA content in eight species representing three genera of the subaerial green algal order Trentepohliales (Chlorophyta). Comparisons of mean fluorescence intensity (If) values of algal nuclear genomes to those of chicken erythrocytes (RBC) resulted in an estimate of 1. 1--4.1 pg for the algae. DNA levels in Cephaleuros parasiticus Karsten for 2 C nuclei in gametophytic phase closely approximate 50% of the 4 C values in the sporophytic phase, confirming previous observations based on culture and ultrastructural studies on the presumptive sexual life cycle in this genus. Genome quantification data for eight Trentepohlialean taxa suggest a doubling sequence for nuclear DNA contents. This phenomenon might reflect the presence of a polyploid series in the order Trentepohliales. Amplification and sequencing of the chloroplast-encoded large subunit ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) gene was used to assess its reliability as a phylogenetic marker of the order Trentepohliales and the green algal classes. Our present results suggest using the rbcL gene sequences is more useful within green algal classes than for the analysis of phylogenetic analysis among major groups of algae.

ISBN

9780599853324

Pages

122

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