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J Phycol. 2008 Apr;44(2):335-49. doi: 10.1111/j.1529-8817.2008.00476.x.

INTER- AND INTRASPECIFIC RELATIONSHIPS BETWEEN NUCLEAR DNA CONTENT AND CELL SIZE IN SELECTED MEMBERS OF THE CENTRIC DIATOM GENUS THALASSIOSIRA (BACILLARIOPHYCEAE)(1).

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1
School of Oceanography, University of Washington, Seattle, Washington 98195, USACytopeia Inc., Seattle, Washington 98125, USALaboratory of Protistology and Aquatic Ecology, Department of Biology, Ghent University, Krijgslaan 281 S8, 9000 Gent, BelgiumSchool of Oceanography, University of Washington, Seattle, Washington 98195, USA.

Abstract

The enormous species diversity of diatoms correlates with the remarkable range of cell sizes in this group. Nuclear DNA content relates fundamentally to cell volume in other eukaryotic cells. The relationship of cell volume to G1 DNA content was determined among selected members of the genus Thalassiosira, one of the most species-rich and well-studied centric diatom genera. Both minimum and maximum species-specific cell volume correlated positively with G1 DNA content. Phylogeny based on 5.8 S and ITS rDNA sequences indicated that multiple changes in G1 DNA content and cell volume occurred in Thalassiosira evolution, leading to a 1,000-fold range in both parameters in the group. Within the Thalassiosira weissflogii (Grunow) G. A. Fryxell et Grunow species complex, G1 DNA content varied 3-fold: differences related to geographic origin and time since isolation; doubling and tripling of G1 DNA content occurred since isolation in certain T. weissflogii isolates; and subcultures of T. weissflogii CCMP 1336 diverged in DNA content by 50% within 7 years of separation. Actin, β-tubulin, and Spo11/TopVIA genes were selected for quantitative PCR estimation of haploid genome size in subclones of selected T. weissflogii isolates because they occur only once in the T. pseudonana Hasle et Heimdal genome. Comparison of haploid genome size estimates with G1 DNA content suggested that the most recent T. weissflogii isolate was diploid, whereas other T. weissflogii isolates appeared to be polyploid and/or aneuploid. Aberrant meiotic and mitotic cell divisions were observed, which might relate to polyploidization. The structural flexibility of diatom genomes has important implications for their evolutionary diversification and stability during laboratory maintenance.

KEYWORDS:

DNA content; aneuploid; cell division; cell size; diatom; genome evolution; genome size; haploid; polyploid

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