|Information about genetic characteristics of peat moss is sparse. Therefore, our working group at the Botanical Institute of the University of Vienna, Austria, investigated for the first time ploidy levels and genome size variations in Austrian Sphagnum. The results have been published in Botanica Acta:
Temsch, E.M., Greilhuber, J., Krisai, R. (1998): Genome size in Sphagnum (peat moss). Bot. Acta 111: 325-330. Read abstract
volume 111, 1998
|Genome size is an important taxonomic factor because it influences cell size and duration of the cell cycle. On the one hand, judging from the high phylogenetic age of peat mosses, one would expect a wide range of genome sizes among their species. On the other hand, their rather uniform phenotypes suggest close similarities in their karyotypes.
The aim of our study was to determine ploidy levels and genome sizes of Austrian Sphagnum by precise measurement of DNA content of their cell nuclei.
|Methods and Materials|
The results of the two methods were nearly identical (r=0.9613).
|Sixty-six capitula samples of 30 species of Sphagnum were collected at various Austrian locations (see species page), fixed overnight mainly in methanol-acetic acid (3:1), and stored in 96% ethanol at -20º C. Genome sizes were determined by Feulgen absorbance photometry conducted on a video-based image analysis system (CIRES). For comparison, 10 samples were analyzed by means of a cytophotometer (MPV2). Pisum sativum, with the known amount of 4.42 pg DNA per unreplicated, haploid genome (1C), was used as internal standard.|
|Genomes of all investigated Sphagnum species were unequivocally either haploid or diploid. DNA content (1C) of 26 haploid species ranged between 0.392 and 0.506 pg (mean: 0.449 pg), the remaining four diploid species (S. palustre, S. papillosum, S. russowii, and S. majus) contained 0.814-0.952 pg (mean: 0.920 pg). Thus, the mean ploidy ratio of 1:2.049 indicates two clearly separated ploidy levels. Wider variations were observed between sections than within sections. In some cases, significant differences were found among accessions of one species.
Two distinct ploidy levels
|This is the first investigation in which DNA content of Sphagnum cell nuclei was precisely measured, and plant cells were used as internal standard. The observed ploidy levels largely agree with publications based on chromosome numbers (x=19 + micro chromosomes), although a few different Sphagnum populations have also been reported from Great Britain, Canada, and Finland.|
The low degree of genome size variation, in spite of the high phylogenetic age of Sphagnum, conforms to the similarity in habit, and might also mirror its highly specialized role in nature.
|Why do gametophytes, the photosynthetic haploid generation of peat moss, all the sudden have diploid genomes?
Diploid gametophytes have two sets of chromosomes. Apparently, during a historic event in their phylogenetic development, a hybrid evolved from two species. It completely retained both genomes of its parent species. Thus, gametophytes of the newly created species are generatively diploid while still being in the haploid phase of the plant's life cycle.
The sporophytes of these species are in the diploid phase of the plant's life cycle. From their 2x2 sets of chromosomes that stem from fertilization, it can be concluded that they are generatively tetraploid.
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