The base number of 'loxoscaphoid' Asplenium species and its implication for cytoevolution in Aspleniaceae.

BACKGROUND AND AIMS: 'Loxoscaphoid' Asplenium species are morphologically a remarkably distinct group of Aspleniaceae. Except for two preliminary chromosome counts of Asplenium theciferum, the cytology of this group of species has, however, been largely unstudied. METHODS: Chromosome counts were obtained by acetocarmine squash preparations of one mitotic cell and several meiotic cells. Relative DNA content of gametophytic and sporophytic cells was determined by flow cytometry. The phylogenetic placement of A. loxoscaphoides, A. rutifolium s.l. and A. theciferum s.l. was investigated through an analysis of rbcL sequences. KEY RESULTS: The dysploid base number is reported to be x = 35 in Asplenium centrafricanum, A. loxoscaphoides, A. sertularioides and A. theciferum. Analysis of rbcL sequences confirms that 'loxoscaphoids' nest robustly within Asplenium. Several high ploidy levels exceeding the tetraploid level were found in A. theciferum s.l. and A. rutifolium s.l. All taxa proved to be sexual. CONCLUSIONS: Four base numbers are known at present for Aspleniaceae: x = 39, 38, 36 and 35. The dysploid base number x = 35 found in the 'loxoscaphoid' Asplenium spp. sheds a novel light on the cytoevolution of the whole family. We postulate a recurrent descending dysploid evolution within Aspleniaceae, leading to speciation at the (sub)generic and species/group level.

Intercellular pectic protuberances in Asplenium: new data on their composition and origin.

BACKGROUND AND AIMS: Projections of cell wall material into the intercellular spaces between parenchymatic cells have been observed since the mid-19th century. Histochemical staining suggested that these intercellular protuberances are probably pectic in nature, but uncertainties about their origin, composition and biological function(s) have remained. METHODS: Using electron and light microscopy, including immunohistochemical methods, the structure and the presence of some major cell wall macromolecules in the intercellular pectic protuberances (IPPs) of the cortical parenchyma have been studied in a specimen of the Asplenium aethiopicum complex. KEY RESULTS: IPPs contained pectic homogalacturonan, but no evidence for pectic rhamnogalacturonan-I or xylogalacturonan epitopes was obtained. Arabinogalactan-proteins and xylan were not detected in cell walls, middle lamellae or IPPs of the cortical parenchyma, whereas xyloglucan was only found in its cell walls. Extensin (hydroxyproline-rich glycoproteins) LM1 and JIM11 and JIM20 epitopes were detected specifically in IPPs but not in their adjacent cell walls or middle lamellae. CONCLUSIONS: It is postulated that IPPs do not originate exclusively from the middle lamellae because extensins were only found in IPPs and not in surrounding cell walls, intercellular space linings or middle lamellae, and because IPPs and their adjacent cell walls are discontinuous.