Mediterranean orchids of the subtribe Orchidinae are highly diverse and display a range of fascinating pollination strategies. Based on observations that orchid-pollinator relationships are often highly specialized and species specific, Darwin and others have argued that selection for different pollinators has been the driving force behind the evolutionary diversification of orchids. This may be true for orchids that attract different, specialized pollinators that act as prezygotic reproductive barriers. It is, however, not clear how closely related co-flowering Mediterranean orchids that share pollinators survive the challenge of sympatry. We show that species pairs with a generalized pool of pollinators have significantly more divergent karyotypes compared with species pairs with different pollinators. These results show that karyotype differences that act as postzygotic reproductive barriers may have played an important role in the evolution of Mediterranean orchid diversity.
Post-translational hydroxylation of peptide-bound proline residues, catalyzed by peptidyl-prolyl-4 hydroxylase (EC 1.14.11.2) using ascorbate as co-substrate, is a key event in the maturation of a number of cell wall-associated hydroxyproline-rich glycoproteins (HRGPs), including extensins and arabinogalactan-proteins, which are involved in the processes of wall stiffening, signalling and cell proliferation. Allium cepa L. roots treated with 3, 4-DL-dehydroproline (DP), a specific inhibitor of peptidyl-prolyl hydroxylase, showed a 56% decrease in the hydroxyproline content of HRGP. Administration of DP strongly affected the organization of specialized zones of root development, with a marked reduction of the post-mitotic isodiametric growth zone, early extension of cells leaving the meristematic zone and a huge increase in cell size. Electron-microscopy analysis showed dramatic alterations both to the organization of newly formed cell walls and to the adhesion of the plasma membranes to the cell walls. Moreover, DP administration inhibited cell cycle progression. Root tips grown in the presence of DP also showed an increase both in ascorbate content (+53%) and ascorbate-specific peroxidase activity in the cytosol (+72%), and a decrease in extracellular "secretory" peroxidase activity (-73%). The possible interaction between HRGPs and the ascorbate system in the regulation of both cell division and extension is discussed.
Karyotype structures and heterochromatin distribution in representative taxa of the genus Ophrys are compared, based on Feulgen-stained and banded somatic metaphase chromosomes. The karyotypes of Ophrys iricolor , O. lupercalis , O. caesiella , O. lutea , O. lunulata , O. x. tardans , O. apifera , O. praecox , O. lacaitae and O. insectifera are described for the first time. The karyological analyses indicate the relationships among the species with respect to asymmetry indices and heterochromatin content. Chromosomal differences have been helpful in clarifying the taxonomic position of Ophrys species that do not have clear affinities. The representative species of Araniferae , Fuciflorae and Ophrys sections exhibited the most asymmetrical karyotypes, while chromosome complements of the O. fusca-O. lutea group, of O. tenthredinifera and of O. bombyliflora proved to be less asymmetrical. Weakly heterochromatic chromosomes, with heterochromatin present mostly in thin centromeric bands, characterizeOphrys C-banded karyotypes. Chromomycin A 3 (CMA) staining revealed that the analysed species exhibit a weak pattern of CMA + bands at centromeric, intercalary or telomeric regions. No DAPI bright blocks were observed. The significance of the karyological data is discussed with regard to the relationships between the analysed species.
Giemsa C-banding is utilized for the first time to characterize eight taxa of the genus Serapias. Heterochromatin distribution indicated that the Serapzh species form a very homogeneous group. All the species possess chromosome pairs with similar heterochromatin patterns. Cbanding showed conspicuous bands located around the centromeres, w i t h some heterochromatic short arms. There was more heterochromatin in S. apulica and S. numka than in the other taxa. Extensive centromeric heterochromatin may indicate recent structural rearrangements in the chromosome complement. Taken altogether, karyomorphology indicates a rather recent origin for the genus Serapias, which might also account for the small amount of interspecific variation observed.
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