Organisation du génome et étude palynologique de quelques espèces algériennes du genre Centaurea L.

Abstract

For a better knowledge of the Algerian flora and in order to assess the interspecific variability and genomes organization, a cytogenetic and palynological study was conducted for the first time on four Algerian species belong the genus Centaurea. Three of them are endemics, by chromomycin fluorochrome banding for GC-rich DNA distribution, fluorescence in situ hybridization for physical mapping of rRNA genes, flow cytometry for genome-size assessment, light and micron microscopy for pollen morphology. Investigated species belong to three different sections and possess three basic chromosome numbers: C. tougourensis subsp. tougourensis 2n=4x=36 (x= 9), C. musimonum 2n= 2x= 20 (x= 10), C. maroccana 2n= 2x=24 (x=12) and C. melitensis 2n= 2x=24 (x=12). The number and distribution of chromomycin positive bands (CMA3) and 18S-5.8S-26S (35S) rDNA loci were different among investigated species and ranged from 6 to 80 chromomycin bands and from 2 to 6 35S rDNA loci. The four species have just one 5S rDNA locus at intercalary position on a separate chromosome pairs, except in the case of C. musimonum in which both rDNA loci were localized on the same chromosome. All rDNA loci were co-localized with CMA3 bands, except three 35S in C. musimonum. Genome size ranged from 2C=1.47 pg to 2C=2.86 pg in diploid species (C. melitensis and C. maroccana, respectively) and to 2C=4.51 pg in tetraploid C. tougourensis subsp. tougourensis. The palynological properties of the four species were investigated for the first time. Polar diameter, equatorial length, apertures and thickness of the exine were measured in detailed. The light and scanning electron microscope investigations revealed tricolporate, prolate-spheroidal pollens. Exine ornementation was tectatae and microechinate. The investigated species pollens belong to Jacea- type. Further invertigations of other Algerian species of the genus Centaurea are required as a study project to contribute to the understanding of biodiversity and enrich databases.