Karyotype analysis ofPsophocarpus tetragonolobus(L.) DC by chromosome banding and fluorescence in situ hybridization

Abstract

Detailed karyotype of Psophocarpus tetragonolobus (L.) DC was constructed on the basis of chromosome lengths, DAPI and CPD banding, silver staining, together with fluorescence in situ hybridization (FISH) with 45S and 5S rDNA sequences as probes. FISH of the 45S rDNA probe on mitotic chromosomes revealed three pairs of 45S rDNA sites including one major and two minors. The major pair of sites was located in the unique secondary constrictions of the satellite chromosome pair, while the minors were located on two pairs of non-satellite chromo- somes. For 5S rDNA, only one pair of sites was detected using FISH. Distinct DAPI and CPD banding patterns were shown simultaneously after combined PI and DAPI (CPD) staining. CPD bands were shown at all 45S rDNA sites and centromeric regions, suggesting the feature of GC-rich sequences in the centromeres. Each chromosome pair could be identified with DAPI and/or CPD banding patterns in combination with chromosome measurements. Sil- ver staining showed variable number of Ag-NORs on mitotic chromosomes, revealing that the major sites were active in every cell, while the minors were activated only in a proportion of the cells, and the level of expression differed between two pairs of minor NORs.