Extended centromere and chromosomal mosaicism in some varieties of grass pea, Lathyrus sativus L.

An abnormal mitotic behavior revealing chromosomal mosaicism was observed in two among the three studied cultivars (cv. Nirmal, cv. Prateek and cv. Ratan) of Lathyrus sativus. Several numerical variants of chromosome complement were detected in the different cells coexisted with normal diploid cells in the somatic tissue of the same root-tip. Somatic chromosome number 2n=14 were found with the greatest frequency (67%); however, a spectrum of quite low percentage of discordant and variable chromosome numbers especially of aneuploidy mode, ranging from 2n=11 (9.6%), 2n=12 (8.7%), 2n=13 (4.7%) and 2n=15 (10.3%) in Nirmal cultivar were observed. In Prateek cultivar, the most interesting cytological character is that karyotype though symmetrical but indicating transition between symmetrical to asymmetrical is slightly bimodal due to presence of one pair of very small chromosomes. In general, most of the chromosomes of all cultivars were nearly median centromered. Although the cv. Ratan shows the normal chromosome number, but in 4 pairs of chromosomes, the centromere region appeared unusually extended'. In Nirmal and Prateek cultivars karyotype, the secondary constriction is proximal on the short arm whereas, in some other metaphase plates, the same constriction bearing macrosatellite is on the long arm of bigger nearly submedian chromosome of pair one. We propose that the differences in satellite position arose by karyotype rearrangements; probably involving translocations. At the same time, extended centromeres may be due to the activities of retrotransposons at the centromere region of the said chromosome of cv.Nirmal.