A study of nucleolar organizers in lentil using FISH and spore quartet analysis

Abstract

The number of nucleolar organizing chromosomes in lentil (Lens culinaris Medik.) was ascertained using classical and molecular cytogenetic approaches, since in an earlier report, only one pair of nucleolar organizing chromosomes was resolved by FISH, although 1-3 nucleolar organizing chromosomes were reported in literature. During the present study, data on the number of nucleoli per cell in the normal lentil material (cv. PL639) was recorded at diakinesis and spore quartet stages of meiosis, and the number of bivalents associated with nucleoli were recorded at diakinesis. Use of a ribosomal DNA probe (pTa71) for FISH revealed only one pair of nucleolar organizing chromosomes on mitotic metaphase chromosomes (as also reported in an earlier study), but at spore quartet stage, 2 signals were observed in a spore (presumably due to decondensed state of chromosomes), suggesting the presence of 2 nucleolar organizing chromosomes. An interchange heterozygote,which had a nucleolar organizing chromosome involved in the interchange, was also used in this study; although at mitotic metaphase, only one pair of nucleolar organizing chromosomes was resolved by FISH, at spore quartet stage, frequencies of nucleoli per spore suggested the presence of 2 nucleolar organizing chromosomes. Taken together the results suggested that in the lentil material used in the present study, there are at least 2 pairs of nucleolar organizing chromosomes.