Localization and activity of rRNA genes on fenugreek (Trigonella foenum-graecum L.) chromosomes by fluorescent in situ hybridization and silver staining

Fenugreek (Trigonella foenum-graecum L.), an annual legume crop grown mainl y for seed at present, has the potential to be a high-quality forage crop i n western Canada. A cytological survey of germplasm stored at the USDA germ plasm center demonstrated a somatic karyotype with a chromosome number of 2 n = 16. Structural details of two pairs of chromosomes (numbers 1 and 2) sh owed secondary constrictions that were presumed to be the site of rRNA gene s. Fluorescent in situ hybridization (FISH) with a heterologous rRNA gene p robe from wheat was utilized to physically map their location for the first time on fenugreek chromosomes. Strong hybridization signals of apparently similar copy-number sequences were detected primarily near the centromere o n the meta-centric chromosome 1 and near the telomere on the acrocentric ch romosome 2. Silver staining of the nucleolar organizing region provided evi dence that both the sites were transcriptionally active and independently c apable of forming a nucleolus. However, the site on chromosome number 2 was relatively more active than the one on chromosome number 1.