VARIATION IN THE RIBOSOMAL-RNA UNITS OF THE GENERA LENS AND CICER

Investigation of the organization of the tandemly repeated 5S and 18-2 5S ribosomal RNA (rRNA) genes was carried out on members of the genera Lens and Cicer using restriction endonuclease digestion and Southern hybridization. The 5S rRNA unit (gene + spacer) in Lens (0.38 to 0.50 kb) and Cicer (0.40 to 0.44 kb) is the largest among the legumes. In L . nigricans and L. culinaris ssp. odemensis a second repeat size was d etected. Restriction maps for the 18-25S units of Lens and Cicer speci es were developed. The 18-25S rRNA unit varied from 8.3 to 9.8 kb in L ens and 10.5 to 11.4 kb in Cicer. The only detectable variability in t he Lens and Cicer 18-25S rRNA unit was in the length of the intergenic spacer (IGS) region, except for a HindIII site in the IGS region of L . nigricans ssp. nigricans and in all Cicer species. Similarities in t he size of both 5S and 18-25S rRNA units were noted between L. culinar is ssp. culinaris and L. culinaris ssp. orientalis, which supports pre vious evidence that L. culinaris ssp. orientalis is the progenitor of the cultivated lentil. Differences in the arrangement of both 5S and 1 8-25S rRNA units were noted between L. nigricans ssp. nigricans and L. nigricans ssp. envoides, indicating either divergent evolution of the se subspecies or alternatively incorrect taxonomy. On the basis of the size of the 5S rRNA unit, C. bijugum, C. chorassanicum and C. echinos permum formed a group with a slightly smaller unit than the other Cice r species. Similarities in the length of both 5S and 18-25S: rRNA unit s of C. arietinum and C, reticulatum possibly confirm C, reticulatum a s the progenitor of C. arietinum. Cicer cuneatum has a smaller 18-25S rRNA unit than the other Cicer species as a result of a smaller interg enic spacer.