Abstract
A detailed cytological and cytochemical investigation involving determination of somatic chromosome number, karyotype, total chromosome length, volume and estimation of 4C nuclear DNA were carried out in 9 different species and varieties of Agave. Of the nine species studied, five belonged to diploid level with 2n=60 chromosomes and the rest were triploid, tetraploid, pentaploid and hexaploid having 2n=90, 120, 150 and 180 chromosomes respectively. Inspite of a distinct bimodal karyotype with very long and very short chromosomes in the 5: 25 ratio and a constant base number of n=30 chromosomes featured in the detailed karyotype analysis, each species has got its own distinct karyotype, differing from the rest in minute details. The total chromosome lengths and volumes differed both within and outside the same ploidy level and the volume did not necessarily increase with the increase in chromosome number.
The amount of 4C nuclear DNA, estimated through Feulgen microspectrophotometry and expressed in arbitrary unit of relative absorbances, did not show much variations in the diploid species, while the triploid species revealed slightly lesser value than that of one specific diploid species. The difference in the amounts of nuclear DNA was insignificant amongst the pentaploid and hexaploid species as compared to the difference of their chromosome numbers. No direct correlation could, however, be established between the cytological parameters and the amounts of nuclear DNA. On the basis of overall analysis, the influence of structural alterations in affecting the amounts of nuclear DNA as well as other cytological characters from diploid to hexaploid level has been suggested.
