Cytophotometric Estimation of 4C DNA Content and Chromosome Analysis in Four Species of Astrophytum Lem. of the Family Cactaceae.

Abstract

Karyotype analysis including determination of somatic chromosome number, chromosome length and volume, 4C DNA content and Interphase Chromosome Volume (INV) were carried out in Astrophytum asterias, A. capricorne, A. myriostigma var. nudum and A. ornatum of the family Cactaceae. Somatic chromosome number was 2n=22 in each of the studied species. Karyotype analysis showed minute structural alterations in the chromosomes. Total chromosome length varied from 56.65 μM in A. myriostigma cv. nudum to 60.76 μM in A. ornatum and the chromosome volume ranged from 48.12 pM3 in A. ornatum to 66.95 μM3 in A. myriostigma var. nudum. Significant changes on the TF% suggested the formation of the median chromosomes from the sub-median types in A. asterias and A. myriostigma var. nudum that might be due to translocation of chromosomes during evolution. Significant variations in the 4C DNA content were noticed among the species which ranged from 9.23 pg in A. capricorne to 10.12 pg in A. myriostigma var. nudum. Total chromosome volume and INV showed high degree of correlation with the nuclear DNA content of the species. Interspecific variability of the nuclear DNA content might be due to the variations in the repetitive DNA sequences of the genome. The structural alterations in the chromosomes as well as loss or addition of highly repetitive sequences in the genome caused variations in the nuclear DNA at interspecific level indicating a micro-change of nuclear material during evolution.