Interspecific variation of nuclear DNA and structural changes in meiotic and mitotic chromosome in some species of Mammillaria (Cactaceae)

摘要

Mitotic and meiotic chromosome number, karyotype, chiasma frequency in pollen mother cells, Interphase Nuclear Volume (INV) and nuclear DNA amounts in 12 species of Mammillaria revealed significant interspecific variations. Significant variations in chromosome structure, chiasma number per nucleus, pollen sterility, INV and 4C DNA were recorded among the species. Chromosome number 2n=22 and n=11 were recorded in all the species like M. armillata, M. asteriflora, M. bocasana, M. booli, M. bombycina, M. decipiens, M. geminispina, M. grandiflora, M. hahniana, M. plumosa, M sempervivi and M. woodsi Chiasma frequency varied from 1.722 in M. woodsi to 2.618 in M. plumosa. The formation of univalents in some of the cells and/or spindle anomalies lead to the formation of pentads, hexads or octads. Pollen sterility varied between 9.02% (M. decipiens) and 20.83% (M, bocasana). Cytophotometric estimation of 4C DNA content showed significant variation among the species (18.42 pg in M. booli to 26.46 pg in M. plumosa). INV varied significantly from 380.00 mu m(3) in M. grandiflora to 840.20 mu m(3) in M. booli. Chiasma frequency was positively correlated with chiasma per bivalent and 4C DNA content, moreover, the total chromosome length also correlated with chromosome volume. These results suggest evolution of Mammillaria through structural alterations of chromosome, chromosome duplication and translocations between the chromosomes. Significant variations in the DNA amount with gross or minor alteration of chisma frequency and karyotype variation leads to genetic drift between the species. [References: 32]