DNA content of colchicine-induced endopolyploid nuclei in vicia faba L.

Abstract

The relationship between ploidy level and nuclear DNA content was investigated by Feulgen microdensitometry in colchicine induced polyploid root-tip meristem cells of three Vicia species. Nuclear DNA content is expected to increase proportionately with the increase in ploidy, assuming DNA constancy. Our results showed that: (i) Absorption readings were significantly lower than expected for cells of higher ploidy levels. (ii) The deviation of the absorption readings obtained below those expected increased progressively with ploidy level. (iii) These trends occurred in absorption estimates of single metacentric chromosomes at metaphase in V. faba, metaphase nuclei in V. faba, and prophase nuclei in all three Vicia species. (iv) Loss of chromosomal DNA, as evidenced by a large and progressive increase in the frequency of occurrence of micronuclei in cells at higher ploidy level, was partly responsible for cell absorption estimates below expectation. (v) Variation in the density and in the absorbance of nuclear DNA may also have been a cause of absorption estimates below expectation. In our opinion, apart from the loss of chromosomal DNA to form micronuclei, it is unlikely that any real decrease in DNA content per genome occurred in cells at higher ploidy levels.