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

Abstract

SUMMARYThe relationship between ploidy level and nuclear DNA content was investigated by Feulgen microdensitometry in coichicine 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.

Genome downsizing in polyploid plants

“…Furthermore, there are examples in which the effect of increased DNA density has not been shown to be responsible for the reduced DNA amounts observed in the polyploids relative to the diploid progenitors (Seal, 1983). Thus, although technical errors may influence C‐value estimations in polyploids (Greilhuber, 1988), especially those studies that do not employ recommended best practice, careful studies where appropriate attention has been paid to methodology (Bennett & Jellings, 1975) argue against technical errors in estimating DNA amounts as being the main cause of the widespread loss of DNA observed in polyploids.…”

Nuclear DNA amounts in angiosperms

“…For example, several workers have noted th at the accuracy of DNA measurements by microdensitometry is markedly influenced by nuclear DNA density. To be specific, DNA am ount tends to be underestim ated as the DNA density increases (M ittwoch 1969;V erm a & Rees 1974;Bennett & Jellings 1975). This error is of particular im portance in species containing a large proportion of heterochrom atin in their genome (N arayan & Rees 1974).…”

Genome variability of plant somatic cells. 1. Variability during ontogenesis

“…У ряда растений увеличение числа хромосом приводит к некратному (более низкому) возрастанию количества ДНК. Это явление наблюдается как у естественных полиплоидов, так и у полиплоидных растений и клеток, полученных в эксперименте [164][165][166][167][168]. В некоторых случаях при неиз менном числе хромосом количество ДНК может возрасти либо много кратно за счет образования политенных хромосом, либо в меньшей степени, в частности, из-за амплификации.…”