Genome size variation in Vicia faba

Abstract

Findings obtained using different approaches indicated the occurrence of genomic size variations within V. faba. Significant differences in the basic amount of nuclear DNA (up to 34.6 per cent) between 39 local populations collected from the Mediterranean Basin were observed by means of Feulgen/DNA cytophotometry. By contrast, no difference in genome size was found when five commercial varieties were compared. Dot blot hybridization of FokI V. faba repeats to genomic DNAs showed up to fourfold differences in the redundancy of these sequences in the nuclear DNA of different accessions. In agreement with the cytophotometric findings, a significant, positive correlation was determined between the DNA contents of populations and the copy numbers of DNA sequences related to FokI repeats. Significant differences between accessions were found in the length of the chromosome complement at metaphase, and these differences were particularly apparent in certain chromosome pairs. A positive correlation was found between the length of the complement and the genome size of the populations. These results are discussed in relation to other data in the literature on intraspecific nuclear DNA changes.Keywords: DNA cytophotometry, FokI DNA sequences, intraspecific DNA changes, karyometry, repetitive DNA, V/cia faba. tntroduction Today, there is a growing consensus of opinion that proliferation or deletion of nuclear DNA sequences does not occur only in the case of divergence and evolution of species. Indeed, many results obtained in different materials have shown that fluid domains, which are capable of rapid quantitative changes, may exist in the genome. These DNA domains, which are generally made up of repeated sequences, possibly occur more commonly, and express their ability to vary more frequently, in plant genomes than in animal genomes (reviewed for plants by Walbot & Cullis, 1985;Cionini, 1989; Bassi, 1990; Cullis, 1990; NagI, 1990).Redundancy variation of DNA sequences may accompany certain developmental processes. It has been suggested that they play a regulatory role in development (Frediani et a!., 1994 and references Because they may be of great biological importance and since many of their aspects are poorly understood, the above-mentioned genomic changes deserve thorough investigation. These changes have been shown to occur in many plant species (see Cavallini & Natali, 1991 show redundancy variations in Helianthus annuus (Natali et al., 1993), while quantitative differences in the nuclear DNA between populations of hexaploid Festuca arundinacea are mainly the result of changes in a fraction of highly repeated sequences (Ceccarelli et a!., 1992). The chromosomal organization of varying DNA sequences, as well as the mechanism by which intraspecific alterations in genome size and organization are produced and controlled, are almost entirely unknown.We investigated the nuclear DNA changes in Vicia faba by studying a number of local populationscollected from the Mediterranean Basin. Results are reported of DNA cytophot...

Nucleotype and phenotype in Vicia faba

“…Each point is the mean of the values obtained by analysing the root meristems of five seedlings obtained from seeds of two local populations of Vicia faba differing in genome size: accession 106367 from Algeria (a) and accession 106858 from Greece (.). Their DNA C-values are 14.29 pg and 11.28 pg, respectively (Ceccarelli et al, 1995). during the first 3 weeks after seed germination.…”

“…The correlation between the mitotic index in the the redundancy of repeated DNA sequences in fluid genomic domains (Ceccarelli et al, 1995), correlate negatively with cell proliferation in the meristems (Fig. 1) and positively with cell enlargement in differentiated tissues (Fig.…”

“…Moreover, the existence of significant correlations between DNA content and plant characters found by studying a number of populations (Figs 1 and 4-7) clearly excludes genetic diversity between them of another kind as responsible for the observed changes in development. Differences of 5-10 per cent in the basic DNA amount may be sufficient to determine changes in the nucleotype expression (Price, 1988), and the genome size may differ up to 34.6 per cent between local populations of Vfaba (Ceccarelli et al, 1995).…”

“…Seeds of 30 local populations of Vicia faba (kindly provided by the Istituto del Germoplasma, CNR, Ban, Italy) with known genome size (Ceccarelli et a!., 1995) were washed in tap water and allowed to germinate in damp vermiculite under sterile condi-…”

“…Changes in the redundancy of repeated DNA sequences, particularly of tandemly repeated FokI elements about 60 bp in length, were proven to be involved in genome size alterations. FokI repeats were found to represent up to 9.47 per cent of the V faba genome and their copy number was shown to vary in the accessions studied from 21.51 x 106 to 5.39 x 106 (Ceccarelli et at., 1995).…”