Nucleotype and phenotype in Vicia faba

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Following the results of a previous investigation which showed significant differences (up to 34.6 per cent) in the basic amount of nuclear DNA between local populations of Vicia faba, the development of plants obtained from seeds collected from different populations was studied. Both cell proliferation in the meristems and cell enlargement in differentiated tissues are affected by the genome size. DNA content and the mitotic index in the root meristem are negatively correlated. The higher proportion of cells entering mitosis in the meristems of plants with a lower amount of DNA is not the result of alterations of the duration of the mitotic cycle, which was found to be quite comparable in two populations with largely differing genome sizes. Cell growth was studied in the epicotyl cortex and the leaf epidermis. In both differentiated tissues, cells were longer or had larger surface areas in populations with higher amounts of DNA than in populations with lower amounts of DNA. By studying plant development, positive correlations were found between the genome size and both the germination power of the seeds and the growth rate of the epicotyl. In contrast, negative correlations were found between the basic amount of nuclear DNA and both the height of the main stem and the fresh weight of plants at anthesis. The possible role that intraspecific alterations of the nucleotype may play in environmental adaptation and species evolution is briefly discussed.