NUCLEOTYPE AND PHENOTYPE IN VICIA-FABA

Following the results of a previous investigation which showed signifi cant 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 diff erentiated tissues are affected by the genome size. DNA content and th e mitotic index in the root meristem are negatively correlated. The hi gher proportion of cells entering mitosis in the meristems of plants w ith a lower amount of DNA is not the result of alterations of the dura tion of the mitotic cycle, which was found to be quite comparable in t wo populations with largely differing genome sizes. Cell growth was st udied in the epicotyl cortex and the leaf epidermis. In both different iated tissues, cells were longer or had larger surface areas in popula tions with higher amounts of DNA than in populations with lower amount s of DNA. By studying plant development, positive correlations were fo und between the genome size and both the germination power of the seed s and the growth rate of the epicotyl. In contrast, negative correlati ons were found between the basic amount of nuclear DNA and both the he ight of the main stem and the fresh weight of plants at anthesis. The possible role that intraspecific alterations of the nucleotype may pla y in environmental adaptation and species evolution is briefly discuss ed.