Natural variation in patterns of polysomaty among individual tomato plants and their regenerated progeny

Using flow cytometry, the patterns of polysomaty were determined in individual organs of seedlings of tomato (Lycopersicon esculentum L. cv. Moneymaker). On average, each organ (i.e. leaf, cotyledon, transition zone from hypocotyl to primary root, and secondary root) displayed its own pattern of polysomaty. However, the percentages of nuclei at each C-level (1C = the DNA content after meiosis) varied greatly among individual plants, notably in cotyledons and transition zones. In the latter organ, the percentages of 2C-nuclei ranged from 19 to 43%. When plotted against the percentage of 2C-nuclei, the percentages of nuclei at other C-levels in leaf, cotyledon and transition zone fitted in a continuous pattern. In agreement with this, the polysomaty patterns of some leaves with relatively high levels of polysomaty were identical to those of the cotyledons with relatively low levels of polysomaty. The same was the case with some cotyledon and transition zone samples. These results might suggest developmental variation among the individual organs. However, the polysomaty patterns of individual cotyledons did not correlate with other parameters of development, such as the size of the organ, nor with the patterns of polysomaty in the leaf or transition zone of the same seedling. In first generation seedlings from plants regenerated from tissue culture, the extent of the variation in polysomaty had increased, especially in the cotyledons. Also, seedling populations of several regenerants displayed aberrant frequency distributions of 2C-nuclei in the cotyledons. However, the second-generation progeny did not show any of these aberrations, and the standard deviations of the second generation cotyledons were comparable to those of the control population. It is concluded that the deviations in the pattern of polysomaty can be due to unstable, epigenetic changes. The results are discussed in relation to the plasticity of the development and differentiation of individual organ