NATURAL VARIATION IN PATTERNS OF POLYSOMATY AMONG INDIVIDUAL TOMATO PLANTS AND THEIR REGENERATED PROGENY

Using flow cytometry, the patterns of polysomaty were determined in in dividual 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 it s own pattern of polysomaty. However, the percentages of nuclei at eac h C-level (1C = the DNA content after meiosis) varied greatly among in dividual plants, notably in cotyledons and transition zones. In the la tter organ, the percentages of 2C-nuclei ranged from 19 to 43%. When p lotted against the percentage of 2C-nuclei, the percentages of nuclei at other C-levels in leaf, cotyledon and transition zone fitted in a c ontinuous pattern. In agreement with this, the polysomaty patterns of some leaves with relatively high levels of polysomaty were identical t o those of the cotyledons with relatively low levels of polysomaty. Th e same was the case with some cotyledon and transition zone samples. T hese results might suggest developmental variation among the individua l organs. However, the polysomaty patterns of individual cotyledons di d not correlate with other parameters of development, such as the size of the organ, nor with the patterns of polysomaty in the leaf or tran sition zone of the same seedling. In first generation seedlings from p lants 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 distr ibutions of 2C-nuclei in the cotyledons. However, the second-generatio n progeny did not show any of these aberrations, and the standard devi ations of the second generation cotyledons were comparable to those of the control population. It is concluded that the deviations in the pa ttern of polysomaty can be due to unstable, epigenetic changes. The re sults are discussed in relation to the plasticity of the development a nd differentiation of individual organs.