DEVELOPMENT OF POLYSOMATY DURING DIFFERENTIATION IN DIPLOID AND TETRAPLOID TOMATO (LYCOPERSICON-ESCULENTUM) PLANTS

Polysomaty was found in all organs of tomato (Lycopersicon esculentum cv. Moneymaker) tested. The first endoreplications occurred in cotyledon and hypocotyl during germination (concurrent with cell elongation). Also the stem and leaves became polysomatic during development (cell elongation and expansion). Finally, new rounds of endoreplications marked the yellowing of the leaves (ageing), during which, in the leaf petiole, levels up to 128C were reached (1C is the DNA content of germ-line cells). Comparing diploid and tetraploid plants, the patterns of polysomaty were similar in four organs tested. The frequency of nuclei at the different C-levels in diploid cotyledons (2C, 51.6% of the nuclei; 4C, 39.0%; 8C, 8.6%; 16C, 0.8%) equalled the corresponding levels in tetraploid cotyledons (2C, 52.1%; 4C, 37.2%; 8C, 9.6%; 16C, 0.9%). Differences in growth and leaf expansion between in vitro- and greenhouse-grown plants were reflected in differences in polysomaty patterns between corresponding cotyledon and leaf tissues. These results indicate that polysomaty is genetically regulated as the number of endoreduplications taking place in the cells, and influenced by the actual growth pattern of the plant. As such, it may be considered as an integral part of the morphogenesis of a plant, from germination to ageing.