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 cotyled on 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 mar ked the yellowing of the leaves (ageing), during which, in the leaf pe tiole, levels up to 128C were reached (1C is the DNA content of germ-l ine cells). Comparing diploid and tetraploid plants, the patterns of p olysomaty were similar in four organs tested. The frequency of nuclei at the different C-levels in diploid cotyledons (2C, 51.6% of the nucl ei; 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 greenho use-grown plants were reflected in differences in polysomaty patterns between corresponding cotyledon and leaf tissues. These results indica te that polysomaty is genetically regulated as the number of endoredup lications taking place in the cells, and influenced by the actual grow th pattern of the plant. As such, it may be considered as an integral part of the morphogenesis of a plant, from germination to ageing.