DNA CONTENT, INTERPHASE AGNOR-AREA, NUMBER OF (3)HRDNA HYBRIDIZATION SIGNALS AND THE METHYLATION LEVEL IN CODING RDNA SEQUENCE IN DIFFERENTORGANS OF LUPINUS-LUTEUS L

Nuclear DNA and AgNOR-area quantity have been measured cytophotometric ally, the number of silver grains after in situ H-3 rDNA/DNA hybridiza tion has been counted, and the level of rDNA methylation has been esti mated in root meristems, differentiated root zones, hypocotyls, cotyle dons, and leaves of 7-day-old seedlings of Lupinus luteus. DNA content increases by endoreplication, reaching the average DNA C-value of 4.2 , in the meristem, 6.6C in hypocotyl, 15.9C in cotyledon, and 3.3C in leaf. The quantity of AgNOR-area, the highest in root meristem, does n ot follow DNA C-value. Number of grains after in situ H-3 rDNA/DNA hyb ridization corresponds to DNA amount, but their distribution differs, showing in many cases perinucleolar localization in organs displaying low AgNOR-area quantity. Southern hybridization has not demonstrated d etectable changes in level rDNA methylation. We suggest that the low l evel of rDNA expression in non-meristematic tissues could be related t o rDNA inactivation caused by its translocation into nucleolus-associa ted heterochromatin.