NUCLEAR AND GENOMIC CHANGES IN FLOATING AND SUBMERGED BUDS AND LEAVESOF HETEROPHYLLOUS WATERCHESTNUT (TRAPA NATANS)

The heterophyllous macrophyte waterchestnut (Trapa natans L.) produces floating and submerged leaves which are strikingly different in morph ology. In the present work, we compared, through cytological, cytochem ical and immunocytochemical analyses, the nuclear features of the shoo t meristem in floating and submerged buds that produce the different l eaves. The occurrence of DNA polymorphism in the two types of leaves w as studied by using the random amplified polymorphic DNA (RAPD) approa ch. The light microscope study of chromatin organization revealed an a rticulate structure of the nuclei, with prominent chromocentres in bot h floating and submerged buds. However, the meristematic nuclei of flo ating buds, as compared to those of submerged buds, displayed peculiar features which seem to be related to a higher proportion of A-T-rich sequences and a higher level of DNA methylation of the nuclear genome. Moreover, RAPD analysis showed polymorphism between the genomic DNAs of floating and submerged leaves. These results show that organs of an individual plant living in different environmental conditions undergo changes in genome organization which may predispose those organs to f unction more effectively in different environments.