HISTONES AND DNA ULTRASTRUCTURAL DISTRIBUTION IN PLANT-CELL NUCLEUS -A COMBINATION OF IMMUNOGOLD AND CYTOCHEMICAL METHODS

In this work we report for the first time the ultra-structural distrib ution of histones and DNA in the nuclear compartments in two different plant cell types: Allium cepa L. root meristems and Capsicum annuum L . microspores and pollen grains, by using antibodies against histones H2B and H4 and anti-DNA, Immunolocalizations were combined with ultras tructural cytochemistry for nucleic acids (methylation-acetylation met hod), DNA (NAMA-Ur) and RNPs (EDTA), to relate the subcellular locatio n of histones and DNA with the chemical subcompartmentalization of the cell nucleus. This is particulary interesting concerning the presence of histones or not on fibers of the interchromatin region and on the fibrillar components of the nucleolus, nuclear subcompartments where t ranscription has been shown to take place at some regions. Our methodo logical approach permitted to define precisely the structures where hi stones were detected in relation to the ultrastructural localization o f chromatin in various structural condensation levels. Concerning the localization of DNA and histones on the different components of the nu cleolus, the combination of immunogold labeling with the methylation-a cetylation cytochemical method, developed in our laboratory, was very useful, thus permitting a clear recognition of the nucleolar component s and a correct assigment of labeling, which is not always evident on uranyl-lead-stained Lowicryl sections. Double immunogold assays were a lso done for a simultaneous visualization of histones and DNA. Our res ults show a coincident distribution of histones and DNA on the same nu clear compartments revealing the presence of both antigens on condense d chromatin, fibers of the interchromatin region, principally located at the periphery of the condensed chromatin, and in the fibrillar comp onents of the nucleolus. (C) 1998 Academic Press.