IS REPETITIVE DNA INVOLVED IN MALE GAMETOGENESIS OF NARCISSUS-PAPYRACEUS

The male gametophyte of the Spermatophyta is of particular interest wh en studying quantitative modifications of repetitive DNA which accompa ny plant differentiation. In fact, this well documented system offers the opportunity to investigate the phenomenon at the nuclear level. In particular, it permits comparison between single haploid nuclei which , though derived from the same mitotic division, have different, well- defined morphological and functional processes. The aim of the present work was to investigate the behaviour of repetitive DNA during male g ametogenesis in Narcissus papyraceus. By the use of A + T and G + C sp ecific fluorochromes (DAPI and Chromomycin A3), and by in situ DNA dig estion with appropriate restriction endonucleases (Eco RI star and Hae III), it is shown that during the course of gametogenesis, generative and vegetative nuclei behave differently with respect to particular s ections of the genome. Characteristic agglomerations of specific A + T rich DNA sequences can be observed, localized by the two distal ends of the spindle-shaped generative nucleus. The surface area occupied by the agglomerations differs significantly at the ends in all observed cases. The above agglomerations are present in most of the generative nuclei and are probably composed of repetitive DNA sequences. Some emb ryological questions are discussed in the light of these results.