Studies on mode of separation of chloroplast genomes in parasexual hybrid calli. I. fraction I protein composition in unseparated hybrid callus

Abstract

The mode of chloroplast genome separation after cell fusion between Nicotiana glauca and N. langsdorffii protoplasts was studied by microscopic observation and iso-electrofocusing analysis of Fraction I protein obtained from somatic hybrid calli. Chloroplasts from one species of plant were observed to spread all over the fused cell at 48 h after cell fusion indicating that two kinds of chloroplasts were mixed together within the same fused cell. Analysis of Fraction I protein showed that 70% of the calli contained two kinds of chloroplast genomes and all contained two kinds of nuclear genomes. Reciprocal fusions between protoplasts from leaves of one species with protoplasts from suspension cultures of the other species also showed a majority of the calli to contain two kinds of chloroplast genomes. Selection of a small piece of the callus followed by further growth and further subdivisions and growth periods caused separation of one of the kinds of chloroplast genomes within the callus leading to the conclusion that the callus was already a mosaic of cells where elimination of one of the two kinds of chloroplast genomes had occurred in some cells. Thus, the separation of chloroplast genomes previously found in leaf cells of parasexual hybrid plants could have been the result of shoot differentiation having occurred in a very restricted region of a callus where cells had already undergone separation of the chloroplast genomes.