In the sexual interspecific cross,Nicotiana rusticaL.xN. tabacumL.,N. rusticacan serve as the female but not as the male parent. By fusion of protoplasts, the barrier to fertilization was overcome and somatic hybrids containingN. tabacumcytoplasm were produced as shown by isoelectric focusing of the Fraction-1 protein (F-1-protein). All somatic hybrids displayed polypeptides of the large subunit of F-1 protein (which is coded by the chloroplast genome) characteristic of only one or the other parental species. Two hybrids had large subunits of theN. tabacumtype and two hybrids had those of theN. rusticatype. Three hybrids contained three smallsubunit polypeptides (coded by the nuclear genome), one being characteristic ofN. rustica, one characteristic ofN. tabacum, and one with an isoelectric point common to both species. A fourth hybrid contained only two small-subunit polypeptides of theN. tabacumtype but in a F-1 protein macromolecule whose large subunits were of theN. rusticatype. One somatic hybrid was self-fertile and its F2progeny contained large- and small-subunit polypeptides indistinguishable in their isoelectric points from those in the parent F1hybrid. All somatic hybrids showed an aneuploid chromosome number and morphological characteristics intermediate between those ofN. rusticaandN. tabacum.
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