Establishment of somatic hybrid cell lines between Zea mays L. (maize) and Triticum sect. trititrigia MacKey (trititrigia)

Somatic hybrid cell lines were constructed by the fusion of protoplasts isolated from cell suspensions of Zea mays L. (maize, 2n=20) and Triticum sect. trititrigia MacKey (trititrigia, 2n=35), a perennial hybrid of Triticum durum Desf. and Elytrigia intermedium (Host) Nevski. Iodoacetamide-inactivated protoplasts of maize were fused with trititrigia protoplasts, which were sensitive to the PEG/DMSO fusion treatment at high pH and high calcium. Based on physiological complementation, approximately 0.002% of the total protoplast cultured following fusion treatment developed into cell colonies, and 79 lines of them, almost a half, were singled out and subcultured. Among the subcultured lines three were, in comparison with the parents, identified as somatic hybrids by their coupled Xba1 restriction patterns of total DNAs probed with the ribosomal DNA of rice. Southern analysis of the digested total DNAs with a mitochondrial gene, atpA, from pea, or a chloroplast gene, trnK, from rice, revealed that all the hybrids carried only the organellar DNAs of trititrigia, which excluded the possibilities of a chimeric callus or any DNA contamination. Cytogenetically, one hybrid was mixoploid with a 2n of 46-67 in which chromosomal endoreduplication, characterized by the appearance of diplochromosomes, was occasionally observed. Its hybridity was reconfirmed by the fact that it bore the satellite chromosomes of both maize and trititrigia, which were distinguishable from each other by size. In contrast, the other two hybrids were aneuploids. The potential of gene transfer between Zea and Triticum species was thus conclusively established.