Letter: Overlooked avian oncornavirus in cultured muscle--functionally significant?

With respect to the maternally inherited large subunit of fraction I protein, Chen et al. (1) found that Triticum boeoticum and T. urartu had identical polypeptide patterns, and Aegilops speltoides had a different one identical with that of the tetraploid wheats. From this evidence they inferred that Ae. speltoides. but neither T. boeoticum nor T. urartu, could have been the maternal parent of the tetraploids. The evidence was obtained from a single accession (the progeny of a single plant) per species, and rests on the tacit assumption that there is no variation within species with reference to the large subunit pattern. In support of that assumption Chen et al. refer to data (2) showing no variation in the large subunit pattern among six accessions of Nicotiana glauca and nine of N. tabacum. Nevertheless, the basic assumption is questionable. It requires that large subunit mutations presumed to distinguish one species from another within a genus (in this case Ae. squarrosa from Ae. speltoides) cannot occur within a given species. One accession of Ae. speltoides suffices to show that it could have been the maternal parent of the tetraploids. but one accession of T. boeoticum is inadequate to show that it could not have been the maternal parent. Our evidence from 742 reciprocal crosses (3) shows that if T. boeoticum and T. urartu are, in fact, the parents of the tetraploids (4). then T. boeoticum must be the maternal parent. Triticum urartu carries a cytoplasmic lethal factor which results in nonviable seed when it is used as the maternal parent in crosses with T. boeoticum or the tetraploid species. B . LENNART JOHNSON Department ofPlant Sciences, University of California, Riverside 92502