Isoelectric-focusing analysis reveals that zein is composed of several polypeptides with a very large variability between lines (Soave et al., 1976, Maydica 21:61-75). F1 kernels obtained by crossing inbred lines with different zein patterns show additivity and dosage effects in reciprocal crosses (Righetti et al., 1977, in Tech. Sep. Barley and Maize Prot.).
Analysis of advanced hybrid generations can furnish information on the number of factors controlling zein heterogeneity. Therefore 24 F5 ears from a single cross hybrid (33-16xM14) were analyzed by the IEF technique. Seven ears which clearly showed IEF hybrid patterns were further analyzed on single kernel basis in order to detect residual heterozygosis. A sample of 20 kernels for each ear was considered.
In the figure IEF patterns of the parental lines, of F1 and of the seven F5 ears given refer only to those bands in which the two parents differ. Only two F5 lines revealed a fixed pattern, while the other showed segregation between kernels. On the basis of these results it can be concluded that there are at least three different groups of genes which control zein IEF heterogeneity. This conclusion agrees with other recent results indicating chromosomal localization of factors controlling the synthesis of zein bands (Soave et al., 1978, T.A.G. 52:263-267; Valentini et al., 1978, in press).
By means of TB-A translocations it was possible to locate a factor for zein band no. 13 on the short arm of chromosome 4. This segment analyzed with TB-4S in different genetic backgrounds (OH-43, N.25) was shown to contain factors controlling the expression of bands 4, 8, 12 and 14. Thus a group of zein genes is located in the short arm of chromosome 4.
E. Ottaviano and C. Soave
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