The occurrence of a high frequency of chromosome breakage in regenerated maize plants led us to speculate that transposable elements might be present. In crosses between regenerated plants and a Ds-containing tester stock, three cases of Ac activity have been found among 66 immature-embryo-derived cell lines (5%).

All cell lines tested in this study were derived from A188 or progeny of crosses of A188 and Oh43 or B73. Regenerated plants or their progeny (all c c) were used to pollinate stocks homozygous for C and Ds at its standard location in chromosome 9. The resulting ears were scored for the presence of colored kernels with colorless sectors, indicating breakage at Ds and subsequent loss of C. Potential cases of Ac were then retested onto c-m-2 to confirm the Ac activity. These tests have identified three cell lines which contain Ac, as summarized in Table 1.

It is important to test whether these embryos contained Ac before culturing. For embryos 4-41 and 1-42, a few seeds were available from the same ears used to initiate the cultures; also available was remnant seed from the parent rows. Twenty-three tests of these controls onto the Ds stock produced no variegated kernels. Our A188 sources were tested since they were involved in the parentage of the R_o plants; no Ac was detected in over 25 crosses. In addition, the fact that all three cell lines are heterogeneous for Ac indicates that the element was not present in the original embryos cultured. Further tests with regenerated plants and controls are in progress.

Table 1. Sumary of cell lines producing regenerated plants with Ac activity.

V. M. Peschke, R. L. Phillips and B. G. Gengenbach

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