--V. M. Peschke, R. L. Phillips, and L. Pritchard
As part of our studies on the activation of transposable elements in tissue culture, we have tested a large number of regenerated plants for Spm activity. We had previously observed that Ac activity could be detected in 3% of the tissue culture-derived plants tested, even though no active Ac elements were present in the explant sources (Science 238:804, 1987). Evola and coworkers (11th Ann. Aharon Katzir-Katchalsky Conference, 1984; 1st Intl. Cong. Plant Mol. Biol., 1985) have also reported the activation of both Ac and Spm in tissue culture-derived materials.
Approximately 500 R1 progeny of 144 regenerated plants were crossed as males onto a c-m(r) tester stock (kindly provided by P. Peterson). The regenerated plants were derived from 62 embryo cell lines, and had been obtained from C. L. Armstrong (Crop Sci. 28:363, 1988) and M. Lee (Genome 29:122, 1987; Genome 29:834, 1987). Based on the testcrosses, Spm activity was observed in two progeny of one regenerated plant, designated 283(1), from Armstrong's material. This plant had been regenerated from Type II (friable embryogenic) callus of an A188 X B73 genetic background after approximately eight months in culture.
As shown in Table 1, 20 tests of three other regenerated plants from the same embryo cell line were negative for Spm activity. This indicates that Spm activity arose during callus growth or plant regeneration and was not present in the embryo used to initiate the callus. Thirteen tests of the inbreds A188 and B73 were also negative for Spm activity.
Table 1. Testcrosses of plants regenerated from cell line which produced
Spm activity.
| Progeny tests | |
| Regenerated plant | Positive:Negative |
| 283 ( 1 ) | 2:2 |
| 283(2) triplet 1 | 0:3 |
| 283 (3) | 0:7 |
| 283(4) twin 2 | 0:10 |
Nearly all of the material tested in the present study had previously
been tested for Ac activity. Plant 283(1) had been used directly
in a testcross for Ac activity, which was negative. Likewise, progeny
of seven regenerated plants which contained Ac activity were tested
for Spm in the present study and in a previous smaller study (Peschke,
M. S. thesis, 1986); all of these tests were negative as well. In addition,
the Ac and Spm activities were detected in plants from different
culture types (Type I vs. Type II), culture media (modified MS vs. N6 +
proline), and genetic background (Oh43 X A188 vs. A188 X B73). This indicates
that activation of transposable elements in tissue culture may occur under
varying conditions and is not limited to a specific culture environment.
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