During the past growing season we screened several new defective kernel mutants as well as a group of such mutants previously identified as promising mutants in our search for auxotrophs. Two of these mutants showed superior growth on enriched medium with little or no growth on basal medium when immature embryos were cultured as previously reported (Sheridan and Neuffer, 1980, 1981). Both of these mutants (E1054 and E1532) proved (as did the previously studied mutant E1121) to require proline as a sole supplement and to be allelic to the pro-1 mutant of Gavazzi et al. (1975) and located on chromosome arm 8L. After several years of screening, in which 108 mutants have been examined by embryo culturing we have found three proline-requiring mutants in our collection of EMS induced defective kernel mutants (Neuffer and Sheridan, 1980) and all three are allelic to pro-1. None of the other 105 mutants have proven to be auxotrophs. We believe that our screening procedure works in detecting auxotrophs and that the single-gene, recessive, defective-kernel mutants may not contain auxotrophs (except for the proline requiring mutant). It seems likely that auxotrophs occur and one possible explanation for our general lack of success is that they may require the mutation of two different loci for their expression. We have begun work on the analysis of defective kernel mutants displaying a 15:1 segregation ratio on self-pollinated segregating ears.
William F. Sheridan and M. G. Neuffer
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