From previous work on mutant induction in maize with EMS, one ear was found which segregated for kernels with orange pigmentation in the pericarp (Neuffer and Chang, 1986). The segregation ratio was 15 normal to 1 orange, indicating duplicate unlinked factors (designated orp1 and orp2). These factors have been located to chromosome arm; orp1 on 4S and orp2 on 10L (Neuffer, Beckett and Wright, 1987). Since the pericarp is maternal, diffusion into the pericarp of a substance from the underlying filial tissue of the doubly homozygous recessive combination is implied. The pigmentation is restricted to the pericarp, suggesting that thesubstance which diffuses into the pericarp is not the pigment assuch but rather a colorless precursor which is converted afterentry into the pericarp. Plants from mutant kernels growpoorly, are somewhat adherent and have thus far died beforereproducing. The mutant kernels have a somewhat flouryendosperm, perhaps a secondary effect of the biochemical lesion. The research proposed is to biochemically characterize thismutant through the identification of the orange pigment andprecursor and through rescue by exogenous feeding. Linkage analysis of both factors will be undertaken as well as transposon tagging of the orp2 locus. Cloning and characterization of the locus and its message is the ultimate goal. Preliminary data suggest that this mutant could be a tryptophan auxotroph. If the biochemical characterization of this corn mutant supports that hypothesis, this will be the first true auxotrophic defined in a commercially important plant and as such, this work could have tremendous impact bothat a fundamental and practical level.
