The rea (red embryonic axis) phenotype describes a new mutation affecting the response of maize embryos to abscisic acid and osmotic stress

During a screen for mutants with defective germination, a new phenotype was observed consisting of red pigmentation of the embryonic axis in the dormant seed. Segregation ratios, as determined in F₂ and back-crossed progeny, indicate that the phenotype is due to a recessive single gene mutation that has been symbolized rea to denote red embryonic axis. A closer inspection of the rea phenotype revealed that the mutant is occasionally viviparous, indicating a defect in abscisic acid (ABA) metabolism. The mutation probably affects ABA sensitivity since no difference in ABA content was detected in mutant versus normal tissues. Moreover, when immature mutant and wild-type embryos were incubated on media containing 10 μM ABA, only the mutants germinated. ABA-regulated gene expression in rea embryos differed from that of embryos of the viviparous mutant vp1 which does not respond to the inhibitory action of ABA at the level of immature embryo germination. These results, therefore, indicate that the two genes exert a different role in the control of embryogenesis.