C-I and light

The C-I allele exhibits a dosage effect. McClintock (Carnegie Yearbook 50:174-181) showed that extra doses of C could overcome the inhibitory action of C-I. Kyle and Styles (MNL 47:181-83) showed that immature seeds competent genetically for pigment synthesis, removed from the ear and placed in germinating conditions, showed increased rates of pigment synthesis and developed more pigment if the seeds were germinated in the light rather than in the dark. Thus it seemed possible that the C allele could be given a competitive boost against C-I action if mature seeds were germinated in the light. The results are shown in Table 1; G86 has the other factors (besides C) required for scutellum pigmentation. Light is effective in boosting the C allele expression with respect to the C-I allele. This is seen most strikingly when the pigment levels in the scutellum and endosperm of G85 x G86 are compared. The endosperm of these seeds is only faintly colored (+), whereas the scutellum is darkly pigmented; this is probably due to the fact that the dosage ratio of C-I to C in the scutellum is 1:1, whereas in the endosperm the ratio is 2:1. These seeds develop no more pigment if germinated in the dark.

The c-p allele is apparently not equivalent to C in competitive ability against the action of C-I. When c-p/c-p/C-I seeds are germinated under light a few pigmented spots become visible (C-I somatic losses) but no additional pigment forms.

Table 1.

Sheila McCormick

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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