Modifying the tissue specific expression of some R alleles --E. Derek Styles In last year's News Letter (p. 124) I described how the expressions of R alleles may be limited, enhanced or modified by factors other than the so-called complementary genes. This is a follow-up to that article, reporting on the expression of some R alleles in the presence of a3 and/or Pl.

R-mb: a) with A3 and pl (normal for W22 lines) and b: marbled aleurone, slight pigment in coleoptile tip, green plant otherwise, including anthers; b) with b, a3 or Pl: similar to above except that the anthers have scattered pigment, distributed more or less longitudinally.

R-scm ('self-color' mutations from R-mb): a) with A3, pl and b: full colored aleurone, but otherwise similar to R-mb in plant color; b) with b, a3 or Pl: scattered pigment in anthers with either a3 or Pl. Red plant tissues with a3.

R-nj: a) with A3, pl and b: aleurone pigment mostly in crown, red seedlings, anthers and silks, some glume and brace root pigment, otherwise green plant; b) with a3 and Pl: aleurone, seedlings, anthers and silks as above, sheath edges and leaf midribs pigmented, cherry pericarp.

R-nj-6 (a compound allele derived by R. A. Brink from R-st:nj (stippled crown)): a) with A3, pl, and b: uneven aleurone pigment, mostly in the crown, green plant and anthers; b) with Pl: aleurone pigment as above, green plant, but red anthers. a3 Pl combination to be tested next year.

The above information on the Navajo alleles supplements our report on these alleles in the 1973 News Letter (Kyle and Styles, MNL 47:184) where we noted that the pericarp of developing R-nj:Cudu and R-nj-6 seeds developed pigment when the seeds were removed from the cob and placed under light.

The point in reporting on the expressions of these R alleles is to re-emphasize the point I tried to make last year, i.e., if R is a 'regulatory locus', it is important to recognize those factors that can regulate the regulator. Beyond differences that can be demonstrated when different alleles are compared against a common genetic background are differences that can be demonstrated only when different alleles are compared against different genetic backgrounds. Thus some alleles seem to increase the limits of their tissue specific activities with a3 and/or Pl, whereas others do not. What part of the locus is responding? What is the difference between those alleles that respond and those that do not? And is the response simply that of boosting a subliminal capacity, or is it creating or releasing a different tissue specific potential?

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