3. Gene action in the Rg mutant.
An investigation of the action of the Rg gene upon the growth and development of maize plants has yielded an abundance of data from which a few observations are cited below.
Thero are indications that the action of the Rg gene produces different end effects in plants grown under varied environmental conditions. Much of the material for this developmental study was grown in the greenhouse (from germination to maturity, both by liquid culture techniques and in large clay pots of soil). We find that progeny from Rg/rg stock (both cross- and self‑pollinated) show no lethality under greenhouse conditions. Neither was zygotic mortality observed in these Rg/rg x Rg/rg crosses. These results are in contrast to those reported by Brink and Senn (Jour. Heredity 22:155‑161. 1931) obtained from plants grown under field conditions.
By examining each leaf of the progeny 1‑2 times daily until maturity was reached, the first visible manifestations of the character were determined and the extent and progression of "ragged" was recorded. Certain progeny (of the inbred Rg/rg stock) always showed the character earlier and exhibited it to a greater degree. It is believed that these plants are homozygous for the Rg gene. Segregation ratios also support this idea, although owing to the number of plants grown (a total of 256 plants) we cannot, at present, be certain of this. Viability and pollen production of these "early ragged" seedlings (early as compared to the time of ragged manifestation by Rg/rg stocks) appears to be good, although in many cases these plants are female sterile. If, in the course of further investigations, these "early ragged" seedlings prove to be homozygous for the Rg gene then here is another example of a dosage effect, in that a “double dose" of the Rg gene results in an earlier initiation of gene action and/or a more widespread action.
It has been pointed out elsewhere (Meriele, Amer. Jour. Bot., February, 1950) that the initial anatomical manifestation of the Rg character is expressed early in the developing leaves by a "plasmolytic-like shrinkage" of the protoplasts of certain cells followed by a cytolysis of these cells. It was further suggested (from the appearance of cells surrounding a cytolysed area) that a diffusable substance may be the product of the Rg gene action. Additional physiological investigations are now in progress to inquire further into the nature and mode of action of this diffusable substance which may be produced by the Rg gene action.
Leo W. Mericle