7. Studies on purple and red aleurone pigments.
Field observations, paper chromatography, and anthocyanin color tests were used in a study of Pr and pr seeds and their pigments. Four widely differerent lines of each genotype were selected and grown in the field in 1950. As only distinct purple and red types were used, the results may not hold for all modifications of purple and red aleurone.
a. The color first appeared 23‑27 days after pollination. A distinct layer of aleurone tissue was present before the pigment appeared. In seeds just turning color, the inner endosperm beneath the colored aleurone area was usually firm, nearly hard; elsewhere soft and milky.
b. In agreement with the report of McClary (CNL, 1942), purple aleurone contains a cyandin derivative, red a pelargonidin derivative. Within the limits of the paper chromatographic method, it may be said that only one of the two pigments occurs in any one seed -- they are not mixed. Pr is chemically as well as phenotypically dominant -- only cyanidin occurs in seeds with one or more doses of Pr. It should be pointed out that the only chemical difference between the two pigments is the extra hydroxyl group on cyanidin.
c. Available evidence indicates that the naturally‑occurring pigments are 3‑monosides of the two anthocyanidins. There is suggestive evidence that these are complexed with one or more organic acids.
d. Intense red (pr in) aleurone apparently differs from dilute red only in concentration of pigment.
e. Color test for separation of Pr from pr seeds in questionable cases: (Cyanidin derivatives give a blue ferric reaction in dilute acid, pelar-gonidin derivatives do not). The pericarp is scraped off in a small area with a knife. The aleorone is scraped through in order to provide both ruptured cells and a white or yellow endosperm background against which to observe the colors. A very small amount of weak (about 1%) HCl is applied, and agitated slightly until the scarlet solution obtained shows that sufficient anthocyanin has dissolved. The change observed with the addition of a drop of solution is to a blue‑purple if Pr, indeterminate if pr. The test is not as clear as that for waxy, but comparison with known Pr or pr makes it satisfactory. It is suggested that the test might be used especially well in separating Pr from pr in. The writer would appreciate hearing of any aberrant results obtained with this test.
E.H. Coe, Jr. (Now Univ. of Illinois)