We are undertaking a genetical‑biochemical study of the development of the endosperm of maize, centering about the "indole cycle" involving tryptophane, auxin, niacin, protein and carbohydrate relationships. This study is based largely upon the findings in Neurospora together with some information available in maize and other plants. Tryptophane appears to be formed by condensation of indole and serine, and in turn to give rise, through one chain of reactions, to niacin, and through a very different chain, to auxin (indole acetic acid). It may also become a protein constituent. How general this pattern may be is not known but the maize story will undoubtedly bear a strong resemblance to this part of the Neurospora story. Some additional features are evident, however.
1. During the development of the maize endosperm, an extremely high concentration of indoleacetic acid is built up, with a peak about the late milk or early dough stages, then dropping down to a lower level during the latter part of the development. A minor portion of this is in the form of free or active auxin, the balance recoverable upon hydrolysis ("bound auxin" or "auxin precursor"). The total amount formed is so great that if it is produced from tryptophane, it would seriously deplete the amount of tryptophane available for conversion to niacin or for protein building.
2. The niacin content of corn is low compared with wheat and most other cereals, which is of special interest as niacin acts as a pellagra preventative.
3. Zein, the principal reserve protein of the corn endosperm is deficient in tryptophane as well as lysine. From published accounts of cereal chemistry it appears that zein is formed chiefly in the later stages of endosperm development. The earlier formed proteins, globulin and glutelin, are rich in tryptophane and lysine.
4. There is a clearly defined correlation between sugary texture of the endosperm and the niacin content (Barton‑Wright and Mather, Cameron and Teas), also a relation between the amylose‑amylopectin ratio and sugary genetic composition. The nature of these relationships is not clear.
5. Earlier work of Hixon, Sprague, and others have shown waxy starch to be composed entirely of amylopectin. Waxy corn also appears to have higher niacin content than the corresponding non‑waxy; also higher auxin content.
We plan to chart the normal development by assaying a series of stages from pollination to maturity to determine the quantities present of the related components, such as free auxin, total auxin, niacin, tryptophane, carbohydrate, protein, etc. Using this as the expected standard behavior, a survey will be made of a large number of endosperm types, differing from the standard by single gene differences, utilizing some of the known endosperm genes, and also a large selection of the numerous mutant endosperm types obtained from our studies on radiation effects. Those showing large departures from the standard will be studied further to determine, as best we can, the primary effect of the particular gene upon the indole cycle and the general consequences thereof. It is hoped that this will give us valuable information on the chemosynthesis of the tryptophane derivatives, which in turn may be of importance to our breeding program designed to increase the tryptophane or niacin content of commercial lines, or to modify the amylose ratio.
Assays for free auxin and total auxin have been completed for the ontogenetic stages of our standard normal (CC5/L317) and work is in progress on other series (Melvin Stehsel). Assays on niacin, carbohydrates, etc. are in progress on the same series (H. J. Teas, J. M. Cameron, Anna C. Newton). Sample assays of mature endosperm of several genetic types show that significant differences are to be expected. Favorable mutant endosperm types are being converted to the same general background as our standards and the bulk of our translocation lines.
H. J. Teas, Anna C. Newton, Melvin Stehsel, S. G. Wildman (Plant Physiology)
J. M. Cameron (Riverside Station, University of California)
Earl B. Patterson, D. S. Robertson, A. E. Longley, and E. G. Anderson