Genetics 5(6): 543-610 (1920)
Genetic Studies on the Protein Content of Maize
E. M. East and D. F. Jones
p. 606
Table 36
Effect of crossing and selection upon protein content. Analysis of selfed ears from high-protein crossed ears in 1916. Plants grown in 1917.
  C23 x B20 A26 x B2 A22 x B2 D27 x AI5 B20 x DI5 B2 x A4 A36 x D18 A28 x D21 A10 x D2 B41 x A46
Percent protein, seed parent 1916 18.16 16.21 15.23 16.33 18.35 18.57 17.85 15.81 15.41 16.15
Percent protein, pollen parent 1916 18.35 18.57 18.57 17.43 15.28 14.77 15.21 16.26 16.55 15.71
Average, parents 1916 18.26 17.39 16.90 16.89 16.82 16.67 16.53 16.04 15.98 15.93
Percent protein offspring selfed 1917 17.59* 15.31 15.53* 14.31 16.05* 15.99 14.66 16.75* 16.25 16.53
  17.25* 14.63 15.17 13.23 15.99 15.12 14.47 15.39 15.65 13.43
  16.93 14.04 14.99 12.01 15.64 15.01 13.82 15.67 13.89 13.11
  16.52 13.60 14.88 11.01 15.61 13.37 13.27 15.42 13.74 12.65
  16.39 13.42 14.78 10.47 25.58 13.36 13.32 14.71 12.37 11.95
  16.25 14.95 14.45 8.89 15.48 13.42 13.18 14.58 12.16 11.92
  16.18 12.94 14.26   15.23 12.89 12.76 14.57 12.13 11.90
  16.09 12.72 13.10   15.02 11.04 12.14 14.22 11.96 11.27
  16.00 12.08 12.44   14.91 10.85 11.79 13.92 10.53 10.65
  13.90 10.58 11.60   14.72 9.87 9.20   9.58 10.32
Average offspring 1917 16.31 13.43 14.12 11.65 15.42 13.09 12.86 15.05 12.83 12.37
Ordinal relation 1917 1 5 4 10 2 6 7 3 8 9
% Decrease in protein 10.63 21.32 14.97 30.06 9.16 24.24 24.13 6.09 19.03 22.66
*Selected for planting 1918.
CybeRose note: I added the last line of this chart to show the % decrease in protein relative to the parental average. In the last three columns, the best seedling showed a small increase.
p. 608-609 Conclusions regarding breeding for high protein  

For one acquainted with that vast reservoir of genetic variability—the maize plant—emphasis as to its breeding possibilities has an empty sound. It is sufficient to say that no one knows the limits of progress when breeding to increase or to decrease any one of its characters. What we have to say regarding breeding for high protein, therefore, concerns breeding methods rather than breeding limits.

High-protein maize can be secured in the shortest possible time and with a minimum expenditure of effort only when selection is based upon an accurate control of the true biological units and when the germ-plasm contributed by each sex is given due consideration and equal opportunity of expression. In practice the basis of such a method is self-fertilization.

The results obtained from continued selection for high protein in self-fertilized lines depend almost exclusively upon the heredity of the original plants chosen as progenitors. Unless adequate possibilities for recombination are thus present, no amount of selection can create the qualities sought, since there is no evidence of frequent mutation. Obviously the chances for success do not depend wholly upon the number of individuals used, and the rigidity of selection. External conditions must be such as will bring out the highest expression of the desired character, and correlation between personal characteristics and genetic constitution must be fairly high; but given these conditions, progress depends upon the magnitude of the operations at the beginning rather than at the end.

In reality this statement is but a rephrasing of old genetic postulates, and their application to the specific problem of breeding maize for high protein. But what of the result? A high percentage of protein may be produced by this method with certainty and rapidity; yet high percentage composition does not insure high production per unit of area. There is a certain amount of antagonism between high yield and high protein; and even if this were not the case, selection for one character alone would tend to be at the neglect of the other. Merely as a matter of probability it would be more difficult to secure a high proportion of certain ingredients together with high yield than it would be to secure either alone. But the truth is that inbred strains showing the highest percent protein are weak and unproductive. As a rule high-protein strains are less vigorous than strains not so selected, and crosses between them generally give lower yields than other crosses. It may well be, therefore, that high-protein maize can be secured only at the expense of maximum total production. Whether it is worth while to produce special types of maize with increased proportions of certain ingredients in spite of their reduced yields, need not be discussed here.

CybeRose note: While the quantity of protein in maize is worth study, it is not immediately relevant to the value of maize as a food source because most of the protein is in the form of indigestable zeins.

American Journal of Botany, 77(8): 973-980 (Aug. 1990)
Zein Degradation in the Endosperm of Maize Seeds During Germination
Kamaruzaman Bin Mohammad, Asim Esen

The prolamin of maize (Zea mays), zein, consists of a group of alcohol-soluble proteins, and it is the major storage protein in maize endosperm. During seed development, zein is deposited in distinct membrane-bround subcellular compartments called protein bodies (Larkins and Hurkman, 1978; Wolf, Khoo, and Seckinger, 1969) Zein is used as the nitrogen source during germination and early seedling growth and as the nitrogen sink during seed development (Tsai, Huber, and Warren, 1978, 1980).

Harvey and Oaks (1974) showed that zein and glutelin degradation in maize endosperm occurred between 3 and 8 days after germination (DAG) and coincided with the appearance of a protease having an acidic pH optimum. The activity of proteases implicated in zein degradation increased remarkably during germination up to 5 DAG and resulted in the appearance of small peptides and individual amino acids without any intermediate size fragments detectable by electrophoresis (Fujiumaki, Abe, and Arai, 1977; Moureaux, 1979).

Physiologia Plantarum 81(3): 377–384 (1991)
Storage protein mobilization during germination and early seedling growth of Zea mays.
Pamela Camp Hay, Tina Ramsaur, Carlene Smith, Jan A. Miernyk

Changes in general protease activity and the levels of the zein storage proteins were monitored during germination and early seedling growth of maize (Zea mays L. inbred A636). General endosperm endoprotease activity, measured in vitro using azocasein as a substrate, increased continuously to day 5 and remained high thereafter. The increase was in parallel with the loss of zein protein as determined by immunoblot analysis, with a total loss of detectable zein by 10 days after inbibition of the seeds.

The nutritional value of maize, in particular the availability of protein, would be increased by germinating the grain (malting) before it is fed to the animals. Malting of seeds for livestock feed has a long history. A.K. of Rodings, Essex (1764) recommended malted peas for hogs, horses and turkeys. Seaman (1868) found malted wheat and barley to be beneficial to sheep and horses, while the raw grain was distinctly harmful. Malted grain (i.e., sprouts) is closer to herbage than raw seeds, making it more suitable feed for herbivores.

See also Thatcher: Factors affecting wheat composition (1910)