Protein polymorphism in maize and its nearest relatives
Multiple electrophoretic forms of four enzymes were studied by the routine disc-PAGE-zymographical procedure and classified into several phenotypes (see also MNL 51:81, 1977). Fast-allelic forms of alcohol dehydrogenase (ADH) and aspartate aminotransferase (AAT) were predominant among the inbreds and also the most frequent in the collection of 33 races representing most of their groups (see M. Goodman and R. McK. Bird, Econ. Botany 31:204, 1977). The frequencies of glutamate dehydrogenase (GDH) phenotypes were similar in inbreds and races, while succinate dehydrogenase (SDH) patterns differed mostly in regard to class A, being more frequent in inbreds than in races. Some of the races--up to 30% in the case of SDH--were polymorphic (Table 4).
Segregation of SDH and GDH patterns was studied in F2 (selfs) and backcrosses. The data obtained in the case of SDH presume: (1) the existence of several non-allelic genes that conforms with the fact that animal SDH consists of two unequal subunits; (2) the allelic control of differences among the phenotypes.
Upon these presumptions two alternative models are suggested to describe the genetic control of SDH:
Model 1 (Fig. 1). Three structural genes control the synthesis of polypeptides SDH1, SDH2 and SDH3. Sdh1 and Sdh3 loci are monomorphic, while Sdh2 is represented by several alleles (A-D). The most mobile band 1 is formed as 2 (SDH1.SDH3) and present in all five phenotypes, while other multiple forms are formed as 2 (SDH2.SDH3) and/or SDH1.SDH2.2SDH3.
Model 2. The enzyme is formed by two heteromeric subunits SDH1.SDH3, and the diversity of phenotypes is attributed to SDH1 posttranslational modification under the control of a series of gene-modificator alleles.
In the case of GDH the analysis of the complicated phenotypes in seven-band x two-band crosses presented considerable difficulties, however, clear segregation of the parent phenotypes conformed to the expected frequencies based on the two-loci control presumption (Table 5). Posttranslational modifications of two polypeptides seem to produce the inverted binomial distribution of staining intensity in the seven-band GDH patterns (maximal staining of the 1st and 7th bands) in the scutella, as well as in other organ-specific GDH phenotypes lacking one or two anodal bands. However, the one-band GDH-pattern found in Job's tears (Coix lacryma-jobi L.) does agree with this two-loci model.
Antigen spectra of reserve globulins in the Andropogoneae were compared by double immunodiffusion and one-dimensional immuno-electrophoresis using antiserum raised against the purified globulin preparation from maize embryos (for details of the procedures see E. E. Khavkin et al., Planta 143:11, 1978).
Considerable quantitative variations were found when we compared globulin immunodiffusion patterns of six races confined to several geographical areas, however, all the antigens were identical (Fig. 2). Globulins of two teosinte races and two gama grass forms of different ploidy were identical to those of maize though even more polymorphic: teosinte Huixta was low and 36n gama grass almost lacking the slow-migrating globulin component. In Job's tears, sorgho and eulalia (Miscanthus) the same globulin component gave the reaction of partial identity with the respective maize protein. Another globulin was identical to that of maize in all the investigated representatives of the tribe Andropogoneae and partially identical in the Paniceae. Thus, no direct discrimination was found among maize, teosinte and gama grass globulins (see also data by J. W. Paulis and J. S. Wall, J. Agr. Food Chem. 25:265, 1977) to contribute to the current dispute on the evolutionary history of maize.
S. E. Misharin, E. A. Mozgova, L. E. Monastyreva T. B. Sukhorzhevskaia and E. E. Khavkin
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