As reported last year (MNL 60:93, 1986), a study to monitor variation in leaf polypeptide synthesis patterns was undertaken for several field management practices and various cultivars of maize. This study involved attempts to report on the phenotypic variation found among the maize cultivars in the field as revealed through electrophoretic and fluorographic procedures in the laboratory. The laboratory work from the 1985 growing season was repeated for the 1986 growing season. A favorable growing season in 1986 produced expected differences among field plots, planting dates and cultivars. The "base-line" of growth measurements (height, number of leaves etc.) for the 1986 season were highly correlated with those reported for the 1985 growing season.
To analyze the detailed information collected from the fluorograms obtained during the two growing seasons, a newly developed technique employing multivariate analyses was performed (P. Fewster and D.B. Walden, in press). These methods involve a principal components analysis and an analysis of concentration, which define and outline any trends in variation (of polypeptide synthesis among cultivars, field plots etc.).
Our system (field grown material, 35S-methionine exposure, electrophoresis, fluorography and statistical analyses) appears sensitive enough to enable preliminary observations on the objectives: 1) to identify proteins that may be unique to cultivars; 2) those that may have a role in heterosis; and 3) those that are of developmental significance.
The analyses revealed that some of the polypeptides synthesized were unique to specific cultivars and specific field plots. Few (less than 1%) differences were found between planting dates of the same cultivar/plot when comparisons were made with leaves of the same age. The variation among cultivars in the control plot was small in general and less than among other comparisons. The stress and optimal field management plots reveal a much greater directed variation in the polypeptide synthesis patterns trends as compared to that of the control or each other. These observations suggest that as the control conditions or those to which the cultivars are most 'adapted' are altered the cultivar responds to this new set of management conditions in ways which result in increased variation in polypeptide synthesis. This variation in polypeptide synthesis may allow the cultivar to adapt to a greater range of growth conditions. Also, polypeptide synthesis patterns throughout development show both similarities and differences between inbreds and hybrids. Our data and analyses confirm the view that hybrids are better able to respond favorably to more extreme management conditions than are the inbred cultivars.
T.G. Crowe and D.B. Walden
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