In a previous communication (Rapela, MNL 59:59-60, 1985) we reported a partial biochemical (SDS-electrophoresis) somaclonal variation analysis of 3 floury-a and 5 normal red flint (NRF) maize plants regenerated through somatic embryogenesis. Cultures were initiated from immature maize embryos between 1 mm and 2 mm long, placed scutellum up on Yu-Pei (Ku et al., 1978) medium containing 1 mg/l 2,4-D, 120 gl1 sucrose and 400 mg/l proline. Embryogenic callus pieces were transferred to modified Murashige-Skoog medium (Green, Hort. Sci. 12:131-134, 1977) in light. Plantlets were transferred to vermiculite and then to soil.
Here we present a more detailed analysis of the biochemical somaclonal variation of these plants in relation to control plants. We have determined the soluble leaf protein pattern and the soluble pollen protein pattern by SDS-electrophoresis in polyacrylamide gels; the endosperm protein pattern according to the procedures of Landry-Moureaux; and the zein polypeptide pattern of the grains derived from selfed regenerated plants.
An analysis based on presence or absence of polypeptides for the electrophoresis and S(minor fraction/major fraction)/5 for the protein pattern was used to obtain the Similarity Index (SI) between regenerated plants of each genotype and the control, and among regenerated plants. The SI analysis of floury-a and NRF plants is shown in Figures 1 and 2, respectively.
It is difficult to make useful morphological evaluations of regenerated maize plants. However, certain biochemical evaluations among plants can be realistically measured by SIs. The occurrence of biochemical somaclonal variation among regenerated plants of each genotype is strongly indicative of considerable changes at the genetic level. The general homogeneity of the SIs for each pair of plants and determination support the relevance of such analysis for breeding purposes. For example, the low SI determined for floury-a 2 and NRF 5 plants in relation to the controls and the rest of regenerated plants of each genotype is of particular interest.
Our results to date suggest that biochemical analysis of electrophoresis and protein pattern of regenerated plants and seeds is worthwhile and that somaclonal variants can be quickly isolated by such techniques.
Miguel Angel Rapela
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