A Partial Survey of the Genus Cucurbita for Electrophoretic Variants of Esterase and Leucine Aminopeptidase

Abstract

Starch gel electrophoretic analysis of crude seed extracts of six species of Cucurbita, including five cultivars of two species and one species hybrid, reveals six distinguishable leucine aminopeptidase mobilities. Two cultivars of C. maxima were found to be polymorphic for this enzyme. Certain species were monomorphic and others polymorphic for alpha-naphthyl acetate esterases. With one possible exception, the species could be identified on the basis of their electrophoretic phenotypes. The systematic and evolutionary significance of the reported enzymatic variants are discussed in terms of the genetic differences they might reflect. Electrophoretic analysis of serum proteins in supporting media is a technique finding increasing application among zoologists for aid in the solution of phyletic problems (Dessauer, 1966; Coates and Twitty, 1967). Plant systematists have to a more limited extent utilized this approach to evolutionary and systematic problems; three such applications using plant proteins have been those of Hall and Johnson (1963), Johnson and Hall (1965), and Boulter et al. (1967). An important extension of the electrophoretic analysis of general proteins, i.e., proteins revealed by staining with Buffalo Black, is the zymogram technique (Hunter and Markert, 1957). This technique reveals specific enzymes following treatment of the gel by appropriate histochemical methods. Only limited application has been made of the zymogram technique to plant taxonomic problems. Yang and Turner (1968) have surveyed four genera (including 17 species) of the Lemnaceae for glutamate, malate and lactate dehydrogenases and betaesterases. These authors concluded that isozyme patterns may prove useful at the species level but not above the generic level for the evaluation of taxonomic relationships. Thurman et al. (1967) have surveyed 103 species of the Fabaceae for formic and glutamic dehydrogenases. These authors were unable to draw any taxonomic conclusions from 1 Present address, Department of Biology, George Mason College of The University of Virginia, Fairfax, Virginia.