PHENOLASE ACTIVITY IN RELATION TO SEED VIABILITY

Oxidase and catalase activity of plant tissues are so frequently used as criteria of metabolism and viability that methods for their quantitative measurement are becoming increasingly important in physiological technique. Quantitative data for catalase, however, are more numerous than those of other oxidases, probably because of the difficulty encountered in making accurate determinations of oxygenases and peroxidases. There are, nevertheless, several important reasons for more frequent estimations of oxidase activity. The physiological function of catalase is still obscure. Oxidases, on the other hand, have been closely associated with the ability of living organisms to bring about transformations of materials otherwise stable at ordinary temperatures. Though our knowledge of oxidation-reduction reactions in vivo is as yet fragmentary, the abundant and diverse experimental evidence which has accumulated makes inescapable the conclusion that oxidases are essential to co-ordinated respiratory and other oxidative activities of plants. The correlation between oxidases and physiological processes has been so definite that these enzymes have been placed in a causal relationship to them. The desirability of a convenient quantitative method for oxidase determination is consequently self-evident. Colorimetric methods for estimation of oxidases have been widely used. These methods have involved the use of such reagents as alpha-naphthol, hydroquinon, pyrogallol, paracresol, orthoand para-aminophenol and others. Though solutions of these reagents are to varying degrees autoxidizable in air, the amount of spontaneous oxidation can be minimized by keeping the hydrion concentration within definite limits for each reagent (6). All of them, however, are appreciably autoxidized in nearly neutral media. This is especially true of two common reagents, phenylenediamine hydrochloride and demethyl-phenylenediamine, which have as a consequence been little used as such in colorimetric estimations of oxidases.