Abstract
The exposure of «Little Marvel» dwarf pea ( Pisum sativum ) seedlings to Ethrel and ultraviolet irradiation, both in dark and visible light, either alone or in combination, reveals that UV and Ethrel exposure has either an enhancement or depressant effect on polyphenol oxidase (PPO) activity. This is apparently a differential and tissue-specific response in terms of the four seedling areas assayed (root tip, dorsal root, proximal stem and leaves). PPO activity was assayed with four different substrates: catechol, caffeic acid, chlorogenic acid and 3,4-dihydroxyphenylalanine (DOPA). With respect to PPO enzymic response, DOPA appears to be the best substrate for measuring PPO activity. Also, results with DOPA show PPO activity to be within similar magnitudes to that of peroxidase enzyme activity, measured in earlier studies. Chlorogenic acid was the next best substrate compared to DOPA, with caffeic acid and catechol apparently being the least promising for PPO activity assays in the particular tissue used in the present investigation. The comparable PPO activity levels are discussed with respect to individual substrates in relation to the particular type of seedling tissue treatment.
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