Peroxidases in Tobacco Abscission Zone Tissue V. Time Course Studies of Polyphenol Oxidase Activity During Ethylene-Induced Abscission

Abstract

Summary Ethylene-induced abscission in flower pedicels of Nicotiana tabacum L. cv. Little Turkish causes a progressive increase in polyphenol oxidase (PPO) activity during the terminal 3 h of a 5 h time course period of ethylene (5 μl/l) treatment, when caffeic acid is used as the substrate. However, with chlorogenic acid as the substrate, PPO activity increases between 3 h and 3.5 h during the 5 h period of ethylene exposure, but decreases between 3.5 h and 4 h, followed by an increase in activity between 4 h and 5 h, when the supernatant enzyme extracts of flower pedicel abscission zone tissues are assayed spectrophotometrically. Non-ethylene-treated abscission zone tissue has a much lower level of PPO activity over the same time-course period, regardless of which substrate is employed. When the abscission zone area of the pedicel is subdivided into proximal, abscission zone and distal portions, respectively, the ethylene-treated tissue has the highest PPO activity in the distal (4.5–5 h) and proximal tissues (4.5 h), followed by the abscission zone tissue (3–4 h), when caffeic acid is used as the substrate. With chlorogenic acid as the substrate, both the distal and abscission zone tissues show a decrease in PPO activity between 2–5 h; however, the proximal tissue demonstrates an increase in PPO activity between 2–3 h and between 4.5–5 h of the 5 h time-course ethylene exposure period. The measurement of PPO activity vs. chlorogenic acid and caffeic acid as specific substrates and the possible role(s) of PPO in tobacco flower pedicel abscission are discussed.