Oxidative modification of the cell wall in tomato plants exposed to ozone

The goal of this research was to define the role of the cell wall in plant exposure to the atmospheric pollutant ozone (O3). To determine if cell wall components are sensitive to oxidation, cell walls were isolated from tomato leaves (Lycopersicon esculentum cv. Roma) and exposed to O3 or pure oxygen. O3 reduced the quantityof a wall-bound benzaldehyde isomer in extractive-free cell wall material thought to have limited enzymatic activity. To determine if this oxidative modification also occurred in vivo, tomato plants were exposed to O3 or filtered air, and the buffer soluble and alkaline hydrolyzed (wall-bound) phenolic compounds were analyzed. Exposure to O3 decreased the quantity of the wall-bound benzaldehyde isomer within 2-3 h of exposure, with a return to control levels by 5 h of exposure. Quantity of the benzaldehyde isomer in the control samples was unchanged throughout the experiment. A glycoside of 5-hydroxyvanillic acid was detected in the buffer soluble fraction of O3-treated samples at 3 h of exposure. Control and O3-treated samples harvested at 5 h of exposure did not contain this compound. Results show that cell wall phenolic compounds are sensitive to oxidative modification by plant exposure to O3. A model illustrates the proposed signaling mechanism involving oxidative breakdown products from the cell wall as elicitor molecules.