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Protection of ash (Fraxinus excelsior) trees from ozone injury by ethylenediurea (EDU): roles of biochemical changes and decreased stomatal conductance in enhancement of growth
Authors:Paoletti Elena  Contran Nicla  Manning William J  Castagna Antonella  Ranieri Annamaria  Tagliaferro Francesco
Affiliation:IPP-CNR, Via Madonna del Piano 10, Sesto Fiorentino, I-50019 Florence, Italy.
Abstract:Treatments with ethylenediurea (EDU) protect plants from ozone foliar injury, but the processes underlying this protection are poorly understood. Adult ash trees (Fraxinus excelsior), with or without foliar ozone symptoms in previous years, were treated with EDU at 450ppm by gravitational trunk infusion in May-September 2005 (32.5ppmh AOT40). At 30-day intervals, shoot growth, gas exchange, chlorophyll a fluorescence, and water potential were determined. In September, several biochemical parameters were measured. The protective influence of EDU was supported by enhancement in the number of leaflets. EDU did not contribute its nitrogen to leaf tissue as a fertiliser, as determined from lack of difference in foliar N between treatments. Both biochemical (increase in ascorbate-peroxidase and ascorbic acid, and decrease in apoplastic hydrogen peroxide) and biophysical (decrease in stomatal conductance) processes regulated EDU action. As total ascorbic acid increased only in the asymptomatic trees, its role in alleviating O(3) effects on leaf growth and visible injury is controversial.
Keywords:Antioxidant   European ash   Foliar nitrogen   Gas exchange   Shoot growth
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