Beschreibung:
<jats:p>Cell capacity for cytosolic <jats:styled-content style="fixed-case">NADPH</jats:styled-content> regeneration by <jats:styled-content style="fixed-case">NADP</jats:styled-content>‐dehydrogenases was investigated in the leaves of two hybrid poplar (<jats:italic>Populus deltoides × Populus nigra</jats:italic>) genotypes in response to ozone (<jats:styled-content style="fixed-case">O<jats:sub>3</jats:sub></jats:styled-content>) treatment (120 ppb for 17 days). Two genotypes with differential <jats:styled-content style="fixed-case">O<jats:sub>3</jats:sub></jats:styled-content> sensitivity were selected, based on visual symptoms and fallen leaves: <jats:italic>Robusta</jats:italic> (sensitive) and <jats:italic>Carpaccio</jats:italic> (tolerant). The estimated <jats:styled-content style="fixed-case">O<jats:sub>3</jats:sub></jats:styled-content> flux (<jats:styled-content style="fixed-case">POD<jats:sub>0</jats:sub></jats:styled-content>), that entered the leaves, was similar for the two genotypes throughout the treatment. In response to that foliar <jats:styled-content style="fixed-case">O<jats:sub>3</jats:sub></jats:styled-content> flux, <jats:styled-content style="fixed-case">CO<jats:sub>2</jats:sub></jats:styled-content> assimilation was inhibited to the same extent for the two genotypes, which could be explained by a decrease in Rubisco (<jats:styled-content style="fixed-case">EC</jats:styled-content> 4.1.1.39) activity. Conversely, an increase in <jats:styled-content style="fixed-case">PEPC</jats:styled-content> (<jats:styled-content style="fixed-case">EC</jats:styled-content> 4.1.1.31) activity was observed, together with the activation of certain cytosolic <jats:styled-content style="fixed-case">NADP</jats:styled-content>‐dehydrogenases above their constitutive level, i.e. <jats:styled-content style="fixed-case">NADP‐G6PDH</jats:styled-content> (<jats:styled-content style="fixed-case">EC</jats:styled-content> 1.1.1.49), <jats:styled-content style="fixed-case">NADP‐ME (malic enzyme)</jats:styled-content> (<jats:styled-content style="fixed-case">EC</jats:styled-content> 1.1.1.40) and <jats:styled-content style="fixed-case">NADP‐ICDH (NADP‐isocitrate dehydrogenase)</jats:styled-content> (<jats:styled-content style="fixed-case">EC1</jats:styled-content>.1.1.42). However, the activity of non‐phosphorylating <jats:styled-content style="fixed-case">NADP‐GAPDH</jats:styled-content> (<jats:styled-content style="fixed-case">EC</jats:styled-content> 1.2.1.9) remained unchanged. From the 11th fumigation day, <jats:styled-content style="fixed-case">NADP‐G6PDH</jats:styled-content> and <jats:styled-content style="fixed-case">NADP‐ME</jats:styled-content> profiles made it possible to differentiate between the two genotypes, with a higher activity in Carpaccio than in Robusta. At the same time, Carpaccio was able to maintain high levels of <jats:styled-content style="fixed-case">NADPH</jats:styled-content> in the cells, while <jats:styled-content style="fixed-case">NADPH</jats:styled-content> levels decreased in Robusta <jats:styled-content style="fixed-case">O<jats:sub>3</jats:sub></jats:styled-content>‐treated leaves. All these results support the hypothesis that the capacity for cells to regenerate the reducing power, especially the cytosolic <jats:styled-content style="fixed-case">NADPH</jats:styled-content> pool, contributes to improve tolerance to high ozone exposure.</jats:p>