The apoplastic antioxidant system and altered cell wall dynamics influence mesophyll conductance and the rate of photosynthesis.
Mesophyll conductance (gm ), the diffusion of CO2 from substomatal cavities to the carboxylation sites in the chloroplasts, is a highly complex trait driving photosynthesis (net CO2 assimilation, AN ). However, little is known concerning the mechanisms by which it is dynamically regulated. The apoplast is considered as a 'key information bridge' between the environment and cells. Interestingly, most of the environmental constraints affecting gm also cause apoplastic responses, cell wall (CW) alterations and metabolic rearrangements. Since CW thickness is a key determinant of gm , we hypothesize that other changes in this cellular compartiment should also influence gm . We study the relationship between the antioxidant apoplastic system and CW metabolism and the gm responses in tobacco plants (Nicotiana sylvestris L.) under two abiotic stresses (drought and salinity), combining in vivo gas-exchange measurements with analyses of antioxidant activities, CW composition and primary metabolism. Stress treatments imposed substantial reductions in AN (58-54%) and gm (59%), accompanied by a strong antioxidant enzymatic response at the apoplastic and symplastic levels. Interestingly, apoplastic but not symplastic peroxidases were positively related to gm . Leaf anatomy remained mostly stable; however, the stress treatments significantly affected the CW composition, specifically pectins, which showed significant relationships with AN and gm . The treatments additionally promoted a differential primary metabolic response, and specific CW-related metabolites including galactose, glucosamine and hydroxycinnamate showed exclusive relationships with gm independent of the stress. These results suggest that gm responses can be attributed to specific changes in the apoplastic antioxidant system and CW metabolism, opening up more possibilities for improving photosynthesis using breeding/biotechnological strategies.
['Clemente-Moreno|María José|MJ|0000-0003-3288-6312', 'Gago|Jorge|J|0000-0002-4293-0105', 'Díaz-Vivancos|Pedro|P|0000-0001-6041-2128', 'Bernal|Agustina|A|0000-0001-7146-2737', 'Miedes|Eva|E|0000-0003-2899-1494', 'Bresta|Panagiota|P|0000-0001-5313-0472', 'Liakopoulos|Georgios|G|0000-0002-7511-0429', 'Fernie|Alisdair R|AR|', 'Hernández|José Antonio|JA|0000-0001-7211-5147', 'Flexas|Jaume|J|0000-0002-3069-175X']
D000975:Antioxidants D002245:Carbon Dioxide D002374:Catalase D002473:Cell Wall D002734:Chlorophyll D055864:Droughts D006861:Hydrogen Peroxide D058503:Mesophyll Cells D009097:Multienzyme Complexes D009247:NADH, NADPH Oxidoreductases D009195:Peroxidase D010788:Photosynthesis D018515:Plant Leaves D054046:Plant Stomata D054712:Salinity D013482:Superoxide Dismutase D014026:Tobacco
apoplast cell wall mesophyll conductance photosynthesis Nicotiana sylvestris reactive oxygen species stress responses