High atmospheric carbon dioxide-dependent alleviation of salt stress is linked to RESPIRATORY BURST OXIDASE 1 (RBOH1)-dependent H2O2 production in tomato (Solanum lycopersicum)

Plants acclimate rapidly to stressful environmental conditions. Increasing atmospheric CO2 levels are predicted to influence tolerance to stresses such as soil salinity but the mechanisms are poorly understood. To resolve this issue, tomato (Solanum lycopersicum) plants were grown under ambient (380 mu mol mol(-1)) or high (760 mu mol mol(-1)) CO2 in the absence or presence of sodium chloride (100 mM). The higher atmospheric CO2 level induced the expression of RESPIRATORY BURST OXIDASE 1 (SlRBOH1) and enhanced H2O2 accumulation in the vascular cells of roots, stems, leaf petioles, and the leaf apoplast. Plants grown with higher CO2 levels showed improved salt tolerance, together with decreased leaf transpiration rates and lower sodium concentrations in the xylem sap, vascular tissues, and leaves. Silencing SlRBOH1 abolished high CO2 -induced salt tolerance and increased leaf transpiration rates, as well as enhancing Na+ accumulation in the plants. The higher atmospheric CO2 level increased the abundance of a subset of transcripts involved in Na+ homeostasis in the controls but not in the SlRBOH1-silenced plants. It is concluded that high atmospheric CO2 concentrations increase salt stress tolerance in an apoplastic H2O2 dependent manner, by suppressing transpiration and hence Na+ delivery from the roots to the shoots, leading to decreased leaf Na+ accumulation.