Effect of NaCl on photosynthesis of two wheat species (Triticum durum and T-aestivum) differing in their sensitivity to salt stress

Two wheat species, Triticum aestivum, cv. Tanit and T. durum, cv. Ben Bachi r, were cultivated hydroponically and subjected to salt stress (50 or 100 m mol/L NaCl) up to 21 days. NaCl treatment resulted in growth reduction for both varieties (but less for Ben Bachir than for Tanit), equivalent Na+ and Cl- absorption by the whole plants, and the capacity for Ben Bachir to tra nsport ions into the leaves where they accumulated. This accumulation proce ss accounts for the maintainance of the water status in Ben Bachir leaves. As a whole, Ben Bachir shows characteristics of a NaCl-tolerant species. Net CO2 uptake by the non-tolerant Tanit variety was markedly reduced at PP FD higher than 500 mu mol m(-2) s(-1), mostly because of stomatal closure, as shown by the decrease in the C-i/C-a ratio, the effect of saturating CO2 concentrations (5%) and the increase in the delta(13)C in the salt-treated leaf tissues. No effect of salt stress could be found either on the initia l slopes of the net CO2 assimilation curve, on the F-v/F-m ratio of chlorop hyll fluorescence, or on the carboxylative capacities in the leaves. As a w hole, these results favour the hypothesis of an exclusive effect of salt st ress on the stomatal behaviour of the treated leaves.