This study carried out in order to investigate the effects of salinity and time after salinisation on carbon isotope discrimination (Δ) of shoots and grains of three spring wheat cultivars (cv). Plants were grown in sand culture medium at four levels of salinity including 0 (control), 100, 200 and 300 mol m-3 of NaCl and CaCl2 from two leaves stage until ripening under controlled environment conditions. Carbon isotope discrimination decreased with increasing salinity but became significant only at the highest level of salinity. In all cvs ratio of intercellular to ambient partial pressure of CO2 (pi/pa) increased with increasing Δ. Although, the regression of Δ and pi/pa is positive, the slope of regression line is different from that predicted by theory, indicating an underestimation of Δ in these samples. Significant differences of Δ between shoot and grains were observed in all cvs and all levels of salinity. Relatively more 13C (lower Δ) was found in grains as compared with shoots. Therefore, Δ might be applicable, as a useful tool, for study of salinity tolerance of wheat genotypes.

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