Abscisic acid concentrations are correlated with leaf area reductions in two salt-stressed rapid-cycling Brassica species

The greater sensitivity of B. carinata to salinity in comparison to B. napus has been linked to a greater reduction in net assimilation rate. Apparently this is not due to ion toxicity; the cause is unknown. In this report, we test the hypothesis that increases in abscisic acid (ABA) are involved in the reduction of growth by salinity. Salinity (8 dS m(-1)) caused an increase of ABA concentrations in the shoot, root and callus of both species. ABA concentrations were lower in the salt-tolerant species, B. napus, than the salt-sensitive species, B. carinata, both in the whole plant and callus. Leaf expansion for both species was equally sensitive to ABA; salt stress did not significantly alter sensitivity to applied ABA. The growth inhibition increased in a hyperbolic manner with an increase in endogenous ABA concentration. These results indicate that ABA in salt-stressed plants may play a role in the inhibition of growth. The photosynthesis of salt-sensitive species, B. carinata, was also decreased by salinity, corresponding to the reduction in growth. The decreased photosynthesis does not appear to be the cause of the growth reduction, because photosynthesis was not inhibited by short-term exposure to salinity and photosynthesis was poorly correlated with endogenous ABA concentrations.