Response of abscisic acid mutants of Arabidopsis to salinity

Increases in abscisic acid (ABA) concentrations in plant tissues correlate with growth inhibition in salt-stressed plants. Therefore, it was hypothesized that Arabidopsis ABA mutants different in, or insensitive to, ABA would respond differently than wild type (wt) to salinity stress. Seeds (wt, abi1-1, abi2-1, abi3-1, and aba1-3) were germinated and grown hydroponically in three separate experiments with different environmental conditions: relative humidity at 80 or 100%, day/night temperatures at 21/18 or 23/20˚C, and light intensity at 125, 200 or 350 μmol photons m^-2 s^-1. Plants were exposed to salinity (either 0, 40 and 80 mM NaCl or 1, 5, and 9 dS m^-1 with a Na/Ca ratio of 10 depending on the experiment) for one to several weeks before harvesting. The effect of salinity on root elongation rates of young seedlings was measured as well. Two-way ANOVA of root elongation rates of young seedlings and the growth of 3-week old plants in hydroponic solutions indicated that salinity inhibited growth, increased ABA and Na concentrations, and reduced K concentrations in all genotypes tested. However, there were no significant interactions with salinity and genotype for root elongation rates, total dry weight, shoot ABA and K concentrations. Shoot Na concentrations were significantly higher in wt plants relative to other genotypes subjected to high salinity stress. aba1-3 had significantly lower ABA concentrations than other genotypes, but the interaction of aba1-3 with salinity was the same as other genotypes. The lack of difference in interaction between genotype and salinity indicates that all genotypes responded in the same manner and amount to salinity for the particular parameter measured. Therefore, it appears that there are no significant differences in growth in response to salinity between the ABA mutants (ABA-deficient and ABA-insensitive) and wt. However, in contrast to the other genotypes, some of the ABA-deficient plants, aba1-3, died when exposed to high salinity and high light intensity. ABA appears to provide a protective role in conditions of high salinity and high light intensity.