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.
Histone demethylases control root elongation in response to stress-signaling hormone abscisic acid
