3.2 Sodium and potassium sequestration in leaf following NaCl
treatments
Plants of SV and SA were grown for 4 or 8 weeks before
their exposure to a range of salt concentrations. Exposure of SVto NaCl concentrations higher than resulted in plant death before the
end of the experiment; so higher NaCl concentration treatments were not
used for SV . Exposure of SA to NaCl concentration up to
did not result in considerable mortality. The concentration of
Na+ in control leaf tissue was considerably higher inSA than in SV (Figure 3A-B). This difference disappeared
after exposure to salt, due to a quick accumulation of
Na+ in the leaf of SV . The accumulation of
Na+ in leaves of SA was much lower at external
NaCl concentrations between 0 and . Na+ accumulation
increased sharply in SV leaves over the experiment (Figure 3A),
whereas leaf Na+ content in SA increased less,
even at higher external concentrations of NaCl (Figure ). The
Na+ levels measured after 12 days NaCl treatment in
Spartina exposed to 400 and NaCl was nearly similar to that of SVsubjected to only NaCl (Figure 3A-B). At NaCl, SV accumulated
more NaCl in the leaf than SA under all salt concentration range
(100-550 mM). This is owing to the exclusion of NaCl to the leaf surface
for Spartina. This exclusion mechanism represents a second barrier ofSA defense against high NaCl concentrations besides the
sequestration of salt in the vacuole. Earlier study performed on
halophyte Aeluropus littoralis , a species that can tolerate up to
NaCl, showed that an increase in leaf epidermal thickness was mainly due
to an increase in cell size following salt accumulation (Barhoumi et
al., 2007).
SA and SV differed also in their K+concentrations in the leaf. Herein, the concentration of
K+ in leaf tissue of plants watered with salt-free
medium was higher by about 30% in SA leaves (Figure 3C-D).
Following salt treatment, the K+ content of the leaf
in SV decreased considerably, especially after 4 and 8 days
treatment at 100 mM NaCl. However, in SA , there was an initial
increase in K+ with the increase in NaCl
concentration; after 12 days of treatments, the K+concentration in the leaf gradually decreased with an increase in the
NaCl concentration (Figure 3D). This also reflected by the ratio
k+/Na+ (Figure 3E-F), where we
observed a dramatic decline in this ratio for SV but very less
and mostly maintain stable with time course in SA , especially at
NaCl concentrations higher than 250 mM (Figure 3E-F).