Efecto mitigante del ácido salicílico y nitrato en las relaciones hídricas y ajuste osmótico en maíz, cv. Lluteño expuesto a salinidad

Abstract

We analyzed the mitigating effect of NO3 - and salicylic acid (SA) on the detrimental effects of salt stress by studying the water status of plants of maize grown in Hoagland's medium with NaCl 100 mM as the saline component, to which SA and NO3 - were added in different concentrations as mitigating agents. We evaluated water potential Ψw, osmotic potential Ψs, relative water content (RWC), turgor potential (Ψp ), and the osmotic adjustment (OA) of leaves and roots. SA 0.5 mM mitigated the effects of salinity by increasing the Ψs of the leaf, the Ψsof theroot, the Ψpof the leaf, RWC and OA of the leaf; while NO3 was only effective in combination with SA, mitigating the effects of salinity by increasing RWC and OA. However, the interaction SA-NO3 reduced leaf Ψw and Ψs of leaves and roots. Mtigation of salt stress was also detected by a positive effect on plant growth. The greatest effect on growth was produced by the NO3 treatments and SA 0.5 mM combined with NO3.

Full text

Cien. Inv. Agr. 37(3):71-81. 2010
www.rcia.uc.cl
research paper
Mitigating effect of salicylic acid and nitrate on water relations and
osmotic adjustment in maize, cv. Lluteño exposed to salinity
Hugo Escobar1, Richard Bustos1, Felipe Fernández1, Henry Cárcamo1,
Herman Silva2, Nicolás Frank2, Liliana Cardemil3
1Laboratorio de Cultivo de Tejidos Vegetales, Facultad de Ciencias Agronómicas, Universidad de Tarapacá,
Velásquez 1775, Arica, Chile.
2Laboratorio de Suelo, Agua y Planta, Facultad de Ciencias Agronómicas, Universidad de Chile, Santa Rosa
11315, La Pintana, Santiago, Chile.
3Laboratorio de Biología Molecular Vegetal, Facultad de Ciencias, Universidad de Chile. Las Palmeras
3425, Macul, Santiago, Chile.
Abstract
H. Escobar, R. Bustos, F. Fernández, H. Cárcamo, H. Silva, N. Frank, and L. Cardemil.
2010. Mitigating effect of salicylic acid and nitrate on water relations and osmotic
adjustment in maize, cv. Lluteño exposed to salinity. Cien. Inv. Agr. 37(3): 71-81. We
analyzed the mitigating effect of NO3
- and salicylic acid (SA) on the detrimental effects of salt
stress by studying the water status of plants of maize grown in Hoagland´s medium with NaCl
100 mM as the saline component, to which SA and NO3
- were added in different concentrations
as mitigating agents. We evaluated water potential (Ψw), osmotic potential (Ψs), relative water
content (RWC), turgor potential (Ψp), and the osmotic adjustment (OA) of leaves and roots.
SA 0.5 mM mitigated the effects of salinity by increasing the Ψw of the leaf, the Ψs of the root,
the Ψp of the leaf, RWC and OA of the leaf; while NO3
- was only effective in combination with
SA, mitigating the effects of salinity by increasing RWC and OA. However, the interaction
SA-NO3
- reduced leaf Ψw and Ψs of leaves and roots. Mitigation of salt stress was also detected
by a positive effect on plant growth. The greatest effect on growth was produced by the NO3
-
treatments and SA 0.5 mM combined with NO3
-.
Key words: nitrate, osmotic potential, osmotic adjustment, salinity mitigation, salicylic acid,
water potential, water relative content.
Introduction
Salinity may cause water stress in plants, which
is rst manifested as an osmotic stress and then
as ionic toxicity, due mainly to an excess of Na+
and Cl- in the tissues. Plants may also have a
nutritional deciency due to the competition of
Na+ y Cl- for the ionic nutrient transporters in the
external zone of the roots.
Maize, cv. Lluteño, is the main cultivated species
in the Lluta Valley, and the most widely cultivat-
ed crop in terms of area in the desert of northern
Chile. It is especially interesting due to its high
tolerance to extreme conditions of salt stress and
the excess of boron in the irrigation water. The
Received August 18, 2009. Accepted November 10, 2009.
Corresponding author: hescobar@uta.cl

CIENCIA E INVESTIGACIÓN AGRARIA72
main drawback with this cultivar is its low yield,
which uctuates between 12.000 and 20.000
ears/ha with a planting density of 30.000-40.000
plants/ha, what means less than one ear per plant.
This low yield may be due to an excessive ab-
sorption of toxic ions such as boron, and to high
concentrations of sodium and chlorine in the ir-
rigation water (Bastías, 2005). In the Lluta valley
the water has concentrations of Na+ from 194 to
480 ppm, Cl- from 397 to 900 ppm and B from
11.7 to 28.7 ppm (Sotomayor et al., 1995). How-
ever, the concentration of these ions should not
be higher than 186, 200 and 0.75 ppm, respec-
tively, to avoid toxic effects on crops, as has been
reported by the Chilean Instituto Nacional de
Normalización (1987). The toxicity induced by
NaCL may be exacerbated by a decient water
absorption generated by the saline stress of the
environment. This salinity can decrease the rela-
tive water content (RWC) and cause cell dehy-
dration (Hasegawa et al., 2000; Ortíz et al., 2003;
Chartzoulakis, 2005). Water stress may activate
molecular signals to counteract the physiological
damage of stress, such as the synthesis of abscis-
ic acid (ABA) causing closure of the stomata to
avoid water loss. The closure of stomata, how-
ever, decreases CO2 assimilation by plants; this
might be a cause of the low yield of maize cv.
Lluteño (Shar p et al., 1993; Wahbi et al., 2005;
Centritto et al., 2005).
Some plants confront salinity by osmotic ad-
justments to absorb and retain water while
maintaining cell turgor (Serraj and Sinclair,
2002; Silva et al., 2007) by means of the accu-
mulation of compatible solutes and osmoregula-
tors (Hasegawa et al., 2000; Chinnusamy et al.,
2005; Munns y Tester, 2008).
Due to its biological and physiological actions,
SA has been considered as a plant hormone
(Canet et al., 2010). As in the case of other
plant hormones, SA may act as a plant regula-
tor and signal messenger in plants under stress
conditions (Harfouchea, 2008). SA activates
defense mechanisms in pathogenicity and tol-
erance mechanisms to counteract different en-
vironmental stress conditions, such as ozone
increase, low and high temperatures, salinity,
anaerobiosis, etc. (Cakmak, 2003; Sawada et
al., 2006; Shi y Zhu, 2008).
The application of SA to cereal plants appears
to decrease the concentrations Na+, Cl- and B
in plant tissues and signicantly improves the
nitrogen absorption of these plants when there
is high salinity associated with boron (Sha-
kirova et al., 2003; Gunes et al., 2005). How-
ever, the signals induced by SA to counteract
saline stress of plants are unknown (Gunes et
al., 2005; Gunes et al., 2007).
In glycophytic plants the lack of nitrogen pro-
duces severe consequences in the synthesis of
proteins, nucleic acids, lipids and amino acids.
Nitrogen deciency also induces the synthesis
of compatible solutes in plants to perform os-
motic adjustments (Huber and Kaiser, 1996;
Viégas and Gomes da Silveira, 2002). The de-
crease in NO3
- is correlated with a high absorp-
tion of Cl-. However, the application of NO3
- in
the soil compensates the decrease of N in leaves
caused by an excess Cl- (Tabatabaei, 2006). Sa-
linity may affect nitrogen uptake by a direct
competition between Cl- and NO3
- ions of the
NO3
- transport system (Pessarakli et al., 1989;
Campbell y Kinghorn, 1990) and/or by altera-
tion of the plasmalemma by affecting the integ-
rity of the proteins of this membrane (Cramer
et al., 1985).
Since SA seems to improve nitrogen absorp-
tion and nitrogen stimulates plant growth by
synthesis of the fundamental biomolecules and
reduces water stress by stimulating the synthe-
sis of compatible solutes, it is necessary to test
the combined effects of SA and NO3
- in the in-
duced salinity tolerance of maize, cv. Lluteño.
The objective of this study was to evaluate the
combined mitigating effect of SA and NO3
- on
the detrimental effects cause by salinity on the
maize plants. If there is an alleviating effect on
salinity stress induced by SA different from that
induced by NO3
- the combined presence of SA
with NO3
- will increase the mitigation induced
by SA or by NO3
- separately, suggesting two in-
teracting routes of transduction signals.
To evaluate this hypothesis, the water status of
the plants was determined (water and osmotic
potentials, relative water content (RWC), pres-
sure potential (turgor potential), and the os-
motic adjustment (OA). For this, experiments

73
VOLUME 37 Nº3 SEPTEMBER - DECEMBER 2010
were performed with 28 days old maize plants,
grown in pots and irrigated with Hoagland´s
medium to which 100 mM NaCl was added.
For mitigation of the stress effects caused by
salinity, SA, NO3
- and combinations of SA and
NO3
- were added to the Hoagland´s medium
supplemented with 100 mM NaCl (Acevedo et
al., 1998, Munns and Tester, 2008).
Materials and methods
Growth conditions and experimental design
The experiment was performed with plants of Zea
mays L., cv. Lluteño, in a greenhouse with natural
light, mean maximum temperature 27.3º C, mean
minimum 11.4º C, PAR 359.8 µmol/m2 s-1 and
relative humidity 50%-80% (day-night). Plants
were established in 15 L pots with a Perlite sub-
strate. Three seeds were planted in each pot.
After 10 days, one of the three seedlings of each
pot was selected to obtain plants with a uniform
size for all the experimental groups; the other
two were removed from the pot. During the rst
28 days plants were irrigated with 100% Hoa-
gland’s solution, pH 6-7 (Hoagland and Arnon,
1950). The plants were watered every two days
with one liter of Hoagland´s solution per pot
when the substrate reached a humidity of 30%
of the eld capacity (FC) (Fuentes, 2003). To
avoid the accumulation of nutrients and salts in
the substrate, every third irrigation the substrate
was washed with distilled water until the elec-
trical conductivity of the substrate was less than
that of the Hoagland´s solution. After 28 days
the experimental treatments with NaCl, NO3
-
and SA began. All these chemical compounds
were added to the Hogland´s medium (Gunes et
al., 2007). Treatments are indicated in Table 1;
there were 9 treatments with 5 repetitions using
5 plants per treatment. Treatments were contin-
ued for 58 days; measurements started after 30
days of treatment. The parameters determined
included water potential (Ψw), osmotic potential
(Ψs), relative water content (RWC), turgor po-
tential and osmotic adjustment (OA).
Tab le 1. Experimental Treatments. In the experiments there were 5 plants for treatment.
Plants were grown in individual pots and irrigated with Hoagland’s medium for 28 days.
After this time the experimental treatments begun.
Treatment group Treatments
T1 Control (Hoagland´s solution only)
T2 Hoagland´s solution + 100 mM NaCl (HS100)
T3 HS100 + 6 mM N03
-
T4 HS100 + 0.1 mM SA
T5 HS100 + 0.5 mM SA
T6 HS100 + 1.0 mM SA
T7 HS100 + 0.1 mM SA + 6 mM N03
-
T8 HS100 + 0.5 mM SA + 6 mM N03
-
T9 HS100 + 1.0 mM SA + 6 mM N03
-
Measurement of water relations
The water potential (Ψw), the osmotic poten-
tial (Ψs) and the relative water content (RWC)
were measured at 9:00 in the sixth complete-
ly expanded leaf. At the same time, the root
osmotic potential (Ψs) was measured. The
reported results are the mean of two values
measured two days apart, each measurement
performed 16 hours after watering.

CIENCIA E INVESTIGACIÓN AGRARIA74
Leaf Ψw was measured with a pressure bomb
(PMS Model 600, USA) according to Scholan-
der et al. (1965). The osmotic potential of
leaves and roots was measured in tissue sec-
tions which were frozen at -20º C for 2 hrs
and then macerated and centrifuged at 13,200
g for 5 min to extract the cell sap. Osmolal-
ity was measured in an osmometer (Roebling
Messtechnick D-14129) using 100 µL of sap
in an Eppendorf tube calibrated with distilled
water. Van’t Hoff’s equation was used to cal-
culate the osmotic potential (Y
s) of the solution
(Nobel, 1991):
Y
s = - C R T [1]
C = Concentration of the solution, expressed
as mola lity.
R = Universal gas constant, 0.083 kg bar mol-1
K-1.
T = Absolute temperature in degrees Kelvin
(298 ºK).
RWC is expressed as:
RWC = 100 x (fresh weight – dry weight)/(turgid
weight – dry weight) [2]
The turgor potential of leaves (Y
p) was estimat-
ed as the difference between the water potential
(Y
w) and osmotic potential (Y
s):
Y
p = Y
w - Y
s [3]
The leaf osmotic adjustment (OA) was ob-
tained using the value of Y
s at maximum tur-
gidity (Y
s
100), which was estimated as the prod-
uct of the values of Y
s and RWC (Irigoyen et
al., 1996):
Y
s
100 = (Y
s x RWC)/100 [4]
OA was then calculated as the difference between
the values of the osmotic potential at maximum
turgidity of the plants treated with salts (Ψs
100s)
and the control plants (Ψs
100c). The water condi-
tion of the substrate must be optimum for this
measurement, to eliminate the possibility of plant
dehydration due to a deciency of irrigation that
could mask the effect of the treatment.
OA = (Ψs
100c - Ψs
100s) [5]
Design and statistical analysis
A completely randomized experimental design
was established with nine treatments and ve
replicates for the measurements of the plant wa-
ter relations parameters. The results obtained
were subject to an analysis of variance (ANO-
VA) and the means were compared according to
Tukey’s test (P ≤ 0.05).
Results
Water Potential (Ψw)
Water potential decreased after treatment with
NaCl. 0.5 mM SA increased the water potential
to a similar value to that of the control without
salinity, annulling the osmotic effect of NaCl.
However, its interaction with NO3
- decreased the
water potential signicantly, as concentrations
of SA-NO3
- increased. Concentrations inferior
or superior to 0.5 mM were not effective in re-
verting Ψw (Figure 1).
Potencial híd. raya
b
d
c
c
b
a
c
c
-1.8
-1.4
-1.0
-0.6
-0.2 0.00.2 0.40.6 0.81.0 1.2
SA (mM)
Ψw(MPa)
Control
NaCl-SA
NaCl-SA-NO
3-
Figu re 1. Mitigating ef fects of SA and SA with 6 mM NO3
- on
the lea f Ψw of plants of ma ize, cv. Lluteño. The deter minations
were per formed 30 days aft er treatment . Each dot corr esponds
to ve independent determinat ions with their SD (vertical
bars). Different letters represent signicant differences
among treatments (Tukey test, P ≤ 0.05).
Osmotic Potential (Ψs) of leaves and roots
Treatment with 100 mM NaCl caused a decrease
in Ψs in both leaves and roots; the decrease was

75
VOLUME 37 Nº3 SEPTEMBER - DECEMBER 2010
greater in the leaves (Figures 2 and 3). In leaves,
the Ψs of the treatments with SA and SA-NO3
-
decreased more than the NaCl treatment. In
roots, the treatment with 0.5 mM SA produced
a Ψs greater than that of the NaCl treatment and
close to the value of the control. The responses
of osmotic potential to the treatments were simi-
lar to those of the water potential.
c
bab ab
b
ab a
ab
-2.5
-2.0
-1.5
-1.0
-0.5
-0.2
0.00.2 0.40.6 0.81.0
1.2
SA (mM)
Ψ
s
leaf (MPa)
Control
NaCl-SA
NaCl-SA-NO
3
-
Figure 2 . Mitigating effects of SA and SA with 6 mM NO3
-
on the leaf Ψs of plants of maize, cv. Lluteño. The determi-
nations were performed 30 days after treatment. Each dot
corresponds to ve independent determinations with their
SD (vertical bars). Different letters represent signicant
differences among treatments (Tukey test, P ≤ 0.05).
c
d
b
cc
c
a
ab
-1.1
-1.0
-0.9
-0.8
-0.7
-0.6
-0.2 0.00.2 0.40.6 0.81.0 1.2
SA (mM)
Ψ
s
root (MPa)
Control
NaCl-SA
NaCl-SA-NO
3
-
Figure 3. Mitigating effects of SA and SA with 6 m M NO3
- on
the root Ψs of plants of maize, cv. Lluteño. The determinations
were performed 30 days after t reatment. Each dot cor responds
to ve independent determinations with thei r SD (vertical
bars). Different letters represent signicant differences among
treatments (Tukey test, P ≤ 0.05).
Relative water content (RWC)
The application of NaCl caused a signicant de-
crease in RWC. The treatments with NO3
-, 0.5 mM
SA-NO3
- and 1.0 mM SA counteracted the effect of
NaCl, returning the RWC to the value of the con-
trol plants without salinity (Figure 4). Although
0.5 mM SA mitigated the effect of 100 mM NaCl,
it did not return RWC to the level of the control.
ab
b
c
c
ab
a
ab
ab
74
76
78
80
82
84
86
88
90
-0.2
0.00.2 0.40.6 0.81.0
1.2
SA (mM)
RWC (%)
Control
NaCl-SA
NaCl-SA-NO
3
-
Figure 4 . Mitigating effects of SA and SA with 6 mM NO3
-
on the leaf RWC of plants of maize, cv. The determinations
were performed 30 days after treatment. Each dot
corresponds to ve i ndependent determinations with their
SD (vertical bars). Different letters represent signicant
differences among treatments (Tukey test, P ≤ 0.05).
Turgor potential (Ψp)
Turgor potential was signicantly affected by
the treatment with 100 mM NaCl. Four of the
treatments mitigated the effect of salinity: NO3
-,
0.1 mM SA, 0.1 mM SA-NO3
- and 0.5 mM SA;
these all produced a turgor potential greater
than that of the control without salt (Figure 5).
The greatest positive effect was produced by 0.5
mM SA, however, when combined with NO3
- it
produced a greater decrease in turgor than that
produced by NaCl. The Ψp of the treatment with
0.5 mM SA-NO3
- was signicantly different
from the control without salt; however, the dif-
ferences between turgor values are small. The
three treatments with greatest growth (Table 2)
(control, NO3
- and 0.5 mM SA-NO3
-) had very
similar turgor values.
e
c
a
d
c
b
f
d
0.0
0.2
0.4
0.6
0.8
1.0
-0.2 0.00.2 0.40.6 0.81.0 1.2
SA (mM)
Ψp(MPa)
Control
NaCl-SA
NaCl-SA-NO
3
-
Figure 5 . Mitigating effec ts of SA and SA with 6 mM NO3
- on
the leaf Ψp of plants of maize, cv. Lluteño. The determinat ions
were per formed 30 days aft er treatment . Each dot corr esponds
to ve independent determinations with their SD (vertical
bars). Different letters represent signicant differences
among treatments (Tukey test, P ≤ 0.05).

CIENCIA E INVESTIGACIÓN AGRARIA76
Osmotic adjustment (OA)
OA was lower in the treatment with NaCl 100 mM.
All the treatments with SA and NO3
- increased the
osmotic adjustment signicantly above the level of
the NaCl treatment. The most efcient conditions
of mitigation and increase of OA were found in the
treatments with all the combinations SA-NO3
- and
with 0.5 mM SA (Figure 6).
bc
ab
cd
d
ab
ab
a
bc
0.0
0.1
0.2
0.3
0.4
0.5
0.6
-0.2 00.2 0.40.6 0.811.2
SA (mM)
OA (MPa)
Control
NaCl-SA
NaCl-SA-NO
3
-
Figure 6. Mitigating effects of SA and SA with 6 mM
NO3
- on the leaf OA of plants of maize, cv. Lluteño. The
determinations were performed 30 days after treat ment. Each
dot cor responds to ve independent determi nations with
their SD (vertical bars). Different letters represent signicant
differences among treatments (Tukey test, P ≤ 0.05).
Discussion
NaCl 100 mM ca use d a signi ca nt dec rea se i n
the water relation parameters RWC, Ψw, leaf
Ψs, root Ψs, Ψp and OA in maize cv. Lluteño.
Our results demonstrate that this decrease
may be reverted with an appropriate concen-
tration of SA interacting with 6 mM NO3
- ap-
plied in the irrigation solution. The mitigating
effect of 0.5 mM SA on the effects of salin-
ity was shown by increases in leaf RWC, leaf
Ψw, root Ψs, leaf Ψp and leaf OA, compared to
the treatment with NaCl. The addition of both
compounds might favor water absorption and
plant growth, and therefore also have a miti-
gating effect. Thus growth, measured by plant
height, leaf area and fresh weight of greenery
and of roots was greater in the treatment with
0.5 mM SA-NO3
-, in spite of the decrease in
the values of Ψw in leaves and Ψs in leaves and
roots.
Tab le 2. Mitigating effects of SA and NO3
- on plant growth. The table shows the plant height, total leaf area, foliage fresh
weight and root fresh weight as % of control pla nts (plants g rown in Hoaghland solution). The gures correspond to ve
different determinations with their SD. Different letters represent sig nicant differences among treatments (Tukey test,
P ≤ 0.05).
Plant growth (% control)
Treatment Plant height Total leaf area Foliage fresh
weight Root fresh weight
1 Control 100.0 ± 5.8 a 100.0 ± 13.2 a 100.0 ± 4.0 a 100.0 ± 9.6 b
2 NaCl 46.9 ± 3.1 c 36.9 ± 5.9 d 36.8 ± 1.2 d 71.1 ± 11.4 cd
3 NaCl-NO3 98.3 ± 5.8 a 67.5 ± 4.4 b 97.0 ± 6.3 a 147.1 ± 13.9 a
4 NaCl-0.1 SA 25.4 ± 0.4 d 19.4 ± 3.7 e 15.7 ± 0.7 e 10.4 ± 1.0 e
5 NaCl-0.5 SA 52.8 ± 5.6 c 47.8 ± 7.0 cd 44.5 ± 0.7 c 80.2 ± 5.2 c
6 NaCl-1.0 SA 18.2 ± 0.3 d 16.9 ± 3.4 e 14.1 ± 0.8 e 15.0 ± 3.1 e
7 NaCl-0.1 SA-NO3 47.0 ± 3.5 c 35.7 ± 4.1 d 39.7 ± 2.8 cd 59.5 ± 4.0 d
8 NaCl-0.5 SA-NO3 59.9 ± 2.5 b 57.6 ± 7.7 bc 65.2 ± 6.0 b 96.3 ± 5.8 b
9 NaCl-1.0 SA-NO3 24.4 ± 0.9 d 15.9 ± 2.5 e 13.9 ± 1.2 e 15.1 ± 1.7 e

77
VOLUME 37 Nº3 SEPTEMBER - DECEMBER 2010
Water potential (Ψw)
It is known that SA with NO3
- reduces Ψw (Song
et al., 2006, Szepesi et al., 2009). The magni-
tude of this reduction will depend on how they
are applied, their concentrations, and the plant
species (Hayat et al., 2008). In the case of
maize cv. Lluteño, concentrations lower than
0.5 mM SA were inefcient, while greater con-
centrations were supraoptimal. This reinforces
the idea that SA acts as a hormonal factor with
a specic optimum concentration.
In contrast to the action of 0.5 mM SA, its com-
bination with 6 mM NO3
- caused a decrease
in leaf Ψw and root Ψ
s. A number of authors
(Wahbi et al., 2005; Centritto et al., 2005) have
suggested that this decrease favors the absorp-
tion of water under saline conditions, and thus
this treatment is positive in terms of produc-
ing greater growth. Nevertheless, the signi-
cant differences between the Ψw of the leaves
and the Ψs of the roots favored growth in plants
with 0.5 mM SA, with or without NO3
-.
Osmotic potential (Ψs) of leaves and roots
Osmotic potential decreased signicantly in
plants treated with NaCl, which has also been
shown for many other species that grow in
saline conditions (Çiçek and Çakirlar, 2002;
Wahbi et al., 2005, Carillo et al., 2008). As in
the case of Ψw, Ψs decreased in plants treated
with 0.5 mM SA-NO3
-, while 0.5 mM SA re-
turned the Ψs of the roots to the values of con-
trol plants. However, in the leaf 0.5 mM SA did
not have this effect. 0.5 mM SA alone and in
combination with NO3
- increased the concen-
trations of sugars in maize cv. Lluteño (unpub-
lished results), which are osmolytes, favorable
for the retention of water in the cell. This re-
tention of water due to increase in sugars may
explain the greater growth of plants subjected
to these treatments.
Relative water content (RWC)
The decrease in the Ψw of the plant, caused by sa-
linity, produced a reduction in Ψs, which resulted
in a reduction in RWC in leaves of the plants of
maize cv. Lluteño. These effects of salinity have
been reported for other species (Çiçek and Çakir-
lar, 2002; Chartzoulakis, 2005). The high con-
centration of salt retains water in the substrate,
which would imply less water absorption by
the roots, aggravated by a loss of water through
the roots (Burgess and Bleby, 2006). The con-
sequence of this water loss is a lower RWC. SA
and NO3
- revert these adverse effects of salinity,
possibly by means of an osmotic regulation at
the level of the leaf and root (Song et al., 2006).
This reversion of the RWC appears to indicate
that these mitigating agents favor the entrance
of water in the roots and/or avoid water loss by
the roots (Carvajal et al., 1999; Hasegawa et al.,
2000; Zhu, 2001; Martinez-Ballesta et al., 2006;
Burgess and Bleby, 2006). The increase in RWC
caused by SA was directly related to its concen-
tration in the experimental range used, support-
ing the idea that SA may be considered as a hor-
mone. However, its molecular role is unknown
(Gunes et al., 2005). NO3
- has been considered
an osmotic regulator due to its ability to replace
other solutes, especially in halophytic plants
(Veen and Kleinendorst, 1986; Song et al., 2006).
If NO3
- is an osmotic regulator, it will diminish
the negative effects caused by the entrance of
NaCl and will facilitate water transport by the
roots, increasing water absorption as well as pro-
viding a nutritional effect (McIntyre et al., 1996;
Song et al., 2006). It is interesting to note that in
halophytic plants a greater salt concentration in-
duces the expression of aquaporin genes, allow-
ing water to enter the plant (Qi et al., 2009). This
may also be the case for NO3
-; it might induce
the expression of aquaporin genes of maize cv.
Lluteño as salinity does for halophytic plants (Qi
et al., 2009).
Because the RWC increased signicantly in the
treatments with 0.5 mM SA, NO3
- and with 0.5
mM SA-NO3
- compared to the NaCl treatment,
the greater growth observed is due to the re-
covery of the RWC. The reversion of the RWC
in plants by these treatments suggests that the
mitigation is produced by root water absorp-
tion. It may be that these treatments (SA, NO3
-,
and SA 0.5 mM-NO3
-) activate the expression of
aquaporins in the plasmalemma of the root and
leaves, as it occurs with salt in halophytic plants
(Qi et al., 2009).

CIENCIA E INVESTIGACIÓN AGRARIA78
Turgor potential (Ψp)
According to Hasegawa et al. (2000), a plant
cell exposed to a saline medium equilibrates its
water potential by decreasing cell water, which
causes a decrease in YP. We observed this ef-
fect in maize cv. Lluteño only in the treatments
Table 1 with NaCl and 0.5 mM SA-NO3
-. The
treatments with NO3
-, 0.1 mM SA-NO3
-, 0.1 mM
SA and 0.5 mM SA caused an increase in turgor.
In contrast, treatments with 1.0 mM SA with or
without NO3
- did not cause variation from con-
trol values.
Therefore, the mitigating action of 0.5 mM SA
is not only due the increase of Ψw and Ψ
s, but
also because it increases Ψp. The greater turgor
induced by SA 0.5 mM was 241.7% of the con-
trol value, which may explain the reversion of
growth to 50% of the control. The reversion of
root growth was even more notable, reaching
80% of the control value. We may speculate that
this greater root growth could be induced by an
increase in ABA in the root, also induced by SA
0.5 mM (Sharp et al., 1993; Szepesi et al., 2009).
The lowest turgor was observed in the treatment
0.5 mM SA-NO3
- (61.1 % of the control), which
was even lower than the NaCl treatment (83%
of control). However, greater growth was pro-
duced when 0.5 mM SA interacted with NO3
-.
Leaf osmotic adjustment (OA)
100 mM NaCl decreased the leaf OA of maize,
cv. Lluteño. All treatments which included SA
and SA-NO3
- reverted the OA, possibly due to
an increase in the osmolyte concentration in
the vacuoles. If this is the case, the increase of
osmolytes would cause the cell to increase the
ow of water towards the vacuole, which would
increase its volume without losing water. The
result would be an increase in Ψp, and plant
growth (Parida and Das, 2005). OA may also be
produced by the participation of other organic
solutes as well as sugars, by which plants may
also recover their Ψw and Ψp (Hasegawa et al.,
2000; De Costa et al., 2007). However, in our
experiments 0.1 mM SA and NO3
- increased OA
less than other treatments did. In summary, the
rest of the treatments produced a highly signi-
cant effect on osmotic regulation of maize, cv.
Lluteño, and their mitigating effects led to a re-
covery of water in the cell.
In summary, our results of determinations of wa-
ter relations in plants of maize cv. Lluteño treated
with 100 mM NaCl lead us to conclude that: 1)
SA is a good mitigator of the effects of salt stress
at a concentration of 0.5 mM. 2) Treatment with
0.5 mM SA in combination with 6 mM NO3
- is a
better treatment than with only one of them re-
verting the negative effect of NaCl on growth. 3)
The reversion of the deteriorating effects of NaCl
by these mitigants implies the reversion of Ψp due
to the increase of OA, which induces the uptake
of water and plant growth.
Acknowledgements
This report is part of the requirements for the
Doctoral Degree in Ciencias Silvoagropecu-
arias of the Facultad de Ciencias Agronómi-
cas, University of Chile given to Hugo Es-
cobar. The research was funded by the Uni-
versidad de Tarapacá and CONICYT through
the Centro de Investigación del Hombre en el
Desierto (CIHDE). We thank the Convenio
de Desempeño Universidad de Tarapacá-
MINEDUC, Libertad Carrasco for help with
the physiological analyses, Francisco Fuentes
and Victor Tello of Universidad Arturo Prat,
Iquique for their help with statistical analy-
ses, and Elvis Hurtado for his permanent as-
sistance in physiological analyses and equip-
ment maintenance.

79
VOLUME 37 Nº3 SEPTEMBER - DECEMBER 2010
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