Antiox Cassantioxidant Enzyme Responses To NaCl Stress in Cassia Angustifolia
Antiox Cassantioxidant Enzyme Responses To NaCl Stress in Cassia Angustifolia
Antiox Cassantioxidant Enzyme Responses To NaCl Stress in Cassia Angustifolia
Introduction
High salinity in the soil is a common environmental
problem, and affects almost all plant functions
(Greenway and Munns 1980). Under salt stress, plants
have adapted to osmotic and ionic stresses. These
mechanisms include osmotic adjustment by accumulation
of compatible solutes such as proline, glycine betaine and
polyols and lowering the toxic concentration of ions in
the cytoplasm by restriction of Na+ influx or its
sequestration into the vacuole and/or its extrusion
(Ghoulam et al. 2002).
Plants that are subjected to environmental stress often
suffer oxidative damage as the balance between the
production of reactive oxygen species (ROS) such as
superoxide radical, hydrogen peroxide and hydroxyl
radical and the quenching activity of antioxidants are
upset (Scandalios 1993). Plants have evolved
mechanisms to protect cell and subcellular systems from
Received 21 March 2003, accepted 15 January 2004.
Abbreviations: ASA - ascorbate; CAT - catalase; DAS - days after sowing; POX - peroxidase; PPO - polyphenol oxidase;
SOD - superoxide dismutase; TBARS - thiobarbituric acid reactive substances.
Acknowledgement: Authors are grateful to Prof. S.K. Agarwal, Mathematical Sciences, University of Texas at El Paso, for his help in
statistical analysis.
* Corresponding author; fax: (+91) 291 2512248, e-mail: sheelaagarwal@yahoo.com
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S. AGARWAL, V. PANDEY
Results
NaCl treatment of seedlings for 5 and 7 DAS resulted in
a significant reduction in the root and shoot length
(Fig. 1A,B). Fresh mass of seedling gradually decreased
with an increase in NaCl concentration at both stages.
The reductions were more pronounced at 100 mM
especially for 5 DAS. The dry mass was also affected by
NaCl treatment; with a greater reduction as the NaCl
concentration increased (Fig. 1C,D). The germination
percentage decreased with increasing salinity at both
stages. At the highest NaCl concentration (100 mM) the
germination percentage was reduced to less than 50 % in
comparison to unstressed seedlings (Fig. 1E). The
presence of NaCl in the medium induced an important
increase in Na+ and Cl- in the seedlings at both stages,
with the highest concentrations being reached at 100 mM
NaCl (Fig. 2).
SOD activity increased significantly at 20 and 50 mM
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Fig. 1. Effect of NaCl stress on senna seedling root length (A), shoot length (B), fresh mass (C), dry mass (D), and on germination
percentage (E). Vertical bars indicate SE of five replicates for each treatment and two dates of sowing.
Discussion
Salinity (NaCl) adversely affected the seedling growth
parameters (germination, fresh and dry mass and root and
shoot length) of senna seedlings. The results are similar
to those of Dash and Panda (2001) in Phaseolus mungo
and Ghoulam and Fares (2001) in sugar beet. Under salt
stress, senna seedlings accumulated more inorganic ions
Na+ and Cl- (Fig. 2). Similar results were reported in
sugar beet cultivars (Ghoulam et al. 2002), in rice (Lutts
et al. 1996) and in Sorghum bicolor (Colmer et al. 1996).
This accumulation of Na+ and Cl ions might be involved
in the osmotic adjustment.
The activity of antioxidant enzymes was reported to
increase under salinity in wheat shoot (Meneguzzo et al.
1999, Sairam and Srivastava 2002) and pea (Hernandez
et al. 1999). Most of the results of the study conducted
here show a correlation between the resistance to NaCl
stress and more effective antioxidative system. The
observed increase in SOD activity (Fig. 3A) could
increase the ability of the seedlings to scavenge
O2- radicals, which could cause membrane damage. At
higher NaCl concentration (100 mM) it seems that such
resistance to oxidative stress may be overcome leading to
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S. AGARWAL, V. PANDEY
Fig. 3. Effect of NaCl stress on SOD (A), CAT (B), POX (C), PPO (D) activities and proline (E), ASA (F), TBARS (G) and H2O2 (H)
contents of senna seedlings. Vertical bars indicate SE of three replicates for each treatment and two dates of sowing.
which may be due to increased activities of dehydroascorbate reductase (DHAR) and monodehydroascorbate
reductase (MDHAR) (not measured). It has been
demonstrated that salt treatment increases lipid
peroxidation or induce oxidative stress in plant tissues
(Mittal and Dubey 1991,Hernandez et al. 1994). The
results reported here show that the degree of
accumulation of TBARS was low indicating a decreased
lipid peroxidation due to salt stress. The elevated
558
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