In vitro-grown cells of Sesuvium portulacastrum L., an important 'salt accumulator' mangrove associate, were incubated on a medium containing different levels of salt, including 0, 100, 200, or 400 mM NaCl, in order to evaluate biochemical, physiological, and growth responses. A significant decrease in callus growth, water status, and cell membrane damage was observed under salt stress. Osmotic adjustment was revealed by the accumulation of inorganic ions, such as sodium (Na ? ), and organic osmolytes (proline, glycine betaine, and total soluble sugars) in NaCl-treated calli compared to control. However, accretion of osmolytes and inorganic ions did not support growth of calli under NaCl stress conditions. The observed reduced growth rate in calli subjected to stress, up to 200 mM NaCl, was coupled with lower catalase and ascorbate peroxidase activities and with a significantly higher superoxide dismutase activity. These findings suggested that S. portulacastrum cell cultures exhibited higher osmotic adjustment to salt stress.
The effect of optimal and supra-optimal concentrations (0, 200, 400 or 600 mM) of NaCl on the growth, osmotic adjustment and antioxidant enzyme defence was studied in the in vitro cultures of Sesuvium portulacastrum. A significant increase in growth, tissue water content (TWC) and fresh to dry weight ratio (FW/DW) was observed in the shoots exposed to 200 mM salt. Minimum damage to the membrane in terms of low relative electrolytic leakage (REL) and malondialdehyde (MDA) content and better osmotic adjustment at 200 mM salt stress was coupled with the higher accumulation of sodium ions and total soluble sugars as against low proline and glycine betaine contents. A fine tuning of antioxidant enzyme activities (superoxide dismutase, catalase and ascorbate peroxidase) was also found to be responsible for the optimum growth of shoots. In contrast, sub-optimal (0 mM) and supra-optimal concentrations (400-600 mM) of NaCl significantly affected the growth, water status and increased the REL as well as MDA content of the shoots due to the accumulation of toxic concentrations of saline ions. The highest accumulation of proline and glycine betaine in addition to antioxidant enzyme activities exhibited higher osmotic adjustment and survival of the shoots under sub-or supra-optimal concentrations of NaCl as a penalty to reduced growth.
International audienceSesuvium portulacastrum L. is a pioneer plant species, used for sand-dune fixation, desalination and phytoremediation along coastal regions. The plant tolerates abiotic constraints such as salinity, drought and toxic metals. S. portulacastrum is also used as a vegetable, fodder for domestic animals and as an ornamental plant. S. portulacastrum grows luxuriantly at 100–400 mM NaCl concentrations. It further grows at severe salinity of 1000 mM NaCl without any toxic symptoms on the leaves. The plant also produces 20-hydroxyecdysone, an insect molting hormone for use in sericulture industry. This review analyses research undertaken during last two to three decades in physiology, biochemistry, molecular biology and biotechnology, to unravel the plasticity of the plant tolerance mechanism. Physiological and biochemical studies evidence the tolerance potential of the plant to abiotic stresses and reveal molecular mechanisms of stress tolerance. Biotechnological studies show the efficacy of the plant to produce pharmaceuticals. Large-scale multiplication of S. portulacastrum in the arid and semiarid regions should reduce the load of saline salts and heavy metals
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