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The current study was carried out to check the influence of the gradient saline (0, 50, 150, 200, 250 and 300 mM NaCl) on

This study intended to focus on the effect of different levels of NaCl (0-400 mM, at regular intervals every 100 mM) on the growth, secondary metabolites, and antioxidant enzyme activities of Polygonum equisetiforme, a wild plant with medicinal and industrial uses, which often grows in harsh environmental conditions. Our results showed that biomass production significantly decreased with salinity, while the leaf relative water content declined only at high levels of NaCl concentration (300-400 mM). In contrast, these higher doses of salt resulted in a significant increase in malondialdehyde (MDA) content. Both proline and soluble sugar (e.g., fructose, glucose, and sucrose) contents were enhanced under saline conditions. The methanolic extracts of the shoots included 10 flavonoids and 9 phenolic acids. The total phenolic acids (TPA), total flavonoid compounds (TFC), and total phenolic compounds (TPC) increased with salinity, particularly at 300 mM NaCl. An increase in TPA resulted especially from an increase in quinic, gallic, and protocatechuic acids (phenolic compounds), followed by quercetin-3-O-galactoside, catechin, and epicatechin (flavonoid compounds). Superoxide dismutase (SOD) activity increased only at high salinity levels (>200 mM), while glutathione reductase (GR), guaiacol peroxidase (GPX), catalase (CAT), and ascorbate peroxidase (APX) activity increased with salinity level. A positive significant correlation between antioxidant DPPH and TPA, TFC, TPC, CAT, and APX suggests a vital protective role in controlling oxidative stress through the scavenging process. Consequently, our results indicated that P. equisetiforme shoots are rich in secondary metabolites, especially phenolic compounds with high potential antioxidant activities. It can be considered a salt-tolerant species able to survive at salinity levels up to 300 mM NaCl.

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Soil and water salinity is a major environmental problem in the dry Mediterranean regions, affecting rangeland production. This study investigated the effects of salinity on the wild perennial grass (Poaceae) species Stipa lagascae R. & Sch., a potential forage plant that could be used to rehabilitate degraded rangelands in dry areas. In a laboratory, 3-month-old S. lagascae seedlings were subjected to increasing salt treatments (0–400 mm NaCl) for 45 days. Physiological and biochemical parameters such as leaf water potential (Ψw), leaf relative water content (RWC), proline, total soluble sugars, Na+, K+ and Ca2+ contents, and catalase, ascorbate peroxidase and glutathione reductase activities were measured. Total soluble sugars and proline concentrations increased and Ψw and RWC decreased with increasing salt concentrations. Lower salt concentrations induced a non-significant degradation of chlorophyll pigments. Shoot Na+ content increased with a salinity level, whereas shoot K+ and Ca2+ concentrations decreased and the K+ : Na+ ratio was lower. The salinity threshold, above which S. lagascae showed signs of damage, occurred at 300 mm. Plants have evolved reactive oxygen species (ROS) scavenging enzymes including catalase, ascorbate peroxidase and glutathione reductase, which provide cells with an efficient mechanism to neutralise ROS. The tolerance strategies of S. lagascae to moderate salinity seem to include osmotic adjustment through total soluble sugars and proline accumulation, and highly inducible antioxidative defence. Further investigations are necessary to study the effect of salt stress on distribution of ions (Na+, K+, Ca2+, Mg2+, Cl–, NO3–, SO42–) and osmotic adjustment. Photosynthesis and water-use efficiency parameters could be also useful tools.

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