Effect of NaCl stress on physiological, antioxidant enzymes and anatomical responses of Astragalus gombiformis

Abstract

The current study was carried out to check the influence of the gradient saline (0, 50, 150, 200, 250 and 300 mM NaCl) on Astragalus gombiformis Pomel. plants grown in pots in greenhouse conditions. The results demonstrated that salt levels above 50 mM substantially reduced the biomass accumulation in both roots and especially in shoots. Similarly, higher salinity (100-300 mM NaCl) resulted significant decline in net photosynthetic (-66.2%), transpiration (-80%), stomatal conductance (-87.7%), intercellular CO2 concentration (-78.1%) and chlorophyll a and b contents (-45.7 and -51%, respectively). Also, leaf relative water content (RWC) was reduced significantly with salinity exceeding 100 mM NaCl, while the leaf water potential (Ψw) decreased significantly as salinity rises. Salt stress increases Na+, Na+/K+ and decreases K+ concentrations in all tissues of A. gombiformis. Compensatory, an accumulation of organic osmolytes such as soluble sugars in response to higher salinity (150-300 mM NaCl) was observed, while proline content increased drastically with progressive salinity. The present study reveals that GPX and GR were highly used to protect from NaCl-induced H2O2. APX might to participate efficiently in restriction of oxidative damages under higher salinity (50-150 mM). The leaf anatomy showed an increase in upper epidermal thickness at higher salt level (300 mM), whereas the total leaf thickness and the mesophyll parenchyma area decreased with salinity exceeding 100 mM NaCl. The distance between vascular bundle and the xylem vessel diameter were reduced only at 300 mM. The stomatal density decreased with enhanced stomata size at 200-300 mM NaCl. Based on these physiological, biochemical and anatomical responses to salinity we conclude that A. gombiformis is unable to maintain the ionic homeostasis and to managing ROS stress at high salinity and therefore can tolerate only mild to moderate salinity.