Eco-physiological adaptations of Panicum antidotale to hyperosmotic salinity: Water and ion relations and anti-oxidant feedback

Abstract

Threshold of salt resistance of plants is determined by their response to osmotic and ionic stress (primary constraints) imposed upon them. However, recent reports emphasize the importance of secondary constraints like oxidative stress. The aim of this study was to determine the effect of salinity on growth, mineral nutrition, water relations, compatible solutes, and the antioxidant system in Panicum antidotale.Five levels of salinity (0, 125, 250, 375 and 500mM NaCl) were applied using a quick check system in a fully randomized greenhouse study. Plant growth parameters, water relations, organic (proline and soluble sugars), inorganic osmolytes (Na+, K+, Ca++and Mg++), and macronutrients such as carbon or nitrogen were measured beside the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APx) and glutathione reductase (GR) and non-enzymatic antioxidant metabolites (oxidized and reduced ascorbate).Sodium chloride concentrations above 125mM substantially inhibited growth. This inhibition was attributed to high energy costs needed for osmotic adjustment, ion compartmentalization, synthesis of organic osmolytes (such as proline and sugars), ROS scavenging and the maintenance of ionic homeostasis. The plants resisted against oxidative stress by increasing activities of antioxidant enzymes such as SOD, APx, GR and CAT and elevating levels of oxidized and reduced ascorbate (DAsA and AsA) at higher salinity. They also maintained a low redox ratio of ascorbate/dehydro-ascorbate and therefore a high capacity to manage oxidative stress. Thus P. antidotale is capable of managing ROS stress at high salinity and therefore can be sustainably grown as a fodder crop in saline arid regions.