Alleviating salt stress in tomato inoculated with mycorrhizae: Photosynthetic performance and enzymatic antioxidants

Abstract

Tomato cultivars (Sultana-7 & Super Strain-B) were germinated with various concentrations (0–200 mM) of NaCl. Seed germination in the Super Strain-B was promoted by 25 mM NaCl. However, the germination of both cultivars was progressively inhibited by 50 and 100 mM NaCl and obstructed at 200 mM NaCl, and this response was more pronounced for Sultana-7. Therefore, Super Strain-B was selected for further investigation, such as growth under NaCl stress (50 & 100 mM) and inoculation with vesicular-arbuscular mycorrhizal fungus (Glomus fasciculatum, VAMF). The leaves of Super Strain-B showed reduced mineral (N, P, K, Mg) uptake and K/Na ratio as well as increased Na uptake and N/P ratio in response to salinity. Moreover, salinity decreased the chlorophyll (Chl) contents coupled with an increase in Chl a/b, Hill-reaction activity, and quenched Chl a fluorescence emission. These changes reflect a disturbance in the structure, composition and function of the photosynthetic apparatus as well as the activity of photosystem 2. The superoxide dismutase and peroxidase activities of leaves were enhanced by salinity, whereas the catalase activity was decreased. Leaf polysaccharides and proteins as well as shoot biomass also decreased as a result of salinity, but the total soluble sugars and root to shoot ratio improved.VAMF enhanced both the photosynthesis and productivity of plants; thus, VAMF may alleviate the adverse effects of salinity in plants by increasing their salt tolerance. Although mycorrhizal infection showed a negative correlation with salinity, it remained relatively high (21 & 25%) at 100 mM NaCl. Keywords: Mycorrhizae, tomato, salinity, minerals, photosynthetic performance and antioxidant enzymes