In arid and semi-arid areas, the concentration of soluble salt in soil is enough to adversely affect plant growth. A cost-effective strategy to deal with salinity is to plant crops with inherent salt tolerance. Reactive oxygen species (ROS), such as superoxide radical (O2? ), hydrogen peroxide (H2 O2), hydroxyl radical (OH) [8] and singlet oxygen (O 1? ) [9] produced in plants during salt stress. These cytotoxic reactive oxygen species can seriously damage the normal metabolism through oxidative damage to lipid [10, 12], protein and nucleic acid [10–1]. This leads to the change of the selective permeability of biofilm [13], so that membrane leakage and the activity of enzymes bound to the membrane change [14].

At present, the physiological and biochemical mechanism of improving the salt tolerance of arbuscular mycorrhizal (AM) tomatoes is not clear, although the improvement of nutrient absorption may be one of the reasons [4-7]. Reactive oxygen species (ROS) such as superoxide radical (O2? ), hydrogen peroxide (H2 O2), hydroxyl radical (OH) [8] and singlet oxygen (O 1? ) [9], these cytotoxic active oxygen components can seriously damage normal metabolism through oxidative damage to lipid [10, 12], protein and nucleic acid [10–1]. This leads to the change of selective permeability of biofilm [13], which leads to the change of membrane leakage and enzyme activity combined with membrane [14].

The induction of ROS scavenging enzymes (such as SOD, POD, APX and CAT) is the most common mechanism of ROS synthesis during detoxification stress response [15]. Under the condition of low phosphorus, SOD and CAT were induced in the roots of Phaseolus vulgaris colonized by Glomus clarum in the late stage of symbiotic development, and their activities were evaluated [16]. Under drought stress, a higher level of SOD activity was also observed in lettuce (Lettuce) roots colonized by Glomus licheniformis or Glomus desert [17].

The most common detoxification mechanism of reactive oxygen species synthesized during stress reaction is to induce reactive oxygen species scavenging enzymes, such as superoxide dismutase (SOD), peroxidase (POD), ascorbic acid-peroxidase (APX) and catalase (CAT)[ 15]. Under the low phosphorus treatment, the arbuscular mycorrhizal fungus Glomus clarum infected the kidney bean, induced the root of the kidney bean to produce SOD and CAT at the late growth stage, and determined their activities [16]. At the same time, under drought stress, lettuce roots infected by arbuscular mycorrhizal fungi Glomus licheniformis or Glomus desert have higher SOD activity [17].

Under the condition of water stress rather than drought stress, the induction of CAT in the root of soybean (Glycine max Merr) colonized by mosses was observed [18]. However, the role of these enzymes in AM tomato is not clear, especially under the condition of persistent salt stress. In this study, the growth parameters, cell membrane permeability, SOD, POD, APX and CAT activities of AM and non-AM tomato roots were measured under 0.5, 1% NaCl and normal conditions. We evaluated the role of these reactive oxygen species scavenging enzymes in the enhanced salt tolerance of AMF. We also try to explain the improvement of salt tolerance of AM tomato from another aspect. "

Under water stress rather than drought stress, it was observed that the colonization of soybean root nodule by Glomus moseri was induced by CAT [18]. However, little is known about the role of these enzymes in AM tomatoes, especially under persistent salt stress. In this study, the growth and development parameters, cell membrane permeability, SOD, POD, APX and CAT activities of AM and non-AM tomato roots with salt contents below 0.5% and 1% were determined. We evaluated the effects of these active oxygen scavenging enzymes, and AMF enhanced their salt tolerance. We also try to explain the improvement of salt tolerance of AM tomato from another angle.