Antioxidant response of cowpea co-inoculated with plant growth-promoting bacteria under salt stress

Abstract

Soil salinity is an important abiotic stress worldwide, and salt-induced oxidative stress can have detrimental effects on the biological nitrogen fixation. We hypothesized that co-inoculation of cowpea plants with Bradyrhizobium and plant growth-promoting bacteria would minimize the deleterious effects of salt stress via the induction of enzymatic and non-enzymatic antioxidative protection. To test our hypothesis, cowpea seeds were inoculated with Bradyrhizobium or co-inoculated with Bradyrhizobium and plant growth-promoting bacteria and then submitted to salt stress. Afterward, the cowpea nodules were collected, and the levels of hydrogen peroxide; lipid peroxidation; total, reduced and oxidized forms of ascorbate and glutathione; and superoxide dismutase, catalase and phenol peroxidase activities were evaluated. The sodium and potassium ion concentrations were measured in shoot samples. Cowpea plants did not present significant differences in sodium and potassium levels when grown under non-saline conditions, but sodium content was strongly increased under salt stress conditions. Under non-saline and salt stress conditions, plants co-inoculated with Bradyrhizobium and Actinomadura or co-inoculated with Bradyrhizobium and Paenibacillus graminis showed lower hydrogen peroxide content in their nodules, whereas lipid peroxidation was increased by 31% in plants that were subjected to salt stress. Furthermore, cowpea nodules co-inoculated with Bradyrhizobium and plant growth-promoting bacteria and exposed to salt stress displayed significant alterations in the total, reduced and oxidized forms of ascorbate and glutathione. Inoculation with Bradyrhizobium and plant growth-promoting bacteria induced increased superoxide dismutase, catalase and phenol peroxidase activities in the nodules of cowpea plants exposed to salt stress. The catalase activity in plants co-inoculated with Bradyrhizobium and Streptomyces was 55% greater than in plants inoculated with Bradyrhizobium alone, and this value was remarkably greater than that in the other treatments. These results reinforce the beneficial effects of plant growth-promoting bacteria on the antioxidant system that detoxifies reactive oxygen species. We concluded that the combination of Bradyrhizobium and plant growth-promoting bacteria induces positive responses for coping with salt-induced oxidative stress in cowpea nodules, mainly in plants co-inoculated with Bradyrhizobium and P. graminis or co-inoculated with Bradyrhizobium and Bacillus.

Halo-tolerant plant growth promoting rhizobacteria for improving productivity and remediation of saline soils

“…HT-endophyte Pseudomonas stutzeri ISE12 isolated from halophyte Salicornia europaea upon inoculation to Brassica napus L. triggered antioxidant system and rearrangement of plant cell wall, consecutively inducing the tolerance in plants [85] . Inoculation of cowpea with HT-PGPR Bradyrhizobium and Pseudomonas graminis showed the accumulation of AsA and GSH and helped plants survival under salt stress [86] .…”

Roles of Plant Growth-Promoting Rhizobacteria (PGPR) in Stimulating Salinity Stress Defense in Plants: A Review

“…The bacterization of plant crops with PGPR and the implementation of these useful rhizobacteria in seed biopriming have demonstrated their beneficial properties in enhancing plant growth and development, and in augmenting plant salt stress tolerance through different mechanisms. PGPR aid to alleviate salinity stress in plants by boosting water absorption capability, enhancing essential nutrients uptake, accumulating osmolytes (OS) (e.g., proline (Pro), glutamate (Glu), glycine betaine, soluble sugars, choline, O-sulphate, and polyols), increasing AEs activities (e.g., superoxide dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), glutathione reductase (GR, EC 1.6.4.2), and non-enzymatic antioxidants (NEAs) (e.g., ascorbate (ASC), glutathione (GSH), tocopherols (TCP), carotenoids (Car), and polyphenols (PPs)) in plant tissues [ 24 , 25 , 26 , 27 , 28 ]. In all types of salinity, sodium chloride (NaCl) is the most soluble and widespread salt [ 17 ] and Na + is the primary cause of ion-specific damage for many plants, especially for graminaceous crops [ 29 ].…”

Downstream Signalling from Molecular Hydrogen

“…ROS also accumulate in the presence of salt, extreme temperature, and pathogens [ 52 ]. Increases in the intracellular ROS under such stress conditions are often accompanied by an increase in antioxidant levels in cells, for example, in the presence of salt [ 53 ], heavy metals [ 54 ], and extreme temperature [ 55 ]. Therefore, the modulation of ROS metabolism is crucial for stress responses: increases in ROS lead to changes in cellular function, whilst antioxidants modulate and dampen that response.…”