The endophytic bacterium Sphingomonas SaMR12 alleviates Cd stress in oilseed rape through regulation of the GSH-AsA cycle and antioxidative enzymes

Abstract

Background: Microbes isolated from hyperaccumulating plants have been reported to be effective in achieving higher phytoextraction efficiency. The plant growth-promoting bacteria (PGPB) SaMR12 from the cadmium (Cd)/ zinc hyperaccumulator Sedum alfredii Hance could promote the growth of a non-host plant, oilseed rape, under Cd stress. However, the effect of SaMR12 on Brasscia juncea antioxidative response under Cd exposure was still unclear. Results: A hydroponic experiment was conducted to study the effects of Sphingomonas SaMR12 on its non-host plant Brassica juncea (L.) Czern. under four different Cd treatments. The results showed that SaMR12 could colonize and aggregate in the roots and then move to the shoots. SaMR12 inoculation promoted plant growth by up to 71% in aboveground biomass and 81% in root biomass over that of the non-inoculated plants. SaMR12-inoculated plants significantly enhanced root Cd accumulation in the 10 and 20 μM Cd treatments, with 1.72-and 0.86-fold increases, respectively, over that of the non-inoculated plants. SaMR12 inoculation not only decreased shoot hydrogen peroxide (H 2 O 2) content by up to 38% and malondialdehyde (MDA) content by up to 60% but also reduced proline content by 7-30% in shoots and 17-32% in roots compared to the levels in non-inoculated plants. Additionally, SaMR12 inoculation promoted the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) and facilitated the relative gene expression levels of dehydroascorbate reductase (DHAR) and glutathione reductase (GR) involved in the glutathione (GSH)-ascorbic acid (AsA) cycle. Conclusions: The results demonstrated that, under Cd stress, SaMR12 inoculation could activate the antioxidative response of B. juncea by decreasing the concentrations of H 2 O 2 , MDA and proline, increasing the activities of antioxidative enzymes, and regulating the GSH-AsA cycle. These results provide a theoretical foundation for the potential application of hyperaccumulator endophytic bacteria as remediating agents to improve heavy metal tolerance within non-host plant species, which could further improve phytoextraction efficiency.

Efficacy of Indole Acetic Acid and Exopolysaccharides-Producing Bacillus safensis Strain FN13 for Inducing Cd-Stress Tolerance and Plant Growth Promotion in Brassica juncea (L.)

“…A positive impact of inoculation with Klebsiella pneumoniae strain K5 on activities of SOD, and CAT has also been reported by Pramanik et al [25]. Wang et al [94,95] reported the effectiveness of Sphingomonas SaMR12 to alleviate Cd-stress in rapeseed by regulating the Reduced glutathione (GSH)-AsA cycle through activities of antioxidant enzyme systems. In our study, the strain FN13 showed significantly better results than other two strains in improving the growth, physiology, and antioxidants status of Brassica juncea (L.) plants that might be due to better survival efficacy of the strain FN13 under Cd-stress.…”

The Growth of Plants and Indigenous Bacterial Community Were Significantly Affected by Cadmium Contamination in Soil-Plant System

“…Although many studies have concerned the in uence of Cd on soil microbial communities, less research has paid attention on plant microbial community (phyllospheric and endophytic) affected by contaminant. The phyllosphere and endosphere bacteria are important in remediation of heavy metal pollutions (Jia, et al, 2018;Wang, et al, 2020b) and some of them could promote the plant growth (Bulgarelli et al, 2013). In this study, there are no signi cant variation for phyllospheric and leaf endophytic bacterial diversities, but root endophytic bacterial diversities under Cd stress was altered (Additional le 2: Fig.…”

“…Phyllosphere (Jia et al, 2018) and endophytic bacteria (Wang et al, 2020b) are also bene cial in phytoremediation. However, less attention has been paid to the effect of Cd on plant microbial community (phyllospheric and endophytic bacterial communities) in the soil-plant ecosystem.…”

A Degeneration Gradient of Poplar Trees Contributes to the Taxonomic, Functional, and Resistome Diversity of Bacterial Communities in Rhizosphere Soils

“…At the genus level, Bradyrhizobium and Mesorhizobium contains species widely known as nitrogen-fixing bacteria with legumes, and they have an outstanding ability to promote the growth of non-legumes through the production of indole-3-acetic acid (IAA) and siderophores, the solubilization of potassium and phosphate [ 37 ]. Members of the Sphingomonas genus increased Arabidopsis thaliana growth rate, alter rhizosphere microbial community structure of plant under drought stress [ 38 ], and alleviate Cd stress in oilseed rape through regulation of the GSH-AsA cycle and antioxidative enzymes [ 39 ]. Variovorax genus has the potential to promote plant growth, due to its ability to hydrolyze cellulose [ 40 ] and to produce plant growth enzymes and substances such as siderophores, IAA and 1-aminocyclopropane-1-carboxylic acid deaminase [ 41 , 42 , 43 ].…”