Improving plant adaptation to soil antimony contamination: the synergistic contribution of arbuscular mycorrhizal fungus and olive mill waste.

BACKGROUND: This study aimed to investigate the alterations in biochemical and physiological responses of oat plants exposed to antimony (Sb) contamination in soil. Specifically, we evaluated the effectiveness of an arbuscular mycorrhizal fungus (AMF) and olive mill waste (OMW) in mitigating the effects of Sb contamination. The soil was treated with a commercial strain of AMF (Rhizophagus irregularis) and OMW (4% w/w) under two different levels of Sb (0 and 1500 mg kg-1 soil). RESULTS: The combined treatment (OMW + AMF) enhanced the photosynthetic rate (+ 40%) and chlorophyll a (+ 91%) and chlorophyll b (+ 50%) content under Sb condition, which in turn induced more biomass production (+ 67-78%) compared to the contaminated control plants. More photosynthesis in OMW + AMF-treated plants gives a route for phenylalanine amino acid synthesis (+ 69%), which is used as a precursor for the biosynthesis of secondary metabolites, including flavonoids (+ 110%), polyphenols (+ 26%), and anthocyanins (+ 63%) compared to control plants. More activation of phenylalanine ammonia-lyase (+ 38%) and chalcone synthase (+ 26%) enzymes in OMW + AMF-treated plants under Sb stress indicated the activation of phenylpropanoid pathways in antioxidant metabolites biosynthesis. There was also improved shifting of antioxidant enzyme activities in the ASC/GSH and catalytic pathways in plants in response to OMW + AMF and Sb contamination, remarkably reducing oxidative damage markers. CONCLUSIONS: While individual applications of OMW and AMF also demonstrated some degree of plant tolerance induction, the combined presence of AMF with OMW supplementation significantly enhanced plant biomass production and adaptability to oxidative stress induced by soil Sb contamination.

Physiological and biochemical responses of wheat to synergistic effects of selenium nanoparticles and elevated CO2 conditions.

Elevating CO2 (eCO2) levels will change behavior and the effect of soil fertilizers and nutrients. Selenium NPs (SeNPs) have arisen as an alternative to conventional Se fertilizers to enrich crops. However, it remains unclear whether eCO2 will change the biological effects of soil SeNPs on plant growth and metabolism. The current study aimed to shed new light on the interactive impacts of eCO2 and SeNPs on wheat plants. Accordingly, the attempts were to reveal whether the application of SeNPs can modulate the eCO2 effects on wheat (Triticum aestivum L.) physiological and biochemical traits. With this goal, a pot experiment was carried out where the seeds were primed with SeNPs and plants were grown under two levels of CO2 concentrations (ambient CO2 (aCO2, 410 µmol CO2 mol-1; and eCO2 (710 µmol CO2 mol-1)) during six weeks after sowing. Although SeNPs+eCO2 treatment resulted in the highest accumulation of photosynthetic pigment content in leaves (+49-118% higher than control), strong evidence of the positive impacts on Rubisco activity (~+23%), and stomatal conductance (~+37%) was observed only under eCO2, which resulted in an improvement in photosynthesis capacity (+42%). When photosynthesis parameters were stimulated with eCO2, a significant improvement in dry matter production was detected, in particular under SeNPs+eCO2 which was 1.8 times higher than control under aCO2. The highest content of antioxidant enzymes, molecules, and metabolites was also recorded in SeNPs+eCO2, which might be associated with the nearly 50% increase in sodium content in shoots at the same treatment. Taken together, this is the first research documenting the effective synergistic impacts of eCO2 and SeNPs on the mentioned metabolites, antioxidants, and some photosynthetic parameters, an advantageous consequence that was not recorded in the individual application of these treatments, at least not as broadly as with the combined treatment.

Isolation and characterization of a plant growth­promoting rhizobacterium strain MD36 that promotes barley seedlings and growth under heavy metals stress.

Plant growth, promoting, bacteria, (PGPB) can improve plant germination and growth in heavy metal-contaminated land and enhance heavy metal removal efficiency. In this study, we isolated PGPR bacterial strains which can withstand heavy metal pollution and tested their ability to improve barley germination under heavy metal stress. Out of 16 multi-resistant heavy metal isolates, strain MD36 was identified by 16S rRNA sequencing and shared close relation to different species of the genus Glutamicibacter. The new isolated strain showed other important PGPR activities, mainly IAA production and salt tolerance. The effect of adding the strain MD36 to barley grains under heavy metal stress enhanced their germination up to 100%, while the percentage of germination ranged between 0 and 20% for non-inoculated grains. In addition, in these conditions, MD36 can significantly enhance barley growth by reducing the heavy metal effect. This study strongly recommends the use of MD36 as seed coatings trials in the field to enhance growth and yield in soils contaminated with heavy metals, as well as in bioremediation of HM-contaminated salt-containing soils and water.