The Effects of the Endophytic Bacterium Pseudomonas fluorescens Sasm05 and IAA on the Plant Growth and Cadmium Uptake of Sedum alfredii Hance

Abstract

Endophytic bacteria have received attention for their ability to promote plant growth and enhance phytoremediation, which may be attributed to their ability to produce indole-3-acetic acid (IAA). As a signal molecular, IAA plays a key role on the interaction of plant and its endomicrobes. However, the different effects that endophytic bacteria and IAA may have on plant growth and heavy metal uptake is not clear. In this study, the endophytic bacterium Pseudomonas fluorescens Sasm05 was isolated from the stem of the zinc (Zn)/cadmium (Cd) hyperaccumulator Sedum alfredii Hance. The effects of Sasm05 and exogenous IAA on plant growth, leaf chlorophyll concentration, leaf Mg2+-ATPase and Ca2+-ATPase activity, cadmium (Cd) uptake and accumulation as well as the expression of metal transporter genes were compared in a hydroponic experiment with 10 μM Cd. The results showed that after treatment with 1 μM IAA, the shoot biomass and chlorophyll concentration increased significantly, but the Cd uptake and accumulation by the plant was not obviously affected. Sasm05 inoculation dramatically increased plant biomass, Cd concentration, shoot chlorophyll concentration and enzyme activities, largely improved the relative expression of the three metal transporter families ZRT/IRT-like protein (ZIP), natural resistance associated macrophage protein (NRAMP) and heavy metal ATPase (HMA). Sasm05 stimulated the expression of the SaHMAs (SaHMA2, SaHMA3, and SaHMA4), which enhanced Cd root to shoot translocation, and upregulated SaZIP, especially SaIRT1, expression to increase Cd uptake. These results showed that although both exogenous IAA and Sasm05 inoculation can improve plant growth and photosynthesis, Sasm05 inoculation has a greater effect on Cd uptake and translocation, indicating that this endophytic bacterium might not only produce IAA to promote plant growth under Cd stress but also directly regulate the expression of putative key Cd uptake and transport genes to enhance Cd accumulation of plant.

Low endogenous NO levels in roots and antioxidant systems are determinants for the resistance of Arabidopsis seedlings grown in Cd

“…Most data currently available on lipid peroxidation in response to Cd stress concern adult plants (Romero-Puertas et al, 2019); less is known about seedlings germinated and grown under Cd treatment. Thus, lipid peroxidation has been observed to increase in Cd-treated 6-day-old Arabidopsis seedlings (Chen et al, 2017), which is in line with our findings.…”

“…Oxidative stress is one of the primary effects of Cd treatment in both adult plants and seedlings (Chen et al, 2017;Gupta et al, 2017;Ortega-Galisteo et al, 2012). We have used the whole seedlings to analyse oxidative markers, as roots and leaves at the seedling stage are still too small to be analysed separately.…”

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

“…Several studies documented that endophytic bacteria associated with plant growth promotion, such as Bacillus licheniformis, enhanced copper (Cu), zinc (Zn), chromium (Cr), Cd and Pb accumulation and distribution in plants grown in heavy metal-contaminated soil, which led to reduced levels of toxic metals in the soil (Brunetti et al 2012). The endophytic bacterium Pseudomonas fluorescens Sasm05 promoted Sedum alfredii Hance growth and enhanced Cd accumulation in response to Cd stress [13].…”

Exogenous hemin improves Cd2+ tolerance and remediation potential in Vigna radiata by intensifying the HO-1 mediated antioxidant defence system

“…Numerous reports have demonstrated that the application of hemin as a potent biostimulator mitigates metal-induced oxidative stress by enhancing the stress tolerance of plants 1,10 . For example, the application of exogenous hemin ameliorates Al and Cd toxicity in Medicago sativa L. 11,12 , induces ammonium tolerance in Oryza sativa L. 10 and enhances salinity stress adaptations in Triticum aestivum L. 13 .…”

“…To the best of our knowledge, the influence of hemin on the cadmium resilience and removal potential of V. radiata has not yet been evaluated. Therefore, the aims of the present work were (1) to investigate the effect of exogenous hemin on the biomass production and chlorophyll content of V. radiata; (2) to analyse the mechanism by which hemin affects Cd tolerance of V. radiata; and (3) to verify the influence of exogenous hemin in improving the Cd phytoremediation efficiency of V. radiata.…”