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Rhizospheric Microbial Inoculation in Developing Stress Tolerance

photosystem II and photosynthetic products when there is a water shortage

(Ruiz-Lozano et al., 2016). Level of strigolactone rises in lettuce and tomato

plants to alleviate drought tensity by symbiosis development while improving

drought resistance (Ruiz-Lozano et al., 2016). AM fungus has also been

identified being a key element in reducing the salinity of soil. Inoculation

with AM have shown to improve plant development in salt-stress conditions.

In a saline environment, they prevent the absorption of sodium or chlorine by

citrus plants (Navarro et al., 2014). As a result, inoculation with PGPR and

various microorganisms can be used to help salt-sensitive crops cope with

salinity stress. Co-inoculation of PGM microorganisms and plant-related

fungi may improve the effectiveness of drought and salinity stress tolerance.

2.6 MICROBES AGAINST HEAVY METAL STRESS

Plant-related microbes, for example, firmicutes, rhizobacteria, mycorrhiza,

etc., as well as heavy metal tolerant microorganisms, have the capability to

enhance the growth and maturation of plants being in metal stress condi­

tions. Efflux, metal impermeability, sequestration of EPS, volatilization,

enzymatic detoxification, and complexation of metals are all methods

involving these bacteria. Furthermore, these bacteria linked with plants

stimulate plant growth and development by reducing ethylene levels,

producing plant growth regulators, including IAA and deaminase ACC, as

well as suppressing diseases (Glick, 2010) (Figure 2.2). Fixation of nitrogen,

nutrient mobilization, siderophores, as well as solubilization of phosphate,

among other things, help plants grow and remove heavy metals (Verma et

al., 2013; Ahmad et al., 2011). Heavy metals have been removed using both

live and non-living microbial biomass. Bioaccumulation of microbes is a

powerful way to remove heavy metals from contaminated soil. Firmicutes,

Actinobacteria along with Proteobacteria have been found to eliminate

larger concentrations of lead, manganese, and Arsenic from soil polluted

by metals (Zhang et al., 2015). According to Fatnassi et al. (2015), copper

(Cu) concentrations above 1 mM harmed Vicia faba plant growth, but when

infected with rhizobia and PGPR, the impacts were mitigated. AM fungi

reduce malonaldehyde and H2O2, minimizing the adverse effects of stress

caused due to deposition of cadmium (Hashem et al., 2016). Jing et al.

(2014) in his research have shown that different species of Enterobacter and

species of Klebsiella are efficient metal tolerant by creating plant growth

chemicals when removing lead, cadmium, and zinc metal from polluted soil

(Table 2.1).