Effective plant-endophyte interplay can improve the cadmium hyperaccumulation in Brachiaria mutica.

Soil contamination due to cadmium (Cd) is a ubiquitous environmental problem for which inexpensive remediation alternatives are required. Phytoaccumulation, the use of plants to extract and accumulate heavy metals from the contaminated environment, is such an alternative. In this study, we aimed at establishing effective plant-bacteria interplay between Brachiaria mutica and Cd-resistant endophytic bacteria eventually leading to improved phytoremediation. B. mutica was grown in a Cd-contaminated soil and inoculated with three Cd-tolerant endophytic bacteria individually as well as in combination. Plant physiological parameters, biomass production, bacterial colonization, and Cd-accumulation were observed at four different Cd exposures, i.e., 100, 200, 400 and 1000 mg kg-1 of soil. The combined application of endophytic bacteria was more effective as compared to their individual applications at all concentrations. Nevertheless, highest performance of consortium was seen at 100 mg Cd kg-1 of soil, i.e., root length was enhanced by 46%, shoot length by 62%, chlorophyll content by 40%, and dry biomass by 64%; which was reduced with the increase in Cd concentration. The bacterial population was highest in the root interior followed by rhizosphere and shoot interior. Concomitantly, plants inoculated with bacterial consortium displayed more Cd-accumulation in the roots (95%), shoots (55%), and leaves (44%). Higher values of BCFroot (> 1), and lower values for BCFshoot and TF (< 1) indicates capability of B. mutica to accumulate high amounts of Cd in the roots as compared to the aerial parts. The present study concludes that plant-endophyte interplay could be a sustainable and effective strategy for Cd removal from the contaminated soils.

AM fungi mediated bioaccumulation of hexavalent chromium in Brachiaria mutica-a mycorrhizal phytoremediation approach.

The experiment was designed to evaluate the roles of Rhizophagus irregularis on chlorophyll fluorescence and chromium bioaccumulation in a grass species (Brachiaria mutica) by supplementing Cr+6 at different concentrations. Arbuscular Mycorrhizal Fungi (AMF) association facilitated lessening of chromium level in contaminated soil and enhanced chromium bioavailability in Brachiaria mutica. The mycorrhizal inoculated increased the chlorophyll (0.925 mg/g), carotenoid (0.127 mg/g), protein (2.883 mg/g), proline (0.889 mg/g) contents and activities of antioxidant enzymes like catalase, ascorbate peroxidase and glutathione peroxidase. The mycorrhizal inoculated plants also showed enhanced overall photosynthetic performance (PIϕ = 2.473) and enhanced PS-II to PS-I electron transport as evident from yield parameter (0.712) and TR0/RC (2.419) for 60 mg/kg Cr+6 treatment. The observations suggest that AMF association could defend the plants from chromium stress by elevating the number of antioxidants in plants. Rhizophagus irregularis was found to maintain a successful symbiotic relationship with Brachiaria mutica in chromium contaminated soil. The observations recommended that Rhizophagus irregularis in association with Brachiaria mutica would be an innovative approach for decontamination of Cr+6.

Pb-induced phytotoxicity in para grass (Brachiaria mutica) and Castorbean (Ricinus communis L.): Antioxidant and ultrastructural studies.

Hydroponics experiment was conducted to investigate the effects of different levels of Pb on Para Grass (Brachiaria mutica) and Castorbean (Ricinus communis L). Generally, Para Grass exhibited higher tolerance to excessive concentrations of Pb in nutrient solution, whereas a consistent decline was observed in growth of Castorbean plants exposed to similar Pb levels. Malondialdehyde (MDA) and H2O2 contents exhibited contrasting results with a general decrease in Para Grass and a linear increase in case of Castorbean. In both species a decrease was noticed in the activities of superoxide dismutase (SOD) and guaiacol peroxidase (G-POD) while catalase (CAT) activity was significantly increased. Ultrastructural studies revealed increased starch grains and adversely affected thylakoid membranes in chloroplasts of leaf cells of plants treated with 500 µM Pb. Photosynthetic parameters such as CO2 assimilation rate, stomatal conductance (gs) and transpiration rate (E) decreased in both plant species under different levels of Pb. Maximum concentrations of Pb in shoots of Para Grass and Castorbean were 1.29 and 0.352 g kg-1, respectively while in roots maximum values were 8.88 and 49.86 g kg-1, respectively. The high concentrations of Pb (about 5%) in the roots of Castorbean plants suggest its possible role in the phytoremediation/rhizofiltration of Pb contaminated water.

Augmentation with potential endophytes enhances phytostabilization of Cr in contaminated soil.

The contamination of soil with heavy metals is a major environmental problem worldwide. The combined use of plants and their associated microbes has gained popularity in recent years for their potential to remediate heavy metal-contaminated soil. In the current study, the effect that augmentation of soil with plant growth-promoting endophytes has on the phytostabilization of chromium (Cr)-contaminated soil was investigated. Three potential endophytic bacterial strains (Enterobacter sp. HU38, Microbacterium arborescens HU33, and Pantoea stewartii ASI11) were inoculated individually as well as in combination to Leptochloa fusca and Brachiaria mutica vegetated in Cr-contaminated soil. The accumulation of Cr in the root and shoot of the plants was determined. Moreover, bacterial persistence in the rhizosphere and endosphere was determined. Augmentation with potential endophytes significantly increased root length (24-45%), shoot height (39-64%), chlorophyll content (20-55%), and the overall biomass (32-61%) of the plants. Although L. fusca and B. mutica showed potential to accumulate Cr in their root and shoot, endophytic augmentation increased uptake, translocation, and accumulation of Cr in the roots and shoots of both plant species. However, L. fusca showed more potential to phytostabilize Cr as compared to B. mutica. Furthermore, the potential endophytes showed more survival and persistence within the roots than in the rhizosphere and shoot interior. This study provides useful evidence of endophyte-assisted phytoremediation to be the most sustainable and affordable approach for in situ remediation of Cr-contaminated soil.