Synergistic effect of Bacillus and Rhizobium on cytological and photosynthetic performance of Macrotyloma uniflorum (Lam.) Verdc. Grown in Cr (VI) contaminated soil.

Macrotyloma uniflorum (horse gram) is considered an under-utilized legume crop despite its nutritional and medicinal values. In India, it has wide acceptance among farming communities. This investigation emphasized on the possible application of two endosymbionts (Bacillus sp. AS03 and Rhizobium sp. AS05) of horse gram cultivated on Cr (VI)-contaminated soil. The photosynthetic performance (PIφ) of Cr treated plants co-inoculated with AS03 and AS05 was significantly improved compared with non-inoculated Cr treated plants based on photosynthetic yield, which was evidenced from the rise in the fluorescence at I-P transient and rate of photosynthesis (pN), indicating synergistic action between plant and bacteria (AS03 and AS05). The smooth electron transport from PS II to PS I was achieved in the Cr stressed plants inoculated with both the bacterial strains. The detrimental effects of Cr toxicity on the root tips were also minimized with bioinoculation as revealed from mitotic index. Plants with dual inoculation of AS03 and AS05 had significantly lesser chromosomal aberration in the roots. Dual inoculation biochar or seed inoculation have beneficial impact on the plant photosynthetic performance along with improved growth of roots in plants treated with Cr (VI). The results of the current work suggest the possitive effect of dual inoculation of Cr tolerant endosymbionts, Bacillus sp. (AS03) and nodulating Rhizobium sp. (AS05), in reducing cytological as well as physiological stress of plants in Cr (VI) contaminated soil.

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.

Assessment of chromium phytotoxicity, phytoremediation and tolerance potential of Sesbania sesban and Brachiaria mutica grown on chromite mine overburden dumps and garden soil.

The addition of toxic chromium in agrarian soils from mine overburden dump is of serious concern. To combat the toxicity of chromium an experiment was carried out at the Department of Botany, Utkal University, India by taking the chromium rich overburden dump (OBD) from Sukinda chromite mine, India. Different proportions of chromium rich OBD (10%, 20%, 30%, 40%, 50%, 70% and 100% OBD) were supplied to garden soil and plants of legume and non-legume categories (Sesbania sesban L. and Brachiaria mutica L.) were grown for assessment of phytoaccumulation ability of chromium, tolerance index, chlorophyll, protein and proline and the activity of oxidative inhibitors enzymes. After 60 days of experimentation, Cr phytotoxicity on physiological and biochemical parameters were assessed. The outcome of the results showed that the activity of antioxidant enzymes enhanced considerably in roots as compared to shoots with enhancing concentration of chromium. To compare the phytoaccumulation ability, the tolerance index (TI), bio-concentration factor (BCF) and transportation index (Ti) were measured in two different species. The results showed that at 100% OBD the TI, BCF and Ti of S. sesban have 22.30, 0.45 and 71.06 and B. mutica have 20.83, 0.43 and 42.45 respectively. The result showed that S. sesban not only had the highest bioaccumulation capacity of chromium but also have high tolerance index and transportation index as compared to B. mutica. Hence S. sesban can be recommended for phytostabilization programme to alleviate toxic chromium from chromite overburden mining sites.

Chromium bioaccumulation, oxidative stress metabolism and oil content in lemon grass Cymbopogon flexuosus (Nees ex Steud.) W. Watson grown in chromium rich over burden soil of Sukinda chromite mine, India.

Lemon grass plants grown in Cr rich over burden soil of Sukinda chromite mine (India) countered Cr toxicity and oxidative stress with the production of reactive oxygen species and induced antioxidative defense system. Varied percentage of Cr rich over burden soil was applied to lemon grass pants to evaluate the actions of oxidative inhibitors enzymes extracted and assayed from both roots and shoots. The study also assessed the oil content and its composition in response to the different percentage of Cr available in over burden soil. In order to evaluate the defense system of a plant against oxidative stress and determine the level of reactive oxygen species, the experiments were undertaken in the presence and absence of Cr in soils. The results indicated that the action of oxidative inhibitor enzymes increased significantly in roots as compared to shoots with increasing concentration of Cr in overburden soil. Higher concentration of Cr in soils inhibited the enzyme activity both in roots and shoots. The level of ROS in plants also enhanced with the increase in the concentration of Cr in the soil. In order to control the oxidative damage in plants, lemon grass can be considered defensive in nature to build up the antioxidant system which can scavenge the reactive oxygen species (ROS).

An in situ study of growth of Lemongrass Cymbopogon flexuosus (Nees ex Steud.) W. Watson on varying concentration of Chromium (Cr+6) on soil and its bioaccumulation: Perspectives on phytoremediation potential and phytostabilisation of chromium toxicity.

Chromium (Cr) contamination in soil is a growing concern in sustainable agricultural production and food safety. Remediation of Cr from contaminated soils is a challenging task which may not only help in sustaining agriculture but also in minimizing adverse environmental impacts. Pot culture experiments were performed with the application of varied concentration of Cr+6 to assess the Chromium accumulation potential of Lemongrass and to study the impact of toxic concentration of Cr+6 on morphological, physiological and biochemical parameters of the plant. The results showed an increasing accumulation trend of Chromium with increasing Chromium concentrations in both root and shoot of 60 days old Lemongrass plants, while the protein and chlorophyll contents decreased. Similarly, accumulation of Cr increased the levels of proline and antioxidant enzymes indicating the enhanced damage control activity. The potentiality of the plant with the capacity to accumulate and stabilize Cr compound in Cr contaminated soil by phytoremediation process has been explored in the present investigation.

Chelate based phytoremediation study for attenuation of chromium toxicity stress using lemongrass: Cymbopogon flexuosus (nees ex steud.) W. Watson.

Chelate employed wrenching out of Chromium from contaminated soils is a comparably new technology. The pot culture experiments were carried out to study the toxicological, physiological and biochemical changes in Lemongrass using different chelators such as Ethylenediaminetetraaceticacid (EDTA), Diethylenetriaminepentaacetic acid (DTPA), Citric acid (CA) and Salicylic acid (SA) and metal ions (Fe, Mg and Zn) in Cr+6 contaminated soil. The application of heavy metal Cr induced number of adverse consequences like reduction in root/shoot length, biomass and chlorophyl content in Lemongrass plants grown in soil with Cr+6 (50mgkg-1). On the contrary, the growth of Lemongrass was stimulated by the addition of chelators such as EDTA, DTPA, Citric acid, salicylic acid including metal ions (Fe, Mg and Zn). The increase in proline content was associated with the synthesis of antioxidant enzymes by the applications of chelators and metal ions. The treated plants with reduced Transportation index (Ti) values indicated more root Chromium accumulation as compared to shoot. The Bio-Concentration Factor (BCF) and Total Accumulation Rate (TAR) of Chromium were elevated with the supplementation of chelators and metal ions, thus, illustrating more metal bioavailability in plants.