Zinc tolerant plant growth promoting bacteria alleviates phytotoxic effects of zinc on maize through zinc immobilization.

The increasing heavy metal contamination in agricultural soils has become a serious concern across the globe. The present study envisages developing microbial inoculant approach for agriculture in Zn contaminated soils. Potential zinc tolerant bacteria (ZTB) were isolated from zinc (Zn) contaminated soils of southern Rajasthan, India. Isolates were further screened based on their efficiency towards Zn tolerance and plant growth promoting activities. Four strains viz. ZTB15, ZTB24, ZTB28 and ZTB29 exhibited high degree of tolerance to Zn up to 62.5 mM. The Zn accumulation by these bacterial strains was also evidenced by AAS and SEM-EDS studies. Assessment of various plant growth promotion traits viz., IAA, GA3, NH3, HCN, siderophores, ACC deaminase, phytase production and P, K, Si solubilization studies revealed that these ZTB strains may serve as an efficient plant growth promoter under in vitro conditions. Gluconic acid secreted by ZTB strains owing to mineral solubilization was therefore confirmed using high performance liquid chromatography. A pot experiment under Zn stress conditions was performed using maize (Zea mays) variety (FEM-2) as a test crop. Zn toxicity reduced various plant growth parameters; however, inoculation of ZTB strains alleviated the Zn toxicity and enhanced the plant growth parameters. The effects of Zn stress on antioxidant enzyme activities in maize under in vitro conditions were also investigated. An increase in superoxide dismutase, peroxidase, phenylalanine ammonia lyase, catalase and polyphenol oxidase activity was observed on inoculation of ZTB strains. Further, ZIP gene expression studies revealed high expression in the ZIP metal transporter genes which were declined in the ZTB treated maize plantlets. The findings from the present study revealed that ZTB could play an important role in bioremediation in Zn contaminated soils.

Zinc biosorption, biochemical and molecular characterization of plant growth-promoting zinc-tolerant bacteria.

Zinc plays a key role in plant nutrition at low levels; however, at higher concentrations Zn ions can be highly phytotoxic and plant growth-promoting rhizobacteria can be used to reduce such metal toxicity. In the present investigation we had reported the zinc biosorption and molecular characterization of plant growth-promoting zinc-tolerant bacteria. Initially, thirty bacteria having zinc solubilizing ability were screened for MIC against zinc ion and displayed high value of MIC ranging from 2.5 to 62.5 mM. Biochemically, all the 30 isolates showed significant difference in the 6 biochemical tests performed. The molecular diversity studies based on the repetitive DNA PCR viz, REP, ERIC and BOX elements showed significant genetic diversity among these 30 zinc-tolerant bacteria. These ZTB strains also showed multiple PGP activities and all ZTB strains were found positive for production of IAA, GA3 and ammonia, whereas 24 were found positive for ACC deaminase activity, 8 showed siderophore production and 9 ZTB isolates were positive for HCN production. Out of 30 isolates, 24 showed phosphorus solubilization activity, 30 showed potash solubilization, 15 showed silica solubilization and 27 showed phytase production activities. All the 30 ZTB stains showed zinc solubilization up to 0.25% insoluble ZnO in the medium, whereas at 2% ZnO in MSM only 12 isolates showed solubilization which were further selected for zinc biosorption and pot studies. The heavy metal removal studies revealed that ZTB stains were able to remove zinc ions effectively from the medium efficiently and the highest zinc biosorption (< 90%) was recorded with the bacterial strain Z-15. Further, the inoculation of ZTB strains under zinc stress conditions (pot containing 1000 mg/kg Zn) resulted in significant increase of shoot length, root length and total chlorophyll content in maize seedlings compared with the uninoculated control. The partial 16S rDNA sequence of the potential ZTB isolates viz. Z-15, Z-24, Z-28 and Z-29 revealed their identity as Serratia sp. The ability of these zinc-tolerant bacteria to tolerate the toxic level of zinc may serve as suitable candidates for developing microbial formulations for the growth of crop plants in Zn-contaminated areas.

Ripening quality of Dusehri mango in relation to harvest time.

The effect of different harvesting time on ripening quality of mango cv. Dusehri was investigated under sub-tropics of northwestern India. Fruits were harvested at 101, 106 and 111 days after fruit set (DAFS) and kept at 25 °C in temperature controlled chamber for ripening. Fruits were analyzed periodically for physico-chemical characteristics at the time of harvest (0 h) and after 72, 96 and 120 h of ripening period. With advancement in ripening period, an increase in physiological loss in weight, soluble solids content (SSC), sensory quality rating, ß-carotene and pulp colour development of mango fruits was recorded. While a decline in fruit firmness and titratable acidity (TA) was observed with ripening period. Fruits picked at 111 DAFS recorded highest SSC (8.01%), sensory rating (4.67), ß-carotene (0.427 mg/100 g) vis-à-vis lowest fruit firmness (15.3 lbf) and TA content (1.56%). The luminosity of fruit pulp decreased with the storage period. The redness and yellowness of the fruit pulp represented by a* and b* values, respectively increased with delay in harvesting period. The rate of ripening was rapid in late harvested fruits as compared to early harvested fruits. After 96 h of ripening period, fruits harvested at 111 DAFS showed very much desirable quality whereas fruits harvested at 101 DAFS showed moderately desirable quality. Results showed that harvesting of mango fruits can be extended to 111 days and such fruits attained optimum ripening quality after 96 h at 25 °C.

Bis(O-ethyl dithio-carbonato-κS,S')bis-(pyridine-3-carbonitrile-κN)nickel(II).

The Ni(2+) ion in the title complex, [Ni(C(3)H(5)OS(2))(2)(C(6)H(4)N(2))(2)], is in a strongly distorted octa-hedral coordination environment formed by an N(2)S(4) donor set, with the Ni(2+) ion located on a centre of inversion. In the crystal, weak C-H⋯S and C-H⋯N inter-actions are observed.