The influences of Cr-tolerant rhizobacteria in phytoremediation and attenuation of Cr (VI) stress in agronomic sunflower (Helianthus annuus L.).

Chromium contamination of agronomic soil has to turn into a serious global problem. This research was pointed to assess the effects of three Cr-tolerant rhizobacteria (SS1, SS3, and SS6) on sunflower growth and heavy metal uptake under Cr smog i.e. 20, 30 and 40 ppm using K2Cr2O7. Root promotion assay and pot experiment were conducted to investigate and evaluate the effects of Cr tolerance rhizobacteria and Cr accumulation capacity of sunflower. From root promotion assay non-significant variation was observed in the root length between SS1 and SS3 compared with un-inoculated whereas SS6 enhanced the root length in the absence and presence of chromium. In addition, inoculation with rhizobacteria alleviated the Cr concentration and endorsed plant growth by enhancing Cr accumulation in sunflower. At different Cr levels, the Cr concentration in shoot was improved by each rhizobacterium though their difference was non-significant with each other, while the percentage increase was half as the Cr level doubled. Different rhizobacterium inoculation significantly (P < 0.05) affected the physiological and morphological characteristics of sunflower and increased the plant height, stem diameter, head diameter, grain yield, oil content of seeds, and total biomass, and among them, SS6 observed best followed by SS1 and SS3 comparing with un-inoculated. Our study illustrates an assessment about Cr-tolerant bacteria and their influences and recommends that these bacteria can effectively be used for crop improvement which provides a potential approach for Cr phytoremediation.

Bahadur A ，Ahmad R ，Afzal A ，Feng H ，Suthar V ，Batool A ，Khan A ，Mahmood-Ul-Hassan M ... -  《-》

Impact of lead tolerant plant growth promoting rhizobacteria on growth, physiology, antioxidant activities, yield and lead content in sunflower in lead contaminated soil.

Present study was conducted to evaluate the effect of lead tolerant plant growth promoting rhizobacteria (LTPGPR) on growth, physiology, yield, antioxidant activities and lead uptake in sunflower in soil contaminated with lead under pot conditions. Three pre-characterized LTPGP strains (S2 (Pseudomonas gessardii strain BLP141), S5 (Pseudomonas fluorescens A506) and S10 (Pseudomonas fluorescens strain LMG 2189)) were used to inoculate sunflower growing in soil contaminated with different levels (300, 600 and 900 mg kg-1) of lead by using lead nitrate salt as source of lead. Treatments were arranged according to completely randomized design with factorial arrangements. At harvesting, data regarding growth attributes (root shoot length, root shoot fresh and dry weights), yield per plant, physiological attributes (Chlorophyll 'a', 'b' and carotenoids content), antioxidant activities (Ascorbate peroxidase, catalase, superoxide dismutase and glutathione reductase), proline and malanodialdehyde content, and lead content in root, shoot and achenes of sunflower were recorded. Data were analysed by standard statistical procedures. Results showed that lead contamination reduced the plants growth, physiology and yield at all levels of lead stress. But application of LTPGPR in soil contaminated with lead improved plant growth, physiology, yield, and antioxidant activities, proline, and reduced the malanodialdehyde content (that is reduced by the application of different strains in lead contamination) of sunflower as compared to plants grown in soil without inoculation. Inoculation also promoted the uptake of lead in root, shoots and reduced the uptake of lead in achenes of plants as compared to plants in lead contamination without inoculation.

Saleem M ，Asghar HN ，Zahir ZA ，Shahid M ... -  《-》

Intercropping with sunflower and inoculation with arbuscular mycorrhizal fungi promotes growth of garlic chive in metal-contaminated soil at a WEEE-recycling site.

Heavy metal (HM) pollution in agricultural soils due to the recycling of waste electrical and electronic equipment (WEEE) has become a serious concern, but most farmers cannot afford the economic losses of fallow land during remediation. Thus, it is imperative to produce low-HM crops while remediating the contaminated soils. A 17-week pot experiment was conducted to investigate the growth and HM (Cd, Cu, Pb, Cr, Zn, and Ni) acquisition of garlic chives (Allium tuberosum Rottl. ex Spreng.) intercropped with sunflower (Helianthus annuus L.) and inoculated with (I+M) or without (I-M) the arbuscular mycorrhizal (AM) fungus Funneliformis caledonium on a severely HM-contaminated soil that was collected from a WEEE-recycling site. Compared with the monoculture control, the I-M treatment significantly (P < 0.05) decreased Cd, Cu, Cr, Zn, and Ni concentrations in the shoots of chives through rhizosphere competition and HM (except Cr) transfer from the root to the shoot of chives, and increased the average shoot fresh weight (i.e., yield) of chives by 794% by alleviating HM toxicity. Compared with the I-M treatment, the I+M treatment significantly increased soil phosphatase activity as well as root mycorrhizal colonization of both sunflower and chives. The I+M treatment had no effect on the tissue P concentration of sunflower but elevated the average dry biomass (shoot plus root) and P acquisition level of sunflower by 179% and 121%, respectively. In addition, the I+M treatment significantly increased the P concentration in the root rather than in the shoot of chives and significantly increased the level of P acquisition by chives, increasing the average yield of chives by 229%. Simultaneously, the I+M treatment significantly increased the level of HM (except Cd) acquisition by sunflower, enhancing the rhizosphere competition by sunflower over chives, and further reducing the transfer of all six HMs from root to shoot in the chives, and inducing significant decreases in chive shoot HM concentrations compared with the monoculture control. Furthermore, the I+M treatment decreased the average total concentrations and increased the average DTPA-extractable concentrations of soil HMs. The results demonstrate the multifunctional role of AM fungi in the intercropping system for both vegetable production and phytoremediation on HM-contaminated soils.

Zhang Y ，Hu J ，Bai J ，Qin H ，Wang J ，Wang J ，Lin X ... -  《-》

Citric acid assisted phytoextraction of chromium by sunflower; morpho-physiological and biochemical alterations in plants.

Soil and water contamination from heavy metals and metalloids is one of the most discussed and burning global issues due to its potential to cause the scarcity of healthy food and safe water. The scientific community is proposing a range of lab and field based physical, chemical and biological solutions to remedy metals and metalloids contaminated soils and water. The present study finds out a possibility of Chromium (Cr) extraction by sunflower from spiked soil under chelating role of citric acid (CA). The sunflower plants were grown under different concentrations of Cr (0, 5, 10 & 20mgkg-1) and CA (0, 2.5 & 5mM). Growth, biomass, gas exchange, photosynthesis, electrolyte leakage (EL), reactive oxygen species (ROS; malondialdehyde (MDA), hydrogen peroxide (H2O2) and the activities of antioxidant enzymes such as, superoxide dismutase (SOD), guaiacole values peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT) were measured. The results depicted a clear decline in plant height, root length, leaf area, number of leaves and flowers per plant along with fresh and dry biomass of all parts of plant with increasing concentration of Cr in soil. Similar reduction was observed in chlorophyll a and b, total chlorophyll, carotenoids, soluble protein, gas exchange attributes and SPAD. The increasing concentration of Cr also enhanced the Cr uptake and accumulation in plant roots, stem and leaves along with the production of ROS and EL. The activities of antioxidant enzymes increased with increasing Cr concentration from 0 to 10mg, but decreased at 20mgkg-1 soil. The CA application significantly alleviated Cr-induced inhibition of plant growth, biomass, photosynthesis, gas exchange, soluble proteins and SPAD value. Presence of CA also enhanced the activities of all antioxidant enzymes and reduced the production of ROS and EL. The chelating potential of CA increased the concentration and accumulation of Cr in plant roots, stem and leaves. It is concluded that the sunflower can be a potential candidate for the remediation of Cr under CA treatment, while the possibility may vary with genotype, Cr level and CA concentration.

Farid M ，Ali S ，Rizwan M ，Ali Q ，Abbas F ，Bukhari SAH ，Saeed R ，Wu L ... -  《-》

Potential applications of Pseudomonas sp. (strain CPSB21) to ameliorate Cr(6+) stress and phytoremediation of tannery effluent contaminated agricultural soils.

Gupta P ，Rani R ，Chandra A ，Kumar V ... -  《Scientific Reports》