Synergistic application of Pseudomonas strains and compost mitigates lead (Pb) stress in sunflower (Helianthus annuus L.) via improved nutrient uptake, antioxidant defense and physiology.

Lead (Pb) is one of the most dreadful non-essential elements whose toxicity has been well reported worldwide due to its interference with the major plant functions and its overall yield. Bioremediation techniques comprising the application of beneficial microorganisms have gained attention in recent times owing to their ecofriendly nature. Addition of organic matter to soil has been reported to stimulate microbial activities. Compost application improves soil structure and binds toxic contaminants due to its larger surface area and presence of functional groups. Furthermore, it stimulates soil microbial activities by acting as C-source. So, in current study, we investigated the individual and synergistic potential of two lead (Pb)-tolerant Pseudomonas strains alongwith compost (1% w/w) in sustaining sunflower growth under Pb contaminated soil conditions. Lead chloride (PbCl2) salt was used for raising desired Pb concentration (500 mg kg-1). Results revealed that Pb stress drastically affected all the measured attributes of sunflower plant, however joint application of rhizobacteria and compost counteracted these adverse effects. Among them, co-application of str-1 and compost proved to be significantly better than str-2, as its inoculation significantly improved shoot and root lengths (64 and 76%), leaf area and leaves plant-1 (95 and 166%), 100-achene weight (200%), no. of flowers plant-1 (138%), chl 'a', 'b' and carotenoid (86, 159 and 33%) contents in sunflower as compared to control treatments. Furthermore, inoculation of Pseudomonas fluorescens along with compost increased the NPK in achene (139, 200 and 165%), flavonoid and phenolic contents (258 and 185%) along with transpiration and photosynthetic rates (54 and 72%) in leaves as compared to control treatment under Pb contamination. In addition, Pb entry to roots, shoots and achene were significantly suppressed under by 87, 90 and 91% respectively due to integrated application of compost and str-1 as evident by maximum Pb-immobilization efficiency (97%) obtained in this treatment. Similarly, bioconcentration factors for roots, shoots and achene were found to be 0.58, 0.18 and 0.0055 with associated translocation factor (0.30), which also revealed phytostabilization of Pb under combined application of PGPR and compost. Since, phytoremediation of heavy metals under current scenario of increasing global population is inevitable, results of the current study concluded that tolerant PGPR species along with organic amendments such as compost can inhibit Pb uptake by sunflower and confer Pb tolerance via improved nutrient uptake, physiology, antioxidative defense and gas exchange.

Ayub A ，Shabaan M ，Malik M ，Asghar HN ，Zulfiqar U ，Ejaz M ，Alarjani KM ，Al Farraj DA ... -  《-》

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 ... -  《-》

Combined application of compost and Bacillus sp. CIK-512 ameliorated the lead toxicity in radish by regulating the homeostasis of antioxidants and lead.

Lead (Pb) contamination is ubiquitous and usually causes toxicity to plants. Nevertheless, application of compost and plant growth promoting rhizobacteria synergistically may ameliorate the Pb toxicity in radish. The present study assessed the effects of compost and Bacillus sp. CIK-512 on growth, physiology, antioxidants and uptake of Pb in contaminated soil and explored the possible mechanism for Pb phytotoxicity amelioration. Treatments comprised of un-inoculated control, compost, CIK-512, and compost + CIK-512; plants were grown in soil contaminated with Pb (500mgkg-1) and without Pb in pot culture. Lead caused reduction in shoot dry biomass, photosynthetic rate, stomatal conductance, relative water contents, whereas enhanced root dry biomass, ascorbate peroxidase, catalase, malondialdehyde and electrolyte leakage in comparison with non-contaminated control. Plants inoculated with strain CIK-512 and compost produced significantly higher dry biomass, photosynthetic rate and stomatal conductance in normal and contaminated soils. Bacterial strain CIK-512 and compost synergy improved growth and physiology of radish in contaminated soil possibly through homeostasis of antioxidant activities, reduced membrane leakage and Pb accumulation in shoot. Possibly, Pb-induced production of reactive oxygen species resulted in increased electrolyte leakage and malondialdehyde contents (r = 0.88-0.92), which led to reduction in growth (r = -0.97) and physiology (r = -0.38 to -0.80), however, such negative effects were ameliorated by the regulation of antioxidants (r = 0.78-0.87). The decreased activity of antioxidants coupled with Pb accumulation in aerial part of the radish indicates the Pb-phytotoxicity amelioration through synergistic application of compost and Bacillus sp. CIK-512.

Ahmad I ，Akhtar MJ ，Mehmood S ，Akhter K ，Tahir M ，Saeed MF ，Hussain MB ，Hussain S ... -  《-》

Pseudomonas fluorescens and L-tryptophan application triggered the phytoremediation potential of sunflower (Heliantus annuus L.) in lead-contaminated soil.

Jaffar MT ，Mushtaq Z ，Waheed A ，Asghar HN ，Zhang J ，Han J ... -  《-》

Exploring the synergistic effects of indole acetic acid (IAA) and compost in the phytostabilization of nickel (Ni) in cauliflower rhizosphere.

Heavy metals (HMs) contamination, owing to their potential links to various chronic diseases, poses a global threat to agriculture, environment, and human health. Nickel (Ni) is an essential element however, at higher concentration, it is highly phytotoxic, and affects major plant functions. Beneficial roles of plant growth regulators (PGRs) and organic amendments in mitigating the adverse impacts of HM on plant growth has gained the attention of scientific community worldwide. Here, we performed a greenhouse study to investigate the effect of indole-3-acetic acid (IAA @ 10- 5 M) and compost (1% w/w) individually and in combination in sustaining cauliflower growth and yield under Ni stress. In our results, combined application proved significantly better than individual applications in alleviating the adverse effects of Ni on cauliflower as it increased various plant attributes such as plant height (49%), root length (76%), curd height and diameter (68 and 134%), leaf area (75%), transpiration rate (36%), stomatal conductance (104%), water use efficiency (143%), flavonoid and phenolic contents (212 and 133%), soluble sugars and protein contents (202 and 199%), SPAD value (78%), chlorophyll 'a and b' (219 and 208%), carotenoid (335%), and NPK uptake (191, 79 and 92%) as compared to the control. Co-application of IAA and compost reduced Ni-induced electrolyte leakage (64%) and improved the antioxidant activities, including APX (55%), CAT (30%), SOD (43%), POD (55%), while reducing MDA and H2O2 contents (77 and 52%) compared to the control. The combined application also reduced Ni uptake in roots, shoots, and curd by 51, 78 and 72% respectively along with an increased relative production index (78%) as compared to the control. Hence, synergistic application of IAA and compost can mitigate Ni induced adverse impacts on cauliflower growth by immobilizing it in the soil.

Khan R ，Sarwar MJ ，Shabaan M ，Asghar HN ，Zulfiqar U ，Iftikhar I ，Aijaz N ，Haider FU ，Chaudhary T ，Soufan W ... -  《BMC PLANT BIOLOGY》