Abstract
The present study was aimed to isolate and characterize plant growth promoting rhizobacteria (PGPR) from the rhizosphere of rainfed area (Karak) in Pakistan. The influence of isolated rhizobacteria, in association with salicylic acid (SA), physiological attributes, drought tolerance potential, and phytoremediation in drought-stressed sunflower exposed was investigated. The isolated bacteria were named P1 and P2 and characterized on the basis of colony morphology and biochemical traits. Both PGPR P1 and P2 were identified on the basis of 16S-rRNA gene sequencing as Planomicrobium chinense strain P1 (Accession No. MF616408) and Bacillus cereus strain P2 (Accession No. MF616406). The fresh cultures (24 h old) of isolates were used to soak the seeds pre-sowing. SA was foliar applied at three-leaf-stage. Likewise, the 30-days-old seedlings (three leaf stage) were exposed to drought stress. Drought stress was imposed to 30-days-old plants (three-leaf stage) by withholding water supply for the next 15 days until the soil water content reached 10%. The PGPR and/or SA treatment resulted in significant accumulation of Cd (84%), Pb (66%), and Ni (65%) in the rhizosphere. PGPR also induced accumulation of Cd and Ni in plant shoot. Combined treatment of PGPR and SA increased the Cu (21%), Co (11%), and Zn (8%) accumulation but decreased (12%) the Fe accumulation as compared to coinoculation of PGPR P1 and P2. Inoculation of plants with PGPR significantly increased shoot length (60%), root length (68%), root fresh (61%), and dry (63%) biomass under water stress. The inoculated plants had increased chlorophyll (67%), carotenoid (70%), leaf protein (64%), sugar (64%), and phenolic (62%) contents while lower leaf proline (62%) content, malondialdehyde (MDA) (64%), and antioxidant enzymes (67%) which suggest their role in drought tolerance. It is concluded that integrative use of PGPR in combination with SA found to be an efficacious strategy to improve the phytoremediation of heavy metals and plant growth under stressed conditions particularly under water-deficient conditions.
Highlights
Various factors such as worldwide development, industrialization, agricultural practices, and anthropogenic activities are the most important factors responsible for soil pollution
Significant increase in cfu was noted in plants from inoculated seeds and sprayed with salicylic acid (SA) followed by those having seed inoculation only (i.e., T6 followed by T5; Table 2)
The coinoculation of two plant growth promoting rhizobacteria (PGPR) along with SA was very effective for growth parameters as well as for the phytoremediation of heavy metals
Summary
Various factors such as worldwide development, industrialization, agricultural practices, and anthropogenic activities are the most important factors responsible for soil pollution. Phytoremediation is an emerging in situ technology and more favorable due to its great potential This includes the usage of plants to clean up the environments by reducing the toxicity, volume, and altering mobility of the contaminants in the soil (Shao-wei and Chang, 2004). Plants help to eliminate different pollutants such as pesticides, metals, oil, and other chemicals and play a central role in preventing the spread of contaminants through wind, rain or underground water from one area to another area. This technology comprised two important mutualistic components, i.e., plants and plant’s root microbes which degrade the toxic metabolites to non-toxic metabolites (Saxena et al, 2005)
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