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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. [ABSTRACT FROM AUTHOR]

Keywords: PGPR; 16S RNA gene sequencing; salicylic acid; phytoremediation; heavy metals NK carried out greenhouse and lab experiments and wrote the manuscript. PGPR, 16S RNA gene sequencing, salicylic acid, phytoremediation, heavy metals. [Extracted from the article]

• Study of the scientific insights into the relationship between cadmium exposure and maize physiology, biochemistry, and accumulation of the heavy metals. • Impacts of high cadmium concentrations on maize growth and yield. • Study of the stress related metabolites like IAA, salicylic acid, proteins, lipid, and sugar contents. Food security is critical for survival but increasing heavy metal particularly cadmium concentration in the environment due to human activity poses a threat to both plants and animals. The experiment was designed to investigate the potential impact of varying concentrations of cadmium on the growth, metabolites, and accumulation of cadmium in the edible portion of maize. The objective was to gain scientific insights into the relationship between cadmium exposure and maize physiology, biochemistry, and accumulation of the heavy metal. Significant reduction was recorded in the agronomic attributes including root shoot length, fresh and dry weight and chlorophyll contents of the maize (p < 0.05). Higher level of cadmium imposes destruction of the antioxidant defense system of the host indicated by the lower catalases activity (92% reduction). Along with this, growth and stress related metabolites like IAA, salicylic acid, proteins, lipid and sugar contents decreased approximately by 50% at the lowest concentration while reaching 70 to 77% at the highest concentration of cadmium. Interestingly, plants exposed to cadmium for 60-days duration approximately 20 to 25 mg/kg of cadmium was accumulated in plants parts of which most of the cadmium (50% or higher) were translocated to the shoot of the host plants. This data also showed that the maximum concentration of cadmium is accumulated in the stem, followed by the leaf, and then the seed. The concentration of cadmium in seeds varies from 2 to 4 mg/kg, which is a highly prohibited amount of cadmium in food for human consumption. [ABSTRACT FROM AUTHOR]