Abstract
Volatile organic compounds (VOCs) produced by rhizobacteria have been proven to stimulate plant growth during germination and seedling stages. However, the modulating effect of bacterial volatiles on the germination of seeds subjected to heavy metal stress is scarcely studied. In this work, the ability of volatiles released by Bacillus sp. MH778713 to induce seed dormancy breakage in Prosopis laevigata and Arabidopsis thaliana seeds were examined. The minimal inhibitory concentration of chromium (Cr) VI that prevents seed germination of P. laevigata and A. thaliana on water-Cr-agar plates was 2500 and 100 mg L–1, respectively. Remarkably, partitioned Petri-dish co-cultivation of Bacillus sp. MH778713 and plant seeds under Cr-stress showed the beneficial effect of volatiles emitted by Bacillus sp. MH778713, helping plant seeds to overcome Cr-stress. Among the metabolites emitted by Bacillus sp. MH778713, octadecane, heneicosane, 2,4-di-tert-butylphenol, hexadecane, eicosane, octacosane, and tetratriacontane were the most abundant. To confirm that these long-chain compounds produced by Bacillus sp. MH778713 could be responsible for the seed dormancy breakage, high pure organic compounds (2,4-di-tert-butylphenol, heneicosane, hentriacontane, and tetracosane) were used directly in germination assays of P. laevigata and A. thaliana seeds instead of volatiles emitted by Bacillus sp. MH778713. All organic compounds allowed Prosopis and Arabidopsis seeds to overcome Cr-toxicity and germinate. The results of this study provide new insight into the role of long-chain bacterial compounds produced by Bacillus sp. MH778713 as triggers of seed abiotic stress tolerance, surmounting chromium stress and stimulating seedling development.
Highlights
Plant growth-promoting rhizobacteria (PGPR) are beneficial plant symbionts capable of providing plants with improved water and nutrient uptake (Vacheron et al, 2013; Backer et al, 2018)
To determine the minimal amount of chromium (VI) that prevent seed germination, surface-sterilized seeds of Prosopis laevigata and Arabidopsis thaliana were placed onto water-agar plates supplemented with 100, 200, 300, . . . up to 2500 mg L−1 of K2CrO4 for germination assays of Prosopis and 10, 20, 30, . . . up to 100 mg L−1 for Arabidopsis
We found out that 100 and 2500 mg L−1 of Cr(VI) precluded seed germination of A. thaliana and P. laevigata, confirming chromium phytotoxic effects
Summary
Plant growth-promoting rhizobacteria (PGPR) are beneficial plant symbionts capable of providing plants with improved water and nutrient uptake (Vacheron et al, 2013; Backer et al, 2018). Rhizobacteria are intimately associated with the root system of the plants and can affect the growth and fitness of plants by modulating nutrient uptake, inducing systemic resistance, and tolerance to. Bacterial volatiles can modulate root architecture, iron uptake, sodium and auxin homeostasis in plants (Zhang et al, 2007; Gutierrez-Luna et al, 2010; Liu and Zhang, 2015). Drought-stressed plants exposed to B. subtilis GB03 VOCs were more tolerant than plants without VOCs treatment due to the accumulation of osmoprotectants such as choline and glycine (Zhang et al, 2010; Liu and Zhang, 2015). The demonstrated efficacy of VOCs in enhancing plant fitness and tolerance to salinity, drought, iron deficiency, and sulfur starvation stress suggest that bacterial volatiles might help plants to tolerate other abiotic stresses, but their effectiveness should be confirmed for each stress condition
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