Long-Chain Hydrocarbons (C21, C24, and C31) Released by Bacillus sp. MH778713 Break Dormancy of Mesquite Seeds Subjected to Chromium Stress

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 sp. MH778713 to induce seed dormancy breakage in and seeds were examined. The minimal inhibitory concentration of chromium (Cr) VI that prevents seed germination of and on water-Cr-agar plates was 2500 and 100 mg L , respectively. Remarkably, partitioned Petri-dish co-cultivation of sp. MH778713 and plant seeds under Cr-stress showed the beneficial effect of volatiles emitted by sp. MH778713, helping plant seeds to overcome Cr-stress. Among the metabolites emitted by 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 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 and seeds instead of volatiles emitted by sp. MH778713. All organic compounds allowed and 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 sp. MH778713 as triggers of seed abiotic stress tolerance, surmounting chromium stress and stimulating seedling development.