Signals from the underground:: bacterial volatiles promote growth in Arabidopsis

Plant-growth-promoting rhizobacteria colonize the root systems of plants and can modulate plant growth by enhancing the availability of nutrients, inducing metabolic activities by phytohormones and analogs, by shifting the phytohormonal balance, by inducing defense programs such as systemic acquired resistance (SAR) and induced systemic resistance (ISR), or by reducing phytotoxic microbial communities. A recently discovered novel mode of growth promotion and induction of ISR is based on airborne volatiles (butanediol, acetoin) released from certain microorganisms. According to studies with mutants of Arabidopsis thaliana, the growth-promotion response appears to be controlled by cytokinins and ethylene.