The effects of bacterial volatile emissions on plant abiotic stress tolerance

Abstract

Plant growth-promoting rhizobacteria (PGPR) are beneficial plant symbionts that have been successfully used in agriculture to increase seedling emergence, plant weight, crop yield, and disease resistance. Some PGPR strains release volatile organic compounds (VOCs) that can directly and/or indirectly mediate increases in plant biomass, disease resistance, and abiotic stress tolerance. This mini-review focuses on the enhancement of plant abiotic stress tolerance by bacterial VOCs. The review considers how PGPR VOCs induce tolerance to salinity and drought stress and also how they improve sulfur and iron nutrition in plants. The potential complexities in evaluating the effects of PGPR VOCs are also discussed.

Keywords: abiotic stress; drought; iron deficiency; plant growth-promoting rhizobacteria; salinity; sulfur nutrition; volatile organic compounds.

FIGURE 1

The effects of microbial volatiles on plant abiotic stress tolerance. VOCs can modulate Arabidopsis sodium homeostasis via tissue-specific regulation of HKT1 and possibly also via the SOS pathway. Accumulation of H₂O₂ and nitric oxide is involved in the VOC-induced drought tolerance in plants. Accumulation of choline synthesized by VOC-induced PEAMT and other osmo-protectants may be a common mechanism for increasing osmotic protection in salt- or drought-stressed plants. VOCs also trigger the expression of FIT1, FRO2, and IRT1 to facilitate iron uptake and plant growth. Under conditions of sulfur starvation, plants directly take up and assimilate the S-containing compounds (e.g., dimethyl disulfide) emitted from some PGPR. See text for details.