Effect of volatiles produced by antagonistic rhizobacteria on arabidopsis thaliana growth.

EFFECT OF VOLATILES PRODUCED BY ANTAGONISTIC RHIZOBACTERIA ON ARABIDOPSIS THALIANA GROWTH A. Giorgio1, P.A.H.M. Bakker2, N.S. Iacobellis1 1Scuola di Scienze Agrarie, Forestali, Alimentari ed Ambientali, Università degli Studi della Basilicata, Viale dell’Ateneo Lucano 10, 85100, Potenza, Italy. 2Plant-Microbe Interactions, Institute of Environmental Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands. E-mail: iacobellis@unibas.it Recent studies have demonstrated that rhizobacteria may employ volatiles as signals in their interactions with plants and rhizosphere microbial communities. In this study we investigated the in vitro effect of volatiles from selected antagonistic bacteria, identified as Pseudomonas and Bacillus spp. and isolated from bean rhizosphere, on the growth of Arabidopsis thaliana Col-0. The effects of bacterial volatiles on A. thaliana seed germination and plant growth depended on the bacterial isolate used, but also on growth conditions for the bacteria and on the plant growth stage at which they are exposed to volatiles. Contrasting effects ranging from inhibition of seed germination to a moderate growth inhibition as well as to an augmented plant biomass were observed. The former effect was observed for some Pseudomonas spp. isolates which demonstrated to produce, beside other volatiles, hydrogen cyanide which may be responsible for the toxic effect on the seed germination. Other Pseudomonas spp. isolates, not producing hydrogen cyanide, showed slight inhibition of A. thaliana growth. In contrast, volatiles from a Bacillus spp. isolate caused a huge biomass increase. Plant growth and development is endogenously regulated by hormones such as SA, JA and ET that are also involved in plant responses to abiotic and biotic stresses. To study the contribution of SA, JA and ET signaling pathways on the growth of A. thaliana mediated by bacterial volatiles, a set of plant hormone mutants, including NahG, jar1-1 and ein2-1, defective in mentioned hormones signaling, were evaluated for their responses to inoculation with these bacteria.