Abstract
BackgroundPlant growth-promoting rhizobacteria (PGPR) are naturally occurring soil bacteria which benefit plants by improving plant productivity and immunity. The mechanisms involved in these processes include the regulation of plant hormone levels such as ethylene and abscisic acid (ABA). The aim of the present study was to determine whether the activity of Bacillus megaterium PGPR is affected by the endogenous ABA content of the host plant. The ABA-deficient tomato mutants flacca and sitiens and their near-isogenic wild-type parental lines were used. Growth, stomatal conductance, shoot hormone concentration, competition assay for colonization of tomato root tips, and root expression of plant genes expected to be modulated by ABA and PGPR were examined.ResultsContrary to the wild-type plants in which PGPR stimulated growth rates, PGPR caused growth inhibition in ABA-deficient mutant plants. PGPR also triggered an over accumulation of ethylene in ABA-deficient plants which correlated with a higher expression of the pathogenesis-related gene Sl-PR1b.ConclusionsPositive correlation between over-accumulation of ethylene and a higher expression of Sl-PR1b in ABA-deficient mutant plants could indicate that maintenance of normal plant endogenous ABA content may be essential for the growth promoting action of B. megaterium by keeping low levels of ethylene production.
Highlights
Plant growth-promoting rhizobacteria (PGPR) are naturally occurring soil bacteria which benefit plants by improving plant productivity and immunity
The aim of the present study was to determine whether the activity of Bacillus megaterium PGPR is affected by the endogenous abscisic acid (ABA) content of the host plant
Experimental design The experiment consisted of a randomized complete block design with two inoculation treatments: (1) non-inoculated control plants and (2) plants inoculated with the PGPR Bacillus megaterium strain which was isolated by MarulandaAguirre et al [24], and two plant ABA line treatments: wild type and an ABA-deficient line
Summary
Plant growth-promoting rhizobacteria (PGPR) are naturally occurring soil bacteria which benefit plants by improving plant productivity and immunity. A wide range of microorganisms which live in the soil are able to establish symbiotic and non-symbiotic associations with their host plants [5]. These microorganisms play important functions in the soil which include: (1) controlling the adverse effects of pathogens on plant growth, (2) alleviating negative effects of soil stresses on plant growth and yield production, (3) biofertilization, (4) enhancing root growth, and (5) rhizoremediation [6,7,8,9]. Ethylene is a plant growth regulator essential for normal growth and development in plants Apart from this key function, ethylene acts as a stress hormone when plants are exposed to salinity, drought, waterlogging, heavy metals or pathogens [12]
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