Involvement of plant endogenous ABA in Bacillus megaterium PGPR activity in tomato plants.
BACKGROUND
Plant 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.


RESULTS
Contrary 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.


CONCLUSIONS
Positive 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.
Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín (EEZ-CSIC), Profesor Albareda 1, 18008 Granada, Spain. rporcel@eez.csic.es.
Rosa
R
Porcel
Ángel María
ÁM
Zamarreño
José María
JM
García-Mina
Ricardo
R
Aroca
D000040:Abscisic Acid / Q000378:metabolism*; D001410:Bacillus megaterium / Q000378:metabolism*; D018551:Solanum lycopersicum / Q000254:growth & development / Q000382:microbiology* / Q000502:physiology
D000040:Abscisic Acid