Plant growth-promoting rhizobacteria and root system functioning

Abstract

The rhizosphere supports the development and activity of a huge and diversified microbial community, including microorganisms capable to promote plant growth. Among the latter, plant growth-promoting rhizobacteria (PGPR) colonize roots of monocots and dicots, and enhance plant growth by direct and indirect mechanisms. Modification of root system architecture by PGPR implicates the production of phytohormones and other signals that lead, mostly, to enhanced lateral root branching and development of root hairs. PGPR also modify root functioning, improve plant nutrition and influence the physiology of the whole plant. Recent results provided first clues as to how PGPR signals could trigger these plant responses. Whether local and/or systemic, the plant molecular pathways involved remain often unknown. From an ecological point of view, it emerged that PGPR form coherent functional groups, whose rhizosphere ecology is influenced by a myriad of abiotic and biotic factors in natural and agricultural soils, and these factors can in turn modulate PGPR effects on roots. In this paper, we address novel knowledge and gaps on PGPR modes of action and signals, and highlight recent progress on the links between plant morphological and physiological effects induced by PGPR. We also show the importance of taking into account the size, diversity, and gene expression patterns of PGPR assemblages in the rhizosphere to better understand their impact on plant growth and functioning. Integrating mechanistic and ecological knowledge on PGPR populations in soil will be a prerequisite to develop novel management strategies for sustainable agriculture.

Influence of plant-growth-promoting bacteria on germination, growth and nutrients’ uptake ofOnobrychis sativaL. under drought stress

“…Khosravi and Mahmoudi (2013) reported a similar reduction in wheat growth indices in the presence of Azotobacter. One of the factors that can prevent plant height and the transfer of auxin is ethylene acetic acid (Vacheron et al 2013). Under normal conditions, drought stress increases ethylene concentration of the plant.…”

The persistence and performance of phosphate-solubilizing Gluconacetobacter liquefaciens qzr14 in a cucumber soil

“…(Bands marked with letters were excised from the polyacrylamide gel and sequenced. Q, Gluconacetobacter liquefaciens qzr14 inoculation; CK, control checks; Q4, Q8, Q12, Q16, and Q20 represent 4, 8, 12, 16, and 20 days after G. liquefaciens qzr14 inoculation; C4, C8, C12, C16, and C20, represent corresponding five control checks) in plant secretions with cucumber growth as these can supply enough nutrients to soil microorganisms (Vacheron et al 2013).…”

Flavonoids in plant rhizospheres: secretion, fate and their effects on biological communication

“…The latter group of bacteria, which do not form special structures, are called plant growth promoting rhizobacteria (PGPR) and have been found to stimulate the growth and health of host plants via various mechanisms, such as phosphate solubilization, siderophore production, phytohormone production, inhibition of pathogen infection, and induction of plant defenses (Vacheron et al 2013). Many plants, both monocots and dicots, act as hosts for these bacteria, and many bacterial genera, such as Pseudomonas, Azospirillum and Bacillus, and even those containing pathogenic bacteria, function as PGPR.…”