Stimulation of nitrogen fixation and induction of flavonoid-like compounds by rhizobacteria

Abstract

N . P AR M AR AN D K. R. D AD AR W AL . 1999. Bacteria belonging to fluorescent Pseudomonas and to the spore-forming Bacillus groups, predominantly found in the rhizosphere and rhizoplane of healthy chickpea plants, were studied in order to determine their effect on effective strains of Rhizobium sp. 'Cicer' (Ca181 and Ca313) and their plant growthpromoting ability under aseptic and soil conditions. Co-inoculation of the rhizobacteria with effective Rhizobium strains of chickpea resulted in a significant increase in nodule weight, root and shoot biomass and total plant nitrogen when grown either in sterilized chillum jars or under pot culture conditions. The Rhizobium stimulatory Pseudomonas sp. 'CRP55b' showed maximum increase in all the symbiotic parameters. On co-inoculation with 'Ca181' and 'Ca313', Pseudomonas sp. 'CRP55b' and 'CRS68' resulted in significant increases in nodule weight, root and shoot biomass and total plant nitrogen. The nodule stimulating rhizobacteria enhanced levels of flavonoid-like compounds in roots on seed bacterization. Also, ethyl acetate extracts of culture supernatant fluids when applied to seeds resulted in enhancement of flavonoids in roots, suggesting that the rhizobacteria have a direct influence on root flavonoids which might be an additional factor in nodule promotion by these bacteria. These rhizobacteria also produced fluorescent compounds with absorption maxima at 252 nm, similar to those of plant flavonoids but having a different Rf value. Whether such fluorescent compounds act as signal molecules for induction of plant flavonoids in plant roots requires further study.

Effects of Plant Growth Promoting Rhizobacteria (PGPRs) on the Biological Nitrogen Fixation, Nodulation, and Growth of Lupinus albus l. cv. Multolupa

“…Parmar and Dadarwal [10] revealed a relation between siderophore production and an increase in the level of flavonoid-like compounds, along with an increase in total plant nitrogen in chickpea. Although within seven days a bacterium can provoke an ISR response [9], the authors decided to rule out this mechanism because this strain does not show any other mechanisms known to induce ISR, siderophore production, or the presence of lipopolysaccharides in the outer membrane (LPS) [32].…”

“…The release of phytohormones by rhizobacteria is an important aspect: all phytohormones are implicated in nodule formation in one way or another [4]. Furthermore, induced systemic resistance (ISR) [7] may have bearing, as this process is associated with the synthesis of phytoalexins [8,9] and flavonoids, where the latter play an important role in the nodulation process [10].…”

Improvement in symbiotic efficiency of chickpea (Cicer arietinum) by coinoculation of Bacillus strains with Mesorhizobium sp. Cicer

“…The fl avonoids released by legume roots are the signal compounds that induce the transcription of rhizobial nodulation genes 23 . Rhizobacteria have been found to enhance the production of fl avonoid-like compounds or phytoalexins in roots of several crop plants 24,25 . The localized plant hormone auxins have been shown to participate in the fundamental responses of nodule morphogenesis, biosynthesis of nodulation factors and induction of root cortical cell mitosis, early nodulin genes and/or nodule-like structures 26 .…”

A large diversity of non-rhizobial endophytes found in legume root nodules in Flanders (Belgium)

“…Most legumes are good pioneer species, adapted to low nutrient soils and/or environments with heavy metals (Gonzalez-Andres et al, 2005;Vidal et al, 2009;Azcon et al, 2010). Multiple studies report on the beneficial effect of co-inoculating rhizobia with other bacteria (Zhang et al, 1996;Parmar and Dadarwal, 1999;Rajendran et al, 2008;Egamberdieva et al, 2010). All previously mentioned studies suggest that besides rhizobia, NRE are present inside root nodules, which may have beneficial effects on the host plant.…”