Interactions of bacterial cytokinins and IAA in the rhizosphere may alter phytostimulatory efficiency of rhizobacteria

Abstract

Phytohormones from rhizobacterial origin have been linked to their phytostimulation potential. However, while studying the efficacy of plant growth promoting bacteria, focus has always been on a single hormone. The role of plant hormones often overlay and they mutually modulate their effect. In current study focus was on the role of two hormones (cytokinins and indole acetic acid) in phytostimulation by rhizobacteria. Endogenous rhizosphere bacteria were isolated and screened for the presence of phytohormones. Bacterial strains from three different genera (Pseudomonas, Bacillus and Azospirillum) were screened positive for cytokinins and IAA. Phytohormones were simultaneously determined in SPE purified bacterial extract by ultra performance liquid chromatography (UPLC) coupled to a tandem mass spectrometer through electrospray interface. Cytokinins and IAA were determined in positive and negative mode, respectively with MRM scan. Zeatin, zeatin riboside and dihydrozeatin riboside were detected and quantified in the selected strains. Significant positive correlation between cytokinins and IAA in bacterial culture and plant endogenous hormones (r = 0.933 and r = 0.983; P = 0.01, respectively) was observed. However, strains with high IAA to cytokinins ratio could hardly enhance in-planta cytokinins, indicating antagonistic relation between the two hormones. Significant correlation of cytokinin with shoot length (r = 0.797; P = 0.01), fresh weight (r = 0.685; P = 0.01) and dry weight (r = 0.704; P = 0.01) was reported under axenic conditions. Bacterial IAA was correlated negatively to root length (r = 0.853; P = 0.01) and positively correlated to the number of roots (r = 0.964; P = 0.01). In natural conditions maximum increase in spike length (33%), number of tillers (71%) and weight of seeds (39%) was documented at final harvest in bacterially inoculated plants.

Effect of Rhizobacterial-Mediated Auxin on Growth Promotion of Wheat and Mung Bean Plant

“…Bacterial phytohormones are the main thing for initiating the signaling pathways in plants [15]. Our work has accordance to [12] and [16], who isolated the auxinproducing rhizobacteria for their further consumption in plant growth experiments. The rhizobacterial auxin was investigated for their positive role on Triticum aestivum and Vigna radiata plant growth promotion in laboratory conditions.…”

Medicago truncatula Gaertn. as a model for understanding the mechanism of growth promotion by bacteria from rhizosphere and nodules of alfalfa

“…Production of these compounds was quantified as ranging from 4.0 to 47.2 µg ml −1 . In the presence of tryptophan (1 %), bacterial strains representing three genera: Pseudomonas , Bacillus and Azospirillum produced IAA in amounts ranging from 1.2 to 44.4 µg ml −1 , but the production was negatively correlated with the root length, while correlating positively with the number of roots in 15-day-old wheat seedlings (Hussain and Hasnain 2011 ). Our results may suggest that indolic compounds production by bacterial strains, except that by P. brassicacearum KK 5, can be responsible for stimulation of M. truncatula root development; the indolic compounds content was positively correlated with the root dry mass ( r = 0.69; P = 0.0001) .…”

Volatile Mediated Interactions Between Bacteria and Fungi in the Soil

“…1 Schematic presentation of organisms involved in volatile interactions above-and belowground (drawn by Marco Kai). 1 plant root, 2 bacteria, 3 fungi, 4 ciliates, 5 amoeba, 6 nematodes, 7 moos, 8 wild boar, 9 plant leaves, 10 plant flowers, 11 insects dense and diverse population of microbiota, including bacteria and fungi (Koske and Gemma, 1992;Chen et al, 2004;Gregory, 2006;Brimecombe et al, 2007;Nannipieri et al, 2007;Hussain and Hasnain, 2011). Bacteria adhere to the root surface itself (rhizoplane) and colonize a narrow soil zone around the plant root (rhizosphere) (Lenc et al, 2011).…”