Journal of Chemical Ecology

, Volume 25, Issue 10, pp 2397–2406 | Cite as

Is IAA the Major Root Growth Factor Secreted from Plant-Growth-Mediating Bacteria?

  • Oz Barazani
  • Jacob Friedman
Article

Abstract

The phytotoxic or promoting effect of bacterial secretions on root growth of young lettuce seedlings (Lactuca sativa) was measured under axenic conditions. It was assumed that the inhibitory or promoting effects of either deleterious rhizobacteria (DRB) or of plant growth promoting rhizobacteria (PGPR) were auxin mediated. To avoid measurements of either parasitism or competition, seedlings were placed adjacent to bacterial colonies, with no contact between the organisms. Auxin excretion rate, evaluated by thin-layer chromatography (TLC) combined with Salkowski's reagent, indicated that all bacteria examined produced and released indole-3-acetic acid (IAA). High levels of IAA (76.6 μM) were excreted by four DRB (Micrococcus luteus, Streptoverticillium sp., Pseudomonas putida, and Gluconobacter sp.) during 84 hr of incubation. High concentrations of IAA released by DRB accounted for the suppression of root growth. Other unidentified fractions in the eluates of DRB also inhibited root elongation, but to a lesser extent. Like DRB, four isolates of PGPR (Agrobacterium sp., Alcaligenes piechaudii, and two different strains of Comamonas acidovorans) secreted IAA, but at lower levels (16.4 μM during a similar period of incubation). PGPR secreted growth promoting substances other than IAA, and these are now being investigated.

Phytotoxicity deleterious rhizobacteria indole-3-acetic acid lettuce Lactuca sativa plant-growth-promoting rhizobacteria 

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Copyright information

© Plenum Publishing Corporation 1999

Authors and Affiliations

  • Oz Barazani
    • 1
  • Jacob Friedman
    • 1
  1. 1.Department of Plant Sciences, The George S. Wise Faculty of Life Sciences, Tel-Aviv UniversityTel AvivIsrael

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