Journal of Chemical Ecology

, Volume 33, Issue 10, pp 1898–1918 | Cite as

Root-secreted Allelochemical in the Noxious Weed Phragmites Australis Deploys a Reactive Oxygen Species Response and Microtubule Assembly Disruption to Execute Rhizotoxicity

  • Thimmaraju Rudrappa
  • Justin Bonsall
  • John L. Gallagher
  • Denise M. Seliskar
  • Harsh P. Bais


Phragmites australis is considered the most invasive plant in marsh and wetland communities in the eastern United States. Although allelopathy has been considered as a possible displacing mechanism in P. australis, there has been minimal success in characterizing the responsible allelochemical. We tested the occurrence of root-derived allelopathy in the invasiveness of P. australis. To this end, root exudates of two P. australis genotypes, BB (native) and P38 (an exotic) were tested for phytotoxicity on different plant species. The treatment of the susceptible plants with P. australis root exudates resulted in acute rhizotoxicity. It is interesting to note that the root exudates of P38 were more effective in causing root death in susceptible plants compared to the native BB exudates. The active ingredient in the P. australis exudates was identified as 3,4,5-trihydroxybenzoic acid (gallic acid). We tested the phytotoxic efficacy of gallic acid on various plant systems, including the model plant Arabidopsis thaliana. Most tested plants succumbed to the gallic acid treatment with the exception of P. australis itself. Mechanistically, gallic acid treatment generated elevated levels of reactive oxygen species (ROS) in the treated plant roots. Furthermore, the triggered ROS mediated the disruption of the root architecture of the susceptible plants by damaging the microtubule assembly. The study also highlights the persistence of the exuded gallic acid in P. australis’s rhizosphere and its inhibitory effects against A. thaliana in the soil. In addition, gallic acid demonstrated an inhibitory effect on Spartina alterniflora, one of the salt marsh species it successfully invades.


Phragmites australis Spartina alterniflora Root exudation Allelopathy Gallic acid Reactive oxygen species Microtubule 



HPB acknowledges the University of Delaware and EPSCoR for a faculty start-up grant. The authors thank Dr. Jung-Youn Lee and Dr. Gili Ben-Nissan, Delaware Biotechnology Institute for providing the microtubule-specific GFP-fusion line of Arabidopsis. The authors also thank Dr. Kirk Czymmek and the faculty of the Bio-imaging Center, Delaware Biotechnology Institute for the help with the microscopic studies.

Supplementary material

10886_2007_9353_MOESM1_ESM.ppt (1.7 mb)
SOM Figure 1. Effect of P. australis root exudates (BB, native; P38, exotic) and gallic acid (GA) on the viability of A. thaliana roots. Post 24 h treated roots were stained with FDA and visualized by imaging using confocal scanning laser microscopy. The figure shows the completely viable roots of the untreated control and the roots, which have lost their complete viability upon treatment with 30% P38 root exudates and 100 μM GA. The images are representative of the roots of at least six plants analyzed and imaged (PPT 1.66 MB)
10886_2007_9353_MOESM2_ESM.ppt (2.1 mb)
SOM Figure 2. HPLC profiles of the standard gallic acid (GA) (a), the GA in the root exudates of P38 (b), ESI-MS spectra of standard GA (c), and the ESI-MS molecular ion (MW = 170) trace of GA in P38 root exudates (d) (PPT 2.08 MB)
10886_2007_9353_MOESM3_ESM.ppt (12.2 mb)
SOM Figure 3. Effect of gallic acid (GA) on three upland native grass species. a Shows the full rhizotoxicity of the roots treated with GA (100 μM) and 100 μg ml−1 (±)-catechin (positive control) when compared to control untreated plants. b and c Shows the effect of GA (100 μM) and (±)-catechin (μg ml−1) on the total fresh weight and root length of the three native grass species. The data shows significantly higher suppression of fresh weight accumulation and root length in GA and catechin-treated plants compared to the control. Different letters on the bars are used to indicate means that differ significantly (P < 0.05) (PPT 12.1 MB)
10886_2007_9353_MOESM4_ESM.ppt (12.3 mb)
SOM Figure 4. Effect of P. australis root exudates (BB, native; P38, exotic) and gallic acid (GA) on the germination of A. thaliana seeds. The figure shows the complete killing of germinated seedlings on BB and P38 plates while no death of the seedlings is evident but the seedlings exhibit completely suppressed root growth on GA plates (a). b Shows more than 95% mortality of the germinated A. thaliana seedlings on BB and P38 plates within a week, and in c after 2 wk on GA-treated plates (Values are presented as the mean ± SD, N = 6). Different letters on the bars are used to indicate means that differ significantly (P < 0.05) (PPT 12.2 MB)
10886_2007_9353_MOESM5_ESM.ppt (1.5 mb)
SOM Figure 5. Effect of gallic acid (GA) (50 μM) (post 5 h treatment) with or without AsA (500 μM) on the generation of root surface ROS and root cell microtubule architecture. The images are representative of the roots of at least six plants analyzed and imaged (PPT 1.47 MB)


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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  • Thimmaraju Rudrappa
    • 1
    • 2
  • Justin Bonsall
    • 1
    • 2
  • John L. Gallagher
    • 3
  • Denise M. Seliskar
    • 3
  • Harsh P. Bais
    • 1
    • 2
  1. 1.Department of Plant and Soil SciencesUniversity of DelawareNewarkUSA
  2. 2.Delaware Biotechnology InstituteNewarkUSA
  3. 3.College of Marine and Earth StudiesUniversity of DelawareLewesUSA

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