Defence Spending Slashed in the Hyperaccumulator Economy?

Thlaspi caerulescens is a ‘metal hyperaccumulator’ which stores metal ions at potentially toxic concentrations in its aerial tissues. We have used a model system comprising Thlaspi and Pseudomonas syringae pv. maculicola to test the possibility that this trait evolved as an anti-pathogen defence. Recent results suggest a trade-off with other defences has occurred.

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Bacterial Growth in planta Vs. Zinc Treatment

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Ganges Viviez Prayon Wilberwiltz

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Helen Fones, Calum Davis, J. Andrew C. Smith and Gail M Preston.Department of Plant Sciences, University of Oxford, South Parks Road, Oxford. OX1 3RB

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Whole Leaf Salicylic Acid Concentration Vs Treatment

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Arabidopsis + Psm

T. caerulescens does not produce H2O2 in response to pathogen attack

In response to inoculation with Psm, the related model non-accumulating plant, Arabidopsis thaliana produces both H2O2 (visulisedusing di-aminobenzidine staining 2 hrs after inoculation, below far left) and Superoxide (visualised using nitroblue tetrazolium 4 hrs post inoculation, below far right). It also produces the signalling molecule salicylic acid (below, graph). All of these responses appear to be absent in T. caerulescens grown at any zinc regime. However, superoxide content appears to covary with zinc (below right).

Thlaspi caerulescens + Psm. Clockwise from top left: 0.04, 10, 30 and 300 μM Zn treatment

Thlaspi caerulescens + Psm. Clockwise from top left: 0.04, 10, 30 and 300 μM Zn treatment

Arabidopsis untreated

Arabidopsis + Psm

T. caerulescens does not produce superoxide in response to pathogen attack

‘Basal’ Defence Responses are Missing or Attenuated in T. caerulescens

1 μM Zn 300 μM Zn

Observations during a glasshouse mildew outbreak prompted this project...

Thlaspi

Pseudomonas

Metal hyperaccumulation restricts the growth of Psmin planta (above). Analysis of the metal content of whole leaves and apoplastic fluid have shown that in planta metal concentrations are sufficient to inhibit bacterial growth.

Bacterial Endophytes Perform Differently in Different Thlaspi Populations

Bacterial endophytes were isolated from a natural population of T. caerulescens in Snowdonia, UK. The growth of selected endophytes was monitored in plants from four European Thlaspi caerulescens populations. Data for strain B11 is shown.

Populations of T. caerulescens vary in their ability to accumulate zinc and in glucosinolate content; preliminary results suggest that there are also differences in other defenses. Any or all of these factors may explain the differences seen in bacterial growth (below centre).

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16S, rpoD and gyrB 3 gene tree of Thlaspi endophytes, and Pseudomonas strains

Viviez

Wilberwiltz

Strain ‘Snowdonia B11’ cell counts after 5 days growth in four populations of T. caerulescens