P-447 - Spatial localisation and mobilisation of zinc contributes to elemental defences in the metal-hyperaccumulating plant Noccaea caerulescens

Noccaea caerulescens is one of approximately 700 plant species with the ability to hyperaccumulate metals in its foliar tissues. The accumulation of metals, including zinc, by N. caerulescens has been demonstrated to provide an "elemental" defence against plant pathogens. Here we use synchrotron X-ray fluorescence (XRF) to demonstrate how zinc is distributed within healthy N. caerulescens leaves and how its distribution changes in response to infection with the model pathogen Pseudomonas syringae. Protocols have been developed for 2-D and tomographic XRF imaging of whole leaves and transverse cross sections and X-ray absorption spectroscopy has been applied to identify the zinc species that are most likely to be present within different compartments within N. caerulescens leaves. Measurement at 2 µm resolution indicates that Noccaea exhibits environment-dependent heterogeneity in zinc accumulation. Interestingly, upon infection with Pseudomonas syringae zinc can be observed to mobilise from the vacuole into the leaf apoplast, potentially enhancing the ability of N. caerulescens to limit bacterial infection. This study highlights the potential for synchrotron X-ray methods for use in plant pathology and has established effective sampling procedures to allow for accurate measurements of elements within plant tissues and their interactions with plant pathogenic microorganisms.