Synchrotron X-ray fluorescence microscopy-enabled elemental mapping illuminates the “battle for nutrients” between plant and pathogen

Abstract

Metal homeostasis is integral to normal plant growth and development. During plant-pathogen interactions, the host and pathogen compete for the same nutrients, potentially impacting on nutritional homeostasis. Our knowledge of outcome of the interaction in terms of metal homeostasis is still limited. Here, we employed X-ray fluorescence microscopy (XFM) beamline at the Australian Synchrotron to visualise and analyse the fate of nutrients in wheat leaves infected with Pyrenophora tritici-repentis, a necrotrophic fungal pathogen. We sought to (i) evaluate the utility of XFM for sub-micron mapping of essential mineral nutrients and ii) examine the spatiotemporal impact of a pathogen on nutrient distribution in leaves. XFM maps of K, Ca, Fe, Cu, Mn, and Zn revealed substantial hyperaccumulation within, and depletion around, the infected region relative to uninfected control samples. Fungal mycelia were visualised as threadlike structures in the Cu and Zn maps. The hyperaccumulation of Mn in the lesion and localised depletion in asymptomatic tissue surrounding the lesion was unexpected. Similarly, Ca accumulated at the periphery of symptomatic region and as micro-accumulations aligning with fungal mycelia. Collectively, our results highlight that XFM imaging provides capability for high resolution mapping of elements to probe nutrient distribution in hydrated diseased leaves in situ.