Wheat is an essential crop, contributing to approximately 18% of human calorie intake globally1. Worth $2 billion annually to the local economy, the wheat industry has particular economic significance in Western Australia (WA)2. Wheat yields are threatened in WA by yellow spot disease, caused by the necrotrophic fungus Pyrenophora tritici repentis (Ptr)3. With emerging fungicide resistance, more resilient varieties of wheat are needed to manage the problem.
Changes in metal ion distribution during yellow spot infection of wheat leaves were previously observed by Naim et al4. It is hypothesised that these changes are involved in nutritional immunity, where the plant or pathogen can actively restrict or accumulate metals (e.g. Mn, Zn, Cu) to deprive the other of essential nutrients or poison them with toxic concentrations. This may be used by the plant as a defense against the pathogen, or by the fungus as an attack on the host, however in practice these are difficult to distinguish.
To understand how metal ion distribution and speciation changes are involved in plant-pathogen interactions and may confer resistance to disease, we have further developed protocols to visualise these changes in situ in infected wheat leaves using X-ray fluorescence microscopy (XFM), X-ray absorption near-edge structure (XANES) spectroscopic mapping, and time-of-flight secondary ion mass spectrometry (TOF-SIMS). In the long term, we aim to link these processes with changes in gene expression to provide an even greater understanding of nutritional immunity in plants, potentially providing an avenue which could be exploited to improve crop resistance or tolerance to disease (for example via selective breeding or fertilisation practices).