Non-invasive microelectrode potassium flux measurements as a potential tool for early recognition of virus-host compatibility in plants

Diseases caused by plant viruses are widespread, resulting in severe economic losses worldwide. Understanding the cellular basis of defense responses and developing efficient diagnostic tools for early recognition of host specificity to viral infection is, therefore, of great importance. In this work, non-invasive ion selective microelectrodes (the MIFE technique) were used to measure net ion fluxes in mesophyll tissue of host (potato, tomato, tobacco) and non-host (sugar beet and periwinkle) plants in response to infection with Potato virus X (PVX). These results were complemented by FLIM (Fluorescence Lifetime Imaging) measurements of PVX-induced changes in intracellular Ca2+ concentrations. Our results demonstrate that, unlike in other plant-pathogen interactions, Ca2+ signaling appears to be non-essential in recognition of the early stages of viral infection. Instead, we observed significant changes in K+ fluxes as early as 10 min after inoculation. Results of pharmacological experiments and membrane potential measurements pointed out that a significant part of these fluxes may be mediated by depolarization-activated outward-rectifying K+ channels. This may suggest that viral infections trigger a different mechanism of plant defense signaling as compared to signals derived from other microbial pathogens; hence, altered Ca2+ fluxes across the plasma membrane may not be a prerequisite for all elicitor-activated defense reactions. Clearly pronounced host specificity in K+ flux responses suggests that the MIFE technique can be effectively used as a screening tool for the early diagnostics of virus-host compatibility.