Continuous monitoring of plant sodium transport dynamics using clinical PET

Abstract

BackgroundThe absorption, translocation, accumulation and excretion of substances are fundamental processes in all organisms including plants, and have been successfully studied using radiotracers labelled with and since 1939. Sodium is one of the most damaging ions to the growth and productivity of crops. Due to the significance of understanding sodium transport in plants, a significant number of studies have been carried out to examine sodium influx, compartmentation, and efflux using - or 24Na-labeled salts. Notably, however, most of these studies employed destructive methods, which has limited our understanding of sodium flux and distribution characteristics in real time, in live plants.Positron emission tomography (PET) has been used successfully in medical research and diagnosis for decades. Due to its ability to visualise and assess physiological and metabolic function, PET imaging has also begun to be employed in plant research. Here, we report the use of a clinical PET scanner with a tracer to examine -influx dynamics in barley plants (Hordeum vulgare L. spp. vulgare – cultivar Bass) under variable nutrient levels, alterations in the day/night light cycle, and the presence of sodium channel inhibitors.Results3D dynamic PET images of whole plants show readily visible translocation from roots to shoots in each examined plant, with rates influenced by both nutrient status and channel inhibition. PET images show that plants cultivated in low-nutrient media transport more than plants cultivated in high-nutrient media, and that uptake is suppressed in the presence of a cation-channel inhibitor. A distinct diurnal pattern of influx was discernible in curves displaying rates of change of relative radioactivity. Plants were found to absorb significantly more during the light period, and anticipate the change in the light/dark cycle by adjusting the sodium influx rate downward in the dark period, an effect not previously described experimentally.ConclusionsWe demonstrate the utility of clinical PET/CT scanners for real-time monitoring of the temporal dynamics of sodium transport in plants. The effects of nutrient deprivation and of ion channel inhibition on sodium influx into barley plants are shown in two proof-of-concept experiments, along with the first-ever 3D-imaging of the light and dark sodium uptake cycles in plants. This method carries significant potential for plant biology research and, in particular, in the context of genetic and treatment effects on sodium acquisition and toxicity in plants.*The authors contributed equally

In vivo imaging and quantification of carbon tracer dynamics in nodulated root systems of pea plants

“…While the physics and technical aspects of the PET instruments are more complex than for scintillation detectors set-ups, PET scanners are routinely applied as a medical diagnostic tool. It has been demonstrated that medical PET scanners could even directly be employed for plant studies (Karve et al, 2015, Ruwanpathirana et al, 2021. A pilot study with a 2-dimensional PET sytem showed the principal feasability of detecting 11 C tracer in nodules (Fujikake et al, 2003), but did not allow for the analysis of local carbon allocation to individual nodules or within a longer time period.…”