Endodermal suberin deposition restricts potassium leakage from roots

The endodermis is a checkpoint for ions and water escaping or entering the root. It has been hypothesized that suberin acts as a physical barrier preventing potassium (K) leakage from the stele during translocation, but attempts to support this idea has yielded contradictory results. We developed a Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) based element bioimaging method to study K leakage from roots with different suberin deposition, where we show that cesium (Cs) is an excellent tracer for K. Element bioimaging of roots and total shoot concentrations from various Arabidopsis thaliana mutants all showed a positive relationship between suberin deposition and K translocation efficiency. In addition, images from the fully suberized barley (Hordeum vulgare) seminal roots revealed a strongly reduced K leakage compared to less suberized root zones. Nodal roots form a scattered deposition of suberin towards the phloem in the mature root zone. This incomplete suberin deposition also restrict K leakage efficiently. Collectively, our findings provide experimental evidence that suberin act as a barrier for K leakage upon root-to-shoot translocation by restricting K movement over the endodermis from the stele to cortex.