Transport processes allow plants to create solute gradients between the environment and the plant cell but also between different cellular compartments. The tight regulation of solute concentrations in the different compartments allows the plant to optimize cellular metabolism. Until recently research on plant transporter was mainly focused on the identification of the substrate for a specific transporter. Transcript analysis has shown that in several cases the transport capacity might be regulated at the transcriptional level. However, our knowledge how the amount of transcripts reflects the protein level is in most cases an open question. There are only a few examples where regulation of the transport activity at the posttranscriptional level has been elucidated. Such a modulation of the transport activity allows a plant to adapt fastly to varying environmental and developmental. Posttranslational modifications may include phosphorylation but also the induction of protein-protein interactions which may change transport activity and properties. The aim of this project is to elucidate regulation mechanisms of transport processes more in depth. We will analyze phosphorylation of some plant transporters in response to growth conditions and search for interacting partners, which might have an impact in the transport activity and possibly substrate specificity. This new knowledge will allow us to integrate transport processes and metabolism.