Figure 1. An overview of transport systems in the plant plasma membrane. All transport is strictly regulated. This is indicated for the H⁺ and Ca²⁺ pumps, which are regulated by binding and release of 14-3-3 protein and calmodulin (CaM), respectively; and for the water channel activity which is regulated by phosphorylation (indicated by a P). E, electrical gradient (membrane potential). Figures drawn by Ingela Johansson and Magnus Alsterfjord.

Figure 2. Receptors in the plasma membrane perceive environmental and endogenous signals. Left, the cytokinin (a hormone) two-component receptor. Right, four examples of receptor-like protein kinases (RLKs) with differing extracellular domains. The signal (a ligand, e.g. a fungal protein) binds to the extracellular domain of the receptor, which induces receptor dimerization or oligomerization that brings the intracellular kinase domains together and allows them to phosphorylate (indicated by a P) and activate one another. This phosphorylation initiates downstream intracellular signal transduction, eventually resulting in intracellular responses, such as the biosynthesis and excretion of enzymes that degrade fungal cell walls (in pathogen defence reactions).