Root Hair Electrophysiology. In: Emons AMC, Ketelaar T, editors. Root Hairs. Berlin: Springer Berlin Heidelberg; 2009. pp. 123-44. [DOI: 10.1007/978-3-540-79405-9_9]

Biochemical and biophysical pH clamp controlling Net H+ efflux across the plasma membrane of plant cells

P-type H⁺ ATPases mediate active H⁺ efflux from plant cells. They generate a proton motive force across the plasma membrane, providing the free energy to drive the transport of other solutes, partly by coupling to H⁺ influx. Wegner & Shabala (2020) recently suggested that passive H⁺ influx can exceed pump-driven efflux due to 'active buffering', that is, cytosolic H⁺ scavenging and apoplastic H⁺ generation by metabolism ('biochemical pH clamp'). Charge balance is provided by K⁺ efflux or anion influx. Here, this hypothesis is extended to net H⁺ efflux: even though H⁺ pumping is faster than backflow via symporters and antiporters, a progressive increase in the transmembrane pH gradient is avoided. Cytosolic H⁺ release is associated with bicarbonate formation from CO₂ . Bicarbonate serves as substrate for the PEPCase, catalyzing the reaction from phosphoenolpyruvate to oxaloacetate, which is subsequently reduced to malate. Organic anions such as malate and citrate are released across the plasma membrane and are (partly) protonated in the apoplast, thus limiting pump-induced acidification. Moreover, a 'biophysical pH clamp' is introduced, that is, adjustment of apoplastic/cytosolic pH involving net H⁺ fluxes across the plasma membrane, while the gradient between compartments is maintained. The clamps are not mutually exclusive but are likely to coexist.

Electrotonic potentials in Aloe vera L.: Effects of intercellular and external electrodes arrangement

Electrostimulation of plants can induce plant movements, activation of ion channels, ion transport, gene expression, enzymatic systems activation, electrical signaling, plant-cell damage, enhanced wound healing, and influence plant growth. Here we found that electrical networks in plant tissues have electrical differentiators. The amplitude of electrical responses decreases along a leaf and increases by decreasing the distance between polarizing Pt-electrodes. Intercellular Ag/AgCl electrodes inserted in a leaf and extracellular Ag/AgCl electrodes attached to the leaf surface were used to detect the electrotonic potential propagation along a leaf of Aloe vera. There is a difference in duration and amplitude of electrical potentials measured by electrodes inserted in a leaf and those attached to a leaf's surface. If the external reference electrode is located in the soil near the root, it changes the amplitude and duration of electrotonic potentials due to existence of additional resistance, capacitance, ion channels and ion pumps in the root. The information gained from this study can be used to elucidate extracellular and intercellular communication in the form of electrical signals within plants.