Elke Barbez

Abstract The regulation of apoplastic pH is critical for plant growth and development, affecting processes such as nutrient uptake, cell wall expansion and intercellular signaling. Conventional methods for measuring apoplastic pH, including pH indicators in growth media and ion-selective electrodes, often fall short of providing the spatial resolution and accuracy needed for detailed studies.

Abstract Apoplastic pH is a key regulator of plant development and environmental responses, influencing processes such as cell expansion, nutrient uptake, and intercellular signaling. Accurate tools for measuring absolute pH values at high spatial resolution are therefore essential, yet limiting. Here, we present a novel calibration-based workflow for the in vivo quantification of absolute apoplastic pH using the fluorescent pH indicator HPTS.

Cell elongation is a crucial process in the growth of plants, both above and below ground. An old theory from the 1970s postulates that plant cells can stretch when the pH of the apoplast, the space outside of the cell membrane, is low (Rayle and Cleland, 1970). A plant hormone, called auxin, mediates this process by activating proton pumps in the cell membrane, leading to an increase in the number of protons into the apoplast and thus a lower pH.