Surfactants may shed novel light on water transport in plants under negative pressure

• Applicant: Professor Dr. Steven Jansen
• Subject Area: Plant Biochemistry and Biophysics ; Ecology and Biodiversity of Plants and Ecosystems ; Plant Physiology
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 383393940

When considering that the flow of water through plants has utmost importance for the functioning of our biosphere as well as the human population, most people would be extremely surprised to learn that it is still unknown how exactly plants accomplish long-distance water transport. While there is massive evidence for water transport in plant xylem under negative pressure, it has been a long-standing question why this system is not constantly failing by pulling in air-bubbles. This project aims to investigate the functional implications of surfactants in the hydraulic transport system of plants, and especially their role in drought-induced embolism formation at the bordered pit level between neighbouring conduits. In particular, the following three hypotheses will be tested: (1) Surfactants occur in xylem sap of seed plants and are most likely insoluble lipids (including phospholipids, galactolipids, and proteins); (2) Interconduit pit membranes may function as nanobubble generators due to their fibrous medium and the presence of surfactants, which are expected to have a dynamic (instead of static) surface tension, and (3) xylem sap surfactants may contribute to water transport under negative pressure by keeping air-bubbles small and stable. These hypotheses will be tested by applying chemical analyses of xylem sap and staining methods for light and transmission electron microscopy on three angiosperm and two gymnosperm species. Measurements will focus on the dynamic surface tension of xylem sap surfactants, the porosity of intervessel pit membranes, the wettability of the hydraulic pathway, and the occurrence of surfactant coated nanobubbles in xylem sap. Experimental work will be combined with a modelling approach to predict the behaviour of an air-water meniscus in the porous cellulose network of pit membranes, and the formation of nanobubbles via bubble snap-off events. Additional experiments with xylem sap will be conducted to test the idea that insoluble surfactants keep air-bubbles small and stable.This innovative project will contribute to our understanding of surfactants in xylem sap, which has been neglected for many years. By better understanding how plants transport water under negative pressure, this proposal will have implications for biomimetic applications, and will increase our understanding of plant water use and drought tolerance, which is especially relevant given current concerns about climate change.

• DFG Programme: Research Grants