Abstract Detail

Ecophysiology

Schenk, H. Jochen [1], Espino, Susana [1], Papahadjopoulos-Sternberg, Brigitte [2], Zuo, Yi Y. [3], Jansen, Steven [4].

How can plants transport water under negative pressure?

Vascular plants transport large quantities of water under negative pressure without constantly creating gas bubbles that would disable their hydraulic systems. Attempts to replicate this feat in artificial systems have invariably resulted in rapid bubble formation, except under highly controlled and extremely simplified conditions, using pure water at mild pressure, with only hydrophilic surfaces present. The hydraulic system of vascular plants, the xylem, in contrast, is complex, with millions of conduits, potentially containing hydrophobic surfaces, dissolved gas-saturation or supersaturation, and surface active molecules that can lower surface tension, all of which factors increase the chances of bubble nucleation. So how do plants transport water under negative pressure? We found that angiosperm xylem contains abundant hydrophobic surfaces as well as insoluble lipid-based surfactants, including phospholipids, as well as proteins, a composition similar to pulmonary surfactants. Surfactants were found in xylem sap and as micelles under transmission electron microscopy clogging pores of inter-vessel pit membranes and deposited on vessel wall surfaces. Surfactant-coated nanobubbles in xylem sap were imaged via freeze-fracture electron microscopy and were found as nanoparticles in xylem sap. Xylem surfactants showed strong surface activity that reduces surface tension to low values when concentrated as they are in pit membrane pores. We propose that, far from contradicting the cohesion-tension theory, xylem surfactants enable water transport under negative pressure by coating hydrophobic surfaces and nanobubbles, thereby keeping them below the critical size at which bubbles would expand to form embolisms. We hypothesize that lipid-based surfactants are a universal requirement for water transport under negative pressure.

1 - California State University Fullerton, Department Of Biological Science, PO Box 6850, Fullerton, CA, 92834-6850, USA
2 - NanoAnalytical Laboratory, 3951 Sacramento Street, San Francisco, CA, 94118, USA
3 - University of Hawaii at Manoa, Department of Mechanical Engineering, 2540 Dole Street, Holmes Hall 302, Honolulu, HI, 96822, USA
4 - Ulm University, Institute for Systematic Botany and Ecology, Albert-Einstein-Allee 11, Ulm, D–89081, Germany

Keywords:
xylem
angiosperms
water relations
cohesion-tension theory
surfactants
phospholipids
wood anatomy.

Presentation Type: Oral Paper
Session: 3, Ecophysiology
Location: 104/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 8:15 AM
Number: 3002
Abstract ID:124
Candidate for Awards:None