Abstract Detail

100 years of Baileyan Trends – Wood Evolution, Function and Future

Schenk, H. Jochen [1], Jansen, Steven [2].

Apoplastic lipids in water-conducting cells: A universal feature in land plants.

Evolution caused many changes in the structure and function of xylem in vascular plants, but one feature that appears to be consistent in all xylem is the presence of apoplastic lipids, which line the lumen-facing wall surfaces of vessels and tracheids. Until very recently, such lipid layers were viewed as rare occurrences, such as in resurrection plants, but new research and a reexamination of previously published work provide evidence for their existence in ferns, gymnosperms, and angiosperms, and even in the hydroids of bryophytes. The new evidence comes from transmission electron micrographs of specimens pretreated with osmium tetroxide, which binds mainly to carbon double bonds in unsaturated fatty acid chains of lipids, from dye injections of fluorescent lipid tracers into xylem, and from lipidomic analyses of xylem sap. Mass spectrometry of xylem sap lipids revealed the presence of phospho- and galactolipids in the sap of angiosperms. Because osmium tetroxide is a standard fixative in transmission electron microscopy (TEM), previously published images of hydroids in bryophytes, and xylem in ferns, gymnosperms, and angiosperms were reexamined to detect apoplastic lipid linings in water-conducting cells. They were evident in nearly every TEM image of specimens prefixed with osmium tetroxide but not in images of specimens treated with other fixatives. The presence of apoplastic lipids in the hydraulic systems of all these very different plants suggests that they play a vital function in plant water transport and are not just cytoplasmic remnants without function, as previously suggested. We hypothesize that apoplastic lipids allow water transport via the cohesion-tension mechanism by preventing embolism formation from pre-existing gas bubbles in the system. While this hypothesis remains to be tested, this presentation focusses on the evidence for apoplastic lipids in water-conducting cells across the phylogeny of land plants.

1 - California State University Fullerton, Department Of Biological Science, PO Box 6850, Fullerton, CA, 92834, United States
2 - Institute Of Systematic Botany And Ecology, Albert-Einstein-Allee 11, Ulm University, Ulm, D-89081, Germany

Keywords:
xylem
apoplast
phospholipids
galactolipids
tracheophytes
Bryophytes
cohesion-tension theory.

Presentation Type: Colloquium Presentations
Session: C06, 100 years of Baileyan Trends - Wood Evolution, Function and Future
Location: 106/Mayo Civic Center
Date: Tuesday, July 24th, 2018
Time: 11:00 AM
Number: C06011
Abstract ID:536
Candidate for Awards:None