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Abstract Detail



Physiology

Garcia Mora, Jessica [1], Mocko, Kerri [2], Michaud, Joseph M. [1], Schenk, H. Jochen [2].

Are amphiphilic lipids in plant xylem responsible for the ionic effect seen in hydraulic conductance through stems?

In vascular plants, water transport occurs mainly under negative pressure through xylem conduits connected via cellulosic pit membranes, a system known as the xylem apoplast. As xylem sap passes through the pit membranes, ions in the sap have been observed to affect stem hydraulic conductance in many plant species, which has been called the ionic effect. It has been suggested that ions in the sap interact with substances in pit membranes, effectively altering pore sizes. Originally, pectin hydrogels were thought to be responsible for this mechanism. However, several recent studies have shown that pit membranes contain no, to very little, pectin. More recently, amphiphilic lipids have been discovered in pit membranes and in small quantities in xylem sap, and we hypothesized that charged headgroups of these polar lipids could be interacting with ions in the sap to cause the ionic effect in vascular plants. This research investigated whether hydraulic conductance through a porous medium consisting of nanocellulose is affected by ionic composition in the presence of polar lipids but not in the absence of lipids. This was done by creating an artificial system that mimicked conditions for stem hydraulic conductance in plant xylem, with experiments repeated on avocado stems (Persea americana var. Fuerte) to compare the effects of ionic solutions on hydraulic conductance in actual xylem. The experiments support the existence of an ionic effect in the presence of polar lipids when solutions containing ions are perfused through a nanocellulose fibril (NCF) layer that mimics a pit membrane, and this effect was not seen in the absence of lipids. As observed in xylem, hydraulic conductance was higher in the lipid treatments than the controls when using KCl solutions or was unchanged when using CaCl2. A possible explanation for the ionic effect could be that potassium ions interact with lipid headgroups in pit membrane pores and thereby affect the adherence of lipid micelles to cellulose microfibrils in pores, depending on the cation either blocking or enlarging the pores. Lipid headgroup interactions with ions could explain the ionic effect in xylem hydraulic conductance and possibly solve a long-standing mystery about water transport in vascular plants.


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1 - California State University Fullerton, Department of Biological Science, PO Box 6850, Fullerton, CA, 92834, USA
2 - California State University Fullerton, Department Of Biological Science, PO Box 6850, Fullerton, CA, 92834, United States

Keywords:
none specified

Presentation Type: Poster
Session: P3, Physiology Posters
Location: Virtual/Virtual
Date: Wednesday, July 21st, 2021
Time: 5:00 PM Time and date to be determined
Number: P3PS002
Abstract ID:858
Candidate for Awards:None


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