Xylem conduits of a resurrection plant contain a unique lipid lining and refill following a distinct pattern after desiccation

• Published in: The New phytologist 2000-11, Vol.148 (2), p.239-255
• Main Authors: WAGNER, H.-J., SCHNEIDER, H., MIMIETZ, S., WISTUBA, N., ROKITTA, M., KROHNE, G., HAASE, A., ZIMMERMANN, U.
• Format: Article
• Language: English
• Subjects: Acetone - pharmacokinetics; Benzene - pharmacokinetics; Biological and medical sciences; Biological Transport, Active - drug effects; Branches; Capillaries; Capillary Action; Desiccation; Fundamental and applied biological sciences. Psychology; Gravitation; Hydrostatic Pressure; Imaging; Kinetics; Light refraction; lipid lining; Lipids; Lipids - analysis; Liquids; Microscopy, Electron; Myrothamnus flabellifolia; NMR imaging; Osmotic Pressure; Plant physiology and development; Plant Stems - chemistry; Plant Stems - drug effects; Plant Stems - metabolism; Plant Stems - ultrastructure; Plants - chemistry; Plants - drug effects; Plants - metabolism; Plants - ultrastructure; polarity of refilling; Raffinose - pharmacology; Research article; resurrection plants; Space life sciences; Tracheids; Water - metabolism; Water and solutes. Absorption, translocation and permeability; Water pressure; Xylem; xylem refilling
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1046/j.1469-8137.2000.00755.x

The axial and radial refilling with water of cut dry branches (up to 80 cm tall) of the resurrection plant Myrothamnus flabellifolia was studied in both acro- and basipetal directions by using 1H-NMR imaging. NMR measurements showed that the conducting elements were not filled simultaneously. Axial water ascent occurred initially only in a cluster of a very few conducting elements. Refilling of the other conducting elements and of the living cells was mainly achieved by radial extraction of water from these initial conducting elements. With time, xylem elements in a few further regions were apparently refilled axially. Radial water spread through the tissue occurred almost linearly with time, but much faster in the acropetal than in the basipetal direction. Application of hydrostatic pressure (up to 16 kPa) produced similar temporal and spatial radial refilling patterns, except that more conducting elements were refilled axially during the first phase of water rise. The addition of raffinose to the water considerably reduced axial and radial spreading rates. The polarity of water climbing was supported by measurements of the water rise in dry branches using the ‘light refraction’ (and, sometimes, the ‘leaf recurving’) method. Basipetal refilling of the xylem conduit exhibited biphasic kinetics; the final rise height did not exceed 20–30 cm. Three-cm-long branch pieces also showed a directionality of water climbing, ruling out the possibility that changes in the conducting area from the base to the apex of the branches were responsible for this effect. The polarity of water ascent was independent of gravity and also did not change when the ambient temperature was raised to c. 40 °C. At external pressures of 50–100 kPa the polarity disappeared, with basipetal and acropetal refill times of the xylem conduit of tall branches becoming comparable. Refilling of branches dried horizontally (with a clinostat) or inverted (in the direction of gravity) showed a pronounced reduction of the acropetal water rise to or below basipetal water climbing level (which was unaffected by this treatment). Unlike water, benzene and acetone climbing showed no polarity. In the case of benzene, the rise kinetics (including the final heights) were comparable with those measured acropetally for water, whereas with acetone the rise height was less. Transmission electron microscopy of dry branches demonstrated that the inner surfaces of the conducting tracheids and vessels were lined wit