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 "H-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. 40mC. 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 with a continuous osmiophilic (lipid) layer, as postulated by the kinetic analysis and light microscopy studies. The thickness of the layer varied between 20 and 80 nm. The parenchymal and intervessel pits as well as numerous tracheid corners contained opaque inclusions, presumably also consisting of lipids. Electron microscopy of rehydrated plants showed that the lipid layer was either thinned or had disintegrated and that numerous vesicle-like structures and lipid bodies were formed (together with various intermediate structural elements). These, many other da...
Many diseases are closely tied to deficient or subnormal metabolic and secretory cell functions. Milder forms of these diseases can be managed by a variety of treatments. However, it is often extremely difficult or even impossible to imitate the moment-to-moment fine regulation and the complex roles of the hormone, factor or enzyme that is not sufficiently produced by the body. Immunoisolated transplantation is one of the most promising approaches to overcome the limitations of current treatments. Non-autologous (transformed) cell lines and allogeneic and xenogeneic cells/tissues that release the therapeutic substances are enclosed in immunoprotective microcapsules. The microcapsules avoid a lifetime of immunosuppressive therapy while excluding an immune response in the host. Research in this direction has shown the feasibility of microcapsules based on hydrogels (particularly of alginate) for transplantation of non-autologous cells and tissue fragments. Numerous technical accomplishments of the immunoisolation method have recently made possible the first successful long-term clinical applications. However, realizing the potential of immunoisolated therapy requires the use of several factors that have received limited attention in the past but are important for the formulation of hydrogel-based immunoisolation systems that are highly versatile, potentially economical and can gain medical approval.
Seasonal variations in osmolality and components of xylem sap in tall birch trees were determined using several techniques. Xylem sap was extracted from branch and trunk sections of 58 trees using the very rapid gas bubble-based jet-discharge method. The 5-cm long wood pieces were taken at short intervals over the entire tree height. The data show that large biphasic osmolality gradients temporarily exist within the conducting xylem conduits during leaf emergence (up to 272 mosmol x kg(-1) at the apex). These gradients (arising mainly from glucose and fructose) were clearly held within the xylem conduit as demonstrated by (1)H NMR imaging of intact twigs. Refilling experiments with benzene, sucrose infusion, electron and light microscopy, as well as (1)H NMR chemical shift microimaging provided evidence that the xylem of birch represents a compartment confined by solute-reflecting barriers (radial: lipid linings/lipid bodies; axial: presumably air-filled spaces). These features allow transformation of osmolality gradients into osmotic pressure gradients. Refilling of the xylem occurs by a dual mechanism: from the base (by root pressure) and from the top (by hydrostatic pressure generated by xylem-bound osmotic pressure). The generation of osmotic pressure gradients was accompanied by bleeding. Bleeding could be observed at a height of up to 21 m. Bleeding rates measured at a given height decreased exponentially with time. Evidence is presented that the driving force for bleeding is the weight of the static water columns above the bleeding point. The pressure exerted by the water columns and the bleeding volume depend on the water-filling status of (communicating) vessels.
In the light of results of clinical trials with immunoisolated human parathyroid tissue Ba2+‐alginate capsules were developed that meet the requirements for long‐term immunoisolated transplantation of (allogeneic and xenogeneic) cells and tissue fragments. Biocompatibility of the capsules was achieved by subjecting high‐M alginate extracted from freshly collected brown algae to a simple purification protocol that removes quantitatively mitogenic and cytotoxic impurities without degradation of the alginate polymers. The final ultra‐high‐viscosity, clinical‐grade (UHV/CG) product did not evoke any (significant) foreign body reaction in BB rats or in baboons. Similarly, the very sensitive pERK assay did not reveal any mitogenic impurities. Encapsulated cells also exhibited excellent secretory properties under in vitro conditions. Despite biocompatible material, pericapsular fibrosis is also induced by imperfect capsule surfaces that can favor cell attachment and migration under the release of material traces. This material can interact with free end monomers of the alginate polymers under formation of mitogenic advanced glycation products. Smooth surfaces, and thus topographical biocompatibility of the capsules (visualized by atomic force microscopy), can be generated by appropriate crosslinking of the UHV/CG‐alginate with Ba2+ and simultaneous suppression of capsule swelling by incorporation of proteins and/or perfluorocarbons (i.e., medically approved compounds with high oxygen capacity). Perfluorocarbon‐loaded alginate capsules allow long‐term non‐invasive monitoring of the location and the oxygen supply of the transplants by using 19F‐MRI. Transplantation studies in rats demonstrated that these capsules were functional over a period of more than two years.
Summary• Lipids play a crucial role in the maintenance of the structural and functional integrity of the water-conducting elements and cells of the resurrection plant Myrothamnus flabellifolia during complete dehydration.• Lipid composition, mobility and distribution within the internodal and nodal xylem regions (including short shoots and leaves) were investigated in the presence and absence of water by using various nuclear magnetic resonance (NMR) spectroscopy and imaging techniques differing greatly in the level of spatial resolution and acquisition of lipid parameters.• Significant findings include: a discontinuity in the branch xylem between an inner zone where no water moves and an outer zone where the water moves; the blocking of water movement in the inner zone by lipids that are not dispersed by water, and the facilitation of water advance in the xylem elements and pits of the outer zone by water-dispersed lipids; the relative impermeability of leaf trace xylem to the rehydrating water and, hence, the relative hydraulic isolation of the leaves.• These results elucidated part of the strategy used by the resurrection plant to cope with extreme drought and to minimize transpirational water loss upon hydration.
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