Water-relation parameters of epidermal and cortical cells in the primary root ofTriticum aestivum L.

Water-relation parameters of root hair cells, hairless epidermal cells, and cortical cells in the primary root of wheat have been measured using the pressure-probe technique. Under well-watered conditions the mean cell turgor of cortical cells was 6.8±1.9 (30) bar (mean±SD; the number of observations in brackets). In hairless epidermal and root hair cells the mean cell turgor was 5.5±1.9 (22) and 4.4±1.5 (15) bar, respectively. Despite the large variability, turgor pressure was significantly lower (confidence interval=0.95) in epidermal cells relative to cortical cells. This may be a consequence of the ultrafiltration of ions by the external cell wall and-or plasmalemma of epidermal cells. The volumetric elastic modulus of the cells ranged from 10 to 150 bar. This parameter was dependent on cell volume, but within experimental accuracy, was independent of cell type. No pressure dependence of the volumetric elastic modulus was observed in these cells. The half-times for water exchange ranged from 1.8 to 48.8 s. The mean value increased in the order root hair < hairless epidermal < cortical cells and was directly related to volume to surface area ratio. Thus the hydraulic conductivities of the three cell types were similar and averaged 1.2±0.9·10^-6 (170) cm s^-1 bar^-1. No polarity was observed between inwardly and outwardly directed water flow. The similarity of the hydraulic conductivities of root hairs to those of other cells indicates that the membranes of root hairs are not particularly specialized for water transport. The overall hydraulic conductivity for radial water flow across the root was estimated from the pressure-probe data using a simple model and was compared with that measured directly on whole roots using an osmotic backflow technique. It was tentatively concluded that upon sudden osmotic perturbation, the major pathway for water transfer across the root may be through the symplasm and involve net flow from vacuole to vacuole.     

The plant cell pressure probe

The pressure probe is a micro manometer for the simultaneous direct recording and manipulation of plant cell hydrostatic pressure. It is used to map in space and time the turgor pressures of individual cells within tissues and organs of intact plants. This is used to study the hydraulic architecture of tissues, tissue movement and the responses of tissues to water stress. The approach can be augmented by simultaneous measurement of individual cell osmotic pressure. This permits the hydraulic driving forces across selectively permeable membranes and walls to be assessed fully. By manipulating manually the pressure, cell wall elasticity and its properties can also be mapped. Under some conditions this can be extended to plastic behaviour.     

Immunologic mechanisms in the pathogenesis of virus-induced murine leukemia. III. Target cell specificity of autoreactive thymocytes.

Thymocytes from preleukemic mice persistently infected with Moloney murine leukemia virus (MuLV-M-carriers) were vigorously autoaggressive toward normal syngeneic target cells; they exhibited a graded response to allogeneic cells, but they spared xenogeneic cells or syngeneic cells infected with MuLV-M or MuLV-G (Gross). Syngeneic target cells infected with nononcogenic lymphocytic choriomeningitis virus (LCMV), or transformed by the chemical carcinogen 3-methylcholanthrene were not similarly spared. This phenomenon, apparently induced by MuLV-M, is not associated with all persistent virus carrier states. Thymocytes from mice persistently infected with LCMV or with the lactic dehydrogenase virus (LDHV) failed to demonstrate an autoaggressive behavior. That transplantable lymphoma cells (derived from MuLV-M-carriers) were autoreactive in a pattern similar to thymocytes from preleukemic mice suggests a unique role for MuLV in the events leading from altered recognition of "self" to lymphoma.     

A protein-glucan intermediate during paramylon synthesis.

A sodium deoxycholate extract containing glucosyltransferase activity was obtained from a particulate preparation from Euglena gracilis. It transferred glucose from UDP-[14C]glucose into material that was precipitated by trichloroacetic acid. This material released beta-(1 leads to 3)-glucan oligosaccharides into solution on incubation with weak acid, weak alkali and beta-(1 leads to 3)-glucosidase. The products of the incubation of the deoxycholate extract with UDP-[14C]glucose were analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Radioactive bands were obtained that had the properties of beta-(1 leads to 3)-glucan covalently linked to protein by a bond labile to weak acid. High-molecular-weight material containing a beta-(1 leads to 3)-glucan was also shown to be present by gel filtration. The bond linking glucan to aglycone is possibly a pyrophosphate linkage. It is proposed that in Euglena gracilis beta-(1 leads to 3)-glucan (paramylon) is synthesized on a protein primer.     

Salt tolerance in the halophyte Suaeda maritima L. Dum.

Osmotic potentials and individual epidermal cell turgor pressures were measured in the leaves of seedlings of Suaeda maritima growing over a range of salinities. Leaf osmotic potentials were lower (more negative) the higher the salt concentration of the solution and were lowest in the youngest leaves and stem apices, producing a gradient of osmotic potential towards the apex of the plant. Epidermal cell turgor pressures were of the order of 0.25 to 0.3 MPa in the youngest leaves measured, decreasing to under 0.05 MPa for the oldest leaves. This pattern of turgor pressure was largely unaffected by external salinity. Calculation of leaf water potential indicated that the gradient between young leaves and the external medium was not altered by salinity, but with older leaves, however, this gradient diminished from being the same as that for young leaves in the absence of NaCl, to under 30% of this value at 400 mM NaCl. These results are discussed in relation to the growth response of S. maritima.     

Liver peptide stabilizing factor protects phosphofructokinase against inactivation by fructose-1,6-bisphosphatase.

Rabbit liver fructose-1,6-bisphosphatase (FDPase) can reversibly inactivate both rabbit muscle and rat liver phosphofructokinases (PFK) under appropriate conditions. The peptide factor which stabilizes rat liver PFK-L₂ against thermal inactivation has now been found to protect both PFKs from inactivation by FDPase. Assay at high ATP (ca. 3 mM) is necessary to demonstrate these reversible changes. In addition, the activation of FDPase by liver cytosol, by oleate plus cytosol, or by oleate plus muscle PFK is lowere about 50% in the presence of peptide factor. These observations suggest an active participation of the peptide factor in regulation of liver glycolysis and gluconeogenesis.