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D T Cooke

Publications and source records attributed to D T Cooke.

11 recordsLinked to original sources
PubMed2001

Both gamma delta T cells and NK cells inhibit the engraftment of xenogeneic rat bone marrow cells and the induction of xenograft tolerance in mice.

In murine allogeneic bone marrow transplantation recipients, treatment of the hosts with a nonmyeloablative regimen, including depleting anti-CD4 and anti-CD8 mAbs, allows establishment of long-term mixed chimerism and donor-specific tolerance. However, in the xenogeneic rat-to-mouse combination, additional anti-Thy1.2 and anti-NK1.1 mAbs are required. We have now attempted to identify the xenoresistant mouse cell populations that are targeted by anti-NK1.1 and anti-Thy1.2 mAbs. C57BL/6 (B6) wild-type, B6 TCRbeta(-/-), and B6 TCRdelta(-/-) mice received anti-CD4 and anti-CD8 mAbs, followed by 3 Gy of whole body irradiation, 7 Gy of thymic irradiation, and transplantation of T cell-depleted rat bone marrow cells. Anti-NK1.1 and anti-Thy1.2 mAbs were additionally administered to some groups. Increased rat chimerism was observed in TCRdelta(-/-) mice treated with anti-CD4, anti-CD8, and anti-NK1.1 mAbs compared with similarly treated TCRbeta(-/-) mice. In TCRbeta(-/-) mice, but not in TCR delta(-/-) mice, donor chimerism was increased by treatment with anti-Thy1.2 mAb, indicating that CD4(-)CD8(-)TCRgammadelta(+)Thy1. 2(+)NK1.1(-) cells (gammadelta T cells) are involved in the rejection of rat marrow. In addition, chimerism was enhanced in both TCRbeta(-/-) and TCRdelta(-/-) mice treated with anti-CD4, anti-CD8, and anti-Thy1.2 mAbs by the addition of anti-NK1.1 mAb to the conditioning regimen. Donor-specific skin graft prolongation was enhanced by anti-Thy1.2 and anti-NK1.1 mAbs in TCRdelta(-/-) mice. Therefore, in addition to CD4 and CD8 T cells, gammadelta T cells and NK cells play a role in resisting engraftment of rat marrow and the induction of xenograft tolerance in mice.

Animals↗
PubMed2000

Root hydraulic conductance: diurnal aquaporin expression and the effects of nutrient stress.

It has been shown that N-, P- and S-deficiencies result in major reductions of root hydraulic conductivity (Lpr) which may lead to lowered stomatal conductance, but the relationship between the two conductance changes is not understood. In a variety of species, Lpr decreases in the early stages of NO3-, H2PO4(2-) and SO4(2-) deprivation. These effects can be reversed in 4-24 h after the deficient nutrient is re-supplied. Diurnal fluctuations of root Lpr have also been found in some species, and an example of this is given for Lotus japonicus. In nutrient-sufficient wheat plants, root Lpr is extremely sensitive to brief treatments with HgCl2; these effects are completely reversible when Hg is removed. The low values of Lpr in N- or P-deprived roots of wheat are not affected by Hg treatments. The properties of plasma membrane (PM) vesicles from wheat roots are also affected by NO3(-)-deprivation of the intact plants. The osmotic permeability of vesicles from N-deprived roots is much lower than that of roots adequately supplied with NO3-, and is insensitive to Hg treatment. In roots of L. japonicus, gene transcripts are found which have a strong homology to those encoding the PIP1 and PIP2 aquaporins of Arabidopsis. There is a very marked diurnal cycle in the abundance of mRNAs of aquaporin gene homologues in roots of L. japonicus. The maxima and minima appear to anticipate the diurnal fluctuations in Lpr by 2-4 h. The temporal similarity between the cycles of the abundance of the mRNAs and root Lpr is most striking. The aquaporin encoded by AtPIP1 is known to have its water permeation blocked by Hg binding. The lack of Hg-sensitivity in roots and PMs from N-deprived roots provides circumstantial evidence that lowered root Lpr may be due to a decrease in either the activity of water channels or their density in the PM. It is concluded that roots are capable, by means completely unknown, of monitoring the nutrient content of the solution in the root apoplasm and of initiating responses that anticipate by hours or days any metabolic disturbances caused by nutrient deficiencies. It is the incoming nutrient supply that is registered as deficient, not the plant's nutrient status. At some point, close to the initiation of these responses, changes in water channel activity may be involved, but the manner in which monitoring of nutrient stress is transduced into an hydraulic response is also unknown.

Aquaporins↗
PubMed1998

Effects of abnormal-sterol accumulation on Ustilago maydis plasma membrane H+-ATPase stoichiometry and polypeptide pattern.

Accumulation of 14alpha-methylated sterols or delta8-sterols in Ustilago maydis affected three aspects of the plasma membrane H+-ATPase. Proton transport was reduced in delta8-sterol-accumulating samples, due to an altered H+/ATP stoichiometry. ATP hydrolytic activity was increased, but no direct correlation with the extent or type of abnormal sterol accumulated could be drawn. Finally, Western blot analysis with antibodies against yeast PMA1 revealed a second lighter band (99-kDa band) in all samples from abnormal-sterol-accumulating sporidia. The conclusions are that the 99-kDa band and a reduced stoichiometry are directly linked to the presence of abnormal sterols, while changes in hydrolytic activity are linked only indirectly.

Adenosine Triphosphate↗
PubMed1996

Purification of pea nodule symbiosomes using an aqueous polymer two-phase system.

Symbiosomes were obtained from mature pea (Pisum sativum cv. Argona) root nodules infected with Rhizobium leguminosarum strain (biov. viciae 3841) and purified using an aqueous polymer two-phase system (APS). The APS consists of a mixture of polymers, usually dextran T500 and poly(ethylene glycol) 3350, prepared as aqueous solutions on a weight per weight basis, where each fraction distributes according to their surface characteristics. Results of ATPase activity, cytochrome c oxidase activity, glucan synthase II activity, NAD(P)H-cytochrome c reductase activity, NO3(-)-sensitive ATPase activity, transport of [14C]malate vs. [14C]glutamate and MAC 57 antigen analysis showed that the APS method provided intact symbiosomes with low bacteroid, plasma membrane, endoplasmic reticulum and/or mitochondria contamination. No complicated equipment is needed and the method was simple and fast, compared with other purification techniques.

Adenosine Triphosphatases↗
PubMed1994

Lipid composition and proton transport in Penicillium cyclopium and Ustilago maydis plasma membrane vesicles isolated by two-phase partitioning.

Plasma membranes have been isolated and purified from two species of fungi, Penicillium cyclopium and Ustilago maydis, using a two-phase aqueous polymer technique. The membranes were characterised using marker enzyme assays (e.g., vanadate-sensitive (Mg(2+)-K+)-ATPase and glucan synthetase II) and lipid composition (sterol enrichment, increased phosphatidylethanolamine/phosphatidylcholine ratio, and the absence of diphosphatidylglycerol). The proton-pumping activities of the plasma membrane-bound H(+)-ATPases from these species were compared. H(+)-ATPase activity was found to be greater in U. maydis than in P. cyclopium, which was attributed to differences in orientation of the plasma membrane vesicles. There was evidence to suggest the presence of redox chain activity in the plasma membranes of both species.

Cell Fractionation↗
PubMed1994

Ca(2+)-ATPase-driven calcium accumulation in Ustilago maydis plasma membrane vesicles.

Ca2+ transport has been measured across plasma membrane vesicles isolated from cells of Ustilago maydis. This transport was found to be ATP- (or to a lesser extent GTP) and Mg(2+)-dependent. Inconsistent release of Ca2+ from intact vesicles was obtained using the calcium ionophore A23187. However, Ca2+ was released by Triton X-100 in a concentration-dependent manner. Transport was inhibited by vanadate (> 50%) and erythrosin B (about 50%), I50 being about 10 microM for both inhibitors. In the presence of the protonophores CCCP or gramicidin, partial inhibition of Ca2+ transport (about 20%) was observed, but the Ca(2+)-channel blockers, nifedipine, diltiazem and verapamil had no effect, although the latter inhibited proton transport. The results indicate that Ca2+ transport in U. maydis is regulated by a P-type ATPase with similar properties to that found in higher plants.

Adenosine Triphosphate↗
PubMed1991

Fluidity and lipid composition of oat and rye shoot plasma membrane: effect of sterol perturbation by xenobiotics.

Oat and rye plants were treated with either tetcyclacis (an experimental plant growth regulator), nuarimol (a fungicide) or gamma-ketotriazole (an experimental herbicide). These treatments reduced shoot growth and changed the lipid composition of the shoot plasma membranes. In oat, both tetcyclacis and nuarimol treatments increased plasma membrane cholesterol and increased the phosphatidylethanolamine/phosphatidylcholine (PE/PC) ratio, whereas gamma-ketotriazole treatment reduced cholesterol and the PE/PC ratio. In rye, all treatments reduced the PE/PC ratio. Generally, the sterol/phospholipid ratio was less in oat than in rye but the cholesterol/phospholipid ratio was greater. With all treatments in oat and rye, increases were observed in unsaturation of the phospholipid acyl chains. The fluidity of membranes was measured by steady-state fluorescence polarisation of the probe diphenylhexatriene; oat membranes were more fluid than rye. Membrane fluidity was greater in plasma membranes from plants treated with the xenobiotics than the controls. The results are discussed in the context of the effect of plasma membrane lipid composition on membrane fluidity, and it is concluded that there appears to be no overall simple relationship between membrane lipid composition and fluidity that holds for all treatments in both species.

Cell Membrane↗