Effect of soil K, Ca and Mg saturation and endomycorrhization on growth and nutrient uptake of sugar maple seedlings

Nutrient imbalances of declining sugar maple (Acer saccharum Marsh.) stands in southeastern Quebec have been associated with high exchangeable Mg levels in soils relative to soil K and Ca. A greenhouse experiment was set up to test the hypothesis that the equilibrium between soil exchangeable K, Ca, and Mg ions influences the growth and nutrient status of sugar maple seedlings. Also tested was whether endomycorrhization can alter nutrient acquisition under various soil exchangeable basic cations ratios. Treatments consisted of seven ratios of soil exchangeable K, Ca, and Mg making up a total base saturation of 58%, and a soil inoculation treatment with the endomycorrhizal fungus Glomus versiforme (control and inoculated), in a complete factorial design. Sugar maple seedlings were grown for 3 months in the treated soils. Plant shoot elongation rate, dry biomass and nutrient concentrations in foliage were influenced by the various ratios of soil cations. The predicted plant biomass and foliar K concentration were highest at a soil Ca saturation of 38%, a soil K saturation of 12%, and a soil Mg saturation of 8%. Potassium concentration in foliage was dependent on the level of Ca and Mg saturation in the soil when soil K saturation was close to 12%. Foliar Ca and Mg levels were more dependent on their corresponding levels in soil than foliar K. Colonization by G. versiforme did not influence seedling growth and macronutrient uptake. The results confirm that growth and nutrition of sugar maple are negatively affected by imbalances in exchangeable basic cations in soils.     

Internalization of phosphatidylinositol-anchored lymphocyte proteins. I. Documentation and potential significance for T cell stimulation

Several proteins that are anchored to the surface of T lymphocytes via a phosphatidylinositol (PI) moiety can initiate cell stimulation upon cross-linking. Inasmuch as these proteins do not traverse the plasma membrane, it is not clear how they are capable of signaling across the membrane. Herein we report two distinct sets of experiments that examine the consequence of cross-linking PI-anchored molecules on murine T cells. We first analyzed the fate of antibody cross-linked TAP (Ly-6A.2) and Thy-1 molecules on T-T hybrids. Using an assay to measure receptor-mediated endocytosis, an intracellular accumulation of 125I labeled anti-TAP and anti-Thy-1 mAb was documented that was specific and Ag dependent. The internalization of these molecules was confirmed by cytotoxicity assays using antibody-toxin conjugates, and electron microscopic studies. Although the PI-anchored proteins lack a cytoplasmic domain that is necessary for the internalization of many receptors, they nevertheless can be induced to enter the cell upon cross-linking. The rate of entry of cross-linked TAP and Thy-1 into cells was shown to be 10 and 2% per hour, respectively, which is considerably less than that observed for the transferrin receptor or TCR/CD3 complex. To assess whether the internalization of TAP and Thy-1 might be of importance in their ability to stimulate T cells, we attempted to cross-link these molecules under conditions where the mAb or its cross-linked complex can not enter the cell. We observed that anti-TAP and anti-Thy-1 mAb conjugated to a cell impermeant matrix fail to stimulate T cells. This loss of stimulatory activity was observed with multiple T-T hybridomas and mAb over a wide titration of antibody concentration and was independent of the mAb isotype. Results from experiments with anti-Ig cross-linking of the mAb-PI anchored protein complex suggested that the loss of T cell stimulation upon mAb immobilization is not simply due to an alteration in the degree of antibody cross-linking. These findings were generalized to three distinct PI-anchored proteins: TAP, Thy-1, and Ly6C on normal T cells. When the same cells were stimulated through the TCR/CD3 complex, only immobilized mAb are stimulatory. These results demonstrate a marked difference in the cross-linking requirements for stimulating T cells through PI-anchored molecules in contrast to the transmembrane TCR complex. Furthermore, these findings raise the possibility that molecular internalization of Ab-PI-anchored complexes may be necessary in signaling through these molecules.     

Impairment of ATP-linked reactions in mitochondria isolated from skeletal muscle of halothane-sensitive pigs

Oxygen consumption was depressed in mitochondria isolated from halothane sensitive pig (HP) muscle. The calculation of the respiratory control ratio (RCR) indicated that mitochondria were more affected at the site-I level of the respiratory chain. Calcium accumulation in these mitochondria was not altered when driven by the oxidation of succinate. This process was abolished when linked to ATP as a source of energy. ATP transport was completely inhibited in (HP) mitochondria.