Drought acclimation of two deciduous tree species of different layers in a temperate forest canopy

Water-use strategies of Populus tremula and Tilia cordata, and the role of abscisic acid in these strategies, were analysed. P. tremula dominated in the overstorey and T. cordata in the lower layer of the tree canopy of the temperate deciduous forest canopy. Shoot water potential (), bulk-leaf abscisic acid concentration ([ABA]_leaf), abscisic acid concentration in xylem sap ([ABA]_xyl), and rate of stomatal closure following the supply of exogenous ABA (v) decreased acropetally through the whole tree canopy, and foliar water content per area (w), concentration of the leaf osmoticum (c), maximum leaf-specific hydraulic conductance of shoot (L), stomatal conductance (g_s), and the threshold dose per leaf area of the exogenous ABA (d_a) required to reduce stomatal conductance increased acropetally through the tree canopy (from the base of the foliage of T. cordata to the top of the foliage of P. tremula) in non-stressed trees. The threshold dose per leaf dry mass of the exogenous ABA (d_w) required to reduce stomatal conductance, was similar through the tree canopy. After a drought period (3 weeks), the , w, L, g_s, d_a and d_w had decreased, and c and v had increased in both species. Yet, the effect of the drought period was more pronounced on L, g_s, d_a, d_w and v in T. cordata, and on , w and c in P. tremula. It was concluded that the water use of the species of the lower canopy layer—T. cordata, is more conservative than that of the species of the overstorey, P. tremula. [ABA]_leaf had not been significantly changed in these trees, and [ABA]_xyl had increased during the drought period only in P. tremula. The relations between [ABA]_leaf, [ABA]_xyl and the stomatal conductance, the osmotic adjustment and the shoot hydraulic conductance are also discussed.     

Dissociation of LPS-induced monocytic ex vivo production of granulocyte colony-stimulating factor (G-CSF) and TNF-alpha in patients with septic shock

Over a 6 month period, in 192 patients admitted to the intensive care unit (ICU), a longitudinal analysis of whole blood lipopolysaccharide (LPS)-induced ex vivo cytokine production was performed on a daily basis until discharge from the ICU or death. Twenty-one patients with proven infections were in septic shock for the first time and for at least 3 days' duration. Ex vivo LPS-inducible release of granulocyte colony-stimulating factor (G-CSF) was upregulated and that of TNF-alpha was downregulated in patients with septic shock, regardless whether they survived or died. In conclusion, LPS-induced ex vivo TNF-alpha and G-CSF cytokine release by monocytes is regulated differentially in patients with septic shock. Since upregulation of LPS-induced production of G-CSF occurred earlier in survivors than in non-survivors, rapidly elevated and sustained G-CSF responsiveness may contribute to survival in septic shock.     

Extracellular beta-glucosidase activity in barley involved in the hydrolysis of ABA glucose conjugate in leaves

Abscisic acid conjugate concentrations increased in barley xylem sap under salinity, whereas it remained at a low level in the intercellular washing fluid (IWF) of barley primary leaves (Hordeum vulgare cv. Gerbel). Here it is shown that IWF contains beta-glucosidase activity which releases abscisic acid (ABA) from the physiologically inactive ABA-glucose conjugate pool in the leaf apoplast. The following data support this conclusion and give the first biochemical and physiological characterization of the extracellular glucosidase activity in barley. Free ABA was released by the incubation of ABA glucose ester with IWF. The product exhibited the retention time of authentic ABA upon separation by thin layer chromatography and was identified by ABA-ELISA. p-Nitrophenol-beta-D-glucopyranoside (pNPG) was used as the substrate for beta-glucosidases. The K(M)(pNPG) was 1.8 mmol l(-1). The activity was affected by ABA glucopyranoside in a competitive type of inhibition with a K(I) of 400 micromol l(-1). Various hormone conjugates were compared with respect to their inhibitory effect on beta-glucosidase activity. Inhibition was highest for the ABA glucopyranoside and the zeatin riboside, but insignificant for ABA methyl ester and zeatin-9-beta-D-glucoside. The specific activity of the beta-glucosidase was 16-fold greater in IWF as compared to crude leaf extracts confirming its extracellular compartmentation. The activity of beta-glucosidase was strongly increased after growth in hydroponic medium supplemented with NaCl. The data support the hypothesis that the glucose conjugate is a long-distance transport form of ABA.     

Molecular mechanisms of high-dose antigen therapy in experimental autoimmune encephalomyelitis: rapid induction of Th1-type cytokines and inducible nitric oxide synthase

High-dose Ag administration induces apoptotic death of autoreactive T cells and is an effective therapy of experimental autoimmune diseases of the nervous system. To explore the role of cytokines in Ag-specific immunotherapy, we analyzed mRNA induction and protein expression for the proinflammatory cytokines TNF-alpha and IFN-gamma, the anti-inflammatory cytokine IL-10, and the cytokine-inducible NO synthase (iNOS) during high-dose Ag therapy of adoptive transfer experimental autoimmune encephalomyelitis (AT-EAE) in the Lewis rat. Using semiquantitative and competitive RT-PCR, we found 5- to 6-fold induction of TNF-alpha mRNA and 3-fold induction of IFN-gamma mRNA in the spinal cord that occurred within 1 h after i.v. injection of Ag and was accompanied by a 2-fold increase of iNOS mRNA. Both IFN-gamma and iNOS mRNA remained elevated for at least 6 h, whereas TNF-alpha mRNA was already down-regulated 6 h after Ag injection. A comparable time course was found for circulating serum levels of TNF-alpha and IFN-gamma. IL-10 mRNA levels did not change significantly following Ag injection. Neutralization of TNF-alpha by anti-TNF-alpha antiserum in vivo led to a significant decrease in the rate of T cell and oligodendrocyte apoptosis induced by high-dose Ag administration, but did not change the beneficial clinical effect of Ag therapy. Our data suggest profound activation of proinflammatory but not of anti-inflammatory cytokine gene expression by high-dose Ag injection. Functionally, TNF-alpha contributes to increased apoptosis of both autoaggressive T cells and oligodendrocytes in the target organ and may thereby play a dual role in this model of Ag-specific therapy of CNS autoimmune diseases.     

Phosphorylation of the beta-amyloid precursor protein at the cell surface by ectocasein kinases 1 and 2

The beta-amyloid precursor protein (betaAPP) is one of the rare proteins known to be phosphorylated within its ectodomain. We have shown previously that betaAPP can be phosphorylated within secretory vesicles and at the cell surface (Walter, J., Capell, A., Hung, A. Y. , Langen, H., Schn?lzer, M., Thinakaran, G., Sisodia, S. S., Selkoe, D. J., and Haass, C. (1997) J. Biol. Chem. 272, 1896-1903). We have now specifically characterized the phosphorylation of cell surface-located betaAPP and identified two ectoprotein kinases that phosphorylate betaAPP at the outer face of the plasma membrane. By using selective protein kinase inhibitors and by investigating the usage of ATP and GTP as cosubstrates, we demonstrate that membrane-bound betaAPP as well as secreted forms of betaAPP can be phosphorylated by casein kinase (CK) 1- and CK2-like ectoprotein kinases. The ectodomain of betaAPP was also phosphorylated by purified CK1 and CK2 in vitro, but not by protein kinases A and C. Phosphorylation of betaAPP by ectoprotein kinases and by purified CK1 and CK2 occurred within an acidic domain in the N-terminal half of the protein. Heparin strongly inhibited the phosphorylation of cell-surface betaAPP by ecto-CK1 and ecto-CK2, indicating a regulatory role of this extracellular matrix component in betaAPP phosphorylation.     

Apoplastic transport of abscisic acid through roots of maize: effect of the exodermis

The exodermal layers that are formed in maize roots during aeroponic culture were investigated with respect to the radial transport of cis-abscisic acid (ABA). The decrease in root hydraulic conductivity (Lp_r) of aeroponically grown roots was stimulated 1.5-fold by ABA (500 nM), reaching Lp_r values of roots lacking an exodermis. Similar to water, the radial flow of ABA through roots (J_ABA) and ABA uptake into root tissue were reduced by a factor of about three as a result of the existence of an exodermis. Thus, due to the cooperation between water and solute transport the development of the ABA signal in the xylem was not affected. This resulted in unchanged reflection coeffcients for roots grown hydroponically and aeroponically. Despite the well-accepted barrier properties of exodermal layers, it is concluded that the endodermis was the more effective filter for ABA. Owing to concentration polarisation effects, ABA may accumulate in front of the endodermal layer, a process which, for both roots possessing and lacking an exodermis, would tend to increase solvent drag and hence ABA movement into the xylem sap at increased water flow (J_Vr). This may account for the higher ABA concentrations found in the xylem at greater pressure difference. Received: 26 January 1999 / Accepted: 26 May 1999