Photosynthesis and water relations of four oak species: impact of flooding and salinity

 As global climate changes, sea level rise and increased frequency of hurricanes will expose coastal forests to increased flooding and salinity. Quercus species are frequently dominant in these forest, yet little is known about their salinity tolerance, especially in combination with flooding. In this study, 1-year-old seedlings of Quercus lyrata Walt. (overcup oak), Q. michauxii Nutt. (swamp chestnut oak), Q. nigra L. (water oak), and Q. nuttallii Palmer (Nuttall oak) were chronically (simulating sea level rise) and acutely (simulating hurricane storm surge) exposed to increased flooding and salinity, individually and in combination. The four species demonstrated two response patterns of photosynthesis (A), conductance, and leaf water potential, apparently related to their relative flood tolerance. In Q. lyrata, Q. nuttallii, and Q. nigra (moderately flood-tolerant), A was not immediately reduced after the initiation of the freshwater flooding, but was reduced as the duration of flooding increased. In the second pattern, demonstrated by the weakly flood-tolerant Q. michauxii, A was immediately reduced by freshwater flooding with an increasing impact over time. Watering with 2 parts per thousand (ppt) saline water did not consistently reduce A, but flooding with 2 ppt reduced A of all species, similar to the response with freshwater flooding. Photosynthesis of all species was reduced by 6 ppt watering or flooding, with the latter treatment killing all species within 8 weeks. When acutely exposed to 30 ppt salinity, A was quickly and severely reduced regardless of whether the seedlings were watered or flooded. Acutely flooded seedlings exposed to high salinity died within 2 weeks, but seedlings watered with 30 ppt saline water recovered and A was not reduced the following spring. As saline flooding of coastal areas increases due to sea level rise, photosynthesis of these species will be differentially affected based primarily on their flood tolerance. This suggests that increased flooding associated with sea level rise will impact these tree species to a greater extent than small increases in soil salinity. High salinity accompanying storm surges will be very harmful to all of these species. Received: 20 October 1997 / Accepted: 2 December 1998     

Effect of hypercholesterolemia on Ca(2+)-dependent K(+) channel-mediated vasodilatation in vivo

Nitric oxide (NO)-mediated and NO-independent mechanisms of endothelium-dependent vasodilatation involve Ca(2+)-dependent K(+) (K(Ca)) channels. We examined the role in vivo of K(Ca) channels in NO-independent vasodilatation in hypercholesterolemia. Hindlimb vascular conductance was measured at rest and after aortic injection of ACh, bradykinin (BK), and sodium nitroprusside in anesthetized control and cholesterol-fed rabbits. Conductances were measured before and after treatment with the NO synthase antagonist N(omega)-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg) or K(Ca) blockers tetraethylammonium (30 mg/kg), charybdotoxin (10 microgram/kg), and apamin (50 microgram/kg). The contribution of NO to basal conductance was greater in control than in cholesterol-fed rabbits [2.2 +/- 0.4 vs. 1.1 +/- 0.3 (SE) ml. min(-1). kg(-1). 100 mmHg(-1), P < 0.05], but the NO-independent K(Ca) channel-mediated component was greater in the cholesterol-fed than in the control group (1.1 + 0.4 vs. 0.3 +/- 0.1 ml. min(-1). kg(-1). 100 mmHg(-1), P < 0.05). Maximum conductance response to ACh and BK was less in cholesterol-fed than in control rabbits, and the difference persisted after L-NAME (ACh: 7.7 +/- 0.7 vs. 10.1 +/- 0.5 ml. min(-1). kg(-1). 100 mmHg(-1), P < 0.005). Blockade of K(Ca) channels with tetraethylammonium or charybdotoxin + apamin almost completely abolished L-NAME-resistant vasodilatation after ACh or BK. The magnitude of K(Ca)-mediated vasodilatation after ACh or BK was impaired in hypercholesterolemic rabbits. Vasodilator responses to nitroprusside did not differ between groups. In vivo, hypercholesterolemia is associated with an altered balance between NO-mediated and NO-independent K(Ca) channel contributions to resting vasomotor tone and impairment of both mechanisms of endothelium-dependent vasodilatation.     

Functionally separate intracellular Ca2+ stores in smooth muscle

In smooth muscle, release via the inositol 1,4,5-trisphosphate (Ins(1,4,5)P(3)R) and ryanodine receptors (RyR) on the sarcoplasmic reticulum (SR) controls oscillatory and steady-state cytosolic Ca(2+) concentrations ([Ca(2+)](c)). The interplay between the two receptors, itself determined by their organization on the SR, establishes the time course and spatial arrangement of the Ca(2+) signal. Whether or not the receptors are co-localized or distanced from each other on the same store or whether they exist on separate stores will significantly affect the Ca(2+) signal produced by the SR. To date these matters remain unresolved. The functional arrangement of the RyR and Ins(1,4,5)P(3)R on the SR has now been examined in isolated single voltage-clamped colonic myocytes. Depletion of the ryanodine-sensitive store, by repeated application of caffeine, in the presence of ryanodine, abolished the response to Ins(1,4,5)P(3), suggesting that Ins(1,4,5)P(3)R and RyR share a common Ca(2+) store. Ca(2+) release from the Ins(1,4,5)P(3)R did not activate Ca(2+)-induced Ca(2+) release at the RyR. Depletion of the Ins(1,4,5)P(3)-sensitive store, by the removal of external Ca(2+), on the other hand, caused only a small decrease ( approximately 26%) in caffeine-evoked Ca(2+) transients, suggesting that not all RyR exist on the common store shared with Ins(1,4,5)P(3)R. Dependence of the stores on external Ca(2+) for replenishment also differed; removal of external Ca(2+) depleted the Ins(1,4,5)P(3)-sensitive store but caused only a slight reduction in caffeine-evoked transients mediated at RyR. Different mechanisms are presumably responsible for the refilling of each store. Refilling of both Ins(1,4,5)P(3)-sensitive and caffeine-sensitive Ca(2+) stores was inhibited by each of the SR Ca(2+) ATPase inhibitors thapsigargin and cyclopiazonic acid. These results may be explained by the existence of two functionally distinct Ca(2+) stores; the first expressing only RyR and refilled from [Ca(2+)](c), the second expressing both Ins(1,4,5)P(3)R and RyR and dependent upon external Ca(2+) for refilling.     

Erythrocyte osmotic fragility of red (Macropus rufus ) and grey (Macropus fuliginosus and Macropus giganteus ) kangaroos and free-ranging sheep of the arid regions of Australia

The mean corpuscular fragility (MCF) of erythrocytes may reflect phylogenetic characteristics as well as an animal's ability to respond to the osmotic challenges associated with cyclic dehydration and rehydration. This type of ecophysiological stress is commonly encountered by animals living in arid regions and low MCF may contribute to their ability to survive and thrive in these xeric habitats. The eastern grey kangaroo has only in recent times extended its range into the arid zone, and is considered a more mesic inhabitant than the red kangaroo. We therefore compared the ability of eastern grey kangaroos and red kangaroos to handle prolonged periods of water restriction, as well as the MCF of the erythrocytes of free-ranging red, eastern grey and western grey kangaroos found at the Fowlers Gap field station. In addition, the MCF of free-ranging sheep inhabiting the same pastures were used as an experimental control; they are phylogenetically unrelated yet are subjected to the same acclimatisation stresses. While red kangaroos exhibited greater tolerance of dehydration compared to eastern grey kangaroos, the MCF of all three kangaroo species was similar and more resilient to osmotic stresses (MCF, 130 mosmol/kg) than erythrocytes of sheep (MCF, 220 mosmol/kg). The MCF did not change with water restriction, however, the erythrocytes of long-term captive populations fed a comparatively better quality diet were more resistant to osmotic shock than the free-ranging animals. Phylogenetic commonality rather than ecophysiological responses to life in the arid zone appeared to influence MCF. The MCF values of sheep corresponded to that of other ovines; similarly the MCF of kangaroos concurred regardless of their preferred habitats, ecological history and differential success in the arid zone. Accepted: 29 August 2000     

Blockade of B7-H1 (programmed death ligand 1) enhances humoral immunity by positively regulating the generation of T follicular helper cells

T follicular helper (T(FH)) cells are critical initiators in the development of T cell-dependent humoral immunity and the generation of protective immunity. We demonstrate that T(FH) cell accumulation and Ab production are negatively regulated by B7-H1 (programmed death ligand 1) in response to both helminth infection and active immunization. Following immunization of B7-H1(-/-) mice with keyhole limpet hemocyanin or helminth Ags, there is a profound increase in induction of T(FH) cells as a result of increased cell cycling and decreased apoptosis relative to wild-type mice. The increase in T(FH) cells in the absence of B7-H1 was associated with significant elevations in Ag-specific Ig response. Cotransfer experiments in vivo demonstrated that B7-H1 expression on B cells was required for negatively regulating T(FH) cell expansion and production of Ag-specific Ig. Treatment of immunized wild-type mice with anti-B7-H1 or anti-programmed death 1 mAbs, but not anti-B7-DC, led to a significant expansion of the T(FH) cell population and an enhanced Ag-specific Ig response. Our results demonstrate that the coinhibitory B7-H1/programmed death 1 pathway can limit the expansion of T(FH) cells and constrain Ag-specific Ig responses. This finding has direct implications for investigations examining the feasibility of therapeutically manipulating this pathway and reveals new insights into the regulation of the humoral immune response.     

Dehydration,with and without heat,in kangaroos from mesic and arid habitats: different thermal responses including varying patterns in heterothermy in the field and laboratory

Field data showing the daily patterns in body temperature (T _b) of kangaroos in hot, arid conditions, with and without water, indicate the use of adaptive heterothermy, i.e. large variation in T _b. However, daily T _b variation was greater in the Eastern Grey Kangaroo (Macropus giganteus), a species of mesic origin, than in the desert-adapted Red Kangaroo (Macropus rufus). The nature of such responses was studied by an examination of their thermal adjustments to dehydration in thermoneutral temperatures (25°C) and at high temperature (45°C) via the use of tame, habituated animals in a climate chamber. At the same level of dehydration M. rufus was less impacted, in that its T _b changed less than that for M. giganteus while it evaporated significantly less water. At a T _a of 45°C with water restriction T _b reached 38.9 ± 0.3°C in M. rufus compared with 40.2 ± 0.4°C for M. giganteus. The ability of M. rufus to reduce dry conductance in the heat while dehydrated was central to its superior thermal control. While M. giganteus showed more heterothermy, i.e. its T _b varied more, this seemed due to a lower tolerance of dehydration in concert with a strong thermal challenge. The benefits of heterothermy to M. giganteus were also limited because of thermal (Q₁₀) effects on metabolic heat production and evaporative heat loss. The impacts of T _b on heat production were such that low morning T _b’s seen in the field may be associated with energy saving, as well as water saving. Kangaroos respond to dehydration and heat similarly to many ungulates, and it is apparent that the accepted notions about adaptive heterothermy in large desert mammals may need revisiting.     

Antibody targeting of camptothecin-loaded PLGA nanoparticles to tumor cells

Antibody targeting of drug substances can improve the efficacy of the active molecule, improving distribution and concentration of the drug at the site of injury/disease. Encapsulation of drug substances into polymeric nanoparticles can also improve the therapeutic effects of such compounds by protecting the molecule until its action is required. In this current study, we have brought together these two rationales to develop a novel immuno-nanoparticle with improved therapeutic effect against colorectal tumor cells. This nanoparticle comprised a layer of peripheral antibodies (Ab) directed toward the Fas receptor (CD95/Apo-1) covalently attached to poly(lactide-co-glycolide) nanoparticles (NP) loaded with camptothecin. Variations in surface carboxyl density permitted up to 48.5 microg coupled Ab per mg of NP and analysis of nanoparticulate cores showed efficient camptothecin loading. Fluorescence visualization studies confirmed internalization of nanoconstructs into endocytic compartments of HCT116 cells, an effect not evident in NP without superficial Ab. Cytotoxicity studies were then carried out against HCT116 cells. After 72 h, camptothecin solution resulted in an IC 50 of 21.8 ng mL (-1). Ab-directed delivery of NP-encapsulated camptothecin was shown to be considerably more effective with an IC 50 of 0.37 ng mL (-1). Calculation of synergistic ratios for these nanoconstructs demonstrated synergy of pharmacological relevance. Indeed, the results in this paper suggest that the attachment of anti-Fas antibodies to camptothecin-loaded nanoparticles may result in a therapeutic strategy that could have potential in the treatment of tumors expressing death receptors.