Filtration rate capacities in 6 species of European freshwater bivalves

Summary Filtration rate capacities in undisturbed freshwater bivalves were determined by means of two different methods (indirect clearance and suction methods) in Anodonta anatina (L.), Unio tumidus Philipsson, Unio pictorum (L.), Unio crassus Philipsson, Dreissena polymorpha (Pallas) and Sphaerium corneum (L.). In A. anatina, D. polymorpha, and S. corneum the filtration rate (FR, 1 h^-1) at 19–20°C as a function of dry tissue weight (DW, g) or ash-free dry weight (AFDW, g) could be expressed by the equations: 1.10 DW^0.78, 6.82 DW^0.88, and 2.14 AFDW^0.92, respectively. In U. tumidus, U. pictorum, and U. crassus filtration rates were comparable with those of A. anatina. In D. polymorpha the b value of the corresponding regression of gill area on dry weight was 0.87. The rates of water transport in freshwater bivalves are 2–8 times lower than in marine bivalves of comparable size. A corresponding difference in the filtration rate per gill area unit is found. The measured filtration rates in undisturbed bivalves are substantially higher (at least 4 times) than previously reported. This indicates that the impact of bivalve water processing on freshwater ecosystems is greater than hitherto suggested.     

Abscisic acid and water transport in sunflowers

The role of abscisic acid (ABA) in the transport of water and ions from the root to the shoot of sunflower plants (Helianthus annuus) was investigated by application of ABA either to the root medium or to the apical bud. The exudation at the hypocotyl stump of decapitated seedlings was measured with and without hydrostatic pressure (0–0.3 MPa) applied to the root. All ABA concentrations tested (10^-10–10^-4 mol·l^-1) promoted exudation. Maximal amounts of exudate (200% of control) were obtained with ABA at 10^-6·mol·l^-1 and an externally applied pressure of 0.1 MPa. The effect was rapid and long-lasting, and involved promotion of ion release to the xylem (during the first hours) as well as an increase in hydraulic conductivity. Abscisic acid applied to the apical bud had effects similar to those of the rootapplied hormone. Increased rates of exudation were also obtained after osmotic stress was applied to the root; this treatment increased the endogenous level of ABA in the root as well as in the shoot. Water potentials of the hypocotyls of intact plants increased when the roots were treated with ABA at 5°C, whereas stomatal resistances were lowered. The results are consistent with the view that ABA controls the water status of the plant not only by regulating stomatal transpiration, but also by regulating the hydraulic conductivity of the root.Abbreviations and symbols ABA abscisic acid - Tv volume flow - Lp hydraulic conductivity - PEG polyethyleneglycol - water potential - osmotic potential - osmotic value - P hydrostatic pressure     

Effects of platelet-activating factor antagonist SRI 63-441 on endotoxemia in sheep

We investigated whether platelet-activating factor (PAF) mediates endotoxin-induced systemic and pulmonary vascular derangements by studying the effects of a selective PAF receptor antagonist, SRI 63-441, during endotoxemia in sheep. Endotoxin infusion (1.3 micrograms/kg over 0.5 h) caused a rapid, transient rise in pulmonary arterial pressure (Ppa) from 16 +/- 3 to 36 +/- 10 mmHg (P less than 0.001) and pulmonary vascular resistance (PVR) from 187 +/- 84 to 682 +/- 340 dyn.s.cm-5 (P less than 0.05) at 0.5 h, followed by a persistent elevation in Ppa to 22 +/- 3 mmHg and in PVR to 522 +/- 285 dyn.s.cm-5 at 5 h in anesthetized sheep. Arterial PO2 (PaO2) decreased from 341 +/- 79 to 198 +/- 97 (P less than 0.01) and 202 +/- 161 Torr at 0.5 and 5 h, respectively (inspired O2 fraction = 1.0). SRI 63-441, 20 mg.kg-1.h-1 infused for 5 h, blocked the early rise in Ppa and PVR and fall in PaO2, but had no effect on the late phase pulmonary hypertension or hypoxemia. Endotoxin caused a gradual decrease in mean aortic pressure, which was unaffected by SRI 63-441. Infusion of SRI 63-441 alone caused no hemodynamic alterations. In follow-up studies, endotoxin caused an increase in lung lymph flow (QL) from 3.8 +/- 1.1 to 14.1 +/- 8.0 (P less than 0.05) and 12.7 +/- 8.6 ml/h at 1 and 4 h, respectively. SRI 63-441 abolished the early and attenuated the late increase in QL.(ABSTRACT TRUNCATED AT 250 WORDS)     

Control ofThrips tabaci [Thysanoptera: Thripidae] on glasshouse cucumber using large introductions of predatory mitesAmblyseius barkeri [Acarina: Phytoseiidae]

The phytoseiid miteAmblyseius barkeri (Hughes) (=Amblyseius mckenziei Sch. & Pr.) was used for biological control ofThrips tabaci Lind. in 7 commercial glasshouses with cucumber (a total of 5780 m²). Predatory mites were introduced 3–4 times in densities ranging from 40 to 300/m² at each release. In 6 of the 7 glasshouses, control of thrips was satisfactory throughout the growing season. Thrips densities were kept below 15 individuals per leaf. In 1 glasshouse, thrips damage was seen on the fruits at densities of 25 thrips per leaf, but the thrips population was quickly reduced and remained at low densities for the next 3 months.      

Primary structure of the hemoglobin α-chain of rose-ringed parakeet (Psittacula krameri)

The structure of the hernoglobin α-chain of Rose-ringed Parakeet was determined by sequence degradations of the intact subunit, the CNBr fragments, and peptides obtained by digestion with staphylococcal Glu-specific protease and trypsin. Using this analysis, the complete α-chain structure of 21 avian species is known, permitting comparisons of the protein structure and of avian relationships. The structure exhibits differences from previously established avian α-chains at a total of 61 positions, five of which have residues unique to those of the parakeet (Ser-12, Gly-65, Ser-67, Ala-121, and Leu-134). The analysis defines hemoglobin variation within an additional avian order (Psittaciformes), demonstrates distant patterns for evaluation of relationships within other avian orders, and lends support to taxonomic conclusions from molecular data.