Feeding tests with caddis larvae (Insecta: Trichoptera) and amphipods (Crustacea: Amphipoda) on Platanus orientalis (Platanaceae) and other leaf litter

In the southern parts of the Mediterranean region, as in the island of Crete, there are few species of riparian trees and shrubs among the dominant Platanus orientalis. Feeding tests have shown that leaves of Platanus are not eaten by aquatic shredders of continental and Cretean origin. The large quantities of organic matter are therefore not used as a source of food and energy by the stream communities. In addition, the high winter flow shortly after leaf fall, and the short courses of rivers result in loss of most of the leaf litter to the sea. The River Continuum Concept does therefore not apply to this region. Field observations have shown that amphipods and limnephilid larvae are shifting from shredding to scraping habits if no leaf litter except Platanus was available.     

Transport and particle size distribution of suspended and benthic organic matter in three headwater streams

The breakdown and decomposition of two species of deciduous leaf litter, Fagus sylvatica L. and Salix viminalis L. and two species of aquatic macrophyte Isoetes lacustris L. and Potamogeton perfoliatus L. were examined in an oligotrophic lake. In all cases plant litter in coarse mesh litter bags lost significantly more material than the fine mesh after 1 years submergence in the lake. This however was considered to be the result of physical environmental factors and microbial activity rather than animal processing. The litter was ranked in order of fastest to slowest rates of decay as follows — Isoetes, Potamogeton, Salix and Fagus. Decomposition processes proceeded at a relatively slow rate as a result of low temperatures and low phosphate and mineral ion concentration. The results suggested that there was an accumulation of organic material in the lake.     

Comparison of Proteoglycans Extracted by Saline and Guanidinium Chloride from Cultured Chick Retinas

Abstract: To compare the loosely associated sulfated proteoglycans with those tightly bound to membranes, retinas from 14-day chick embryos were subjected to progressively disruptive techniques. The most easily removed proteoglycans were isolated from the medium in which the tissue was labeled with [³⁵S]sulfate. On the average, 25% of the glycosaminoglycans were in the labeling medium, 39% were in proteoglycans extracted from the tissue in the balanced salt solution, 32% were in a 4 m -guanidinium chloride (GuCl) fraction, and 4% remained unextracted. These glycosaminoglycans contained, respectively, 28, 28, 40, and 4% of the incorporated [³⁵S]sulfate. On the basis of electrophoretic mobility and TLC of chondroitinase digests, the ratio of ³⁵S in chondroitin sulfate to that in heparan sulfate was 4–7 times higher in the medium and balanced salt extracts than in the GuCl extracts. In both extracts there was more ³⁵S in chondroitin-6-sulfate than in chondroitin-4-sulfate. Dialysis of the extracts against 0.5 M-NaCl resulted in the precipitation of about 12% of the glycosaminoglycans in the saline extracts and about 40% in GuCl extract. These subfractions, which were relatively enriched in heparan sulfate, were largely soluble in dithiothreitol in 8 m -urea (DTT). Similarities between the proteoglycans in the medium and those extracted by balanced salt solutions suggest that the saline-extracted proteoglycans were for the most part loosely associated with cell surfaces or extracellular matrices, whereas the GuCl-extracted proteoglycans probably were bound to membranes.     

Nitrogen fixation in hardwood forests of the northeastern United States

Summary Nitrogen-fixing activity in hardwood forests of the northeastern United States occurred in wood litter, greater than 2 cm in diameter. Activity in large dead wood was independent of species, in the case of deciduous wood litter, but was restricted to partially decayed wood with a high moisture content. Maximum rates of activity were observed in the summer months, minimum rates in the winter. Evidence from six stands of varying ages showed that fixation in large wood litter occurred in only 25% of the samples assayed.Fixation was highest in the youngest, 4 years, and oldest, over 200 years, stands; being about 2 kg/ha/yr. The quantity of nitrogen fixed appears to be related to the biomass of dead wood. Large amounts of wood litter in the youngest stands were from slash left after cutting. As the supply of slash is exhausted by decay, nitrogen fixation decreases, with a low around year 20. Fixation then gradually increases as natural thinning adds wood to the litter compartment.Apparently, the amount of nitrogen fixed in dead wood the first 20 years following clearcutting can only replace a modest fraction of the amount lost as a result of the cutting and product removal. Finally, the results indicate that nitrogen fixation in wood litter does not equal nitrogen fixation in a northern hardwood forest calculated using a mass balance approach, suggesting that additional nitrogen inputs exist.     

The mechanism of bicarbonate assimilation by the polar leaves of Potamogeton and Elodea. CO2 concentrations at the leaf surface

Abstract. Photosynthetic utilization of HCO, in leaves of Poiamogeton and Elodea occurs at the lower leaf side, with subsequent OH∼ release at the upper side. It is accompanied by transport of cations, in the present experiment K +, across the leaf. The resulting pH and K+ concentration changes near the leaf surface were recorded with miniature electrodes. From the pH and K+ concentration the concentrations of the different inorganic carbon species were calculated and compared with photosynthetic O, production. HCO⁻₃ utilization is accompanied by a drastic increase in the free CO₂ concentration near the lower epidermis. Experiments with CO₂− and HCO₃⁻free solutions showed an oscillating acidification near the lower epidermis and alkalinization near the upper epidermis. It is concluded that the acidification results from the activity of light-dependent H+ pumps. The finding that an increase in pH at the upper side always coincided with a decrease at the lower in these experiments shows that the H+ pumps and the OH− extruding mechanism are coupled although occurring in different cell layers. Previously we have suggested that the first step in the process of photosynthetic HCO₃⁻ utilization is external conversion of HCO₃⁻" by acidification caused by light-dependent H+ pumps. The present results strongly support this hypothesis. Two possible pathways for the accompanying K + transport are discussed. The model presented here explains the known inhibiting effects of buffers and high pH on photosynlhetic HCO₃⁻ utilization.     

Polychlorinated biphenyls as inducers of hepatic microsomal enzymes: Structure-activity rules

A number of highly purified polychlorinated biphenyl (PCB) isomers and congeners were synthesized and administered to male Wistar rats at dosage levels of 30 and 150 μmol · kg⁻¹. The effects of this in vivo treatment on the drug-metabolizing enzymes were determined by measuring the microsomal benzo[a]pyrene (B[a]P) hydroxylase, dimethylaminoantipyrine (DMAP) N-demethylase and NADPH-cytochrome c reductase enzyme activities, the cytochrome b₅ content and the relative peak intensities and spectral shifts of the reduced microsomal cytochrome P-450: CO and ethylisocyanide (EIC) binding difference spectra. The results were compared to the effects of administering phenobarbitone (PB), 3-methylcholanthrene (MC) and PB plus MC (coadministered) to the test animals. The synthetic PCB congeners used in this study included 3,4,4′,5-tetrachlorobiphenyl (TCBP-1), 2,3′,4,4′-tetrachlorobiphenyl (TCBP-2), 2,3′,4,4′,5′-pentachlorobiphenyl (PCBP-1), 2,3,4,4′,5-pentachlorobiphenyl (PCBP-2), 2,3,3′,4,4′,5-hexachlorobiphenyl (HCBP-1), 2,3,3′,4′,5,6-hexachlorobiphenyl (HCBP-2), 2,3,3′,5,5′,6-hexachlorobiphenyl (HCBP-3), 2,2′,3,5,5′,6-hexachlorobiphenyl (HCBP-4) and 2,3,3′,4,5,5′-hexachlorobiphenyl (HCBP-5) and were used to reappraise the structure-activity rules for PCBs as hepatic microsomal enzyme inducers. The results suggested that (a) PCBs which induce MC or mixed-type activity must be substituted at both para positions, at least two meta positions but not necessarily on the same phenyl ring and can also contain one ortho chloro substituent; (b) due to the considerable structural diversity of the PB-type inducers the rules for induction of this activity by PCB congeners are not readily defined.     

Ascaris sp.: water loss during desiccation of embryonating eggs

The ability of embryonating eggs of Ascaris lumbricoides to avoid desiccation by reducing the loss of water through the egg shell was investigated. When exposed to desiccation the eggs lost water at a rate dependent upon the relative humidity and ambient temperature, eventually resulting in the collapse of the eggs and the death of the enclosed embryo. The eggs are small with a large surface to volume ratio. A low permeability to gaseous exchange thus restricts water loss while still ensuring an adequate supply of oxygen for embryonic development. Relative humidity did not appear to affect the rate of development. In eggs exposed to desiccation at various constant temperatures, the rate of water loss increased as an exponential function of increasing temperature. When eggs were exposed to various temperatures before exposure to desiccation at 22 C, the rate of water loss increased as a function of increasing pretreatment temperature. After exposure to 63–65 C, the ability of the egg shell to slow down the loss of water was destroyed. These phenomena suggest that there is not a simple “critical” or “transition” temperature, but a gradual melting of the complex mixture of components forming the lipid layer.     

Inhibition of Na+ and K+-stimulated ATPase of rabbit heart sarcolemma after, administration of heparin.

Intravenous heparin administration caused a marked inhibition of Mg⁺⁺-dependent (Na⁺+K⁺)-stimulated ATPase activity of sarcolemmal (SL) membranes prepared from rabbit heart, whereas basal Mg⁺⁺-ATPase was not affected. The inhibition depended on K⁺ concentration and was reversed only in the presence of albumin. Plasma free fatty acid (FFA) concentrations were raised in all animals, after heparin administration. The results obtained support the concept that FFA or other lipids originating in the plasma by the action of lipolytic enzymes released by heparin are involved in the mechanism of inhibition.