A review of the salt sensitivity of the Australian freshwater biota

In Victoria, Australia, both dryland salinity and salinity in irrigation regions are serious agricultural problems. One option to control the latter is to pump groundwater to maintain it below the surface. However, this leaves a saline wastewater for disposal, probably into local streams or wetlands. This review of the salt sensitivity of the biota of Australian streams and wetlands gives information of interest to those responsible for developing controls on these discharges. The review addresses the lethal and sub-lethal effects of salinity on microbes (mainly bacteria), macrophytes and micro-algae, riparian vegetation, invertebrates, fish, amphibians, reptiles, mammals, and birds. Data suggest that direct adverse biological effects are likely to occur in Australian river, stream and wetland ecosystems if salinity is increased to around 1 000 mg L⁻¹. The review highlights a general lack of data on the sensitivity of freshwater plants and animals to salinity increases.     

Identification of the Ca(2+)-independent endocytic hyaluronan receptor in rat liver sinusoidal endothelial cells using a photoaffinity cross-linking reagent.

The Ca(2+)-independent endocytic hyaluronan (HA) receptor in rat liver sinusoidal endothelial cells (LECs) was identified using a novel cross-linking derivative of HA. The heterobifunctional, photoactivatable, reducible reagent sulfosuccinimidyl 2-(p-azidosalicylamido)ethyl-1,3'-dithiopropionate (SASD) was coupled to the terminal amino group of uniquely modified HA-amine oligosaccharides (M(r) approximately 60,000) and subsequently iodinated. 125I-ASD-HA bound to cultured LECs with similar specificity and affinity as a previously characterized 125I-HA-amine/Bolton-Hunter adduct. Permeabilized LECs were incubated with 125I-ASD-HA with 10 mM EGTA and photolysed with UV light. Detergent extracts were reduced to release the HA oligosaccharides and radiolabeled proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. Two polypeptides were consistently and equally labeled at M(r) = 175,000 and 166,000. Photoaffinity labeling of these two proteins was virtually identical in cultured LECs or membranes and was competed greater than 90% with a 100-fold excess of HA. As with the previously characterized bona fide LEC HA receptor, cross-linking was also competed by chondroitin sulfate and heparin, but less efficiently by chondroitin and not with galacturonan. We conclude that the Ca(2+)-independent LEC HA receptor is composed of at least two polypeptides of M(r) approximately 175,000 and 166,000 and may exist as a heterodimer of M(r) approximately 340,000. We also conclude that the LEC HA receptor is distinct from the CD44 family of HA-binding proteins.     

Immunolocalization of membrane-associated CTP:phosphocholine cytidylyltransferase in phosphatidylcholine-deficient Chinese hamster ovary cells.

The location of CTP:phosphocholine cytidylyltransferase in Chinese hamster ovary (CHO) cells made deficient in phosphatidylcholine was determined by immunofluorescence techniques. A rabbit polyclonal antibody was raised against a synthetic peptide corresponding to the amino-terminal 17 amino acid residues of rat liver cytidylyltransferase. The antibody recognized both native and denatured cytidylyltransferase from both rat liver and CHO cells. CHO cells were treated with phospholipase C to alter the lipid composition of the plasma membrane and to elicit translocation of cytidylyltransferase from the less active soluble pool to an activated membrane fraction. Visualization of cytidylyltransferase by indirect immunofluorescence revealed staining of the nuclear envelope in phospholipase C-treated cells but not in untreated cells. CHO cells were also starved for choline and supplemented with a choline analogue to provide an alternative technique of rendering the cells phosphatidylcholine-deficient. Although this treatment should affect different cellular membranes than those affected by phospholipase C treatment, cytidylyltransferase still translocated to the nuclear envelope, as shown by indirect immunofluorescence. These results indicate that activated, membrane-bound cytidylyltransferase is associated with the nuclear membrane and suggest that the nuclear membrane may be a site of de novo phosphatidylcholine synthesis.     

The ANF-C receptor is not linked to adenylyl cyclase inhibition in bovine pulmonary artery endothelial cells.

The possible inhibition of adenylyl cyclase activity by atrial peptides selective for the ANF-C receptor was investigated in bovine pulmonary artery endothelial cells. In these cells isoprenaline, guanine nucleotide and forskolin dose-dependently increased activity over basal levels. In the presence of rANF(99-126), these dose-dependent increases were not reduced, nor were they affected by the ANF-C receptor selective analogue C-ANF(102-121). Furthermore, the selective analogues rANF(103-123) and des[Cys105,Cys121]rANF104-126 had no effect on basal or stimulated adenylyl cyclase activity. It can be concluded that ANF-C receptors are not linked to inhibition of adenylyl cyclase in these cells.     

LEAFY controls floral meristem identity in Arabidopsis.

The first step in flower development is the generation of a floral meristem by the inflorescence meristem. We have analyzed how this process is affected by mutant alleles of the Arabidopsis gene LEAFY. We show that LEAFY interacts with another floral control gene, APETALA1, to promote the transition from inflorescence to floral meristem. We have cloned the LEAFY gene, and, consistent with the mutant phenotype, we find that LEAFY RNA is expressed strongly in young flower primordia. LEAFY expression procedes expression of the homeotic genes AGAMOUS and APETALA3, which specify organ identify within the flower. Furthermore, we demonstrate that LEAFY is the Arabidopsis homolog of the FLORICAULA gene, which controls floral meristem identity in the distantly related species Antirrhinum majus.     

Coated pits and asialoglycoprotein receptors redistribute to the substratum during hepatocyte adhesion to galactoside surfaces

Rat hepatocytes bind in a sugar-specific and concentration-dependent manner to flat polyacrylamide matrices containing covalently attached galactosyl (Gal) groups. Previous studies (Weigel, P.H., J. Cell Biol. 87, 855, 1980) concluded that binding was likely mediated by the asialoglycoprotein receptor. Here we confirm that adhesion is mediated by this receptor, since cell binding is inhibited by antireceptor antibody and a threshold binding response is also observed when hepatocytes adhere to surfaces coated with asialoorosomucoid, a ligand for this receptor. Cells that had bound to a Gal surface and were then sheared from the surface left a membrane patch behind on the substratum. The cytoplasmic side of these plasma membrane patches was visualized on the substratum by indirect immunofluorescence using antireceptor antibody or anticlathrin antibody. The density of punctate coated pits, visualized with the latter antibody, was enriched in a circular membrane region of about 4 microns 2 area that mediated cell binding. This zone also contained concentrated receptors, although the staining pattern with antireceptor antibody was more uniform and less punctate. The results show that both asialoglycoprotein receptors and coated pits are redistributed at the substratum interface on hepatocytes bound to Gal surfaces.     

Total cellular activity and distribution of a subpopulation of galactosyl receptors in isolated rat hepatocytes are differentially affected by microtubule drugs,monensin, low temperature,and chloroquine

We studied the effects of low temperature (20–37°C), monensin, chloroquine, and microtubule drugs on the cellular distribution and activity of galactosyl (Gal) receptors in isolated rat hepatocytes. After equilibration at 37°C, hepatocytes were incubated at 37°C, 31°C, 25°C, or 20°C or treated with or without inhibitors at 37°C in the absence of ligand. The cells were then assayed at 4°C for ¹²⁵I-asialo-orosomucoid binding, to measure receptor activity, or ¹²⁵I-anti-Gal receptor IgG binding, to measure receptor protein. Surface or total (surface and intracellular) Gal receptor activity and protein were measured on intact or digitonin-permeabilized cells, respectively. These inhibitors fell into two categories. Type I inhibitors (sub-37°C temperatures or colchicine) induced receptor redistribution but not inactivation. Treated cells lost up to 40% of surface Gal receptor activity and protein. Lost surface receptors were recovered intracellularly with no loss of receptor activity. Type II inhibitors (monensin or chloroquine) induced receptor inactivation but not redistribution. Treated cells lost 50–65% of their surface Gal receptor activity but only ? 15% of their surface receptor protein. These cells lost up to 60% of total cellular Gal receptor activity with no loss of total receptor protein. Of the total inactive Gal receptors, up to 50% and75%, respectively, were present intracellularly in monensin-and chloroquine-treated cells. Loss of ligand binding to permeable treated cells was not due to changes in receptor affinity. A third category, Type III inhibitors (metabolic energy poisons that deplete ATP) induce both Gal receptor redistribution and inactivation (Biochemistry 27:2061, 1988). We conclude that only one of the two previously characterized subpopulations of Gal receptors on hepatocytes, termed State 2 receptors (J Biol Chem 265:629, 1990), recycles constitutively. The activity and distribution of State 2 but not State 1 Gal receptors are differentially affected by these specific drugs or treatments.