Phases in the development of riverine plankton: Examples from the rivers Rhine and Meuse

Observations on phyto and zooplankton in two hydrographically different rivers were compared in order to discriminate phases in plankton development. Along the longitudinal axis of the River Rhine a gradual increase in the development of phytoplankton was observed, which reached its maximumca. 100 km before the river flows into its artificial sedimentation area. The development of rotifer populations was slightly retarded as compared with that of phytoplankton and highest population densities were only reached in the sedimentation area. Crustaceans developed in significant numbers, not until the river water had entered the sedimentation area. Development of zooplankton coincided here with a strong decrease in the density of phytoplankton. A similar trend in plankton development was observed in the River Meuse, although in this river the highest densities of phyto and zooplankton already occurred in its middle reaches. The differences in the timing of plankton growth in the two rivers are probably caused by differences in flow regime between both rivers. The River Rhine, which is fed by rainwater and melting of glaciers in the Alps, has a relatively constant discharge. On the other hand, the low discharge of the rain-fed River Meuse combined with an increased residence time of the water as a consequence of large numbers of weirs, allows a full cycle of plankton development long before its discharge into the sea. This phenomenon was also reflected in the silicate cycle in the Meuse, where the consumption by planktonic diatoms and the regeneration of silicate of deposits seem to be important. In contrast, in the main branches of the River Rhine only the effects of silicate consumption were detectable.     

Effect of protein synthesis inhibitors on the formation of crystalloid inclusions in the endoplasmic reticulum of beetroot cells

Thin slices of beetroot tissue develop long ER lamellae during a period of aerated washing. After 2–3 days crystalloid bodies begin to appear within the ER cisternae and these were shown to consist largely of protein.The effect of inhibitors of RNA and protein synthesis on the formation of ER lamellae and crystals was studied, and results indicate that protein synthesis, but not synthesis of m-RNA, is essential for both processes. It is also suggested that the protein-synthesizing system associated with the ER is more stable than the cytoplasmic polyribosome system, which may require the continued production of m-RNA after slicing.This research was supported by grants from the Australian Research Grants Committee.     

Localization of polyphosphates at the outside of the yeast cell plasma membrane

Under appropriate experimental conditions toluidine blue is bound to the yeast cell surface, without penetrating into the cells. Based on experimental observations it is highly probable that the dye is bound to polyphosphates, localized outside the plasma membrane. The probable localization of polyphosphates outside the plasma membrane is important in the context of the proposed involvement of polyphosphates in glucose transport in yeast.     

Chloride and sulphur concentrations in chloroplasts of spinach

Chloride concentrations within individual chloroplasts, the adjacent cytoplasm and nearby vacuoles of spinach mesophyll cells (Spinacea oleracea L. cv. Hybrid 102) were determined by means of electron probe X-ray microanalysis in the cleavage plane of quench frozen tissue, which was maintained at liquid nitrogen temperatures. The accuracy of quantitative data obtained with this technique is greatly improved by the adoption of a peak to background ratio method and use of carbon slurry standards, which mimic the quench frozen tissue and its X-ray fluorescence. Chloroplasts were incapable of maintaining relatively high levels of Cl^? under conditions of low Cl^? availability (zero Cl^? or 20 μM Cl^? in nutrient solution), and under conditions of Cl^? stress (100 or 200 mM Cl^?) chloroplasts had only a limited capacity to maintain a Cl^? concentration at a level below that of the cytoplasm and vacuole. However, under conditions of Cl^? stress the concentration of Cl^? in cytoplasm immediately adjacent to chloroplasts was substantially higher than in the chloroplasts or more distant cytoplasm. Thus, Cl^? levels in chloroplasts are apparently not as tightly regulated as was suggested by estimates of Cl^? concentration based on aqueous isolation of chloroplasts. Levels of S in chloroplasts were relatively high (equivalent to 40–60 mM SO₄^2? in S standards) and constant for all treatments, with the possible exception of lower S levels in chloroplasts of leaves approaching premature senescence as a result of salt stress. It is implied that the stability of the S-content results largely from its presence in macromolecular components of chloroplasts (sulfolipids and proteins).     

Transport-associated phosphorylation of 2-deoxy-d-glucose in Saccharomyces fragilis

2-Deoxy-d-glucose transport and metabolism was studied in Saccharomyces fragilis. Inside the cells four phosphorylated and three non-phosphorylated derivatives were found and identified. Accumulation of phosphorylated 2-deoxyglucose derivatives was balanced by a concomitant decrease of cellular ATP, orthophosphate and polyphosphates.The free sugar was concentrated against a concentration gradient, contradicting facilitated diffusion. Pulse labeling experiments revealed transport-associated phosphorylation.Theoretical considerations and analysis of the effects of iodoacetate showed that an intracellular hexokinase activity was not involved in 2-deoxyglucose phosphorylation, although this sugar is a good substrate for the enzyme in in vitro experiments.     

Inhibition of enzymes and oxidative damage of red blood cells induced by t-butylhydroperoxide-derived radicals

The effects of t-butylhydroperoxide (tBHP), its alkoxyl radical (tBuO.) and its peroxyl radical (tBuOO.) in model systems and on red blood cells were studied. Glyceraldehyde-3-phosphate dehydrogenase was strongly inhibited by tBHP via a direct reaction of the hydroperoxide with an essential sulfhydryl group in the enzyme molecule. Several other enzymes were unaffected by tBHP. Alcohol dehydrogenase was strongly inhibited by tBuO. but was much less sensitive to tBuOO.. Lysozyme, lactate dehydrogenase and trypsin, on the other hand, were very sensitive to the peroxyl and not, or much less, to the alkoxyl radical, whereas acetylcholinesterase was very sensitive to both radicals. tBuOO. caused covalent binding of tryptophan, tyrosine, histidine and methionine to serum albumin. The corresponding alkoxyl radical was ineffective in this respect. Conversely, tBuO. caused peroxidation of linolenic acid, whereas tBuOO. did not. Incubation of human erythrocytes with tBHP caused lipid peroxidation and K+ leakage. Both effects were caused by tBHP-derived radicals generated in a reaction of the hydroperoxide with hemoglobin. With radical scavengers it was possible to dissociate tBHP-induced lipid peroxidation and K+ leakage, demonstrating that these two processes are not causally related. Experimental results indicate that tBuO. causes lipid peroxidation, whereas tBuOO. is responsible for K+ leakage.