Anomalous properties of water in macromolecular gels.

Low molecular weight solutes often exhibit elution characteristics on gel filtration columns which deviate from ideal behaviour. In many previous studies this anomalous behaviour was attributed to the existence of extremely narrow pores in the gel, inaccessible even to very small solute molecules, to explain Kd values lower than unity. Kd values of small solutes higher than unity were usually ascribed to adsorption of the solute to the gel matrix. In the present paper several observations are presented that contradict these suggestions. Experimental evidence indicates that with small solute molecules Kd values differing from unity can be fully explained by the anomalous properties of vicinal water layers at the gel matrix-water interface.     

Active transport of L-sorbose and 2-deoxy-D-galactose in Saccharomyces fragilis.

Sorbose and 2-deoxy-D-galactose are taken up in Saccharomyces fragilis by an active transport mechanism, as indicated by the energy requirement of the process and the accumulation of free sugar against the concentration gradient. There are no indications for transport-associated phosphorylation as mechanism of energy coupling with these two sugars. The measured sugar-proton cotransport and the influx inhibition by uncouplers suggest a chemiosmotic coupling mechanism. Thus there are at least two different active transport mechanisms operative in Saccharomyces fragilis: transport-associated phosphorylation in the case of 2-deoxy-D-glucose and chemiosmotic coupling in the case of sorbose and 2-deoxy-D-galactose. The differences between the two mechanisms are discussed. Uncouplers do not stimulate downhill sorbose transport in energy-depleted cells and evoke an almost complete inhibition of efflux and of exchange transport. The differences between this sugar-proton cotransport system and similar systems in bacteria and Chlorella are discussed.     

Effect of xylose incubation on the glucose transport system in Saccharomyces cerevisiae

Incubation of Saccharomyces cerevisiae with xylose and ethanol for 16 hours leads to a decrease of hexokinase (and glucokinase) activity in the cells. It does not alter the levels of polyphosphate, orthophosphate and ATP. The transport of the glucose derivative 2-deoxy-D-glucose, a sugar that can be phosphorylated, is inhibited after this treatment, whereas transport of 6-deoxy-D-glucose, which has a blocked phosphorylation site, is not inhibited. Even though, both deoxyglucoses use the same transport system. The decrease in initial velocity of 2-deoxy-D-glucose transport is most pronounced under anaerobic conditions. Incubation of the cells with antimycin A, a treatment which has a similar effect as anaerobiosis, shows, that the inhibition of the transport of 2-deoxy-D-glucose is presumably the result of an increase in the Km of the carrier transport. Transport of glucose is probably regulated by kinase enzymes.     

Photodynamic treatment of yeast cells with the dye toluidine blue: all-or-none loss of plasma membrane barrier properties.

Photodynamic treatment of Kluyveromyces marxianus with the sensitizer Toluidine blue leads to the loss of colony forming capacity. In this paper, the influence of this treatment on the barrier properties of the plasma membrane has been studied. Photodynamic treatment with the dye Toluidine blue resulted in efflux of potassium ions and E260-absorbing material. Moreover, cells became stainable with erythrosine. It is concluded that the permeability change induced by photodynamic treatment proceeds in an all-or-none fashion. Treatment of this yeast strain, with the dye and light, also induced a diminution of the cell volume. This process is most likely not coupled to the cellular potassium content, but rather to the integrity of the vacuole. These data suggest that the vacuole has an important function in the maintenance of cell volume. Finally, it was observed that the loss of cell viability was not induced by the all-or-none loss of barrier properties.     

The influence of ozone on human red blood cells. Comparison with other mechanisms of oxidative stress

Exposure of red blood cells to ozone resulted in K+ leakage, lipid peroxidation and inhibition of some membrane-associated enzymes. On the other hand, carrier-mediated transport of glucose, leucine, sulfate and glycerol and the nonspecific permeation of glycerol, L-glucose and erythritol were not affected by ozone. The cellular level of reduced glutathione declined, whereas the ATP content of the cells was quite insensitive to ozone exposure. It was shown that, most probably, lipid peroxidation and K+ leakage are not causally related. Further, K+ leakage did not reflect gradual, progressive loss of K+ from all cells simultaneously, but occurred in an all-or-none fashion. Finally, ozone-induced damage was compared to damage induced by H2O2, t-butyl hydroperoxide and photosensitizers plus light. It appeared that the pathways leading to membrane deterioration are quite dissimilar in these various forms of oxidative stress.     

Rapid action of abscisic acid on photosynthesis and stomatal resistance

Summary (RS)-Abscisic acid, a natural plant hormone, has been found to inhibit photosynthesis in both detached and attached primary wheat leaves. The action occurs rapidly and is accompanied by large increases in stomatal diffusive resistance.This research was supported by the Wheat Industry Research Council.     

The ultrastructure of wheat leaves I. Changes due to natural senescence and the effects of kinetin and ABA on detached leaves incubated in the dark

Summary Detached wheat leaves incubated in water in darkness rapidly lose starch and are ultrastructurally degenerate by 5 days. Chloroplast ribosomes disappear before cytoplasmic ribosomes and groups of wavy membranes can be detected in both mature and degenerating chloroplasts. Large lipid bodies appear in the cytoplasm and vacuole during senescence, and osmiophilic fibrils and deposits develop in the microbodies. Treatment with kinetin via the transpiration stream markedly delays the loss of starch and maintains, but does not increase, chloroplast and cytoplasmic ribosome populations. ABA accelerates degenerative changes as compared with the water treated control leaves but does not induce any specific ultrastructural effects.