No abstract

The dependence of 3[H]-L-glutamate uptake on the presence of sodium, chloride, or calcium ions or on a combination of the three was investigated in astrocyte primary cultures. A stimulating effect on glutamate uptake by each of the ions tested was found. In addition to the comparably small effect by calcium alone, calcium exhibits a synergistic effect on the sodium- and chloride-dependent uptake. The sodium-dependent transport accumulates the glutamate analogue D-aspartate as well as L-glutamate. L-aspartate is taken up by about 50% of the values observed for L-glutamate transport. Sodium-dependent glutamate uptake is strongly inhibited by aspartate-beta-hydroxamate (A beta H) and threo-beta-hydroxyaspartate (T beta H). Quisqualate is less potent in inhibiting this uptake. In contrast, the chloride- and the calcium-dependent uptake systems do not handle D- and L-aspartate as substrates. A beta H and T beta H are only poor inhibitors of these transporters while quisqualate reduces glutamate uptake almost completely. Kinetic data of all uptake systems were estimated. High and low affinity components of each individual system are demonstrated by Eadie-Hofstee analysis. Hill plots indicate that high and low affinity uptake may be due either to two respective uptake sites for Na(+)-, Cl(-)-, and Ca(++)-dependent glutamate transport, or to two glutamate binding sites for each single transport system with negative cooperativity.

Near-isogenic lines of the wheat {Triticutn aestivum L.) cultivar Prelude, carrying eitber tbe sr5 gene for susceptibility or tbe Sr5 allele for resistance to stem rust {Puccinia gratttinis Pers. f.sp. tritici Erics. & E. Henn.) ' •^' ere inoculated witb race 32 of tbe fungus wbicb possesses tbe P5 gene for-avirulence. Enzyme extracts prepared 'It different times after inoculation were separated by non-denaturing gel electropboresis and tbe gels were stained '"'-peroxidase acti\-ity using different substrates. Botb anodic and cathodic gels were run.In anodic separations, resistant and susceptible plants initially botb exbibited decreases in tbe activity of two 'soenzymes of low-molecular mass, increases in two enzymes of intermediate molecular mass, and induction of two new bigb molecular mass isoperoxidases. In susceptible plants, tbese changes proceeded until 3 days after 'noculation, when a general decrease in all isoenzymes was observed until 8 days after inoculation. In contrast, in plants, tbe increases continued up to 7 days after inoculation. In addition, one isoperoxidase appeared 2-3 days after inoculation only in tbe incompatible interaction.lie separations revealed tbat l:)asic isoperoxidases increased after inoculation as well. In tbe group of small 8S1C isoenzymes, two new bands appeared following inoculation. Only slight differences were seen between tbe **o isolines.Injecting an elicitor isolated from germinated urediniospores into tbe intercellular spaces of wbeat lea\-es induces Epical symptoms of tbe resistant reaction in botb isolines. Correspondingly, tbe isoperoxidase pattern of tbê compatible interaction, including tbe resistance related isoenzyme, was induced in botb isolines. I he results are compared witb previously reported cbanges in enzyme activities of tbe lignin biosyntbetic Pathway, including tbe total activity of peroxidase. Tbe relationship of different isoenzymes to tbe lignification sponse as a decisive mechanism of the hypersensitive resistant reaction is discussed.

Ganglioside GM1 3H-labelled at the terminal galactose was added to astrocyte cell cultures. GM1 incorporation was studied in the two typical forms of astrocytes in cell culture of flat and stellate morphology. There was a strong time- and concentration-dependent increase in GM1 incorporation for both cell types of astrocytes. The incorporation of GM1 into the stellate form increased continuously up to 48 h (maximum time studied), while the incorporation into the flat form reached a plateau at the same time. After 2 h of GM1 incubation additional gangliosides appeared; the latter resulted from the metabolism of the GM1 incorporated, indicating that astrocytes in cell culture can biosynthesize more complex gangliosides. To confirm that GM1 was indeed incorporated into astrocytes, two other different approaches were used. Astrocyte cells treated with 3H-GM1 were visualized using autoradiography. The specific marker for GM1, rhodamine-labelled choleratoxin, was used to detect the incorporated GM1 using fluorescence microsocpy. In both cases GM1 treated cells were intensely labelled. These observations indicate that exogenous GM1 ganglioside can also be integrated into the astrocyte membranes as occurs in other types of cells and membranes.