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J E Tillberg

Publications and source records attributed to J E Tillberg.

5 recordsLinked to original sources
PubMed2000

Fructan accumulation induced by nitrogen deficiency in barley leaves correlates with the level of sucrose:fructan 6-fructosyltransferase mRNA.

Hydroponically cultivated barley plants were exposed to nitrogen (N)-deficiency followed by N-resupply. Metabolic and genetic regulation of fructan accumulation in the leaves were investigated. Fructan accumulated in barley leaves under N-deficiency was mobilized during N-resupply. The enhanced total activity of fructan-synthesizing enzymes, sucrose:sucrose 1-fructosyltransferase (EC 2.4.1.99) and sucrose:fructan 6-fructosyltransferase (6-SFT; EC 2.4. 1.10) caused by N-deficiency decreased with the mobilization of fructan during N-resupply. The activity of the barley fructan-degrading enzyme, fructan exohydrolyase (EC 3.2.1.80) was less affected by the N status. The low level of foliar soluble acid invertase activity under N-deficiency conditions was maintained during the commencement of N-resupply but increased subsequently. Further analyses by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, western blot and northern blot demonstrated that the fructan accumulation and the total activity of fructan-synthesizing enzymes correlated with the 6-SFT mRNA level. We suggest that the changes in fructan levels under N stress are intimately connected with the regulation of fructan synthetic rate which is mostly controlled by 6-SFT.

Fructans↗
PubMed1977

CO2 reduction by intact chloroplasts under a diminished proton gradient.

9-Aminoacridine has been used to monitor the intrathylakoid pH of photosynthetically competent intact chloroplasts. Values obtained from 9-aminoacridine accumulation in the chloroplasts must be corrected for light-dependent binding of 9-aminoacridine to the thylakoid membranes. During nitrite reduction by intact chloroplasts, the intrathylakoid proton concentration increased. It decreased somewhat during CO2 reduction. However, low concentrations of uncoupling amines such as NH3 or cyclohexylamine, which rapidly penetrated the chloroplast envelope and decreased the intrathylakoid proton concentration, failed to reduce, and actually stimulated, rates of CO2-dependent oxygen evolution even under rate-limiting light. In contrast, low concentrations of carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) OR NIGERICIN, WHICH INHIBITED CO2 reduction, even appeared to increase the intrathylakoid proton concentration. As indicated by measurements of the 515 nm signal of the chloroplasts, the light-induced membrane potential was not much affected by low concentrations of the uncoupling amines, but was decreased by FCCP and by high concentrations of the amines. Even in the presence of high concentrations of NH4C1, ATP/ADP ratios of illuminated chloroplasts remained far above the ratios observed in the dark. In contrast, low concentrations of FCCP were sufficient to reduce ATP/ADP ratios to the dark value even under high intensity illumination. The observations are difficult to explain within the framework of the chemiosmotic hypothesis as presently discussed.

Acridines↗
PubMed1971

Microcalorimetric Measurements of the Heat Evolution and Its Sensitivity to Dinitrophenol during Different Stages of Synchronous Cultures of Scenedesmus.

The applicability of the LKB flow microcalorimeter in a microalgal system was tested. Respiration and its sensitivity to 2,4-dinitrophenol during different stages of a synchronous culture of Scenedesmus obtusiusculus were studied. In cells harvested during the first 8 hours of illumination, heat evolution was 10 to 15 microwatts per 10 million cells and then rose to a peak of about 80 microwatts per 10 million when the cells were harvested in the beginning of the dark period, just before the onset of the divisions. Calculated per milligram dry weight, the highest values were about 140 microwatts, also obtained early in the dark period, after which the values dropped. They were roughly 90 microwatts per milligram at the onset of light and a little below 70 microwatts per milligram after 8 hours of illumination. Thus, the synthesis of new cell material does not give rise to actively respiring mitochondria during the first half of the light period, after which the situation is reversed. Low concentrations of dinitrophenol increased heat evolution, and high concentrations were inhibitory. Cells from the early stages of development were more sensitive to dinitrophenol than older cells. Young cells gave a transient peak of heat evolution even when the steady state was inhibited. Coupled oxidative phosphorylation seems necessary for substrate mobilization and transport to the mitochondria of the young cells. Possibly, young cells use mainly fatty acids and old cells carbohydrates as their main substrate for respiration.

Journal Article↗