Mobilization of respiratory metabolism in potato tubers by carbon dioxide

Applying high concentrations of CO₂ to whole potato tubers stimulated a rapid and pronounced respiratory gas exchange, which persisted for a prolonged time. The upsurge in respiration was proportional to the applied CO₂ concentrations and was further augmented by high O₂ levels. Tests using whole potatoes, or potato tissue slices from tubers previously treated with CO₂, indicated that the rapid CO₂-induced respiration is sensitive to cyanide during the first 24 hours of CO₂ application. The respiratory rise cannot be attributed to the emergence of a cyanide-resistant alternative electron transport pathway, although prolonged applications of CO₂, up to 72 hours, led to a gradual development of the pathway. CO₂-stimulated respiration was accompanied by a pronounced decline in the content of starch and glucose 6-phosphate, suggesting an active utilization of respiratory substrates. The ATP content in the CO₂-treated potatoes increased markedly, resembling similar increases in tissues undergoing respiratory upsurge.     

Regulation of sucrose and starch metabolism in potato tubers in response to short-term water deficit

To investigate the effect of water stress on carbon metabolism in growing potato tubers (Solanum tuberosum L.), freshly cut and washed discs were incubated in a range of mannitol concentrations corresponding to external water potential between 0 and −1.2 MPa. (i) Incorporation of [¹⁴C]glucose into starch was inhibited in water-stressed discs, and labeling of sucrose was increased. High glucose overrode the changes at low water stress (up to −0.5 MPa) but not at high water stress. (ii) Although [¹⁴C]sucrose uptake increased in water-stressed discs, less of the absorbed [¹⁴C]sucrose was metabolised. (iii) Analysis of the sucrose content of the discs confirmed that increasing water deficit leads to a switch, from net sucrose degradation to net sucrose synthesis. (iv) In parallel incubations containing identical concentrations of sugars but differing in which sugar was labeled, degradation of [¹⁴C]sucrose and labeling of sucrose from [¹⁴C]glucose and fructose was found at each mannitol concentration. This shows that there is a cycle of sucrose degradation and resynthesis in these tuber discs. Increasing the extent of water stress changed the relation between sucrose breakdown and sucrose synthesis, in favour of synthesis. (v) Analysis of metabolites showed a biphasic response to increasing water deficit. Moderate water stress (0–200 mM mannitol) led to a decrease of the phosphorylated intermediates, especially 3-phosphoglycerate (3PGA). The decrease of metabolites at moderate water stress was not seen when high concentrations of glucose were supplied to the discs. More extreme water stress (300–500 mM mannitol) was accompanied by an accumulation of metabolites at low and high glucose. (vi) Moderate water stress led to an activation of sucrose phosphate synthase (SPS) in discs, and in intact tubers. The stimulation involved a change in the kinetic properties of SPS, and was blocked␣by protein phosphatase inhibitors. (vii) The amount of ADP-glucose (ADPGlc) decreased when discs were incubated on 100 or 200 mM mannitol. There was a strong correlation between the in vivo levels of ADPGlc and 3PGA when discs were subjected to moderate water stress, and when the sugar supply was varied. (viii) The level of ADPGlc increased and starch synthesis was further inhibited when discs were incubated in 300–500 mM mannitol. (ix) It is proposed that moderate water stress leads to an activation of SPS and stimulates sucrose synthesis. The resulting decline of 3PGA leads to a partial inhibition of ADP-glucose pyrophosphorylase and starch synthesis. More-extreme water stress leads to a further alteration of partitioning, because it inhibits the activities of one or more of the enzymes involved in the terminal reactions of starch synthesis. Received: 26 August 1996 / Accepted: 5 November 1996     

In situ staining of activities of enzymes involved in carbohydrate metabolism in plant tissues.

A powerful technique is described to localize the activities of a range of enzymes in a wide variety of plant tissues. The method is based on the coupling of the enzymatic reaction to the reduction of NAD and subsequent reduction and precipitation of nitroblue tetrazolium. Enzymes that did not reduce NAD could be visualized by coupling their activities to glucose-6-phosphate dehydrogenase activity via one or more intermediary 'coupling' enzymes. The method is shown to be applicable for the detection of the activities of hexokinase, fructokinase, sucrose synthase, uridine 5'-diphospho-glucose pyrophosphorylase, ADP-glucose pyrophosphorylase, phosphoglucomutase, and phosphoglucose isomerase. It could be used for all tissues tested, including green leaves, stems, roots, fruits, and seeds. The method is specific, very sensitive, and has a high spatial resolution, giving information at the cellular and the subcellular level. The localization of sucrose synthase, invertase, and uridine 5'-diphospho-glucose pyrophosphorylase in transgenic potato plants, carrying a cytokinin biosynthesis gene, is studied and compared with wild-type plants.     

The metabolism of histone fractions. VI. Differences in the phosphorylation of histone fractions during the cell cycle

Phosphorylation of histone fractions in the presence and absence of DNA synthesis was measured using the new “isoleucine-limiting” method for synchronizing Chinese hamster cells in early G₁-phase. Using preparative electrophoresis, histone f1 phosphorylation was found to be dependent upon cell-cycle position, being absent in G₁-arrested and G₁-traversing cells and active in the S-phase. The absence of f1 phosphorylation in G₁-arrested cells, which are known to exhibit f1 turnover, indicates that f1 phosphorylation is not an obligatory part of the f1 turnover process. In contrast to histone f1, it was found that histone f2a2 phosphorylation is independent of cell-cycle position, occurring with equal magnitude in the G₁-traversing state when DNA synthesis is essentially absent and in the S-phase when DNA synthesis is active. When cells were arrested in the G₁-state by isoleucine deprivation, f2a2 phosphorylation continued to be active, occurring at 56% of the rate observed in the G₁-traversing state. These results indicate that phosphorylation of histone f2a2 is independent of f2a2 synthesis, independent of DNA synthesis, and independent of histone f1 phosphorylation. Because f2a2 is actively phosphorylated in G₁-arrested cells known to be active in the synthesis of various types of RNA (including messenger) as well as in G₁-traversing and S-phase cells, we feel that phosphorylation of histone f2a2 should continue to be considered in models concerning activation of DNA template activity.     

Aerobic and anaerobic carbohydrate metabolism and egg production of Schistosoma mansoni in vitro.

When S. mansoni adults were cultured in vitro for 12 days in a diphasic medium, their gross morphology, motor activity, frequency of sexual pairings, rates of glucose utilization and of lactic acid production were the same in the presence (90% N2/5% O2/5% CO2) or absence (95% N2/5% CO2) of oxygen. Therefore, no Pasteur effect, nor any reduction in lactic acid formation, was demonstrable under aerobic conditions. While aerobic conditions did not affect the rate of glycolysis, they had a marked effect on egg production. In the presence of oxygen, the rate of egg-laying reached a maximum between days 4 and 6. The average number of viable eggs produced per worm pair during this period was 118 (Sx equals 2.2), which is within the overall range (68 to 248) recorded by others for this same strain in vivo. Conversely, under anaerobic conditions in vitro, virtually no eggs were laid. It remains to be determined whether oxidative metabolism actually is required for energy to produce eggs, or whether some reaction yielding no ATP is essential for completion of their developmental process, such as tanning of the eggshall brought about by the oxidation of some phenolic compounds.     

Studies on the intermediary carbohydrate metabolism of aquatic animals; the distribution of acid-soluble phosphorus and certain enzymes in dolphin tissues

1. Liver, kidney, brain, skeletal muscle, and cardiac muscle from one newborn and three adult long-snouted dolphins (Stenella plagiodon) were obtained for enzyme studies. 2. All of the dolphin tissues exhibited cytochrome oxidase, succinic dehydrogenase, and malic dehydrogenase activity. Considerable differences in the enzyme activities of the various tissues were noted, with cardiac muscle exhibiting the highest respiratory enzyme activity. The enzyme activities of dolphin tissues were lower than those of the corresponding rat tissues. 3. All of the dolphin tissues exhibited adenosine triphosphatase activity which was accelerated by magnesium and manganese but, in contrast to rat tissues, was only slightly activated by calcium. 4. Measurements of the distribution of acid-soluble phosphorus in dolphin tissues indicated that glycolysis in all of the tissues examined proceeded through the Emden-Meyerhof phosphorylation scheme. 5. The average glycogen content of dolphin skeletal muscle was 0.98 per cent as compared with 0.16 to 0.20 per cent for rat skeletal muscle. The high glycogen content of dolphin skeletal muscle indicates a ready source of substrate for glycolysis even during submergence when the blood supply may be differentially shunted to other organs. 6. Measurements of the organ weights of dolphins showed that the lungs occupy over three times and the liver one-half as much of the total body weight as do these organs in the rat. The heart and the thyroid gland of the dolphin are also larger in proportion to the total body weight than in the rat while the relative weights of the other tissues in the two species are about the same.