Localization of Some Enzymes of β-oxidation of Fatty Acids in the Peroxisomes of Tetrahymena*

Mitochondria and peroxisomes were prepared from homogenates of Tetrahymena pyriformis by sedimentation through sucrose gradients. Catalase and isocitrate lyase served as peroxisomal markers; lactic dehydrogenase and glutamic dehydrogenase as mitochondrial markers. Acetyl-CoA synthetase, octanoyl-CoA synthetase, palmitoyl-CoA synthetase, 3-β hydroxyacyl CoA dehydrogenase, and thiolase activities were found in both the peroxisomes and the mitochondria. It is suggested that β-oxidation of fatty acids accurs in both organelles in Tetrahymena.     

Concanavalin A-Sepharose Chromatography of Hexosaminidase Isozymes Secreted By Tetrahymena*

Tetrahymena pyriformis strain HSM secretes 4 isozymes of hexosaminidase. Purified isozymes B₁ and B₂ are eluted from the void volume of a concanavalin A-Sepharose column, suggesting that they are not glycosylated. Purified isozymes A₁ and A₂ bind to the column and are eluted at ～0.1 M α-methylmannoside, suggesting that these isozymes are glycoproteins. In agreement with earlier deductions based on a differential kinetic assay for the A and B isozymes, the elution pattern of hexosaminidase activity from material secreted by cells grown to early and late stationary phase was consistent with these secretions containing primarily the B and the A isozymes, respectively.     

Ultraviolet light and the mitotic cycle in the sea urchin''s egg

The effect of ultraviolet light in delaying certain events in the cell division cycle has been examined. The time to fusion of the egg and sperm nucleus is not affected by doses of ultraviolet that cause considerable delay in other parts of the cycle. The principal delay occurs before anaphase. Between anaphase and cleavage there is only slight delay. The "refractory period" during which the radiation does not delay the immediate cycle of cell division, does not seem to represent complete refractoriness of the mitotic cycle to interference during this period.     

Photodynamic hemolysis at low temperatures

It is shown that photodynamic hemolysis may occur at –79°C. if the erythrocytes are suspended in a solution containing 70 per cent glycerol which prevents hemolysis by freezing; but that there is no hemolysis under the same conditions at –210°C. At the higher temperature the viscosity of the solution is still low enough to permit appreciable movement of molecules, whereas at the lower temperature the molecules must be virtually immobile. The findings are compatible with the idea that the dye molecule acts in a cycle, bringing about successive oxidations by O₂ molecules, as has been shown for photodynamic hemolysis at room temperature. The assumption of a combination between dye, O₂, and substrate does not explain photosensitized hemolysis in the semi-solid state. The mechanism of photosensitized oxidation by O₂ is discussed.     

Is stimulation of leaf photosynthesis by elevated carbon dioxide concentration maintained in the long term? A test with Lolium perenne grown for 10 years at two nitrogen fertilization levels under Free Air CO2Enrichment (FACE)

Photosynthesis is commonly stimulated in grasslands with experimental increases in atmospheric CO₂ concentration ([CO₂]), a physiological response that could significantly alter the future carbon cycle if it persists in the long term. Yet an acclimation of photosynthetic capacity suggested by theoretical models and short‐term experiments could completely remove this effect of CO₂. Perennial ryegrass (Lolium perenne L. cv. Bastion) was grown under an elevated [CO₂] of 600 µmol mol^?1 for 10 years using Free Air CO₂Enrichment (FACE), with two contrasting nitrogen levels and abrupt changes in the source : sink ratio following periodic harvests. More than 3000 measurements characterized the response of leaf photosynthesis and stomatal conductance to elevated [CO₂] across each growing season for the duration of the experiment. Over the 10 years as a whole, growth at elevated [CO₂] resulted in a 43% higher rate of light‐saturated leaf photosynthesis and a 36% increase in daily integral of leaf CO₂ uptake. Photosynthetic stimulation was maintained despite a 30% decrease in stomatal conductance and significant decreases in both the apparent, maximum carboxylation velocity (V_c,max) and the maximum rate of electron transport (J_max). Immediately prior to the periodic (every 4–8 weeks) cuts of the L. perenne stands, V_c,max and J_max, were significantly lower in elevated than in ambient [CO₂] in the low‐nitrogen treatment. This difference was smaller after the cut, suggesting a dependence upon the balance between the sources and sinks for carbon. In contrast with theoretical expectations and the results of shorter duration experiments, the present results provide no significant change in photosynthetic stimulation across a 10‐year period, nor greater acclimation in V_c,max and J_max in the later years in either nitrogen treatment.     

Effects of Mitochondrial Protein Synthesis Inhibitors on the Incorporation of Isoleucine into Plasmodium falciparum In Vitro1

Plasmodium falciparum was grown in human erythrocytes in vitro and the effect of chloramphenicol, erythromycin, and tetracycline on growth and maturation of the parasites and on their ability to incorporate [³H]isoleucine into protein was observed. Exposure of rings to high concentrations of chloramphenicol had little effect on subsequent maturation of the rings whereas brief (4 h) exposure of trophozoites caused a dose-dependent inhibition of subsequent ring formation. Incorporation of [³H]isoleucine into protein was not affected during at least 6 h of exposure to high concentration of the three drugs examined, but appreciable inhibition was observed after 21 h, with chloramphenicol being the least effective inhibitor. These results suggest that there is a stage-specific effect of inhibition of mitochondrial protein synthesis on subsequent development and that the mitochondria are essential for growth and development even though they lack a functional Krebs cycle.     

Isolation and characterization of variant wheat cultivars for ABA sensitivity

Genetic variants for abscisic acid (ABA) sensitivity are important for investigating the role of ABA sensitivity in conditioning plant response to environmental stress, and especially to those soil conditions that may elicit a root-mediated hormonal signal. This study was performed in order to isolate variation in ABA sensitivity among wheat (Triticum aestivum and T. durum) cultivars, as characterized by two plant responses: (i) shoot growth reduction in response to 5×10^?2mol m^?3 ABA (racemic) in the root medium of hydroponically grown plants, and (ii) changes in transpiration and gas exchange in a bioassay of detached leaves (leaflaminac) infused with 10^?4mol m^?3 ABA. Very significant (P≤0.01) and repeatable differences were found among 36 wheat cultivars and 19 landraces in the growth rate in ABA-containing nutrient solutions, expressed as a percentage of the growth rate in control nutrient solutions (ABA/control ratio). In duplicate experiments, the ABA/control ratio ranged between 60 and 83% for the least sensitive cultivars (V2151-3, Bethlehem, K1056 and Sunstar) and between 9 and 19% for the most sensitive cultivars (Sundor, Comet, Barkaec and V5). In the transpiration bioassay, performed with seven selected cultivars, it was found that the reductions in transpiration of ABA-infused leaves corresponded very well with the reductions in growth in response to ABA in the root media. Measurement of gas exchange in the detached leaves of two cultivars differing in ABA sensitivity (Bethlehem and Sundor) showed that variable ABA sensitivity was expressed very well in the stomatal conductance, carbon exchange rate (CER) and photosynthetic capacity (CER/C_i ratio) of the leaf. These results therefore allowed us to isolate wheat variants for ABA sensitivity and to conclude that, while ABA sensitivity is expressed in the growth of plants challenged by ABA in the root medium, the control of sensitivity resides, at least partly, in the leaf.     

Delay of cleavage of the Arbacia egg by ultraviolet radiation

While our data do not permit us to state the exact locus or mode of action of ultraviolet radiation in the Arbacia egg, certain general conclusions may be reached. The amount of delay of cleavage of these eggs is determined by two principal factors: (1) The extent of an effect, resulting from photochemical action induced by ultraviolet radiation, which is reversible in a biological sense, the reversibility not being directly dependent upon the process of cell division. (2) The sensitivity of the cell division process to the effects of the ultraviolet-induced photochemical reaction. This factor varies with the stage of cell division, the cell being insensitive during a period corresponding to most of mitosis. It seems likely that these findings may apply to cell division in general, but, since the quantitative relationships observed must, in this case, reflect the integration of two semi-independent factors, the over-all picture may appear quite different for different kinds of cells.