Evidence for Na-Independent HCO(3) Uptake by the Cyanobacterium Synechococcus leopoliensis

At low levels of dissolved inorganic carbon (DIC) and alkaline pH the rate of photosynthesis by air-grown cells of Synechococcus leopoliensis (UTEX 625) was enhanced 7- to 10-fold by 20 millimolar Na⁺. The rate of photosynthesis greatly exceeded the CO₂ supply rate and indicated that HCO₃⁻ was taken up by a Na⁺-dependent mechanism. In contrast, photosynthesis by Synechococcus grown in standing culture proceeded rapidly in the absence of Na⁺ and exceeded the CO₂ supply rate by 8 to 45 times. The apparent photosynthetic affinity (K_½) for DIC was high (6-40 micromolar) and was not markedly affected by Na⁺ concentration, whereas with air-grown cells K_½ (DIC) decreased by more than an order of magnitude in the presence of Na⁺. Lithium, which inhibited Na⁺-dependent HCO₃⁻ uptake in air-grown cells, had little effect on Na⁺-independent HCO₃⁻ uptake by standing culture cells. A component of total HCO₃⁻ uptake in standing culture cells was also Na⁺-dependent with a K_½ (Na⁺) of 4.8 millimolar and was inhibited by lithium. Analysis of ¹⁴C-fixation during isotopic disequilibrium indicated that standing culture cells also possessed a Na⁺-independent CO₂ transport system. The conversion from Na⁺-independent to Na⁺-dependent HCO₃⁻ uptake was readily accomplished by transferring cells grown in standing to growth in cultures bubbled with air. These results demonstrated that the conditions experienced during growth influenced the mode by which Ssynechococcus acquired HCO₃⁻ for subsequent photosynthetic fixation.     

The Effect of pH, O(2), and Temperature on the CO(2) Compensation Point of Isolated Asparagus Mesophyll Cells

The effect of pH, O₂ concentration, and temperature on the CO₂ compensation point (Г[CO₂]) of isolated Asparagus sprengeri Regel mesophyll cells has been determined in a closed, aqueous environment by a sensitive gas-chromatographic technique. Measured values range between 10 and 100 microliters per liter CO₂ depending upon experimental conditions. The Г(CO₂) increases with increasing temperature. The rate of increase is dependent upon the O₂ concentration and is more rapid at high (250-300 micromolar), than at low (30-60 micromolar), O₂ concentrations. The differential effect of temperature on Г(CO₂) is more pronounced at pH 6.2 than at pH 8.0, but this pH-dependence is not attributable to a direct, differential effect of pH on the relative rates of photosynthesis and photorespiration, as the O₂-sensitive component of Г(CO₂) remains constant over this range. The Г(CO₂) of Asparagus cells at 25°C decreases by 50 microliters per liter when the pH is raised from 6.2 to 8.0, regardless of the prevailing O₂ concentration. It is suggested that the pH-dependence of Г(CO₂) is related to the ability of the cell to take up CO₂ from the aqueous environment. The correlation between high HCO₃⁻ concentrations and low Г(CO₂) at alkaline pH indicates that extracellular HCO₃⁻ facilitates the uptake of CO₂, possibly by increasing the flux of inorganic carbon from the bulk medium to the cell surface. The strong O₂− and temperature-dependence of Г(CO₂) indicates that isolated Asparagus mesophyll cells lack an efficient means for concentrating intracellular CO₂ to a level sufficient to reduce or suppress photorespiration.     

Effect of serial intrauterine dimethyl sulfoxide infusions on the incidence of periglandular fibrosis in category II horse endometria

High concentrations of dimethyl sulfoxide (DMSO) have been shown to cause gross structural changes in collagen fibers in vitro. As endometrial fibrosis is a major cause of infertility in mares, the effect of serial DMSO infusions on periglandular fibrosis of Category II endometria was investigated. Initially, six mares with Category I endometria were serially infused with DMSO to determine whether such therapy would incite fibrosis. Four mares, serially infused with saline, served as controls in each experiment. One hundred milliliters of 75% DMSO was infused initially, followed by the same volume of 25% DMSO daily for 6 d. Endometrial biopsies obtained 21 d after the last infusion displayed no significant difference in the incidence of periglandular fibrosis when compared with the Day 0 biopsies. Examination of treated uteri at necropsy showed no gross evidence of adhesions or ulcerations.     

Failure of embryos from bluetongue infected cattle to transmit virus to susceptible recipients or their offspring

Sixty heifers were infected with bluetongue virus (BTV) by the bites of the vector and by inoculation with insect origin virus. During the acute and convalescent stages of the infection, embryos were collected nonsurgically from these animals and washed according to the recommendations of the International Embryo Transfer Society (1). No BTV was isolated from 77 of these embryos when they were inoculated onto cell culture and into embryonating chicken eggs. There was no evidence of lateral BTV transmission when 231 of these embryos were transferred into susceptible recipients, nor was there evidence of vertical BTV transmission to the 88 calves resulting from these transfers. Another six donors that were assumed to have recovered from a natural infection of BTV, were added to the study to increase the probability of obtaining embryos from a persistently infected BTV carrier. However, it was determined later that these animals had not been infected with BTV but with the closely-related epizootic hemorrhagic disease virus (EHDV). Embryos were collected from these donors and washed as above. Neither BTV nor EHDV was isolated from 26 of these embryos by the inoculation of cell culture and embryonating chicken eggs. There was no evidence of lateral BTV or EHDV transmission to recipients of 15 of these embryos or of vertical BTV or EHDV transmission to the resulting 7 calves. However, two recipients of embryos from one of these donors developed antibodies to BTV 6 to 9 months after transfer. Passive antibodies to BTV were also detected in their calves. There is good evidence that these two recipients acquired BTV from natural exposure to infected insect vectors and not from the transferred embryos.     

Light-Dependent Tyrosine Phosphorylation in the Cyanobacterium Prochlorothrix hollandica

A light-dependent tyrosine kinase activity is present in soluble extracts from the cyanobacterium Prochlorothrix hollandica. The substrate of this tyrosine kinase activity is a soluble 88-kD protein that is phosphorylated when cultures of P. hollandica are adapted to high-light conditions. This phosphoprotein was identified by probing western blots of 32P-labeled soluble proteins from P. hollandica with an antibody specific for phosphotyrosine. This specificity was confirmed by competition experiments in which the antibody binding was abolished completely in the presence of excess phosphotyrosine but not phosphoserine and phosphothreonine. The kinetics of phosphorylation in vivo were determined by probing western blots with this antibody. Within 1 h following a switch from extended darkness to high light (200 [mu]mol photons m-2 s-1), the 88-kD protein was detectable upon India ink staining of western blots. After 3 h, the antibody recognized the phosphorylated form of this polypeptide. Within 6 h of a downshift from high to low light, the 88-kD protein was dephosphorylated. In vitro phosphorylation studies also showed that cell extracts can phosphorylate a tyrosine-containing artificial substrate; acid hydrolysis of both the artificial substrate and the 88-kD protein showed that phosphorylation occurred exclusively on tyrosine residues. Finally, experiments with high-light-adapted Synechococcus sp. PCC7942 suggest that a similar tyrosine phosphorylation event occurs in a phycobilisome-containing cyanobacterium.     

Inhibition of microsporidian spore germination

Microsporidia are obligate intracellular parasites that are increasingly recognized as significant causes of disease in AIDS patients. Gordon Leitch, Govinda Visvesvara and Qing He here describe the deployment of the microsporidian spore infection apparatus, the polar filament, and show how this may be a useful site for chemotherapeutic interdiction of the infections caused by these parasites.