Citrus tristeza virus: survival at the edge of the movement continuum

Systemic invasion of plants by viruses is thought to involve two processes: cell-to-cell movement between adjacent cells and long-distance movement that allows the virus to rapidly move through sieve elements and unload at the growing parts of the plant. There is a continuum of proportions of these processes that determines the degrees of systemic infection of different plants by different viruses. We examined the systemic distribution of Citrus tristeza virus (CTV) in citrus species with a range of susceptibilities. By using a "pure" culture of CTV from a cDNA clone and green fluorescent protein-labeled virus we show that both cell-to-cell and long-distance movement are unusually limited, and the degree of limitation varies depending on the citrus host. In the more-susceptible hosts CTV infected only a small portion of phloem-associated cells, and moreover, the number of infection sites in less-susceptible citrus species was substantially decreased further, indicating that long-distance movement was reduced in those hosts. Analysis of infection foci in the two most differential citrus species, Citrus macrophylla and sour orange, revealed that in the more-susceptible host the infection foci were composed of a cluster of multiple cells, while in the less-susceptible host infection foci were usually single cells, suggesting that essentially no cell-to-cell movement occurred in the latter host. Thus, CTV in sour orange represents a pattern of systemic infection in which the virus appears to function with only the long-distance movement mechanism, yet is able to survive in nature.     

Production,characteristics and applications of the cell-bound phytase of <Emphasis Type="Italic">Pichia anomala</Emphasis>

Among several yeasts isolated from dried flowers of Woodfordia fruticosa, Pichia anomala produced a high titre of cell-bound phytase. The optimization of fermentation variables led to formulation of media and selection of cultural variables that supported enhanced phytase production. The enzyme productivity was very high in fed batch fermentation in air-lift fermentor as compared to that in stirred tank fermentor. Amelioration in the cell-bound phytase activity was observed when yeast cells were permeabilized with Triton-X-100. The enzyme is thermostable and acid stable with broad substrate specificity, the characteristics that are desirable for enzymes to be used in the animal feed industry. The phytase-encoding gene was cloned and sequenced. The 3D structure of the enzyme was proposed by comparative modeling using phytase of Debaryomyces occidentalis (50% sequence identity) as template. When broiler chicks, and fresh water and marine fishes were fed with the feed supplemented with yeast biomass containing phytase, improvement in growth and phosphorus retention, and decrease in the excretion of phosphorus in the faeces were recorded. The cell-bound phytase of P. anomala could effectively dephytinize wheat flour and soymilk.     

Charge and Discharge Processes and Sodium Storage in Disodium Pyridine‐2,5‐Dicarboxylate Anode—Insights from Experiments and Theory

A combined experimental and computational study of disodium pyridine‐2,5‐dicarboxylate (Na₂PDC) is presented exploring the possibility of using it as a potential anode for organic sodium‐ion batteries. This electrode material can reversibly insert/release two Na cations per formula unit, resulting in high reversible capacity of 270 mA h g^?1 (236 mA h g^?1 after accounting for the contribution from Super P carbon) with excellent cyclability 225 mA h g^?1, with retention of 83% capacity after 100 cycles, and good rate performance with reversible capacity of 138 mA h g^?1 at a 5 C rate. The performance of disodium pyridine dicarboxylate is therefore found to be superior to that of the related and well investigated disodium terephthalate. The material shows two voltage plateaus at about 0.6 V up to Na₂₊₁PDC and then 0.4 V up to full sodiation, Na₂₊₂PDC. The first plateau is attributed to the coordination of inserted Na to nitrogen atoms with bond formation, i.e., a different mechanism from the terephthalate analog. The subsequent plateau is due to coordination to the carboxylic groups.     

The relationship between δ-aminolaevulinate synthetase induction and the concentrations of cytochrome P-450 and catalase in rat liver

The porphyrinogenic drug 2-allyl-2-isopropylacetamide causes the degradation of microsomal cytochrome P-450 and inhibits the synthesis of catalase in rat liver. The inhibition of catalase synthesis follows the induction of delta-aminolaevulinate synthetase and the consequent overproduction of haem. The allylisopropylacetamide-mediated breakdown of cytochrome P-450 is a rapid event and has a reciprocal relationship to the pattern of delta-aminolaevulinate synthetase induction. Breakdown of cytochrome P-450 appears to be one of the conditions leading to the ;derepression' of delta-aminolaevulinate synthetase.     

A model for the regulation of δ-aminolaevulinate synthetase induction in rat liver

A reciprocal relationship exists between the cytochrome P-450 content and delta-aminolaevulinate synthetase activity in adult rats. In young rats the basal delta-aminolaevulinate synthetase activity is higher and the cytochrome P-450 content is lower compared with the adult rat liver. Administration of allylisopropylacetamide neither induces the enzyme nor causes degradation of cytochrome P-450 in the young rat liver, unlike adult rat liver. Allylisopropylacetamide fails to induce delta-aminolaevulinate synthetase in adrenalectomized-ovariectomized animals or intact animals pretreated with successive doses of the drug, in the absence of cortisol. The cortisol-mediated induction of the enzyme is sensitive to actinomycin D. Allylisopropylacetamide administration degrades microsomal haem but not nuclear haem. Haem does not counteract the decrease in cytochrome P-450 content caused by allylisopropylacetamide administration, but there is evidence for the formation of drug-resistant protein-bound haem in liver microsomal material under these conditions. Phenobarbital induces delta-aminolaevulinate synthetase under conditions when there is no breakdown of cytochrome P-450. On the basis of these results and those already published, a model is proposed for the regulation of delta-aminolaevulinate synthetase induction in rat liver.     

Removal of C-ring from the CD-ring skeleton of 1alpha,25-dihydroxyvitamin D3 does not alter its target tissue metabolism significantly

It is now well established that 1alpha,25(OH)2D3 is metabolized in its target tissues through the modifications of both side chain and A-ring. The C-24 oxidation pathway is the side chain modification pathway through which 1alpha,25(OH)2D3 is metabolized into calcitroic acid. The C-3 epimerization pathway is the A-ring modification pathway through which 1alpha,25(OH)2D3 is metabolized into 1alpha,25(OH)2-3-epi-D3. During the past two decades, a great number of vitamin D analogs were synthesized by altering the structure of both side chain and A-ring of 1alpha,25(OH)2D3 with the aim to generate novel vitamin D compounds that inhibit proliferation and induce differentiation of various types of normal and cancer cells without causing significant hypercalcemia. Previously, we used some of these analogs as molecular probes to examine how changes in 1alpha,25(OH)2D3 structure would affect its target tissue metabolism. Recently, several nonsteroidal analogs of 1alpha,25(OH)2D3 with unique biological activity profiles were synthesized. Two of the analogs, SL 117 and WU 515 lack the C-ring of the CD-ring skeleton of 1alpha,25(OH)2D3. SL 117 contains the same side chain as that of 1alpha,25(OH)2D3, while WU 515 contains an altered side chain with a 23-yne modification combined with hexafluorination at C-26 and C-27. Presently, it is unknown how the removal of C-ring from the CD-ring skeleton of 1alpha,25(OH)2D3 would affect its target tissue metabolism. In the present study, we compared the metabolic fate of SL 117 and WU 515 with that of 1alpha,25(OH)2D3 in both the isolated perfused rat kidney, which expresses only the C-24 oxidation pathway and rat osteosarcoma cells (UMR 106), which express both the C-24 oxidation and C-3 epimerization pathways. The results of our present study indicate that SL 117 is metabolized like 1alpha,25(OH)2D3, into polar metabolites via the C-24 oxidation pathway in both rat kidney and UMR 106 cells. As expected, WU 515 with altered side chain structure is not metabolized via the C-24 oxidation pathway. Unlike in rat kidney, both SL 117 and WU 515 are also metabolized into less polar metabolites in UMR 106 cells. These metabolites displayed GC and MS characteristics consistent with A-ring epimerization and were putatively assigned as C-3 epimers of SL 117 and WU 515. In summary, we report that removal of the C-ring from the CD-ring skeleton of 1alpha,25(OH)2D3 does not alter its target tissue metabolism significantly.