Influence of salicylic acid on biosynthesis of nucleic acids in <Emphasis Type=Italic>Polyscias filicifolia</Emphasis> cell culture under the action of unfavorable temperatures

Amounts of DNA and RNA was increased (from 20 to 50%) in the presence of salicylic acid in cells of Polyscias filicifolia tissue culture grown in Murachige-Skoog modified medium. Treatment of the tissue culture with salicylic acid resulted in a significant increase of intracellular protein and decrease of proteolytic activity. In cells treated with salicylic acid, the amounts of DNA and RNA was higher in conditions of heat (3 h, 45°C) and cold (24 h, 7°C) stress in comparison with cells exposed to unfavorable temperatures without the initial treatment with salicylic acid.     

Recent breakthroughs in the study of salicylic acid biosynthesis

Salicylic acid is an important regulator of induced plant resistance to pathogens. Consequently, the biosynthesis of salicylic acid and its regulation has received a lot of attention. Salicylic acid can be made from phenylalanine via cinnamic and benzoic acid. Recently, genetic studies in Arabidopsis have shown that salicylic acid is made in the chloroplast from isochorismate, a pathway that is known to operate in prokaryotes.     

Melting temperatures of nucleic acids: discrepancies in analysis

Melting temperature, T(m), is an important property of nucleic acid duplexes. It is typically determined from spectroscopic or calorimetric melting experiments. More than one analytical method has been used to extract T(m) values from experimental melting data. Unfortunately, different methods do not give the same results; the same melting data can be assigned different T(m) values depending upon which method is used to process that data. Inconsistencies or systematic errors between T(m)s reported in published data sets can be significant and add confusion to the field. Errors introduced from analysis can be greater than experimental errors, ranging from a fraction of degree to several degrees. Of the various methods, the most consistent and meaningful approach defines melting temperature as the temperature at the transition midpoint where half of the base pairs are melted and standard free energy is zero. Assuming a two-state melting behavior, we present here a set of general equations that can be used to reconcile these analytical T(m) differences and convert results to the correct melting temperatures at the transition midpoint. Melting temperatures collected from published sources, which were analyzed using different methods, can now be corrected for these discrepancies and compared on equal footing. The similar corrections apply to T(m) differences between calorimetric and spectroscopic melting curves. New algorithm for selection of linear sloping baselines, 2nd derivative method, is suggested, which can be used to automate melting curve analysis.     

Influence of testosterone on polyunsaturated fatty acid biosynthesis in Sertoli cells in culture

Sertoli cells play a central role in spermatogenesis, its development and regulation. They are target cells for androgen action in the seminiferous tubules. The Sertoli cell is considered to be the most important cell type in the testis with regard to essential fatty acid metabolism. We studied the response to testosterone of cultured Sertoli cells from immature rats by determining the fatty acid composition of total cellular lipids as well as by the biosynthesis of polyunsaturated fatty acids. Fatty acid methyl esters were analysed by gas liquid chromatography and radiochromatography. Two doses of testosterone were tested (150 and 300 ng ml(-1)). Significant differences were found in fatty acids derived from total cellular lipids after 8 days in culture in the presence of testosterone (300 ng ml(-1), for 48 h). Compared to controls, the hormone produced a significant increase of 16:1 and 18:1 n-9, and of 18:2 n-6, and a decrease of 20:4 and 22:5 n-6 in total cellular lipids. The decrease in the n-6 fatty acid ratios 20:4/20:3, 20:4/18:2 and 24:5/24:4, and the increase in 18:1n-9/18:0 and 16:1n-9/16:0 ratios were taken as an indirect signal of testosterone effects on Delta5, Delta6 and Delta9 desaturase activities. The drop in Delta5 and Delta6 desaturase activities was corroborated by analysing the transformation of [1-14C]20:3 n-6 into its higher homologues. We concluded that testosterone modifies the fatty acid pattern of cultured Sertoli cells, and this hormone is involved in polyunsaturated fatty acid biosynthesis, modulating Delta5 and Delta6 desaturases activity.     

Influence of culture conditions on the cell yield and amylases biosynthesis in continuous culture by Schwanniomyces castellii

Schwanniomyces castellii excreted -amylase and amyloglucosidase into the medium in the presence of starch. The biosynthesis and the rate of excretion were influenced by dissolved oxygen (specially for -amylase), pH of the culture and dilution rate. The cell yield observed (0.59) remained constant up to D=0.35h^-1 with starch as substrate. But in the case of growth on glucose, the yield observed was equal to 0.62 up to a dilution rate of D=0.18 h^-1. Beyond this value Y x/s decreased and ethanol was produced. The onset of fermentation dependend partly on the nature of the substrate and not only on the environment in particular on the quantity of dissolved oxygen present.     

乳杆菌对数生长期培养基滤液核酸组分分析

目的通过对乳杆菌对数生长期培养基滤液中核酸组分的分析,阐明乳杆菌DM9811对数生长期培养基滤液中核酸的性质。方法应用核酸的分离、纯化及电泳分析技术。结果乳杆菌对数生长期培养基滤液中核酸组分为RNA,其片段大小为100 bp左右。乳杆菌对数生长期培养基滤液中核酸组分为RNA,为对数期产生且呈时间依赖关系。结论核酸组分不仅仅是遗传信息的载体,还可能作为有效的信息分子。     

Influence of metal ions on the formation of mycobactin and salicylic acid in Mycobacterium smegmatis grown in static culture

Mycobacterium smegmatis was grown on trace-metal-free medium in static culture. Throughout the growth phase, the concentration of mycobactin increased continuously, reaching a maximum of about 30 to 40 mug of mycobactin/mg of cell dry weight after 6 days; the concentration of salicylic acid remained approximately constant at 1 to 2 mug of salicylic acid/mug of cell dry weight. Fe(2+) (or Fe(3+)), Zn(2+), Mn(2+), and Mg(2+) were all essential to a maximum formation of mycobactin. Optimum concentrations required were: Fe(2+), about 1.8 mum; Mn(2+) and Zn(2+), about 0.5 mum; and Mg(2+), at least 0.17 mm. Higher levels of Fe(2+) (9 to 90 mum) and Zn(2+) (2 to 7 mum) repressed mycobactin to about half the maximum value. No other cation or anion apparently is required for mycobactin biosynthesis. Salicylic acid concentration increased about fourfold when iron was omitted from the medium, but this is not as great as the increase reported previously for this strain of M. smegmatis. Mycobactin formation in another strain of M. smegmatis, NCIB 8548, showed similar dependencies on Fe(2+), Zn(2+), and Mn(2+). Maximum accumulation of mycobactin with this strain was 85 mug of mycobactin/mg of dry cell weight, under iron-deficient (1.8 mum Fe(2+)) conditions.     

Inhibition of proteoglycan biosynthesis by hyaluronic acid in chondrocytes in cell culture

The depression of proteoglycan synthesis in ten-day-old high density chondrocyte cultures was shown to be dependent on both the concentration and time of exposure of the cells to hyaluronic acid. Hyaluronic acid had no effect on the overall protein synthesis by the cultured cells. Using benzyl-β-D-xyloside an exogenous acceptor, it was shown that glycosaminoglycan biosynthesis by the chondrocytes was not affected by hyaluronic acid. It was concluded that hyaluronic acid was effecting glycosaminoglycan chain initiation, hence proteoglycan biosynthesis, either by specifically depressing the synthesis of the core protein or by repressing the activity of the xylosyltransferase.