Inheritance of leaf peroxidase isoenzymes in Nicotiana alata and linkage with the S-incompatibility locus

Summary Genetic analysis of peroxidase isoenzymes observed by electrophoresis shows that each of the two cathodic bands are controlled by one gene, respectively, P_I and P_II. Each gene has two allele forms; presence of activity (dominant) and absence of activity (recessive). The same situation is found for one anodic band; the three other anodic bands are controlled by a single gene with three active allele forms. No progenies seem to be produced from gametes P _I ^- P _II ^- (no activity of P_I or P_II). Investigation of the incompatibility system and the isoperoxidases demonstrates that the loci P_I, P_II and S are located in the same chromosome. P_I is closely linked to the S locus (3 cM); the distance between P_II and the S locus is 34 cM.     

A mathematical model of kinetics of the biosynthesis of tetracyclines

Summary A mathematical model simulating the behaviour or Streptomyces aureofaciens in batch culture under conditions when tetracyclines are synthesized in excessive amounts has been formulated. The response of the mathematical model to the experimental conditions applied corresponds with data obtained in the experiments. The mathematical model demonstrated that the level of tetracycline production is determined during the period of culture growth beginning with exhaustion of inorganic phosphate from the medium and ending with inhibition of the synthesis of enzymes caused by the synthesized tetracyclines. Further tetracycline synthesis is then proportional to the amount of enzymes synthesized in this interval.List of symbols E Activity of ACT-oxygenase (10×nkat/g) - P Product concentration (mg/l) - k ₁-k ₆ Rate constants - K _S Saturation constant (g sugar/l) - K _I1 Inhibition constant (mg product/l) - K _I2 Inhibition constant (mM phosphate/l) - K _I3 Inhibition constant (mg product/l) - S ₁ Substrate sucrose (g sugar/l) - S ₂ Substrate concentration — phosphate (mM/l) - r _P Specific rate of product formation (mg product/g · h) - r _E Specific rate of enzyme synthesis (10×nkat/g² · h), Expressed by activity units - t Cultivation time (hour) - X Biomass dry weight (g/l) - Y _S/X Yield coefficient - Specific growth rate (h^-1)     

The comparison of lectins from albumin complexes of certain representatives of the speciesPhaseolus vulgaris

Using biospecific chromatography on D-Glc-Separon-fetuin, lectins were isolated from seed albumin complexes of four cultivars ofPhaseolus vulgaris (Veltruská Saxa, Vainica Saavegra, Krupnaya sakharnaya, Olympia) andPhaseolus vulgaris ssp.aborigineus (wild form, considered to be one of the ancestors of cultivated beans). In the lectins isolated the agglutinating activity against human erythrocytes of the A, B, and O groups was estimated, as well as against trypsin-treated and non-treated rabbit erythrocytes. Further analyses involved their mitogenic activity against lymphocytes of murine spleen, their isoelectric points by isoelectric focusing in polyacrylamide gels, and eventually their immunospecific similarity with the lectins of the standard cultivar ofPhaseolus vulgaris, Veltruská Saxa. The lectins of all taxa were mitogenic, but differed from one another in their agglutinating activity and in the number and isoelectric points of the zones, as revealed by both isoelectric focusing and immunoelectrophoresis. In the case of the cultivar Vainica Saavegra, which is a seggregating population, even the lectins of individual seed groups were different.     

Bactrodesmiastrum,a new genus of lignicolousHyphomycetes

A new genusBactrodesmiastrum Hol.-Jech. is established for a fungus of dematiaceous hyphomycetes collected on decaying wood ofFagus sylvatica in Czechoslovakia. The only species,B. obscurum Hol.-Jech. is described and illustrated.     

Effect of the adrenergic beta receptor blocker propranolol on the dilatation of cerebrocortical vessels evoked by arterial hypoxia

In order to elucidate the importance of adrenergic beta receptors in the regulation of cerebral microcirculation during arterial hypoxia, chloralose anaesthetized cats were treated with propranolol hydrochloride. Arterial hypoxia, lasting for approximately 4 min, was induced by respiring the animals with a gas mixture containing 7% oxygen balanced in nitrogen gas. Arterial hypoxia was induced in the same animals before and during continuous infusion of propranolol (0.05 mg/kg/min into the lingual artery). Cerebrocortical vascular volume ( CVV ) and NADH fluorescence were measured through a cranial window with a microscope fluororeflectometer . Control arterial hypoxia (no treatment) increased CVV and NADH reduction by 22.2 +/- 2% and 20.4 +/- 2.1%, respectively. Following 1 mg/kg propranolol treatment arterial hypoxia of the same severity resulted in only approximately 2/3 of the CVV response obtained during the control arterial hypoxia. Since arterial hypoxia induced similar changes in arterial blood gases, arterial blood pressure, and intracranial pressure in both cases, our results indicate that the cortical vasodilatation occurring during arterial hypoxia is due, at least in part, to the activation of adrenergic beta receptors.     

Molecular biology of photosynthesis

Book reviews

Molecular biology of photosynthesisGovindjee, H.J. Bohnert, W. Bottomley, D.A. Bryant, J.E. Mullet, W.L. Ogren, H. Pakrasi, and C.R. Somerville (Eds.), Dordrecht: Kluwer Academic Publishers, 1989. xxvii + 815 pages. £130.00. ISBN 0-7923-0097-1     

Minor and trace elements in human milk from Guatemala,Hungary, Nigeria,Philippines, Sweden,and Zaire

Concentrations of As, Ca, Cd, Cl, Co, Cr, Cu, F, Fe, Hg, I, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sb, Se, Sn, V, and Zn were determined in human whole milk samples from Guatemala, Hungary, Nigeria, Philippines, Sweden, and Zaire; in most of these countries, three groups of subjects representing different socioeconomic conditions were studied. Analytical quality control was a primary consideration throughout. The analytical techniques used were atomic absorption spectrophotometry, atomic emission spectrometry with an inductively coupled plasma, colorimetry, electrochemistry, using an ion-selective electrode and neutron activation analysis. The differences between median concentrations of Ca, Cl, Mg, K, Na, and P (minor elements) were lower than 20% among the six countries. Among trace elements, concentrations observed in Filipino milk for As, Cd, Co, Cr, Cu, F, Fe, Mn, Mo, Ni, Pb, Sb, Se, and V were higher than for milk samples from other countries. The remaining five countries showed a mixed picture of high and low values. In the case of at least some elements, such as, F, I, Hg, Mn, Pb, and Se, the environment appears to play a major role in determining their concentrations in human milk. The nutritional status of the mother, as reflected by her socioeconomic status, does not appear to influence significantly the breast milk concentrations of minor and trace elements. Significant differences exist between the actual daily intakes observed in this study and current dietary recommendations made by, for example, WHO and the US National Academy of Sciences. These differences are particularly large (an order of magnitude or more!) for Cr, F, Fe, Mn, and Mo; for other elements, such as, Ca, Cu, Mg, P, and Zn, they amount to at least a factor 2. In the opinion of the present authors, these findings point to the need for a possible reassessment of the dietary requirements of young infants with respect to minor and trace elements, particularly for the elements Ca, Cr, Cu, F, Fe, Mg, Mn, Mo, P, and Zn.     

Influence of extracellular magnesium on the contractile and endothelium-dependent dilatory responses of feline mesenteric arteries.

To clarify the effect of extracellular magnesium on the vascular reactivity of feline isolated mesenteric arteries, the effects of slight alterations in the extracellular magnesium concentration on the contractile and endothelium-dependent dilatory responses were investigated in vitro. The contractions, induced by noradrenaline 10(-8)-10(-5) M, were not affected in the mesenteric artery at low extracellular magnesium (0.8 mM versus to the normal, 1.2 mM). High (1.6 and 2.0 mM) magnesium exerted a modest inhibitory effect on the contractile responses. This depression of the contraction was accompanied with a significant shift to the right in the EC50 value for noradrenaline. The endothelium-dependent relaxations induced by acetylcholine 10(-8)-10(-5) M, were inhibited by high (1.6 and 2.0 mM) magnesium. Lowering of the extracellular magnesium concentration to 0.8 mM, however, failed to alter the dilatory potency of acetylcholine. The depression of the dilatory responses was also accompanied with a shift to the right in the EC50 values for acetylcholine. The present results show, that contractions and endothelium-dependent relaxations of the mesenteric artery are modulated by the extracellular magnesium asymmetrically: slight magnesium deficiency does not affect these responses, whereas elevation of the concentration of this ion inhibits both processes. Extracellular magnesium probably affects rather the binding of these contractile and endothelium-dependent dilatory agonists to their receptors than the calcium influx into the endothelial- and smooth muscle cells in this vessel.