A model for seasonal phytoplankton blooms

We analyse a generic bottom-up nutrient phytoplankton model to help understand the dynamics of seasonally recurring algae blooms. The deterministic model displays a wide spectrum of dynamical behaviours, from simple cyclical blooms which trigger annually, to irregular chaotic blooms in which both the time between outbreaks and their magnitudes are erratic. Unusually, despite the persistent seasonal forcing, it is extremely difficult to generate blooms that are both annually recurring and also chaotic or irregular (i.e. in amplitude) even though this characterizes many real time-series. Instead the model has a tendency to 'skip' with outbreaks often being suppressed from 1 year to the next. This behaviour is studied in detail and we develop analytical expressions to describe the model's flow in phase space, yielding insights into the mechanism of the bloom recurrence. We also discuss how modifications to the equations through the inclusion of appropriate functional forms can generate more realistic dynamics.     

Indole-3-propionic acid, a melatonin-related molecule, protects hepatic microsomal membranes from iron-induced oxidative damage: relevance to cancer reduction

Excessive free iron and the associated oxidative damage are commonly related to carcinogenesis. Among the antioxidants known to protect against iron-induced oxidative abuse and carcinogenesis, melatonin and other indole compounds recently have received considerable attention. Indole-3-propionic acid (IPA), a deamination product of tryptophan, with a structure similar to that of melatonin, is present in biological fluids and is an effective free radical scavenger. The aim of the study was to examine the effect of IPA on experimentally induced oxidative changes in rat hepatic microsomal membranes. Microsomes were preincubated in presence of IPA (10, 3, 2, 1, 0.3, 0.1, 0.01 or 0.001 mM) and, then, incubated with FeCl(3) (0.2 mM), ADP (1.7 mM) and NADPH (0.2 mM) to induce oxidative damage. Alterations in membrane fluidity (the inverse of membrane rigidity) were estimated by fluorescence spectroscopy and lipid peroxidation by measuring concentrations of malondialdehyde+4-hydroxyalkenals (MDA+4-HDA). IPA, when used in concentrations of 10, 3 or 2 mM, increased membrane fluidity, although at these concentrations it did not influence lipid peroxidation significantly. The decrease in membrane fluidity due to Fe(3+) was completely prevented by preincubation in the presence of IPA at concentrations of 10, 3, 2 or 1 mM. The enhanced lipid peroxidation due to Fe(3+) was prevented by IPA only at the highest concentration (10 mM). It is concluded that Fe(3+)-induced rigidity and, to a lesser extent, lipid peroxidation in microsomal membranes may be reduced by IPA. However, IPA in high concentrations increase membrane fluidity. Besides melatonin, IPA may be used as a pharmacological agent to protect against iron-induced oxidative damage to membranes and, potentially, against carcinogenesis.     

Carcinogen-Induced, Free Radical-Mediated Reduction in Microsomal Membrane Fluidity: Reversal by Indole-3-propionic Acid

Chromium (Cr) is a well established carcinogen, with Cr(III) accounting for much of the intracellular oxidative damage that this transition metal induces. Indole-3-propionic acid (IPA), a melatonin-related molecule, is a reported antioxidant and free radical scavenger. Concentration (1, 10, 100, 500, or 1000 M) and time (15, 30, 45, 60, or 90 min)-dependent effects of Cr(III) in the presence of H₂O₂ (0.5 mM), as well as the protective effect of IPA on Cr(III)-induced alterations in membrane fluidity (the inverse of membrane rigidity), as an index of membrane damage, were estimated by fluorescence spectroscopy. Cr(III), in a concentration- and a time-dependent manner, decreased membrane fluidity, with marked effects at a concentration of 500 M and 60 min of incubation. IPA (5, 3, or 1 mM) prevented the Cr(III)-induced decrease in membrane fluidity. It is concluded that the carcinogen Cr(III), in the presence of H₂O₂, generates free radicals, which decrease membrane fluidity in rat microsomal membranes. Membrane alterations are pharmacologically prevented by the antioxidant IPA.     

Inhibitory effect of bombesin and SMS 201-995 on DNA synthesis in the rat thyroid lobes incubated in vitro

The effects of 4-h incubation in the presence of bombesin on the incorporation of [3H]-thymidine into DNA of the rat thyroid lobes, collected from animals treated in vivo with a long-acting somatostatin analog (SMS 201-995) or with 0.9% NaCl, were investigated. It was shown that not only in vivo injections of SMS 201-995, but also, unexpectedly, in vitro incubation with bombesin inhibited [3H]-thymidine incorporation. The two examined substances did not reveal any additive action in their inhibitory effects on the thyroid growth.     

La protection contre l'immunisation anti-Rh conférée par l'incompatibilité ABO

Résumé La coïncidence entre l'incompatibilité ABO et Rh a des conséquences diverses: la protection vis-à-vis de l'immunisation anti-Rh conférée par l'incompatibilité ABO, généralement totale, exceptionnellement nulle, se traduit quelquefois par un retard dans l'apparition des anticorps anti-Rh à la suite de stimulations répét'ees ou par leur taux particulièrement faible. La signification du phénomène ne peut apparaître que par l'étude détaillée de toutes les sollicitations antigéniques ayant concouru à l'immunisation. Même si l'on restreint cette étude aux seuls cas où l'immunisation est apparue dès la deuxième grossesse, le nombre d'observations actuellement disponibles est insuffisant. D'une première série de 90 cas ici réunis se dégagent les conclusions suivantes: la valeur antigénique, préparante et déclenchante, d'une grossesse incompatible est très inférieure à celle d'une grossesse compatible; l'intervention d'une grossesse incompatible se traduit généralement par une immunisation tardive et de faible intensité; la protection est atténuée ou annulée lorsque les érythrocytes foetaux pénétrant dans la circulation maternelle sont peu accessibles à l'action des anticorps maternels correspondants, notamment lorsqu'il s'agit d'antigènes incomplètement mûris du sousgroupe A₂ ou provenant d'un foetus loin du terme normal; le titre de l'anticorps maternel anti-A ou anti-B est à cet égard indifférent. Une grossesse incompatible peut, dans des circonstances rares, jouer un rôle antigénique tout à fait comparable à celui d'une grossesse compatible.

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Summary The double ABO- and Rh-incompatibility between mother and child generally affords complete protection against anti-Rh immunization; on very rare occasions the protective mechanism fails; sometimes the ABO-antagonism results in the delayed appearance of low-titered anti-Rh antibodies. The significance of this phenomenon cannot be understood unless all the antigenic stimuli are known in detail. The available data are as yet insufficient and their analysis should be limited to the two-children families. From the series of the 90 cases collected here, the following conclusions may be drawn: both the sensitizing and the immunizing properties of an incompatible pregnancy are much lower than those of a compatible one; when antigenic, the incompatible erythrocytes evoke weaker antibodies and/or of later appearance; protection may be lowered or cancelled out when the survival of incompatible foetal erythrocytes entering the maternal circulation is abnormally prolonged, namely in the case of premature delivery and in the presence of a weak antigen, i.e. A₂ even in a full-term foetus; the titre of maternal anti-A and anti-B antibodies is of no importance in this instance.

     

INFLUENCE OF SOIL PROPERTIES AND PHOSPHATE ADDITION ON ARSENIC UPTAKE FROM POLLUTED SOILS BY VELVETGRASS (HOLCUS LANATUS)

Four kinds of soil material were used in a pot experiment with velvetgrass (Holcus lanatus). Two unpolluted soils: sand (S) and loam (L) were spiked with sodium arsenite (As III) and arsenate (As V), to obtain total arsenic (As) concentrations of 500 mg As kg^?1. Two other soils (ZS I, ZS III), containing 3320 and 5350 mg As kg^?1, were collected from Zloty Stok where gold and arsenic ores were mined and processed for several centuries. The effects of phosphate addition on plants growth and As uptake were investigated. Phosphate was applied to soils in the form of NH₄H₂PO₄ at the rate 0.2 g P/kg. Average concentrations of arsenic in the shoots of velvetgrass grown in spiked soils S and L without P amendment were in the range 18–210 mg As kg^?1 d.wt., whereas those in plants grown on ZS I and ZS II soils were considerably lower, and varied in the range 11–52 mg As kg^?1 d.wt. The addition of phosphate caused a significant increase in plant biomass and therefore the total amounts of As taken up by plants, however, the differences in As concentrations in the shoots of velvetgrass amended and non-amended with phosphate were not statistically significant.