Guanine nucleotides protect against kainate toxicity in an ex vivo chick retinal preparation

Ex vivo preparations of chick neural retina have been successfully used in the assessment of excitotoxicity and in the evaluation of the protective effects of glutamate antagonists. Using a variation of this approach, and measuring the acute and delayed toxic effects of kainate (KA) in terms of lactate dehydrogenase release, we have shown that guanine nucleotides behave as effective neuroprotecting agents. The anti-excitotoxic potency of guanine nucleotides (in the case of GMP and GDPβS it is about 100 times lower than that of DNQX, a powerful kainate antagonist) correlates well with their ability to displace KA from retinal KA receptors.     

Reversibility of H+-ATPase and H+-Pyrophosphatase in Tonoplast Vesicles from Maize Coleoptiles and Seeds

Tonoplast-enriched vesicles isolated from maize (Zea mays L.) coleoptiles and seeds synthesize ATP from ADP and inorganic phosphate (Pi) and inorganic pyrophosphate from Pi. The synthesis is consistent with reversal of the catalytic cycle of the H⁺-ATPase and H⁺-pyrophosphatase (PPase) vacuolar membrane-bound enzymes. This was monitored by measuring the exchange reaction that leads to ³²Pi incorporation into ATP or inorganic pyrophosphate. The reversal reactions of these enzymes were dependent on the proton gradient formed across the vesicle membrane and were susceptible to the uncoupler carbonyl cyanide p(trifluoromethoxy)-phenylhydrazone and the detergent Triton X-100. Comparison of the two H⁺ pumps showed that the H⁺-ATPase was more active than H⁺-PPase in coleoptile tonoplast vesicles, whereas in seed vesicles H⁺-PPase activity was clearly dominant. These findings may reflect the physiological significance of these enzymes in different tissues at different stages of development and/or differentiation.     

The loss of immunity in directly transmitted infections modeling: Effects on the epidemiological parameters

When directly transmitted infectious diseases are modeled assuming an everlasting induced immunity (and constant contact rate), there are well-established formulas to deal with, which is not true if we include the loss of induced immunity. In general, the immunity induced by the disease is everlasting. We propose a model considering the loss of immunity and present methods for the estimation of two epidemiological parameters: the force of infection and the basic reproduction ratio. We also analyze the effects of the loss of immunity on these parameters. Based on these results, we conclude that reinfection can play an important role in highly vaccinated populations.     

The expression of the salt-responsive gene salT from rice is regulated by hormonal and developmental cues

The expression pattern of the salT gene was analyzed in different cell types and organs of rice (Oryza sativa L.) in response to saline and hormonal treatments to obtain detailed information on the physiological cues controlling gene expression. Gel blot analysis of RNA and in-situ hybridization performed on seedlings grown for 10 ds in the presence of 1% NaCl revealed that salT was expressed mainly in the younger tissues of the plant. In contrast, 6-week-old plants exhibited maximal salT mRNA accumulation in sheaths of older leaves. In addition, salT was normally expressed in rapidly dividing suspension-cultured cells, but not in quiescent ones. Altogether, these results may indicate that salT expression in each region of the plant is dependent on the metabolic activity of the cells as well as on whether or not they are stressed. The effects of two growth regulators, abscisic acid (ABA) and gibberellic acid, were investigated in combination with the effects of NaCl. Gibberellic acid had a synergistic effect on the induction of the salT gene when combined with 0.5% NaCl, but did not induce salT on its own. At 10 μM, ABA induced salT both in the absence of NaCl and in its presence. Whereas 1 μM ABA acted additively with NaCl to induce gene expression, 5 μM ABA with NaCl was only as effective as NaCl alone. This may indicate that the two stimuli act independently and possibly through antagonistic signal transduction pathways. Received: 26 March 1998 / Accepted: 11 July 1998     

Induction of astaxanthin accumulation by nitrogen and magnesium deficiencies in Haematococcus pluvialis

Haematococcus pluvialis was cultured under N– and Mg+2-deficient conditions with two light intensities: 40 and 230 mol m² s–1. Highest astaxanthin concentration, 49.5 g·ml–1, was obtained when high light was applied under N-deficient conditions. N-deficiency has a greater effect than high light intensity on astaxanthin synthesis by exerting a stronger blocking effect on cell division. The effect of high light was synergetic with the other stress conditions in stimulating the synthesis of astaxanthin. Mg+2 deficiency also stimulated the synthesis of astaxanthin but produced lower concentrations: 7 and 26 g·ml–1 for low and high light intensities respectively. When both N and Mg+2 were absent from the culture media the concentration of astaxanthin was lower than with N-deficiency alone but higher than with Mg+2-deficiency. © Rapid Science Ltd. 1998     

Efficient shoot organogenesis of eggplant (Solanum melongena L.) induced by thidiazuron

Morphogenesis from several explant types excised from in-vitro-grown plantlets of a Brazilian eggplant (Solanum melongena L.) variety (F-100) was evaluated in response to thidiazuron (TDZ). Leaves and cotyledons were found to be the most responsive explants. Optimal shoot bud induction rates (75–100 buds/explant) were achieved in the presence of 0.2 μm TDZ. Organogenic calli were transferred to growth regulator free MS medium before shoot excision. Rooting was induced on half-strength MS medium supplemented with 0.6 μm IAA. Received: 1 March 1997 / Revision received: 29 October 1997 / Accepted: 15 November 1997     

High levels of soluble IFN γ receptor α chain in the plasma of rheumatoid arthritis patients

Soluble receptors for hormones and cytokines have beendescribed. They can serve as natural blockers of theirrespective ligands. The natural soluble interferongamma receptor (sIFNR) has been isolated andcharacterized only in urine. Chromatography of human(hu) plasma from rheumatoid arthritis (RA) patientsand controls on immobilized hu IFN orantibodies against IFN R chainpermitted us to isolate the sIFNR. Thereceptor isolated from one control is a protein witha molecular weight between 60-67 kDa depending on thepresence of reducing agents. We detected asignificantly higher level of plasma sIFNR inpatients with rheumatoid arthritis than in apparentlyhealthy subjects.     

The influence of aquatic surface respiration (ASR) on cardio-respiratory function of the serrasalmid fish Piaractus mesopotamicus

When exposed to severely hypoxic water, many teleosts skim the better oxygenated surface layer (aquatic surface respiration, ASR). Information is scarce concerning the thresholds triggering ASR and its cardio-respiratory consequences. To assess the ambient conditions leading to ASR and to evaluate its effects on cardio-respiratory function, we exposed specimens of Piaractus mesopotamicus to gradual hypoxia (water oxygen tension ranging from 120 to 10 torr) with or, alternatively, without access to the surface. Concurrently, ASR, cardiac and respiratory frequencies, O₂ uptake and gill ventilation were monitored. With surface access, ASR developed below the critical tension for O₂ uptake (34 torr) by normal gill ventilation. Moreover, the time spent in ASR increased with prolonged hypoxic exposure to a maximum of 95% of total time. Without surface access, the species exhibited hypoxic bradycardia, that had not occurred in the group with fully developed ASR. Even without ASR, P. mesopotamicus recovered readily from hypoxic exposure, showing that this species possesses a number of mechanisms to cope with environmental hypoxia.     

High-Andean vegetation and environmental gradients in northwestern Patagonia,Argentina

Abstract. We analysed the heterogeneity of high-elevation vegetation on three mountains along a west-east transect at 41 °S lat. in the Andes of northwestern Patagonia, Argentina. In this area, high-Andean vegetation occurs as islands on mountain tops above Nothofagus pumilio forests ? with the timberline at ca. 1700 m a.s.l. We recorded floristic, topographic and substrate data in 166 sites stratified according to longitude, altitude, slope and aspect. Vegetation data were classified with TWINSPAN and ordinated with Detrended Correspondence Analysis. The relationship between environmental and floristic variation was analysed using Canonical Correspondence Analysis. In order of importance, geographical longitude, altitude and aspect were the major determinants of vegetation variation, whereas substrate texture and slope appeared less important. The combination of these factors resulted in two main vegetation gradients. The first gradient is related to a moisture availability gradient, primarily determined by longitude and secondarily to variation in wind exposure (east vs. west aspect). The second vegetation gradient is related to variation in temperature, primarily determined by altitude, and secondarily by variation in insolation related to the contrast between north and south aspects. The four communities obtained with TWINSPAN are therefore associated with four characteristic habitat types: moist-cold, moist-warm, dry-cold and dry-warm. The community of warm and dry environments is the richest and has elements in common with dry steppe communities situated at lower elevations to the east, while the vegetation of the cold-moist habitat type has unique elements that are typical of the southern Andes. Although current climatic factors appear to be the major determinants of high-Andean vegetation gradients, historical events of Pleistocene times probably also affected the vegetation patterns we see today.     

In vitro shoot culture and microtuber induction in the steroid yam Dioscorea composita Hemsl

The individual effects of sucrose, plant growth regulators and basal salt media formulations were investigated on microtuber induction and development in shoot cultures of the steroid yam Dioscorea composita. Sucrose at 8% (w/v) was the single most significant medium constituent for microtuber induction. Of the four cytokinins tested, 6-benzyladenine at 1.25 and 2.5 μM showed strong inhibitory effects on microtuber induction. By contrast, the auxins α-naphthaleneacetic acid and indole-3-butyric acid at 5.0 μM showed striking promotive effects on microtuber induction and growth. In the presence of either one of these auxins at 5.0 μM shoot cultures produced microtubers weighing 300–400 mg fresh weight whilst kinetin, 6-(γ,γ-dimethylallylamino)-purine, 6-benzyladenine and abscisic acid failed to promote microtuber growth (microtubers weighed generally <200 mg). Media formulations Lloyd and MacCown and White supported the lowest frequencies of microtuber induction when kinetin was present at 2.5 μM. Anderson Rhododendron was as effective as Murashige and Skoog overall in promoting both microtuber induction and growth. When removed from cultures and planted in sterilized moist sand, microtubers sprouted readily (60–87% within 2 weeks) and produced vigorous shoot growth and after 5–7 months minitubers of sizes (30–80 g) suitable for direct field planting. This revised version was published online in June 2006 with corrections to the Cover Date.