Effects of zooplankton and conductivity on tropical Utricularia foliosa investment in carnivory

Investment by bladderwort (Utricularia foliosa) in carnivory was estimated in lakes from the Colombian and Brazilian Amazon with different dissolved mineral nutrients and prey availability. As zooplankton abundance in the lake decreased, an increase in the number of bladders per leaf and in the mean bladder size was observed. However, this investment increment in carnivory diminished as the overall availability of dissolved ions in the lake increased. Our results show that carnivorous plants U. foliosa optimise their investment in carnivory, changing bladder number and bladder size according to zooplankton abundance and conductivity.     

Respiratory metabolism during cold storage of apple fruit. I. Sucrose metabolism and glycolysis

This study provides the first report on the occurrence of the respiratory climacteric during cold storage of apple fruit ( Malus domestica Borkh. cv. Reinette du Canada). The respiratory pattern at 4°C was very similar to that observed during postharvest ripening at room temperature, except that shelf life was considerably extended and the onset of the climacteric delayed. Increasing the calcium content of the apple fruit significantly reduced loss of firmness during cold storage, but showed no effect on respiration or on the other parameters determined. A gradual accumulation of soluble sugars occurred during the first 60 days after harvest and was effectively completed before the climacteric peak was reached. This increase in sugars correlated with an increase in the activity of sucrose-phosphate synthase (EC 2.4.1.14), and a marked change in the kinetic properties of the enzyme was observed after sucrose accumulation ceased. Changes in the hexose-phosphate pool and in glycolytic and gluconeogenic activities indicated an initial increase in the gluconeogenic flow at early stages of the climacteric, followed by activation of glycolysis, with the carbon flow being most likely regulated at the reversible phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate (mostly via pyrophosphate:fructose-6-phosphate phosphotransferase, EC 2.7.1.90) and at the pyruvate kinase (EC 2.7.1.40) steps. The results presented indicate that the respiratory climacteric does not occur to accommodate extra ATP requirements during sucrose synthesis nor can it be a consequence of an increased supply of respiratory substrate.     

Chronopharmacology of Melatonin: Inhibition by Benzodiazepine Antagonism

We endeavored to determine whether three behavioral effects of melatonin in rodents, i.e., depression of locomotor activity in hamsters, analgesia in mice, and impairment of 3-mercaptopropionic acid (3-MP) convulsions, exhibited the time dependency known to occur for several neuroendocrine effects of the hormone. Activity was monitored and registered by means of an optical acto-meter, and analgesia was assessed by the hot-plate procedure. Locomotor activity, analgesia, and seizure susceptibility were maximal at the beginning of the scoto-phase and minimal at noon. The effects of melatonin on the three parameters peaked at early night. The administration of the benzodiazepine antagonist fluma-zenil, although unable by itself to modify locomotor activity, pain, or seizure threshold, blunted the activity of melatonin. These results suggest that the time-dependent effects of melatonin on specific rodent behaviors may be mediated by central synapses employing 7-aminobutyric acid (GABA) as an inhibitory transmitter.     

High copy number of highly similar mariner-like transposons in planarian (Platyhelminthe): evidence for a trans-phyla horizontal transfer

Several DNA sequences similar to the mariner element were isolated and characterized in the platyhelminthe Dugesia (Girardia) tigrina. They were 1,288 bp long, flanked by two 32 bp-inverted repeats, and contained a single 339 amino acid open-reading frame (ORF) encoding the transposase. The number of copies of this element is approximately 8,000 per haploid genome, constituting a member of the middle- repetitive DNA of Dugesia tigrina. Sequence analysis of several elements showed a high percentage of conservation between the different copies. Most of them presented an intact ORF and the standard signals of actively expressed genes, which suggests that some of them are or have recently been functional transposons. The high degree of similarity shared with other mariner elements from some arthropods, together with the fact that this element is undetectable in other planarian species, strongly suggests a case of horizontal transfer between these two distant phyla.      

Assessing horizontal transfer of nifHDK genes in eubacteria: nucleotide sequence of nifK from Frankia strain HFPCcI3

The structural genes for nitrogenase, nifK, nifD, and nifH, are crucial for nitrogen fixation. Previous phylogenetic analysis of the amino acid sequence of nifH suggested that this gene had been horizontally transferred from a proteobacterium to the gram-positive/cyanobacterial clade, although the confounding effects of paralogous comparisons made interpretation of the data difficult. An additional test of nif gene horizontal transfer using nifD was made, but the NifD phylogeny lacked resolution. Here nif gene phylogeny is addressed with a phylogenetic analysis of a third and longer nif gene, nifK. As part of the study, the nifK gene of the key taxon Frankia was sequenced. Parsimony and some distance analyses of the nifK amino acid sequences provide support for vertical descent of nifK, but other distance trees provide support for the lateral transfer of the gene. Bootstrap support was found for both hypotheses in all trees; the nifK data do not definitively favor one or the other hypothesis. A parsimony analysis of NifH provides support for horizontal transfer in accord with previous reports, although bootstrap analysis also shows some support for vertical descent of the orthologous nifH genes. A wider sampling of taxa and more sophisticated methods of phylogenetic inference are needed to understand the evolution of nif genes. The nif genes may also be powerful phylogenetic tools. If nifK evolved by vertical descent, it provides strong evidence that the cyanobacteria and proteobacteria are sister groups to the exclusion of the firmicutes, whereas 16S rRNA sequences are unable to resolve the relationships of these three major eubacterial lineages.      

The Biology of Gregarina fernandoi n. sp. in the Cockroach Pysnoscelus surinamensis with Observations on its Development and Cytochemical Nature

SYNOPSIS. Gregarina fernandoi n. sp. is a eugregarine. Its structure, development and life history in the gut of the cockroach Pycnoscelus surinamensis are described. It is named as a new species on the basis of its size, nuclear structure, structure and form of the gametocyst and oocyst. Observations were made on the different stages of the parasite and related to the pH of the gut. In the ceca, pH 4.5–5, the parasite was in its early stages of development, in the midgut, pH 6.5–7, it was in syzygy and in the rectum, pH 7.5–8, gametocysts were found.     

The macrophage adherence phenomenon: Its relationship to prostaglandin E2 and superoxide anion production and changes in transmembrane potential

Mononuclear phagocytes are undoubtedly the sine qua non of chronic inflammatory reactions. This is demonstrated by their unique ability to function as phagocytic, secretory, or effector cells during the course of an immune event. Although macrophages can perform a variety of immune tasks, their ability to function appropriately is dependent upon the mode of elicitation, the stimulus under investigation, the source of the macrophages (peritoneal, alveolar, etc.), and whether the macrophages are monolayers or in suspension. We have examined the relationship between adherent and non-adherent elicited peritoneal macrophages in terms of prostaglandin E₂ (PGE₂) and superoxide anion (O₂) production; in addition, we hae studied these elicited macrophages in suspension for their ability to undergo transmembrane potential changes in response to several stimuli. Non-adherent, elicited peritoneal macrophages demonstrated an increase in basal PGE₂ production, and were refractory to particulate stimulus. After monolayer formation, basal PGE₂ levels dropped and the cell could respond to both soluble and particulate stimuli. Only adherent macrophages could respond to a specific challenge and synthesize O₂. Both O₂ production and depolarization of the transmembrane potential were suppressed in cell in suspension. Furthermore, both exogenous PGE₂ and supernatant from macrophages in suspension could modulate O₂ production by PMA challenged macrophages monolayers. These studies indicate that PGE₂ may modulate macrophage function and dictate activity as macrophages go from the non-adherent to adherent state.     

Efflux Pumps Involved in Toluene Tolerance in Pseudomonas putida DOT-T1E

The basic mechanisms underlying solvent tolerance in Pseudomonas putida DOT-T1E are efflux pumps that remove the solvent from bacterial cell membranes. The solvent-tolerant P. putida DOT-T1E grows in the presence of high concentrations (e.g., 1% [vol/vol]) of toluene and octanol. Growth of P. putida DOT-T1E cells in LB in the presence of toluene supplied via the gas phase has a clear effect on cell survival: the sudden addition of 0.3% (vol/vol) toluene to P. putida DOT-T1E pregrown with toluene in the gas phase resulted in survival of almost 100% of the initial cell number, whereas only 0.01% of cells pregrown in the absence of toluene tolerated exposure to this aromatic hydrocarbon. One class of toluene-sensitive octanol-tolerant mutant was isolated after Tn5-′phoA mutagenesis of wild-type P. putida DOT-T1E cells. The mutant, called P. putida DOT-T1E-18, was extremely sensitive to 0.3% (vol/vol) toluene added when cells were pregrown in the absence of toluene, whereas pregrowth on toluene supplied via the gas phase resulted in survival of about 0.0001% of the initial number. Solvent exclusion was tested with 1,2,4-[¹⁴C]trichlorobenzene. The levels of radiochemical accumulated in wild-type cells grown in the absence and in the presence of toluene were not significantly different. In contrast, the mutant was unable to remove 1,2,4-[¹⁴C]trichlorobenzene from the cell membranes when grown on Luria-Bertani (LB) medium but was able to remove the aromatic compound when pregrown on LB medium with toluene supplied via the gas phase. The amount of ¹⁴C-labeled substrate in whole cells increased in competition assays in which toluene and xylenes were the unlabeled competitors, whereas this was not the case when benzene was the competitor. This finding suggests that the exclusion system works specifically with certain aromatic substrates. The mutation in P. putida DOT-T1E-18 was cloned, and the knockedout gene was sequenced and found to be homologous to the drug exclusion gene mexB, which belongs to the efflux pump family of the resistant nodulator division type.The sensitivity of microorganisms to toxic organic solvents is related to the logarithm of the partition coefficient of the solvent in a mixture of octanol and water (log P_ow). Aromatic hydrocarbons with a log P_ow of between 1.5 and 3.5 are extremely toxic to living organisms (47). These chemicals dissolve in the cytoplasmic membrane, disorganize it, and collapse the cell membrane potential; this, together with the induced loss of lipids and proteins, leads to irreversible damage resulting in the death of the cell (8, 47, 50).Independent laboratories have isolated Pseudomonas putida strains tolerant to different aromatic hydrocarbons such as toluene, styrene, and p-xylene (6, 15, 42, 48). All four isolated strains were able to grow in liquid culture medium to which a high concentration (1% [vol/vol]) of these aromatic hydrocarbons was added. Tolerance to organic solvents in these P. putida strains is achieved by a series of biochemical mechanisms that actively remove the organic solvent from cell membranes (16, 43) and by physical barriers that help the cell to become (to a certain degree) impermeable to the solvent (13, 37, 43, 48). The physical barriers involve the ordered organization of the cell surface lipopolysaccharides (37) together with modified phospholipids (4, 37, 43, 49). Modifications in phospholipids upon exposure to an organic solvent involve both a short-term response, in which the level of the trans isomers of unsaturated phospholipids increases, and a long-term response consisting of a modification of the polar head groups of phospholipids (4, 43, 49) and an increase in the total amount of phospholipids per dry weight (49). For P. putida DOT-T1, it was suggested that an energy-dependent exclusion system (such as an efflux pump) is critical for tolerance to solvents (43). This conclusion was based on the following findings: (i) P. putida DOT-T1 treated with the uncoupler carbonyl cyanide p-trifluoromethoxyphenyl hydrazone accumulated higher levels of 1,2,4-[¹⁴C]trichlorobenzene in cell membranes than did untreated cells, and (ii) P. putida DOT-T1 mutants which were sensitive to toluene, octanol, and other chemicals accumulated 5- to 20-fold-higher levels of 1,2,4-[¹⁴C]trichlorobenzene in cell membranes than did the wild-type strain. Similar observations have been reported for Pseudomonas sp. strain S12 (16).In this study, we report that P. putida DOT-T1 uses at least two efflux pumps for toluene exclusion, one that seems to be expressed constitutively and a second inducible one. A mini-Tn5′phoA-Km^r knocked out the constitutive efflux system of P. putida DOT-T1E. The mutant was shown to be hypersensitive to toluene but not to octanol. The Km^r marker of the mini-Tn5 and the 3′ adjacent chromosomal DNA were cloned, and the wild-type gene was rescued by colony screening hybridization and sequenced. Sequence analysis showed that the knocked-out gene in the mutant was a homolog of the mexB gene, which belongs to the efflux pump family of the resistant nodulator division type (34–36, 38–41).     

Short repetitive sequences in green algal mitochondrial genomes: potential roles in mitochondrial genome evolution

Current data on green algal mitochondrial genomes suggest an unexpected dichotomy within the group with respect to genome structure, organization, and sequence affiliations. The present study suggests that there is a correlation between this dichotomy on one hand and the differences in the abundance, base composition, and distribution of short repetitive sequences we observed among green algal mitochondrial genomes on the other. It is conceivable that the accumulation of GC- rich short repeated sequences in the Chlamydomonas-like but not Prototheca-like mitochondrial genomes might have triggered evolutionary events responsible for the distinct series of evolutionary changes undergone by the two green algal mitochondrial lineages. The similarity in base composition, nucleotide sequence, abundance, and mode of organization we observed between the short repetitive sequences present in Chlamydomonas-like mitochondrial genomes on one hand and fungal and vertebrate homologs on the other might extend to some of the roles that the short repetitive sequences have been shown to have in the latter. Potential involvements we propose for the short repetitive sequences in the evolution of Chlamydomonas-like mitochondrial genomes include fragmentation and scrambling of the ribosomal-RNA-coding regions, extensive gene rearrangements, coding-region deletions, surrogate origins of replication, and chromosomal linearization.