Marine incursions,cryptic species and ecological diversification in Amazonia: the biogeographic history of the croaker genus Plagioscion (Sciaenidae)

Aim We propose a phylogenetic hypothesis for the marine‐derived sciaenid genus Plagioscion in the context of geomorphology and adaptation to freshwaters of South America, and assess the extent to which contemporary freshwater hydrochemical gradients influence diversification within a widely distributed Plagioscion species, Plagioscion squamosissimus. Location Amazon Basin and South America. Methods Using nuclear and mitochondrial DNA sequence data, phylogenetic analyses were conducted on the five nominal Plagioscion species, together with representatives from Pachyurus and Pachypops, using character and model‐based methods. Genealogical relationships and population genetic structure of 152 P. squamosissimus specimens sampled from the five major rivers and three hydrochemical settings/‘colours’ (i.e. white, black and clear water) of the Amazon Basin were assessed. Results Phylogenetic analyses support the monophyly of Plagioscion in South America and identify two putative cryptic species of Plagioscion. Divergence estimates suggest that the Plagioscion ancestor invaded South America via a northern route during the late Oligocene to early Miocene. Within P. squamosissimus a strong association of haplotype and water colour was observed, together with significant population structure detected between water colours. Main conclusions Our analyses of Plagioscion are consistent with a biogeographic scenario of early Miocene marine incursions into South America. Based on our phylogenetic results, the fossil record, geomorphological history and distributional data of extant Plagioscion species, we propose that marine incursions into western Venezuela between the late Oligocene and early Miocene were responsible for the adaptation to freshwaters in Plagioscion species. Following the termination of the marine incursions during the late Miocene and the establishment of the modern Amazon River, Plagioscion experienced a rapid diversification. Plagioscion squamosissimus arose during that time. The formation of the Amazon River probably facilitated population and range expansions for this species. Further, the large‐scale hydrochemical gradients within the Amazon Basin appear to be acting as ecological barriers maintaining population discontinuities in P. squamosissimus even in the face of gene flow. Our results highlight the importance of divergent natural selection through time in the generation and maintenance of sciaenid diversity in Amazonia.     

Growth Phase-Dependent Regulation of Vsr Endonuclease May Contribute to 5-Methylcytosine Mutational Hot Spots in Escherichia coli

Using rabbit polyclonal antibodies, we have shown that the Dcm cytosine methylase of Escherichia coli is maintained at a constant level during cell growth, while Vsr endonuclease levels are growth phase dependent. Decreased production of Vsr relative to Dcm during the log phase may contribute substantially to the mutability of 5-methylcytosine.     

3-Mercaptopropionic acid administration increases the affinity of [H]Quinuclidinyl benzilate binding to membranes of the striatum and cerebellum

It is known that quinuclidinyl benzilate (QNB) binds specifically and with high affinity to the cholinergic muscarinic receptor and that behaves as a potent antagonist of this receptor.

We have analysed -[³H]QNB binding to rat CNS membranes after the administration of the convulsant 3-mercaptopropionic acid (MP) (150 mg·kg⁻¹, i.p.). The studies were done in rats killed at two stages: during and after seizures. No changes in [³H]QNB binding to hippocampus and cerebral cortex membranes were found. [³H]QNB binding increased about 40 and 80% in striatum and cerebellum membranes, respectively. The changes were observed both in seizure and postseizures states. The study was extended to the assay of [³H]QNB binding kinetic constants in the anatomical areas modified by the convulsant. The analysis of the saturation curves indicated an increase in the binding affinity but no change in the number of binding sites. Hill number values were near the unit suggesting a non-cooperative interaction between the ligand and the receptor, and the labelling of a homogeneous population of receptor sites.

The results suggest the participation of some cholinergic pathways in the development and maintenance of MP-induced seizures.     

Diaphragmatic activity is a determinant of postnatal lung growth

To test the hypothesis that activity of respiratory muscles determines regional growth of lung parenchyma, we studied the effects of unilateral diaphragmatic paralysis on contralateral/ipsilateral lung growth in cats and piglets. Five 10- to 12-wk-old cats and five 8-wk-old piglets underwent unilateral diaphragmatic paralysis by thoracic and cervical phrenectomy, respectively. Five to seven weeks after surgery, when the cats were killed for studies of lung growth, gain in body weight was the same as in five sham-operated controls. At this time, mean pleural pressure ipsilateral to the paralyzed hemidiaphragm was the same as contralateral mean pleural pressure during tidal breathing, and values did not differ from controls. However overall functional residual capacity was lower in the phrenectomized cats (35 +/- 4 ml) than in the controls (55 +/- 11 ml, P less than 0.01). Growth of contralateral lungs relative to ipsilateral lungs was greater in the phrenectomized cats than in the controls, as shown by ratios of contralateral/ipsilateral wet lung weight (1.44 vs. 1.34, P less than 0.01), maximum inflation volume (1.53 vs. 1.33, P less than 0.05), and total protein content (1.45 vs. 1.26, P less than 0.05). Ratios of total protein to DNA and RNA to DNA were unchanged. One week after surgery in the piglets, the ratio of contralateral/ipsilateral wet lung weight was increased (1.61 vs. 1.29, P less than 0.01) and total weight of both lungs was reduced. We conclude that regional growth of lung parenchyma by cell proliferation depends in part on regional distribution of respiratory muscle activity.     

Nitrogen Source Regulates Glutamate Dehydrogenase NADP Synthesis in Neurospora crassa

Neurospora crassa glutamate dehydrogenase-NADP (EC 1.3.1.3) has a higher activity when mycelium is grown on ammonium or nitrate as nitrogen source than when grown on glutamate or glutamine. Quantitative immunoelectrophoresis established that, under all conditions, enzyme activity corresponded to enzyme concentration. Isotope incorporation studies demonstrated that the nitrogen source exerts its regulation at the level of de novo enzyme synthesis.     

Rotavirus RNA replication: VP2, but not VP6, is necessary for viral replicase activity.

Temperature-sensitive mutants of simian rotavirus SA11 were previously developed and organized into 10 of a possible 11 recombination groups on the basis of genome reassortment studies. Two of these mutants, tsF and tsG, map to genes encoding VP2 (segment 2) and VP6 (segment 6), respectively. To gain insight into the role of these proteins in genome replication, MA104 cells were infected with tsF or tsG and then maintained at permissive temperature (31 degrees C) until 9 h postinfection, when some cells were shifted to nonpermissive temperature (39 degrees C). Subviral particles (SVPs) were recovered from the infected cells at 10.5 and 12 h postinfection and assayed for associated replicase activity in a cell-free system shown previously to support rotavirus genome replication in vitro. The results showed that the level of replicase activity associated with tsF SVPs from cells shifted to nonpermissive temperature was ca. 20-fold less than that associated with tsF SVPs from cells maintained at permissive temperature. In contrast, the level of replicase activity associated with tsG SVPs from cells maintained at nonpermissive temperature was only slightly less (twofold or less) than that associated with tsG SVPs from cells maintained at permissive temperature. Analysis of the structure of replicase particles from tsG-infected cells shifted to nonpermissive temperature showed that they were similar in size and density to virion-derived core particles and contained the major core protein VP2 but lacked the major inner shell protein VP6. Taken together, these data indicate that VP2, but not VP6, is an essential component of enzymatically active replicase particles.     

Establishment of transformed root cultures of Perezia cuernavacana producing the sesquiterpene quinone perezone

Summary The sesquiterpene quinone currently known as perezone is abundantly produced by the roots of Perezia cuernavacana. This compound is of biotechnological interest since it may be used as a pigment and has several pharmacological properties. In this work we demonstrate that perezone is also produced in transformed root cultures of P. cuernavacana. Hairy roots were induced by inoculation of internodal segments of sterile plants of P. cuernavacana with Agrobacterium rhizogenes AR12 strain. The axenic liquid MS medium cultures of the hairy roots isolated from the internodes showed active growth in the absence of growth regulators. The transformed nature of the tissue was confirmed by genomic integration (PCR and slot blot hybridization) and expression (enzyme activity) of the marker gus-gene. The production of perezone by a transformed root culture was evidenced by IR spectroscopy. Our results offer an alternative for enhanced production of perezone and represent an advantage over its extraction from natural plant populations which present problems in their agronomic culture.     

Permineralized seed fern cupules from the Triassic of Antarctica: implications for cupule and carpel evolution

In this paper we describe the first anatomically preserved Mesozoic seed fern cupule–Petriellaea. The multiovulate cupules were produced singly at the end of a short dichotomizing axis. Cupules are bilateral with a dorsal groove and transverse narrow ventral opening. The vascular system of the cupule consists of a series of traces that extend up the dorsal surface of the cupule and down the ventral face. Ovules are orthotropus, sessile, and borne on the adaxial surface of the leaflike cupule either singly or in multiple rows. They are up to 1.5 mm long, triangular in transverse section, and characterized by a multilayered integument. Nucellus and integument are fused throughout their length, but no pollen chamber is present. In the chalaza is a small vascular disc of transfusion tracheids that represents the extent of the ovule vascular system. Ovules are interpreted as being fossilized at a prepollination stage, although a few possess some evidence of a cellularized megagametophyte. These permineralized cupules indicate that in at least one Mesozoic seed fern group, ovule enclosure resulted from the transverse folding (tip to petiole) of a megasporophyll bearing adaxial ovules. Cupule morphology and ovule enclosure in other Late Paleozoic and Mesozoic seed ferns is discussed.