Ochratoxin A,an in vivo inhibitor of renal phosphoenolpyruvate carboxykinase

Ochratoxin A, a nephrotoxin produced as a secondary metabolite by A. ochraceus, is a potent inhibitor of renal PEPCK activity, in vivo. When fed orally to rats for 2 days, renal PEPCK activity is reduced 50% by a total dose of 0.3-0.5 mg toxin. Renal gluconeogenic capacity is reduced only after PEPCK activity is inhibited by 50%. Hepatic PEPCK activity is unaffected up to 1.5-2.0 mg ochratoxin A, which were the highest doses tested. Other enzymes located in proximal convoluted tubules, including phosphatedependent glutaminase, γ-glutamyl transpeptidase, pyruvate carboxylase, and Na,K-ATPase, are not affected. Renal protein synthesis from [³H]phenylalanine or [³H]leucine is inhibited 30–40% by ochratoxin A in vivo. By covalently coupling the toxin to albumin with carbodiimide or mixed anhydride, the inhibitory effect on renal PEPCK activity is retained, but protein synthesis is not affected and cytological evidence of nephrotoxicity is lost. Injection of the ochratoxin A-albumin carbodiimide complex results in a decrease of hepatic PEPCK activity as well. Removal of the phenylalanine group from the toxin prevents the in vivo inhibition of PEPCK activity, as well as protein synthesis. We conclude that the decrease in renal PEPCK activity, in vivo, requires the phenylalanine group of ochratoxin A, and occurs by a mechanism independent of the known nephrotoxicity effects.     

Ascorbate-independent carotenoid de-epoxidation in intact spinach chloroplasts

Slow (> 1 s) light-induced absorbance changes in the 475–530 nm spectral region were examined in Type A chloroplasts from spinach. The most prominent absorption change occurred at 505 nm. The difference spectrum for this light-induced increase, its absence in osmotically shocked chloroplasts and restoration by ascorbate, and its sensitivity to dithiothreitol indicate that the absorption change is due to carotenoid de-epoxidation. The reaction in intact chloroplasts is characterized by its independence of exogenous ascorbate and a rate constant 3- to 8-fold higher than that reported previously for chloroplasts supplemented with ascorbate.The relevance of carotenoid de-epoxidation to other photosynthetic processes was examined by comparing their sensitivities to dithiothreitol. Levels of dithiothreitol that eliminate the 505 nm shift are without effect on saturated rates of CO₂ fixation and do not appreciably inhibit fluorescence quenching. We conclude that carotenoid de-epoxidation is not directly involved in the reactions of photosynthesis or in the regulation of excitation allocation between the photosystems.     

The impact of ticks on pheasant territoriality

Pheasants are competent reservoir hosts for the Lyme disease spirochaete, Borrelia burgdorferi s.l., and carry large, but highly over-dispersed, infestations of the vector ticks, Ixodes ricinus . The effects of experimental reduction of tick infestation levels on the survival and territorial behaviour of male pheasants were studied. Over three years in two woodlands in southern England, birds were marked individually and half were fitted with a slow-release acaricide, which substantially reduced their tick burdens from March to August. Acaricide treatment affected reproductive success but had no discernible impact on the survival rates of male pheasants. The degree of wattle inflation by males, an indicator of territorial status and a correlate of harem acquisition, was significantly greater among treated males. In each year, a significantly higher proportion of treated (overall 44%) than control (22%) males acquired harems. Males that acquired females ranged over small areas on field edges. By contrast, those with no females ranged more widely in woods and the adjoining fields, increasing their exposure to questing ticks. The relative contribution of such roving males to tick-borne pathogen transmission may thus increase.     

FLAVONOID EVOLUTION IN DENDROSERIS (COMPOSITAE,LACTUCEAE) FROM THE JUAN FERNANDEZ ISLANDS,CHILE

Leaf flavonoid chemistry was examined from the three subgenera and 11 species of the endemic genus Dendroseris (Compositae, Lactuceae) of the Juan Fernandez Islands, Chile. Eight of the species are restricted to the older island (Masatierra, ca. 4 million years old), which is also closer to the mainland. Three species, one from each subgenus, are restricted to Masafuera, which is younger geologically (1–2 million years old) and 145 km further west of Masatierra. A total of 16 compounds was identified, with the 7-0-glucosides of the flavones apigenin and luteolin accounting for 12 of the constituents. Two glucosides of the flavonol quercetin were detected. Despite considerable interpopulation variation within species, six of the taxa have distinctive flavonoid profiles. Although there are few absolute differences among the subgenera, they can be distinguished chemically. Subgenus Rea contains the greatest number of compounds, and a previous cladistic analysis based on morphological features suggested this subgenus as most primitive. Subgenus Phoenicoseris is considered highly derived morphologically, and it has a reduced flavonoid chemistry. Very little reduction in flavonoid diversity was seen in the morphologically specialized subg. Dendroseris as compared to subg. Rea. A trend in reduction of numbers of compounds was seen for two of the three species on the younger island of Masafuera when compared to their presumed ancestors on Masatierra. Flavonoids of selected species of Hieracium and Hypochaeris, presumptive mainland progenitors of Dendroseris, reveal a close chemical affinity with the former genus.     

Prehistoric Warfare in the American Southwest

Prehistoric Warfare in the American Southwest. Steven A. LeBlanc. Salt Lake City: University of Utah Press, 1999 400 pp.     

Coexistence of natural enemies in a multitrophic host–parasitoid system

Abstract.  1. This study explored the temporal and spatial aspects of coexistence over many generations in a multispecies host–parasitoid assemblage.
2. The long-term interaction between the cabbage root fly, Delia radicum (Diptera: Anthomyiidae), and two of its natural enemies, Trybliographa rapae (Hymenoptera: Fitigidae) and Aleochara bilineata (Coleoptera: Staphylinidae), in a cultivated field at Silwood Park over 19 years was explored.
3. Although time series showed that the populations were regulated, the impact of the natural enemies was highly variable. Within-year determinants showed that the spatial response of the specialist parasitoid, T. rapae , was predominantly independent of host density while A. bilineata acted simply as a randomly foraging generalist parasitoid.
4. These findings are compared and contrasted with an earlier investigation of the same system when only the first 9 years of the time series were available. This study demonstrated the potential of long-term field studies for exploring hypotheses on population regulation, persistence, and coexistence.     

Identification and sequence of a Na+-linked gene from the marine bacterium Alteromonas haloplanktis which functionally complements the dagA gene of Escherichia coli

A 4.0 kb fragment from a plasmid genomic DNA library of the marine bacterium Alteromonas haloplanktis ATCC 19855 was found in the presence of Na+ to complement the dagA gene of Escherichia coli. We have completely sequenced this fragment and the position of the Na(+)-linked D-alanine glycine permease gene (dagA) on the fragment has been determined by complementation. The predicted carrier protein consists of 542 amino acid residues (M(r) 58,955). Its hydropathy profile suggests it is composed of eight transmembrane segments with a long hydrophilic region between segments six and seven. Significant similarity has been found between this Na(+)-linked permease and the Na+/proline permeases of E. coli and Salmonella typhimurium and the human and rabbit intestinal Na+/glucose cotransporters.     

A new species of solanum section geminata (Solanaceae) from western Mexico

Solanum malacothrix S. Knapp is described from the slopes of the Sierra Madre del Sur in the Río Balsas drainage in the state of Guerrero. It is apparently rare, and has been collected only twice. Its relationship to other species in Mexico and northern South America is discussed.     

Effect of an abiotic disturbance on a lotic predator-prey interaction

Summary A model derived from marine research, and recently applied to stream communities, suggests that community structure is more likely to be influenced by predators in benign versus harsh abiotic regimes. Experiments were conducted to determine if increasing the harshness of a particular regime would alter the impact of a stream invertebrate predator on prey densities in field enclosures. Density of a stonefly predator, Kogotus nonus, was varied in containers exposed to low (benign) and high (harsh) levels of fine sediment. As predicted by the model, the harsher regime eliminated predator effects in two of three experiments. In the third experiment, however, high levels of sediment actually enhanced the impact of the predator on the prey community. A consideration of the possible mechanisms underlying this model led to the conclusion that increasing the harshness of a regime can be expected to produce outcomes ranging from elimination to enhancement of predator effects, depending on how the regime is perceived by the predator versus the prey.     

Cloning and characterization of a linear 2.3 kb mitochondrial plasmid of maize

Summary A linear 2.3 kb DNA molecule found in maize mitochondria was cloned into pUC8. A natural deletion of this plasmid, found in cmsT and some N (fertile) types of maize plants, was mapped to one end of the plasmid. A minor sequence homology to S-2, another linear mitochondrial plasmid, was detected, as well as more significant sequence homology with chloroplast and maize nuclear DNA. Hybridization to teosinte mitochondrial DNA (mtDNA) revealed the presence of part of the maize plasmid in the high molecular weight mtDNA of the maize relatives. RNA dot hybridization indicates that the plasmid is transcribed in mitochondria. The termini of the 2.3 kb linear plasmid contain inverted repeated sequences; of the first 17 nucleotides of the termini, 16 are identical to the terminal inverted repeats of the linear S plasmids found in the mitochondria of cmsS maize plants.