Differentiation and structural decline in the leaves and bark of birch (Betula pendula) under low ozone concentrations

Summary Leaf and bark structure of a birch clone (Betula pendula Roth) continuously exposed to charcoal-filtered air or charcoal-filtered air plus ozone (0.05, 0.075, 0.1 l 1^-1) was investigated throughout one growing season. Increasing ozone dose influenced leaf differentiation by reducing leaf area and increasing inner leaf air space, density of cells developing into stomata, scales and hairs. When approximately the same ozone dose had been reached, macroscopical and microscopical symptoms appeared irrespective of the ozone concentration used during treatment. Structural decline began in mesophyll cells around stomatal cavities (droplet-like exudates on the cell walls), continued with disintegration of the cytoplasma and ended in cell collapse. Epidermal cells showed shrinkage of the mucilaginous layer (related to water loss). Their collapse marked the final stage of leaf decline. When subsidiary cells collapsed, guard cells passively opened for a transitory period before collapsing and closing. With increasing ozone dose starch remained accumulated along the small leaf veins and in guard cells. IIK-positive grains were formed in the epidermal cells. This contrasted with the senescent leaves, where starch was entirely retranslocated. Injury symptoms in stem and petiole proceeded from the epidermis to the cambium. Reduced tissue area indicated reduced cambial activity. In plants grown in filtered air and transferred into ozone on 20 August, injury symptoms developed faster than in leaves formed in the presence of ozone. Results are discussed with regard to O₃-caused acclimation and injury mechanisms.     

The distance dependence prediction of the Janzen-Connell hypothesis: a meta-analysis

The Janzen-Connell hypothesis explains the maintenance of tropical diversity through the interacting effects of parent-centered dispersal patterns and distance- and density-dependent propagule survival. These effects were thought to support regular spacing of species within tropical forest, enhancing diversity. One of the predictions of the hypothesis is that seed and seedling survival should improve with increased parental distance. Although there are many independent tests of this hypothesis for individual species, there are few synthetic studies that have brought these data together to test its validity across species. This paper reports the results of a meta-analysis of the effect of distance on enhancing propagule survival, employing an odds-ratio effect size metric. We found no general support for the distance-dependent prediction of the hypothesis, and conclude that further testing to explore this hypothesis as a diversity-maintaining mechanism is unnecessary. However, we did find that distance from parent slightly reduces survivorship in the temperate zone, as contrasted with the tropics, and we saw stronger evidence in support of the hypothesis for seedlings than for seeds. The phenomenon of enhanced propagule survival with distance from the parent may be important for the population biology of particular species, but it is not a general phenomenon across communities, life history stages or life forms.     

Benzothiadiazole induces disease resistance in Arabidopsis by activation of the systemic acquired resistance signal transduction pathway

Benzothiadiazole (BTH) is a novel chemical activator of disease resistance in tobacco, wheat and other important agricultural plants. In this report, it is shown that BTH works by activating SAR in Arabidopsis thaliana. BTH-treated plants were resistant to infection by turnip crinkle virus, Pseudomonas syringae pv ‘tomato’ DC3000 and Peronospora parasitica. Chemical treatment induced accumulation of mRNAs from the SAR-associated genes, PR-1, PR-2 and PR-5. BTH treatment induced both PR-1 mRNA accumulation and resistance against P. parasitica in the ethylene response mutants, etr1 and ein2, and in the methyl jasmonate-insensitive mutant, jar1, suggesting that BTH action is independent of these plant hormones. BTH treatment also induced both PR-1 mRNA accumulation and P. parasitica resistance in transgenic Arabidopsis plants expressing the nahG gene, suggesting that BTH action does not require salicylic acid accumulation. However, because BTH-treatment failed to induce either PR-1 mRNA accumulation or P. parasitica resistance in the non-inducible immunity mutant, nim1, it appears that BTH activates the SAR signal transduction pathway.     

Autonomous replication in Drosophila melanogaster tissue culture cells

This study addresses the ability of DNA fragments from various sources to mediate autonomous DNA replication in cultured Drosophila melanogaster cells. We created a series of plasmids containing genomic DNA fragments from the Ultrabithorax gene of Drosophila and tested them for autonomous replication after transfection into Schneider line 2 cells. We found that all plasmids containing Drosophila DNA fragments were able to replicate autonomously, as were plasmids containing random human and Escherichia coli genomic DNA fragments. Most of the plasmids were detectable 18 days after transfection in the absence of selection, suggesting that transfected DNA is maintained in Drosophila cells without rapid loss or degradation. The finding that all plasmids containing Drosophila, human, or bacterial DNA replicate autonomously in Drosophila cells suggests that the signals that direct autonomous replication in Drosophila contain a low degree of sequence specificity. A two-dimensional gel analysis of initiation on one of the plasmids was consistent with many dispersed initiation sites. Low sequence specificity and dispersed initiation sites also characterize autonomous replication in human cells and Senopus eggs and may be general properties of autonomous replication in animal cells.     

Effects of magnesium and iron on lipid peroxidation in cultured hepatocytes

In primary cultures of rat hepatocytes, the effects of extracellular Mg²⁺ and Fe on lipid peroxidation (LPO) as measured by means of malondialdehyde (MDA) formation were investigated.Incubation of hepatocytes at decreasing extracellular Mg²⁺ concentration enhanced LPO, depending on extracellular Fe. About 96% of MDA accumulated in the culture medium. Addition of desferrioxamine prevented LPO.Additionally, the formation of oxygen free radicals was determined by fluorescence reduction of cis-parinaric acid. With this method, an immediate decay of fluorescence was found after addition of Fe²⁺. Fluorescence reduction was completely prevented by desferrioxamine, indicating the function of extracellular Fe. This mechanism may operate additionally to the increase in intracellular Fe and intracellular formation of oxygen free radicals during Mg deficiencyin vivo.     

Isolated sheep heart hypothermic (5–13 °C) perfusion with fresh blood: Successful preservation for 24–72 hours with continuous strong ventricular activity

Isolated lamb hearts perfused with fresh whole blood at 10 and 13 °C in an ex vivo perfusion circuit continuously contracted at a rate of 15 to 20 times/min with a peak left ventricular systolic pressure (LVPSP) up to 70 mm Hg. These contractions persisted for the duration of the hypothermic study, up to three days with no change in vascular resistance. On rewarming to 38 °C, the hearts resumed regular and efficient contractions. Hearts perfused at 5 °C, however, exhibited no electrical or mechanical activity during hypothermic preservation and were uniformly poorly preserved.Quality of heart preservation was improved if, prior to final cooling, hearts were first rewarmed to 38 °C, followed by cooling. Change of the support animal, or interruption of flow of fresh blood into the perfusion circuit, resulted in cessation of ventricular contractions, ventricular fibrillation, and poor organ preservation.     

Non-random X-chromosome expression early in mouse development

We have used a sensitive electrophoretic technique for estimating the activity, or ratio, of two allozymes of the X-chromosome-linked enzyme phosphoglycerate kinase (PGK-1), in order to investigate the randomness of X-chromosome expression in the derivatives of the three primary cell lineages of the early mouse conceptus. The maternally derived Pgk-1 allele is preferentially expressed in the derivatives of the primitive endoderm and trophectoderm lineages at 6 1/2 days post coitum in Pgk-1^a/Pgk-1^b heterozygous conceptuses, and in the one informative 5 1/2-day heterozygous conceptus analysed. This evidence for preferential expression of the maternally derived X chromosome (X^m), so soon after the time of X-chromosome inactivation, favors the possibility that the preferential expression of X^m is a consequence of primary non-random X-chromosome inactivation, rather than a secondary selection phenomenon. The majority of embryos analysed at 4 1/2 and 5 1/2 days pc produced only a single PGK-1 band, corresponding to the allozyme produced by the Pgk-1 allele on X^m, although 50% of these embryos should have been heterozygous females. Possible explanations are discussed.     

Copper Toxicosis in Bedlington Terriers

Copper toxicosis of Bedlington Terriers (Chronic progressive hepatitis) is a genetically transmitted disease. The typical feature of this disease is accumulation of copper in the liver tissue. The changes vary from mild hepatitis to chronic progressive hepatitis and cirrhosis. The material of this study consists of 2 cases of copper toxicosis examined at the Department of Pathology in Helsinki in the years 1980–82. Moreover a re-examination of tissue samples was made of all Bedlington Terriers examined during the years 1969–1982 at the same department. Six of the 14 examined dogs showed a positive reaction for copper in their liver tissues. The possible relationship of the examined dogs is not yet known.