Influence of Abscisic Acid on Phosphorus Metabolism and Respiration in Potato Tuber Discs. Comparison with the Cycloheximide Effect

Ageing of discs of potato tuber by incubation in an aerated medium, produces an increase in the rates of respiration and of phosphate uptake. The presence of cycloheximide (CHM) or abscisic acid (ABA) in the uptake medium, does not change uptake by fresh tissue over 3–4 h. On the other hand, CHM causes an inhibition of the rate of uptake by aged tissue although ABA does not. The addition of CHM or ABA to the ageing medium, prevents totally (CHM) or only partially (ABA) the increase in phosphate uptake. The analysis of ³²P-incorporation into the various phosphorylated fractions after 24 h of ageing with CHM or ABA show that CHM induces a large inhibition of the rate of uptake with an almost complete inhibition of ³²P-incorporation into the various phosphorylated fractions. By contrast, ABA produces equal inhibition of ³²P labelling of all fractions including all acid-soluble components. CHM prevents the increase in the rate of respiration, whereas ABA causes a slight stimulation. In both cases, no important effect on ATP content was observed. These results are discussed in terms of a comparison of ABA and CHM actions. They lead to the hypothesis of a specific effect of ABA on the development of the uptake mechanism.     

The presence of conifer resin decreases the use of the immune system in wood ants

Abstract.  1. Wood ants ( Formica paralugubris ) incorporate large amounts of solidified conifer resin into their nest, which reduces the density of many bacteria and fungi and protects the ants against some detrimental micro-organisms. By inducing an environment unfavourable to pathogens, the presence of resin may allow workers to reduce the use of their immune system.
2. The present study tested the hypothesis that the presence of resin decreases the immune activity of wood ants. Specifically, three components of the humoral immune defences of workers kept in resin-rich and resin-free experimental nests (antibacterial, lytic, and prophenoloxidase activities) were compared.
3. The presence of resin was associated with reduced bacterial and fungal densities in nest material and with a small decrease in worker antibacterial and lytic activities. The prophenoloxidase activity was very low in all workers and was not affected by the presence of resin.
4. These results suggest that collective medication with resin reduces pathogen pressure, which in turn decreases the use of the inducible part of the immune system. More generally, the use of plant secondary compounds might be an efficient and economical way to fight pathogens.     

Microclimatic buffering and resource‐based habitat in a glacial relict butterfly: significance for conservation under climate change

In contrast to several organisms that have already shown range shifts to the north as a response to climate change, southern populations of relict species are trapped in isolated altitudinal habitats. Therefore, there is a growing interest to better understand their habitat use, with particular attention to the thermal aspects and associated significance for their habitat management. We address this issue by a study of larval habitat use relative to vegetation structure and microclimate in a glacial relict butterfly of peat bog ecosystems, using a functional, resource‐based habitat approach. We analysed caterpillar presence and density relative to vegetation composition (reflecting gradients of humidity, temperature, and natural succession of the peat bog) and to the availability and quality of thermal refuges for caterpillars (i.e., structures provided by Sphagnum hummocks). We also tested caterpillar survival rates under different temperature and humidity treatments. We found that (1) Boloria aquilonaris was a specialist butterfly of early successional stages with very humid zones of peat bog, (2) the lack of Sphagnum hummocks reduced larval habitat suitability, and hence the population density, and (3) a reduction of the thermal buffering ability of Sphagnum hummocks was observed in less humid, degraded parts, or late‐successional stages of peat bog. A larval rearing experiment showed a significant impact of temperature on caterpillar survival; survival being higher at lower temperature. Our field and laboratory results support the idea that the thermal environment exploited by caterpillars should be considered as a functional resource and included in a population‐specific habitat definition. Appropriate management of the peat bog habitat of this glacial relict species should not exclusively focus on the larval and adult feeding resources, but also on the quality of thermal refuges provided by Sphagnum hummocks in humid zones of the peat bog, especially in the current critical context of climate warming.     

Characterization and PCR multiplexing of polymorphic microsatellite loci for the locust Locusta migratoria

Because of the scarcity of polymorphic genetic markers available in locust species, only a few population genetics studies have been carried out on this taxon. We isolated and characterized 11 polymorphic microsatellite loci in the pest locust Locusta migratoria capito, and described experimental conditions for polymerase chain reaction (PCR) multiplexing and simultaneously genotyping these loci. The number of alleles per locus ranged from six to 25, and the expected heterozygosity ranged from 0.431 to 0.957. Results of cross‐taxon amplification tests are reported in six other Locusta migratoria subspecies, six species of the Oedipodinae subfamily and two other pest locust species.     

A Freeze-Fracture Study of the Cortex of Xenopus laevis Eggs

The organization of the cortex of Xenopus laevis eggs was investigated by freeze-fracture electron microscopy. The cortical endoplasmic reticulum (CER) formed a network surrounding and interconnecting the cortical granules. It formed junctions with the plasma membrane and was confluent with the ER in subcortical regions. Intramembranous particles (IMP₁) were only present in the P face of the CER, the E face being apparently devoid of pits and particles. Arrays of densely packed IMP₁, having a mean diameter of 17 nm, were restricted to the microvillar region of the plasma membrane. The cortical granule membrane also contained IMP₁ (mean diameter, 21 nm) that were sparsely and randomly distributed. Several types of cortical granule seemed to exist based on an analysis of the distribution of the different IMP sizes.