Aestival dormancy in the cabbage moth Mamestra brassicae L. (Lepidoptera: Noctuidae)

Summary In a geographically wide distribution the life cycles of different populations of the cabbage moth Mamestra brossicae are adapted to a remarkable diversity of climatic conditions. This is undoubtedly a proof of its success in adaptation. Some populations living in regions characterized by a drought period interrupting the growth season are capable of distinguishing between one critical day length signalling the onset of the drought period and another signalling the end of the growth season. This study, therefore, is primarily concerned with the geographical patterns in the variability of the adaptional responses of populations exposed to environmental conditions requiring different strategies and tactics in, synchronizing individual, life cycles. It is also a contribution to our understanding of evolutionary mechanisms maintaining median responses to photoperiodically inductive day lengths in geographically different populations. The populations investigated originated from regions differing in predictability of the incidence, onset and duration of a drought period: Freiburg (48.0°N, Southern Germany), Avignon (44.0°N, Southern France), and Argelès (42.5°N, Southern France). Geographical variation with respect to both onset and duration of a drought period consequently results in clinal variation of the variability of innate day length thresholds triggering aestival dormancy and of innate duration of aestivation. In this paper we considered the influence of geographically changing temperatures on aestival dormancy induction. Even in southern populations of M. brassicae a temperature dependent switch off-mechanism exists which prevents aestival dormancy under certain environmental conditions. The effective temperatures vary geographically, too. What the geographical patterns in adaptive responses really are, is discussed.This research was supported by the Deutsche Forschungsgemeinschaft (Sa 259/3-1)     

Molecular hydrogen from water radiolysis as an energy source for bacterial growth in a basin containing irradiating waste

Although being deionized, filtered and therefore normally deeply oligotrophic, the water from a basin containing irradiating waste presented relatively high bacterial concentrations (ca 10(5) cfu ml(-1)) and biofilm development at its surface and on the walls. This water was characterized by a high concentration of molecular H2 due to water radiolysis, while its electrochemical potential was around +400 mV due the presence of dissolved O2 and active oxygen compounds. This combination of H2 availability and of an oxidant environment is completely original and not described in nature. From surface and wall biofilms, we enumerated the autotrophic populations ( approximately 10(5) bacteria ml(-1)) able to grow in presence of H2 as energy source and CO2 as carbon source, and we isolated the most abundant ones among cultivable bacteria. They efficiently grew on a mineral medium, in the presence of H2, O2 and CO2, the presence of the three gases being indispensable. Two strains were selected and identified using their rrs gene sequence as Ralstonia sp. GGLH002 and Burkholderia sp. GGLH005. In pure culture and using isotope exchange between hydrogen and deuterium, we demonstrated that these strains are able to oxidize hydrogen as energy source, using oxygen as an electron acceptor, and to use carbon dioxide as carbon source. These chemoautotroph hydrogen-oxidizing bacteria probably represent the pioneer bacterial populations in this basin and could be primary producers in the bacterial community.     

A Single Amino Acid Tunes Ca2+ Inhibition of Brain Liver Intestine Na+ Channel (BLINaC)

Ion channels of the degenerin/epithelial Na⁺ channel gene family are Na⁺ channels that are blocked by the diuretic amiloride and are implicated in several human diseases. The brain liver intestine Na⁺ channel (BLINaC) is an ion channel of the degenerin/epithelial Na⁺ channel gene family with unknown function. In rodents, it is expressed mainly in brain, liver, and intestine, and to a lesser extent in kidney and lung. Expression of rat BLINaC (rBLINaC) in Xenopus oocytes leads to small unselective currents that are only weakly sensitive to amiloride. Here, we show that rBLINaC is inhibited by micromolar concentrations of extracellular Ca²⁺. Removal of Ca²⁺ leads to robust currents and increases Na⁺ selectivity of the ion pore. Strikingly, the species ortholog from mouse (mBLINaC) has an almost 250-fold lower Ca²⁺ affinity than rBLINaC, rendering mBLINaC constitutively active at physiological concentrations of extracellular Ca²⁺. In addition, mBLINaC is more selective for Na⁺ and has a 700-fold higher amiloride affinity than rBLINaC. We show that a single amino acid in the extracellular domain determines these profound species differences. Collectively, our results suggest that rBLINaC is opened by an unknown ligand whereas mBLINaC is a constitutively open epithelial Na⁺ channel.     

The regulation of exogenous NAD(P)H oxidation in spinach (Spinacia oleracea) leaf mitochondria by pH and cations.

Essentially chlorophyll-free mitochondria were isolated from green leaves of spinach (Spinacia oleracea L. cv. Viking II). Uncoupled oxidation of exogenous NADPH (1 mM) to oxygen had an optimum at pH 6.0, and activity was relatively low at pH 7.0, even in the presence of 1 mM-CaCl2. There was a proportional increase in the apparent Km for NADPH with decreasing H+ concentrations, suggesting that NADPH protonated on the 2'-phosphate group was the true substrate. Exogenous NADH was oxidized by oxygen with an optimum at pH 6.9. Under low-cation conditions, EGTA or EDTA (both 1 mM) had no effect on the Vmax. of NADH oxidation, although the removal of bivalent cations from the membrane surface by the chelators could be observed by use of 9-aminoacridine fluorescence. In contrast, under high-cation conditions, chelators lowered the Vmax. by about 50%, probably due to a better approach of the negatively charged chelators to the negative membrane surface than under low-cation conditions. In a low-cation medium, the Vmax. of NADH oxidation was increased by about 50% by the addition of cations. This was caused by a lowering of the size of the negative surface potential through charge screening. In contrast with other cations, La3+ inhibited NADH oxidation, possibly through binding to lipids essential for NADH oxidation. The apparent Km for NADH varied 6-fold in response to changes in the size of the surface potential, suggesting that the approach of the negatively charged NADH to the active site is hampered by the negative surface potential. The results demonstrate that the spinach leaf cell can regulate the mitochondrial NAD(P)H oxidation through several mechanisms: the pH; the cation concentration in general; and the concentration of Ca2+ in particular. The results also emphasize the importance of electrostatic considerations when investigating the kinetic behaviour of membrane-bound enzymes.     

An efficient procedure for serial nucleic acid hybridizations by titration analysis.

A simplified and efficient procedure has been developed for performing hybridization reactions and analyses of the percentage of hybridization on glass plates. This method is as accurate as conventional methods, while considerably reducing the time and costs to perform the hybridization in titration hybridization experiments.