Glass transition temperatures and fermentative activity of heat-treated commercial active dry yeasts

Differential scanning calorimetry thermograms of various samples of commercial instant active dry yeasts revealed a clear glass transition typical of amorphous carbohydrates and sugars. The resulting glass transition temperatures were found to decrease with increasing moisture content. The observed glass curve was similar to that of pure trehalose, which is known to accumulate in large amounts in baker's yeast. The effect of heat treatment at various temperatures on the fermentative activity (as measured by the metabolic production of CO(2)) of dry yeast was studied. First-order plots were obtained representing the loss of fermentative activity as a function of heating time at the various temperatures assayed. Significant losses of fermentative activity were observed in vitrified yeast samples. The dependence of rate constants with temperature was found to follow Arrhenius behavior. The relationship between the loss of fermentative activity and glass transition was not verified, and the glass transition was not reflected on the temperature dependence of fermentative activity loss.     

Genes normally expressed in the endosperm are expressed at early stages of microspore embryogenesis in maize

Reproduction in flowering plants is characterized by double fertilization and the resulting formation of both the zygotic embryo and the associated endosperm. In many species it is possible to experimentally deviate pollen development towards an embryogenic pathway. This developmental switch, referred to as microspore embryogenesis or androgenesis, leads to the formation of embryos similar to zygotic embryos. In a screen for genes specifically expressed during early androgenesis, two maize genes were isolated by mRNA differential display. Both genes represent new molecular markers expressed at a very young stage of androgenic embryogenesis. When their expression pattern was studied during normal reproductive development, both showed early endosperm-specific expression. Investigation of the cytological features of young androgenic embryos revealed that they present a partially coenocytic organization similar to that of early endosperm. These findings suggest that maize androgenesis may possibly involve both embryogenesis and the establishment of endosperm-like components.     

Commercial baker's yeast stability as affected by intracellular content of trehalose, dehydration procedure and the physical properties of external matrices

The effects of vacuum-drying and freeze- drying on the cell viability of a commercial baker's yeast, Saccharomyces cerevisiae, strain with different endogenous contents of trehalose were analyzed. An osmotolerant Zygosaccharomyces rouxii strain was used for comparative purposes. Higher viability values were observed in cells after vacuum-drying than after freeze-drying. Internal concentrations of trehalose in the range 10–20% protected cells in both dehydration processes. Endogenous trehalose concentrations did not affect the water sorption isotherm nor the T _g values. The effect of external matrices of trehalose and maltodextrin was also studied. The addition of external trehalose improved the survival of S. cerevisiae cells containing 5% internal trehalose during dehydration. Maltodextrin (1.8 kDa) failed to protect vacuum-dried samples at 40 °C. The major reduction in the viability during the freeze-drying process of the sensitive yeast cells studied was attributed to the freezing step. The suggested protective mechanisms for each particular system are vitrification and the specific interactions of trehalose with membranes and/or proteins. The failure of maltodextrins to protect cells was attributed to the fact that none of the suggested mechanisms of protection could operate in these systems. Received: 6 December 1999 / Received revision: 8 May 2000 / Accepted: 19 May 2000     

An estimation of 137Cs accumulation in forest fungi by the soil properties

A method of calculation of radiocaesium uptake by forest mushrooms as a function of soil properties is presented. Calculated value of 137Cs transfer factor for Xerocomus badius in the contaminated area of Bryansk Province of Russia is in a good agreement with experimental data.     

Adaptation of Spodoptera exigua (Lepidoptera: Noctuidae) to barley trypsin inhibitor BTI-CMe expressed in transgenic tobacco

Nicotiana tabacum plants were transformed with the cDNA of barley trypsin inhibitor BTI-CMe under the control of the 35S CaMV promoter. Although the transgene was expressed and the protein was active in the homozygous lines selected, growth of Spodoptera exigua (Lepidoptera: Noctuidae) larvae reared on transgenic plants was not affected. The protease activity in larval midgut extracts after 2 days feeding on transformed tobacco leaves from the highest expressing plant showed a reduction of 25% in the trypsin-like activity compared to that from insects fed on non-transformed controls. The susceptibility of digestive serine-proteases to inhibition by BTI-CMe was confirmed by activity staining gels. This decrease was compensated with a significant induction of leucine aminopeptidase-like and carboxipeptidase A-like activities, whilechymotrypsin-, elastase-, and carboxipeptidase B-like proteases were not affected.     

A neural set point for the long-term control of arterial pressure: beyond the arterial baroreceptor reflex

Arterial baroreceptor reflex control of renal sympathetic nerve activity (RSNA) has been proposed to play a role in long-term control of arterial pressure. The hypothesis that the "set point" of the acute RSNA baroreflex curve determines the long-term level of arterial pressure is presented and challenged. Contrary to the hypothesis, studies on the long-term effects of sinoaortic denervation (SAD) on arterial pressure and RSNA, as well as more recent studies of chronic baroreceptor "unloading" on arterial pressure, suggest that the basal levels of sympathetic nerve activity and arterial pressure are regulated independent of arterial baroreceptor input to the brainstem. Studies of the effect of SAD on the long-term salt sensitivity of arterial pressure are consistent with a short-term role, rather than a long-term role for the arterial baroreceptor reflex in regulation of arterial pressure during changes in dietary salt intake. Renal denervation studies suggest that renal nerves contribute to maintenance of the basal levels of arterial pressure. However, evidence that baroreflex control of the kidney plays a role in the maintenance of arterial pressure during changes in dietary salt intake is lacking. It is proposed that a "baroreflex-independent" sympathetic control system must exist for the long-term regulation of sympathetic nerve activity and arterial pressure. The concept of a central nervous system "set point" for long-term control of mean arterial pressure (CNS-MAP set point), and its involvement in the pathogenesis of hypertension, is discussed.     

Effect of sarcolemmal rupture on myocardial electrical impedance during oxygen deprivation

Plasma membrane disruption is a characteristic feature of cell death induced by hypoxia or ischemia. Here, we investigated whether analysis of tissue electrical impedance allows detection of ongoing cell membrane rupture and necrotic cell death in hypoxic or ischemic myocardium. Twenty-eight isolated rat hearts were submitted to 5 h of ischemia (n = 8) or hypoxia (n = 20). Myocardial electrical impedance and lactate dehydrogenase (LDH) release were monitored. The time course of hypoxia-induced cell death was modified by altering pH (pH 7.4 or 6.4, 5 h) or by adding 3 or 10 mM glycine. Ischemia and hypoxia induced an increase in electrical impedance, followed by a plateau, and later a reduction. During hypoxia, LDH release started after a prolonged lapse of time (80.00 +/- 8.37 min at pH 7.4 and 122.50 +/- 11.82 min at pH 6.4). The onset of LDH release was followed by the onset of the late reduction in electrical impedance, and both were delayed by acidic pH (P < 0.05) and by glycine (P < 0.05). The times of onset of LDH release and of late electrical changes were significantly correlated (r = 0.752, P < 0.001). In separate experiments, induction of sarcolemmal rupture with Triton X-100 (n = 6) mimicked the late effects of ischemia or hypoxia on tissue impedance. The protective effects of glycine and acidosis on membrane disruption were confirmed (propidium iodide) in energy-deprived HL-1 cardiomyocytes. These results describe for the first time a late fall in electrical impedance in myocardium submitted to prolonged oxygen deprivation and demonstrate that this fall allows detection of ongoing cell necrosis.     

Effects of Dihydrotestosterone on Brain mRNA Levels of Steroid 5α-Reductase Isozymes in Early Postnatal Life of Rat

We studied the expression of type 1 (5α-R1) and type 2 (5α-R2) 5α-reductase isozymes (5α-R) and their regulation by dihydrotestosterone (DHT) in the prefrontal cortex of male and female rats during postnatal sexual differentiation of the central nervous system (CNS), using one-step quantitative RT-PCR coupled with laser-induced fluorescence capillary electrophoresis. We found a higher expression of 5α-R2, which is considered a masculinizing enzyme, in the female versus male CNS, and observed sexual dimorphism in the regulation of both 5α-R isozymes by DHT. These results open up a new research line that could improve understanding of the role of 5α-R isozymes in the physiology of the CNS.     

Rapid method for enumeration of viable Legionella pneumophila and other Legionella spp. in water

A sensitive and specific method has been developed to enumerate viable L. pneumophila and other Legionella spp. in water by epifluorescence microscopy in a short period of time (a few hours). This method allows the quantification of L. pneumophila or other Legionella spp. as well as the discrimination between viable and nonviable Legionella. It simultaneously combines the specific detection of Legionella cells using antibodies and a bacterial viability marker (ChemChrome V6), the enumeration being achieved by epifluorescence microscopy. The performance of this immunological double-staining (IDS) method was investigated in 38 natural filterable water samples from different aquatic sources, and the viable Legionella counts were compared with those obtained by the standard culture method. The recovery rate of the IDS method is similar to, or higher than, that of the conventional culture method. Under our experimental conditions, the limit of detection of the IDS method was <176 Legionella cells per liter. The examination of several samples in duplicates for the presence of L. pneumophila and other Legionella spp. indicated that the IDS method exhibits an excellent intralaboratory reproducibility, better than that of the standard culture method. This immunological approach allows rapid measurements in emergency situations, such as monitoring the efficacy of disinfection shock treatments. Although its field of application is as yet limited to filterable waters, the double-staining method may be an interesting alternative (not equivalent) to the conventional standard culture methods for enumerating viable Legionella when rapid detection is required.