Why is stress so deadly? An evolutionary perspective

The reaction of the body to prolonged stress has many harmful effects. Classical theory assumes that stress responses have evolved due to their short-term selective advantages ('flight or fight'), and despite their adverse long-term effects. In contrast, we demonstrate that the adverse effects of stress responses may have a selective advantage. Using an analytical model we show that a gene that causes the early death of a relatively unfit individual can increase in frequency in a structured population even if it has no positive effect on that individual. This result offers a new perspective on the relations between stress factors, stress responses and stress-related diseases.     

Transgenic tobacco plants overexpressing the Met25 gene of Saccharomyces cerevisiae exhibit enhanced levels of cysteine and glutathione and increased tolerance to oxidative stress

Summary. The cysteine biosynthesis pathway differs between plants and the yeast Saccharomyces cerevisiae. The yeast MET25 gene encoded to O-acetylhomoserine sulfhydrylase (AHS) catalyzed the reaction that form homocysteine, which later can be converted into cystiene. In vitro studies show that this enzyme possesses also the activity of O-acetyl(thiol)lyase (OASTL) that catalyzes synthesis of cysteine in plants. In this study, we generated transgenic tobacco plants expressing the yeast MET25 gene under the control of a constitutive promoter and targeted the yeast protein to the cytosol or to the chloroplasts. Both sets of transgenic plants were taller and greener than wild-type plants. Addition of SO₂, the substrate of the yeast enzyme caused a significant elevation of the glutathione content in representative plants from each of the two sets of transgenic plants expressing the yeast gene. Determination of non-protein thiol content indicated up to four-folds higher cysteine and 2.5-fold glutathione levels in these plants. In addition, the leaf discs of the transgenic plants were more tolerant to toxic levels of sulphite, and to paraquat, an herbicide generating active oxygen species.     

TMV-induced expression of tobacco β-glucanase promoter activity is mediated by a single, inverted, GCC motif

Tobacco basic β-1,3-glucanase has been implicated in plant development and defense responses against pathogens. We examined the functional cis-elements involved in the response of basic β-1,3-glucanase promoter (gglb50) to infection with tobacco mosaic virus (TMV). In plants transformed with chimeric gglb50-β-glucuronidase (GUS) reporter gene, significant GUS-activity levels were measured in the leaves and in roots. Activity in the leaves was further induced (10-fold) by TMV infection. Maximal virus-induced activity was directed by a promoter region between −1233 to +19 (gglb-1233). A 5′ deletion to −1038, which removed two TAAGAGCCGCC motifs (GCC-boxes), reduced virus-induced activity. However, when the gglb-1233 promoter was mutated by base substitutions within a third, inverted, GCC-box located between positions −106 and −95, virus-induced promoter activity was abolished. Duplication of a small region containing this inverted GCC-box in the context of the gglb-1233 promoter resulted in increased virus-induced activity. Gel retardation assay demonstrated nuclear-factor binding to the inverted GCC-box. These studies strongly suggest the inverted GCC-box as a regulatory element essential for TMV-induced activity directed by the gglb50 promoter.     

Phosphorylation of tyrosine in cultured human placenta

The [³²P]phosphoamino acids in proteins of first trimester and term-cultured human placentas have been separated and their relative amounts were measured. A significant phosphorylation of tyrosine residues could be detected in the cultured placental tissue at different stages of gestation. The phosphotyrosine accounts for 2–4% of the total acid-stable phosphate in the phosphoamino acids after partial acid hydrolysis. The difference in the extent of [³²P]tyrosine in various placentas seems to be a function of biological variation of the individual placentas, rather than a function of placental age and stage of gestation. In contrast, a significant difference in the phosphorylation ratio of serine and threonine could be measured between first trimester and term placentas. As more evidence is accumulating that protein phosphorylation of tyrosine is involved in the processes of cellular growth and proliferation, our findings of the relatively high tyrosine phosphorylation in human placenta strongly suggest that this type of protein phosphorylation may play an important role in the placental growth and development. Furthermore, these findings may correlate with the existence of the endogenous RNA virus-like particles found in normal human placenta.     

Early perturbation in mitochondria redox homeostasis in response to environmental stress predicts cell fate in diatoms

Diatoms are ubiquitous marine photosynthetic eukaryotes that are responsible for about 20% of global photosynthesis. Nevertheless, little is known about the redox-based mechanisms that mediate diatom sensing and acclimation to environmental stress. Here we used a redox-sensitive green fluorescent protein sensor targeted to various subcellular organelles in the marine diatom Phaeodactylum tricornutum, to map the spatial and temporal oxidation patterns in response to environmental stresses. Specific organelle oxidation patterns were found in response to various stress conditions such as oxidative stress, nutrient limitation and exposure to diatom-derived infochemicals. We found a strong correlation between the mitochondrial glutathione (GSH) redox potential (E_GSH) and subsequent induction of cell death in response to the diatom-derived unsaturated aldehyde 2E,4E/Z-decadienal (DD), and a volatile halocarbon (BrCN) that mediate trophic-level interactions in marine diatoms. Induction of cell death in response to DD was mediated by oxidation of mitochondrial E_GSH and was reversible by application of GSH only within a narrow time frame. We found that cell fate can be accurately predicted by a distinct life-death threshold of mitochondrial E_GSH (−335 mV). We propose that compartmentalized redox-based signaling can integrate the input of diverse environmental cues and will determine cell fate decisions as part of algal acclimation to stress conditions.     

Nerve-dependent changes in content of ribosomes, polysomes, and nascent peptides in newt limb regenerates.

Regeneration of a newt limb requires a constant supply of adequate amounts of a neuronal contribution at the amputation site. Denervation during the early stages of regeneration precludes its growth and morphogenesis. It has been reported that denervation of a regenerating limb lowers the efficiency of incorporation of radioactive amino acids to 60% of contralateral control levels. To gain more insight into the mechanism responsible for this decrease, we examined the effects of denervation on the size distribution and quantity of regenerate polysomes. We characterized the [³⁵S]methionine-labeled nascent peptidyl-tRNA from polysomes by hydroxyapatite chromatography. Moreover, we show that the labeled nascent peptides on polysomes can serve as a measure to quantitate the relative amounts of ribosomes on polysomes and the relative size of the translational machinery. Thus, we report that [³⁵S]methionine-labeled nascent polypeptides on polysomes from denervated regenerates contain about 48% less radioactivity than those from controls. Despite decreased incorporation of [³⁵S]methionine into nascent peptides, the relative distribution of radioactivity across linear sucrose gradients is not significantly altered by denervation. Studies of polysomes labeled with [³H]uridine prior to denervation indicate that ribosome content is depressed by denervation. Our results suggest that the nerve-dependent decrease in protein synthesis is mediated by decreasing the number of ribosomes active in protein synthesis. In addition, similarities in the ratios of free monosomes to polysomes and the relative size distribution of polypeptides between denervated and innervated regenerates indicate that in denervated regenerates the number of translatable mRNA molecules decreases in a coordinate manner with the number of ribosomes active in protein synthesis.     

On the founder effect and the evolution of altruistic traits: An ecogenetical approach

The evolution of some altruistic traits in a population repeatedly recolonizing temporal habitats is studied. Special consideration is given to the joint effect of the population density and gene frequencies.