EVOLUTIONARY ADAPTATION TO TEMPERATURE. IX. PREADAPTATION TO NOVEL STRESSFUL ENVIRONMENTS OF ESCHERICHIA COLI ADAPTED TO HIGH TEMPERATURE

Abstract Stressful environments may be considered as those that reduce fitness, sometimes due in part to the increased metabolic expenditure required to sustain life. Direct adaptation to a stressor is expected to increase fitness and reduce maintenance metabolism, with the latter leading to increased biomass production. In this study, we test the general hypothesis that such adaptation to one stressor can preadapt organisms to novel stressful environments. Six lines of Escherichia coli propagated for 2000 generations at 41–42°C (42 group), a stressful temperature, were compared to six control lines propagated for 2000 generations at 37°C (37 group) and to the common ancestor of both groups. We assayed biovolume yield (a measure of growth efficiency) and competitive fitness in the 42 group's selective high temperature environment as well as five novel stressful environments–acid, alkali, ethanol, high osmolarity and peroxide. As previously reported, at high temperature the 42 group had both higher yield and fitness than the 37 group and ancestor. In the novel environments, the 42 group generally produced yields higher than the 37 group (and marginally higher than the ancestor), but we found no differences in competitive fitness among the 37 and 42 groups and the ancestor. We also found that the performance of lines within groups was not correlated across stressful environments for either yield or relative fitness. Because previous adaptation to one stressor did not improve our measure of Darwinian fitness in novel stressful environments, we conclude that the 42 group shows no useful preadaptation, or cross‐tolerance, to these types of environments.     

UV-B预处理诱导拟南芥耐旱性的提高

为了解UV-B提高拟南芥(Arabidopsis thaliana)耐旱性的生理机制,将2周龄的野生型拟南芥(WT)和sto突变体幼苗用不同剂量UV-B预处理1周,再用30%PEG模拟干旱处理24 h,对植株的表型进行统计,并测定类黄酮、脯氨酸和MDA含量。结果表明,低剂量UV-B预处理能够提高拟南芥的耐旱性,植株的类黄酮与脯氨酸含量分别提高了20%～40%和50%～65%,细胞膜受损程度降低,从而提高了保水性。低剂量UV-B提高拟南芥耐旱性的效应在sto突变体中消失,证明这种效应在分子机制上可能与STO蛋白相关。     

Endogenous ligands for κ-opiate receptors

The receptor preferences of opioids in the mouse vas deferens was tested by means of tolerance and cross-tolerance studies. The preparations were rendered tolerant in situ by superfusion with the κ-receptor agonist dynorphin and with α-neoendorphin, respectively, and set up in vitro in the presence of the respective peptide to maintain tolerance. The investigations revealed strong κ-agonistic activities both of α-neoendorphin and of dynorphin and its fragments 1–13 and 1–11. As the dynorphin chain shortened, the κ-receptor activity declined and δ-receptor activity became progressively apparent. Interestingly, the octapeptide met-enkephalin[Arg⁶,Gly⁷,Leu⁸], a fragment of the adrenal medulla proenkephalin, also displayed considerable κ-agonistic properties under the experimental conditions employed. Presumably, the decapeptide α-neoendorphin and the octapeptide met-enkephalin[Arg⁶,Gly⁷,Leu⁸] cover in addition to the κ-receptor population in the MVD further opiate receptors, most probably δ-receptors.     

Survival types of high mountain plants under extreme temperatures

Extreme temperatures are a main factor limiting plant growth in high mountain habitats. During winter, the risk of frost damage is highest at windblown and often snow-free sites. During summer, actively growing plants are particularly endangered by episodic cold spells, but also by short-term overheating. The current review gives an overview of extreme temperatures in the European Alps and observations of temperature damage on plants in their natural habitats. Furthermore, seasonal time courses of frost and heat resistance derived from laboratory tests on different plant growth forms are presented. Study species were the cushion plants Silene acaulis, Minuartia sedoides, Saxifraga oppositifolia and Carex firma collected on wind-exposed ridges; the rosette plant Soldanella alpina collected on snow-protected sites, and three Sempervivum species collected in xerothermic habitats.     

Lack of tolerance and morphine-induced cross-tolerance to the analgesia of chimeric peptide of Met-enkephalin and FMRFa

Chimeric peptide of Met-enkephalin and FMRFa (YGGFMKKKFMRFa-YFa), a κ-opioid receptor specific peptide, did not induce tolerance and cross-tolerance effects to its analgesic action on day 5 after pretreatment with either YFa or morphine for 4 days. However, pretreatment with YFa for 4 days led to the development of cross-tolerance to the analgesic effects of morphine and also 4 days of pretreatment of morphine resulted in the expression of tolerance to its own analgesic effects. Similar expression of tolerance and cross-tolerance were also observed when YFa was compared with the κ receptor agonist peptide dynorphin A(1–13) [DynA(1–13)]. Cross-tolerance effects between YFa and DynA(1–13) analgesia were also not observed on day 5. Interestingly, when YFa and DynA(1–13) were tested for their analgesic effects for 5 days, reduction in analgesia on day 3 was observed in case of DynA(1–13) whereas YFa maintained its analgesia for 5 days. Thus, chimeric peptide YFa may serve as a useful probe to understand pain modulation and expression of tolerance and cross-tolerance behavior with other opioids.     

Common and distinctive responses of rice seedlings to saline- and osmotically-generated stress

Drought and salinity are the major abiotic factors limiting productivityin rice (Oryza sativa L.). Although both generate osmoticstress, ion toxicity is an additional and important component of salinity. Tostudy the morphological and anatomical responses to those types of stress, weused in vitro grown rice seedlings. Based on an initialscreening of several non-penetrating osmotica on seedling growth, we selectedsorbitol to compare its osmotic effects during seedling development with thosegenerated by NaCl stress. At comparable levels of osmolality, the reduction inroot and leaf growth as well as their delayed development were similar for bothsaline- and osmotically-generated stress. Some changes observed in root anatomyand most of the variations in leaf anatomy features caused by the treatmentscould be ascribed to osmotic stress. However, there were evident differences inthe morphology of the root system as well as in chlorophyll levels as afunctionof the stress treatment. Furthermore, the larger size of epidermal andbulliformcells was distinctively related to saline stress. The results obtained providetools for the in vitro identification of either specificorcross-tolerant phenotypes.     

Endogenous ligands for kappa-opiate receptors

The receptor preferences of opioids in the mouse vas deferens was tested by means of tolerance and cross-tolerance studies. The preparations were rendered tolerant in situ by superfusion with the kappa-receptor agonist dynorphin and with alpha-neoendorphin, respectively, and set up in vitro in the presence of the respective peptide to maintain tolerance. The investigations revealed strong kappa-agonistic activities both of alpha-neoendorphin and of dynorphin and its fragments 1-13 and 1-11. As the dynorphin chain shortened, the kappa-receptor activity declined and delta-receptor activity became progressively apparent. Interestingly, the octapeptide met-enkephalin[Arg6,Gly7,Leu8], a fragment of the adrenal medulla proenkephalin, also displayed considerable kappa-agonistic properties under the experimental conditions employed. Presumably, the decapeptide alpha-neoendorphin and the octapeptide met-enkephalin[Arg6,Gly7,Leu8] cover in addition to the kappa-receptor population in the MVD further opiate receptors, most probably delta-receptors.     

Dynorphin (1-13): analgesia, hypothermia, cross-tolerance with morphine and beta-endorphin

Intracerebroventricular administration of 20, 40 and 60 nmol of dynorphin (1-13) produced analgesia, as assessed by flinch/jump response to footshock, and hypothermia in the rat. Rats developed tolerance to both the analgesic and thermic effects of the 20 nmol dose of dynorphin. Dynorphin and beta-endorphin showed cross-tolerance with respect to their analgesic but not their thermic effects. Dynorphin and morphine also produced cross-tolerant analgesic effects. Naloxone (10 mg/kg, IP) completely blocked the barrel rolling produced by 20 nmol dynorphin but did not alter its analgesic or thermic effects.