Expression of Embryonic Haemoglobin in ts AEV-Transformed Embryonic Erythroid Cells During Temperature-Induced Differentiation

Cells prepared from 1-day-old chick blastoderms were infected with a temperature-sensitive mutant of avian erythroblastosis virus ( ts AEV). Clonal strains of transformed erythroblasts were isolated from the infected blastoderm cells. By shift to the nonpermissive temperature, these cells could be induced to differentiate into erythrocyte-like cells which expressed embryonic haemoglobins. Embryonic haemoglobins could not be detected in ts AEV-transformed erythroblasts from adult bone marrow when induced to differentiate under the same conditions. In contrast to normal primitive erythrocytes, ts AEV-infected embryonic erythroblasts differentiated in vitro expressed also adult haemoglobin. These results suggest an influence of the haematopoietic environment on the switch from embryonic to adult erythrocytes.     

Identification and functional characterization of the Arabidopsis Snf1‐related protein kinase SnRK2.4 phosphatidic acid‐binding domain

Phosphatidic acid (PA) is an important signalling lipid involved in various stress‐induced signalling cascades. Two SnRK2 protein kinases (SnRK2.4 and SnRK2.10), previously identified as PA‐binding proteins, are shown here to prefer binding to PA over other anionic phospholipids and to associate with cellular membranes in response to salt stress in Arabidopsis roots. A 42 amino acid sequence was identified as the primary PA‐binding domain (PABD) of SnRK2.4. Unlike the full‐length SnRK2.4, neither the PABD‐YFP fusion protein nor the SnRK2.10 re‐localized into punctate structures upon salt stress treatment, showing that additional domains of the SnRK2.4 protein are required for its re‐localization during salt stress. Within the PABD, five basic amino acids, conserved in class 1 SnRK2s, were found to be necessary for PA binding. Remarkably, plants overexpressing the PABD, but not a non‐PA‐binding mutant version, showed a severe reduction in root growth. Together, this study biochemically characterizes the PA–SnRK2.4 interaction and shows that functionality of the SnRK2.4 PABD affects root development.     

Do drivers intentionally target wildlife on roads?

Despite frequent reliance on surveys to document public attitudes towards conservation issues (such as invasive‐species control), only rarely do researchers assess the validity of statements made by the public in response to such surveys. Therefore, how well responses match actual behaviour remains an open question. We conducted a survey asking drivers if they had seen and/or run over (intentionally or not) snakes, native frogs or invasive cane toads (Rhinella marina) on roads in the Northern Territory of Australia. To compare actual driver behaviour to the survey responses, we also carried out field experiments where we quantified the rates at which model snakes, frogs and toads (and controls) were run over on a rural highway. Our results show a discrepancy between survey responses and driver behaviour: for example, 25% of the people we surveyed indicated that they intentionally run over cane toads, yet field experiments showed that model toads were run over no more frequently than expected by chance, or than any other type of model.     

Identification and Characterization of Epithelial Cells in Mammalian Tissues by Immunofluorescence Microscopy Using Antibodies to Prekeratin

The occurrence of intermediate-sized filaments containing prekeratin-like proteins ('cytokeratins') has been examined in various organs of rat and cow by electron microscopy and by immunofluorescence microscopy on frozen sections using antibodies to defined constitutive proteins of various types of intermediate-sized filaments (prekeratin, vimentin, desmin). Positive cytokeratin reaction and tonofilament-like structures have been observed in the following epithelia: epidermis; ductal, secretory, and myoepithelial cells of sweat glands; mammary gland duct; myoepithelial cells of lactating mammary gland; milk secreting cells of cow; ductal, secretory, and myoepithelial cells of various salivary glands; tongue mucosa; bile duct; excretory duct of pancreas; intestinal mucosa; urothelium; trachea; bronchi; thymus reticulum, including Hassall corpuscles; mesothelium; uterus; and ciliated cells of oviduct. None of the epithelial cells mentioned has shown significant reaction with antibodies to vimentin, the major component of the type of intermediate-sized filaments predominant in mesenchymal cells. The widespread, if not general occurrence of cytokeratin filaments in epithelial cells is emphasized, and it is proposed to use this specific structure as a criterion for true epithelial character or origin.     

Strategies in energy consumption and partitioning in Collembola

Abstract. 1. Consumption (in Joules), partitioning of assimilated energy between maintenance (standard metabolism and locomotory activity) and prcduction (growth and reproduction) and assimilation efficiency were studied in the laboratory using adults of the coexisting species Orchesella cincta (L.) and Tomocents minor Lubbock (Collembola, Entomobryidae).
2. A higher energy demand for maintenance was established in O.cincta , compared with T.minor , caused by a higher mobility and a higher live weight-specific oxygen consumption (metabolic rate).
3. The energy required for higher maintenance in O.cincta , compared with T.minor , was derived from production, both from growth and reproduction.
4. The increase in live weight (in mg) during a moulting interval (feeding instar plus reproductive instar) was less in O.cincta than in T.minor , and was less in males than in females.
5. Reproduction (in Joules) was less in O.cincta than in T.ninor . The numbers of eggs produced were equal, but their energetic content was less in O.cincta . Survival of the eggs was similar.
6. Consumption (in Joules) and assimilation efficiency (on an energetic basis) during a moulting interval (feeding instar plus reproductive instar) were similar in both species.     

Reassessing the role of phospholipase D in the Arabidopsis wounding response

Plants respond to wounding by means of a multitude of reactions, with the purpose of stifling herbivore assault. Phospholipase D (PLD) has previously been implicated in the wounding response. Arabidopsis ( Arabidopsis thaliana ) AtPLD α 1 has been proposed to be activated in intact cells, and the phosphatidic acid (PA) it produces to serve as a precursor for jasmonic acid (JA) synthesis and to be required for wounding-induced gene expression. Independently, PLD activity has been reported to have a bearing on wounding-induced MAPK activation. However, which PLD isoforms are activated, where this activity takes place (in the wounded or non-wounded cells) and what exactly the consequences are is a question that has not been comprehensively addressed. Here, we show that PLD activity during the wounding response is restricted to the ruptured cells using ³²P_i-labelled phospholipid analyses of Arabidopsis pld knock-out mutants and PLD -silenced tomato cell-suspension cultures. pldα1 knock-out lines have reduced wounding-induced PA production, and the remainder is completely eliminated in a pldα1 / δ double knock-out line. Surprisingly, wounding-induced protein kinase activation, AtLOX2 gene expression and JA biosynthesis were not affected in these knock-out lines. Moreover, larvae of the Cabbage White butterfly ( Pieris rapae ) grew equally well on wild-type and the pld knock-out mutants.     

Advanced snowmelt causes shift towards positive neighbour interactions in a subarctic tundra community

Positive and negative species interactions are important factors in structuring vegetation communities. Studies in many ecosystems have focussed on competition; however, facilitation has often been found to outweigh competition under harsh environmental conditions. The balance between positive and negative species interactions is known to shift along spatial, temporal and environmental gradients and thus is likely to be affected by climate change. Winter temperature and precipitation patterns in Interior Alaska are rapidly changing and could lead to warmer winters with a shallow, early melting snow cover in the near future. We conducted snow manipulation and neighbour removal experiments to test whether the relative importance of positive and negative species interactions differs between three winter climate scenarios in a subarctic tundra community. In plots with ambient, manually advanced or delayed snowmelt, we assessed the relative importance of neighbours for survival, phenology, growth and reproduction of two dwarf shrub species. Under ambient conditions and after delayed snowmelt, positive and negative neighbour effects were generally balanced, but when snowmelt was advanced we found overall facilitative neighbour effects on survival, phenology, growth and reproduction of Empetrum nigrum, the earlier developing of the two target species. As earlier snowmelt was correlated with colder spring temperatures and a higher number of frosts, we conclude that plants experienced harsher environmental conditions after early snowmelt and that neighbours could have played an important role in ameliorating the physical environment at the beginning of the growing season.