Effect of Photoperiod and Electrical Potentials Applied to Petioles on the Glucose-6-phosphate Dehydrogenase Activity used as Marker of Floral Induction in Shoot Apices of Spinach I

The increase of glucose-6-phosphate dehydrogenase (G-6-PD) activityhas been proposed as an early marker of floral evocation inthe shoot apical meristem of spinach. This induction is obtainedby the transfer of vegetative plants from short days to continuouslight. The exposure of a single leaf to continuous light inducedthe same effect as that produced with the whole plant. In vegetativeconditions (short days), an electrical potential of ten volts(electrical current: 12·5 µA) applied to the petioleof a single leaf induced a weak increase of G-6-PD activityin the shoot apex, while under inductive conditions, this increasewas similar to that of control plants (transferred to continuouslight). Application of an electrical potential to the petioleand the root inhibits the increase linked to the inductive transfer.These results show that an externally applied electrical potentialmay interact with the natural electrical gradients along theshoot and consequently inhibit the normal floral developmentby an as yet unspecified mechanism. Spinacia oleracea, floral induction, interorganic relations, glucose-6-phosphate dehydrogenase, shoot apex, electrical potentials     

The conformationally dynamic C helix of the RIalpha subunit of protein kinase A mediates isoform-specific domain reorganization upon C subunit binding

Different isoforms of the full-length protein kinase A (PKA) regulatory subunit homodimer (R2) and the catalytic (C) subunit-bound holoenzyme (R2C2) have very different global structures despite similar molecular weights and domain organization within their primary sequences. To date, it has been the linker sequence between the R subunit dimerization/docking domain and cAMP-binding domain A that has been implicated in modulating domain interactions to give rise to these differences in global structure. The small angle solution scattering data presented here for three different isoforms of PKA heterodimer (deltaR-C) complexes reveal a role for another conformationally dynamic sequence in modulating inter-subunit and domain interactions, the C helix that connects the cAMP-binding domains A and B of the R subunit. The deltaR-C heterodimer complexes studied here were each formed with a monomeric N-terminal deletion mutant of the R subunit (deltaR) that contains the inhibitor sequence and both cAMP-binding domains. The scattering data show that type IIalpha and type IIbeta deltaR-C heterodimers are relatively compact and globular, with the C subunit contacting the inhibitor sequence and both cAMP-binding domains. In contrast, the type Ialpha heterodimer is significantly more extended, with the C subunit interacting with the inhibitor sequence and cAMP-binding domain A, whereas domain B extends out such that its surface is almost completely solvent exposed. These data implicate the C helix of RIalpha in modulating isoform-specific interdomain communication in the PKA holoenzyme, adding another layer of structural complexity to our understanding of signaling dynamics in this multisubunit, multidomain protein kinase.     

Evaluation of a Community’s Risk for Canine Parvovirus and Distemper Using Antibody Testing and GIS Mapping of Animal Shelter Intakes

This cross-sectional study aimed to identify where dogs with negative antibody tests to canine parvovirus (CPV) and canine distemper virus (CDV) originated when entering a community shelter, using a commercially available ELISA antibody test and Geographic Information Systems mapping. Of 2745 canines entering during a three-month period, 1056 test results were obtained. Dogs or puppies weighing over 2 lb were eligible if they could be humanely, nonchemically restrained for phlebotomy. Age and minor health issues weren't exclusions. Dogs were excluded if trained personnel were concerned health would be compromised by phlebotomy. Blood samples were collected within 24 hours of entry. Four hundred and twenty-seven (40%) dogs had positive antibody test results for both viruses, 422 (40%) were positive for CPV, 37 (4%) were positive for CDV, and 170 (16%) were negative for both. Mapping revealed geographic patterns for dogs with negative antibody tests. This shelter admitted dogs with negative CPV and/or CDV antibody tests from defined community areas. Targeting vaccination efforts in communities to areas where dogs with negative antibody tests originate could be an effective wellness strategy.     

Chloroplast DNA phylogeography of the argan tree of Morocco

Polymorphisms in the chloroplast genome of the argan tree (Sapotaceae), an endemic species of south-western Morocco, have been detected by restriction site studies of PCR-amplified fragments. A total of 12 chloroplast DNA (cpDNA) and two mitochondrial DNA (mtDNA) fragments were amplified and digested with a single restriction enzyme ( Hin fI). Polymorphisms were identified in six of the cpDNA fragments, whereas no mtDNA polymorphisms were detected in a survey of 95 individuals from 19 populations encompassing most of the natural range of the species. The cpDNA polymorphisms allowed the identification of 11 haplotypes. Two lineages, one in the south-east and the other in the north-west, divide the range of the argan tree into two distinct areas. The level of genetic differentiation measured at the haplotype level ( G _STc= 0.60) (i.e. with unordered haplotypes) was smaller than when phylogenetic relationships were taken into account ( N _STc= 0.71–0.74) (ordered haplotypes), indicating that population history must be considered in the study of the geographical distribution of cpDNA lineages in this species. If contrasted with the level of nuclear genetic differentiation measured in a previous study with isozymes ( G _STn= 0.25), the results indicate a relatively high level of gene flow by seeds, or conversely a relatively low level of gene flow by pollen, as compared with other tree species. Goats and camels could have played an important role in disseminating the fruits of this tree.     

Physiological Responses of Spring Durum Wheat Cultivars to Early-season Drought in a Mediterranean Environment

The Mediterranean climate of North Africa is characterized byuncertain rainfall immediately after seedling emergence, leadingto drought early in the growing season which depresses durumwheat production. However, there is limited understanding ofthe physiological basis of resistance of spring durum wheatto drought in rainfed Mediterranean regions. The objectivesof this study were to examine differences in some physiologicalcharacters among spring durum wheat cultivars in response toduration of early-season drought, and to determine the relationshipof these characters to drought resistance. In two field experiments(1995 and 1996 growing seasons) and a glasshouse experiment(1996), six spring sown durum wheat cultivars were evaluatedunder four water regimes: well irrigated and three differentwater deficits from emergence until the onset of tillering,mid-tillering or at the end of tillering. Cultivars differedin their response. Decreases in photosynthesis soon after droughtstress was imposed resulted mainly from reduced stomatal conductance.Continued water deficits also reduced mesophyll photosyntheticactivity. Possible factors determining the drought-resistanceof a cultivar are lower sensitivity of CO₂exchange rate, netCO₂uptake to water loss ratio, stomatal resistance, relativewater content and greater osmotic adjustment under stress. Furthermore,there is sufficient intraspecific variation in these physiologicalattributes to suggest their use as selection tools.Copyright1998 Annals of Botany Company Wheat;Triticum durumDesf.; early-season drought; physiological responses.     

The Influence of Plant-Growth Factors on the Initiation and Growth of Crown-Gall Tumours on Primary Pinto Bean Leaves

The number of tumours developing on primary pinto bean leaves(Phaseolus vulgaris L. variety Pinto) inoculated with Agrobacteriumtumefaciens (Smith and Town.) Conn, strain B6, was increasedby as much as 100 per cent through the addition of several plant-growthfactors and antagonists of some of these factors to the freshlyinoculated leaves. Naphthylacetic acid, gibberellic acid, (2-chloroethyl)trimethylammonium chloride, and adenine gave a biphasic responsewith optimal promotions of tumour initiation at 10^-5 to 10^-4mg/ml. Tri-iodobenzoic acid and 4-chlorophenoxyisobutyric acidwere most active at 10^-1 mg/ml. Mean tumour diameter showeda direct correlation with tumour number in these experiments.The results show tumour initiation to be sensitive to growthfactor changes, possibly through a heightened traumatic responseof the wounded leaves. The growth of the tumours was unaffectedby these additions except as they altered tumour number andthis secondarily affected tumour growth.     

Flow-cytometric analysis of mitochondria-associated fluorescence in young and old human fibroblasts

Rhodamine 123 fluorescence in populations of young and old human fibroblasts was analysed and quantified with a fluorescence-activated cell sorter (FACS). Old fibroblasts exhibited a higher mean relative fluorescence than young fibroblasts. Moreover, two distinct subpopulations were evident in the fluorescence distributions of old cells--but not in those of young cells.     

Gamete membrane fusion in hamster spermatozoa with reacted equatorial segment

Mammalian spermatozoa must undergo many changes to be able to fertilize the oocyte. One of these changes, the acrosome reaction, has been established as a requisite for gamete membrane fusion to occur; it consists of the fusion and vesiculation of the sperm plasma membrane with the outer acrosomal membrane of the principal segment of the acrosome. Reaction of the equatorial segment has occasionally been observed. The objective of the present work was to determine whether the presence of the sperm plasma membrane over the equatorial segment is necessary for gamete membrane fusion to occur. Golden hamster spermatozoa were capacitated in vitro in TAPL 10K, and the maximum possible percentage of acrosome reaction was determined at 82.79% + 1.69% SD (P = 0.27; r = 0.21). Ultrastructural studies showed that 93.6% of the reacted spermatozoa in this population had their principal and equatorial segments reacted. The fertilizing ability of these spermatozoa was assayed using zona-free hamster oocytes. The percentage of fertilized ova obtained was 98.8% (308/312). Ultrastructural studies snowed the presence of spermatozoa with reacted equatorial segment inside the cytoplasm of immature oocytes. The evidence presented in this work demonstrates that the plasma membrane of spermatozoa with reacted equatorial segment retains its ability to fuse with the oocyte.     

A SIMPLE ALTERNATIVE TO GENERALIZED PROCRUSTES ANALYSIS: APPLICATION TO SENSORY PROFILING DATA

A statistical method for analyzing sensory profiling data obtained by means of fixed vocabulary or free choice profiling is discussed. The most interesting feature of this method is that it involves only simple statistical treatment and can therefore be performed using standard software packages. The outcomes of this method are compared to those of Generalized Procrustes Analysis on the basis of two data sets obtained, respectively, by means of fixed vocabulary and free choice profiling. A significance test is also discussed in order to assess whether the overall configuration of the products is meaningful. This significance test is based upon a simulation study involving the permutation procedure.