Growth changes in the shoot apex of Sinapis alba during transition to flowering

The aim of the work was to report morphological changes whichoccur in the shoot apex during the morphogenetic switch to floweringin the model long day (LD) plant, Sinapis alba. During the floraltransition induced by 1 LD the growth rate of all componentsof the shoot apex is modified profoundly. The earliest changes,detected at 24 h after start of LD, include a decrease in plastochronduration and an increase of growth of leaf primordia. One daylater, the meristem dome starts to increase in volume, apicalinternodes have an increased height and there is a precociousoutgrowth of axillary meristems. All these changes precede initiationof flower primordia, which starts at about 60 h after the startof LD. Later changes include meristem doming, a decrease inthe plastochron ratio and a shift to a more complex phyllotaxis.All the changes, except the decreased plastochron ratio, arecharacteristics of an apex with an increased tempo of growth.The stimulation of longitudinal growth (height of apical intemodes)is more marked and occurs earlier than the reduction of radialgrowth (plastochron ratio). Key words: Axillary meristem, internode growth, leaf growth, plastochron ratio, plastochron duration     

Utility of the white gene in estimating phylogenetic relationships among mosquitoes (Diptera: Culicidae)

The utility of a nuclear protein-coding gene for reconstructing phylogenetic relationships within the family Culicidae was explored. Relationships among 13 species representing three subfamilies and nine genera of Culicidae were analyzed using a 762-bp fragment of coding sequence from the eye color gene, white. Outgroups for the study were two species from the sister group Chaoboridae. Sequences were determined from clone PCR products amplified from genomic DNA, and aligned following conceptual intron splicing and amino acid translation. Third codon positions were characterized by high levels of divergence and biased nucleotide composition, the intensity and direction of which varied among taxa. Equal weighting of all characters resulted in parsimony and neighboring-joining trees at odds with the generally accepted phylogenetic hypothesis based on morphology and rDNA sequences. The application of differential weighting schemes recovered the traditional hypothesis, in which the subfamily Anophelinae formed the basal clade. The subfamily Toxorhynchitinae occupied an intermediate position, and was a sister group to the subfamily Culicinae. Within Culicinae, the genera Sabethes and Tripteroides formed an ancestral clade, while the Culex-Deinocerites and Aedes- Haemagogus clades occupied increasingly derived positions in the molecular phylogeny. An intron present in the Culicinae- Toxorhynchitinae lineage and one outgroup taxon was absent in the basal Anophelinae lineage and the second outgroup taxon, suggesting that intron insertions or deletions may not always be reliable systematic characters.      

DNA markers linked to a T10 loose smut resistance gene in wheat (Triticum aestivum L.).

Screening for loose smut resistance in wheat is difficult. Selecting lines with DNA markers linked to loose smut resistance would be more reliable and less costly. Molecular markers linked to a race T10 loose smut resistance gene were identified using a F6 single seed descent segregating population. A RAPD marker and a RFLP marker were located on opposite flanks of the resistance gene and were shown to be loosely linked. The RAPD marker was converted to a user friendly polymorphic SCAR marker that represented a single genetically defined locus in hexaploid wheat. Using these two bracketing markers simultaneously, the error rate for T10 resistance selection due to crossing-over was reduced to 4%. These markers can be used for a faster and more reliable selection of T10 resistant plants than previous conventional loose smut ratings.     

Negative impacts of high temperatures on growth of black spruce forests intensify with the anticipated climate warming

An increasing number of studies conclude that water limitations and heat stress may hinder the capacity of black spruce (Picea mariana (Mill.) B.S.P.) trees, a dominant species of Canada's boreal forests, to grow and assimilate atmospheric carbon. However, there is currently no scientific consensus on the future of these forests over the next century in the context of widespread climate warming. The large spatial extent of black spruce forests across the Canadian boreal forest and associated variability in climate, demography, and site conditions pose challenges for projecting future climate change responses. Here we provide an evaluation of the impacts of climate warming and drying, as well as increasing [CO₂], on the aboveground productivity of black spruce forests across Canada south of 60°N for the period 1971 to 2100. We use a new extensive network of tree‐ring data obtained from Canada's National Forest Inventory, spatially explicit simulations of net primary productivity (NPP) and its drivers, and multivariate statistical modeling. We found that soil water availability is a significant driver of black spruce interannual variability in productivity across broad areas of the western to eastern Canadian boreal forest. Interannual variability in productivity was also found to be driven by autotrophic respiration in the warmest regions. In most regions, the impacts of soil water availability and respiration on interannual variability in productivity occurred during the phase of carbohydrate accumulation the year preceding tree‐ring formation. Results from projections suggest an increase in the importance of soil water availability and respiration as limiting factors on NPP over the next century due to warming, but this response may vary to the extent that other factors such as carbon dioxide fertilization, and respiration acclimation to high temperature, contribute to dampening these limitations.     

β-Glucosidase biosynthesis inThermomonospora curvata

Summary -Glucosidase biosynthesis was induced inThermomonospora curvata during early exponential growth on cellobiose, cellulose and protein-extracted lucerne fibre in mineral salts minimal medium at 53°C. Only about 3% of the total culture -glucosidase was found in cell-free fluid when the actinomycete was grown on cellobiose or purified cellulose. A variety of non-lytic agents including detergents, salts, proteinase and electroporation failed to release the cellbound enzyme. However, cells grown on the fibre released more than 50% of their -glucosidase. The maximal amount of extracellular accumulation was dependent on the initial concentration of fibre in the medium. Thermal instability at 53°C was the major cause for low exracellular -glucosidase activity in cellobiose- and cellulose-grown cultures. In cultures grown on the fibre, the extracellular enzyme was stabilized against thermal denaturation by the composition of the cell-free fluid, but was degraded by transient proteinase activity. Proteolysis decreased the average beta-glucosidase specific activity from about 460mU/mg extracellular protein to about 80mU/mg within 1 day after the appearance of the proteinase.

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Biosynthèse de -glucosidase chez Thermomonospora curvata

Résumé La biosynthèse de -glucosidase a été induite chezThermomonospora curvata pendant la phase exponentielle précoce de croissance sur cellobiose, sur cellulose et sur fibre de lucerne dont on avait extrait les protéines, en milieu minéral minimum à 53°C. A peine 3% de la -glucosidase totale dans la culture a été retrouvée dans le milieu acellulaire lorsque l'actinomyète a crû sur cellobiose ou sur cellulose purifiée. Une foule d'agents non-lytiques, comprenant des détergents, des sels, la protéinase et l'électroporation n'ont pas réussi à libérer l'enzyme liée aux cellules. Toutefois, les cellules développées sur la fibre ont libéré plus de 50% de leur -glucosidase. La quantité maximum d'accumulation extra-cellulaire a dépendu de la concentration initiale de fibre dans le milieu. L'instabilité thermique à 53°C a été la casue majeure des seuils faibles de -glucosidase extra-cellulaire dans les cultures sur cellobiose ou cellulose. Dans les cultures développées sur fibre, l'enzyme extra-cellulaire était stabilisée contre la dénaturation thermique par la composition du milieu acellulaire, mais elle était dégradée par l'activité transitoire de la protéinase. La protéolyse a décru l'activité spécifique moyenne de la -glucosidase d'environ 460 mU/mg de protéine extra-cellulaire à environ 80 mU/mg endéans la journée après l'apparition de la protéinase.

     

Enhanced inflorescence development in tomato by growth substance treatments in relation to 14C-assimilate distribution

Inflorescence development in tomato plants ( Lycopersicon esculentum Mill., cv. King Plus) grown under a low-light regime is promoted by exogenous applications of a mixture of N⁶-benzyladenine (BA) and gibberellins A₄₊₇ (GA) directly on the inflorescence. The photosynthetic rate of the young mature leaf, which feeds the developing inflorescence, and the proportion of ¹⁴C-assimilates exported from the source leaf are not affected by the growth substance treatment, but the pattern of ¹⁴C-assimilate distribution is altered. Assimilate supply to the treated inflorescence increases concomitantly with a decrease in the ¹⁴C import into the apical shoot, reflecting a competition between these two plant parts. The increased assimilate accumulation in the treated inflorescence is apparent 1 day after the first application of BA+GA, and precedes any morphological changes in the reproductive structure. These results are discussed in relation to nutritional hypotheses that regard assimilate supply as limiting for reproductive development.     

Flowering in Xanthium strumarium: INITIATION AND DEVELOPMENT OF FEMALE INFLORESCENCE AND SEX EXPRESSION

Vegetative plants of Xanthium strumarium L. grown in long days were induced to flower by exposure to one or several 16-hour dark periods. The distribution of male and female inflorescences on the flowering shoot was described, and a scoring system was designed to assess the development of the female inflorescences. The time of movement of the floral stimulus out of the induced leaf and the timing of action of high temperature were shown to be similar for both the apical male and lateral female inflorescences.