Kinetics of leucrose formation from sucrose by dextransucrase

Leucrose formation from sucrose and fructose by dextransucrase is of practical interest. It has been investigated at different experimental conditions, including the influence of temperature on reaction rate and selectivity. Under appropriate conditions high product yield can be obtained. Furthermore, a model is presented that allows interpretation of the experimental data.     

Variability and stochasticity of meal size and feeding frequency in the Little Sheanvater Puffinus assimilis

The pattern of chick feeding in Little Shearwater Puffinus assimilis on Selvagem Grande was examined by weighing chicks at 4–h intervals throughout eight successive nights and daily for a further 11 days (19 days in all). Individual meals fed to chicks averaged 23.2 g (s.d. ±4.7) or 13.6% of adult mass. Mass increments over 24 h (NET) were linearly related to the sum of positive mass increments over 4–h intervals during the night (SUM) by the equation NET = 0.36SUM - 5.89 (r²= 0.60). Using this relationship, I estimated that over a period of 18 nights, a mean of 95% of chicks were fed each night, and the mean interval between feeds was 1.05 nights, with a maximum of three nights. There was no significant day-to-day variation in feeding rate. These results were not compatible with the prevalent idea that the purpose of large fat deposits in Procellariiformes is to tide chicks over periodic fasts resulting from poor feeding conditions. On average, chicks required 16 g of food per day to maintain constant mass and converted 33% of their intake of food above this requirement into biomass. Meal size and feeding frequency were independent of chick size and body condition (body-mass corrected for body-size), and the masses of food received by individual chicks each night varied in direct proportion to previous values. These results suggest that the rate of food supply to chicks was not regulated by adjustment according to chicks' nutritional requirements. To some extent, this supports the hypothesis that lipid accumulation among Procellariiformes is related to stochastic variation in food supply rate, resulting from an absence of regulation of feeding. However, feeding was not stochastic, in that adults tended to deliver consistent amounts of food to their chicks, and the pattern of feeding among even the worst-fed chicks was inconsistent with a need for large lipid stores based upon chance variation in food delivery.     

Vacuolar ion currents in the primitive green algaEremosphaera viridis: The electrical properties are suggestive of both the Characeae and higher plants

Summary The electrical properties of the vacuolar membrane of the primitive green algaEremosphaera virdis were investigated using the patch-clamp technique. In whole vacuole measurements two types of transport systems with long activation time-constants were identified. The first, showing marked outward rectification, was activated by an increase in the cytosolic calcium concentration. Furthermore, it displayed sensitivity to micromolar concentrations of the anion channel blocker Zn²⁺ and to acidification of the cytosol. In contrast, the second time-activated current component was almost insensitive to changes in cytosolic pH and was blocked by the potassium channel inhibitor TEA. In addition to these slowly activating current components, the vacuolar membrane contained at least two further transport systems, responsible for an instantaneous current. These two current components were distinguished by their different sensitivity to protons, cytosolic calcium, and TEA. Comparing these electrical properties to those observed in vacuoles of higher plants or in cytoplasmic droplets from characean algae, respectively, it seems thatEremosphaera is intermediate, corresponding to the systematic position of this simple green alga.Abbreviations [Ca²⁺]_cyt cytosolic free calcium concentration - EGTA ethyleneglycol-bis(-aminoethylether)N,N,N,N-tetraacetic acid - HEPES N-[2-hydroxyethyl]piperazine-N-[2-ethanesulfonic acid] - I electric current - IRC inward rectifying current - MES 2-[N-morpholino]ethanesulfonic acid - ORC outward rectifying current - pH_cyt cytosolic pH - pH_vac vacuolar pH - P_o open probability - P_x permeability coefficient of ion species X - TEA tetraethylammonium chloride - Tris tris[hydroxymethyl]aminomethane - V voltage     

Further development of a transcervical technique for artificial insemination in sheep using previously frozen semen

A transcervical technique (the Guelph System for transcervical AI) was used to inseminate 2060 ewes on 65 farms (average 31 ewes, range 5 to 107) in Ontario, Canada, from October 1990 to September 1992, using previously frozen semen. Estrus was synchronized using progestagen pessaries and PMSG with median inseminations done at 54 h from pessary removal. Maiden ewes were not included. Only ewes in which the cervix could be penetrated were inseminated with 150 million spermatozoa per insemination. A total of 1809 were penetrated and inseminated (penetration rate 87.8%). Success of penetration increased from 76.3% in the first 500 ewes to 97.9% in the last 500 (P=0.01). Cervical penetration was more successful in ewes in the accelerated lambing program (92.3%, average 3.1 mo since the previous lambing) than those in the annual lambing program (82.4%, average 7.0 mo since the previous lambing; P=0.06). The lambing rate for ewes bred during the combined traditional breeding seasons (Fall of 1990, 1991, 1992) was 50.7% compared to 24.4% for ewes bred at other periods (P=0.00001). The average time required for handling and insemination decreased from 8.62 min in the first 500 ewes to 3.62 min in the last 500 ewes. The Guelph System for Transcervical AI was found to be successful for cervical penetration in most ewes. Penetration success was affected by period since the last lambing and by inseminator experience. The lambing rate was higher for ewes bred during the traditional Fall breeding seasons than during other times of the year.     

Species composition of dabbling duck assemblages: ecomorphological patterns compared with null models

Ecomorphological patterns of breeding dabbling duck (Anas spp.) assemblages were studied in six regions in northern Europe. Observed spacings among species in terms of bill lamellar density and body length were compared with expected spacings based on null models incorporating different levels of constraints (regional species pools, species relative abundances, lake size and habitat requirements of species). Deviations of observed spacings from expected ones were compared with prey abundance and prey size diversity in the lakes. Observed spacings in terms of body length, but not in terms of bill lamellar density, were greater than expected on the basis of null models. The most abundant species were generally relatively more different than less abundant species in terms of body length but not in terms of bill lamellar density. Deviations between observed and expected spacings in terms of body length were more like those predicted by the competition hypothesis in lakes with low food abundance than in lakes with high food abundance. Patterns in bill lamellar spacings were not related to food abundance nor to food size diversity. In general, patterns in body length spacings were consistent with the competition hypothesis whether the null model used in comparisons was constrained or not.     

Gravitropically-stimulated seedlings show autotropism in weightlessness

In a spaceflight experiment, autotropism by oat ( Avena sativa L.) coleoptiles following gravitropic responses was prominent in weightlessness: counter-reactions led to the straightening of the curved coleoptiles. This was not the case during clinorotation on earth. The autotropic reactions appeared to be related to the stimulus received during the stimulus period, i.e. the greater the response the greater the autotropic counter-reaction. Previous models of the gravitropic system which predicted that coleoptiles would not straighten in weightlessness are disproved. A modification to one of the models is proposed which includes the autotropic response observed in spaceflight. The nature of the counter-reactions in the absence of gravitropic stimulation is discussed.     

Association of the Decline of Nashi Pears with an MLO

Mycoplasma-like organisms (MLOs) were constantly detected by the DAPI technique and by restriction fragment length polymorphism (RFLP) analysis of PCR-amplified DNA in trees of Pyrus pyrifolia cvs Hosui and Kosui grafted on P. communis, seedlings rootstock with symptoms similar to the slow form of pear decline. These symptoms included upward curling of the leaves along the midrib. Leaves were abnormally thick and later turned reddish while major veins became swollen and brown. Trees with symptoms were usually 4–5 years old and were growing in the major pear areas of central Italy. The incidence of affected trees was particularly high in one orchard adjacent to a pear orchard strongly affected with the slow form of pear decline. In this case the distribution pattern of affected Nashi trees suggests that the causal agent was introduced from the adjacent pear orchard by an aerial vector. Although oriental pears are well-known hosts of the pear-decline agent when used as rootstocks of French cultivars, this is the first report of pear decline in P. pyrifolia varieties.