Phosphorus depletion in the rhizosphere as influenced by soil moisture

To study the influence of soil moisture on phosphorus (P) depletion in the rhizosphere, maize (Zea mays cv. Trak) was pre-grown in vermiculite filled-PVC tubes for 9 days and then the plants with the tubes were transplanted into soil columns maintained at two soil moisture levels () of 0.14 and 0.20 cm³ cm^–3 for 10 days. The soil columns were separated at 1 cm depth by a nylon screen of 53 m inner mesh size, into 1 cm soil layer above and 3 cm soil column below screen. A root mat developed over the screen, but root hairs only could penetrate it. Regardless of the soil moisture level in the columns, and adequate and equal water and nutrients supply was maintained via wicks from an external nutrient solution to the plant roots in vermiculite. After 10 days, the soil columns were separated from the root mats, quickly frozen in liquid nitrogen and sliced into thin layers (0.2mm) using a refrigerated microtome to give soil samples at defined distances from the root mats for analyses. Lower soil moisture (=0.14) resulted in narrower and steeper depletion profile of 0.5 M NaHCO₃ extractable P (NaHCO₃-P_i) as compared to higher soil moisture (=0.20). Depletion of P in soil solution in the immediate vicinity of root mats did not differ much but the extension of the depletion zones was 0.10 cm at =0.14 and 0.20 cm at =0.20. The depletion up to 0.05cm with =0.14 and up to 0.07 cm with =0.20 was uniform, and may be attributed to the depletion in the root hair zone. Beyond the root hair zones, the theory of diffusion and mass flow was able to explain the observed differences in shape and extent of the P depletion profiles at the two soil moisture levels.     

Determination of the overall volumetric mass transfer coefficient kLa,by a temperature dependent change of gas solubility

Summary The solubility of oxygen in the liquid phase of a bioreactor was changed by a ramp change of temperature, and k_La was determined from the resulting return to equilibrium of dissolved oxygen activity. The maximum k_La that can be measured by this method in a standard laboratory scale bioreactor is 145 h^–1 corresponding to a temperature change rate of 320°C h^–1.Nomenclature p Difference between p_G and p_L (% saturation) - T Ramp change of temperature (°C) - E Temperature-compensated output from the oxygen electrode (A) - E_u Uncompensated output from the oxygen electrode (A) - k_La Overall volumetric mass transfer coefficient (h^–1) - k_La_Tm Overall volumetric mass transfer coefficient at temperature T_m (h^–1) - P_G Dissolved oxygen activity in equilibrium with the gas phase (% saturation) - p_L Dissolved oxygen activity (% saturation) - p_Lm Dissolved oxygen activity at time t_m (% saturation) - t Time (h) - t_m Time of maximum p (h) - T Temperature (°C) - T_cal Calibration temperature of the oxygen electrode (°C) - T_m Final temperature after a temperature shift (°C) - T_n Temperature at time t_n     

Variation and taxonomy in Hordeum depressum and in the H. brachyantherum complex (Poaceae)

The variation pattern in the perennial Hordeum brachyantherum complex and in the annual H. depressum are described. The diploid form of H. brachyantherum s. lat., endemic to California in USA, previously recognized as a separate species is here treated as a subspecies ( H. brachyantherum ssp. californicum ). Despite its restricted distribution it shows a considerable variation and overlap in morphology with the tetraploid ssp. brachyantherum , and no unambiguous determination based on morphology between the two tax a is possible. The tetraploid cytotype has a large distribution area in western North America and easternmost Asia and a very wide morphological variation. It has also a small disjunct distribution area in easternmost Canada. A single hexaploid population from California is referred to ssp. brachyantherum .     

Slow cortical potential biofeedback and the startle reflex

The negativity of slow cortical potentials (SCP) of the surface EEG is a measure of brain excitability, correlating with motor and cognitive preparation. Selfcontrol of SCP positivity has been shown to reduce seizure activity. Following SCP biofeedback from a central EEG electrode position, subjects gained bidirectional control over their SCP. The current study used a modified feedback methodology, and found a positive relationship between negativity and magnitude of EMG startle response (a measure of cortical and subcortical arousal, particularly aversive response disposition). Greater success in SCP differentiation was associated with self-report of less relaxation during negativity training.This research was supported by the Deutsche Forschungsgemeinschaft under grant No. SFB 307.     

The influence of lecithin on plasma choline concentrations in triathletes and adolescent runners during exercise

An investigation was carried out on the effect of lecithin (phosphatidylcholine, 90%) on the plasma choline concentrations during continuous strain in 10 top level triathletes (4 women and 6 men), trial I, and 13 excellent adolescent runners (3 girls and 10 boys), trial II. Venous blood, collected before and immediately after the race, was separated and plasma was assayed by an improved high performance liquid chromatography method for choline. Each study comprised three experiments. In trial I the triathletes performed two periods of bicycle exercise each lasting 2 h at an average speed of 35 km · h^–1, and in the second study (trial II) the subjects were subjected to severe physical stress on two occasions during cross-country races of durations between 30–60 min according to their ages. The participants received either a placebo or 0.2 g lecithin · kg body mass^–1, 1 h before each exercise. As a control the same dose of lecithin was administered without any exercise (both trials I and II). Bicycle exercise without lecithin supply decreased plasma choline concentrations in all the triathletes, on average by 16.9% (P0.01). When lecithin was given before exercise, average plasma choline concentrations remained at the same level as the initial values. The supply of lecithin without exercise led to a significant increase of the plasma choline concentrations, on average by 26.9% (P0.01). In trial II, when running without a supply of lecithin, the mean plasma choline concentrations in the adolescent runners remained stable which may have been due to the duration of the physical stress. When lecithin was given before exercise, plasma choline concentrations increased, on average by 18.9% (P0.01). The administration of lecithin without exercise led in these participants to an increase in plasma choline concentrations, on average by 54% (P0.001).It was found from the present study that a combination of both lecithin intake and hard physical stress prevented in most subjects a decrease in plasma choline and this could affect performance.     

AICAR is not an endogenous mutagen in Escherichia coli

A number of observations in the Escherichia coli and Salmonella typhimurium literature could be explained by the hypothesis that a particular purine ribonucleotide precursor can be converted to the corresponding deoxyribonucleotide triphosphate, thereby becoming a base-analogue mutagen. The metabolite in question, AICAR (5-amino-4-carboxamide imidazole riboside 5′-phosphate), is also a by-product of histidine biosynthesis, and its (ribo)triphosphate derivative, ZTP, has been detected in E. coli. We constructed E. coli tester strains that had either a normal AICAR pool (pur ⁺ his ⁺ strains cultivated without purines or histidine) or no AICAR pool (purF hisG mutant strains, lacking the first enzyme of each pathway and cultivated in the presence of adenine and histidine). Using a set of lacZ mutations, each of which can revert to Lac⁺ only by a specific substitution mutation, we found that no base substitution event occurs at a higher frequency in the presence of an AICAR pool. We conclude that the normal AICAR pool in E. coli is not a significant source of spontaneous base substitution mutagenesis.     

Intergeneric hybridization between Hordeum and Hordelymus (Poaceae)

Intergeneric hybridization between the monotypic Eurasian genus Hordelymus and species of Hordeum was performed. Hybrids were obtained in nine combinations and the meiotic pairing was analyzed in four combinations (6 families). Hordelymus europaeus is probably an alloploid with two different genomes. The very low pairing in the hybrids with H. jubatum, H. brachyantherum , and H. pusillum indicates that these species do not have any genomes in common with Hordelymus. The hybrids with H. depressum have an intermediate pairing which suggests that there is a certain homoeology in one genome.