Nutrient inflows into apple roots. I. 32P-orthophosphate uptake from solution by M.9 rootstocks and Worcester Pearmain seedlings

Abstract. The rates of uptake of ³²P-labelled orthophosphate by whole root systems of young apple trees (M.9 rootslocks and Worcester Pearmain seedlings) were measured in solution culture. Using a solution depletion technique, the ³²P-phosphate uptake rates per unit length, surface area or fresh weight of roots were determined as a function of ³²P-phosphate concentration in solution at the root surface over the range 0.25–10 mmol m⁻³. The effect of P concentration within various plant parts on the relation between uptake rate and external P concentration was studied using plants differing in internal P levels.
The apparent minimutn P concentration below which P uptake ceased was of the order of 0.25–0.50 mmol m⁻³. Fluxes, inflows and unit absorption rates increased approximately proportionately with solution concentration up to 10mmolm⁻³. Except perhaps in the case of the low-P M.9 plant, there was no evidence of a diminishing returns type of relationship over the range of solution concentrations examined. The threshold P concentration in solution above which uptake rates cease to increase thus appears to be higher for apples than for other species.
At any given P concentration, fluxes, inflows and unit absorption rates were higher for M.9 than for Worcester and for low-P plants than for high-P plants. The difference between plants of different P status was more marked for M.9 and seems to be more closely related to shoot P levels than to root P.     

Quasi-elastic light scattering of Artemia ribosomes sedimented in a CsCl density gradient

It is impossible to measure the diffusion coefficient of macromolecules directly and accurately by quasi—elastic light scattering, when aggregates cannot be eliminated from the solutions to be investigated. Nevertheless, a simple method can be applied to overcome this problem in many cases. Aggregates are separated from the monomeric macromolecules by rate-zonal sedimentation in a CsCl density gradient in a transparent centrifugation tube; the monomers are then located by laser light scattering intensity measurements; photon correlation spectroscopy of the scattered light finally yields their diffusion coefficient. The viscosity of aqueous CsCl solutions at different temperatures and concentrations allows a good separation by centrifugation and a low uncertainty in the reduction of the measured diffusion coefficient to standard conditions.The application of the method to eukaryotic large ribosomal subunits is described as an example.     

Differential cardiovascular effects mediated by mu and kappa opiate receptors in hindbrain nuclei

To further investigate the role of opioid peptides and specific opiate receptor subtypes in central cardiovascular regulation by hindbrain nuclei, mu (D-Ala²,MePhe⁴,Gly-ol⁵ enkephalin, DAGO), delta (D-Ala²,D-Leu⁵ enkephalin, DADL) or kappa (MRZ 2549) agonists were microinjected into hindbrain nuclei of spontaneously or artificially respired, pentobarbital-anesthetized rats. In the nucleus tractus solitarius (NTS), DAGO and DADL (0.3 nmol) elicited pressor responses and tachycardia. MRZ (3.0–16 nmol) depressed blood pressure in spontaneously breathing rats, but accelerated heart rate in artificially ventilated animals. Blood pressure and heart rate of spontaneously breathing animals were not altered following nucleus ambiguus (NA) injection of DAGO or DADL (0.3 nmol), but were elevated in artificially respired animals; MRZ (3.0–10 nmol) injected into the NA depressed blood pressure in both groups. These data suggest that in the absence of respiratory depression, NTS and NA mu receptors mediate pressor responses and tachycardia; kappa receptors in the NA mediate a decrease in blood pressure but cardioacceleration in the NTS.     

Estimation of growth yield and maintenance coefficient of plant cell suspensions

Methodology is presented for the determination of growth yield (Y(g)) and maintenance coefficient (m) for carbon utilization of plant cells grown in suspension culture. Estimation of Y(g) and m requires measurements of specific growth rate (micro) and specific rate of substrate uptake (q) at different growth limiting substrate concentrations. Batch culture of tobacco cells did not permit evaluation of Y(g) and m because micro is constant and maximal during most of the growth cycle. In batch culture, the period of declining specific growth rate is extremely brief because of the rapid transition from logarithmic growth to stationary phase. This occurs because the K(m) for growth is relatively small compared to the initial sucrose concentration. Thus, when the substrate level reaches the K(m), the large mass of cells rapidly depletes the remaining substrate. In contrast, semicontinuous culture facilitates the determination of Y(g) and m because various steady-state growth rates can be achieved. Mathematical expressions were developed to determine the effective values of micro and q over the semicontinuous replacement interval. The validity of this approach was verified by conducting simulations using experimentally determined parameters.     

Effects of temperature on acaricidal and insecticidal activities of the benzoylureas flucycloxuron and diflubenzuron

Effects of temperature on the activity of flucycloxuron on larval stages of Panonychus ulmi (Koch), based on LC₅₀ values, were highly significant (P < 0.001) with temperature coefficients of-1.7 in both the ranges of 15° to 25°C and 20° to 30°C. The slopes of probit regression lines at 15° and 20°C were significantly steeper than those at 25° and 30°C. As a consequence the temperature coefficients based on LC₉₀ values were-4.4 and-2.2, for the 2 temperature ranges. The ovicidal activity of flucycloxuron on P. ulmi was low and was only statistically detectable at 20°C (LC₉₀ of 84 mg a.i./l). In studies with larvae of Aedes aegypti (Linnaeus), Leptinotarsa decemlineata (Say), Plutella xylostella (Linnaeus), Spodeptera exigua (Hübner) and Spodoptera littoralis (Boisduval) probit regression lines were parallel over temperature. The activity of flucycloxuron on these five insect species was not affected by temperature. Based on LC₅₀ values, diflubenzuron showed positive temperature coefficients on P. xylostella of + 2.1 at 15° to 25°C and + 2.5 at 20° to 30°C. For S. littoralis the temperature coefficient was positive (+ 2.4) at 15° to 25°C but negative (-1.9) at the 20° to 30°C range. Temperature coefficients of diflubenzuron were neutral for A. aegypti, L. decemlineata and S. exigua. In the design and analysis of these studies special allowance was made for date effects and variation in natural mortality over temperature.     

Crossing experiments in Allium L. section Cepa

VAN RAAMSDONK, L. W. D., WIETSMA, W. A. & DE VRIES, J. N., 1992. Crossing experiments in Allium L. section Cepa . A full diallel was carried out with six diploid species of Allium section Cepa and A. roylei of section Rhizirideum , High isolation barriers were found between the related species A. cepa and A. oschaninii , between A. oschaninii and A. vavilovii , and between A. galanthum and A. pskemense . On the contrary, the species A. cepa and A. roylei , belonging to different sections, show only slight isolation barriers. The Wallace effect, which is the development of internal isolation barriers as such, is likely to have taken place in the evolution of A. oschaninii and A. vavilovii , and possibly also between A. galanthum and A. pskemense .     

A small protein in model membranes: a time-resolved fluorescence and ESR study on the interaction of M13 coat protein with lipid bilayers

Model membranes with unsaturated lipid chains containing various amounts of M13 coat protein in the -helical form were studied using time-resolved fluorescence and ESR spectroscopy. The lipid-to-protein (L/P) ratios used were > 12 to avoid protein-protein contacts and irreversible aggregation leading to -polymeric coat protein. In the ESR spectra of the 12-SASL probe in dioleoyl phosphatidylcholine (DOPC) bilayers no second protein induced component is observed upon incorporation of M13 coat protein. However, strong effects are detected on the ESR lineshapes upon changing the protein concentration. The ESR lineshapes are simulated by assuming a fixed ratio between the parallel (D) and perpendicular (D) diffusion coefficients of 4, and an order parameter equal to zero. It is found that increasing the protein concentration from L/P to L/P 15 results in a decrease of the rotational diffusion coefficient D from 3.4 × 10⁷ to 1.9 × 10⁷ s^–1. In the time-resolved fluorescence experiments with DPH-propionic acid as a probe, it is observed that increasing the M13 coat protein concentration causes an increase of the two fluorescent lifetimes, indicating an increase in bilayer order. Analysis of the time-resolved fluorescence anisotropy decay allows one to quantitatively determine the order parameters P₂ and P₄, and the rotational diffusion coefficient D of the fluorescent probe. The order parameters P₂ and P₄ increase from 0.34 to 0.55 and from 0.59 to 0.77, respectively, upon adding M13 coat protein to DOPC bilayers with an L/P ratio of 35. The rotational diffusion coefficient D of the DPH-propionic acid probe decreases on incorporating M13 coat protein, in accordance with the ESR results. It is concluded that M13 coat protein in the -monomeric state is not able to produce a long living lipid boundary shell and consequently an immobilization of the lipids. An overall effect on the lipids is induced, resulting in a reduction in the dynamics and an increase in average lipid order. The hydrophobic region of M13 coat protein is proposed to perfectly match the lipid bilayer, resulting in a relatively small distortion of the bilayer structure of the lipid system.     

Phytoplankton primary production and nutrients in the Oosterschelde (The Netherlands) during the pre-barrier period 1980–1984

Phytoplankton primary production, nutrient concentrations and turbidity were monitored at three stations in the Oosterschelde during 1980–1984 as part of an ecosystem study.From comparisons of dissolved nutrient ratios with the nutrient requirements of phytoplankton, and of ambient nutrient concentrations with half-saturation constants for nutrient uptake by natural phytoplankton populations it was concluded that silicate was a limiting nutrient for diatoms after the spring bloom until the end of the summer. Dissolved inorganic nitrogen and phosphate were not considered to be limiting to phytoplankton growth.In general, the phytoplankton growing season started during the first fortnight of April and ended at the end of September. Column production in the whole Oosterschelde varied between 201 and 540 g C m^–2 yr^–1 and was, on average, 25% higher in the western part than in the eastern part. Basin production in the Oosterschelde varied between 120 and 466 g C m^–2 yr^–1 and was, on average, 55% higher in the western part than in the eastern part; this difference could be explained by differences in the ratio of euphotic depth to mean depth of the compartments.Estimated carbon-specific growth rates in the eastern part varied between < 0.1 and 3 d^–1 and in the western part between < 0.1 and 1 d^–1. This difference could be explained by the great differences in depth of the compartments. Carbon-specific growth rates are discussed in relation to phytoplankton loss rates. It is suggested that in the eastern part sedimentation must be an important sink for phytoplankton.Communication no. 473 of the Delta Institute for Hydrobiological Research, Yerseke, The Netherlands.     

Structure--activity relationships of chemical inducers of carotenoid biosynthesis

Fifteen amines having a profound effect on carotenogenesis in Marsh seedless grapefruit are reported. The compounds fall into three series: Et₂N(CH₂)_nMe (n = 4–8), Et₂N(CH₂)_nPh (n = 1–5), and Et₂NCH₂CH₂OC₆H₄R (R=H, p-Me, p-Et, p-iso-Pr, p-tert-Bu), There was up to an 11-fold increase in the total carotene content. Lycopene, not normally accumulated, became a major pigment. The inducing ability of the amines on carotenoid biosynthesis is correlated with the octanol-water partition coefficient. The mode of action appears to be similar to that of 2-(4-chlorophenylthio)triethylamine hydrochloride.