Influence Of External Concentration Research Articles

RADICULAR UPTAKE KINETICS OF 15NO− 3, CO(15NH2)2, AND 15NH4 + IN WHOLE RICE PLANTS

The mechanism of uptake of nitrate, urea, and ammonium by roots of intact plants (Oryza sativa L.) was studied using enriched nitrogen 15N as a tracer in order to establish an absorption kinetic model and the influence of external concentration on uptake. Rice plants at 30 and 60 days after germination were submitted to different contact times with two concentrations of an external solution containing these nitrogenous sources. In the treatment with nitrate, the relative uptake rate decreased with increasing plant age, for both concentrations tested. For urea, this rate was higher in dry matter of old plants at low external concentration (1.0 μmol g−1) and for ammonium a higher relative rate of uptake was found in young plants at low external concentration and at high concentration, old plants had higher relative rate of uptake, as had been seen with nitrate and urea uptake. In the experiment related to the influence of external concentration on the radicular uptake, plants were used at 30 days after germination and have shown the occurrence of a multiphasic system (4 isotherms) for the three treatments. Each isotherm is associated with the Michaelis-Menten kinetics and the transition between phases is carried out by jumps. The Vmax (maximum uptake rate) and Km (affinity of carrier to ion) values, calculated by Lineweaver-Burk and Hofstee transformations, increased with the increasing external concentration.

Potassium flux in juvenile striped bass (Morone saxatilis): influence of external concentrations of sodium chloride and calcium

Whole-body influx and efflux of K(+) were determined for 25-day-old striped bass,Morone saxatilis, in conditions that simulated harvesting fish from ponds. During the first 5h in fresh water with combined high NaCl (80 mM) and low Ca(2+) (0.12 mM) concentrations, a combination that is acutely lethal to this age of striped bass, K(+) influx for fish in 0.07 mM K(+) was 21±1.7 (SEM) compared to 3.4±0.33 nmol g(-1) h(-1) for fish in water with low Na(+) (0.25 mM) or high Ca(2+) (2.5 mM) concentrations. Influx of K(+) was inhibited during the first few hours after fish were placed in flux chambers. Potassium efflux as percentage of(42)K lost per hour was two-fold higher from fish in the high Na-low Ca treatment compared to fish in low concentrations of Na(+) or high concentrations of Ca(2+). Potassium efflux was probably much greater than influx, but exact values for efflux could not be calculated from the data available. Survival of fish in water with high Na-low Ca was not increased by addition of KCl to the water, indicating that the net loss of K(+) was probably not the cause of death.

Selective behaviour of hyperfiltration cellulose acetate membranes: Part I. selectivity to cations and electroosmotic flow

Concentration potentials and electroosmotic flow through five asymmetric cellulose acetate membranes cured at 55, 65, 75, 85 and 95°C are measured in solutions in NaCl, CsCl HCl, CaCl 2 and LaCl 3. The influence of external concentration, counterion valency and curing temperature of membranes on their apparent transport numbers, permselectivity and electroosmotic permeability are determined. Hyperfiltration membranes exhibited the behaviour of loose, weakly charged cationic membranes. Selective behaviour is stronger the higher the curing temperature and the cation charge and the lower the external concentration. Counterions of high membrane affinity cause selectivity reversal. Results are correlated with the expected potential profile through asymmetric membranes. Electroosmotic permeability rises with the decrease in solution concentration up to a limiting value. Water transport measured in the presence of alkali and alkaline earth cations increases with hydrated size and/or charge of cations parallel to the cation-water friction coefficient. The electrokinetic cross coefficient obtained from electroosmotic measurements is found to vary with current density

The Influence of External Concentration on Sodium Ion Absorption by Carrot Root Tissue 4

The Influence of External Concentration on Sodium Ion Absorption by Carrot Root Tissue 4

The influence of external concentration on the position of the equilibrium attained in the intake of salts by plant cells

The intake and translocation of dissolved substances in the living plant present one of the outstanding problems of the physiology of nutrition, and one which has for a long time attracted the attention of plant physiologists. We know the metallic or ash constituents of the plant are taken in by the root in the form of salts, and eventually find their way, in some form or another, to every part of the organism. What is the mechanism of their intake and of their translocation from cell to cell ? Can the movement be explained as a simple diffusion phenomenon, or are adsorption phenomena concerned, or chemical combinations, or is the process still more complex ? The work recorded in this paper forms a first instalment of an attempted analysis of these phenomena of the intake and movement of salts in the living plant.