Rate Of Ion Uptake Research Articles

Nitrogen utilization by plant species from acid heathland soils

Seven heathland species, four herbaceous plants and three dwarf shrubs, were tested for their capacity to utilize NH4+ or NO3-. When cultured in solution at pH 4.0 with 2 mol m(-3) N, all species showed similar growth responses with respect to N source. Nitrate was assimilated almost equally well as ammonium, with relative growth rate generally averaging 5-8% lower for NO3- grown plants, albeit not always significantly, However, N source was significantly and consistently correlated with biomass partitioning, as NH4+-fed plants allocated more dry matter to shoots and less to roots when compared to NO3-- fed plants, The strong difference in biomass partitioning may relate to the relative surplus of carbon per unit plant N (or, alternatively, the relatively suboptimal rate of N assimilation per unit plant C) in NO3--fed plants. Inherently slow-growing dwarf shrubs accumulated virtually no free nitrate in their tissues and reduction of nitrate was strictly root-based, Faster-growing herbaceous plants, however, partitioned the assimilation of nitrate over both shoots and roots, thereby accumulating relatively high tissue NO3--levels. ion uptake rates depended clearly on the 'relative shoot demand', At similar shoot demands, especially in the herbaceous species, specific uptake rates for N and total inorganic (non-N) anions were higher in NH4+-fed plants, whereas the uptake rate for total (non-N) cations was higher in NO3--fed plants, Rate of P uptake was enhanced with increasing plant demand, but was independent of the N source, Net H+ extrusions ranged from 1.00 to 1.34 H+ per NH4+, and from -0.48 to -0.77 H+ per NO3- taken up. [KEYWORDS: Ammonium; biomass partitioning; heathland plants; low ph; nitrate; nitrate reductase activity; relative shoot demand; specific absorption rate Zea-mays l; chemical-composition; functional equilibrium; ricinus-communis; vascular plants; lolium-perenne; root-zone; growth; form; absorption]

Kinetics of the repression of tylosin biosynthesis by ammonium ion in Streptomyces fradiae

Nitrogen regulation of tylosin synthesis in Streptomyces fradiae NRRL 2702 was studied in batch and chemostat cultures using a soluble synthetic medium. In batch cultures, valine dehydrogenase (VDH; EC 1.4.1.8), threonine dehydratase (TDT; EC 4.2.1.16) and aspartate aminotransferase (ASAT; EC 2.6.1.1) reached their highest specific activities at 120 h. The specific activities of the three enzymes showed close correlation with the value of specific tylosin formation rate ( q TYL). In chemostat cultures, the maximum value of q TYL was 1.14 tylosin per mycelial mass per h (mg g −1 h −1) at the specific growth rate of 0.05 h −1, and after reaching a rate of 0.1 h −1, q TYL decreased with increasing levels of the specific growth rate. This value of q TYL was 3.5-times as large as that of maximum q TYL observed in the batch culture. The specific formation rates of VDH, TDT, ASAT and tylosin were repressed by high levels of specific ammonium ion uptake rate.

Metal binding affinity of imidazole ligands immobilized on poly(glycidyl methacrylateco-ethylene dimethacrylate) and on silica

Four new chelating ion-exchangers have been obtained by ring-opening reaction of the epoxy groups on poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) (GMA-EDMA) and on two types of epoxy-modified silica with the primary amine group of histamine and the primary amine group of 4-(5-methyl-4-imidazolyl)-1-amino-3-thiabutane (memia). The ligand concentration on the resins varied between 0.25 and 1.9 mmol of the ligand per gram of solid carrier, the highest ligand concentration being obtained for histamine-modified GMA-EDMA. For all materials the batch extraction capacities, in the pH range 0.5–5.7, were higher for Cu 2+ than for Cd 2+, Zn 2+, Ni 2+, Co 2+ and Ca 2+. The highest capacity for Cu 2+ was found for GMA-EDMA functionalized with histamine, i.e. 1.1 mmol Cu 2+ per g resin. No detectable uptake of Ca 2+ took place on any of the new materials in the pH range studied. Competitive experiments, which were performed with solutions containing mixtures of metal chloride salts showed that the ion exchange materials described here selectively sorb Cu 2+. Kinetic experiments suggest that the rate of metal ion uptake, and also of metal ion stripping with H 2SO 4, is mainly determined by the particle size of the carrier material and less by the anchored ligand and the type of backbone material (silica or GMA-EDMA). Apparently, diffusion of the metal ions into the pores of the solid supports is rate determining. Good results, viz. loading and de-loading (stripping) within a few seconds, were obtained with ion-exchange material based on the silica Sorbsil C200, which consists of small porous particles.

Sodium relations in Chenopodiaceae: a comparative approach

ABSTRACTSodium relations of 15 species of Chenopodiaceae were studied in seedlings grown on quartz sand at 10 mol m−3 of sodium and potassium. Uptake of sodium and potassium into whole plants and shoots was followed over 2 weeks. High alkali ion uptake rates were found in all species. The apparent selectivity of alkali ion uptake showed a continuous variation between species, from nearly perfect sodium exclusion to negligible cation selection. K/Na ratios above 6 were found in the shoots of eight species. For most of these plants above ground sodium concentrations were highest in the hypocotyls. However, in Chenopodium hybridum (shoot K/Na = 10) and C. urbicum (shoot K/Na = 17) above ground sodium concentrations were lowest in hypocotyls and highest in leaves, as in those species accumulating larger amounts of sodium. These differences are discussed with respect to the underlying mechanisms of ion regulation.

The effect of calcium phosphate ceramic composition and structure on in vitro behavior. II. Precipitation

The formation of a biologically equivalent carbonate-containing apatite on the surface of synthetic calcium phosphate ceramics (CPC) may be an important step leading to bonding with bone. Reactions of several single phases CPCs upon immersion into a simulated physiologic solution (SPS) with an electrolyte composition of human plasma were determined. The CPCs covered a wide range of solution stabilities from low-soluble hydroxyapatites (HA) to metastable tricalcium phosphates (TCP) and tetracalcium phosphate (TTCP). Changes in chemical compositions of SPS and infrared spectral features after CPC immersion were analyzed. New phase formation was observed on all the CPCs. However, kinetics, compositions, and structures of the new phases were significantly different. The studied CPCs can be characterized by the time to new phase formation in vitro; the minimum time for measurable precipitate formation was found to increase in the order: not-well-crystallized HAs < well-crystallized HAs < alpha-TCP, TTCP < beta-TCP. Among the CPCs only not-well-crystallized HAs led to immediate new phase formation. The metastable CPCs, beta-TCP, alpha-TCP, and TTCP required an induction time during which dissolution occurred. beta-TCP showed the longest induction time and the lowest lattice ion uptake rate of all the CPCs tested. Only the not-well-crystallized HAs elicited immediate formation of carbonated HA. The well-crystallized HAs and beta-TCP did not elicit carbonated apatite formation within the time frame of the experiment. Instead, intermediate phases were formed. On alpha-TCP amorphous calcium phosphate (ACP) with a relatively low carbonate content was formed. TTCP was found to transform extensively to poorly crystallized carbonated apatite after 2 days of immersion.

Uptake of cerium, cobalt and cesium by Potamogeton crispus

AbstractCerium, cobalt and cesium and their isotopes were taken up inside Potamogeton crispus. The rate of uptake was subjected to environmental parameters such as pH, temperature, and interference by certain ions. Accumulation of cerium and cobalt inside 1 g of Potamogeton reached a quantity of 12 mg of Ce (III) and 3‐6 mg of Co (II). Also I g of Potamogeton can accumulate 12 KBq, 17 KBq and 20 KBq of Ce144, Co60 and Cs137 respectively. Rates of ion uptake by Potamogeton were increased by increasing pH and temperature and decreased in the presence of chemical additives. Potamogeton could be used to treat low level liquid radioactive waste.

Respiratory energy requirements of roots vary with the potential growth rate of a plant species

The rates of growth, net rate of nitrate uptake and root respiration of 24 wild species were compared under conditions of optimum nutrient supply. The relative growth rate (RGR)of the roots of these species varied between 110 and 370 mg g‐1 day‐1 and the net rate of nitrate uptake between 1 and 7 mmol (g root dry weight)‐1 day‐1. The rate of root respiration was positively correlated with the RGR of the roots. Root respiration was also calculated from the measured rate of growth and nitrate uptake, using previously determined values for the costs of maintenance, growth and ion uptake of two slow‐growing species. The calculated rate of respiration was slightly lower than the measured one for slow‐growing species, but twice as high as measured rates for rapid‐growing species. This discrepancy was not due to a relatively smaller electron flow through the alternative pathway and, consequently, a more efficient ATP production in the fast‐growing species. Neither could variation in specific costs for root growth or maintenance explain these differences. Therefore, we conclude that fast‐growing species have lower specific respiratory costs for ion uptake than slow‐growing ones. Due partly to these lower specific costs of nutrient uptake, the fraction of respiration that rapid‐growing species spend on anion uptake is lower than that of slow‐growing species, in spite of the much higher rate of ion uptake of the fast‐growing ones.

Reversal of changes in left ventricular diastolic filling associated with normal aging using diltiazem

Congestive heart failure is a common problem in clinical geriatrics and often the result of diastolic rather than systolic dysfunction. 1 Normal aging is associated with a reduction in the rate of calcium ion uptake by the sarcoplasmic reticulum. 2 Because intracellular handling of calcium may affect isovolumic relaxation and left ventricular (LV) compliance, a calcium antagonist may be beneficial. The pattern of LV diastolic filling may be accurately characterized by both pulsed Doppler transmitral flow velocities 3 and radionuclide scintigraphy. 4 The present study tests the hypothesis that a calcium antagonist, diltiazem, may be effective in reversing the impairment of early diastolic LV filling seen in elderly subjects.

EFFECT OF NH4+, NO3+, AND Cl- IONS ON ION UPTAKE AND SOLUTION pH IN HYDROPONIC CULTURE OF AGERATUM AND SALVIA

Ageratum and salvia were grown in hydroponic solutions containing either NH4+, NO3-, or both NH4+ and NO3- with or without Cl- to study changes in solution pH and ion uptake rate. pH of both NH4+ and NH4+ + NO3- solutions was steadily decreased as time passed. A drop in pH front 6.50 to 3.57 within 3 days was recorded with NH4+. The pH changes were also affected by the presence of Cl-. The NO3- treatment maintained its initial solution pH over time regardless of the presence of Cl-. pH change by ageratum was greater than that by salvia, especially when plants were in NH4+ + NO3- solution. N uptake was maximum in NH4+ + NO3- solution with Cl-. Uptake of NO3- was suppressed by NH4+, but NH4+ uptake was not affected by NO3-. NH4+ and NO3- counteracted each other in influencing the Cl- uptake. Uptake of other ion was also affected by plant species as well as N source and Cl-. In ageratum transpiration rate was lowered by Cl- in both NH4+ and NO3- treatments.

Azolla pinnata r.br. and lemna minor l. for removal of lead and zinc from polluted water

The uptake of lead and zinc by Azolla pinnata R.Br. (water velvet) and Lemma minor L. (duckweed) was investigated in solutions, enriched with 1.0.2.0.4.0 and 8.0 mg/l of these two metal ions, which were renewed on alternate days over a 14 day test period. The uptake rate of both metal ions was highest when the initial concentration in the test solution was 1.0 mg/l. The concentration of lead or zinc remaining in the residual solutions after treatment with duckweed or water velvet at 1.0 and 2.0 mg/l levels, increased with the passage of time. At 4.0 and 8.0 mg/l levels, the concentration of lead or zinc remaining in the residual solutions either continuously increased with the passage of time or, first sharply increased (8–10 days) and then remained almost constant. The presence of one metal ion in solution decreased the uptake rate of the other; e.g. when water velvet was kept in a solution containing lead alone at 8.0 mg/l level, the value of the concentration factor was 54.5. However, in the presence of equal concentrations of zinc (mixed metal group), the value of the concentration factor for lead decreased to 35.44, indicating the influence caused by the presence of the zinc ion. The effect of these metal ions on biomass growth rate was also studied.

Calpain I activates Ca2+ transport by the reconstituted erythrocyte Ca2+ pump

Calpain I purified from human erythrocyte cytosol activates both the ATP hydrolytic activity and the ATP-dependent Ca2+ transport function of the Ca2(+)-translocating ATPase solubilized and purified from the plasma membrane of human erythrocytes and reconstituted into phosphatidylcholine vesicles. Following partial proteolysis of the enzyme by calpain I, both the initial rates of calcium ion uptake and ATP hydrolysis were increased to near maximal levels similar to those obtained upon addition of calmodulin. The proteolytic activation resulted in the loss of further stimulation of the rates of Ca2+ translocation or ATP hydrolysis by calmodulin as well as an increase of the affinity of the enzyme for calcium ion. However, the mechanistic Ca2+/ATP stoichiometric ratio was not affected by the proteolytic treatment of the reconstituted Ca2(+)-translocating ATPase. The proteolytic activation of the ATP hydrolytic activity of the reconstituted enzyme could be largely prevented by calmodulin. Different patterns of proteolysis were obtained in the absence or in the presence of calmodulin during calpain treatment: the 136-kDa enzyme was transformed mainly into a 124-kDa active ATPase fragment in the absence of calmodulin, whereas a 127-kDa active ATPase fragment was formed in the presence of calmodulin. This study shows that calpain I irreversibly activates the Ca2+ translocation function of the Ca2(+)-ATPase in reconstituted proteoliposomes by producing a calmodulin-independent active enzyme fragment, while calmodulin antagonizes this activating effect by protecting the calmodulin-binding domain against proteolytic cleavage by calpain.

Luxury consumption and specific utilization rates of three macroelements in two Taraxacum microspecies of contrasting mineral ecology

Plants of Taraxacum sellandii Dahlst., a microspecies adapted to fertile, and Taraxacum nordstedtii Dahlst., adapted to infertile soils, were cultured hydroponically, either on a complete nutrient solution or on one deprived of nitrogen, phosphorus, or potassium ions. For all four treatments, the growth and internal mineral concentration of the plants was monitored. For plants cultured on a complete nutrient solution, the uptake rates of nitrate, phosphate, and potassium ions were determined. Luxury consumption of the three macronutrients was computed as the excess of ion absorption over the ion uptake rates minimally required to sustain maximum growth. In these calculations the critical N, P, or K+ concentrations, earlier derived, were used as parameters describing the mineral status minimally required to allow maximum growth. Efficiency in use of the three macroelements at various levels of mineral accumulation was also computed. Finally, the response to phosphate starvation as related to phosphate uptake capacity and the accumulation of P was investigated.The physiological properies investigated provide a causal background for the superior adaptation of T. nordstedtii as compared to T. sellandii to infertile sites. Taraxacum nordstedtii had a higher relative luxury consumption of NO3–, H2PO‐4, and K+, a higher efficiency in N and P use at N– and (severe) P‐deficiency, respectively; and, after phosphate starvation, a relatively high preservation of phosphate uptake capacity and an enlargement of P storage. In combination with the low potential growth, luxury consumption will be particularly effective in T. nordstedtii in preventing or minimizing mineral deficiency. The distribution of minerals between cytoplasm and vacuoles as a factor in mineral use efficiency is discussed.

Root Respiration and Growth in Plantago major as Affected by Vesicular-Arbuscular Mycorrhizal Infection

Effects of vesicular-arbuscular mycorrhizal (VAM) infection and P on root respiration and dry matter allocation were studied in Plantago major L. ssp. pleiosperma (Pilger). By applying P, the relative growth rate of non-VAM controls and plants colonized by Glomus fasciculatum (Thaxt. sensu Gerdemann) Gerdemann and Trappe was increased to a similar extent (55-67%). However, leaf area ratio was increased more and net assimilation rate per unit leaf area was increased less by VAM infection than by P addition. The lower net assimilation rate could be related to a 20 to 30% higher root respiration rate per unit leaf area of VAM plants. Root respiration per unit dry matter and specific net uptake rates of N and P were increased more by VAM infection than by P addition. Neither the contribution of the alternative respiratory path nor the relative growth rate could account for the differences in root respiration rate between VAM and non-VAM plants. It was estimated that increased fungal respiration (87%) and ion uptake rate (13%) contributed to the higher respiratory activity of VAM roots of P. major.

Kinetics of Ion Transport by Macrocyclic Carriers in Liquid Membrane Systems

Abstract The relationship between the extractability of a metal ion (K+ or Pb2+) and the rate of its transfer by neutral macrocyclic carriers (dibenzo-18-crown-6, dicyclo-hexano-18-crown-6, 18-crown-6, and polynactin) was investigated in chloroform membrane systems. The experimentally determined apparent rate constants are compatible with the diffusion-limited process. Both the rate of ion uptake and the rate of ion transport depend crucially on the extractability of the metal ion rather than on the apparent rate constant.

Effects of Growing Wheat in Hypoxic Nutrient Solutions and of Subsequent Transfer to Aerated Solutions. II. Concentrations and Uptake of Nutrients and Sodium in Shoots and Roots

We report on the effects of hypoxia (low O2 concentrations) in the nutrient solution on the net uptake of Cl-, N, P, K+ and Na+ by 26-30-day-old wheat plants (Triticum aestivum L.). Plants treated with hypoxia had been grown at 0.003 mol O2 m-3 for 10 days; four consecutive samplings were taken between 10 and 14 days to assess the uptake of nutrients. After the first sampling, one group of plants exposed to hypoxia was returned to aerated solutions containing 0.27 mol O2 m-3 . Seminal and crown roots grown in hypoxic solutions showed remarkably few differences in ion relations, despite the high porosity and the fast growth of the crown roots. The exception was with K+ /Na+; a decrease in this ratio due to growth in hypoxic solutions was more pronounced for seminal than for crown roots. Concentrations of elements in the shoots were nearly always lower for plants grown at 0.003 than for plants grown at 0.27 mol O2 m-3 ; the only exception was for Na+ which increased in plants grown in the hypoxic solutions. Comparisons with published critical nutrient concentrations indicate that decreased growth at 0.003 mol O2 m-3 was not due to reduced nutrition of the plants. For N, this conclusion is supported by higher concentrations of soluble amino acids in plants at 0.003 than at 0.27 mol O2 m-3 . The reduction in net transport to the shoots of N, P, Cl- and K+ was due to a combination of decreases in root /shoot ratio and an inhibition of ion uptake per unit root weight. This inhibition was not due to permanent damage as it was reversible. A rapid restoration of concentrations of N, P, Cl- and K+ in the shoot upon transfer from 0.003 to 0.27 mol O2 m-3 was attributed to a combination of higher net rates of ion uptake by the roots compared with continuously aerated plants and a rapid expansion of the root system.

Interference of Italian Ryegrass (Lolium multiflorum) in Wheat (Triticum aestivum)

Wheat (Triticum aestivumL.) grain yields were reduced an average of 4.2% for every 10 Italian ryegrass [Lolium multiflorum(Lam.) # LOLMU] plants/m2within the range of 0 to 100 Italian ryegrass plants/m2. Yield reductions caused by Italian ryegrass were attributed primarily to decreased crop tillering. Italian ryegrass densities as high as 80 plants/m2had little effect on wheat head or kernel weights. In greenhouse experiments, the growth response of Italian ryegrass to increasing concentrations of NO3–and K+was greater than that of wheat. Net uptake rates for NO3–by both species growing in nutrient solution were 1.5 times greater than net uptake rates for K+. Nitrate and potassium Imaxvalues for Italian ryegrass were approximately twice the corresponding values for wheat. Although Italian ryegrass responded more to changes in nutrients and had greater ion uptake rates compared to wheat, Italian ryegrass accumulated more biomass when grown in monoculture than when grown in association with wheat. This difference was probably due to the initial size of the seedlings. Wheat seedlings were much larger than Italian ryegrass seedlings during the first 20 days following emergence.

Ionic balance, proton efflux, nitrate reductase activity and growth ofHippophaë rhamnoides L. ssp.rhamnoides as influenced by combined-N nutrition or N2 fixation

Growth of 2-month-old nonnodulatedHippophae rhamnoides seedlings supplied with combined N was compared with that of nodulated seedlings grown on zero N. Plant growth was significantly better with combined N than with N2 fixation and, although not statistically significant for individual harvests, tended to be highest in the presence of NH 4 + , a mixture of NH 4 + and NO 3 − producing the highest yields. Growth was severely reduced when solely dependent on N2 fixation and, unlike the combined-N plants, shoot to root ratios had only slightly increased after an initial decrease. An apparently insufficient nodule mass (nodule weight ratio <5 per cent) during the greater part of the experimental period is suggested as the main cause of the growth reduction in N2-fixing plants. Thein vivo nitrate reductase activity (NRA) of NO 3 − dependent plants was almost entirely located in the roots. However, when grown with a combination of NO 3 − and NH 4 + , root NRA was decreased by approximately 85 per cent.H. rhamnoides demonstrated in the mixed supply a strong preference for uptake of N as NH 4 + , NO 3 − contributing only for approximately 20 per cent to the total N assimilation. Specific rates of N acquisition and ion uptake were generally highest in NO 3 − +NH 4 + plants. The generation of organic anions per unit total plant dry weight was approximately 40 per cent less in the NH 4 + plants than in the NO 3 − plants. Measured extrusions of H+ or OH− (HCO 3 − ) were generally in good agreement with calculated values on the basis of plant composition, and the acidity generated with N2 fixation amounted to 0.45–0.55 meq H+. (mmol Norg)−1. Without acidity control and in the presence of NH 4 + , specific rates of ion uptake and carboxylate generation were strongly depressed and growth was reduced by 30–35 per cent. Growth of nonnodulatedH. rhamnoides plants ceased at the lower pH limit of 3.1–3.2 and deterioration set in; in the case of N2-fixing plants the nutrient solution pH stabilized at a value of 3.8–3.9 without any apparent adverse effects upon plant performance. The chemical composition of experimental and field-growing plants is being compared and some comments are made on the nitrogen supply characteristics of their natural sites.

Ion uptake and respiration of dry bean roots subjected to localized anoxia

Ion uptake by dry bean root systems was examined during a three day treatment period. Three aeration treatments were applied to split root systems where both halves were aerated, both halves were nonaerated and one half aerated and the remaining half nonaerated (localized anoxia). Ion absorption was similar for the aerated control and localized anoxia treatments. The nonaerated control absorbed 2, 40, and 60 percent of the aerated control for K+, Ca++, and NO3−, respectively. Ion absorption by stressed plants appeared to increase directly with root growth in the aerated portions of the localized anoxia treatments. Localized anoxia resulted in greater potassium ion uptake per unit root weight and in greater root respiration rates of the aerated half of the Pinto III cultivar root system. Transpiration rates of Seafarer subjected to localized anoxia were 135% of the aerated control. The additional water use may have contributed to greater ion uptake, by mass flow, in the nonaerated portion of the localized anoxia treatment. Nutrient solutions of the nonaerated controls became more alkaline during stress than did the nonaerated portions of the localized anoxia treatments, indicating a possible direct or indirect effect of the aerated portions of the localized anoxia treatments on the corresponding nonaerated half. Compensation in ion uptake by dry bean roots subjected to localized anoxia appeared to be the result of increased root growth, greater respiration rates, greater transpiration rates and, for Pinto III, an increase in the ion uptake rate per unit root weight. This compensatory uptake of water and nutrients by the root system may be one mechanism by which roots overcome localized stress within a soil profile.

Potassium and Phosphorus

Abstract Aeration of submersed corn roots doubles the subsequent uptake rate of ions. This augmentation is accompanied by hyperpolari‐zation of membrane potential, depends upon aeration and protein synthesis, and is associated with changes in membrane proteins. Potassium uptake (86Rb) by excised and intact roots before and after augmentation was measured, and potassium losses by roots at different temperatures or in the presence of dinitrophenol was followed. Relevant effluxes of potassium follow excision and/or submersion or roots, and a metabolism‐dependent process must be carried out by roots in order to recover the control of membrane permeability. Moreover, we show that corn hybrids of different maturity classes differ not only for initial ion uptake rates but also for the ability to recover control of membrane permeability.

Salt Tolerance in the HalophyteSuaeda maritimaL. Dum. Growth, Ion and Water Relations and Gas Exchange in Response to Altered Salinity

Clipson, N. J. W. 1987. Salt tolerance in the halophyte Suaeda maritima L. Dum. Growth, ion and water relations and gas exchange in response to altered salinity.—J. exp. Bot. 38: 1996-2004. Shoot and root fresh and dry weights and shoot sodium, chloride and potassium contents were measured and shoot relative growth rates calculated in seedlings of Suaeda maritima over a period of lid following a raising of culture solution salinity from 0 to 200 mol m 3 NaCl. Growth, growth rates and sodium and chloride contents, as compared to plants growing in the absence of salt were increased whilst potassium contents declined. Shoot sodium accumulation rate and the rate of transport of sodium from root to shoot, osmotic potential, and rates of photosynthesis and transpiration were also measured for up to 72 h after transfer of plants originally growing at 0 and 200 mol m-3 NaCl to 200 and 400 mol m3 NaCl respectively. Ion uptake and transport rates were maximal 6-12 h after transfer and then declined to new steady-state levels within 48 h; osmotic potentials were lowered over a 72 h period on average by approximately 10 MPa; and after 9 h photosynthetic and transpiration rates were reduced by about 20% and 30% respectively. Results are discussed in terms of the ability of halophytes to adjust to fluctuating salinity and to salt tolerance mechanisms in general.