Tissue Ion Concentrations Research Articles

Ion accumulation in the cell walls of rice plants growing under saline conditions: evidence for the Oertli hypothesis

Abstract. When plants of rice (Oryza saliva L.) are subjected to mildly saline (50mol m−3 NaCl) conditions, the leaves show symptoms of water deficit, even though ion accumulation has been more than sufficient to adjust to the decrease in external water potential. After a few days of exposure to salt, there is a negative correlation, in a population of leaves, between the leaf water concentration (g water per g dry weight) and their sodium concentration (mmol Na per g dry weight). Ion concentrations in the cell walls and the cytoplasm of cells of plants grown in low salinity were measured by X‐ray microanalysis. The NaCl concentration in solution in the apoplast was calculated to be around 600mol m−3 in leaves of plants whose roots were exposed to only 50 mol m−3 NaCl. This constitutes strong evidence that an important factor in salt damage in rice is dehydration due to the extracellular accumulation of salt as suggested in the Oertli hypothesis. The implication, that changes in tissue ion concentration and solute potentials equivalent to the external medium is not evidence of plant osmotic adjustment to salinity, is discussed.

Acid-base and electrolyte regulation, and haemolymph gas transport in crayfish, Astacus astacus, exposed to soft, acid water with and without aluminium

Intermoult crayfish (Astacus astacus) were exposed to acid (pH 4), soft water ([Ca++]=100 μmol·l−1) in the absence and presence of aluminium (25 μmol·l−1) for variable time periods (up to 21 days) in order to assess the consequences for acid-base and electrolyte balance and haemolymph gas transport. Haemolymph osmolality and concentration of major ions decreased drastically and to a similar extent in acid and acid-aluminium water. Muscle tissue ion concentrations were, however, regulated at an almost constant level. A severe metabolic acidosis was gradually developed, attaining a haemolymph metabolic acid load of 6–7 mequiv·l−1 after 12–21 days. The acidosis was partially compensated by ventilatory means, with the postbranchial haemolymph PCO2 decreasing earlier in acidaluminium-exposed than in acid-exposed specimens. Hyperventilation seemed to be a direct acid-base regulatory response, since the rise in postbranchial PCO2 had only minimal influence on haemolymph O2 transport. The Bohr effect of Astacus astacus haemocyanin was low (δlog P50/GdpH=-0.24), and the mean P50 only increased from 15 to 19 mmHg after 21 days of acid exposure. The decrease in O2 affinity with decreasing pH was accompanied by a decrease in the cooperativity of O2 binding. The haemolymph haemocyanin concentration was not affected by acid and acid-aluminium exposure, but decreased after 21 days due to starvation. Muscle tissue aluminium concentrations were unaffected, whereas gill tissue concentrations increased in acid-aluminium exposed crayfish, most likely due to accumulation of aluminium on the gill surface. Mortality was low, and an internal hypoxia and lactacidosis was not developed in either of the experimental groups. This suggests that the gas transfer qualities of the chitincovered gills of crayfish are much less sensitive to acid and acid-aluminium stress than the gills of teleost fish.

Increased drug cytotoxicity at reduced pH counteracts cyclophosphamide resistance in cultured rat mammary carcinoma cells.

The sensitivity of a cyclophosphamide (CP)-resistant MIR rat mammary carcinoma cell variant (MIRCPr) in monolayer culture towards the cytotoxic effect of mafosfamide (an analogue of "activated" CP) was measured as a function of extracellular pH (pHe). An inverse correlation was found between cell survival and the H+ ion concentration in the culture medium. At pHe 7.4, the fraction of clonogenic MIRCPr cells exposed to mafosfamide (7.5 micrograms/ml) for 24 hr was 1 X 10(-1) in relation to untreated control cells. At pHe 6.2, however, this value was reduced to 3 X 10(-4), i.e., a value equal to that for the CP-sensitive parental MIR cells exposed to the same concentration of mafosfamide at pHe 7.4. Our data indicate complete compensation of CP resistance in MIRCPr cells at pHe 6.2. MIRCPr cells were not resistant to the cytotoxic effect of nornitrogen mustard. This suggests that resistance to CP in MIRCPr cells is due to enzymatic inactivation of the primary intermediates in CP bioactivation. The alkylating activity of nornitrogen mustard (and less so that of phosphoramide mustard) is strongly enhanced at low pH. In MIRCPr cells shifted to an acidic environment, therefore, a (putative) decrease in the intracellular concentration of alkylating CP metabolites may be counteracted by an enhancement of their alkylating activity (on a molar basis). By parenteral administration of glucose, the pH in malignant tumors of both animal and human origin can be lowered to values between 5.6-6.6. Our data suggest that an upshift of H+ ion concentration in malignant tissues may at least partially counteract CP resistance in cancer cells in vivo.

Effect of NaCl Salinity and Putrescine on Shoot Growth, Tissue Ion Concentration and Yield of Rice (Oryza sativa L. var. GR‐3)

AbstractInteractive effect of NaCl salinity and putrescine on shoot growth, ion (Na+, K+ and CI−) concentration in leaf, stem and inflorescence and yield of rice (Oryza sativa L. var. GR‐3) were studied. When rice plants were subjected to salt stress (12 dS/m) the extension growth and dry weight of shoot system as well as total leaf area and chlorophyll content were found markedly reduced. Analysis of leaf, stem and inflorescence of salt‐stressed plants showed higher concentration of Na+ and Cl ions and lower concentration of K+ ion compared to the control. Salinization also caused a considerable fall in grain yield.Foliar application of putrescine (10−5M) significantly increased the growth and yield of salt‐stressed plants. Putrescine treatment decreased the influx of Na+ and Cl− ions and increased the K+ level in all the tissues of salinized plants examined. Putrescine also increased the chlorophyll content in salt‐stressed plants. These results suggest that exogenous application of putrescine can be used successfully to ameliorate the stress injuries caused by NaCl salinity in rice plants to a considerable extent.

Effect of Salinity on Leaf Ionic Content and Photosynthesis of Taxodium distichum L.

Bald cypress (Taxodium distichum L.) seedlings were subjected to flooding with salinity levels ranging from 0-140 moles m-3 NaCl. Imposition of salinity was designed to simulate the increase in salinity level which some of Louisiana's extensive cypress forests are currently experiencing due to rapid subsidence in the Mississippi River Deltaic Plain. The effect of salt water on leaf tissue ion concentrations and subsequent changes in net photosynthesis were measured. Leaf concentrations of Na, K, Ca and Mg increased substantially as salinity of floodwater increased. Net photosynthesis declined from 7.6 ,umol.m-2s-1 to 0.9 ,umol.m-2s-1 when salinity increased from 0-140 moles m-3 NaCl. Despite the parallel reduction in both stomatal conductance and net photosynthesis, the leaf internal CO2 concentrations remained relatively constant over the entire range of salt concentrations. These results suggest that elevated floodwater salinity causes excess accumulation of several ions in the bald cypress leaf tissue. Consequently, increase in leaf ionic content is primarily the cause of reductions in photosynthesis which is accompanied by simultaneous diffusional limitations caused by stomatal closure. INTRODUCTION Significant parts of coastal forests including bald cypress (Taxodium distichum L.) stands are currently being subjected to saltwater intrusion caused by rapid subsidence and compaction of recent Mississippi River alluvial sediment. Salinity in streams flowing through the extensive cypress forests bordering Lake Pontchartrain has been reported as high as 50 moles m-3 NaCl (Salinas et al., 1986). The continuous land subsidence in wetland coastal areas and the projection indicating faster sea level rises in the future (Hoffman et al., 1983) may result in elimination of many salt-sensitive, but otherwise flood-tolerant species by exposing them to high salinity. Despite the potential impact of saltwater intrusion on survival, productivity and species composition of coastal vegetation, there is little information on the extent of salt tolerance and the physiological characteristics of these species. Assessment of physiological response of bald cypress seedlings to salt stress is important in order to identify the level of tolerance and possible adaptation/acclimation to salinity conditions. Salt stress reduces growth through several effects including water stress, excess ion and biochemical relations (Greenway and Munns, 1980). Presumably, plants can survive sublethal salt stress as long as they are able to photosynthesize positively. The photosynthetic rates of glycophytes, however, declines in response to salinity. Such response has been attributed to stomatal closure as well as direct effect of excess ion content on photosynthetic processes (Seemann and Critchley, 1985). Reports of photosynthetic response of bald cypress to salinity is limited to those of Pezeshki et al., (1986) and Pezeshki et al., (1987). The former studied the photosynthetic response of different leaf age group under salinity and the latter reported photosynthetic responses to a wide range of floodwater salinity. Generally, significant declines in net photosynthesis have been observed as a result of both flood and salt stresses in bald cypress. In our continuous efforts to further investigate the response of this key wetland tree species to increased inundation and salinity, this study was conducted to examine the effects of floodwater salinity on leaf ionic contents and the subsequent effects on photosynthesis.

Salt tolerance in Aster tripolium L. II. Ionic regulation.

Measurements of tissue ion contents (Na, K and Cl) were carried out at frequent intervals on plants of Aster tripolium L. grown at a range of salinities for 36 d. Aster tripolium behaved as a typical halophyte showing high levels of inorganic ion accumulation even at low salinities. As salinity increased Na replaced K to a large extent in the shoot but root K was unaffected up to 500 mol m-3 external NaCl. Shoot (Na + K) concentration on a tissue water basis was maintained constant in all treatments throughout the experiment, whereas shoot (Na + K) on a dry weight basis showed marked fluctuations in some treatments. An increase in (Na + K) per gram dry weight was, however, accompanied by a parallel increase in fresh weight: dry weight (FW : DW) ratio. Transport of (Na + K) to the shoot per unit root weight changed during the experiment in the manner expected, given the observed changes in shoot relative growth rate and FW : DW to result in a constant shoot (Na + K) concentration on a water basis. Chloride was the major balancing anion in the shoot at high salinity, but never accounted for more than 38% of the (Na + K) found in the root tissue. At all salinities (Na + K) salts accounted for the majority of the measured shoot sap osmotic potential. The interactions between salinity, growth, ion transport and osmotic adjustment are discussed.

Control of Na+ and K+ transport in Spergularia manrina. II. Effects of plant size, tissue ion contents and root‐shoot ratio at moderate salinity

In this paper we continue our analysis of Na+ and K+ uptake in vegetative Spergularia marina (L.) Griseb. plants growing on 0.2x sea water in solution culture. We consider the relationships between isotope uptake and plant size, root: shoot ratio (RSR) and total ion contents, both individually (with the linear effects of time removed) and in combinations through stepwise multiple linear regression. The results differ from those of other studies, representing in our case inherent variability in a homogeneous population under steady‐state growth conditions. The results were broadly similar for 22Na+ and 42K+. Total uptake was significantly and negatively correlated with RSR and root weight (Wr), and positively with root K+ content (Kr). These 3 variables were mutually correlated, however, and this was reflected in the multiple analyses as a reduction or loss of significance of one or more of the measures. Transport to the shoot was very highly correlated with total uptake (r2 > 0.99 for both isotopes), resulting in nearly identical regression results. In multiple regression analyses of root data alone, accumulation was related only to root contents, but in a manner inconsistent with the allosteric regulation hypothesis, the most significant correlation being positive with Kr. The results were nearly identical for the two isotopes. The results were not consistent with a single factor regulatory system involving only initial root plamalemma ion influx. The observed Na+‐K+ and root‐shoot balances seem to require at least involvement of symplast‐to‐medium and symplast‐to‐xylem transport steps. Though the biochemical and biophysical signalling and transduction steps are not known, a physiological working hypothesis is presented, in which the positive correlation of uptake with root contents is balanced by a negative feedback signal deriving from plant size and by the diluting effects of growth. Considered over the vegetative period, these would produce the observed stability of plant contents during growth. The negative interaction with RSR is postulated to manifest the integrating system required to deliver ions to the shoot at the required rates.

Changes in tissue ion contents and ultrastructure of food-deprived immature American eels, Anguilla rostrata (LeSueur)

The fasting-induced ultrastructural and ionic changes which occur in American eel (Anguilla rostrata) tissues were studied following 6 (fasted) and 12 (starved) months of food deprivation. Muscle and liver Na+ and Ca2+ ion contents generally rose at the expense of plasma ion concentrations; K+ levels changed little. The fiber area (size) of red (RM) and white (WM) muscles declined with the length of the fast. However, the relative proportion of RM myofibrils actually increased suggesting that red fiber performance was maintained during the fasting period. WM performance probably drops significantly as a result of a decreased fiber size and the relative volume of myofibrils present. Liver morphometric changes became apparent only after 12 months of food deprivation, although a significant increase was noted in the volume of the cell occupied by endoplasmic reticulum at 6 months. These studies indicate that tissue ultrastructural changes occurred with food deprivation in eels and that these were consistent with previously observed alterations in tissue protein and enzyme activities. It is proposed that these modifications are associated with the mobilization of tissue metabolic reserves, and not necessarily a dramatic metabolic reorganization of American eel tissues during food deprivation.

A program in BASIC for calculation of tissue extracellular space and ion distributions in vivo using morphometric and/or extracellular tracer methods

A BASIC program is presented to calculate extracellular space, ion and water contents, and ion concentrations in biological tissue treated as a two-compartment system, cellular and extracellular. The program requires that four experimentally determined variables be entered for each ion species to be analyzed, if the size of the extracellular compartment is known or to be assumed: tissue ion content, plasma ion concentration, and wet and dry tissue weights. If the extracellular compartment is to be quantified, then two options are available: first, morphometric analysis to obtain the mean ratio of extracellular area to tissue area; second, analysis of the tissue content and plasma concentration of a marker which is confined to the extracellular compartment after it is injected intravenously and allowed to equilibrate. All other required input data are obtained from the literature or analytical protocol and may be treated as constants. Although the program was designed for in vivo determinations of ion and water distributions in cardiac muscle, it may be generally applied to other tissues and experimental conditions directly or with minor modifications.

Adenosine-stimulated astroglial swelling in cat cerebral cortex in vivo with total inhibition by a non-diuretic acylaryloxyacid derivative.

The intact cerebral cortices of cats were exposed in vivo under normothermic conditions and superfused with isotonic artificial cerebrospinal fluid containing added 0.125 mM adenosine. This resulted in chloridecation-rich cerebrocortical swelling which was shown by electron microscopy to be associated with an expanded astroglial compartment. The addition of DCPIB, a non-diuretic acylaryloxyacid analogue of ethacrynic acid and an inhibitor of coupled chloride-cation transport in cerebral cortex in vitro, totally blocked astroglial swelling and the concomitant increases in tissue ion contents. These studies support our previous experiments on the mechanism of formation of astroglial swelling. The pathological consequences of astroglial swelling and the clinical applications of these findings are discussed.

THE SOLUTE AND WATER RELATIONS OF AGROSTIS STOLONIFERA ECOTYPES DIFFERING IN THEIR SALT TOLERANCE

SUMMARYThe water, ion, proline, amide, amino acid and quaternary onium contents of ecotypes of Agrostis stolonifera isolated from salt marsh, spray zone and inland habitats were determined over a range of external salt concentrations. When grown at high salinites the plants exhibited inhibition in the root water absorption and reduction in the shoot water content, these being most pronounced in the inland ecotype and least in the salt marsh ecotype. In the presence of salt the accumulation of Na+ and Cl− in both shoots and roots was accompanied by a decline in tissue potassium content. At high salinities the increase in tissue ion content was greatest in the inland ecotype and least in the salt marsh ecotype. Proline, asparagine, glutamine, serine and glycine betaine showed increases in response to salinity, these being most pronounced in the salt marsh ecotype. The inland and spray zone ecotypes exhibited marked decreases in the aspartate and glutamate contents when grown at high salinities.With polyethylene glycol or mannitol in culture solutions, the salt marsh ecotype exhibited a greater ability to resist losses in shoot water content and to increase shoot proline, asparagine, glutamine and serine contents, than the inland and spray zone ecotypes.Changes in the solute and water status are discussed in relation to salt tolerance of the ecotypes.

Effects of Ouabain and Low Temperature on the Sodium Efflux Pump in Excised Corn Roots

Ouabain (0.05 millimolar) and low temperature (4 C) both caused the tissue Na(+) content of excised 5-day-old corn roots to increase, indicating that there is an inhibition of the Na(+) efflux pump. Na(+) efflux was measured utilizing three different methods. Each method gave similar results in terms of rate and ouabain sensitivity. With one of these methods, the compartmental efflux method, it was demonstrated that rates for Na(+) efflux increase as the external Na(+) concentration is increased; e.g. the efflux rates are 0.529, 1.78, and 3.64 microequivalents per gram fresh weight per hour for external NaCl concentrations of 1, 10, and 30 millimolar, respectively. The data indicate that the Na(+) efflux pump is located in the plasmalemma of root cells.Na(+) efflux was stimulated for 30 to 60 minutes after the introduction of ouabain. This was followed in 60 to 90 minutes by an inhibition of Na(+) efflux. The Na(+) efflux rate returned to the original level on the removal of ouabain.The transport of Na(+) to the xylem vessels was stimulated by ouabain which most likely is a consequence of the ouabain-induced increase in cytoplasmic Na(+) content.Ouabain (0.05 millimolar) had little or no effect on K(+) and Cl(-) contents, and this implies the lack of an effect of ouabain on K(+) and Cl(-) fluxes. Ouabain at a concentration of 0.01 millimolar had no effect on Na(+) flux or on tissue ion content. With 0.5 millimolar ouabain the tissue contents of K(+), Na(+), and Cl(-) were greatly reduced.Evidence is presented indicating that ouabain has no effect on Na(+) efflux in pea roots.

Electrolyte and water balance in muscle tissue of the crab Hemigrapsus nudus

Sodium, potassium, calcium, and magnesium ion concentrations of total muscle tissue, blood and total muscle chloride ion concentrations, and blood and muscle tissue hydration were measured in summer- and winter-adapted populations of the shore crab Hemigrapsus nudus exposed to a series of experimental salinities, and at one temperature. When muscle ion concentrations were expressed as a function of extracellular water, changes in these concentrations were nearly identical to those concentrations found in blood and paralleled blood concentration changes with experimental salinity changes. Blood water content remained constant, and summer animal values were higher when compared with winter animal values. Muscle water content decreased significantly over the range of experimental salinities, approximately 15 g/kg wet weight of tissue decrease for each 25% increase in seawater concentration. Average extracellular volume was calculated for summer-adapted crabs to be 23.6% tissue wet weight and for winter-adapted crabs it was 18.8% tissue wet weight. Possible mechanisms are discussed which may explain how anisosmotic regulation (osmotic and ionic regulation between body fluids and the external environment) and isosmotic regulation (osmotic and ionic regulation between tissue and body fluids) contribute to the adaptation of this crab to an estuarine environment.

Histogenesis of the pituitary in rainbow trout (Salmo gairdneri) in different ambient salinities with particular reference to the rostral pars distalis.

The pituitary gland is first evident in rainbow trout two weeks before hatching. Differentiation of prolactin and ACTH cells is not marked until 3-4 days after hatching when the follicular arrangement of the prolactin cells become apparent. There is no difference in the time of development of either prolactin or ACTH cells in larvae reared in different ambient salinities despite marked changes in tissue ion and water content. This suggests that prolactin and ACTH do not play the osmo- and iono-regulatory roles in larval rainbow trout that they are considered to play in adult salmonids.

The use of lanthanum to estimate the numbers of extracellular cation-exchanging sites in the guinea-pig's taenia coli, and its effects on transmembrane monovalent ion movements.

1. Tissues were allowed to equilibrate in a Tris-buffered Krebs solution and were then exposed to similar solutions containing up to 5 mM-La. La caused shrinkage and significant losses of tissue K, Na, Mg and Ca. The shrinkage was exactly accountable for by a reduction in the extracellular space (e.c.s.) as measured by [14C]sucrose. No significant change was seen in tissue Cl content. Exposure for 1 hr to 5 mM-La led to a total cation loss of 24-3 +/- 1-6 m-equiv/kg or, correcting for the small change in Cl content, a loss of positive charge of 23-8 +/- 2-2 m-equiv/kg fresh wt. 2. Using the radioisotope 140La it was shown that this loss of cation was balanced by an uptake of La3+. 3. Subtraction of the ions in the measured [14C]sucrose space from the total tissue ion contents led to estimates of the "cellular" ion contents. The effects of 1 hr exposure to 5 mM-La on these were a loss of 12-9 +/- 2-4 m-equiv/kg of cation and a gain of 10-0 +/- 2-6 m-equiv/kg of Cl. 4. Similar changes in ion content were produced by La on "Na-loaded" and "K-loaded" tissues, these being tissues which by exposure to K-free or Na-free (high K) solutions had replaced all their K with Na or vice versa. 5. The uptakes of 24Na and 36Cl by Na-loaded tissues were both describable as the sum of two exponentail processes: a fast component (t 1/2 congruent to 1/2 min), which was presumed to be extracellular and a slower, presumed transmembrane, component. La reduced the rapid component of uptake of 24Na by an amount greater than that predicted by the reduction in the e.c.s., the extra amount lost being some 10--15 m-equiv/kg. La also reduced the amount of rapidly exchanging 36Cl, bwt this reduction was entirely accounted for by the change in the e.c.s. La reduced the rate constant of the slow component of 24Na uptake. 6. La reduced the rapidly exchanging component of 42K uptake by normal tissues by an amount equivalent to about 0-5 m-mole/kg fresh wt. of K in excess of the change in the extracellular space. 7. La had little effect on the effluxes of 36Cl and 42K from normal tissues. However, it reduced the size of the fastest component of exchange of 42K efflux from K-loaded tissues by an amount equal to some 10-15 m-equiv/kg in excess of the reduction in the e.c.s. A similar reduction in the rapidly exchanging component of 24Na efflux from normal tissues was also seen. La slowed the efflux of 24Na from Na-loaded tissues at times when the tracer lost could safely be regarded as intracellular. 8. The taenia coli when exposed to K-free solutions gains Na and loses K. In the presence of La the gain in Na was completely blocked. K was still lost, however, being accompanied by Cl and increased shrinkage. La also prevented the uptake of Na from high Na media by ion-depleted tissues (produced by exposure to sucrose media), while having little effect on the uptake of K from high K media by such tissues. 9 Tedia by such tissues. 9. The cation displaced by La in excess of that lost due to the reduction of the e.c.s...

Interaction of Salinity and Anaerobiosis in Barley and Rice

Interaction of Salinity and Anaerobiosis in Barley and Rice

Effects of NH4 and NO3 Nutrition with and without pH Adjustment on Tomato Growth, Ion Composition, and Water Relations1

Abstract Fertilization of tomato (Lycopersicon esculentum Mill.) in solution culture with NH4-N resulted in reduced shoot and root concentration of Ca, Mg, K, P, and NO3, increased leaf and root resistances to water flux, and decreased water use efficiency as compared to plants cultured with NO3-N. Solution adjustment to pH 6.5 decreased shoot/root fresh weight ratio with both N forms; decreased leaf diffusive resistance and water stress but increased root resistance to water flux and shoot NH4 concentration under NH4-N nutrition. Solution pH had little effect on tissue ion concentration.

Thyroid thermogenesis. Relationships between Na+-dependent respiration and Na+ + K+-adenosine triphosphatase activity in rat skeletal muscle.

The effect of thyroid status on QO2, QO2 (t) and NaK-ATPase activity was examined in rat skeletal muscle. QO2(t) (i.e. Na+-transport-dependent respiration) was estimated with ouabain or Na+-free media supplemented with K+. In contrast to the effects of ouabain on ion composition, intracellular K+ was maintained at about 125 meq/liter, and intracellular Na+ was almost nil in the Na+-free media. The estimates of QO2(t) were independent of the considerable differences in tissue ion concentrations. The increase in QO2(t) account for 47% of the increase in QO2 in the transition from the hypothyroid to the euthyroid state and 84% of the increase in the transition from the euthyroid to the hyperthyroid state. Surgical thyroidectomy lowered NaK-ATPase activity of the microsomal fraction (expressed per milligram protein) 32%; injections of triodothyronine (T3) increased this activity 75% in initially hypothyroid rats and 26% in initially euthyroid rats. Thyroidectomy was attended by significant falls in serum Ca and Pi concentrations. Administration of T3 resulted in further declines in serum Ca and marked increases in serum Ps concentrations. Similar effects were seen in 131I-treated rats, but the magnitude of the declines in serum Ca were less. The effects of T3 on QO2, QO2(t), and NaK-ATPase activity of skeletal muscle were indistinguishable in the 131I-ablated and surgically thyroidectomized rats. In thyroidectomized or euthyroid rats given repeated doses of T3, QO2(t) and NaA-ATPase activity increased proportionately. In thyroidectomized rats injected with single doses of T3, either 10, 50, or 250 mug/100 g body wt, QO2(t) increased linearly with NaK-ATPase activity. The kinetics of the NaK-ATPase activity was assessed with an ATP-generating system. T3 elicited a significant increase in Vmax with no change in Km for ATP.

The effects of salt depletion on blood and tissue ion concentrations in the freshwater mussel,Ligumia subrostrata (Say)

The extracellular and intracellular fluid volumes of pondwater acclimatedLigumia subrostrata are equal (3.9 ml/g dry tissue). Total blood solute is 47 mOsm and is composed primarily of Na (19.1 mM), Cl (10.6 mM), HCO3 (12.7 mM), Ca (4.3 mM), and K (0.5 mM). Major intracellular solutes are K (14.0 mM), Na (7.0 mM) and Cl (2.4 mM).L. subrostrata continuously exposed to deionized water at 20°C exhibit a maximum decrease of 23% in extracellular fluid total solute within 30 days. The maximum [Na] and [Cl] losses are 40% and 76% respectively, while [Ca] and [HCO3] increase by 44% and 37% respectively. No apparent change in extracellular [K] occurs. Intracellular [Na] decreases 53% and [Cl] decreases 79%, but [K] declines only 15%. Intracellular fluid volume, extracellular fluid volume, and total body water decrease 17%, 31%, and 22% respectively. Inulin clearance is 0.41 ml/g dry tissue·h for pondwater acclimated mussels and declines to 0.24 ml/g dry tissue·h during salt depletion. When salt depleted mussels are returned to solutions containing Na or Cl, they experience a net uptake of salt. The accumulated ions are about equally distributed in the extra- and intracellular compartments.

Plant adjustment to osmotic stress in balanced mineral-nutrient media

Studies of salt tolerance of plants grown in balanced nutrient solutions revealed that growth rate was more a function of the duration of the applied stress than the rapidity with which a particular osmotic concentration was reached in the root medium.The low osmotic potentials initially attained by plants subjected to osmotic stress resulted from both a decrease in water content and an increase in ion concentration in the plant tissues. However, the importance of dehydration in the adjustment process decreased within a relatively short time, and ion uptake was noted to be the predominant factor in the adjustment of the plant sap throughout the vegetative period. With the exception of restrictions on growth, symptoms of ion toxicity were not observed with these balanced solutions, although exposure to stress in one of the treatment series lasted for 84 days.Substantial increases in osmotic potential on the removal of stress were apparently the result of passive diffusion of ions back to the substrate, rather than an increase in the water content of the tissues as previously reported. The cations K+ and Ca2+ provided the major contribution to changes in the osmotic potential of the foliar sap, but significant changes were noted in all of the ions measured.