Osmotic Adjustment of Cultured Tobacco Cells (Nicotiana tabacum var. Samsum) Grown on Sodium Chloride

Insight into Membrane Stability and Physiological Responses of Selected Salt-Tolerant and Salt-Sensitive Cell Lines of Troyer Citrange (Citrus sinensis [L.] x Citrus trifoliata [L.] Raf.) under Salt Stress

The aim of this study was to evaluate the membrane integrity and some physiological responses of rootstock citrus calli under exposure to different concentrations of NaCl. Selected salt-tolerant cell lines were compared with salt-sensitive calli of Troyer’s citrange (Citrus sinensis [L.] x Citrus trifoliata [L.] Raf.) (TC) with respect to growth, water content, Na+, K+ and Cl− ion content as well as cell membrane stability under exposure to different NaCl concentrations. The results show that the stressed sensitive lines have a consistently high ion efflux. The values recorded for these sensitive calli are 3 to 6 times higher than those of the tolerant calli. Thus, only selected halotolerant calli were able to maintain the integrity of their membranes under salt stress conditions. In the sensitive calli, NaCl always induces a slowing down of growth even from 4 g L−1, and the reduction in the relative growth rate is higher than 50% and reaches more than 90% for the three culture durations at 8 g L−1 NaCl. For the salt-tolerant selected lines, the relative growth rate seems to be slightly slowed down until the second month of culture but becomes equal to that of the control at the third month, whether at 4 or 8 g L−1 NaCl. At the end of the third month, the relative growth rate of the selected calli is 100% at 8 g L−1 NaCl. The water content is twice as high in the selected tolerant calli as in the sensitive ones after three months of salt treatment at 8 g L−1 NaCl. After long-term culture, the halotolerant calli absorbed similar or even higher amounts of Na+ and Cl− than the salt-sensitive lines. However, by the 3rd month, the recorded accumulation rate dropped in the unselected but continued to increase in the tolerant calli (4-fold higher at 12 g L−1 NaCl than the control). Furthermore, exposure of both types of calli (salt-sensitive and salt-tolerant) to equal concentrations of NaCl resulted in greater loss of K+ by the NaCl-sensitive lines. However, for tolerant lines, K+ uptake is not affected at 4 g L−1 NaCl and the decrease in tissue content is less than 25% at 8 g L−1 NaCl. From this observation, it can be concluded that growth and the ability to retain high levels of internal K+ are correlated.

Metabolic Adjustment of Arabidopsis Root Suspension Cells During Adaptation to Salt Stress and Mitotic Stress Memory

Sessile plants reprogram their metabolic and developmental processes during adaptation to prolonged environmental stresses. To understand the molecular mechanisms underlying adaptation of plant cells to saline stress, we established callus suspension cell cultures from Arabidopsis roots adapted to high salt for an extended period of time. Adapted cells exhibit enhanced salt tolerance compared with control cells. Moreover, acquired salt tolerance is maintained even after the stress is relieved, indicating the existence of a memory of acquired salt tolerance during mitotic cell divisions, known as mitotic stress memory. Metabolite profiling using 1H-nuclear magnetic resonance (NMR) spectroscopy revealed metabolic discrimination between control, salt-adapted and stress-memory cells. Compared with control cells, salt-adapted cells accumulated higher levels of sugars, amino acids and intermediary metabolites in the shikimate pathway, such as coniferin. Moreover, adapted cells acquired thicker cell walls with higher lignin contents, suggesting the importance of adjustments of physical properties during adaptation to elevated saline conditions. When stress-memory cells were reverted to normal growth conditions, the levels of metabolites again readjusted. Whereas most of the metabolic changes reverted to levels intermediate between salt-adapted and control cells, the amounts of sugars, alanine, γ-aminobutyric acid and acetate further increased in stress-memory cells, supporting a view of their roles in mitotic stress memory. Our results provide insights into the metabolic adjustment of plant root cells during adaptation to saline conditions as well as pointing to the function of mitotic memory in acquired salt tolerance.

Salt intolerance in Arabidopsis: shoot and root sodium toxicity, and inhibition by sodium-plus-potassium overaccumulation

Arabidopsis plants in NaCl suffering half growth inhibition do not suffer osmotic stress and seldom shoot Na (+) toxicity; overaccumulation of Na (+) plus K (+) might trigger the inhibition. It is widely assumed that salinity inhibits plant growth by osmotic stress and shoot Na(+) toxicity. This study aims to examine the growth inhibition of Arabidopsis thaliana by NaCl concentrations that allow the completion of the life cycle. Unaffected Col-0 wild-type plants were used to define nontoxic Na(+) contents; Na(+) toxicities in shoots and roots were analyzed in hkt1 and sos1 mutants, respectively. The growth inhibition of Col-0 plants at 40 mM Na(+) was mild and equivalent to that produced by 8 and 4 mM Na(+) in hkt1 and sos1 plants, respectively. Therefore, these mutants allowed to study the toxicity of Na(+) in the absence of an osmotic challenge. Col-0 and Ts-1 accessions showed very different Na(+) contents but similar growth inhibitions; Ts-1 plants showed very high leaf Na(+) contents but no symptoms of Na(+) toxicity. Ak-1, C24, and Fei-0 plants were highly affected by NaCl showing evident symptoms of shoot Na(+) toxicity. Increasing K(+) in isotonic NaCl/KCl combinations dramatically decreased the Na(+) content in all Arabidopsis accessions and eliminated the signs of Na(+) toxicity in most of them but did not relieve growth inhibition. This suggested that the dominant inhibition in these conditions was either osmotic or of an ionic nature unspecific for Na(+) or K(+). Col-0 and Ts-1 plants growing in sorbitol showed a clear osmotic stress characterized by a notable decrease of their water content, but this response did not occur in NaCl. Overaccumulation of Na(+) plus K(+) might trigger growth reduction in NaCl-treated plants.

Glucose-6-phosphate dehydrogenase-dependent hydrogen peroxide production is involved in the regulation of plasma membrane H+-ATPase and Na+/H+ antiporter protein in salt-stressed callus from Carex moorcroftii

Glucose-6-phosphate dehydrogenase (G6PDH) is important for the activation of plant resistance to environmental stresses, and ion homeostasis is the physiological foundation for living cells. In this study, we investigated G6PDH roles in modulating ion homeostasis under salt stress in Carex moorcroftii callus. G6PDH activity increased to its maximum in 100 mM NaCl treatment and decreased with further increased NaCl concentrations. K+/Na+ ratio in 100 mM NaCl treatment did not exhibit significant difference compared with the control; however, in 300 mM NaCl treatment, it decreased. Low-concentration NaCl (100 mM) stimulated plasma membrane (PM) H+-ATPase and NADPH oxidase activities as well as Na+/H+ antiporter protein expression, whereas high-concentration NaCl (300 mM) decreased their activity and expression. When G6PDH activity and expression were reduced by glycerol treatments, PM H+-ATPase and NADPH oxidase activities, Na+/H+ antiporter protein level and K+/Na+ ratio dramatically decreased. Simultaneously, NaCl-induced hydrogen peroxide (H₂O₂) accumulation was abolished. Exogenous application of H₂O₂ increased G6PDH, PM H+-ATPase and NADPH oxidase activities, Na+/H+ antiporter protein expression and K+/Na+ ratio in the control and glycerol treatments. Diphenylene iodonium (DPI), the NADPH oxidase inhibitor, which counteracted NaCl-induced H₂O₂ accumulation, decreased G6PDH, PM H+-ATPase and NADPH oxidase activities, Na+/H+ antiporter protein level and K+/Na+ ratio. Western blot result showed that G6PDH expression was stimulated by NaCl and H₂O₂, and blocked by DPI. Taken together, G6PDH is involved in H₂O₂ accumulation under salt stress. H₂O₂, as a signal, upregulated PM H+-ATPase activity and Na+/H+ antiporter protein level, which subsequently resulted in the enhanced K+/Na+ ratio. G6PDH played a central role in the process.

Nitric oxide increases mitochondrial respiration in a cGMP-dependent manner in the callus from Arabidopsis thaliana

Nitric oxide (NO) acts as a key molecule in many physiological processes in plants. In this study, the roles of NO in mitochondrial respiration were investigated in the calli from wild-type Arabidopsis and NO associated 1 mutant (Atnoa1) which has a reduced endogenous NO level. Long-term exposure of wild-type Arabidopsis callus to sodium nitroprusside (SNP) increased mitochondrial respiration in both cytochrome and alternative pathways. In Atnoa1 callus, the capacity of both the cytochrome pathway and the alternative pathway was lower than that in wild-type callus. Further study indicated that NO enhanced the transcript abundance of genes encoding mitochondrial respiration-chain proteins as well as the protein expression of the NADH-ubiquinone reductase 75 kDa subunit and the alternative oxidase 1/2 in wild-type and Atnoa1 calli. 2-Phenyl-4,4,5,5-tetremethy-limidazolinone-1-oxyl-3-oxide (PTIO), a NO scavenger, inhibited the effects of NO in both calli. Co-incubation of callus with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a guanylate cyclase inhibitor, also abolished NO effects. The membrane-permeable cGMP analog 8Br-cGMP mimicked NO effects. Moreover, the alternative pathway showed a higher sensitivity to the cellular cGMP changes than the cytochrome pathway did in gene transcription, protein expression and O(2) consumption. Taken together, NO could enhance mitochondrial respiration in both cytochrome and alternative pathways in a cGMP-dependent manner in Arabidopsis.

Glucose-6-phosphate dehydrogenase plays a central role in modulating reduced glutathione levels in reed callus under salt stress

In the present study, we investigated the role of glucose-6-phosphate dehydrogenase (G6PDH) in regulating the levels of reduced form of glutathione (GSH) to the tolerance of calli from two reed ecotypes, Phragmites communis Trin. dune reed (DR) and swamp reed (SR), in a long-term salt stress. G6PDH activity was higher in SR callus than that of DR callus under 50-150 mM NaCl treatments. In contrast, at higher NaCl concentrations (300-600 mM), G6PDH activity was lower in SR callus. A similar profile was observed in GSH contents, glutathione reductase (GR) and glutathione peroxidase (GPX) activities in both salt-stressed calli. After G6PDH activity and expression were reduced in glycerol treatments, GSH contents and GR and GPX activity decreased strongly in both calli. Simultaneously, NaCl-induced hydrogen peroxide (H2O2) accumulation was also abolished. Exogenous application of H2O2 increased G6PDH, GR, and GPX activities and GSH contents in the control conditions and glycerol treatment. Diphenylene iodonium (DPI), a plasma membrane (PM) NADPH oxidase inhibitor, which counteracted NaCl-induced H(2)O(2) accumulation, decreased these enzymes activities and GSH contents. Furthermore, exogenous application of H2O2 abolished the N-acetyl-L: -cysteine (NAC)-induced decrease in G6PDH activity, and DPI suppressed the effect of buthionine sulfoximine (BSO) on induction of G6PDH activity. Western-blot analyses showed that G6PDH expression was stimulated by NaCl and H2O2, and blocked by DPI in DR callus. Taken together, G6PDH activity involved in GSH maintenance and H2O2 accumulation under salt stress. And H2O2 regulated G6PDH, GR, and GPX activities to maintain GSH levels. In the process, G6PDH plays a central role.

Nitric oxide functions as a signal in salt resistance in the calluses from two ecotypes of reed

Calluses from two ecotypes of reed (Phragmites communis Trin.) plant (dune reed [DR] and swamp reed [SR]), which show different sensitivity to salinity, were used to study plant adaptations to salt stress. Under 200 mm NaCl treatment, the sodium (Na) percentage decreased, but the calcium percentage and the potassium (K) to Na ratio increased in the DR callus, whereas an opposite changing pattern was observed in the SR callus. Application of sodium nitroprusside (SNP), as a nitric oxide (NO) donor, revealed that NO affected element ratios in both DR and SR calluses in a concentration-dependent manner. N(omega)-nitro-l-arginine (an NO synthase inhibitor) and 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxyde (a specific NO scavenger) counteracted NO effect by increasing the Na percentage, decreasing the calcium percentage and the K to Na ratio. The increased activity of plasma membrane (PM) H(+)-ATPase caused by NaCl treatment in the DR callus was reversed by treatment with N(omega)-nitro-l-arginine and 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxyde. Western-blot analysis demonstrated that NO stimulated the expression of PM H(+)-ATPase in both DR and SR calluses. These results indicate that NO serves as a signal in inducing salt resistance by increasing the K to Na ratio, which is dependent on the increased PM H(+)-ATPase activity.

On the variability of plant bio-concentration factors (BCF) of environmental radionuclides: a case study on the effects of surface film and free space on the interpretation of 99mTcO4- sorption in duckweed

The present paper addresses plant bioaccumulation factor (BCF) variability, and specifically focuses attention upon the handling of duckweed (Lemna gibba) material, sampled from experimental media, especially considering accumulation/kinetic studies with 99mTcO4-. In these short-term studies, relatively small BCF-values may be encountered, with related interferences in its assessment due to the presence of 99mTcO4- in the surface film medium (SF) and in the cellular water free spaces (FS). The sample handling methods used to remove the SF + FS component of the accumulated 99mTcO4- consisted of blotting, centrifugation and rinsing. The three methods were investigated using D-[1-(14)C]mannitol, 42K+, 82Br- and 99mTcO4- radioisotopes, which were measured by beta- and gamma-spectrometry, in both solution and solid samples. Centrifugation seems the most promising method to remove SF + FS 99mTcO4-. Results based on both mass analysis and radioactivity determinations in centrifugated fluids are independent of applied concentrations (10(-11) to 10(-13) mol m(-3) 99mTcO4-), and are invariably compatible with the conceptual idea of the FS as a free-entrance phase for solutes. Blotting results in an overestimation of BCF values (up to factor 3 for the 99mTcO4- experiments performed), probably due to the incomplete removal of the SF + FS, and is suggested to yield irregular results, leading to high variances in BCF values obtained. The application of an efflux/rinsing period is indicated to result in an underestimation of BCF values (up to factor 10 for the 99mTcO4- experiments performed), probably due to excess removal of (non-SF + FS) components of accumulated solutes. Here we advocate centrifugation as a routine sample handling method to avoid SF + FS interferences in short-term (kinetic) 99mTcO4- uptake studies in duckweed. Moreover, the results suggest a more general applicability of centrifugation as a sample handling method to avoid SF + FS interferences in short-term element accumulation studies; centrifugation approaches should, however, be adjusted to plant cell characteristics.

Stimulation of anthraquinone production in suspension cultures of Cassia acutifolia by salt stress

Suspension cultures of Cassia acutifolia were established by transferring callus tissues derived from root, hypocotyl and cotyledon explants onto liquid MS-medium supplemented with 1.0 mg/l 2.4-D and 0.1 mg/l kinetin and containing increasing levels of NaCl. The stress induced by salt NaCl raised anthraquinone content and reduced growth of cultures. The levels of anthraquinones and their glycosides as sennosides showed distinct changes in cells and media as well as in the different cultures initiated from various explants. Furthermore, the salt stress tended to affect more drastically the productivity of anthraquinones in hypocotyl and cotyledon cell cultures than in root cultures.

Growth, proline accumulation and water relations of NaCl-selected and non-selected callus lines of Dactylis glomerata L

Sodium chloride-tolerant calli were selected from leaf-derived embryogenic calli of Dactylis glomerata L. on agar solidified medium supplemented with 200 mM NaCl, a concentration lethal to non-selected calli. Growth characteristics, water relations and proline accumulation pattern were compared in selected and non-selected lines. The objective was to gain an understanding of the mechanism(s) of tolerance in the NaCl-tolerant line. Growth in the selected line, as expressed in terms of tolerance index (ratio of fresh wt. on NaCl medium:fresh wt. on NaCl free medium x 100), was greater than that of the non-selected line at all levels of NaCl between 50 and 300 mM. There was no significant difference in proline accumulation in the selected and non-selected lines. Maintenance of turgor by osmotic adjustment was observed in the non-selected line despite decreased growth. In contrast, the selected line lost either the need or the ability to adjust osmotically. There was little or no increase in symplastic osmolality in the selected line when exposed to NaCl. Presumably, selection was made for a salt-excluding tissue that has lost the ability to accumulate solutes and adjust turgor with NaCl stress.

Solute Accumulation in Tobacco Cells Adapted to NaCl

Cells of Nicotiana tabacum L. var Wisconsin 38 adapted to NaCl (up to 428 millimolar) which have undergone extensive osmotic adjustment accumulated Na(+) and Cl(-) as principal solutes for this adjustment. Although the intracellular concentrations of Na(+) and Cl(-) correlated well with the level of adaptation, these ions apparently did not contribute to the osmotic adjustment which occurred during a culture growth cycle, because the concentrations of Na(+) and Cl(-) did not increase during the period of most active osmotic adjustment. The average intracellular concentrations of soluble sugars and total free amino acids increased as a function of the level of adaptation; however, the levels of these solutes did not approach those observed for Na(+) and Cl(-). The concentration of proline was positively correlated with cell osmotic potential, accumulating to an average concentration of 129 millimolar in cells adapted to 428 millimolar NaCl and representing about 80% of the total free amino acid pool as compared to an average of 0.29 millimolar and about 4% of the pool in unadapted cells. These results indicate that although Na(+) and Cl(-) are principal components of osmotic adjustment, organic solutes also may make significant contributions.

Variation from plant tissue cultures: Biotechnological application to improving salinity tolerance

Breeding for salt tolerance in crop plants is envisaged as one way to combat a worldwide problem of increasing soil salinity in agricultural land. Tissue culture techniques may prove valuable as a means of achieving this goal. In this review, reports of the selection and characterization of plant cell cultures tolerant to excess salt are assessed, in the context of variability from tissue culture and the significance of cellular physiological adaptation to salinity. The examples of plant regeneration from salt grown cell cultures are also outlined, with emphasis on correlation to the effect of salt on cell cultures, genetic variability for salt tolerance in vitro, and the value of regenerates in the development of salt tolerant plants.

Retention of shoot regeneration capacity of tobacco callus by Na2SO 4

Callus of tobacco (Nicotiana tabacum L. cv. Wisconsin 38) was grown in the light on shoot-forming medium in the presence of Na2SO4 for over a year. An increase in Na2SO4 concentration resulted in decreasing callus growth, decreasing percentage of calli producing shoots and number of shoots per callus, and increasing callus percent dry weight. Regeneration of shoots from callus grown in the absence of Na2SO4 began to decline after 14 months in culture, and shoot regeneration capacity was completely lost after 18 months. In contrast, 18-month old callus continuously grown in the presence of Na2SO4 retained the ability to form shoots. The highest percent of callus pieces that formed shoots and the maximum number of shoots per callus occurred at 70 mM (1%) Na2SO4. All plants arising from the 18-month old callus were polyploid. Both 9- and 18-month old callus exhibited more negative water and osmotic potentials in the presence of increasing Na2SO4 concentration.

Adaptation of Tobacco Cells to NaCl

Cell lines of tobacco (Nicotiana tabacum L. var Wisconsin 38) were obtained which are adapted to grow in media with varying concentrations of NaCl, up to 35 grams per liter (599 millimolar). Salt-adapted cells exhibited enhanced abilities to gain both fresh and dry weight in the presence of NaCl compared to cells which were growing in medium without NaCl (unadapted cells). Tolerance of unadapted cells and cells adapted to 10 grams per liter NaCl was influenced by the stage of growth, with the highest degree of tolerance exhibited by cells in the exponential phase. Cell osmotic potential and turgor varied through the growth cycle of unadapted cells and cells at all levels of adaptation, with maximum turgor occurring at approximately the onset of exponential fresh weight accumulation.Adaptation to NaCl led to reduced cell expansion and fresh weight gain, while dry weight gain remained unaffected. This reduction in cell expansion was not due to failure of the cells to maintain turgor since cells adapted to NaCl underwent osmotic adjustment in excess of the change in water potential caused by the addition of NaCl to the medium. Tolerance of the adapted cells, as indicated by fresh or dry weight gain, did not increase proportionately with the increase in turgor. Adaptation of these glycophytic cells to NaCl appears to involve mechanisms which result in an altered relationship between turgor and cell expansion.

Abscisic Acid accelerates adaptation of cultured tobacco cells to salt

Adaptation of tobacco (Nicotiana tabacum L. var Wisconsin 38) cells to NaCl was accelerated by (+/-) abscisic acid (ABA). In medium with 10 grams per liter NaCl, ABA stimulated the growth of cells not grown in medium with NaCl (unadapted, S-0) with an increasing response from 10(-8) to 10(-4) molar. ABA (10(-5) molar) enhanced the growth of unadapted cells in medium with 6 to 22 grams per liter NaCl but did not increase the growth of cells previously adapted to either 10 (S-10) or 25 (S-25) grams per liter NaCl unless the cells were inoculated into medium with a level of NaCl higher than the level to which the cells were adapted. The growth of unadapted cells in medium with Na(2)SO(4) (85.5 millimolar), KCl (85.5 or 171 millimolar), K(2)SO(4) (85.5 millimolar) was also stimulated by ABA. ABA (10(-8)-10(-4) molar) did not accelerate the growth of unadapted cells exposed to water deficits induced by polyethylene glycol (molecular weight 8000) (5-20 grams per 100 milliliters), sorbitol (342 millimolar), mannitol (342 millimolar) or sucrose (342 millimolar). These results suggest that ABA is involved in adaptation of cells to salts, and is not effective in promoting adaptation to water deficits elicited by nonionic osmotic solutes.

Relation between Ion Accumulation of Salt-Sensitive and Isolated Stable Salt-Tolerant Cell Lines of Citrus aurantium

Four selected NaCl-tolerant cell lines of Sour orange (Citrus aurantium) were compared with the nonselected cell line in their growth and internal ion content of Na(+), K(+), and Cl(-) when exposed to increasing NaCl concentrations. No difference was found among the various NaCl-tolerant cell lines in Na(+) and Cl(-) uptake, and all these cell lines took up similar or even larger amounts of Na(+) and Cl(-) than the NaCl-sensitive cell line. Exposure of cells of NaCl-sensitive and NaCl-tolerant lines to equal external concentrations of NaCl, resulted in a greater loss of K(+) from the NaCl-sensitive cell line. This observation leads to the conclusion that growth and ability to retain high levels of internal K(+) are correlated. Exposure of the NaCl-tolerant cell lines to salts other than NaCl resulted in even greater tolerance to Na(2)SO(4), but rather poor tolerance to K(+) introduced as either K(2)SO(4) or KCl; the latter has a stronger inhibitory effect. The NaCl-sensitive cell line proved to be more sensitive to replacement of Na(+) by K(+). Analyses of internal Na(+), K(+), and Cl(-) concentrations failed to identify any particular internal ion concentration which could serve as a reliable marker for salt tolerance.

Use of Na-Nuclear Magnetic Resonance To Follow Sodium Uptake and Efflux in NaCl-Adapted and Nonadapted Millet (Panicum miliaceum) Suspensions

Cellular Na(+) transport was followed in vivo by (23)Na nuclear magnetic resonance (NMR) using anionic dysprosium-based shift reagents to resolve internal and external (23)Na(+) resonances. Proso millet (Panicum miliaceum) cell suspensions adapted for rapid growth on 130 mm NaCl had biphasic (23)Na efflux kinetics when shifted to low Na(+) medium, while nonadapted cells had little measurable Na(+) efflux after preloading with (23)NaCl. Uptake of (23)Na was also observed using (23)Na NMR. The resonance frequency of the external Na(+)-dysprosium (III) triphosphate, relative to that of the (23)Na in the cells, was sensitive to pH, permitting the pH of the external medium to be followed during the course of in vivo experiments.

Solutes contributing to osmotic adjustment in cultured plant cells adapted to water stress

Osmotic adjustment was studied in cultured cells of tomato (Lycopersicon esculentum Mill cv VFNT-Cherry) adapted to different levels of external water potential ranging from -4 bar to -28 bar. The intracellular concentrations of reducing sugars, total free amino acids, proline, malate, citrate, quaternary ammonium compounds, K(+), NO(3) (-), Na(+), and Cl(-) increased with decreasing external water potential. At any given level of adaptation, the maximum contribution to osmotic potential was from reducing sugars followed by potassium ions. The sucrose levels in the cells were 3- to 8-fold lower than reducing sugar levels and did not increase beyond those observed in cells adapted to -16 bar water potential. Concentrations of total free amino acids were 4- to 5-fold higher in adapted cells. Soluble protein levels declined in the adapted cell lines, but the total reduced nitrogen was not significantly different after adaptation. Uptake of nitrogen (as NH(4) (+) or NO(3) (-)) from the media was similar for adapted and unadapted cells. Although the level of quaternary ammonium compounds was higher in the nonadapted cells than that of free proline, free proline increased as much as 500-fold compared to only a 2- to 3-fold increase observed for quaternary ammonium compounds. Although osmotic adjustment after adaptation was substantial (up to -36 bar), fresh weight (volume increase) was restricted by as much as 50% in the adapted cells. Altered metabolite partitioning was evidenced by an increase in the soluble sugars and soluble nitrogen in adapted cells which occurred at the expense of incorporation of sugar into cell walls and nitrogen into protein. Data indicate that the relative importance of a given solute to osmotic adjustment may change depending on the level of adaptation.

Aspects of Salt Tolerance in a NaCl-Selected Stable Cell Line of Citrus sinensis

A NaCl-tolerant cell line which was selected from ovular callus of ;Shamouti' orange (Citrus sinensis L. Osbeck) proved to be a true cell line variant. This conclusion is based on the following observations. (a) Cells which have been removed from the selection pressure for at least four passages retain the same NaCl tolerance as do cells which are kept constantly on 0.2 molar NaCl. (b) Na(+) and Cl(-) uptake are considerably lower in salt-tolerant cells (R-10) than in salt-sensitive cells (L-5) at a given external NaCl concentration. (c) Growth of salt-tolerant cells is markedly suppressed upon replacement of NaCl by KCl, whereas the growth of salt-sensitive cells is only slightly affected. Accumulation of K(+) and Cl(-) accompanies the inhibition of growth. Experiments carried out with sodium and potassium sulfate suggest that the toxic effect is due to the accumulated Cl(-). (d) Removal of Ca(2+) from the growth medium severely inhibits the growth of salt-tolerant cells in the presence of NaCl, while it has a minor effect on growth of salt-sensitive cells in the presence of NaCl. (e) Electron micrographs show that the salt-tolerant cells have very big vacuoles when exposed to salt, while the size of the vacuoles of the salt-sensitive cells does not change.

Growth, water content, and solute accumulation of two tobacco cell lines cultured on sodium chloride, dextran, and polyethylene glycol

Simulated drought tolerance was compared for an NaCl-adapted and a nonadapted cell line of tobacco (Nicotiana tabacum var. Samsum) to determine the relationship of salt and drought tolerances. The osmotic adjustment and growth of these two lines was followed when cultured on solid media which contained isosmotic concentrations of NaCl, KCl, polyethylene glycol (PEG) or dextran. One line was adapted to growth on 130 millimolar NaCl, but the other was not.The growth of NaCl-adapted and nonadapted cell lines was equally inhibited (61 per cent of control) by 130 millimolar NaCl. Growth inhibition was greater on PEG or dextran than on NaCl. Growth ceased on the second passage of dextran for the nonadapted cells, while the NaCl-adapted cells grew slowly for four passages on dextran. Water contents for both cell lines were 95 per cent on NaCl or KCl and 70 to 88 per cent on PEG 1540 or 4000 or dextran after the second passage on these media.On dextran or PEG 4000, 46 to 89 per cent of the cellular osmotic potential was produced by the solutes initially present in the medium. Similarly, on NaCl, almost 100 per cent was attributable to solutes in the medium. It was concluded that cells grown on the nonpenetrating solutes had a more negative osmotic potential than those grown in the absence of added solute due to partial dehydration, greater uptake of external ions, and possibly the production of unidentified osmotica. Adjustment to growth on penetrating solutes may have enabled the adapted line to overcome the osmotic stress produced by nonpenetrating dextran.