Physiological responses of Caloglossa leprieurii (Ceramiales, Rhodophyta) to salinity stress

Marine, estuarine and freshwater isolates of Caloglossa leprieurii (Montagne) J. Agardh exhibit a high salinity tolerance, reflected by broad cell viability and growth rate. Osmotic adjustment is shown to rely to a large extent on ion-transport systems, with K⁺ and Cl- accumulated in osmotically- significant quantities and active Na⁺ extrusion. The ion concentrations contribute a large proportion (67–94%) to internal osmotic pressure. The concentration of the organic osmolyte mannitol in all populations was strongly salinity dependent. Mannitol made a lower contribution to the internal osmotic pressure, when compared to ion concentrations, but nonetheless represented an important proportion of the internal osmolality. The response of the three isolates is discussed in relation to the salinity of their respective environments.     

Dynamics of Salt Secretion by Sporobolus spicatus(Vahl) Kunth from Sites of Differing Salinity

Secretion of salts by bicellular salt glands and the water relationsof the grass Sporobolus spicatus were investigated at four sitesalong the coast of the Red Sea in Egypt that differed in theextremity of salinity and drought. Salt eliminated by the leaveswas similar in its composition at all sites. Na⁺and Cl^-werethe dominant ions in the soil, and together comprised about93% of the dry weight of secreted salt. The molar ratio of K⁺:Na⁺inthe plant leaves was more than ten-fold that in the interstitialsoil solution and thirteen-times that in the secreted salts,reflecting the high selectivity of the secretion mechanism forNa⁺. The concentration of Na⁺in the solution transported tothe leaves between 0900 and 1500 h was less than 0.1% of thatin the soil solution. Accumulation of salts by the plant shoots,which increased with increasing soil salinity and drought, wasmaximal during the day when the extent of secretion greatlyreduced. The ionic osmotic potential (     

Overexpression of wheat Na+/H+ antiporter TNHX1 and H+-pyrophosphatase TVP1 improve salt- and drought-stress tolerance in Arabidopsis thaliana plants

Transgenic Arabidopsis plants overexpressing the wheat vacuolarNa⁺/H⁺ antiporter TNHX1 and H⁺-PPase TVP1 are much more resistantto high concentrations of NaCl and to water deprivation thanthe wild-type strains. These transgenic plants grow well inthe presence of 200 mM NaCl and also under a water-deprivationregime, while wild-type plants exhibit chlorosis and growthinhibition. Leaf area decreased much more in wild-type thanin transgenic plants subjected to salt or drought stress. Theleaf water potential was less negative for wild-type than fortransgenic plants. This could be due to an enhanced osmoticadjustment in the transgenic plants. Moreover, these transgenicplants accumulate more Na⁺ and K⁺ in their leaf tissue thanthe wild-type plants. The toxic effect of Na⁺ accumulation inthe cytosol is reduced by its sequestration into the vacuole.The rate of water loss under drought or salt stress was higherin wild-type than transgenic plants. Increased vacuolar soluteaccumulation and water retention could confer the phenotypeof salt and drought tolerance of the transgenic plants. Overexpressionof the isolated genes from wheat in Arabidopsis thaliana plantsis worthwhile to elucidate the contribution of these proteinsto the tolerance mechanism to salt and drought. Adopting a similarstrategy could be one way of developing transgenic staple cropswith improved tolerance to these important abiotic stresses. Key words: H⁺-pyrophosphatase, Na⁺/H⁺ antiporter, salt and drought tolerance, sodium sequestration, transgenic Arabidopsis plants     

Role of Vacuolar Membrane Transport Systems in Plant Salinity Tolerance

About 20% of all irrigated land is adversely affected by salinity hazards and therefore understanding plant defense mechanisms against salinity will have great impact on plant productivity. In the last decades, comprehension of salinity resistance at molecular level has been achieved through the identification of key genes encoding biomarker proteins underpinning salinity tolerance. Implication of the vacuolar transport systems in plant salinity tolerance is one example of these central mechanisms rendering tolerance to saline stress. One important organelle in plant cells is the central vacuole that plays pivotal multiple roles in cell functioning under normal and stress conditions. This review thus attempts to address different lines of evidence supporting the role of the vacuolar membrane transport systems in plant salinity tolerance. Vacuolar transport systems include Na⁺(K⁺)/H⁺ antiporters, V-ATPase, V-PPase, Ca²⁺/H⁺ exchangers, Ca²⁺-ATPase, ion channels, aquaporins, and ABC transporters. They contribute essentially in retaining a high cytosolic K⁺/Na⁺ ratio, K⁺ level, sequestrating Na⁺ and Cl^? into vacuoles, as well as regulation of other salinity responsive pathways. However, little is known about the regulation and functions of some of the vacuolar transporters under salinity stress and therefore need more exploration and focus. Numerous studies demonstrated that the activities of the vacuolar transporters are upregulated in response to salinity stress, confirming their central roles in salinity tolerance mechanism. The second line of evidence is that manipulation of one of the genes encoding the vacuolar transport proteins results in some successful improvement of plant salinity tolerance. Therefore, transgene pyramiding of more than one gene for developing genotypes with better and strong salinity tolerance and productivity should gain more attention in future research. In addition, we should move step further and verify the experimental data obtained from either a greenhouse or controlled environment into field trials in order to support our claims.

     

Ionic and Water Relations Responses of Two Populations of a Non-Halophyte to Salinity

Bowman, W. D. 1988. Ionic and water relations responses of twopopulations of a non-halophyte to salinity.–J. exp. Bot39: 97–105 Salinity-induced changes in the ionic and water relations inplants from two naturally-occurring populations of the C₄ non-halophyteAndropogon glomeratus were measured to detect differences inthe capacity to adjust osmotic potentials and in ion contentpotentially responsible for the osmotic adjustment Pressure-volumecurves and leaf ion content were measured in plants from twopopulations, salt marsh and inland, after long-term exposureto three salinity levels. Osmotic adjustment and decreases inthe bulk tissue elasticity occurred to a similar extent in bothpopulations with increasing salinity. Cl^– concentrationsincreased with increasing salinity in both populations, whereasleaf Na⁺ concentrations increased only in the inland population,but were higher at all salinities in the marsh population. K⁺concentrations changed little with increasing salinity. Prolineconcentrations increased only at the highest salinity level,and did not difler significantly between populations. Theseresults suggest a role for Na⁺ uptake and regulation in osmoticadjustment in the marsh population, contrasting with studiesof salt tolerance in other nonhalophytic grasses     

Solute Regulation in the Euryhaline Marine Alga Enteromorpha prolifera (O. F. Mull) J. Ag.

Young, A. J., Collins, J. C. and Russell, G. 1987. Solute regulationin the euryhaline marine alga Enteromorpha prolifera (O. F.Mll) J. Ag.—J. exp. Bot. 38: 1298–1308. The physiological basis for salt tolerance has been studiedin the euryhaline alga Enteromorpha prolifera. Levels of inorganicions and organic (compatible) solutes have been measured. K⁺makes the major contribution towards the internal osmotic potentialof the cell, while Cl^– and, in particular, Na⁺ contentsare low. Levels of the organic solute ß-dimethylsulphonio-propionate(DMSP) are high but are fairly insensitive to changes in theexternal salinity. Levels of amino-acids, calcium, phosphateand sulphate contribute relatively little towards the internalosmotic potential of the alga. As salinity is altered there are marked changes in the tissuewater content and volume. These changes directly affect theconcentration of the osmotic solutes within the cell. In diluteseawaters there is an increase in turgor as there is littlechange in the internal solute content of the cell compared tovalues in normal sea water. Inorganic ions, in particular K⁺,and organic solutes are accumulated in concentrated seawaters,although concentrations greater than 2·00 x seawaterresult in a reduction in the internal osmotic potential of thecell, mainly through loss of K⁺. Key words: Enteromorpha, salinity, osmoregulation     

Ionic Relations of Garden Orache, A triplex hortensis L.: Growth and Ion Distribution at Moderate Salinity and the Function of Bladder Hairs

The growth of garden orache, A triplex hortensis was studiedunder conditions of mild NaCl or Na₂SO₄ salinity. Growth, drymatter production and leaf size were substantially stimulatedat 10 mM and 50 mM Na⁺ salts. Increased growth, however, appearedto be due to a K⁺-sparing effect of Na⁺ rather than to salinityper se. The distribution of K⁺ and Na⁺ in the plant revealeda remarkable preference for K+ in the roots and the hypocotyl.In the shoot the K/Na ratio decreased strongly with leaf age.However, the inverse changes in K⁺ and Na⁺ content with leafage were dependent on the presence of bladder hairs, which removedalmost all of the Na⁺ from the young leaf lamina. Measurementsof net fluxes of K⁺ and Na⁺ into roots and shoots of growingAtriplex plants showed a higher K/Na selectivity of the netion flux to the root compared to the shoot. With increasingsalinity the selectivity ratio S_{K, Na}^* of net ion fluxes tothe roots and to the shoots was increased. The data suggestthat recirculation of K⁺ from leaves to roots is an importantlink in establishing the K/Na selectivity in A. hortensis plants.The importance of K⁺ recirculation and phloem transport forsalt tolerance is discussed. Key words: Atriplex hortensis, Salinity, Potassium, Sodium, K⁺ retranslocation, Bladder hairs, Growth stimulation     

Salt Tolerance in Simmondsia chinensis: Water Balance and Accumulation of Chloride, Sodium and Proline Under Low and High Salinity

The response of jojoba [Simmondsia chinensis (Link) Schneid]plants to salinity was studied in solution culture. At concentrationsof 0, 100, 200 and 600 m-mol l^–1 NaCI it was found thatjojoba plants have high tolerance to NaCl. The growth of theseplants was not affected by salinity. They accumulated largeamounts of Cl^–, Na⁺ and proline. These amounts decreasedrapidly in plants transferred back to control medium. Potassiumcontent decreased in NaCl-treated plants and tended to increaserapidly to the control level in plants transferred to controlmedium. The effect of salinity on water balance was not appreciable.As suggested for other xerophytic species, it could be assumedthat the high tolerance of jojoba to salinity plays an importantrole in its ability to endure periods of drought. The role ofproline during or after stress remains an open question. Simmondsia chinensis (Link) Schneid, jojoba, salt tolerance, sodium accumulation, chloride ion accumulation, proline accumulation, xerophytism, drought tolerance     

短期NaCl胁迫对不同小麦品种幼苗K+吸收和Na+、K+积累的影响

为研究盐胁迫下小麦幼苗生长及Na⁺、K⁺的吸收和积累规律,以中国春、洲元9369和长武134等3种耐盐性不同小麦品种为材料,采用非损伤微测技术检测盐胁迫2 d后的根系K⁺离子流变化,并对植株体内的Na⁺、K⁺含量进行测定。结果表明:短期(2d)盐胁迫对小麦生长有抑制作用,且对根系的抑制大于地上部,耐盐品种下降幅度小于盐敏感品种。盐胁迫下,小麦根际的 K⁺大量外流,盐敏感品种中国春K⁺流速显著高于耐盐品种长武134,最高可达15倍。小麦幼苗地上部分和根系均表现为Na⁺积累增加,K⁺积累减少,Na⁺/K⁺比随盐浓度增加而上升。中国春限Na⁺能力显著低于长武134,Na⁺/K⁺则显著高于长武134。综上所述,盐胁迫下造成小麦组织器官中Na⁺/K⁺比上升的主要原因是根系K⁺大量外流和Na⁺的过量积累,耐盐性不同的小麦品种间差异显著,并认为根系对K⁺的保有能力可能是作物耐盐性评价的一个重要指标。     

Control of xylem Na+ loading and transport to the shoot in rice and barley as a determinant of differential salinity stress tolerance

Control of xylem Na⁺ loading has often been named as the essential component of salinity tolerance mechanism. However, it is less clear to what extent the difference in this trait may determine differential salinity tolerance between species. In this study, barley (Hordeum vulgare L. cv. CM72) and rice (Oryza sativa L. cv. Dongjin) plants were grown under two levels of salinity. Na⁺ and K⁺ concentrations in the xylem sap, and shoot and root tissues were measured at different time points after stress onset. Salt‐exposed rice plants prevented xylem Na⁺ loading for several days, but failed to control this process in the longer term, ultimately resulting in a massive Na⁺ shoot loading. Barley plants quickly increased xylem Na⁺ concentration and its delivery to the shoot (most likely for the purpose of osmotic adjustment) but were able to reduce this process later on, keeping most of accumulated Na⁺ in the root, thus maintaining non‐toxic shoot Na⁺ level. Rice plants increased shoot K⁺ concentration, while barley plants maintained higher root K⁺ concentration. Control of xylem Na⁺ loading is remarkably different between rice and barley; this difference may differentiate the extent of the salinity tolerance between species. This trait should be investigated in more detail to be used in the breeding programs aimed to improve salinity tolerance in crops.     

NaCl Uptake in Roots of Zea mays Seedlings: Comparison of Root Pressure Probe and EDX Data

The extent by which salinity affects plant growth depends partlyon the ability of the plant to exclude NaCl. To study the uptakeof NaCl into excised roots of Zea mays L. cv. ‘Tanker’,two different techniques were applied. A root pressure probewas used to record steady state as well as transient valuesof root (xylem) pressure upon exposure of the root to mediacontaining NaCl and KCl as osmotic solutes. In treatments withNaCl, pressure/time responses of the root indicated a significantuptake of NaCl into the xylem. NaCl induced kinetics were completelyreversible when the NaCl solution was replaced by an isosmoticKCl solution. This indicated a passive movement of Na⁺-saltsacross the root cylinder. Root samples were taken at differenttimes of exposure to NaCl and prepared for X-ray microanalysis(EDX analysis). Radial profiles of ion concentrations (Na⁺,K⁺, Cl^–) were measured in cell vacuoles and xylem vesselsalong the root axis. Na⁺ appeared rapidly in mature xylem (earlymetaxylem) and living xylem (late metaxylem) before it was detectablein vacuoles of the root cortex. EDX results confirmed that thekinetics observed by the pressure probe technique correspondedmainly to an influx of Na⁺-salts into early metaxylem. In latemetaxylem, the uptake of Na⁺ was associated with a decline ofK⁺. The Na⁺/K⁺ exchange indicated a mechanism to reduce sodiumfrom the transpiration stream. Ion localization, ion transport, maize, root pressure, salinity, water relations, X-ray microanalysis, Zea mays     

Effect of Sudden Salt Stress on Ion Fluxes in Intact Wheat Suspension Cells

Although salinity is one of the major problems limiting agriculturalproduction around the world, the underlying mechanisms of highNaCl perception and tolerance are still poorly understood. Theeffects of different bathing solutions and fusicoccin (FC),a known activator of plasma membrane ATPase, on plasma membranepotential (E_m) and net fluxes of Na⁺, K⁺and H⁺were studied inwheat suspension cells (Triticum aestivum) in response to differentNaCl treatments. E_mof cells in Murashige and Skoog (MS) mediumwas less negative than in cells exposed to a medium containing10 mM KCl + 0.1 m M CaCl₂(KSM) and to a basic salt medium (BSM),containing 1 m M KCl and 0.1 m M CaCl₂. Multiphasic Na⁺accumulationin cells was observed, peaking at 13 min after addition of 120m M NaCl to MS medium. This time scale was in good agreementwith net Na⁺flux changes measured non-invasively by moving ion-selectivemicroelectrodes (the MIFE system). When 120 m M NaCl was addedto all media studied, a quick rise of Na⁺influx was reversedwithin the first 20 min. In both 120 and 20 m M NaCl treatmentsin MS medium, net Na⁺efflux was observed, indicating that activeNa⁺transporters function in the plant cell response to saltstress. Lower external K⁺concentrations (KSM and BSM) and FCpre-treatment caused shifts in Na⁺fluxes towards net influxat 120 m M NaCl stress. Copyright 2000 Annals of Botany Company Sodium, potassium, proton, membrane potential, fusicoccin, salt stress, wheat, Triticum aestivum     

Differences in efficient metabolite management and nutrient metabolic regulation between wild and cultivated barley grown at high salinity

Physiological and biochemical responses of Hordeum maritimum and H. vulgare to salt stress were studied over a 60‐h period. Growth at increasing salinity levels (0, 100, 200 and 300 mM NaCl) was assessed in hydroponic culture. H. maritimum was shown to be a true halophyte via its typical behaviour at high salinity. Shoot growth of cultivated barley was gradually reduced with increasing salinity, whereas that of wild barley was enhanced at 100 and 200 mm NaCl then slightly reduced at 300 mM NaCl. The higher salt tolerance of H. maritimum as compared to H. vulgare was due to its higher capacity to maintain cell turgor under severe salinity. Furthermore, H. maritimum exhibited fine regulation of Na⁺ transport from roots to shoots and, unlike H. vulgare, it accumulated less Na⁺ in shoots than in roots. In addition, H. maritimum can accumulate more Na⁺ than K⁺ in both roots and shoots without the appearance of toxicity symptoms, indicating that Na⁺ was well compartmentalized within cells and substituted K⁺ in osmotic adjustment. The higher degree of salt tolerance of H. maritimum is further demonstrated by its economic strategy: at moderate salt treatment (100 mm NaCl), it used inorganic solutes (such as Na⁺) for osmotic adjustment and kept organic solutes and a large part of the K⁺ for metabolic activities. Indeed, K⁺ use efficiency in H. maritimum was about twofold that in H. vulgare; the former started to use organic solutes as osmotica only at high salinity (200 and 300 mm NaCl). These results suggest that the differences in salt tolerance between H. maritimum and H. vulgare are partly due to (i) differences in control of Na⁺ transport from roots to shoots, and (ii) H. maritimum uses Na⁺ as an osmoticum instead of K⁺ and organic solutes. These factors are differently reflected in growth.     

Effect of NaCI Salinity on Flows and Partitioning of C, N, and Mineral Ions in Whole Plants of White Lupin, Lupinus albusL.

Plants of Lupinus albus L., cv. Ultra, were grown hydroponicallywith NO₃^–-nutrition for 51 d under control (0.05 mol m^–3Na⁺ and 10 mol m^–3 Cl^–) and saline (40 mol m^–3NaCI) conditions. Plants were harvested 41 and 51 d after germinationand analysed for content and net increment of C, N and the mineralcations K⁺, Na⁺, Mg²⁺, and Ca²⁺ and the anions Cl^–, NOJ,malate, phosphate, and SO₄^2–. Roots, stem interaodes,petioles and leaflets were analysed separately. During the studyperiod net photosynthesis, respiratory losses of CO₂ from shootand root and the composition of the spontaneously bleeding phloemsap and the root pressure xylem exudate were also determined.Using molar ratios of C over N in the transport fluids, incrementsof C and N, and photosynthetic gains as well as respiratorylosses of C, the net flows of C and N in the xylem and phloemwere then calculated as in earlier studies (Pate, Layzell andMcNeill, 1979a). Knowing the carbon flows, the ratios of ionto carbon in the phloem sap, and ion increments in individualorgans, net flows of K⁺, Na⁺, and Cl^– over the study periodwere also calculated. Salt stress led to a general decrease of all partial componentsof C and N partitioning indicating that inhibitions were notdue to specific effects of NaCI salinity on photosynthesis oron NO₃ uptake. However, there were differences between variouslyaged organs, and net phloem export of nitrogenous compoundsfrom ageing leaves was substantially enhanced under saline conditions.In addition, NO₃^–reduction in the roots was specificallyinhibited. Uptake and xylem transport of K⁺ was more severelyinhibited than photosynthetic carbon gain or NO₃^– uptakeby the root. K⁺ transport in the phloem was even more severelyrestricted under saline conditions. Na⁺ and Cl^– flowsand uptake, on the other hand, were substantially increasedin the presence of salt and, in particular, there were thenmassive flows of Na^– in the phloem. The results are discussedin relation to the causes of salt sensitivity of Lupinus albus.The data suggest that both a restriction of K⁺ supply and astrongly increased phloem translocation of Na⁺ contribute tothe adverse effects of salt in this species. Restriction ofK⁺ supply occurs by diminished K⁺ uptake and even more by reducedK⁺ cycling within the plant. Key words: Lupinus albus, salt stress, phloem transport, xylem transport, partitioning, carbon, nitrogen, K⁺, Na⁺, CI^–     

Marker-free transgenic durum wheat cv. Karim expressing the AlSAP gene exhibits a high level of tolerance to salinity and dehydration stresses

We have recently isolated the AlSAP (stress-associated protein) gene from the halophyte grass Aeluropus littoralis and demonstrated that AlSAP expression improves tolerance to continuous salt and drought stresses in transgenic tobacco. To extend these findings to an important crop, we generated marker-free transgenic durum wheat plants of the commercial cv. Karim expressing the AlSAP gene. The integration and expression of AlSAP in T3 homozygous plants were ascertained by Southern, Northern and Western blotting respectively. AlSAP wheat lines exhibited improved germination rates and biomass production under severe salinity and osmotic stress conditions. Following a long-term salt or drought stress greenhouse trial, AlSAP lines produced normally filled grains whereas wild-type (WT) plants either died at the vegetative stage under salt stress or showed markedly reduced grain filling under drought stress. Measurements of the RWC (relative water content) and endogenous Na⁺ and K⁺ levels in leaves of AlSAP plants, showed a lower water loss rate and a higher Na⁺ accumulation in senescent-basal leaves, respectively, compared to those of WT plants. Taken together, these results extend to cereals the high potential of the AlSAP gene for engineering effective drought and salt tolerance.     

Overexpression of <Emphasis Type="Italic">OsVP1</Emphasis> and <Emphasis Type="Italic">OsNHX1</Emphasis> Increases Tolerance to Drought and Salinity in Rice

Drought and salinity are major abiotic stresses affecting rice production. To improve plant tolerance to salinity and drought, we overexpressed rice Na⁺/H⁺ exchangers (OsNHX1) and H⁺-pyrophosphatase in tonoplasts (OsVP1) in a japonica elite rice cultivar, Zhonghua 11. Compared with our wild-type control, transgenic plants overexpressing both genes incurred less damage when exposed to long-term treatment with 100 mM NaCl or water deprivation. Under high-saline conditions, the transformants accumulated less Na⁺ and malondialdehyde in the leaves, thereby allowing the plants to maintain a low level of leaf water potential and reduce stress-induced damage. Those transgenics also had higher photosynthetic activity during the stress period. Under those conditions, they also showed an increase in root biomass, which enabled more water uptake. These results suggest that OsVP1 and OsNHX1 improve the tolerance of rice crops against drought and salt by employing multiple strategies in addition to osmotic regulation.     

Osmotic and ionic regulation in Nitella

When the osmotic value of an internodal cell of Nitella flexiliswas modified by the method of transcellular osmosis, the normalosmotic value was chiefly restored by the release or absorptionof K⁺. The release or uptake of Na⁺ was observed only when themodification of osmotic value was significant. Both the uptakeand release of K⁺ were linearly dependent on the degree of modificationof the osmotic value. The effectiveness of alkali metal cationsin restoring the osmotic value in cells of lower osmotic valueswas in the order K⁺>Rb⁺>Na⁺, Cs⁺>Li⁺. The absorptionof K⁺ by cells of lower osmotic values depended strongly ontemperature, while the release of K⁺ from cells of higher osmoticvalues did not. To clarify whether the Nitella cell regulates the osmotic valueor regulates the concentration of K⁺ in the vacuole, the cellsap was exchanged for artificial cell saps whose osmotic valuesand ionic concentrations were varied independent of each other.It was shown that in Nitella two regulating mechanisms are operating,one which regulates the osmotic value of the cell sap irrespectiveof the level of vacuolar K⁺ (0.1–140 mM) and another whichregulates the vacuolar K⁺-level when it is abnormaly high (>160mM). Both mechanisms are assumed to operate in order to keepthe concentration of K⁺ in the cytoplasm at a constant level.The presence of Na⁺ (0–100 mM) and Ca²⁺ (5–40 mM)did not affect the movement of K⁺ during osmoregulation. ¹Present address: Sanki Engineering Limited, Nagaokakyo, Kyoto,Japan. (Received December 19, 1973; )     

The Effect of Salinity on Germination and Its Correlation with K+, Na+, Cl- Accumulation in Germinating Seeds of Triticum aestivum L. cv. Akbar

NaCl salinity stress consistantly decreased the rate of germinationof wheat. GA alone or in combination with kinetin alleviatedthe inhibitory effect of salinity on germination. However, kinetinfurther decreased the rate of germination under NaCl salinitystress. NaCl salinity increased accumulation of Na⁺ and Cl^–while it decreased K⁺ accumulation in germinating seeds. GAcaused an increase in K⁺ accumulation and a decrease in Cl^–accumulation in the germinating seeds while kinetin increasedCl^– accumulation in salinity stressed plants. The co-relationbetween the effect of salinity on germination and that on accumulationof ions is discussed. (Received February 12, 1992; Accepted August 4, 1992)     

Ecotypic Variation in the Osmotic Responses of Enteromorpha intestinalis (L.) Link.

Young, A. J., Collins, J. C. and Russell, G. 1987. Ecotypicvariation in the osmotic responses of Enteromorpha intestinalis(L.) Link.—J. exp. Bot. 38: 1309–1324. The physiological basis for salt tolerance has been studiedin the euryhaline marine alga Enteromorpha intestinalis. Adaptationto dilute and concentrated seawaters has been investigated inthree separate populations of this alga: marine, rock pool andestuarine. Internal K⁺, Na⁺ and Cl^– levels have been determined usingtracer efflux analyses. K⁺ has been shown to be the major osmoticsolute within this alga. Cellular levels of Cl^– and, inparticular, Na⁺ are low although levels in the cell wall arehigh. Levels of these ions varied considerably between the separateplants; K⁺ levels within marine plants of E. intestinalis aretwo to four times those found in the other populations. Thetertiary sulphonium compound ß-dimethylsulphonio-propionateis maintained at relatively high levels, although it remainsfairly insensitive to change in the external salinity. Changes in the tissue water content and cell volume are large,particularly within the estuarine plants. The thin cell wallsof these plants allow large changes in volume in the diluteconditions experienced in an estuary, while low turgor preventscell rupture. Thicker cell walls and small cells of the marineand rock pool plants assist in tolerating high and low externalosmotic potential—the estuarine plants respond poorlyto concentrated seawater. Key words: Enteromorpha, osmoregulation, ecotypes