盐胁迫对不同生境盐地碱蓬光合及离子积累的影响

为了探讨盐地碱蓬(Suaeda salsa)适应不同生境的生理机制, 研究了盐处理(1、200和600 mmol·L^-1 NaCl)对盐碱地和潮间带两种生境盐地碱蓬地上部分及根系有机干重、叶片叶绿素含量及光合放氧速率、叶片和根中离子积累的影响。结果表明: 200 mmol·L^-1 NaCl对两种生境盐地碱蓬地上部分及根系的有机干重无显著影响, 说明两种生境盐地碱蓬均具有较强的抗盐性; NaCl处理显著降低了两种生境盐地碱蓬叶片的光合放氧速率; 各浓度NaCl处理下, 盐碱地生境盐地碱蓬叶片的光合放氧速率均高于潮间带生境的, 潮间带生境盐地碱蓬叶片中叶绿素a与叶绿素b的比值均高于盐碱地生境的; 各浓度NaCl处理下, 潮间带生境盐地碱蓬叶片中的Cl^-含量均低于盐碱地生境的; 与叶片中情况相反, 高盐处理下, 潮间带生境盐地碱蓬根中的Cl^-含量均高于盐碱地生境的。说明与盐碱地生境盐地碱蓬相比, 潮间带生境盐地碱蓬的根系可能对Cl^-具有较强的积累或限制其向地上部分运输的能力, 这些特征可能是盐地碱蓬适应不同生境的结果。     

盐旱互作对不同生境盐地碱蓬种子萌发和幼苗生长的影响

研究了盐旱互作对潮间带和盐碱地生境盐地碱蓬棕色种子萌发、地上部生长和离子积累的影响。不同盐浓度预处理后,未萌发的种子风干后复水,其萌发率与对照相比没有降低,说明两种生境盐地碱蓬种子萌发期间都耐干湿交替。400mmol/LNaCl溶液浇灌的潮间带生境盐地碱蓬幼苗在第3次干旱处理后萎蔫幼苗的百分比高于盐碱地生境的,而复水后正常幼苗的百分比却相反。400mmol/LNaCl溶液处理下,第3次干旱处理复水后,盐碱地生境盐地碱蓬幼苗地上部离子含量(主要是Na+和Cl-)高于潮间带生境的。表明在干旱情况下,盐碱地生境盐地碱蓬幼苗能积累更多的无机离子,降低渗透势,提高根系吸收水分的能力。上述结果说明,盐碱地生境盐地碱蓬幼苗较潮间带生境盐地碱蓬幼苗更耐盐与干旱的交互作用。     

Root morphology is related to the phenotypic variation in waterlogging tolerance of two populations of Suaeda salsa under salinity

The effects of waterlogging and salinity on seedling emergence, seedling growth and ion accumulation in a euhalophyte Suaeda salsa in an intertidal zone and on saline inland soil were investigated. Seedlings of S. salsa from the intertidal zone emerged more rapidly than those of the inland population under both waterlogged and drained conditions. Waterlogging and salinity had no adverse effects on seedling emergence of S. salsa from the intertidal zone, but markedly inhibited this parameter in the inland population. Waterlogging did not affect the seedling survival, shoot dry mass, and shoot height in high salinity in S. salsa from the intertidal zone, while the opposite trend was shown in the inland population. The root dry mass was higher in S. salsa from the intertidal zone as compared to the inland population, in waterlogged treatments by 1.9, 1.3, and 1.5 times in 1, 200, and 600 mM NaCl, respectively, and in drained treatments by 1.8, 2.3, and 3.0 times in 1, 200, and 600 mM NaCl, respectively. Waterlogging increased Na⁺ and K⁺ concentrations in high salinity, but waterlogging had no effect on Cl^- concentration in shoots of S. salsa from the intertidal zone. In all NaCl treatments, waterlogging had no effect on concentrations of these ions in shoots of S. salsa from the saline inland site. In a field investigation, the fresh mass of shoots and roots were lower, whereas the root/shoot ratio was 1.5 times higher in S. salsa from the intertidal zone, compared with the inland population. These findings indicate that S. salsa population from the intertidal zone is more waterlogging tolerant than the inland population. S. salsa from the intertidal zone produced relatively more root biomass and this might help anchor plants against tidal action in the intertidal zone. The physiological and morphological characteristics may determine the natural distributions of the two S. salsa populations in their different saline environments.     

Accumulation of ions during seed development under controlled saline conditions of two Suaeda salsa populations is related to their adaptation to saline environments

Controlled conditions were used to investigate the relationship between ion distribution in developing seeds of two Suaeda salsa populations and seed germination and seedling emergence. Seeds were harvested from S. salsa plants that had been treated with 1 or 400 mM NaCl for 122 (saline inland population) or 135 days (intertidal zone population) in a glasshouse. Germination and seedling emergence were evaluated under salinity. In both populations, more ions were accumulated in the pericarps of plants cultured in 400 mM NaCl than in 1 mM NaCl. Pericarps accumulated much higher ion concentrations in the intertidal zone population than in the saline inland population, while the opposite trend occurred for ion accumulation in the embryos. Seeds of plants from the intertidal zone population germinated more rapidly than those from plants of the saline inland population, regardless of the NaCl concentration during seed germination. However, seedling emergence under high salinity was lower with seeds from the intertidal zone population than with seeds from the saline inland population. In conclusion, S. salsa in the intertidal zone employs superior control of ion compartmentalization in the pericarps to tolerate salinity but requires a minimal level of ions in embryos to ensure seedling establishment in highly saline environments. This indicates that euhalophytes require salts during the mature seed stage to maintain seed viability and to ensure seedling emergence and population establishment.     

不同生境盐地碱蓬对氮饥饿的响应

为了探讨不同生境盐地碱蓬对低氮生境的适应机制,测定了盐渍环境下(200 mmol/L Na Cl)不同浓度硝态氮(0.3、5 mmol/L NO~-_3-N)预处理两种生境盐地碱蓬经氮饥饿后的NO~-_3含量、硝酸还原酶(NR)活性、光合特性及生长状况。结果表明,0.3和5 mmol/L NO~-_3-N处理以及进行氮饥饿时,潮间带生境盐地碱蓬叶片NO~-_3含量均高于内陆生境盐地碱蓬。与内陆生境盐地碱蓬相比,氮饥饿后,潮间带生境盐地碱蓬叶绿素含量、NR活性和光合放氧速率下降幅度均小于内陆生境盐地碱蓬,在0.3mmol/L NO~-_3-N预处理进行氮饥饿时趋势更加明显。0.3 mmol/L NO~-_3-N预处理后氮饥饿对潮间带生境盐地碱蓬根冠比没有影响,却降低内陆生境盐地碱蓬根冠比。上述结果表明,低氮条件下潮间带生境盐地碱蓬具有较高的NO~-_3储存能力,在环境持续氮素缺乏时具有较高的NO~-_3-N再利用能力,能更好地维持氮代谢以及光合性能。说明潮间带生境盐地碱蓬能更好地适应低氮生境。     

盐胁迫下盐地碱蓬体内无机离子含量分布特点的研究

用不同浓度NaCl溶液处理盐地碱蓬（Suaeda salsa)植株后,测定并比较老叶、幼叶及根部的无机离子含量和对K的选择性,叶片及根部的Na^ 、Cl^-含量随盐度的增加而升高,且累积趋势相似,盐胁迫下根部Na^ 、Cl^-及总离子含量（K^ 、Na^ 、Ca^2 ,NO3^-,Cl^-)明显低于叶片,说明盐地碱蓬地盐胁迫下,以叶片优先积累大量离子（如Na^ ,Cl^-) 为其适应特征。NaCl处理下,叶片的K^ ,Ca^2 含量低于对照,但随盐度的增加保持相对稳定,而根部K^ 含量,K/Na比、对K的选择性则高于叶片,这对盐胁迫下地上部的K^ 亏缺有一定补偿作用。低盐度处理（100mmol/LNaCl)促进NO3^-的吸收,另外随盐度的增加,叶片渗透势下降,渗透调节能力增强,幼叶渗透势低于老叶,但渗透调节能力相同。     

盐胁迫下盐芥渗透调节物质的积累及其渗透调节作用

用含有NaCl0、50、100、200、300、400mmol/L的Hoagland培养液处理盐芥幼苗一定时间后,分别测定其根和叶含水量、渗透势、几种无机和有机渗透调节物质含量,并计算了渗透调节物质在不同条件下的计算渗透势值(COP).结果表明:随盐处理浓度的增加,盐芥根和叶的含水量和渗透势逐渐降低;Na 和Cl-是根和叶积累的无机渗透调节物质;SS、OA和FAA是根积累的有机渗透调节物质,Pro是叶和根积累的有机渗透调节物质.Na X-ray微区分析表明液泡是积累Na 的主要部位.     

Photosynthetic limitations of a halophyte sea aster (Aster tripolium L) under water stress and NaCl stress

To understand the mechanisms of salt tolerance in a halophyte, sea aster ( Aster tripolium L.), we studied the changes of water relation and the factors of photosynthetic limitation under water stress and 300 mM NaCl stress. The contents of Na(+) and Cl(-) were highest in NaCl-stressed leaves. Leaf osmotic potentials ( Psi(s)) were decreased by both stress treatments, whereas leaf turgor pressure ( Psi(t)) was maintained under NaCl stress. Decrease in Psi(s) without any loss of Psi(t) accounted for osmotic adjustment using Na(+) and Cl(-) accumulated under NaCl stress. Stress treatments affected photosynthesis, and stomatal limitation was higher under water stress than under NaCl stress. Additionally, maximum CO(2) fixation rate and O(2) evolution rate decreased only under water stress, indicating irreversible damage to photosynthetic systems, mainly by dehydration. Water stress severely affected the water relation and photosynthetic capacity. On the other hand, turgid leaves under NaCl stress have dehydration tolerance due to maintenance of Psi(t) and photosynthetic activity. These results show that sea aster might not suffer from tissue dehydration in highly salinized environments. We conclude that the adaptation of sea aster to salinity may be accomplished by osmotic adjustment using accumulated Na(+) and Cl(-), and that this plant has typical halophyte characteristics, but not drought tolerance.     

Effect of salinity on germination,seedling emergence,seedling growth and ion accumulation of a euhalophyte Suaeda salsa in an intertidal zone and on saline inland

The effect of salinity on germination, seedling emergence, seedling growth and ion accumulation of a euhalophyte Suaeda salsa L. in an intertidal zone and on saline inland were investigated. Brown seeds of S. salsa were heavier and better developed than black seeds in both the intertidal zone and on saline inland. The brown seeds/black seeds ratio for S. salsa in the intertidal zone was much higher than that for S. salsa on saline inland. More germinated seeds grew as seedlings under high salinity for S. salsa from the intertidal zone than S. salsa on saline inland; high salinity decreased the shoot length more severely for S. salsa from saline inland than for S. salsa from the intertidal zone; the seedling growth at a range of NaCl, measured either as shoot length or shoot dry weight, for S. salsa from the intertidal zone was lower than that of S. salsa from saline inland. In conclusion, for S. salsa from the intertidal zone there appears to be selection for slower growth and producing more brown seeds. The establishment of populations of S. salsa in different saline environments depends on the responses of seed germination, seedling emergence and seedling growth to salinity. These characteristics may determine the natural distributions of S. salsa populations in different saline environments.     

Identification and functional characterization of cation-chloride cotransporters in plants

Chloride (Cl(-)) is an essential nutrient and one of the most abundant inorganic anions in plant tissues. We have cloned an Arabidopsis thaliana cDNA encoding for a member of the cation-Cl(-) cotransporter (CCC) family. Deduced plant CCC proteins are highly conserved, and phylogenetic analyses revealed their relationships to the sub-family of animal K(+):Cl(-) cotransporters. In Xenopus laevis oocytes, the A. thaliana CCC protein (At CCC) catalysed the co-ordinated symport of K(+), Na(+) and Cl(-), and this transport activity was inhibited by the 'loop' diuretic bumetanide, a specific inhibitor of vertebrate Na(+):K(+):Cl(-) cotransporters, indicating that At CCC encodes for a bona fide Na(+):K(+):Cl(-) cotransporter. Analysis of At CCC promoter-beta-glucuronidase transgenic Arabidopsis plants revealed preferential expression in the root and shoot vasculature at the xylem/symplast boundary, root tips, trichomes, leaf hydathodes, leaf stipules and anthers. Plants homozygous for two independent T-DNA insertions in the CCC gene exhibited shorter organs such as inflorescence stems, roots, leaves and siliques. The elongation zone of the inflorescence stem of ccc plants often necrosed during bolt emergence, while seed production was strongly impaired. In addition, ccc plants exhibited defective Cl(-) homeostasis under high salinity, as they accumulated higher and lower Cl(-) amounts in shoots and roots, respectively, than the treated wild type, suggesting At CCC involvement in long-distance Cl(-) transport. Compelling evidence is provided on the occurrence of cation-chloride cotransporters in the plant kingdom and their significant role in major plant developmental processes and Cl(-) homeostasis.     

Effect of salinity on growth, ion accumulation and the roles of ions in osmotic adjustment of two populations of Suaeda salsa

The effect of salinity on growth, ion accumulation and the roles of ions in osmotic adjustment of two populations of Suaeda salsa were investigated. Seeds were collected from an intertidal zone or a saline inland zone in the Yellow River Delta in Shandong province, China. Seedlings were exposed to 10, 100, 200, 400 or 600 mM NaCl for 18 days in a greenhouse. NO₃ ^? concentration in the soil where S. salsa grows in an intertidal zone was much lower than that for the second population, but leaf NO₃ ^? concentration was the same in the two populations under field conditions. When plants were cultured in a greenhouse under natural light conditions, S. salsa from the intertidal zone showed fewer main stem branches and lower relative shoot growth compared to S. salsa from saline inland. Leaf Cl^? concentration of saline inland S. salsa was significantly higher than that of S. salsa from the intertidal zone, while the opposite was true for the concentration of NO₃ ^? in leaves of plants. For S. salsa from the intertidal zone NO₃ ^? contributed more than Cl^? to the osmotic potential, whereas S. salsa from the saline inland exhibited a reverse relationship under saline conditions, indicating that NO₃ ^? plays an important osmotic role in S. salsa from the intertidal zone in high salinity. In conclusion, S. salsa from the intertidal zone may employ superior control of ion uptake and content than S. salsa from the saline inland zone. The two populations of Suaeda salsa presented different ability in chloride exclusion and nitrate accumulation. These characteristics may affect the distributions of S. salsa in natural highly saline environments.     

NaCl homoeostasis as a factor for the survival of the evergreen halophyte Armeria maritima (Mill.) Willd. under salt stress in winter

The combination of NaCl and low temperature stress makes winter a critical time for evergreen halophytes at temperate latitudes. As part of a study of ecotypic differentiation of the evergreen Armeria maritima (Mill.) Willd., inland and salt-marsh populations were compared with respect to their growth and survival, osmotic adjustment and NaCl concentrations (based on dry weight) under salt stress in pot experiments in winter. Increased leaf necrosis in all populations under salt stress indicated a higher NaCl sensitivity in winter than in summer. Plants from inland populations were more sensitive than salt-marsh populations. Inland and salt-marsh populations showed similar capacities for seasonal osmotic adjustment, high seasonal increase of praline concentration and long-term betaine accumulation. Inland and salt-marsh populations allocated Na and Cl preferentially to the shoot. In inland populations, Na and Cl accumulated to high concentrations in leaves, whereas the much lower NaCl concentration in salt-marsh populations suggested that in these plants, Na uptake was regulated to match the growth-dependent ion demand of the shoot. The prevention of NaCl accumulation in times of slow growth by a NaCl homoeostasis system seemed to be an important adaptation with respect to the survival of evergreen plants in salt marshes.     

Ecophysiological responses of the euhalophyte Suaeda salsa to the interactive effects of salinity and nitrate availability

Effects of salinity and nitrate nitrogen (NO₃⁻-N) on ion accumulation and chlorophyll fluorescence were monitored for two populations of Suaeda salsa grown from seeds in a greenhouse experiment. One population inhabits the intertidal zone and the other occurs on inland saline soils. Ion contents in soils and in leaves of the two populations were also investigated in field. In the greenhouse, seedlings were exposed to a NaCl concentration of 0.6 and 35.1 ppt, with 0.1 or 5 mM NO₃⁻-N treatments for 20 days. The contents of Na⁺ and Cl⁻ were higher, but NO₃⁻ was lower in soils of the intertidal zone than at the inland site. In the field, ion concentrations and the estimated contribution of these ions to osmotic potential in leaves showed no difference between the two populations, except that the estimated contribution of Na⁺ to osmotic potential in leaves of the intertidal population was lower than that in the inland population. In the greenhouse, in contrast, the concentration of Cl⁻ was lower, but NO₃⁻ concentration and the estimated contribution of NO₃⁻ to osmotic potential were higher, in the leaves of plants from the intertidal zone. Salinity had no effect on the maximal efficiency of PSII photochemistry (Fv/Fm) and the actual PSII efficiency (ΦPSII). The results indicated that S. salsa from the intertidal zone was better able to regulate Cl⁻ to a lower level, and accumulate NO₃⁻ even with low soil NO₃⁻ concentrations. Tolerance of the PSII machinery to high salinity stress may be an important characteristic for the studied species supporting growth in highly saline environments.     

Trade-off between leaf chlorophyll and betacyanins in Suaeda salsa in the Liaohe estuary wetland in northeast China

Aims Pigment composition is an important functional trait that can be affected by environmental factors. The objective of this study was to investigate the effect of soil salinity on pigment composition in Suaeda salsa by comparing chlorophyll and betacyanin content in the Liaohe estuary wetland, a typical coastal wetland in northeast China.Methods We investigated the plant biomass, percentage of red leaves and pigment content (chlorophyll a, chlorophyll b and betacyanins) in S. salsa in intertidal and supratidal zones of the upper, middle and lower reaches of the Liaohe estuary wetlands. The Na + content of both the soil and plant was also measured. Full analysis of variance and multivariate analysis were used to compare differences in pigment content and Na + content between the supratidal and intertidal zones.Important findings Pigment composition was significantly affected by soil salinity. With increasing soil salinity, the percentage of red leaves was higher in the intertidal zone than in the supratidal zone. In all three reaches, plants had lower chlorophyll a content and higher betacyanin content in the intertidal zone than in the supratidal zone. Compared to chlorophyll a, chlorophyll b was less sensitive to soil salinity. There were no differences in chlorophyll b content between the intertidal and supratidal zones in the upper and lower reaches. Furthermore, pigment composition was associated with both the plant tissue and soil Na + content. Compared to the supratidal zone, the intertidal zone had a higher Na + content in plants. There was a negative relationship between plant chlorophyll content and soil Na + content, but a positive relationship between betacyanin content and soil Na + content. Overall, the results indicated that there might be a trade-off between leaf chlorophyll and betacyanin content in S. salsa to maintain its growth and survival in high salinity environments.     

Ecophysiological responses of the euhalophyte Suaeda salsa to the interactive effects of salinity and nitrate availability

Effects of salinity and nitrate nitrogen (NO₃⁻-N) on ion accumulation and chlorophyll fluorescence were monitored for two populations of Suaeda salsa grown from seeds in a greenhouse experiment. One population inhabits the intertidal zone and the other occurs on inland saline soils. Ion contents in soils and in leaves of the two populations were also investigated in field. In the greenhouse, seedlings were exposed to a NaCl concentration of 0.6 and 35.1 ppt, with 0.1 or 5 mM NO₃⁻-N treatments for 20 days. The contents of Na⁺ and Cl⁻ were higher, but NO₃⁻ was lower in soils of the intertidal zone than at the inland site. In the field, ion concentrations and the estimated contribution of these ions to osmotic potential in leaves showed no difference between the two populations, except that the estimated contribution of Na⁺ to osmotic potential in leaves of the intertidal population was lower than that in the inland population. In the greenhouse, in contrast, the concentration of Cl⁻ was lower, but NO₃⁻ concentration and the estimated contribution of NO₃⁻ to osmotic potential were higher, in the leaves of plants from the intertidal zone. Salinity had no effect on the maximal efficiency of PSII photochemistry (Fv/Fm) and the actual PSII efficiency (ΦPSII). The results indicated that S. salsa from the intertidal zone was better able to regulate Cl⁻ to a lower level, and accumulate NO₃⁻ even with low soil NO₃⁻ concentrations. Tolerance of the PSII machinery to high salinity stress may be an important characteristic for the studied species supporting growth in highly saline environments.     

Leaf gas exchange and solute accumulation in the halophyte Salvadora persica grown at moderate salinity

The domestication of halophytes has been proposed as a strategy to expand cultivation onto unfavorable land. However, halophytes mainly have been considered for their performance in extremely saline environments, and only a few species have been characterized in terms of their tolerance and physiological responses to moderately high levels of salinity. Salvadora persica is an evergreen perennial halophyte capable of growing under extreme conditions, from very dry environments to highly saline soils. It possesses high potential economic value as a source of oil and medicinal compounds. To quantify its response to salinity, S. persica seedlings were exposed to 200 mM NaCl for 3 weeks, and growth, leaf gas exchange and solute accumulation were measured. The presence of NaCl induced a 100% increase in fresh weight and a 30% increase in dry weight, relative to non-salinized controls. Increases in fresh weight and dry weight were not associated with higher rates of net CO(2) assimilation, however. Analysis of ion accumulation revealed that S. persica leaves accumulated Na(+) as a primary osmoticum. The concentration of Na(+) in leaves of salinized plants was approximately 40-fold greater than that measured in non-salinized controls, and this was associated with significant reductions in leaf K(+) and Ca(2+) concentrations. In addition, a significant accumulation of proline, probably associated with osmotic adjustment and protection of membrane stability, occurred in roots of salinized plants.     

Na(+) and Cl(-) transport by the urinary bladder of the freshwater rainbow trout (Oncorhynchus mykiss)

Freshwater (FW) rainbow trout (Oncorhynchus mykiss) urinary bladders mounted in vitro under symmetrical saline conditions displayed electroneutral active absorption of Na(+) and Cl(-) from the mucosal side; the transepithelial potential (V(t)) was 0.1 mV, and the short-circuit current was less than 1 microA cm(-2). Removal of Na(+) from mucosal saline decreased Cl(-) absorption by 56% and removal of Cl(-) decreased Na(+) absorption by 69%. However, active net absorption of both Na(+) and Cl(-) was not abolished when Cl(-) or Na(+) was replaced with an impermeant ion (gluconate or choline, respectively). Under physiological conditions with artificial urine (?Na(+) = 2.12 mM, ?Cl(-) = 3.51 mM) bathing the mucosal surface and saline bathing the serosal surface, transepithelial potential (V(t)) increased to a serosal positive approximately +7.6 mV. Unidirectional influx rates of both Na(+) and Cl(-) were 10-20-fold lower but active absorption of both ions still occurred according to the Ussing flux ratio criterion. Replacement of Na(+) with choline, or Cl(-) with gluconate, in the mucosal artificial urine yielded no change in unidirectional influx of Cl(-) or Na(+), respectively. However, kinetic analyses indicated a decrease in maximum Na(+) transport rate (J(max)) of 66% with no change in affinity (K(m)) in the low Cl(-) mucosal solution relative to the control solution. Similarly, there was a 79% decrease in J(max) values for Cl(-), again with no change in K(m), in the low-Na(+) mucosal bathing. The mucosal addition of DIDS, amiloride or bumetanide (10(-4) M) had no effect on either Na(+) or Cl(-) transport, under either symmetrical saline or artificial urine/saline conditions. Addition of the three drugs simultaneously (10(-4) M), or chlorothiazide (10(-3) M), under symmetrical saline conditions also had no effect on Na(+) or Cl(-) transport rates. Cyanide (10(-3) M) addition to mucosal artificial urine caused a slowly developing decrease of Na(+) influx to 59% and Cl(-) influx to 50% in the period after drug addition. Na(+) and Cl(-) reabsorption appears to be a partially coupled process in the urinary bladder of O. mykiss; transport mechanisms are both dependent upon and independent of the other ion.     

Lotus tenuis tolerates the interactive effects of salinity and waterlogging by 'excluding' Na+ and Cl- from the xylem

Salinity and waterlogging interact to reduce growth of poorly adapted species by, amongst other processes, increasing the rate of Na(+) and Cl(-) transport to shoots. Xylem concentrations of these ions were measured in sap collected using xylem-feeding spittlebugs (Philaenus spumarius) from Lotus tenuis and Lotus corniculatus in saline (NaCl) and anoxic (stagnant) treatments. In aerated NaCl solution (200 mM), L. corniculatus had 50% higher Cl(-) concentrations in the xylem and shoot compared with L. tenuis, whereas concentrations of Na(+) and K(+) did not differ between the species. In stagnant-plus-NaCl solution, xylem Cl(-) and Na(+) concentrations of L. corniculatus increased to twice those of L. tenuis. These differences in xylem ion concentrations, which were not caused by variation in transpiration between the two species, contributed to lower net accumulation of Na(+) and Cl(-) in shoots of L. tenuis, indicating that ion transport mechanisms in roots of L. tenuis were contributing to better 'exclusion' of Cl(-) and Na(+) from shoots, compared with L. corniculatus. Root porosity was also higher in L. tenuis, due to constitutive aerenchyma, than in L. corniculatus, suggesting that enhanced root aeration contributed to the maintenance of Na(+) and Cl(-) 'exclusion' in L. tenuis exposed to stagnant-plus-NaCl treatment. Lotus tenuis also had greater dry mass than L. corniculatus after 56 d in NaCl or stagnant-plus-NaCl treatment. Thus, Cl(-) 'exclusion' is a key trait contributing to salt tolerance of L. tenuis, and 'exclusion' of both Cl(-) and Na(+) from the xylem enables L. tenuis to tolerate, better than L. corniculatus, the interactive stresses of salinity and waterlogging.     

Measurements of redox activity at the plasmalemma

Salt (NaCl) tolerance of 3 eucalypt species ( Eucalyptus alba Reinw. ex Bl., E. camaldulensis Dehnh and E. microtheca f.v. Muell.) was studied: three-month-old seedlings grown in a greenhouse were watered by a saline solution (up to 700 m M ) for 1 month. Mineral, water and sugar contents were highly affected by the saline stress. Sodium, K and Ca were accumulated in the leaves. No significant differences were found between E. camaldulensis and E. microtheca , the tolerant species, in water and mineral contents. Sugar contents were greater in E. microtheca . In E. microtheca Na was highly accumulated in roots [up to 910 μmol (g fresh weight)⁻¹], less in stems [up to 580 μmol (g fresh weight)-1] and leaves [up to 410 μmol (g fresh weight)^−r]. Chloride was also accumulated, its content was greater than the total content of Na and K, especially in the salt-tolerant provenance. Potassium and Ca contents were variously affected by the saline stress whereas soluble protein, amino acid and sugar contents were increased. Just after the saline stress, plants showed a large increase in the Na content of the leaf while the decrease in the K content of the stem and leaf continued. Plants were killed by the stress, probably because of too high accumulation of Na in leaves or roots according to the provenance. Osmoregulation and especially the participation of Na are discussed.     

Organ-Specific Responses of Vacuolar H~+-ATPase in the Shoots and Roots of C_3 Halophyte Suaeda salsa to NaCl

Suaeda salsa L. is a halophytic species that is well adapted to high salinity. In order to understand its salt tolerance mechanism, we examined the growth and vacuolar H+-ATPase (V-ATPase) response to NaCl within the shoots and roots. The growth of shoots, but not roots, was dramatically stimulated by NaCl. Cl? and Na+ were mainly accumulated in shoots. V-ATPase activity was significantly increased by NaCl in roots and especially in shoots. Interestingly, antisera ATP95 and ATP88b detected three V1 subunits...