Effects of salt stress on purslane (Portulaca oleracea) nutrition

The objective of this study was to determine the influence of saline stress on the chemical composition of purslane (Portulaca oleracea), in particular the mineral composition. Four salinity levels were investigated using irrigation solutions with electrical conductivity values of 0.8, 6.8, 12.8 and 24.2 dS m^?1 and two planting dates (May and July) were tested. Samples of full‐grown leaf and stems of purslane were harvested after 7 and 15 days of the saline treatment exposure. Chemical analysis (dry matter basis) of leaves showed significant differences among the different saline treatments for all the characteristics measured. Salinity levels, planting date and harvest time significantly influenced (P < 0.05) the levels of crude protein, total lipids, ash and carbohydrate content. Salinity treatments did not significantly (P > 0.05) affect the water content of purslane leaves. The crude protein content of purslane leaves decreased with increasing salinity levels and time of exposure to treatment. However, carbohydrates and mineral residue content increased. An unusual phenomenon was noted for intermediate salinity levels, whereby an increase in total lipid content was measured in leaves of plants exposed to salinity treatments of 6.8 and 12.8 dS m^?1. The highest mineral residue content was seen in leaves of purslane exposed to the highest salinity treatment. The mineral composition was also affected by salinity levels, Na and Cl uptake, and accumulation increased with increasing salinity in irrigation solution; Mg concentration was not significantly (P > 0.05) affected by salinity levels, although a slight increase was seen, and Ca, K and Zn levels significantly (P < 0.05) decreased. Ca and Zn preferentially accumulated in the leaves, while K and Na values were higher in the stems. A significant increase (P < 0.05) in relative ratio of Na/K, Mg/K, Na/Ca and Mg/Ca was observed with increasing salinity levels. A decrease in the yield of purslane was only observed for the most severe saline treatment, where the highest ratio of Mg/Ca was seen. This study reveals that purslane is relatively tolerant to conditions of moderate salinity, thus improving its potential to become a key vegetable crop for animal and human consumption.     

THE EFFECTS OF SODIUM CHLORIDE ON HIGHER PLANTS

(1) This review concentrates on the effect of sodium chloride on the growth of higher plants, being primarily concerned with relatively high concentrations i.e. 50 mmol 1^-1 and above, though something is also said about those instances when sodium acts as a micronutrient. Emphasis is placed on particular species or genera for which enough information is available to discuss possible mechanisms. (2) Trace amounts of sodium are required for the growth of plants using the C₄ pathway of carbon fixation and may also be important in plants with Crassulacean acid metabolism. (3) The increased growth of Beta vulgaris brought about by sodium chloride can in part be explained by a sparing effect on potassium. However, growth is still increased when sufficient potassium is available. Complementary studies with rubidium indicate that the hormone balance in the plant may be changed. Sodium chloride also increases the level of sucrose in storage roots and allows beet plants to withstand water stress more readily, possibly by increased turgor pressure. (4) Sodium chloride increases production of dry matter in C₄ species of Atriplex under conditions of low relative humidity because water loss is reduced and photo-synthesis hardly affected. (5) Succulence in many plants is stimulated by salinity. The essential basis of the phenomenon is an increased water potential gradient between the leaf and the external medium. In some instances, it is the accumulation of chloride which is important; in others it is the accumulation of cations, when potassium can be as effective as sodium. (6) Salinity reduces the final area achieved by growing leaves. Most of the studies have been made on Phaseolus vulgaris and an important early event is the reduction in the rate of expansion of the epidermal cells and this may be accompanied by a decrease in their number. Reduction of epidermal cell size is a result of water stress; sodium chloride may directly affect cell division, though water stress cannot be ruled out. Whether salinity brings about inhibition of cell division depends upon the calcium content of the medium – a high content is accompanied solely by a reduction in epidermal cell size. (7) Hormones, as yet unspecified, may play an important part in response of a growing leaf to salinity. However, there is no evidence that sodium chloride per se has an effect on hormone balance within the plant. So far, any measured changes in levels of specific hormones can be ascribed to the osmotic effects of the saline medium. (8) Two estimates by flux analysis of cytoplasmic concentration of sodium in plants growing in conditions of high salinity give a value of around 150 mmol 1^-1. There is no similar information for chloride. Other techniques (histochemistry and X-ray micro-probe analysis) give questionable information. (9) There is now extensive information to show that enzymes of halophytes (other than ATPases) do not differ significantly from those of other higher plants with respect to their sensitivity in vitro to sodium chloride. There is a need for further work with respect to the activity of enzymes in the presence of those metabolites which have the highest cytoplasmic concentration. (10) Sodium-stimulated ATPases have been isolated from plant cells but their distribution amongst higher plants is restricted. (11) There are a number of reports of changed metabolism brought about by saline treatments but it is not clear how far the effects of sodium chloride and water stress are confounded. (12) Sodium appears to increase the sucrose levels in sugar beet by an inhibitory effect on product starch-granule-bound ADP-glucose starch synthase. (13) Reversal of a sodium pump located at the plasmalemma might have an effect on cell turgor. (14) Sodium (like other monovalent cations) causes loss of materials from plant cells, possibly through an effect on carrier proteins; calcium prevents this from happening. Calcium also allows plants to grow better in saline conditions by a depression of sodium uptake by and transport within the plant. The properties and composition of the membranes of mesophytes and halophytes need to be compared. (15) A saline medium exerts a major effect on plant growth through water stress to which a halophyte must adapt. As well as this, the cytoplasmic concentration of sodium chloride must be kept lower than the total cellular concentration of the salt. Unless this happens, it is likely that enzymic activity will be reduced due, in some instances, to an unspecific effect of a high concentration of monovalent cations and/or chloride and in other instances to competition between sodium and other cations, specifically potassium, for activation sites on enzymes, e.g. pyruvate kinase. (16) Further work is required to separate the osmotic effects from the specific effect of sodium chloride after it has entered the plant. As well as this, it has become clear that more information is needed about the mineral nutrition of halophytes.     

Phelipanche aegyptiaca parasitism impairs salinity tolerance in young leaves of tomato

The parasite Phelipanche aegyptiaca infests tomato, a crop plant that is commonly cultivated in semi‐arid environments, where tomato may be subject to salt stress. Since the relationship between the two stresses —salinity and parasitism – has been poorly investigated in tomato, the effects of P. aegyptiaca parasitism on tomato growing under moderate salinity were examined. Tomatoes were grown with regular or saline water irrigation (3 and 45 mM Cl^?, respectively) in soils infested with P. aegyptiaca . The infested plants accumulated higher levels of sodium and chloride ions in the roots, shoots and leaves (old and young) under both salinity levels vs. non‐infected plants. There was a positive linear correlation between P. aegyptiaca biomass and salt accumulation in young tomato leaves, and a negative linear correlation between parasite biomass and the osmotic potential of young tomato leaves. Concentrations of the osmoprotectants proline, myoinositol and sucrose were reduced in infected tomato plants, which impaired the host's osmotic adjustment ability. The sensitivity of P. aegyptiaca to salt stress was manifested as a decrease in biomass. In conclusion, P. aegyptiaca parasitism reduced the salt tolerance of tomato plants by promoting the accumulation of salts from the rhizosphere and impairing the host's osmotic adjustment ability.     

Effect of salinity stress on organic and mineral constituents in the leaves of pigeonpea (Cajanus cajan L. Var. C-11)

Summary Effects of sodium chloride and sodium sulphate on the content of some organic and inorganic constituents in the leaves of pigeonpea (Cajanus cajan L. Var. C-11) were studied. Increased water content under saline conditions made the leaves succulent. The concentration of reducing sugars appeared to be higher while that of total sugars and starch was lower. The plants also failed to accumulate proline at higher salinity levels. Phosphorus and potassium content were lowered while those of calcium, magnesium, sodium, chloride and sulphate were increase under both salinities. This indicates that there is no regulation on the uptake of latter elements under saline conditions.     

Endophytic bacterium Bacillus subtilis (BERA 71) improves salt tolerance in chickpea plants by regulating the plant defense mechanisms

Plant growth-promoting endophytic bacteria can stimulate the growth, nutrient acquisition, symbiotic performance and stress tolerance of chickpea plants under saline soil conditions. The aim of this study was to investigate the stress-adaptive mechanisms of chickpea plants mediated by Bacillus subtilis (BERA 71) under saline conditions. Inoculation with BERA 71 enhanced plant biomass and the synthesis of photosynthetic pigments and reduced the levels of reactive oxygen species (ROS) and lipid peroxidation in plants under conditions of stress. Furthermore, the activities of ROS-scavenging antioxidant enzymes (superoxide dismutase, peroxidase, catalase and glutathione reductase), the levels of non-enzymatic antioxidants (ascorbic acid and glutathione) and the total phenol content were increased in stressed plants during bacterial association. The bacteria decreased sodium accumulation and enhanced the nitrogen, potassium, calcium and magnesium content in the plants. The suppression of ROS generation and of lipid peroxidation and the accumulation of proline in BERA-71-inoculated plants enhanced the membrane stability under salinity stress and non-stress conditions.     

Abscisic acid alters carbohydrate accumulation induced by differential response to sodium salts in the halophyte Prosopis strombulifera

Abstract

The role of abscisic acid (ABA) was analyzed in roots and leaves of the halophyte Prosopis strombulifera in response to low osmotic potential (Ψo: ?1.0, ?1.9, and ?2.6?MPa) induced by sodium chloride (NaCl), sodium sulfate (Na₂SO₄), and the iso-osmotic combination of both compounds (NaCl?+?Na₂SO₄). P. strombulifera plants were sprayed with ABA, as well as with inhibitors of ABA biosynthesis (sodium tungstate and fluridone). Different parameters were measured, including total plant height, leaf number, root length, root and shoot biomass, water content, transpiration rate, and total soluble carbohydrates, specific carbohydrates and ABA concentrations. Results showed that sodium salts affected growth parameters in varying ways, depending on the type of salts used as well as the osmotic potentials. ABA-sprayed plants displayed the lowest transpiration values. These plants had a higher content of total soluble carbohydrates in roots, greater root biomass and length and increased root/shoot rate. This study shows that ABA triggers different biochemical and physiological responses after the perception of a stressful condition, and that the interaction between different concentrations and types of salts, and the addition of ABA or its inhibitors generates responses that affect development and growth in the halophyte P. strombulifera.     

Volume regulation in vitro of muscle fibres of the crab,Hemigrapsus edwardsi

Summary Isolated flexor muscles of the shore crab,Hemigrapsus edwardsi were maintained in saline solutions for periods of 2–12 h.In hypotonic saline solutions containing less than 400 mM sodium chloride, the fibres rapidly died. In 400 mM sodium chloride saline the fibres showed partial volume readjustment associated with reduction in the amount of intracellular ninhydrin-positive substances (NPS).In saline (460 mM sodium chloride) containing ouabain (2–5 mM) the fibres lost water and potassium, gained sodium and chloride, but the amount of NPS was not significantly changed.In hypertonic saline (550 mM sodium chloride) the fibres showed a partial recovery of volume during the 8 h experimental period. Associated with this was a rise in the amount of intracellular NPS.It was concluded that the ability of the muscle fibres ofHemigrapsus edwardsi to respond to a hyperosmotic challenge in an amino acid free medium, by an increase in intracellular amino acid levels, must represent a synthesis of these compounds from an intracellular source. This may be an adaptive feature of osmotic readjustment in this rather permeable crab.     

The role of arbuscular mycorrhizal fungi in alleviating salt stress in Medicago sativa L. var. icon

Medicago sativa L. is the most important forage crop in arid and semi-arid areas, where increased salinity is a major factor limiting plant growth and crop productivity. The role of arbuscular mycorrhizal (AM) fungus Glomus viscosum H.T. Nicolson strain A6 in protecting alfalfa plants from salt stress, induced by sodium chloride (NaCl), was studied in two ways. Firstly, the root systems of 3-month old M. sativa plants, both mycorrhizal (AM+) and non-mycorrhizal (non-AM) (M. sativa L. var. icon), were placed in solutions of increasing salt concentrations (0, 50, 100, 150, 200 mM NaCl) to study the wilting response. G. viscosum improved the tolerance to salinity stress and the benefit was expressed in terms of the time required to reach the T4 stage in the wilting experiment. Secondly, to evaluate the ability of the Glomus-alfalfa symbiosis to tolerate salt, a pot experiment was set up in a glasshouse in which 3-month old alfalfa plants (M. sativa var. icon) were grown in a peat substratum at three salinity levels (0, 100, 150 mM NaCl). The AM symbiosis stimulated plant height, leaf area, root density, fresh and dry plant weight under saline conditions. Furthermore, proline accumulation was higher in mycorrhizal M. sativa plants than in non-mycorrhizal plants under conditions of salt stress. These and other results indicated that the micropropagated selected clone of M. sativa var. icon, when in symbiosis with G. viscosum H.T. Nicolson strain A6, exhibited better growth and physiological activities under saline conditions than non-AM plants. The AM+ plants also had lower sodium and chloride concentrations in tissues than non-AM plants.     

Expression of the Arabidopsis vacuolar H+‐pyrophosphatase gene (AVP1) improves the shoot biomass of transgenic barley and increases grain yield in a saline field

Cereal varieties with improved salinity tolerance are needed to achieve profitable grain yields in saline soils. The expression of AVP1, an Arabidopsis gene encoding a vacuolar proton pumping pyrophosphatase (H⁺‐PPase), has been shown to improve the salinity tolerance of transgenic plants in greenhouse conditions. However, the potential for this gene to improve the grain yield of cereal crops in a saline field has yet to be evaluated. Recent advances in high‐throughput nondestructive phenotyping technologies also offer an opportunity to quantitatively evaluate the growth of transgenic plants under abiotic stress through time. In this study, the growth of transgenic barley expressing AVP1 was evaluated under saline conditions in a pot experiment using nondestructive plant imaging and in a saline field trial. Greenhouse‐grown transgenic barley expressing AVP1 produced a larger shoot biomass compared to null segregants, as determined by an increase in projected shoot area, when grown in soil with 150 mm NaCl. This increase in shoot biomass of transgenic AVP1 barley occurred from an early growth stage and also in nonsaline conditions. In a saline field, the transgenic barley expressing AVP1 also showed an increase in shoot biomass and, importantly, produced a greater grain yield per plant compared to wild‐type plants. Interestingly, the expression of AVP1 did not alter barley leaf sodium concentrations in either greenhouse‐ or field‐grown plants. This study validates our greenhouse‐based experiments and indicates that transgenic barley expressing AVP1 is a promising option for increasing cereal crop productivity in saline fields.     

Dog Red Blood Cells : Adjustment of salt and water content in vitro

Dog red blood cells (RBC) lack a ouabain-sensitive sodium pump, and yet they are capable of volume regulation in vivo. The present study was designed to find in vitro conditions under which dog RBC could transport sodium outward, against an electrochemical gradient. Cells were first loaded with sodium chloride and water by preincubation in hypertonic saline. They were then incubated at 37°C in media containing physiologic concentrations of sodium, potassium, chloride, bicarbonate, glucose, and calcium. The cells returned to a normal salt and water content in 16–20 h. Without calcium in the medium the cells continued slowly to accumulate sodium. Removal of glucose caused rapid swelling and lysis, whether or not calcium was present. The net efflux of sodium showed a close relationship to medium calcium over a concentration range from 0 to 5 mM. Extrusion of salt and water was also demonstrated in fresh RBC (no hypertonic preincubation) when calcium levels in the media were sufficiently raised. The ion and water movements in these experiments were not influenced by ouabain or by removal of extracellular potassium. Magnesium could not substitute for calcium. It is concluded that dog RBC have an energy-dependent mechanism for extruding sodium chloride which requires external calcium and is quite distinct from the sodium-potassium exchange pump.     

Laboratory study of heavy metal phytoremediation by three wetland macrophytes

Detention ponds and constructed wetlands have proven to be effective in reducing peak stormwater runoff volume and flow, and recent interest has extended to utilizing them to improve stormwater runoff quality. A review of stormwater runoff studies indicated that lead, zinc, copper, cadmium, phosphorus, and chloride are contaminants of primary concern. In laboratory settings, the uptake of contaminants by three wetland plant species, Glyceria grandis, Scirpus validus, and Spartina pectinata, was examined and removal rates from nutrient solutions inflow and nonflow reactors were measured. The removal rates varied by plant species and target contaminant, and no one species was the best accumulator of all six contaminants. Belowground tissues of all three species accumulated higher concentrations of the four heavy metals and aboveground tissues accumulated higher concentrations of phosphorus and chloride. Plants grown in flow reactors showed significantly higher accumulation rates than those grown in nonflow reactors. Also, plants grown hydroponically accumulated higher concentrations of the six target contaminants than those grown in sand reactors. However, those grown in sand had a much greater increase of biomass and removed a greater mass of the six target contaminants. Removal rates measured in these experiments can be used to design detention ponds to maximize stormwater remediation.     

Nitrate‐dependent shoot sodium accumulation and osmotic functions of sodium in Arabidopsis under saline conditions

Improving crop plants to be productive in saline soils or under irrigation with saline water would be an important technological advance in overcoming the food and freshwater crises that threaten the world population. However, even if the transformation of a glycophyte into a plant that thrives under seawater irrigation was biologically feasible, current knowledge about Na⁺ effects would be insufficient to support this technical advance. Intriguingly, crucial details about Na⁺ uptake and its function in the plant have not yet been well established. We here propose that under saline conditions two nitrate‐dependent transport systems in series that take up and load Na⁺ into the xylem constitute the major pathway for the accumulation of Na⁺ in Arabidopsis shoots; this pathway can also function with chloride at high concentrations. In nrt1.1 nitrate transport mutants, plant Na⁺ accumulation was partially defective, which suggests that NRT1.1 either partially mediates or modulates the nitrate‐dependent Na⁺ transport. Arabidopsis plants exposed to an osmotic potential of ?1.0 MPa (400 mOsm) for 24 h showed high water loss and wilting in sorbitol or Na/MES, where Na⁺ could not be accumulated. In contrast, in NaCl the plants that accumulated Na⁺ lost a low amount of water, and only suffered transitory wilting. We discuss that in Arabidopsis plants exposed to high NaCl concentrations, root Na⁺ uptake and tissue accumulation fulfil the primary function of osmotic adjustment, even if these processes lead to long‐term toxicity.     

Salinity tolerance of Gambusia affinis (Baird & Girard) and Heteropneustes fossilis (Bloch)

The present paper describes the results of a study on the salinity tolerance of two freshwater fishes, Gambusia affinis (Baird & Girard) and Heteropneustes fossilis (Bloch). The two species were treated with various concentrations of sea water and three most common salts found in the saline waters of Iraq, namely sodium chloride, calcium chloride and potassium chloride. The mortality rates following these treatments were recorded. Both species showed the highest degree of resistance for sea water and sodium chloride, and the lowest degree of tolerance to potassium chloride. Gambusia affinis was more resistant to these salts and sea water than H. fossilis .     

松嫩平原碱化草地植物-环境系统的仿真模拟

 本研究以系统仿真的方法对松嫩平原碱化草地植物—环境系统进行模拟。模型的系统变量包括植物种的地上、地下生物量,土壤水分、有机质。可溶性和交换性Na+和Ca++浓度和植物的凋落物生物量。模型所考虑的过程有：不同土壤碱化条件下的植物生长季节动态;土壤水、盐运动;植物的蒸腾作用;土壤表面的蒸发;凋落物的积累和分解;土壤有机质的积累和矿化;地下生物量对土壤持水和导水特性的控制作用,以及收获强度对系统平衡的影响等。模型成功地解释了植物生物量形成过程与环境之间的动态耦合、相关作用。模拟结果说明：与地下生物量密切相关的土壤非毛管孔隙度与土壤的碱化和脱碱过程有极强的相关作用,这种作用是通过改变土壤的饱和持水量来实现的。非毛管孔隙度随地下生物量增加,导致饱和含水量增加和脱碱作用加强。收获强度过大导致地下生物量的减少、非毛管孔隙度的减少和碱化作用的加强。     

松嫩平原碱化草地植物－环境系统的仿真模拟

本研究以系统仿真的方法对松嫩平原碱化草地植物－环境系统进行模拟。模型的系统变量包括植物种的地上、地下生物量,土壤水分、有机质、可溶性和交换性Ｎａ￣＋和Ｃａ￣＋＋浓度和植物的凋落物生物量。模型所考虑的过程有：不同土壤碱化条件下的植物生长季节动态;土壤水、盐运动;植物的蒸腾作用;土壤表面的蒸发;凋落物的积累和分解;土壤有机质的积累和矿化;地下生物量对土壤持水和导水特性的控制作用,以及收获强度对系统平衡的影响等。模型成功地解释了植物生物量形成过程与环境之间的动态耦合、相关作用。模拟结果说明：与地下生物量密切相关的土壤非毛管孔隙度与土壤的碱化和脱碱过程有极强的相关作用,这种作用是通过改变土壤的饱和持水量来实现的。非毛管孔隙度随地下生物量增加．导致饱和含水量增加和脱碱作用加强。收获强度过大导致地下生物量的减少、非毛管孔隙度的减少和碱化作用的加强。     

The use of halophytic plants for salt phytoremediation in constructed wetlands

This research studied the use of constructed wetlands (CWs) to reduce water salinity. For this purpose, three halophytic species of the Chenopodiaceae family (Salicornia europaea, Salsola crassa, and Bienertia cycloptera) that are resistant to saline conditions were planted in the CWs, and experiments were conducted at three different salinity levels [electrical conductivity (EC)～2, 6, 10 dS/m]. EC and concentrations of calcium (Ca), magnesium (Mg), sodium (Na), and chlorine (Cl) were measured before and after phytoremediation with a retention time of 1 week. The results suggested that these plants were able to grow well and complete their life cycles at all the salinity levels within this study. Moreover, these plants reduced the measured parameters to acceptable levels. Therefore, these plants can be considered good options for salt phytoremediation.     

Improving water use efficiency by changing hydraulic and stomatal characteristics in soybean exposed to drought: the involvement of nitric oxide

A variety of cellular responses is needed to ensure the plants survival during drought, but little is known about the signaling mechanisms involved in this process. Soybean cultivars (EMBRAPA 48 and BR 16, tolerant and sensitive to drought, respectively) were exposed to the following treatments: control conditions (plants in field capacity), drought (20% of available water in the soil), sodium nitroprusside (SNP) treatment (plants irrigated and treated with 100-µM SNP [SNP–nitric oxide (NO) donor molecule], and Drought + SNP (plants subjected to drought and SNP treatment). Plants remained in these conditions until the reproductive stage and were evaluated for physiological (photosynthetic pigments, chlorophyll a fluorescence and gas exchange rates), hydraulic (water potential, osmotic potential and leaf hydraulic conductivity) and morpho-anatomical traits (biomass, venation density and stomatal characterization). Exposure to water deficit considerably reduced water potential in both cultivars and resulted in decrease in photosynthesis and biomass accumulation. The addition of the NO donor attenuated these damaging effects of water deficit and increased the tolerance index of both cultivars. The results showed that NO was able to reduce plant's water loss, while maintaining their biomass production through alteration in stomatal characteristics, hydraulic conductivity and the biomass distribution pattern. These hydraulic and morpho-anatomical alterations allowed the plants to obtain, transport and lose less water to the atmosphere, even in water deficit conditions.     

Osmotic properties of spermatozoa from felids producing different proportions of pleiomorphisms: influence of adding and removing cryoprotectant

The spermatozoon of felids (cats) survives cryopreservation inconsistently. Using ejaculates from three species (domestic cat [normospermic versus teratospermic], the normospermic serval and the teratospermic clouded leopard), this study (1) determined the influence of adding and removing two permeating cryoprotectants (glycerol and dimethylsulfoxide) and (2) assessed the impact of one-step versus multi-step cryoprotectant removal on sperm motility and membrane integrity. Spermatozoa were exposed in a single step to various anisotonic solutions or to 1M solutions of glycerol or dimethylsulfoxide. In both cases, sperm then were returned to near isotonic conditions in a single or multi-step with de-ionized water, Ham's F10 medium or saline. Percentage of sperm motility was measured subjectively, and plasma membrane integrity was assessed using a dual fluorescent stain and flow cytometry. Sperm motility was more sensitive to anisotonic conditions than membrane integrity. Rapid dilution into various test solutions and removal of cryoprotectant with de-ionized water reduced (P<0.01) sperm motility compared to control spermatozoa maintained in Ham's F10. Exposing sperm from all species to a 1M solution of either cryoprotectant resulted in >85% spermatozoa retaining intact membranes. However, return to isotonicity with de-ionized water in a single step or multiple steps always caused severe plasma membrane disruption. In contrast, sperm motility and membrane integrity in all species and populations remained unaffected (P>0.05) when spermatozoa were returned to isotonicity in multiple steps with Ham's F10 medium or 0.9% sodium chloride. Results demonstrate that: (1) felid spermatozoa are resistant to hypertonic stress; (2) sperm motility is more sensitive to changes in osmolality than membrane integrity; and (3) removal of cryoprotectant in multiple steps with an isotonic solution minimizes loss of sperm motility and membrane disruption in both normospermic and teratospermic males.     

Some mechanisms of salt tolerance in crop plants

Summary In the first part of this review the main features of salt tolerance in higher plants are discussed. The hypothesis of intracellular compartmentation of solutes is used as a basis for models of tolerance mechanisms operating in roots and in leaves. Consideration is given to the implications of the various mechanisms for the yield potential of salt-tolerant crop plants.Some work on the more salt-tolerant members of the Triticeae is then described. The perennial speciesElytrigia juncea andLeymus sabulosus survive prolonged exposure to 250 mol m^–3 NaCl, whereas the annual Triticum species are severely affected at only 100 mol m^–3 NaCl. In the perennial species the tissue ion levels are controlled within narrow limits. In contrast, the more susceptible wheats accumulate far more sodium and chloride than is needed for osmotic adjustment, and the effects of salt stress increase with time of exposure.Two different types of salt tolerance are exhibited in plants capable of growing at high salinities. In succulent Chenopodiaceae, for example, osmotic adjustment is achieved mainly by accumulation of high levels of sodium and chloride in the shoots, accompanied by synthesis of substantial amounts of the compatible solute glycinebetaine. This combination of mechanisms allows high growth rates, in terms of both fresh and dry weight. At the opposite end of the spectrum of salt tolerance responses are the halophytic grasses, which strictly limit the influx of salts into the shoots, but suffer from very much reduced growth rates under saline conditions. Another variation is shown in those species that possess salt glands. The development and exploitation of crop plants for use on saline soils is discussed in relation to the implications of these various mechanisms.     

丛枝菌根根外菌丝网络形成过程中的时间效应及植物介导作用

以豆科植物紫花苜蓿为试验材料,应用三室(供体室-间隔室-受体室)培养系统,研究在供体和受体紫花苜蓿根系之间菌丝网络形成的时间效应以及间隔室中不同植物对菌丝网络建成的介导作用.第一个试验在供体和受体植物生长8、10、12、14周之后进行收获以检验菌丝网络形成的时间效应;第二个试验则在间隔室分别种植紫花苜蓿、羊草和独行菜,以考察菌根依赖性不同的植物对菌丝网络形成的介导作用.试验结果显示:(1)接种丛枝菌根真菌的供体紫花苜蓿根系能够形成良好的菌根共生,其外延菌丝可穿过尼龙网和间隔室侵染受体植物根系;植物生长8周后,在受体植物根系检测到菌根侵染,证实供体和受体植物间形成了根间菌丝网络;10周后,尽管供体室和受体室植物的侵染率已无差异,但二者的生物量和地上部磷浓度差异却加大,表现出菌丝网络对植物种内竞争影响的不对称性.(2)试验条件下,不同介导植物对受体植物的菌根侵染及生物量均无明显影响,但显著降低了供体植物生物量和地上部磷浓度;间隔室无介导植物或种植独行菜时,受体植物地上部和根系生物量显著低于供体植物,而当介导植物为紫花苜蓿和羊草时,受体和供体植物生物量无显著差异.研究表明,植物根间菌丝网络的形成受时间和介导植物的影响,同时也具有调节植物间资源分配和植物相互作用的功能.