The influence of silicon application on growth and photosynthesis response of salt stressed grapevines (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L.)

The influences of silicon (Si) on parameters, such as plant growth, pigment contents, photosynthesis, chlorophyll fluorescence, soluble sugar and starch concentration, and some cell ultra-structures, were investigated in grapevines under salt stress. Compared with the control, the treatment with 100 mM NaCl dramatically inhibited the growth of grapevines and greatly decreased the content of pigments. Silicon treatment in the absence of salt had negative effects in most observed parameters. However, the addition of Si under salt stress improved all growth parameters and increased the pigments and photosynthetic rates compared with the NaCl treatment. Furthermore, investigation of chlorophyll fluorescence, soluble sugars, starch concentration and cell ultra-structure indicated that photosynthesis in the NaCl treatment decreased. The supplement of silicon mitigated the inhibited photosynthesis caused by NaCl, and increased the maximum yield and potential photochemical efficiency of the photochemical reactions in photosystem II. On the other hand, the addition of exogenous Si and NaCl also increased the concentration of soluble sugars and starch, and influenced ultra-structural changes. It is possible that silicon might play an important role in protecting photosynthetic machinery from damage and improving the salt-tolerance of the grape by increasing the concentration of soluble sugars and starch.     

Separate and combined effects of silicon and selenium on salt tolerance of wheat plants

Soil salinity is the leading global abiotic stress which limits agricultural production with an annual increment of 10%. Therefore; a pot experiment was conducted with the aim to alleviate the salinity effects on wheat seedlings through exogenous application of silicon (Si) and selenium (Se). Treatments included in the study were viz. (Ck) control (no NaCl nor Si and Se added), only salinity (50 mM NaCl), salinity + Si (50 mM NaCl with 40 mM Si), salinity + Se (50 mM NaCl with 40 mM Se) and salinity + Si + Se (50 mM NaCl + 40 mM Si + 40 mM Si). The salt stress impaired the growth (root and shoot dry weight, root: shoot ratio, seedlings biomass), water relations, photosynthetic attributes, transpiration rate and chlorophyll contents of wheat seedlings. Nonetheless, the foliar application of Si and Se alone and in combination improved the growth, water relations, photosynthetic attributes, transpiration rate and chlorophyll contents of wheat seedlings under stressed conditions. Moreover, an increase in antioxidant enzyme activity and accumulation of osmo-protectants (proline, soluble protein and soluble sugar) was noted under stressed conditions, which was more pronounced in wheat seedling which experienced combined application of Si and Se. To conclude that, foliar application of Si alone mitigated the adverse effect of salinity, while the combined application of Si and Se was proved to be even more effective in alleviating the toxic effects of salinity stress on wheat seedlings.     

Effect of salinity on seed germination,ion content and photosynthesis of cotyledons in halophytes or xerophyte growing in Central Asia

Aims We investigated the impact of salinity on seed germination, chlorophyll content, chloroplast structure and photosynthesis of the green embryos in desiccated seeds of the xerophyte Haloxylon persicum, xero-halophyte Haloxylon ammodendron and euhalophyte Suaeda physophora.Methods Seeds of H. persicum, H. ammodendron and S. physophora were collected from natural environment in Fukang, Xinjiang province. Pretreatment with 700 mM NaCl was carried out to stimulate the natural 'seed priming'; we analyzed the joint effect of salinity and different species on germination physiology and cotyledonal structure and photosynthetic function changes during germination and recovery stage.Important findings We found that seeds did not suffer ion toxicity for the two halophytes H. ammodendron and S. physophora, as evidenced by the high final germination after ungerminated seeds pretreated with 700 mM NaCl were transferred to distilled water, but the final germination of the xerophyte H. persicum was significantly lower than that of control. The Na + concentration in embryos increased under salinity for all species, while K + concentration decreased by salinity only for H. persicum and H. ammodendron, i.e. the concentration of K + in embryos of H. persicum and H. ammodendron decreased by 36% and 46%, respectively. For all species, whether dry intact seeds or cotyledons of dry seeds imbibed in deionized water and NaCl solution, had high chlorophyll content. Treatment with NaCl also caused chloroplast thylakoids to swell and chlorophyll content to decrease in seeds of H. persicum, but no significant change was observed in the more salt-tolerant species S. physophora and H. ammodendron. Fluorescence measurement showed that 700 mM NaCl decreased the Fv/Fm ratio of cotyledons in seeds for all species, especially for H. persicum and H. ammodendron. Photosynthetic oxygen releasing was detected from the seeds that were moistened with distilled water and 700 mM NaCl for 6 or 24 h and from the seeds that were initially moistened with 700 mM NaCl in darkness for 10 days, then transferred to distilled water for another 6 and 24 h. The results indicated that the chlorophyll in cotyledon of desiccated seed had photosynthetic function in early germination stage, even under high-saline condition. In addition, the photosynthesis of chlorophyll in the embryonic cotyledons of desiccated seeds during germination was similar to that in leaves of young seedlings for all species. In conclusion, the chloroplasts of the two halophytes were more salt resistant compared with the xerophyte H. persicum. The photosynthetic function of chlorophyll in cotyledons of mature seeds may be ecologically important for seedling development in early stage for plants growing in extremely saline or arid environments.     

5-Aminolevulinic acid improves photosynthetic gas exchange capacity and ion uptake under salinity stress in oilseed rape (Brassica napus L.)

Salinity is one of the major constraints in oilseed rape (Brassica napus L.) production. One of the means to overcome this constraint is the use of plant growth regulators to induce plant tolerance. To study the plant response to salinity in combination with a growth regulator, 5-aminolevulinic acid (ALA), oilseed rape plants were grown hydroponically in greenhouse conditions under three levels of salinity (0, 100, and 200 mM NaCl) and foliar application of ALA (30 mg/l). Salinity depressed the growth of shoots and roots, and decreased leaf water potential and chlorophyll concentration. Addition of ALA partially improved the growth of shoots and roots, and increased the leaf chlorophyll concentrations of stressed plants. Foliar application of ALA also maintained leaf water potential of plants growing in 100 mM salinity at the same level as that of the control plants, and there was also an improvement in the water relations of ALA-treated plants growing in 200 mM. Net photosynthetic rate and gas exchange parameters were also reduced significantly with increasing salinity; these effects were partially reversed upon foliar application with ALA. Sodium accumulation increased with increasing NaCl concentration which induced a complex response in the macro-and micronutrients uptake and accumulation in both roots and leaves. Generally, analyses of macro- (N, P, K, S, Ca, and Mg) and micronutrients (Mn, Zn, Fe, and Cu) showed no increased accumulation of these ions in the leaves and roots (on dry weight basis) under increasing salinity except for zinc (Zn). Foliar application of ALA enhanced the concentrations of all nutrients other than Mn and Cu. These results suggest that under short-term salinity-induced stress (10 days), exogenous application of ALA helped the plants improve growth, photosynthetic gas exchange capacity, water potential, chlorophyll content, and mineral nutrition by manipulating the uptake of Na⁺.     

Effects of NaCl on physiology and leaf ultrastructure in the halophyte Kalidium foliatum

We studied the effects of salt exposure on the growth and physiology of the xerohalophyte Kalidium foliatum. Plants were grown for 21 days under greenhouse conditions in the presence of between 0 and 500 mM NaCl. Optimum root activity and chlorophyll content were observed at 200 mM and 300 mM NaCl, respectively. Superoxide production increased with increasing NaCl concentration throughout the studied range. These results indicate that moderate salinity has a stimulating effect on the growth of K. foliatum. NaCl also induced leaf ultra‐structural changes. The chloroplasts and cell nuclei all displayed an elliptic shape between 0 and 300 mM NaCl. However, they appeared to be swollen between 400 and 500 mM NaCl. The mitochondria were unaffected by salinity, and all organelles remained intact under NaCl stress. These results provide insights into the mechanism of salt tolerance in K. foliatum.     

Growth,photosynthesis and ion balance of sesame (Sesamum indicum L.) genotypes in response to NaCl concentration in hydroponic solutions

A hydroponic, greenhouse experiment was conducted to assess the effects of NaCl on growth, gas-exchange parameters, chlorophyll (Chl) content, and ion distribution in seven sesame (Sesamum indicum L.) genotypes (Ardestan, Varamin, Naz-Takshakhe, Naz-Chandshakhe, Oltan, Yekta, Darab). The plants were grown in 4-L containers and subjected to varying levels of salinity (0, 30, and 60 mM NaCl). After 42 days, salt treatments induced decreases of plant fresh and dry mass, total leaf area, and plant height in all genotypes. Increasing NaCl concentration caused significant, genotypedependent decrease in the net photosynthetic rate, stomatal conductance, Chl content, and maximum quantum efficiency of photosystem II, while it increased the intercellular CO₂ concentration. Based on the dry matter accumulation under salinity, the genotypes were categorized in two groups, i.e., salt-tolerant and salt-sensitive. The impact of salt on plant ion concentrations differed significantly among the sesame genotypes and between both two groups. The plant Na⁺ concentrations were significantly lower in Ardestan, Darab, and Varamin genotypes than those found in the remaining genotypes. The highest plant K⁺ and Ca²⁺ concentrations together with the lowest Na⁺/K⁺ and Na⁺/Ca²⁺ ratios were observed in Ardestan, Varamin, and Darab genotypes. Our results indicated the presence of differences in salt response among seven sesame genotypes. It suggested that growth and photosynthesis could depend on ion concentrations and ratios in sesame.     

Salt tolerance of Hibiscus hamabo seedlings: a candidate halophyte for reclamation areas

In order to evaluate the salinity tolerance of Hibiscus hamabo Siebold & Zuccarini (Malvaceae), a candidate halophyte for reclamation areas, we analyze the effects of NaCl concentration, ranging from 0 to 500?mM, on the morphological, photosynthetic and chlorophyll fluorescent traits of this species. The optimal concentration for the germination of H. hamabo was 25?mM NaCl, and the optimal concentration for the survival and growth of H. hamabo ranged from 5 to 10?mM NaCl. Growth traits of H. hamabo at 25?mM, including the plant height, canopy diameter, number of leaves and width of the largest leaf, showed no statistical differences from the control. Net photosynthetic rate, stomatal conduction, light utilization efficiency, water utilization efficiency, maximal photosynthetic rate, light saturation point and chlorophyll content were the highest at 7.5?mM NaCl. F _v/F _m and F _v/F ₀ at 5 and 7.5?mM were significantly higher than the others, while F ₀ was significantly lower. F _m and F _v at NaCl concentrations ranging from 2.5 to 10?mM were significantly higher than the others. Pearson correlation analysis showed that the chlorophyll content, maximal photosynthetic rate and light saturation point were significantly positively correlated with the number of leaves, while F ₀ was significantly negatively correlated with the width of the largest leaf. Light compensation point was significantly negatively correlated with plant height, leaf number, width of the largest leaf and canopy diameter, and might be a good indicator for the salt tolerance of H. hamabo.     

Salt stress and fluctuating light have separate effects on photosynthetic acclimation,but interactively affect biomass

In nature, soil salinity and fluctuating light (FL) often occur concomitantly. However, it is unknown whether salt stress interacts with FL on leaf photosynthesis, architecture, biochemistry, pigmentation, mineral concentrations, as well as whole-plant biomass. To elucidate this, tomato (Solanum lycopersicum) seedlings were grown under constant light (C, 200 μmol m⁻² s⁻¹) or FL (5–650 μmol m⁻² s⁻¹), in combination with no (0 mM NaCl) or moderate (80 mM NaCl) salinity, for 14 days, at identical photoperiods and daily light integrals. FL and salt stress had separate effects on leaf anatomy, biochemistry and photosynthetic capacity: FL reduced leaf thickness as well as nitrogen, chlorophyll and carotenoid contents per unit leaf area, but rarely affected steady-state and dynamic photosynthetic properties along with abundance of key proteins in the electron transport chain. Salt stress, meanwhile, mainly disorganized chloroplast grana stacking, reduced stomatal density, size and aperture as well as photosynthetic capacity. Plant biomass was affected interactively by light regime and salt stress: FL reduced biomass in salt stressed plants by 17%, but it did not affect biomass of non-stressed plants. Our results stress the importance of considering FL when inferring effects of salt-stress on photosynthesis and productivity under fluctuating light intensities.     

高温和低湿对干热河谷7个植被恢复树种光合参数的影响

采用人工气候室控制环境条件,研究了高温（30℃和40℃）对印楝（Azadirachta indica A．Juss．）、木豆[Cajanus cajan（Linn．）Huth]、赤桉（Eucalyptus camaldulensis Dehn．）、蓝桉（E．globulus Labillardiere）、柠檬桉（E．citriodoraHook．）、大叶相思（Acacia auriculiformis A．Cunn．）和麻风树（Jatropha curcas Linn．）7个干热河谷植被恢复树种幼苗叶片光合参数的影响,以及低湿条件对麻风树幼苗叶片光合参数的影响,并对高温及低湿条件下各树种叶片光合参数与叶片含水量的关系进行了探讨。结果表明：在高温条件下,供试树种叶片的净光合速率（Pn）和Fv／Fm值均随叶片含水量的提高逐渐增加,但在40℃条件下各树种的Pn以及刚nn值均明显降低,表明叶片含水量高有利于各树种叶片Pn和n／Fm的提高,而40℃高温则对其Pn和Fv／Frn有明显抑制作用。在非干旱条件下,高温对各树种幼苗的Pn、气孔导度（Gs）、胞间c0：浓度（ci）和蒸腾速率（Tr）均有不同程度影响。在40℃条件下,供试树种中印楝和赤桉幼苗的Pn降幅最小;大叶相思、蓝桉和木豆幼苗的Gs明显增加;各树种幼苗的ci均明显提高;除印楝外,其他6个树种幼苗的Tr明显加剧且叶片水分利用效率降低。在叶片含水量较高的状况下,供试7个树种中印楝和赤桉幼苗的FV／Fm值受高温的影响较小。在空气相对湿度20％的条件下,麻风树幼苗的Pn、Cs、ci及Tr均明显降低,且均随叶片含水量的提高而增加,表明叶片含水量下降是麻风树幼苗光合作用减弱的重要影响因素。研究结果表明：干热河谷地区的高温引起的植物光合限制以非气孔因素为主导;在供试的7个树种中,印楝和赤桉对干热河谷高温干旱生境的适应或忍耐能力较强。     

Intrinsic water use efficiency controls the adaptation to high salinity in a semi-arid adapted plant,henna (Lawsonia inermis L.)

Adaptation to salinity of a semi-arid inhabitant plant, henna, is studied. The salt tolerance mechanisms are evaluated in the belief that gas exchange (water vapor and CO₂) should play a key role on its adaptation to salt stress because of the strong evaporation conditions and soil water deficit in its natural area of distribution. We grow henna plants hydroponically under controlled climate conditions and expose them to control (0 mM NaCl), and two levels of salinity; medium (75 mM NaCl) and high (150 mM NaCl). Relative growth rate (RGR), biomass production, whole plant and leaf structure and ultrastructure adaptation, gas exchange, chlorophyll fluorescence, nutrients location in leaf tissue and its balance in the plant are studied. RGR and total biomass decreased as NaCl concentration increased in the nutrient solution. At 75 mM NaCl root biomass was not affected by salinity and RGR reached similar values to control plants at the end of the experiment. At this salinity level henna plant responded to salinity decreasing shoot to root ratio, increasing leaf specific mass (LSM) and intrinsic water use efficiency (iWUE), and accumulating high concentrations of Na⁺ and Cl⁻ in leaves and root. At 150 mM NaCl growth was severely reduced but plants reached the reproductive phase. At this salinity level, no further decrease in shoot to root ratio or increase in LSM was observed, but plants increased iWUE, maintaining water status and leaf and root Na⁺ and Cl⁻ concentrations were lower than expected. Moreover, plants at 150 mM NaCl reallocated carbon to the root at the expense of the shoot. The effective PSII quantum yield [Y(II)] and the quantum yield of non-regulated energy dissipation [Y(NO)] were recovered over time of exposure to salinity. Overall, iWUE seems to be determinant in the adaptation of henna plant to high salinity level, when morphological adaptation fails.     

Abscisic acid, indole-3-acetic acid and mineral–nutrient changes induced by drought and salinity in longan (Dimocarpus longan Lour.) plants

Longan species (Dimocarpus longan Lour.) exhibit a high agronomic potential in many subtropical regions worldwide; however, little is known about its responses to abiotic stress conditions. Drought and salinity are the most environmental factors inducing negative effects on plant growth and development. In order to elucidate the responses of longan to drought and salinity, seedlings were grown under conditions of drought and salt stresses. Drought was imposed by suspending water supply leading to progressive soil dehydration, and salinity was induced using two concentrations of NaCl, 100 and 150 mM in water solution, for 64 days. Data showed that salt concentrations increased foliar abscisic acid (ABA) and only 150 mM NaCl reduced indole-3-acetic acid (IAA) and increased proline levels. NaCl treatments also increased Na⁺ and Cl^? content in plant organs proportionally to salt concentration. Drought increased leaf ABA but did not change IAA concentrations, and also increased proline synthesis. In addition, drought and salt stresses reduced the photosynthesis performance; however, only drought decreased leaf growth and relative leaf water content. Overall, data indicate that under severe salt stress, high ABA accumulation was accompanied by a reduction of IAA levels; however, drought strongly increased ABA but did not change IAA concentrations. Moreover, drought and high salinity similarly increased (or maintained) ion levels and proline synthesis. Data also suggest that ABA accumulation may mitigate the impact of salt stress through inducing stomatal closure and delaying water loss, but did not mediate the effects of long-term drought conditions probably because leaves reached a strong dehydration and the role of ABA at this stage was not effective to detain leaf injuries.     

Physiological response of the facultative halophyte,Aeluropus littoralis,to different salt types and levels

The present study investigated the effects of NaCl, KCl and Na₂SO₄ salts on the C₄ excreting halophyte Aeluropus littoralis in relation to growth, mineral status and photosynthesis in greenhouse conditions. Plantlets were subjected to five salinity levels: 0, 200, 400, 600 and 800 mM for 30 days. Growth decreased progressively with salinity increase, its reduction might be correlated with the high sodium (and/or chloride) accumulation in plant tissues, the decrease of leaf water status and the decline of the net photosynthetic rate and the intrinsic water use efficiency. Na₂SO₄ appeared more toxic than KCl and NaCl, especially at 200 mM. At 200 mM, Na₂SO₄ reduced plant growth by 61% while for other salt forms, the reductions were less than 20%. At this salt level, stomatal conductance showed a consistent pattern with plant growth and could adequately explain the variations between the effects of the three salt types.     

Salt tolerance of the annual halophyte <Emphasis Type="Italic">Cakile maritima</Emphasis> as affected by the provenance and the developmental stage

Though halophytes are naturally adapted to salinity, their salt-tolerance limits are greatly influenced by their provenance and developmental stage. In the present study, physio-biochemical responses of two Tunisian ecotypes of the oilseed coastal halophyte Cakile maritima (Brassicaceae) to salinity (0–400 mM NaCl) were monitored during germination and vegetative growth stages. Tabarka and Jerba seeds were collected from humid or arid climatic areas, respectively. Plant response to salinity appeared to depend on the ecotype and salinity levels. Increasing salinity inhibited germination process. Jerba seeds were found to be more salt tolerant than the Tabarka ones. At the autotrophic stage of growth and under salt-free conditions, Jerba was less productive than Tabarka (in terms of dry matter accumulation), but plant biomass production and leaf expansion (area and number) of the former ecotype were progressively improved by 100 mM NaCl, as compared to the control. In contrast, at the same salt concentration, these parameters decreased under increasing salinity in Tabarka (salt sensitive). Leaf chlorophyll content was reduced at severe salinity, but this effect was more conspicuous in the sensitive Tabarka plants. Na⁺ contents in the Jerba and Tabarka leaves collected from the 400 mM NaCl-treated plants were 17- and 12-fold higher than in the respective controls. This effect was accompanied by a significant reduction in the leaf K⁺, Mg²⁺ and Ca²⁺ contents, especially in the salt-treated Tabarka. A significant accumulation of proline and soluble carbohydrates in leaves was found during the period of intensive leaf growth. These organic compounds likely play a role in leaf osmotic adjustment and in protection of membrane stability at severe salinity.     

盐胁迫对两种淫羊藿属植物生长及各器官总黄酮含量的影响

采用不同浓度NaCl(0、100、200、300和500 mmol/L)的Hoagland's培养液处理两种淫羊藿属植物--淫羊藿、箭叶淫羊藿幼苗,处理30 d后分别测定其株高、叶表面积、干物质生物量以及根、茎、叶的总黄酮含量,以明确淫羊藿属两种药用植物的抗盐特性.结果显示:(1)盐胁迫对淫羊藿和箭叶淫羊藿的生长均有影响,随着NaCl处理浓度的增加,淫羊藿、箭叶淫羊藿的株高和叶表面积均逐渐显著减小;各器官干物质生物量逐渐降低,但淫羊藿的干物质下降量较小(不显著),且同一处理下淫羊藿的生物量明显小于箭叶淫羊藿.(2)随着NaCl胁迫浓度的增加,除淫羊藿茎的总黄酮含量一直呈下降趋势外,淫羊藿根、叶和箭叶淫羊藿根、茎、叶均呈现在低浓度范围内总黄酮含量增加,且箭叶淫羊藿的含量高于淫羊藿;而在高浓度盐胁迫下,其总黄酮含量均呈下降的趋势,且淫羊藿的含量高于箭叶淫羊藿.研究表明,淫羊藿的抗盐性明显高于箭叶淫羊藿,适于高盐土壤环境种植,但在低盐环境条件下,种植箭叶淫羊藿可显著提高总黄酮产量并提高经济效益.     

Adequate S supply protects barley plants from adverse effects of salinity stress by increasing thiol contents

As the salt-affected areas are expected to increase substantially in subsequent years, the impact of salinity on plant growth and yield is likely to increase. One of the first consequences of plant exposure to high saline concentrations is the formation of reactive oxygen species (ROS). In order to allow adjustment of the cellular redox state, plant antioxidative system has to be activated. This system involves several enzymes and compounds, as the sulphur-containing metabolite glutathione (GSH). Therefore, our aim was to determine whether adequate sulphur nutrition might alleviate the adverse effects of salt stress on barley plants grown in the presence of different sulphate application rate and exposed to 100 mM NaCl, by studying differences in growth parameters, lipid peroxidation, sulphate and thiol accumulation and sulphur assimilation pathway. In salt-treated plants, an adequate sulphur supply allows adequate GSH synthesis (high-thiol concentration) thus avoiding the effects of ROS on photosynthetic functions (no effect on both chlorophyll and protein content), whereas in S-deficient plants, salt stress leads to excess ROS production that induces stress and plants showed reduction of photosynthetic efficiency (loss of chlorophyll and protein contents). As thiol levels are more abundant in S-sufficient plants than in those S-deficient, one might expect that S-sufficient plants are more able to remove the harmful effects of high salinity. The comparison of malondialdehyde levels between +S and ?S salt-treated plants strongly supports this idea. In conclusion, we found that plant sulphur nutritional status plays a key role in the metabolic modifications necessary to cope with salt stress.     

Salt tolerance strategies of Lygeum spartum L.: A new fodder crop for Algerian saline steppes

Lygeum spartum L. is a native species in Algerian salt steppes. The plant is of interest because of its tolerance to environmental stresses and its use as a fodder grass for livestock in low-rainfall Mediterranean areas. Nevertheless, plant responses of this plant to salt stress are still not investigated in detail. Therefore, L. spartum L. was grown in hydroponic conditions to investigate the effect of salinity (0, 30, 60 and 90 mM NaCl) on growth, water relations, gas exchange, leaf chlorophyll concentration, glycine betaine and mineral uptake. Plant growth was reduced at 60 and 90 mM NaCl, but was not significantly lower than in the controls at 30 mM NaCl. Sodium (Na⁺), chloride (Cl⁻) and glycine betaine contents in plants increased, whereas calcium (Ca²⁺), potassium (K⁺), relative water content (RWC), root hydraulic conductivity (L₀) and chlorophyll content decreased with an increase in salinity. Water potential (Ψ_ω) and osmotic potential (Ψ_π) of plants decreased with an increase in salinity. No change was observed in the turgor potential (Ψ_τ). Photosynthesis parameters (CO₂ assimilation rate, stomatal conductance and transpiration rate) did not change significantly at 30 mM NaCl, as compared to the control. Higher salt levels impaired photosynthetic capacity of L. spartum mainly via a stomatal limitation leading to a low CO₂ assimilation rate. This might be a consequence of the reduced whole-plant hydraulic conductivity under salt stress. The results demonstrated that L. spartum L. can be characterised as a moderately salt-tolerant species. Salt tolerance in this species is achieved by appropriate osmotic adjustment involving accumulation of ions and glycine betaine. At high salinities, growth reduction probably occurs as a result of high concentrations of Na⁺ and Cl⁻ and their interference with other ions such as Ca²⁺ and K⁺. This plant can be used locally as a fodder for livestock and to stabilise sand dunes and rehabilitate salt soils.     

Varied tolerance to NaCl salinity is related to biochemical changes in two contrasting lettuce genotypes

Salt stress perturbs a multitude of physiological processes such as photosynthesis and growth. To understand the biochemical changes associated with physiological and cellular adaptations to salinity, two lettuce varieties (Verte and Romaine) were grown in a hydroponics culture system supplemented with 0, 100 or 200 mM NaCl. Verte displayed better growth under 100 mM NaCl compared to Romaine, but both genotypes registered relatively similar reductions in growth under 200 mM NaCl treatment. Both varieties showed differences in net photosynthetic activity in the absence of salt and 8 days after salt treatment. These differences diminished subsequently under prolonged salt stress (14 days). Verte showed enhanced leaf proline and restricted total cations especially Na⁺, lesser malondialdehyde (MDA) formation and lignification in the roots under 100 mM NaCl salinity. Membrane damage estimated by electrolyte leakage increased with elevated salt concentrations in roots of both varieties, but Verte had significantly lower electrolyte leakage relative to Romaine under 100 mM NaCl. Moreover, Verte also accumulated greater levels of carotenoids under increasing NaCl concentrations compared to Romaine. Taken together, these findings suggest that the greater tolerance of Verte to 100 mM NaCl is related to the more restricted accumulation of total cations and toxic Na⁺ in the roots and enhanced levels of antioxidative metabolites in root and leaf tissue.     

Leaf gas exchange,water relations,nutrient content and growth in citrus and olive seedlings under salinity

The effects of salinity on growth, leaf nutrient content, water relations, gas exchange parameters and chlorophyll fluorescence were studied in six-month-old seedlings of citrus (Citrus limonia Osbeck) and rooted cuttings of olive (Olea europaea L. cv. Arbequina). Citrus and olive were grown in a greenhouse and watered with half strength Hoagland’s solution plus 0 or 50 mM NaCl for citrus, or plus 0 or 100 mM NaCl for olive. Salinity increased Cl⁻ and Na⁺ content in leaves and roots in both species and reduced total plant dry mass, net photosynthetic rate and stomatal conductance. Decreased growth and gas exchange was apparently due to a toxic effect of Cl⁻ and/or Na⁺ and not due to osmotic stress since both species were able to osmotically adjust to maintain pressure potential higher than in non-salinized leaves. Internal CO₂ concentration in the mesophyll was not reduced in either species. Salinity decreased leaf chlorophyll a content only in citrus.     

Role of Salicylic Acid in Promoting Salt Stress Tolerance and Enhanced Artemisinin Production in Artemisia annua L.

In the present investigation, the role of salicylic acid (SA) in inducing salinity tolerance was studied in Artemisia annua L., which is a major source of the antimalarial drug artemisinin. SA, when applied at 1.00 mM, provided considerable protection against salt stress imposed by adding 50, 100, or 200 mM NaCl to soil. Salt stress negatively affected plant growth as assessed by length and dry weight of shoots and roots. Salinity also reduced the values of photosynthetic attributes and total chlorophyll content and inhibited the activities of nitrate reductase and carbonic anhydrase. Furthermore, salt stress significantly increased electrolyte leakage and proline content. Salt stress also induced oxidative stress as indicated by the elevated levels of lipid peroxidation compared to the control. A foliar spray of SA at 1.00 mM promoted the growth of plants, independent of salinity level. The activity of antioxidant enzymes, namely, catalase, peroxidase, and superoxide dismutase, was upregulated by salt stress and was further enhanced by SA treatment. Artemisinin content increased at 50 and 100 mM NaCl but decreased at 200 mM NaCl. The application of SA further enhanced artemisinin content when applied with 50 and 100 mM NaCl by 18.3 and 52.4%, respectively. These results indicate that moderate saline conditions can be exploited to obtain higher artemisinin content in A. annua plants, whereas the application of SA can be used to protect plant growth and induce its antioxidant defense system under salt stress.     

Salt impact on photosynthesis and leaf ultrastructure of <Emphasis Type="Italic">Aeluropus littoralis</Emphasis>

The effects of salinity (400 mM NaCl) on growth, biomass partitioning, photosynthesis, and leaf ultrastructure were studied in hydroponically grown plants of Aeluropus littoralis (Willd) Parl. NaCl produced a significant inhibition of the main growth parameters and a reduction in leaf gas exchange (e.g. decreased rates of photosynthesis and stomatal conductance). However, NaCl salinity affected neither the composition of photosynthesis pigments nor leaf water content. The reduction in leaf gas exchange seemed to correlate with a decrease in mesophyll thickness as well as a severe disorganisation of chloroplast structure, with misshapen chloroplasts and dilated thylakoid membranes. Conspicuously, mesophyll chloroplasts were more sensitive to salt treatment than those of bundle sheath cells. The effects of NaCl toxicity on leaf structure and ultrastructure and the associated physiological implications are discussed in relation to the degree of salt resistance of A. littoralis.