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.     

Enhancement of phenylethanoid glycosides biosynthesis in cell cultures of <Emphasis Type="Italic">Cistanche deserticola</Emphasis> by osmotic stress

The effect of osmotic stress on cell growth and phenylethanoid glycosides (PeGs) biosynthesis was investigated in cell suspension cultures of Cistanche deserticola Y. C. Ma, a desert medicinal plant grown in west region of China. Various initial sucrose concentrations significantly affected cell growth and PeGs biosynthesis in the suspension cultures, and the highest dry weight and PeGs accumulation reached 15.9 g l⁻¹-DW and 20.7 mg g⁻¹-DW respectively at the initial osmotic stress of 300 mOsm kg⁻¹ where the sucrose concentration was 175.3 mM. Stoichiometric analysis with different combinations of sucrose and non-metabolic sugar (mannitol) or non-sugar osmotic agents (PEG and NaCl) revealed that osmotic stress itself was an important factor for enhancing PeGs biosynthesis in cell suspension cultures of C. deserticola. The maximum PeGs contents of 26.9 and 23.8 mg g⁻¹-DW were obtained after 21 days at the combinations of 87.6 mM sucrose with 164.7 mM mannitol (303 mOsm kg⁻¹) or 20 mM PEG respectively, which was higher than that of C. deserticola cell cultures grown under an initial sucrose concentration of 175.3 mM after 30 days. The stimulated PeGs accumulation in the cell suspension cultures was correlated to the increase of phenylalanine ammonium lyase (PAL) activity induced by osmotic stress.     

The ATP pool in relation to the production of glycerol and heat during growth of the halotolerant yeast Debaryomyces hansenii

In a study of the halotolerant yeast Debarymyces hansenii cultured in 4 mM and 2.7 M NaCl the intracellular ATP pool, the heat production, the oxygen uptake, and, in the high culture salinity also, the intracellular glycerol concentration were found to be correlated. The intracellular ATP in the 2.7 M NaCl culture had a constant concentration of 3.5 mM ATP during the second half of the lag phase, while in 4 mM NaCl it rose to a maximum of 3.1 mM during the late log phase. The intracellular glycerol concentration in 2.7 M NaCl was about 1.3M during the entire exponential growth phase. Sine the glycerol concentration of the medium was not more than 0.23 mM, glycerol must contribute to the osmotic balance of the cells in high salinity. The corresponding maximum values for the 4 mM NaCl culture were 0.16 M and 0.08 mM. The experimental enthalpy changes were approximately the same for the two salinities, viz. about-1200 kJ per mole consumed glucose. The Y _m-values for the 4 mM and 2.7 M NaCl cultures were 91 and 59, respectively, the difference being a consequence of the decreased efficiency of growth in high salinity.Abbreviations CFU colony-forming units - PCA perchloric acid - TCA trichloroacetic acid     

Provenance variation in tolerance of Melaleuca cajuputi trees to interactive effects of aluminum and salt

A future rise in sea level will expand areas of salt-affected acid sulfate soil, calling for studies on plant tolerance to combined aluminum (Al) and salt (NaCl) stress. We investigated random amplified polymorphic DNA (RAPD) profiles and tolerance to Al and NaCl alone and in combination in 14 Melaleuca cajuputi Powell provenances. Two-month-old seedlings were grown with or without 10 mM Al and/or 50 mM NaCl at pH 3.8 for 3 months. Plant growth was reduced mostly by combined Al and NaCl stress and then by NaCl and least by Al. Moreover, Al enhanced the effect of NaCl on growth and vice versa. There were significant differences in plant growth among provenances under all treatments; however, positive relationships were found among Al tolerance, NaCl tolerance, and combined Al and NaCl tolerance. Provenance variation in stress tolerance increases with the increasing levels of stress effect. Furthermore, NaCl tolerance tended to have a positive relationship with osmotic potential. Leaf sap K concentration was decreased by NaCl and increased by Al; however, provenances that were more tolerant to NaCl tended to have lower K concentrations. RAPD analysis also revealed genetic variation among provenances. These results suggest that the low tolerance to combined Al and NaCl stress in M. cajuputi is largely due to low tolerance to NaCl and the effect of interaction between Al and NaCl. Provenance variation in stress tolerance was significant and could be partly explained by the variation in genetic material and the ability of plants to reduce ion excess stress in their shoots.     

Responses of grass pea seedlings to salinity stress in in vitro culture conditions

Physiological and molecular mechanisms of adaptation to abiotic stresses of grass pea (Lathyrus sativus L.) are still poorly understood. Responses of four genotypes of grass pea to salinity stress in tissue culture conditions were investigated at early seedling growth stages. Salinity stress was induced in the agar media by adding 0, 50, 100 and 200 mM of NaCl. Germination and seedling emergence percentage was not significantly affected by 50 and 100 mM of NaCl. However, NaCl in 200 mM concentration lowered level of these parameters. Generally, exposure to NaCl stress significantly reduced length of grass pea seedling organs (root and shoot) but did not influence the content of dry weight in shoots and increased it in the roots in two cases. Increasing salt concentration decreased integrity of cellular membranes both in root and shoot tissues. Higher accumulation of phenolic compounds and significant changes in activity of antioxidant enzymes (peroxidase and catalase) were observed in the roots but not in the shoots. Similarly, the content of proline increased mostly in the roots from moderate (100 mM) salinity conditions. Adverse conditions did not resulted in alterations in photosynthetic pigments content of any tested genotypes. The better performance of shoots than roots may result from in vitro conditions in which experiments were conducted.

     

Plant growth and responses of antioxidants of <Emphasis Type="Italic">Chenopodium album</Emphasis> to long-term NaCl and KCl stress

The effects of long-term NaCl and KCl treatment on plant growth and antioxidative responses were investigated in Chenopodium album, a salt-resistant species widely distributed in semi-arid and light-saline areas of Xinjiang, China. Growth parameters [plant height, branch number, leaf morphology and chlorophyll (Chl) content], the level of oxidative stress [superoxide anion radical (O₂ ⁻), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) concentrations], activity of antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), peroxidase (POX)], the contents of non-enzymatic antioxidants [carotenoids (Car) and ascorbic acid (AsA)] and expression of selected genes were investigated. Plants were grown in the presence of 0, 50, and 300 mM NaCl or KCl for 2 months. Growth was stimulated by 50 mM NaCl or KCl, maintained stable at 300 mM NaCl, but was inhibited by 300 mM KCl. Three hundred mM NaCl did not affect O₂ ⁻, H₂O₂, MDA, Car and AsA, but increased the activities of SOD, CAT and POX compared to the controls. RT-PCR analysis suggested that expression of some genes encoding antioxidant enzymes could be induced during long-term salt stress, which was consistent with the enzyme activities. Treatment with 300 mM KCl was associated with elevated oxidative stress, and significantly decreased Car and AsA contents. These results suggest that an efficient antioxidant machinery is important for overcoming oxidative stress induced by treatment with high NaCl concentrations in C. album. Other strategies of ion regulation may also contribute to the differential tolerance to Na and K at higher concentrations.     

In vitro selection and identification of sweetpotato (<Emphasis Type="Italic">Ipomoea batatas</Emphasis> (L.) Lam.) plants tolerant to NaCl

In vitro selection of sweetpotato (Ipomoea batatas (L.) Lam.) plants tolerant to NaCl was achieved using embryogenic suspension cultures of sweetpotato cv. Lizixiang and gamma-ray induced mutation. Cell aggregates from embryogenic suspension cultures of Lizixiang were irradiated with 80 Gy gamma-ray, and 1 week after irradiation they were cultured in a selective medium containing 342 mM NaCl for in vitro selection. A total of 276 plants were regenerated from the irradiated 2,783 cell aggregates by a two-step in vitro selection procedure. After the regenerated plants were propagated into plant lines on the basal medium, they were cultured on the medium supplemented with 86, 171, 257 and 342 mM NaCl, respectively, in order to evaluate their in vitro salt tolerance. Of them 18 plant lines showed significantly higher in vitro salt tolerance than control plants. Proline and superoxide dismutase (SOD) were more accumulated in these 18 plant lines than in control plants when both were exposed to NaCl. Salt tolerance of the 18 plant lines was further evaluated with Hoalgland solution containing different concentrations of NaCl in a greenhouse. The results indicated that 3 of them had significantly better growth and rooting ability than the remaining 15 plant lines and control plants at 171 mM NaCl.     

Metabolic shift from secondary metabolite production to induction of anti-oxidative enzymes during NaCl stress in <Emphasis Type="Italic">Swertia chirata</Emphasis> Buch.-Ham.

Swertia chirata Buch.-Ham. is an endangered medicinal plant having high medicinal value. Present study was envisaged to understand in vitro induction of marker secondary metabolites using NaCl elicitation. 50 and 100 mM of NaCl concentrations were applied on 1-month-old static culture shoots. Plants were assessed for cellular damage, anti-oxidative enzymatic system and production of secondary metabolites. There was significant (p ≤ 0.05) increase in secondary metabolites at 50 mM NaCl without any cellular damage or induction of anti-oxidative enzymes. Initial increase in metabolic content of secondary metabolites was observed during 100 mM NaCl treatment, which falls back to normal levels at the seventh day. There was concurrent induction of scavenging enzymes during this period. Results suggest channelling of different defence strategies in response to differential NaCl treatment. Biochemical relationship between induction of anti-oxidative enzymes and production of secondary metabolites has further been discussed in light of physiological requirements.     

Adaptation of Chinese hamster ovary cells to high potassium ion-containing medium for enhancement of follicle-stimulating hormone production

In this study, a suspension culture of recombinant Chinese hamster ovary (CHO) cells producing follicle-stimulating hormone (FSH) was used to investigate the effects of potassium ion (K⁺) on cell growth and FSH production. Cell growth was significantly suppressed at a K⁺ concentration higher than 60 mM, but specific FSH productivity (q _FSH) was enhanced more than 2-fold compared to the value obtained at 4 mM K⁺. In an attempt to alleviate the cell growth suppression at a high K⁺ concentration, the cells were adapted at 60 mM K⁺ in a repeated batch mode. During adaptation, the growth rate increased from 0.010 to 0.020 h⁻¹, andq _FSH also gradually increased and reached 11.1 ng/(10⁶ cells h), which was even higher than that of the unadapted cells at 60 mM K⁺. The adapted cells showed a 2.6-fold increase in maximum FSH titer at 80 mM K⁺ compared to the unadapted cells at 4 mM K⁺. Taken together, these results demonstrate the potential of using culture media containing cells adapted to high K⁺ concentrations, for the enhancement of recombinant protein production.     

Effect of high sodium chloride concentrations on the pigment content and free-radical processes in corn seedlings leaves

The effect of sodium chloride on general morphometrical parameters of seedlings, and biochemical parameters in the leaves of corn seedlings was studied. Exposure to 100 and 200 mM NaCl slowed down the growth of stem and roots, whereas 100 and 200 mM NaCl during 24 h enhanced the concentration of chlorophylls, carotenoids, anthocyans, and thiobarbituric acid reactive substances. The decrease in protein carbonyl groups was found at 24-hour exposure to 200 mM salt. The treatment during 24, 48 and 72 h to 200 mM salt increased the level of total and high molecular mass thiols, whereas low molecular mass thiol content was by 20-25% higher at 48 h exposure to all used salt concentrations. The activity of guaiacol peroxidase was higher only at 24 h exposure to 100 and 200 mM salt, and catalase--at 50 mM during 48 h. At 72-hour exposure, catalase activity was by 27 and 41% higher in seedlings, exposed to 50 and 200 mM NaCl, respectively. Therefore, it is concluded the plant exposure to 50-200 mM salt initially developed oxidative stress, inducing adaptive response--an increase in antioxidant potential and efficiency of systems of energy production. That results in plant adaptation to unfavourable conditions.     

Restoration of Growth of Durum Wheat (Triticum durum var. waha) Under Saline Conditions Due to Inoculation with the Rhizosphere Bacterium Azospirillum brasilense NH and Extracts of the Marine Alga Ulva lactuca

Inoculation with the rhizosphere bacterium Azospirillum brasilense NH, originally isolated from salt-affected soil in northern Algeria, greatly enhanced growth of durum wheat (Triticum durum var. waha) under saline soil conditions. Important plant parameters like the rate of germination, stem height, spike length, dry weight of roots and shoots, chlorophyll a and b content, proline and total sugar contents, 1000-seed weight, seed number per spike, and weight of seeds per spike were measured. At salt stress conditions (160 and 200 mM NaCl) A. brasilense NH restored almost completely vegetative growth and seed production. The combination with extracts of the marine alga Ulva lactuca resulted in even more improved salt tolerance of durum wheat. Proline and total sugar accumulation, a sign of physiological plant stress under inhibitory salt conditions, was reduced in plants inoculated with A. brasilense NH with and without addition of algal extracts. Inoculation with the salt-sensitive A. brasilense strain Sp7 could not restore salt-affected plant growth at 200 mM NaCl. Furthermore, it could be demonstrated by fluorescence in situ hybridization and confocal laser scanning microscopy that A. brasilense NH is able to colonize roots of durum wheat endophytically under salt-stressed conditions. Thus, the salt-tolerant rhizobacterium A. brasilense NH could effectively provide alone or in combination with extracts of U. lactuca a promising solution to overcome salt inhibition which is a major threat hindering productive wheat cultivation in arid saline soils.     

Effect of varying NaCl doses on flavonoid production in suspension cells of Ginkgo biloba: relationship to chlorophyll fluorescence,ion homeostasis,antioxidant system and ultrastructure

Ginkgo suspension cells were used to investigate the mechanism that governs the shift between primary and secondary metabolism under NaCl elicitation. The production of three flavonol glycosides, chlorophyll fluorescence, ion content, the antioxidant system, and the cellular ultrastructure in the presence of NaCl doses from 5 to 175 mM were examined. At low salt doses (5–50 mM), cell growth and flavonol glycosides accumulation were stimulated without damaging cell structure or inducing oxidative stress by maintaining high K⁺ and chlorophyll content. At moderate salt doses (75–125 mM), the cells could withstand the salt stress without an impact on survival by changing internal cellular structure, maintaining high levels of K⁺ and Ca²⁺ and increasing anti-oxidative enzyme activities rather than flavonol glycosides to counteract the inhibition of the photosystem II, the accumulation of Na⁺ and hydrogen peroxide (H₂O₂) in the cells. This allowed cells to divert their metabolism from growth to defense-related pathways and tolerate NaCl stress. At higher salinity (150–175 mM), the cellular structure was damaged, and the high Na⁺ and low K⁺ content led to osmotic stress, and therefore, the stimulation of peroxidase (POD) and catalase (CAT) was not enough to cope with high H₂O₂ accumulation. The high production of flavonol glycosides may be a response of elicitation stimulation to serious damage at 175 mM NaCl. In conclusion, the use of 175 mM NaCl may be desirable for the induction of flavonol glycoside production in Ginkgo suspension cells.     

Osmotic Shock Augments Ethanol Stress in <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> MTCC 2918

Yeast cells sense and respond to hypertonicity. Saccharomyces cerevisiae MTCC 2918 was tested for its metabolic status in 1 M NaCl by cell viability analysis, intracellular glycerol content and total antioxidant capacity. Yeast cell viability was maximum in 1 M NaCl and 24 h addition of 1 M NaCl was effective in induction of hyperosmolarity. Increased glycerol contents in cells treated with salt indicated adaptation to osmotic stress with a maximum of 240.87 ± 0.38 mg/g dry weight (DW) at 72 h. The total antioxidant status with 1 M NaCl was 9.29 ± 0.39 mM/g DW at 96 h reflecting free radical quenching to overcome stress with increasing growth period. Considering that pre-adaptation to one type of stress evoked a protective response to other stress factors, we have attempted the cross adaptation of osmotic shock to high ethanol concentrations. In effect, we observed that osmotic shock lowered the cell survival by augmentation of cell toxicity by ethanol due to stress induction during exponential phase. Glycerol accumulation to an order of 470.27 ± 0.53 mg/g DW at 48 h in 1 M NaCl and 12% ethanol indicated that both stresses culminated in membrane disruption further leading to cell burst and contributed to the stress overload.     

Effects of NaCl salinity on growth, morphology, photosynthesis and proline accumulation of Salvinia natans

The effects of NaCl salinity on growth, morphology and photosynthesis of Salvinia natans (L.) All. were investigated by growing plants in a growth chamber at NaCl concentrations of 0, 50, 100 and 150 mM. The relative growth rates were high (ca. 0.3 d⁻¹) at salinities up to 50 mM and decreased to less than 0.2 d⁻¹ at higher salinities, but plants produced smaller and thicker leaves and had shorter stems and roots, probably imposed by the osmotic stress and lowered turgor pressure restricting cell expansion. Na⁺ concentrations in the plant tissue only increased three-fold, but uptake of K⁺ was reduced, resulting in very high Na⁺/K⁺ ratios at high salinities, indicating that S. natans lacks mechanisms to maintain ionic homeostasis in the cells. The contents of proline in the plant tissue increased at high salinity, but concentrations were very low (<0.1 μmol g⁻¹ FW), indicating a limited capacity of S. natans to synthesize proline as a compatible compound. The potential photochemical efficiency of PSII (F_v/F_m) of S. natans remained unchanged at 50 mM NaCl but was reduced at higher salinities, and the photosynthetic capacity (ETR_max) was significantly reduced at 50 mM NaCl and higher. It is concluded that S. natans is a salt-sensitive species lacking physiological measures to cope with exposure to high NaCl salinity. At low salinities salts are taken up and accumulate in old leaves, and high growth rates are maintained because new leaves are produced at a higher rate than for plants not exposed to salt.     

Effect of 24-epibrassinolide on biomass, growth and free proline concentration in Spirulina platensis (Cyanophyta) under NaCl stress

In this study, biomass, growth and free proline concentration were investigated in Spirulina platensis treated with different concentrations of NaCl (50, 100, 150, and 200 mM) and 24-epibrassinolide (24-epiBL) hormone (0.5, 1.0, and 3.0 μM) over 5 days. As a result of analysing the cultures under salinity stress, it was determined that biomass and growth rate decreased significantly, while proline concentration increased considerably under salinity stress. The increase in the concentration of proline suggests a role in response to NaCl stress. Among the cultures treated with different concentrations of 24-epiBL, maximum growth was determined at the cultures at 1.0 μM 24-epiBL. Algal growth was also greater at the 0.5 and 3.0 μM concentrations of 24-epiBL with respect to control cultures. With respect to control, 24-epiBL affected growth rate and biomass positively, but proline concentration did not change. Among the cultures supplied with different combinations of NaCl and 24-epiBL, growth rate increased in 150/0.5 and 150/3.0 mM/μM concentrations, but was maximal for the culture containing 150/1.0 mM/μM combination. The increase in algal growth suggests a role for 24-epiBL in partially alleviated to NaCl stress. These results suggest that 24-epiBL may have a protective role for S. platensis reducing the inhibitor effects of salinity stress.     

Partitioning of carbohydrates in salt-sensitive and salt-tolerant soybean callus cultures under salinity stress and its subsequent relief

Salt tolerant (R100) and sensitive (S100) cell lines of Glycine max (L.) that differ in their ability to accumulate sodium (Na) and chloride (Cl) under 100 mM salt stress, were used to compare the contribution of carbohydrates in osmotic adjustment. Calliwere exposed to a 100 mM NaCl concentrations for 12 days followed by 16 days of relief from stress to determine the effect of salinity changes of sugar content in the two cell lines. The salt-tolerant and the salt-sensitive cell lines differed in the time at which, and the type of sugar, that increased during salt stress. However, recovery in sugar content parameters during relief from stress were similar in the two cell lines. The concentration of glucose and fructose increased at a rate closely corresponding to the increase in fresh weight, while the concentration of sucrose decreased to the control level coincident with relatively rapid growth.     

Solutes Involved in Osmotic Adjustment to Increasing Salinity in Suspension Cells of Alternanthera philoxeroides Griseb

Cell recovery from osmotic stress was studied in suspension cell cultures from Alternanthera philoxeroides [Mart.] Griseb. Changes in different classes of cellular solutes were measured after cells were transferred from 0 to 200 mM NaCl (high salt) to obtain an integrated picture of the solute pools involved in osmotic adjustment. By 2 h, cellular [Na⁺] and [Cl⁻] had increased several-fold, potentially accounting for the osmotic adjustment that produced a rapid recovery of cell turgor. There was a four-fold increase in the concentration of quaternary ammonium compounds (QAC) by 12 h and a slower increase for several days afterward. Betaine aldehyde dehydrogenase (BADH) is required for synthesis of glycine betaine, a QAC produced by a range of organisms in response to osmotic stress. Western-blot analysis for BADH suggested that glycine betaine was a significant component of the QAC solutes. The amount of BADH was generally similar at different sampling times for control and high salt cells, unlike previous reports of stimulation by osmotic stress in intact plants of some species. Between 3 and 7 days after cell transfer to high salt, other organic solutes increased in concentration and [Na⁺] and [Cl⁻] decreased. In A. philoxeroides, high [Na⁺] and [Cl⁻] produce rapid osmotic adjustment but organic solutes apparently replace these potentially harmful inorganic ions after the recovery of turgor.     

Effects of NaCl and KNO3 concentrations on the abscisic acid content of Dunaliella sp. (Chlorophyta)

Abscisic acid (ABA) is a hormone which has a number of roles during the life cycle of a plant. We demonstrated the occurrence of ABA in a halotolerant green alga, Dunaliella sp. isolated from a salt pond near Adelaide, South Australia, using thin layer chromatography (TLC), high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). The variation of cellular ABA and protein content during the growth of an axenic clonal culture of Dunaliella sp. was investigated under different concentrations of NaCl and KNO₃.Experimental results can be summarized as follow: (1) ABA content was changed with the growth stage of culture: A rapid increase in ABA content was observed in the logarithmic phase. After this, the content rapidly decreased to very low values. (2) ABA content was also affected by the NaCl concentration. The content had a minimum value at the NaCl concentration (15%) where growth rate was maximal, and higher values at higher or lower concentrations of NaCl. (3) The ABA content also increased with decreasing nitrogen concentration of the medium.     

The effect of conditioned medium obtained from <Emphasis Type="Italic">Scenedesmus subspicatus</Emphasis> on suspension culture of <Emphasis Type="Italic">Silene vulgaris</Emphasis> (<Emphasis Type="Italic">Caryophyllaceae</Emphasis>)

The effect of culture filtrate (conditioned medium, CM) containing cell exudates obtained from green alga, Scenedesmus subspicatus, on cell suspension of dicotyledonous plant Silene vulgaris was examined. The addition of diluted CM to the modified MS medium, supplemented with dicamba and BAP, stimulates cell biomass production. The biomass was composed of association of single non-dividing cells, cells during mitosis stage and cellular aggregates. Silene cells began mitotic divisions earlier in the presence of CM in medium when compared to control treatments. Results of performed bioassay showed that some factor or factors released by green alga to the culture medium could be responsible for sustained proliferation of phylogenetically distant species cells. Although it is still unclear which culture constituent influenced most the mitotic response of Silene suspension, results point at versatile stimulatory character of green alga exudates in higher plant cell culture.     

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.