CARBOHYDRATE AVAILABILITY,RESPIRATION, AND THE GROWTH OF KENAF (HIBISCUS CANNABINUS) UNDER MODERATE SALT STRESS

Salt stress may impose osmotic and respiratory costs on nonhalophytes that limit the availability of carbohydrates for growth. This was examined in kenaf (Hibiscus cannabinus L.) by the analysis of soluble carbohydrates, starch, and respiration rates in mature and expanding leaves from plants exposed to moderate salt stress. Plants were grown for 35 days in solution culture at 1, 37, and 75 mM NaCl under greenhouse conditions. Total carbohydrates increased in mature and expanding leaves with increasing salinity. The majority of this increase was as starch. Mature leaf respiration also increased under salt stress. The net accumulation of non-osmotically active carbohydrates in expanding leaves suggests that growth was not limited by the generation or availability of carbohydrates but rather by the ability of the plant to effectively utilize this substrate in osmotic adjustment and growth.     

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.     

Nitrogen application improves gas exchange characteristics and chlorophyll fluorescence in maize hybrids under salinity conditions

The understanding of crop physiological responses to salinity stress is of paramount importance for selection of genotypes with improved tolerance to this stress. Maize (Zea mays L.) hybrids Pioneer 32B33 and Dekalb 979 were grown in pots and subjected to three levels of salinity under four nitrogen levels to determine the role of nitrogen under saline conditions. Salinity stress effects on gas exchange characteristics and chlorophyll fluorescence of maize hybrids were evaluated under semi-controlled conditions. Under salinity stress, the changes in the net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) were similarly directed: all decreased and were lower than in control at the higher salinity level (10 dS/m). Water use efficiency was increased with increasing salinity since transpiration was stronger depressed by salt than photosynthesis. Plants subjected to the lower level of salinity did not differ from control in tested characteristics. Nitrogen application ameliorated the effects of salinity.     

Effects of salt stress on nitrogenase activity and growth of four legumes

The effects of salt stress on nitrogenase (N2-ase) activity, growth and nitrogen content ofVicia faba (L.),Medicago sativa (L.) Merrill,Glycine max andVigna sinensis (L.) were investigated. Four levels of salinity were applied and salt treatments were imposed on inoculated and N-fertilized plants.M. sativa tolerated mild levels of salinity but higher salt concentrations depressed N₂-ase activity of this species. The other three legumes were considerably affected by salt treatments, and N₂-ase activity was significantly reduced by salinity. Vicia faba, carrying elongate nodules, could restore a partial N₂-ase activity upon recovery from salt stress whereasG. max andV. sinesis, both with spherical nodules, could not regain significant activity when salinity was removed. Salt stress retarded growth of both inoculated and N-fertilized plants. The nitrogen content of both treatments was also affected by salinity and the effect was more severe for inoculated than N-fertilized plants.     

Changes in Sugars, Sucrose Synthase Activity and Proteins in Salinity Tolerant Callus and Cell Suspension Cultures of Brassica oleracea L.

Salt tolerant callus and cell suspension cultures of Brassica oleracea L. var. botrytis were obtained by the selection of cells from cultures growing in medium supplemented with 85, 170, and 255 mM NaCl. Salt adapted calli and cell suspensions differed in their RNA and protein concentrations. These concentrations tend to diminish in calli and increase in cell suspensions, both at one or three weeks periods of growth in NaCl. Contents of sucrose and reducing sugars, however, accumulate similarly both in calli and cell suspensions after NaCl treatments. The activity of sucrose synthase was higher in salt adapted cells than in controls. Calli exposed to 255 mM NaCl for six months synthesized a 27 kDa polypeptide, while a 13 kDa polypeptide present in control conditions was absent under salinity. Several high molecular mass polypeptides (> 200 kDa) were visualized in control calli and at moderate salt concentrations, when conditions of the gel were modified.     

Comparison of mitochondrial ascorbate peroxidase in the cultivated tomato, Lycopersicon esculentum, and its wild, salt-tolerant relative, L. pennellii– a role for matrix isoforms in protection against oxidative damage

Mitochondria require robust antioxidant defences to prevent lipid peroxidation and to protect tricarboxylic acid cycle enzymes from oxidative damage. Mitochondria from wild, salt‐tolerant tomato, Lycopersicon pennellii (Lpa) did not exhibit lipid peroxidation in response to high salinity (100 mm NaCl), whereas those isolated from cultivated tomato, L. esculentum (Lem), accumulated malondialdehyde. The activity, intraorganellar distribution and salt response of mitochondrial ascorbate peroxidase (mAPX) differed dramatically in the two species. In Lem mitochondria, the majority (84%) of mAPX was associated with membranes, being located either on the inner membrane, facing the intermembrane space, or on the outer membrane. Total mAPX activity did not increase substantially in response to salt, although the proportion of matrix APX increased. In contrast, 61% of Lpa mAPX activity was soluble in the matrix, the remainder being bound to the matrix face of the inner membrane. Salt treatment increased the activity of all mAPX isoforms in Lpa, without altering their intramitochondrial distribution. The membrane‐bound isoforms were detected in mitochondria of both species by western blotting and found to be induced by salt in Lpa. These observations suggest that matrix‐associated APX isoforms could act in concert with other mitochondrial antioxidants to protect against salt‐induced oxidative stress.     

Physiological adaptative characteristics of Imperata cylindrica for salinity tolerance

Two populations of cogongrass [Imperata cylindrica (L.) Raeuschel], one from the saline regions of the Salt Range and the other from the non-saline regions of Faisalabad were assessed for salinity tolerance on the basis of some key morphological and physiological attributes. It was hypothesized that the tolerant population from the Salt Range must have developed some specific structural modifications, which are responsible for its better survival under high salinities. These adaptive components can be effectively used in modern technologies for improving degree of tolerance of other sensitive crops. The population from the Salt Range markedly excelled the Faisalabad population in terms of growth and physiological attributes measured in this study. The Faisalabad population of I. cylindrica was unable to survive at the highest salt level (200 mM NaCl). The tolerance of the Salt Range population to salt stress was found to be related to high accumulation of organic osmotica, particularly total free amino acids and proline as well as Ca²⁺ in the shoot. The distinctive structural modifications in the Salt Range population were found to be enhanced succulence, well-developed bulliform cells in leaves and smaller stomatal area.     

New perspective on the mechanism of alleviating salt stress by spermidine in barley seedlings

Salt stress is considered to be a major limiting factor for plant growth and crop productivity. Salt injuries in plants are mostly due to excess Na⁺ entry. A possible survival strategy of plants under saline environments is the effective compartmentation of excess Na⁺ by sequestering Na⁺ in roots and inhibiting transport of Na⁺ from roots to shoots. Our previous study showed that exogenous application of polyamines (PAs) could attenuate salt injuries in barley plants. In order to further understand such protective roles of PAs against salt stress, the effects of spermidine (Spd) on sodium and potassium distribution in barley (Hordeum vulgare L.) seedlings under saline conditions were investigated. The results showed that exogenous application of Spd induced reductions in Na⁺ levels in roots and shoots with comparison of NaCl-treated plants, while no significant changes in K⁺ levels were observed. Correspondingly, the plants treated with Spd exogenously maintained high values of [K⁺]/[Na⁺] as compared with salt-stressed plants. Moreover, it was shown by X-ray microanalysis that K⁺ and Na⁺ accumulated mainly in the exodermal intercellular space and cortical cells of roots under salinity stress, and low accumulation was observed in endodermal cells and stelar parenchyma, indicating Casparian bands possibly act as ion transport barriers. Most importantly, Spd treatment further strengthened this barrier effects, leading to inhibition of Na⁺ transport into shoots. These results suggest that, by reinforcing barrier effects of Casparian bands, exogenous Spd inhibits Na⁺ transport from roots to shoots under conditions of high salinity which are beneficial for attenuating salt injuries in barley seedlings.     

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.     

Contribution of inorganic cations and organic compounds to osmotic adjustment in root cultures of two <Emphasis Type="Italic">Centaurium</Emphasis> species differing in tolerance to salt stress

The effect of reduced availability of sugars on growth and essential metabolic processes in roots, resulting from decreased photosynthesis under salinity, was excluded by establishing a non-photosynthetic model-system in this study: root cultures of Centaurium maritimum (L.) Fritch and Centaurium spicatum (L.) Fritch. The contribution of inorganic cations and organic compounds (e.g. carbohydrates and amino acids) to the osmotic adjustment (OA) in roots during short-term exposure to various salt concentrations (0, 50, 100 or 200 mM NaCl) was emphasized. Observed morphological and histological changes in roots were species specific, and were dependent on salinity level. Although C. spicatum appears to be more tolerant to salt stress, both species employed similar strategies in response to elevated salinity to different extents, and displayed effective OA mechanisms. Under low and moderate salinity, inorganic cations were the major contributors to OA in roots of both species, followed by soluble sugars, while the relative contribution of proline (Pro) and free amino acids was insignificant. Osmotic adjustment under severe stress appears to be mediated by increased accumulation of organic compounds. The analysis of the intraspecies variability in salt response of C. spicatum and C. maritimum roots enabled the identification of some organic compounds which could be used as potential biochemical markers in screening for salt tolerance, including Pro in C. spicatum, and trehalose and polyols in C. maritimum.     

Selection and characterization of sodium chloride-tolerant callus of Glycine max (L.) Merr cv. Acme

Callus cultures were initiated from soybean (Glycine max (L.) Merr cv. Acme) cotyledons onMiller's basal medium supplemented with 2 mg L^–1NAA and 0.5 mg L^–1 kinetin. Growing cells wereexposed to increasing concentrations of NaCl in themedium. A concentration of 100 mM NaCl completelyinhibited callus growth. After incubation for 28 d,cells which could tolerate this concentration of NaClgrew to form cell colonies. A NaCl-tolerant line wasobtained through continuous subculturing on 100 mMNaCl. Salt tolerance in this culture was characterizedby an altered growth behavior, reduced cell volume, and accumulation of Na⁺, Cl^–, proline and sugars when grown under salt stress, as well as on normal media. These characteristics, which proved tobe stable after the culture was transferred to asalt-free medium, is commonly associated with halophytes. Presented data suggest that this salt tolerance is the result of a shift towards a halophytic behavior.     

Combination of endophytic and rhizospheric plant growth promoting rhizobacteria in <Emphasis Type="Italic">Oryza sativa</Emphasis> shows higher accumulation of osmoprotectant against saline stress

The effect of endophytic and rhizospheric bacteria was studied on salt stress in a local paddy rice (Oryza sativa L.) variety GJ-17. Plants inoculated with endophytic bacterium Pseudomonas pseudoalcaligenes showed significantly higher concentration of glycine betaine-like quaternary compounds and higher shoot biomass at lower salinity levels. While at higher salinity levels, mixture of both P. pseudoalcaligenes and Bacillus pumilus showed better response against the adverse effects of salinity. However, accumulation of proline showed an opposite trend against plant growth promoting rhizobacteria (PGPR) treatment in salinity stress. Proline concentration increased with salinity but decreased in plants inoculated with either of the PGPRs or mixture of both P. pseudoalcaligenes and B. pumilus. The present study shows that inoculation of paddy rice (Oryza sativa L.) with a mixture of endophytic and rhizospheric bacteria could serve as a useful tool for alleviating salinity stress.     

Effect of NaCl on fatty acids, phenolics and antioxidant activity of Nigella sativa organs

The objective of this study was to investigate the effect of salinity on growth, fatty acid composition, phenol content and antioxidant activity of Nigella sativa organs. Plants were grown hydroponically under NaCl stress (0, 20 40 and 60 mM). The results indicated that salinity affected N. sativa growth. The fatty acid composition of the leaves and the roots was investigated for the first time and major fatty acids were linolenic acid (58.1%) in the leaves and linoleic (43.9%) and palmitic (33.3%) acids and in the roots. Total fatty acid (TFA) content of the leaves decreased at 60 mM NaCl while root TFA increased at 20 and 40 mM NaCl. Moreover, the fatty acid composition was affected by NaCl; in leaves, the double bond index (DBI) decreased accompanied by a decrease of the level of linolenic acid which reached 14% at 60 mM NaCl. However, root DBI degree increased at 40 at 60 mM NaCl provoked mainly by the increase of the amount of linoleic acid by 15 and 8%, respectively, and the decrease of the amount of palmitic acid by 20 and 14%, respectively. Salt stress increased total polyphenol and individual phenolic acid contents in shoots. Moreover, the antiradical activity of the shoots (DPPH) increased at 60 mM NaCl. However, in roots, the total polyphenol content and the antiradical activity decreased sharply with increasing NaCl doses. Data reported here revealed the variation of fatty acids and phenolic compound contents in different organs of N. sativa, and the possible role of theses changes in the plant salt response were discussed.     

Antioxidant responses of shoots and roots of lentil to NaCl-salinity stress

The effect of salt stress (100 mM and 200 mM NaCl) on antioxidant responses in shoots and roots of 14-day-old lentil (Lens culinaris M.) seedlings was investigated. Salt stress caused a significant decrease in length, wet-dry weight and an increase in proline content of both shoot and root tissues. In leaf tissues, high salinity treatment resulted in a 4.4 fold increase in H₂O₂ content which was accompanied by a significant level of lipid peroxidation and an increase in electrolyte leakage. Root tissues were less affected with respect to these parameters. Leaf tissue extracts exhibited four activity bands, of which two were identified as Cu/Zn-SOD and others as Fe-SOD and Mn-SOD. Fe-SOD activity was missing in root extracts. In both tissues Cu/Zn-SOD activity comprised 70–75% of total SOD activity. Salt stress did not cause a significant increase in total SOD activity of leaf tissues but a significant enhancement (88%) was observed in roots mainly due to an enhancement in Cu/ZnSOD isoforms. Compared to leaf tissues a significantly higher constitutive ascorbate peroxidase (APX) and glutathion reductase (GR) activity was observed in root tissues. Upon salt stress no significant change in the activity of APX, catalase (CAT) and GR was observed in root tissues but a higher APX activity was present when compared to leaf tissues. On the other hand, in leaf tissues, with the exception of CAT, salt stress caused significant enhancement in the activity of other antioxidant enzymes. These results suggested that, root tissues of lentil are protected better from NaCl stress induced oxidative damage due to enhanced total SOD activity together with a higher level of APX activity under salinity stress. To our knowledge this is the first report describing antioxidant enzyme activities in lentil.     

Potato plants bearing a vacuolar Na<Superscript>+</Superscript>/H<Superscript>+</Superscript> antiporter HvNHX2 from barley are characterized by improved salt tolerance

Two cultivars of potato (Solanum tuberosum L.) were transformed with a barley antiporter gene HvNHX2 driven by the CaMV 35S promoter. The expressed transgene conferred a higher NaCl tolerance to one of the cultivars. Under salt stress, the more salt-tolerant transgenic plants had longer roots, higher dry weight, and suppressed cell expansion as compared to wild-type plants. The salt tolerance of the plants grown in vitro was not accompanied by elevated total sodium in any plant organs tested. Instead, higher potassium was found in roots of transgenic plants. Possible mechanisms of plant salt tolerance are discussed.     

Effect of Sodium Chloride Stress and Nitrogen Source on Respiration, Growth and Photosynthesis in Lucerne (Medicago sativa L.)

The effects of salinity at different light intensities on freshweight growth and on carbon dioxide influx and efflux were examinedin young plants of lucerne (Medicago sativa L.) that had beengrown in solution culture with nitrogen supplied either as nitrateor by a symbiotic rhizobium. Although the inoculated plantsgrew more slowly than those supplied with nitrate, NaCl at alevel equivalent to an osmotic stress of –0.3 MPa didnot reduce the growth rate of either type of plant under a 12h day-length in a growth chamber. With a day-length of 5 h saltstress (0.0 to –0.6 MPa) did not greatly affect grossphotosynthesis of plants grown on nitrate but respiration ratereached a maximum at –0.3 MPa and declined at larger saltconcentrations. Salt diminished both gross and net photosynthesisin the inoculated plants at a 5 h day-length without stimulatingrespiration. The relationship between photosynthesis and respiration as thephoton flux density was successively decreased was used to inferthe effect of salt on maintenance respiration of the plantssupplied with nitrate. Growth and maintenance components ofrespiration could not clearly be separated in the inoculatedplants suggesting that these were unable to maintain themselvesunder the combined stresses of salt and low light intensity.This view was supported by chemical analysis of the plant material.We conclude that the failure of the inoculated plants to adaptto these conditions could be attributed to the greater demandfor assimilates by the rhizobium. Key words: Medicago sativa, Nitrogen source, Salt stress     

NaCl-induced changes in plasma membrane lipids and proteins of <Emphasis Type="Italic">Zea mays</Emphasis> L. cultivars differing in their response to salinity

Two contrasting maize (Zea mays L.) cultivars, i.e., Giza 2 (salt tolerant) and Trihybrid 321 (salt sensitive), were grown hydroponically to study NaCl effect (100 mM) on root plasma membrane (PM) lipid and protein alterations. The PM total sterols of Trihybrid 321 were decreased while that of Giza 2 was increased in response to salt. Salt imposition had no significant effect on PM total glycolipids and proteins of both cultivars. The PM total phospholipids were increased in Trihybrid 321 but it did not change significantly in Giza 2 after salinity stress. Molecular percentage of PM phospholipids and fatty acids of both cultivars was different in absence (0 mM) and presence (100 mM) of salt. The most abundant phospholipids in untreated Trihybrid 321 PM were phosphatidylglycerol (PG), phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS), which changed into PG, PS, phosphatidylinositol (PI) and PC after salt treatment. However, the dominant phospholipids of the control PM of Giza 2 were PC, PE, PS and PG, which changed into PG, PE, PS and diphosphatidylglycerol (DPG) after salt imposition. Over 60% of the total fatty acids were saturated in control and salinized PM of both cultivars, which was increased after salt stress. The predominant fatty acid in the control and salinized PM of Trihybrid 321 was C18:1 and C17:0, respectively. However, in control and treated PM of Giza 2, the predominant fatty acid was C17:0 and C20:0, respectively. Qualitative and quantitative differences in PM protein patterns were found in both cultivars with and without salt. PM lipid changes enhanced membrane integrity, reflected in different ion accumulation (Mansour et al. 2005), and hence salt tolerance of Giza 2.     

Effect of NaCl and CaCl<Subscript>2</Subscript> on the antioxidant mechanism of leaves and stems of the rootstock CAB-6P (<Emphasis Type="Italic">Prunus cerasus</Emphasis> L.) under in vitro conditions

The effect of salinity on the non-enzymic and enzymic antioxidant activity, shoot proliferation and nutrient accumulation was studied in in vitro cultures of the rootstock CAB-6P (Prunus cerasus L.). Three concentrations (0, 30 and 60 mM) of NaCl or CaCl₂ were added to a modified MS medium. Between the two salt treatments used, only the explants treated with CaCl₂ presented significant decrease in growth parameters. The concentrations of Na⁺ and Cl⁻ in the explants treated with NaCl were increased, as NaCl in the culture medium increased. Furthermore, in the explants treated with CaCl₂ the concentrations of Ca²⁺ and Cl⁻ were increased while that of K⁺ decreased, as CaCl₂ concentration increased. The activity of peroxidase in leaves as well as the number of its anionic isoforms was increased under 30 mM CaCl₂ as well as 60 mM NaCl or CaCl₂. On the contrary, increasing salinity, from 0 to 60 mM CaCl₂, resulted in a reduction of the catalase activity in leaves followed by disappearance of the only one catalase isoform that was detected in leaves (60 mM CaCl₂). In the stems of the explants treated with NaCl the peroxidase activity was reduced. In the stems and leaves of the explants grown in saline substrate the non-enzymic antioxidant activity was significantly increased. The results suggest that the stems and leaves of CAB-6P explants presented variable antioxidant responses that were depended on the salt form used. The contribution of enzymic and non-enzymic protection mechanisms to the adaptation of CAB-6P explants under salinity stress is discussed.     

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.     

Investigation of the effects of Vesicular Arbuscular Mycorrhiza on mineral nutrition and growth of <Emphasis Type="Italic">Carthamus tinctorius</Emphasis> under salt stress conditions

Salt stress is considered as one of the most important abiotic factors limiting plant growth and yield in many areas of the world. It has been shown that Vesicular Arbuscular Mycorrhizal Fungi (AMF) can alleviate this deficiency. The effects of AMF inoculation on growth variables and mineral nutrition of Carthamus tinctorius L. under salt stress condition were studied. Plants were grown in a sterilized, low-P sandy soil with Glomus etunicatum inoculum (10–12 spore/g soil) in a greenhouse. RLC (Root Length Colonized) percent was higher in control plants than treated ones with different salt concentrations. Shoot and root weights, height, the number of leaves, the number of lateral branches, and also leaf area of mycorrhizal (M) plants were higher than nonmycorrhizal (NM) ones in both controlled and salt-treated plants. P, Zn, Fe, Ca, K, Cu, and N contents in M plants were higher than in NM plants in control, low and medium salinity conditions, but Na content was lower in aerial parts of the M plants. The results showed a higher tolerance of inoculated M plants toward salt stress and their better growth.