Deleterious Effects Of Salt Stress Research Articles

Effect of silicon on seed germination and the physiological characteristics of Glycyrrhizauralensisunder different levels of salinity

SummarySalt stress is a major abiotic factor which adversely affects crop yields and quality. Silicon (Si) has been widely reported to have a beneficial influence on ameliorating the deleterious effects of salt stress. However, the mechanisms by which Si mediates salt stress responses and the quantitative relationship between Si concentration and the level of salt stress are still poorly understood. This study was conducted to determine the effects of varying concentrations of Si (1, 2, 4, 6, or 8 mM) on the characteristics of seed germination, superoxide dismutase (SOD) activity, and proline and malondialdehyde (MDA) concentrations in Glycyrrhiza uralensis seeds subjected to different levels of salt stress.The results showed that the addition of Si significantly affected the seed germination percentage and seedling emergence in G. uralensis in a concentration-dependent manner. In general, low Si concentrations ( 4 mM) enhanced seed germination, seedling emergence, and the seedling vitality index (SVI), while high concentrations of Si ( 6 mM) inhibited seed germination. The effects of Si concentration (1, 2, 4, 6, or 8 mM) on seed germination also varied depending on the level of salt stress. Under 50 mM NaCl or 100 mM NaCl stress, low Si concentrations ( 4 mM) significantly increased the SVI, while high Si concentrations ( 6 mM) significantly decreased seed germination, seedling emergence, and the SVI. Under 150 mM NaCl stress, low Si concentrations ( 4 mM) promoted seed germination, and all Si concentrations significantly promoted seedling emergence. The results also showed that a suitable Si concentration (4 mM) significantly increased SOD activity, but decreased proline and MDA concentrations. These results indicated that Si was directly involved in the physiological process of seed germination and seedling growth in G. uralensis under salt stress conditions, and that the effect was dependent on the level of salt stress and on Si concentration.

Reversion of deleterious effects of salt stress by activation of ROS detoxifying enzymes via foliar application of 24-epibrassinolide in rice seedlings

We evaluated the effects of foliar application of 24-epibrassinolide (EBL) on growth, oxidative metabolism and water relations of rice seedlings cv. J-104, stressed with 100 mmol L−1 NaCl for 7 days and recovered without NaCl in the nutrient solution during the next 15 days. Measurements were made at the beginning, at the end and after recovery from salt stress. Salinity decreased growth but the effects were observed during the recovery period. Foliar application of EBL restored growth in salt stressed seedlings. Water relations were affected by salt stress but spraying EBL only restored turgor potential. Proline concentration increased after recovery in salt stressed seedlings and application of EBL reverted this effect by 35 %. Lipid peroxidation and protein oxidation increased with salt stress and seedlings sprayed with EBL showed lower damage to membranes and proteins than salt stressed plants without EBL application. Antioxidant enzymes responded variably to salt stress, peroxidases and SOD either decreased or were little affected by salt stress, whereas catalase activity increased with salinity. The effect of EBL on antioxidant enzymes was in general to increase activities of catalase, ascorbate peroxidase and SOD. The protective effects of EBL of salt stressed rice seedlings may be associated with a decrease of oxidative stress probably modulated by proline accumulation via catalase and SOD, evidenced by a reduction of lipid peroxidation and proteins oxidation, and maintenance of chlorophylls concentration.

Plant Growth-promoting Rhizobacteria Mitigate Deleterious Effects of Salt Stress on Strawberry Plants (Fragaria ×ananassa)

The effect of selected plant growth-promoting rhizobacteria (PGPR) on the growth, chlorophyll content, nutrient element content, and yield of strawberry plants under natural field salinity conditions stress was investigated. Field experiments were conducted using a randomized complete block design with five PGPRs (Bacillus subtilis EY2, Bacillus atrophaeus EY6, Bacillus spharicus GC subgroup B EY30, Staphylococcus kloosii EY37, and Kocuria erythromyxa EY43) and a control (no PGPR) in 2009 and 2010. PGPR inoculations significantly increased the growth, chlorophyll content, nutrient element content, and yield of strawberry plants. PGPR treatments lowered electrolyte leakage of plants under saline conditions. The leaf relative water content (LRWC) of plants rose with bacterial inoculation. All nutrient element contents of leaves and roots investigated were significantly increased with PGPR inoculations with the exception of sodium (Na) and chlorine (Cl). The highest efficiency to alleviate salinity stress on the yield and nutrient uptake of strawberry plants was obtained from EY43 (228 g per plant) and EY37 (225 g per plant) treatment and the yield increasing ratio of plants was 48% for EY43 and 46% for EY 37 compared with the control treatment (154 g per plant). The highest nitrogen (N), potassium (K), phosphorus (P), calcium (Ca), magnesium (Mg), sulfur (S), manganese (Mn), copper (Cu), and iron (Fe) concentrations were obtained from EY43 and followed by E6, E37, and E30, and increasing ratio of leaves and root N, P, K, Ca, Mg, S, Mn, Cu, and Fe contents were 22% to 33%, 34% to 8.8%, 89% to 11%, 11.0% to 7.2%, 5.1% to 6.2%, 97% to 65%, 120% to 140%, 300% to 15%, and 111% to 9.0%, respectively. The results of the study suggested that PGPR inoculations could alleviate the deleterious effects of salt stress conditions on the growth and yield of strawberry plants under salinity conditions.

Comparative roles of brassinosteroids and polyamines in salt stress tolerance

Salt stress is among the major abiotic stresses that adversely affect the global crop production and its adverse impacts are getting more serious in the regions where saline water is used for irrigation. It induces reactive oxygen species, alters the activity of antioxidant system and adversely affects the process of photosynthesis. Various strategies have been employed to mitigate the deleterious effects of salt stress. Presently, the recommended strategies to overcome the adverse effects of salt stress include the use of tolerant cultivars, ameliorative water management and diverse cultural practices. However, none of these approaches have been found to be fully effective under salt stress conditions. An alternative and technically simpler approach to induce salt stress tolerance is the exogenous application of plant growth regulators (PGRs). This technique has gained significant importance during the past decade. PGRs have been implicated to regulate a wide range of metabolic and physiological activities in plants, ranging from cell division and organogenesis to protection against biotic and abiotic stresses. One of the important factors for enhanced plant productivity by PGRs is their efficiency to overcome the salt-induced stress conditions. Recent findings on the effects of brassinosteroids and polyamines on the salt stress tolerance of crops open new avenues to address the salinity problems. This review enlightens the role of brassinosteroids and polyamines in different plant processes like their role in regulation of photosynthesis, antioxidant systems and other related aspects, thereby improving overall performance of plants.

Alleviation of deleterious effects of salt stress by applications of supplementary potassium–calcium on spinach

The aim of the present study is to investigate the effects of salinity and the influence of supplemental K+ and Ca2+ on the alleviation of the deleterious effects of salinity stress in spinach plants. Spinach cultivars used were Green Gold, Larissa, Mikado, Ohio and Matador. In addition to four NaCl levels of 50, 100, 150 and 200 mM, the treatments were repeated with 10 mM K and 10 mM Ca at each NaCl level. The results revealed that Na+ and Cl− concentrations were significantly increased and the K+, Ca2+ and NO3 − concentrations were decreased with increasing NaCl concentrations in the growth medium. Being very important to the physiology and biochemistry of plants decreases in K+, Ca2+ and NO3 − reduced both growth and the yield. The additions of K+ and Ca2+ reduced the Na+ and Cl− concentrations in the plant tissues, increased the K+, Ca2+ and NO3 − concentrations, resulting in an improvement in the marketable yield of the spinach plants. Even though the effects of supplemental K+ and Ca2+ were similar in some plants at different salt concentrations, the effect of additional Ca2+ alone was higher overall. Thus, the results of this study confirmed the principal effects of K+ and Ca2+ supplies in reducing the detrimental effects of salinity.

Mitigation effects of glycinebetaine on oxidative stress and some key growth parameters of maize exposed to salt stress

The aim of the current study was to investigate the effects of glycinebetaine (GB) on oxidative stress and some key growth parameters in maize (Zea mays L. 'DK 647 F1') grown under saline conditions. Maize seedlings were grown in pots containing perlite. The experiment was designed in a 2 × 2 factorial arrangement with 2 levels (0 and 100 mM) of sodium chloride (NaCl) and 2 levels (25 and 50 mM) of GB sprayed onto leaves of maize seedlings. Saline stress caused a considerable decline in total dry matter, chlorophyll content, relative water content (RWC), peroxidase (POD; EC. 1.11.1.7), and catalase (CAT; EC. 1.11.1.6); however, it increased proline, polyphenol oxidase (PPO; 1.10.3.1), and electrolyte leakage. Foliar application of both GB doses mitigated the deleterious effects of salinity stress to variable extents on the key growth parameters tested. As expected, sodium (Na^+) concentrations were higher in the tissues of plants grown under saline conditions, and the GB treatments significantly reduced Na^+ concentration in the plant tissues. Salinity stress reduced both calcium (Ca^{2+}) and potassium (K^+) in the leaves, and GB treatments increased concentrations of both elements in plant tissues; however, their levels were still lower than control values. In particular, foliar application of 50 mM GB mitigated some of the deleterious effects of salt stress by improving proline, Ca^{2+}, and K^+ levels and maintaining membrane permeability.

Mitigation of Salt Stress-Induced Inhibition of Plantago crassifolia Reproductive Development by Supplemental Calcium or Magnesium

In Plantago crassifolia, a moderate halophyte characteristic of borders of salt marshes in the Mediterranean region, reproductivedevelopment is more sensitive to high soil salinity than vegetative growth. To investigate the possible role of calcium and magnesiumsalts in the responses of this species to salt stress, adult plants were submitted over a 2-month period to treatments with 300 mMNaCl-a concentration which affects, but does not completely inhibit seed formation in P. crassifolia-either alone or combined with lowconcentrations of CaCl2 (10 mM) or MgCl2 (20 mM). The NaCl treatment did not affect plant vegetative growth and had a stimulatingeffect on flowering. Yet almost half the spikes produced had aborted seeds, and the effect on seed number and quality-estimated bytheir mean weight and germination capacity-was obviously deleterious. Addition of calcium or magnesium chloride during the saltstresstreatment completely counteracted the negative effect of NaCl on the ‘reproductive success’ of the plants: the number, weightand germination frequency of the seeds were similar to that in the control, non-stressed plants. These results indicate that both divalentcations can suppress or mitigate the deleterious effects of salt stress. While this protective role is well established in the case of calcium,we provide here the first experimental evidence of a similar function for magnesium.

A role for antioxidants in acclimation of marine derived pathogenic fungus (NIOCC 1) to salt stress

Salinity tolerance a key factor helps in understanding the ionic homeostasis in general, which is a fundamental cellular phenomenon in all living cells. Here, a marine derived pathogenic fungus was examined for its adaptation under salt stress using antioxidant properties. The aqueous extracts of halophilic fungus exhibited different levels of antioxidant activity in all the in vitro tests such as α,α-diphenyl-β-picrylhydrazyl (DPPH·), Hydroxyl Radical Scavenging Assay (HRSA), Metal chelating assay and β-carotene–linoleic acid model system. The antioxidant capacity of marine fungus exposed to high salt condition showed an increase in activity. In addition, the production of intra and extracellular antioxidant enzymes of the fungus at various salt stresses were analyzed and discussed for their possible role in the stress mechanism. The marine derived fungus was identified as Phialosimplex genus, which is associated with infections in dogs. Thus the present study elucidates that the scavenging activity is one of the protective mechanisms developed in the fungus to avoid the deleterious effect of salt stress. In addition, the study also helps in understanding how the pathogenic fungus tackles the oxidative burst i.e. hypersensitivity reaction performed by host to kill the pathogens.

Efeitos do estresse salino na germinação, emergência e estabelecimento da plântula de cajueiro anão precoce

We investigated the effects of salinity on (germination, emergence and establishment of dwarf-cashew seedling) trying to establish a link between development and ion accumulation in the seedling tissues. In a greenhouse, cashew nuts were sown in trays containing vermiculite moistened with distilled water (0.0 dS m-1) or with NaCl solutions with electrical conductivities ranging between 3.0 to 18.0 dS m-1. We determined the percentage of seedlings that reached the development stages studied and the time and speed at which this occurred, as well as cotyledon and embryonic axis dry mass and the Na+, K+ and Cl- contents of embryonic axis. Salinity delayed emergence and establishment seedling, however, only the final percentage of established seedlings was reduced, accompanied by inhibition of depletion of reserves and a decrease in embryonic axis dry mass. Na+ and Cl- contents increased with salinity, but this was more pronounced in established seedlings, in which there was a reduction in content of K+. Results suggest that dwarf cashew seedlings are more sensitive to salinity during the establishment stage and that deleterious effects of salt stress are mediated, at least in part, by excessive accumulation of Na+ and Cl- in the seedling tissues.

English

The effect of selected plant growth promoting rhizobacteria (PGPR) on growth,chlorophyll content, nutrient uptake and yield of lettuce under salt stress was investigated. The study was conducted in pot experiments. Seeds were coated with suspensions of Bacillus subtilis, Bacillus atrophaeus, Bacillus spharicus,Staphylococcus kloosii and Kocuria erythromyxa, which were isolated from highly salty soils. Pots were irrigated with NaCl solutions of 0, 50 or 100 mM. Salinity negatively affected growth and chlorophyll content of lettuce; however, PGPR treatments positively affected growth parameters such as head weight, head height, root diameter and chlorophyll content compared to non-treated plants that were challenged with salt stress. Leaf number was affected by neither salt nor PGPR treatments. Nutrient contents of the leaves of lettuce plants were significantly affected by salt stress and PGPR treatments. All nutrient element contents investigated were significantly decreased except for Na and Cl under salt stress. PGPR under salinity conditions usually increased plant nutrient element contents of the leaves. It can be concluded from the study that treatment with PGPR can ameliorate the deleterious effects of salt stress on nutrition and on the growth parameters of lettuce plants under salinity conditions. Key words: Plant growth promoting rhizobacteria, plant nutrient, salinity stress, lettuce.

RESPONSE OF SALT STRESSED STRAWBERRY PLANTS TO FOLIAR SALICYLIC ACID PRE-TREATMENTS

Salinity has deleterious effects on plant growth and development through membrane stability, photosynthetic activity, protein content, and ionic composition; however, salicylic acid (SA) could restore these properties in plants. The objective of this study was to determine the ameliorative effects of SA as foliar pre-treatments on membrane permeability, proline and protein contents, chlorophyll a, b and total chlorophyll and ionic composition of strawberry cv. ‘Camarosa’ under saline conditions. Membrane permeability and proline content significantly increased and protein and chlorophyll contents significantly decreased by 6 mS cm−1 application without SA treatment compared with the control (2 mS cm−1) treatment. Membrane permeability decreased from 6.9 in 0 mM SA treatment to 5.2 by application of 1.0 mM SA under saline conditions and same to the control (5.2). Compared with 0 mM SA treatment, the average increases of proline and protein contents were 66.7% in 0.25 mM SA treatment and 62.2% in 0.1 mM SA treatment in 6 mS cm−1 level, respectively. Chlorophyll b and total chlorophyll significantly increased by 0.25 mM SA treatments under saline conditions. The lowest and the highest chlorophyll b and total chlorophyll were obtained from 0 mM SA treatment (19.6 and 44.5 mg L−1) and 0.25 mM SA treatment (28.6 and 52.9 mg L−1) in 6 mS cm−1 salinity level. Ionic compositions of leaves were significantly affected by salinity and SA treatments. Nitrogen in 1.0 mM SA treatment and P contents of leaves in 0.1 mM SA treatment significantly increased but Na and Cl contents of leaves significantly decreased by SA treatments in 6 mS cm−1 salinity level. The results of this study were clearly indicated that the SA application on strawberry plants could ameliorate the deleterious effect of salt stress on membrane permeability, proline, protein, and chlorophyll contents. Therefore, SA treatment could offer an economic and simple application to salinity stress.

EFFECTS OF PLANT GROWTH PROMOTING BACTERIA ON YIELD, GROWTH, LEAF WATER CONTENT, MEMBRANE PERMEABILITY, AND IONIC COMPOSITION OF STRAWBERRY UNDER SALINE CONDITIONS

Plant growth promoting effects of Bacillus subtilis EY2, Bacillus atrophaeus EY6, Bacillus spharicus GC subgroup B EY30, Staphylococcus kloosii EY37 and Kocuria erythromyxa EY43 were tested on strawberry cv. ‘Fern’ in terms of fruit yield, growth, chlorophyll reading value, leaf relative water content (LRWC), membrane permeability and ionic composition of leaves and roots under saline conditions. Compared with 0 mM sodium chloride (NaCl) treatment, the average decrease of yield and LRWC were 51.6% and 21.0%, respectively, when 35 mM NaCl was applied. However, EY30, EY37, and EY43 treatments under saline condition (35 mM NaCl) significantly increased fruit yield (54.4%, 51.7% and 94.9%) compared with 35 mM NaCl treatment without plant growth promoting bacteria (PGPB). The LRWC increased from 72.0% in 35 mM NaCl treatment to 88.4%, 86.6%, 84.2%, 83.5%, and 86.2% by EY2, EY6, EY30, EY37, and EY43 applications, respectively. The lowest membrane permeability among the bacterial strains was obtained from EY37 treatment (37) while it was 33 and 58 in 0 mM NaCl and 35 mM NaCl treatments, respectively. The concentration of all plant tissue nutrients investigated [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg)] with the exception of root phosphorus (P) and Mg concentration significantly decreased with 35 mM salt treatment. Nitrogen content of leaves varied between 3.04 and 3.14% in bacterial treatments under saline conditions while it was 2.71% in 35 mM NaCl treatment. In contrast sodium (Na) and chloride (Cl) of leaves and Cl content of roots were significantly decreased by root inoculation with all bacterial treatments in comparison to 35 mM NaCl treatment with no inoculation. Treatment with Bacillus EY30, Staphylococcus EY37 and Kocuria EY43 to strawberry plants can ameliorative the deleterious effect of salt stress on fruit yield, growth and nutrition. These results demonstrate that PGPB treatment could be offer an economic and simple means to increased plant resistance for salinity stress.

Phosphorus and humic acid application alleviate salinity stress of pepper seedling

Humic acid is a commercial product that contains many elements which improve the soil fertility and increase the availability of nutrient elements. It consequently affects plant growth and yield and ameliorates the deleterious effects of salt stress. The objective of the study was to determine the effect of humic acids and phosphorus on growth and nutrient content of pepper seedlings (cv. Demre) grown under moderate salt stress in growth chamber conditions. Applications of different levels of phosphorus [0 (P0), 50 (P1), 100 (P2) and 150 (P3) mg kg-1] and humic acid [0 (HA0), 750 (HA1) and 1500 (HA2) mg kg-1] to growing media containing moderate salt dose (8 mM NaCl treatment) were studied. The study was replicated four times with 20 plants in each replicate. Humic acid (HA) and phosphorus applications increased the growth and growth parameter of plants. In company, effects of HA and P application was more effective on growth and growth parameter than each separate effect. The optimum total yield was obtained from 69 mg kg-1 P application with HA2 doses according to regression analysis. Humic acid application significantly increased N, P, K, Ca, Mg, S, Mn and Cu contents of shoot of pepper seedling. Also, N, P, K, Ca, S, Fe, Mn, Zn and Cu contents of root were increased with humic acid application. Na contents of both shoot and root of pepper decreased with increased humic acid doses. It can be concluded that high humic acid doses has positive effects on salt tolerance based on the plant growth parameters and nutrient contents. The present study suggests that HA treatments can ameliorate the deleterious effects of salt stress on pepper plants and HA could offer an economical and simple application to reduce problems of pepper production in moderately saline soil. Key words: Nutrient uptake, plant growth parameter, salt stress, pepper.

Influence of Arbuscular Mycorrhizal (AM) Fungi and Salinity on Seedling Growth, Solute Accumulation, and Mycorrhizal Dependency of Jatropha curcas L.

Production of Jatropha curcas as a biodiesel feedstock on marginal lands is growing rapidly. Biomass production on these lands is limited. Hence, the objective of this study was to evaluate the effect of arbuscular mycorrhiza (AM) fungi and salinity (0.1, 0.2, 0.3, 0.4, and 0.5% NaCl) on (1) seedling growth, leaf relative water content (RWC), lipid peroxidation, solute accumulation (proline and sugars), and photosynthetic pigments (Chl a and b) of Jatropha; (2) mycorrhizal colonization (%) and mycorrhizal dependency (MD) of Jatropha; and (3) glomalin content (Bradford reactive soil protein) in soil. Increased soil salinity significantly (P < 0.05) decreased AM root colonization (r 2 = 0.98) of AM-inoculated plants and decreased survival (r 2 = 0.93) and growth (shoot length, r 2 = 0.89; tap root length, r 2 = 0.93; shoot diameter, r 2 = 0.99; shoot dry weight, r 2 = 0.92; and root dry weight, r 2 = 0.92) of non-AM-inoculated Jatropha. Under salt stress, AM-inoculated Jatropha plants had greater dry weight of shoots and roots, better leaf water status, less leaf membrane damage (low lipid peroxidation activity), higher solute (proline and sugars), and higher leaf chlorophyll concentrations than non-AM-inoculated plants. The mycorrhizal dependency (MD) of Jatropha increased from 12.13 to 20.84% with salinity (0–0.4% NaCl). Root AM colonization (%) and glomalin content in soil were negatively correlated with salinity (P < 0.05, r = −0.95). We conclude that inoculation with AM fungi lessens the deleterious effect of salt stress on seedling growth parameters under salt levels up to 0.5% NaCl (electrical conductivity of 7.2 dS m−1). Inoculation of Jatropha seedlings with AM fungi can promote the establishment of Jatropha under NaCl-induced stress.

Pretreatment with H2O2 in maize seeds: effects on germination and seedling acclimation to salt stress

The aim of this study was to evaluate the effects of H2O2 on germination and acclimation of maize plants subject to salt stress. Three experiments using BRS3003 seeds, a triple hybrid of maize, were carried out in a growth room and in greenhouse. In the first experiment, H2O2 accelerated the germination percentage of seeds at 100 mM, but not at 500 mM. In the second experiment, the pretreatment of seeds was observed to induce a pronounced increase in ascorbate peroxidase (APX) and catalase (CAT) enzyme activity after 30 h of soaking in H2O2. It was also observed that guaiacol peroxidase (GPX) activity was smaller in the seeds soaked in H2O2 for 12, 24, 30, 36 and 42 h, in relation to those soaked in distilled water. The superoxide dismutase (SOD) activity was not affected by the pretreatment of seeds, except for the 24 h treatment. Only one CAT isoform was detected. In the third experiment, seeds were pretreated with 36 h soaking in 100 mM H2O2 solution or in distilled water and later cultivated in Hoagland's nutrient solution or nutrient solution with 80 mM NaCl. The results showed the pretreatment of seeds with H2O2 induced acclimation of the plants to salinity. It decreased the deleterious effects of salt stress on the growth of maize. In addition, the differences in antioxidative enzyme activities may explain the increased tolerance to salt stress of plants originated from H2O2 pretreated seeds.

Use of Bioinoculants in Ameliorative Effects on Radish Plants Under Salinity Stress

ABSTRACT The aim of this study was to evaluate the effect of plant growth promoting bacteria (PGPB) on emergence, growth, physiology, and mineral content of radish under salinity stress. The study was conducted in pot experiments using a mixture of soil: sand (1:1 v: v) under greenhouse conditions. Bacillus subtilis EY2, Bacillus atrophaeus EY6, and Bacillus spharicus GC subgrup B EY30 were isolated in highly salty soils in Upper Coruh Valley in Turkey. Seeds were soaked in the bacterial suspension incubated at 27°C for 2 h. Emergence percentage (EP) was reduced and mean emergence time (MET) raised with sodium chloride (NaCl) solutions. Inoculated seeds displayed greater EP and less MET compared to the non-inoculated ones. Salinity negatively affected growth of radish; however, plant growth promoting bacteria treatments positively affected growth parameters such as fresh weight (278% for shoot, 371% for root) and dry weights (250% for shoot, 422% for root) compared to non-treated plants that were challenged with salt stress. Furthermore, selected bacteria caused an increase in uptake of minerals except sodium (Na) compared to the non-treated controls in both salt stress and salt stress absence. Sodium concentration of plant leaves was increased by salt stress while bacterial inoculation decreased its concentration. Bacterial treatments increased chlorophyll content and decreased electrolyte leakage of plants in saline conditions. Leaf relative water content (LRWC) of plants in the salt stress condition increased with bacterial application, but reduced without bacterial application. The present study suggests that PGPB seed treatments can ameliorate the deleterious effects of salt stress on radish plants and PGPB could offer an economical and simple application to reduce problems of radish production in an Aridisol caused by high salinity.

Influence of arbuscular mycorrhizae on photosynthesis and water status of maize plants under salt stress

The influence of arbuscular mycorrhizal (AM) fungus Glomus mosseae on characteristics of the growth, water status, chlorophyll concentration, gas exchange, and chlorophyll fluorescence of maize plants under salt stress was studied in the greenhouse. Maize plants were grown in sand and soil mixture with five NaCl levels (0, 0.5, 1.0, 1.5, and 2.0 g/kg dry substrate) for 55 days, following 15 days of non-saline pretreatment. Under salt stress, mycorrhizal maize plants had higher dry weight of shoot and root, higher relative chlorophyll content, better water status (decreased water saturation deficit, increased water use efficiency, and relative water content), higher gas exchange capacity (increased photosynthetic rate, stomatal conductance and transpiration rate, and decreased intercellular CO(2) concentration), higher non-photochemistry efficiency [increased non-photochemical quenching values (NPQ)], and higher photochemistry efficiency [increased the maximum quantum yield in the dark-adapted state (Fv/Fm), the maximum quantum yield in the light-adapted sate (Fv'/Fm'), the actual quantum yield in the light-adapted steady state (phiPSII) and the photochemical quenching values (qP)], compared with non-mycorrhizal maize plants. In addition, AM symbiosis could trigger the regulation of the energy biturcation between photochemical and non-photochemical events reflected in the deexcitation rate constants (kN, kN', kP, and kP'). All the results show that G. mosseae alleviates the deleterious effect of salt stress on plant growth, through improving plant water status, chlorophyll concentration, and photosynthetic capacity, while the influence of AM symbiosis on photosynthetic capacity of maize plants can be indirectly affected by soil salinity and mycorrhizae-mediated enhancement of water status, but not by the mycorrhizae-mediated enhancement of chlorophyll concentration and plant biomass.

Application of municipal solid waste compost reduces the negative effects of saline water in Hordeum maritimum L.

The efficiency of composted municipal solid wastes (MSW) to reduce the adverse effects of salinity was investigated in Hordeum maritimum under greenhouse conditions. Plants were cultivated in pots filled with soil added with 0 and 40tha−1 of MSW compost, and irrigated twice a week with tap water at two salinities (0 and 4gl−1 NaCl). Harvests were achieved at 70 (shoots) and 130 (shoots and roots) days after sowing. At each cutting, dry weight (DW), NPK nutrition, chlorophyll, leaf protein content, Rubisco (ribulose-bisphosphate carboxylase/oxygenase) capacity, and contents of potential toxic elements were determined. Results showed that compost supply increased significantly the biomass production of non salt-treated plants (+80%). This was associated with higher N and P uptake in both shoots (+61% and +80%, respectively) and roots (+48% and +25%, respectively), while lesser impact was observed for K+. In addition, chlorophyll and protein contents as well as Rubisco capacity were significantly improved by the organic amendment. MSW compost mitigated the deleterious effect of salt stress on the plant growth, partly due to improved chlorophyll and protein contents and Rubisco capacity (−15%, −27% and −14%, respectively, in combined treatment, against −45%, −84% and −25%, respectively, in salt-stressed plants without compost addition), which presumably favoured photosynthesis and alleviated salt affect on biomass production by 21%. In addition, plants grown on amended soil showed a general improvement in their heavy metals contents Cu2+, Pb2+, Cd2+, and Zn2+ (in combined treatment: 190%, 53%, 168% and 174% in shoots and 183%, 42%, 42% and 114% in roots, respectively) but remained lower than phytotoxic values. Taken together, these findings suggest that municipal waste compost may be safely applied to salt-affected soils without adverse effects on plant physiology.

Nursery inoculation of tomato with arbuscular mycorrhizal fungi and subsequent performance under irrigation with saline water

Protected horticultural crops as well as those planted in open fields particularly in the Mediterranean region have to cope with increasing salinization ofirrigation water. High salinity of the supply water has detrimental effects on soil fertility and plant nutrition and reduces crop growth and yield. This study was conducted to determine if pre-inoculation of transplants with arbuscular mycorrhizal (AM) fungi alleviates salt effects on growth and yield of tomato (Lycopersicon esculentum Mill. Cv. Marriha) when irrigated with saline water. Tomato seeds were sown in polystyrene trays with 20 cm 3 cells and treated with AM fungi (AM) or without (nonAM) Glomus mosseae. Once the seedlings were reached appropriate size, they were transplanted into nonsterile soil in concrete blocks (1.6 m 3m 0.75 m) under greenhouse conditions. The soil electrical conductivity (ECe) was 1.4 dS m 1 . Plants were irrigated with nonsaline water (ECw = 0.5 dS m 1 ) or saline water (ECw = 2.4 dS m 1 ) until harvest. These treatments resulted with soil EC at harvest 1.7 and 4.4 dS m 1 for nonsaline and saline water treatments, respectively. Root colonization with AM fungi at flowering was lower under saline than nonsaline conditions. Pre-inoculated tomato plants with AM fungi irrigated with both saline and nonsalinewater had greater shoot and root dry matter (DM) yield and fruitfresh yield than nonAM plants. The enhancement in fruit fresh yield due to AM fungi inoculation was 29% under nonsaline and 60% under saline water conditions. Shoot contents of P, K, Zn, Cu, and Fe were higher in AM compared with nonAM plants grown under nonsaline and saline water conditions. Shoot Na concentrations were lower in AM than nonAM plants grown under saline water conditions. Results indicate that pre-inoculation of tomato transplants with AM fungi improved yield and can help alleviate deleterious effects of salt stress on crop yield. # 2006 Elsevier B.V. All rights reserved.

Pretreatment with Antioxidants Decreases the Effects of Salt Stress on Chloroplast Ultrastructure in Rice Leaf Segments (Oryza sativa L.)

We investigated the kinds of active oxygen species leading to the destruction of chloroplast ultrastructure in salt-stressed rice plants. After the seedlings were grown for 3 wks, leaf segments (5 mm square) were cut from the middle portion of the 5th leaves. Leaf segments were incubated in 200 mM NaCl under dark or light conditions for 24 hr. The chlorophyll content in the leaf segments drastically decreased in light between 12- and 24 hr in 200 mM NaCl, but, no reduction was observed in the dark. In electron microscopic studies, 200 mM NaCl caused swelling of thylakoids and destruction of thylakoid membranes in light. On the other hand, no ultrastructural changes were observed under dark condition. In one experiment, leaf segments were incubated in 200 mM NaCl for 24 hr in light after preincubation with antioxidants for 12 hr in light. Pretreatment with ascorbate and benzoate, which scavenge H2O2 and ˁOH, respectively, effectively suppressed the reduction of chlorophyll content and the destruction of chloroplasts by NaCl in light. However, Tiron and DABCO, which scavenge O2- and 1O2, respectively, could not suppress the effects of salt stress in light. Fe-SOD activity was increased about eight time by salt stress (200 mM NaCl), but, catalase activity was reduced to 69% of the control and ascorbate peroxidase activity was not affected by NaCl. These results suggested that salt-induced injury in chloroplasts is dependent on light, and that H2O2 and ˁOH are responsible for the deleterious effects of salt stress on chlorophyll content and chloroplast ultrastructure.