NaCl-induced Stress Research Articles

Green-synthesized lignin nanoparticles enhance Zea mays resilience to salt stress by improving antioxidant metabolism and mitigating ultrastructural damage

Soil salinity poses a substantial threat to agricultural productivity, resulting in far-reaching consequences. Green-synthesized lignin nanoparticles (LNPs) have emerged as significant biopolymers which effectively promote sustainable crop production and enhance abiotic stress tolerance. However, the defensive role and underlying mechanisms of LNPs against salt stress in Zea mays remain unexplored. The present study aims to elucidate two aspects: firstly, the synthesis of lignin nanoparticles from alkali lignin, which were characterized using Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), Fourier Infrared Spectroscopy (FT-IR) and Energy Dispersive X-Ray Spectroscopy (EDX). The results confirmed the purity and morphology of LNPs. Secondly, the utilization of LNPs (200 mg/L) in nano priming to alleviate the adverse effects of NaCl (150 mM) on Zea mays seedlings. LNPs significantly reduced the accumulation of Na+ (17/21%) and MDA levels (21/28%) in shoots/roots while increased lignin absorption (30/31%), resulting in improved photosynthetic performance and plant growth. Moreover, LNPs substantially improved plant biomass, antioxidant enzymatic activities and upregulated the expression of salt-tolerant genes (ZmNHX3 (1.52 & 2.81 FC), CBL (2.83 & 3.28 FC), ZmHKT1 (2.09 & 4.87 FC) and MAPK1 (3.50 & 2.39 FC) in both shoot and root tissues. Additionally, SEM and TEM observations of plant tissues confirmed the pivotal role of LNPs in mitigating NaCl-induced stress by reducing damages to guard cells, stomata and ultra-cellular structures. Overall, our findings highlight the efficacy of LNPs as a practical and cost-effective approach to alleviate NaCl-induced stress in Zea mays plants. These results offer a sustainable agri-environmental strategy for mitigating salt toxicity and enhancing crop production in saline environments.

Morpho-physiological effects of irrigation with saline water in ex vitro plants of Juglans regia ‘Sorrento’

Soil salinization is a global problem limiting growth and economical yield in fruit species including walnut. Knowledge of the response of varieties and cultivars to salinity can represent an important contribution to future walnut plantation in areas affected by soil salinization. Juglans regia ‘Sorrento’ is a commercially important Italian variety. The present work aimed to explore the morpho-physiological response to NaCl-induced stress in ‘Sorrento’ plants using clonally propagated ex vitro plantlets to reduce the impact of genetic variation. Ex vitro acclimatized plants were exposed to salinity conditions by irrigating pot soil with half-strength Hoagland solution containing 100 mM NaCl for 20 days. Salt-induced effects on plant growth, chlorophyll and carotenoid content, osmolality, membrane injury and on activities of antioxidant enzymes catalase and guaiacol peroxidase (G-POD) in leaves were evaluated. Morphological and growth parameters were not significantly altered by salt stress with respect to the control. Slight differences in leaf necrosis and absence of injury in the membranes, stable content of photosynthetic pigments, and an increase in G-POD activity were also found in salt-treated plants. These results collectively suggest that ‘Sorrento’ has potential for the cultivation in salinized environments.

Cucumber and salinity

Salinity is becoming more expanded globally. Soil salinity imposes a great challenge for vegetable-crops production in arid and semiarid regions. Cucumber (Cucumis sativus L.) is the fourth most important vegetable crop worldwide. In this review, we discuss the complex network of effects, and the ways cucumber responds to salinity. Salt stress inhibits almost all growth phases and yield components of cucumber. Accumulation of Na+ and/or Cl- ions in cucumber tissues disturbs the absorption of other ions causing ionic imbalance which affect stomatal opening. Nevertheless, high levels of NaCl in soil inhibit water uptake in the root medium exposing cucumber to osmotic stress. Osmotic stress broadly interrupts metabolic pathways by altering enzymatic activity. Both, ionic and osmotic stresses induce ROS amassing in cucumber tissues. ROS directly constrain photosynthesis by decreasing levels of total chlorophyll and degrading PSII as well as corrupting thylakoid membranes. Ultimately, NaCl-induced stress inhibits cucumber seed germination, roots and shoots growth and development, fruit quality and yield production

Salt-Induced Stress Impacts the Phytochemical Composition and Aromatic Profile of Three Types of Basil in a Genotype-Dependent Mode.

Basil (Ocimum basilicum L.) is among the most widely used aromatic plants of Lamiaceae, often grown in areas where salinity is an adverse factor. Most studies on the effect of salinity on basil focused on the influence of salt stress on productive traits, while few reported on how it affects the phytochemical composition and the aroma profile. Three basil cultivars (Dark Opal, Italiano Classico, and Purple Ruffles) were grown hydroponically for 34 days with two nutrient solutions that differed in NaCl concentration [no NaCl (Control) and 60 mM NaCl]. Yield, secondary metabolite concentration (β-carotene and lutein), antioxidant activity [1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reduction antioxidant power (FRAP)], and aroma profile based on composition of volatile organic compounds (VOCs) were appraised in response to salinity applications. Salt stress significantly reduced fresh yield in Italiano Classico and Dark Opal by 43.34 and 31.69%, respectively, while no effect was observed in Purple Ruffles. Furthermore, the salt-stress treatment increased β-carotene and lutein concentrations, DPPH, and FRAP activities, and the total nitrogen content of the latter cultivar. CG-MS analysis revealed significant differences in VOCs composition of the basil cultivars, with Italiano Classico and Dark Opal characterized by the predominance of linalool (average 37.52%), which, however, was negatively affected by salinity. In Purple Ruffles, the predominant VOC compound, estragole (79.50%), was not affected by the deleterious effects of NaCl-induced stress.

Arbuscular Mycorrhizal Fungi Isolated from Highly Saline “Sabkha Habitat” Soil Alleviated the NaCl-Induced Stress and Improved Lasiurus scindicus Henr. Growth

Salt stress is one of the most significant abiotic stresses that substantially negatively impact plant growth and productivity. However, a slew of research thus far has investigated the ameliorating properties of arbuscular mycorrhizal (AM) symbiosis and their potential to improve plant tolerance to salt stress. The present study aimed to evaluate and compare the role of mycorrhizal inocula obtained from Sabkha (S-AMF) and non-Sabkha (NS-AMF) habitats of Saudi Arabia on the morphological, physiological, and biochemical behaviors of the Lasiurus scindicus plant. For this reason, arbuscular mycorrhizal fungi (AMF) isolated from Sabkha and non-Sabkha soils were treated with salinity-exposed L. scindicus. The results revealed that the AMF-treated plants had higher growth metrics and increased synthesis of photosynthetic pigments, which were reduced by salt stress. Furthermore, the application of AM symbiosis induced an increase in the activities of the antioxidant system, which resulted in a reduction of the plant oxidative damage. It was also found that the increased accumulation of proline and phenols acted as a protective measure. Moreover, plants inoculated with S-AMF had the highest ameliorating responses on all the studied parameters compared to NS-AMF. This could be attributed to the presence of habitat-specific AMF, which may have induced adaptive plasticity in plants to tolerate or resist extreme salinity. However, further study in exploring the S-AMF diversity is needed to make it an ecofriendly choice for the restoration of salinity-affected ecosystems.

Inoculation of barley with Trichoderma harzianum T-22 modifies lipids and metabolites to improve salt tolerance.

Soil salinity has a serious impact on plant growth and agricultural yield. Inoculation of crop plants with fungal endophytes is a cost-effective way to improve salt tolerance. We used metabolomics to study how Trichoderma harzianum T-22 alleviates NaCl-induced stress in two barley (Hordeum vulgare L.) cultivars, Gairdner and Vlamingh, with contrasting salinity tolerance. GC-MS was used to analyse polar metabolites and LC-MS to analyse lipids in roots during the early stages of interaction with Trichoderma. Inoculation reversed the severe effects of salt on root length in sensitive cv. Gairdner and, to a lesser extent, improved root growth in more tolerance cv. Vlamingh. Biochemical changes showed a similar pattern in inoculated roots after salt treatment. Sugars increased in both cultivars, with ribulose, ribose, and rhamnose specifically increased by inoculation. Salt stress caused large changes in lipids in roots but inoculation with fungus greatly reduced the extent of these changes. Many of the metabolic changes in inoculated cv. Gairdner after salt treatment mirror the response of uninoculated cv. Vlamingh, but there are some metabolites that changed in both cultivars only after fungal inoculation. Further study is required to determine how these metabolic changes are induced by fungal inoculation.

Assessment of NaCl-Induced Stress in Tomato (Lycopersicon esculentum L.)

Comparative study about the salt-induced oxidative stress and lipid peroxidation has been realised in primary root tissues for Tomato (Lycopersicon esculantum L.) in order to evaluate their responses to salt stress. Salinity impacts in terms of root growth, H2O2 generation, lipid peroxidation and membrane destabilisation were more pronounced in roots. Salt treatment in form of NaCl was given to the roots of the tomato plants in hydroponics culture. Root length was measured by centimetre scale, H2O2 and lipid peroxidation was confirmed by spectrophotometer. Absorbance for H2O2 estimation was recorded at 480 nm whereas for Lipid peroxidation was done at 600nm. When the tomato plants were treated with different concentrations of NaCl, it was observed that as the concentration of NaCl was increasing, there was decreased root growth resulting in reduced root length and proportionate increase in the amount of H2O2 production level with increase in the concentrations of NaCl treatment upto 300mM Concentration and Significant increase in Lipid peroxidation was observed with the increase in NaCl concentrations upto 500mM Concentration. Comparative response may be helpful in developing a better understanding of tolerance mechanisms to salt stress in Tomato.

Abscisic, gibberellic, and salicylic acids effects on germination indices of corn under salinity and drought stresses

ABSTRACT The expression of genes that control germination-related processes in corn (Zea mays L.) is influenced by environmental factors. Germination of seeds may be facilitated by hormonal priming. The purpose of this investigation was to quantify the effects of different germination temperatures [(5, 10, 15, 20, 25, 30, 35, and 40°C), NaCl-induced stress (0, −0.4, −0.8, and −1.2 MPa), and priming solutions (control, hydropriming, abscisic acid (ABA), gibberellic acid (GA), and salicylic acid (SA)] (Experiment 1). Effects of germination temperatures, PEG 6000-induced stress (0, −0.4, −0.8, and −1.2 MPa), and priming solutions were also evaluated separately (Experiment 2). In both cases, a completely randomized design with four replications was used. Increasing temperatures from 5 to 25°C gradually improved germination percentage and rate, whereas temperatures > 25°C decreased these indices. After imposing drought (PEG 6000-induced stress) or salinity (NaCl-induced stress) treatments, hormonal priming caused germination to occur at a lower base temperature, compared with the non-priming treatment. However, the effect of hormonal priming was dependent on temperature. At sub-optimal temperatures (< 25°C), the highest germination percentage and rate were recorded after GA priming. At above-optimal temperatures (> 25°C), ABA priming resulted in the highest germination percentage and rate. Moreover, hydrothermal time constant decreased in hormone-treated seeds. Based on coefficient of determination (R2 ) and root mean square error (RMSE), a dent-like model predicted cardinal temperatures more accurately than a beta model did. Generally, GA-, SA-, and ABA-priming were recommended under sub-optimal, optimal, and above-optimal temperatures, respectively.

Potassium and calcium improve salt tolerance of Thymus vulgaris by activating the antioxidant systems

Thyme (Thymus vulgaris L.) is an important wild aromatic plant of the Mediterranean region which also has wide-ranging therapeutic properties. Its growth and chemical properties can be modified by agricultural practices especially mineral nutrition and irrigation. An experiment was undertaken to determine the effectiveness of exogenous foliar application of potassium and calcium against the adverse effects of NaCl-induced stress on Thyme. Salt stress decreased growth and photosynthetic assimilation rate. Leaf spray with K+ or Ca2+ reduced salt-induced damage by maintaining K+/Na+ and Ca2+/Na+ ratios, resulting in photosynthesis improvement under salt conditions. Salt-affected plants had higher concentrations of hydrogen peroxide (H2O2) and malondialdehyde (MDA) in their shoot tissues indicating oxidative damage to their cell membranes; Increased K+ and Ca2+ supply reduced the accumulation of both. Salinity appears to have upregulated the activity of antioxidant defense enzymes superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase, glutathione reductase, peroxide guaiacol, Monodehydroascorbate reductase, as well as Dehydroascorbate reductase. The application of K+ and Ca2+ solutions onto the foliage of NaCl-affected plants further enhanced the activity of the antioxidant enzymes of the ascorbate glutathione cycle potentially allowing a better protection of the cell membranes from reactive oxygen species.

Regulation and remodeling of intermediate metabolite and membrane lipid during NaCl-induced stress in freshwater microalga Micractinium sp. XJ-2 for biofuel production.

Microalgae can accumulate a large fraction of reduced carbon as lipids under NaCl stress. This study investigated the mechanism of carbon allocation and reduction and triacylglycerol (TAG) accumulation in microalgae under NaCl-induced stress. Micractinium sp. XJ-2 was exposed to NaCl stress and cells were subjected to physiological, biochemical, and metabolic analyses to elucidate the stress-responsive mechanism. Lipid increased with NaCl concentration after 0-12 hr, then stabilized after 12-48 hr, and finally decreased after 48-72 hr, whereas TAG increased (0-48 hr) and then decreased (48-72 hr). Under NaCl-induced stress at lower concentrations, TAG accumulation, at first, mainly shown to rely on the carbon fixation through photosynthetic fixation, carbohydrate degradation, and membrane lipids remodeling. Moreover, carbon compounds generated by the degradation of some amino acids were reallocated and enhanced fatty acid synthesis. The remodeling of the membrane lipids of NaCl-induced microalgae relied on the following processes: (a) Increase in the amount of phospholipids and reduction in the amount of glycolipids and (b) extension of long-chain fatty acids. This study enhances our understanding of TAG production under NaCl stress and thus will provide a theoretical basis for the industrial application of NaCl-induced in the microalgal biodiesel industry.

Aquaponic and Hydroponic Solutions Modulate NaCl-Induced Stress in Drug-Type Cannabis sativa L.

The effects of salt-induced stress in drug-type Cannabis sativa L. (C. sativa), a crop with increasing global importance, are almost entirely unknown. In an indoor controlled factorial experiment involving a type-II chemovar (i.e., one which produces Δ9-tetrahydrocannabinolic acid ~THCA and cannabidiolic acid ~ CBDA), the effects of increasing NaCl concentrations (1–40 mM) was tested in hydroponic and aquaponic solutions during the flowering stage. Growth parameters (height, canopy volume), plant physiology (chlorophyll content, leaf-gas exchange, chlorophyll fluorescence, and water use efficiency), and solution physicochemical properties (pH, EC, and nutrients) was measured throughout the experiment. Upon maturation of inflorescences, plants were harvested and yield (dry inflorescence biomass) and inflorescence potency (mass-based concentration of cannabinoids) was determined. It was found that cannabinoids decreased linearly with increasing NaCl concentration: -0.026 and -0.037% THCA·mM NaCl-1 for aquaponic and hydroponic solutions, respectively. The growth and physiological responses to NaCl in hydroponic—but not the aquaponic solution—became negatively affected at 40 mM. The mechanisms of aquaponic solution which allow this potential enhanced NaCl tolerance is worthy of future investigation. Commercial cultivation involving the use of hydroponic solution should carefully monitor NaCl concentrations, so that they do not exceed the phytotoxic concentration of 40 mM found here; and are aware that NaCl in excess of 5 mM may decrease yield and potency. Additional research investigating cultivar- and rootzone-specific responses to salt-induced stress is needed.

Silicon Confers Soybean Resistance to Salinity Stress Through Regulation of Reactive Oxygen and Reactive Nitrogen Species.

Salt stress is one of the major abiotic stressors that causes huge losses to the agricultural industry worldwide. Different strategies have been adopted over time to mitigate the negative impact of salt stress on plants and reclaim salt-affected lands. In the current study, we used silicon (Si) as a tool for salinity alleviation in soybean and investigated the influence of exogenous Si application on the regulation of reactive oxygen and reactive nitrogen species and other salt stress–related parameters of the treated plants. Our results revealed that the canopy temperature was much higher in sole NaCl–treated plants but declined in Si + NaCl–treated plants. Furthermore, the chlorophyll contents decreased with sole NaCl treatment, whereas Si + NaCl–treated plants showed improved chlorophyll contents. In addition, Si application normalized the photosynthetic responses, such as transpiration rate (E) and net photosynthesis rate (PN) in salt-treated plants, and reduced the activity of ascorbate peroxidase and glutathione under salt stress. The expression levels of antioxidant-related genes GmCAT1, GmCAT2, and GmAPX1 started to decline at 12 h after addition of Si to NaCl-treated plants. Similarly, the S-nitrosothiol and nitric oxide (NO)–related genes were upregulated in the salt stress condition but reduced after Si supplementation. Si application downregulated genes associated with reactive oxygen species and reactive nitrogen species and reduced enzymatic and non-enzymatic antioxidants of the treated plants. Results of the current study conclude that Si mitigated the adverse effects of NaCl-induced stress by modulating the crosstalk between antioxidants and NO scavengers. It is suggested that Si may be used in agricultural systems for alleviating salt stress.

Sodium Chloride Induced Stress Responses of Antioxidative Activities in Leaves and Roots of Pistachio Rootstock.

Salinity substantially affects plant growth and crop productivity worldwide. Plants adopt several biochemical mechanisms including regulation of antioxidant biosynthesis to protect themselves against the toxic effects induced by the stress. One-year-old pistachio rootstock exhibiting different degrees of salinity tolerance were subjected to sodium chloride induced stress to identify genetic diversity among cultivated pistachio rootstock for their antioxidant responses, and to determine the correlation of these enzymes to salinity stress. Leaves and roots were harvested following NaCl-induced stress. The results showed that a higher concentration of NaCl treatment induced oxidative stress in the leaf tissue and to a lesser extent in the roots. Both tissues showed an increase in ascorbate peroxidase, superoxide dismutase, catalase, glutathione reductase, peroxidase, and malondialdehyde. Responses of antioxidant enzymes were cultivar dependent, as well as temporal and dependent on the salinity level. Linear and quadratic regression model analysis revealed significant correlation of enzyme activities to salinity treatment in both tissues. The variation in salinity tolerance reflected their capabilities in orchestrating antioxidant enzymes at the roots and harmonized across the cell membranes of the leaves. This study provides a better understanding of root and leaf coordination in regulating the antioxidant enzymes to NaCl induced oxidative stress.

The interactive effect of nitrate/ammonium ratio and sodium chloride on Tunisian medicinal plant (Nigella sativa L)

This study was carried out to investigate the effects of salt (60 mM NaCl) in nigella (Nigella sativa L.) amended with different nitrogen (N) forms. Plants were grown for 2 weeks under hydroponic conditions in the presence of 3 regimes of nitrogen: nitrate (NO3−) alone, ammonium (NH4+) alone, or the mixture of NO3− and NH4+ combined or not with 60 mM sodium chloride (NaCl). Results indicated that N. sativa performs much better when fed with 2.5: 0.00 mM and 1.25: 1.25 mM NO3−: NH4+, than the other ratios. NaCl addition reduced chlorophyll concentration regardless of N source. In the absence of NaCl, photosynthesis rate was more important in exclusively NO3− amended plants than other ratios. NaCl restricted transpiration and stomatal conductance, excepting in 00: 2.5 NO3−/NH4+-feed plants. As compared to their respective control, the nutrition of NO3− feed plants was more affected by salt than that of NH4+-feed ones. Na+ was less accumulated in the tissues of plants amended with NH4+ than if fed with NO3−. This behavior could maintain the ratio of K+/Na+ in the shoot of NH4+-fed plants. NaCl increased the antioxidant activity independently of nitrate/ammonium ratio. The considerable advantage of NH4+ nutrition under salt could be related with high production of total phenolic compounds and flavonoids.Hence, we showed that Nigella sativa was more sensitive to salt if cultivated in the presence of NO3−/NH4+ ratio higher than 1. NH4+ alleviates NaCl-induced stress by the reduction of the Na+ accumulation in the organs and an increase in antioxidative responses.

Correction to: NaCl-induced stress: physiological responses of six halophyte species in in vitro and in vivo culture

In the original article, some of the values in the fifth column of Table 2 and in the fifth and eighth columns of Table 4 are incorrect. The corrected values are in bold typeface in both tables below.

NaCl-induced stress: physiological responses of six halophyte species in in vitro and in vivo culture

To investigate the mechanisms underlying salt tolerance, physiological parameters of six halophyte species [Vitex rotundifolia L., Clerodendrum inerme (L.) Gaertn, Phyla nodiflora (L.) Greene, Scaevola sericea Vahl, Alternanthera bettzickiana (Regel) Nichols, and Dracaena cambodiana Pierre ex Gagn] under NaCl stress in in vitro and in vivo culture tests were examined. Membership function analysis and cluster analysis divided the six species, based on their salt tolerance level, into three groups: Group 1 (highly salt tolerant) included C. inerme, A. bettzickiana and S. sericea; Group 2 (moderately salt tolerant) included P. nodiflora; Group 3 (weakly salt tolerant) included V. rotundifolia and D. cambodiana. In response to in vitro NaCl stress, all six species showed a significant increase in the activities of antioxidant enzymes. NaCl stress enhanced free proline content in the leaves of all six species. CAT, SOD activity and proline accumulation were significantly correlated with the growth of C. inerme, P. nodiflora and A. bettzickiana under in vitro NaCl treatment. We conclude that NaCl-tolerant plants may suffer slight damage within a certain salt concentration, as evidenced by the activities of antioxidant enzymes and the accumulation of free proline. Six halophytic species showed a different salt tolerance level under in vitro and in vivo culture tests, due to the activities of antioxidant enzymes and the accumulation of free proline.

Enhanced Lipid Production and Molecular Dynamics under Salinity Stress in Green Microalga Chlamydomonas reinhardtii (137C).

Microalgal lipids are a source of valuable nutritional ingredients in biotechnological industries, and are precursors to biodiesel production. Here, the effects of salt-induced stresses, including NaCl, KCl, and LiCl stresses, on the production of lipid in green microalga Chlamydomonas reinhardtii (137c) were investigated. NaCl stress dramatically increased saturated fatty acids (SFAs), which accounted for 70.2% of the fatty acid methyl ester (FAMEs) under stress. In contrary, KCl stress led to a slight increase in SFAs (47.05%) with the remaining being polyunsaturated fatty acids (PUFAs) (45.77%). RT-PCR analysis revealed that the genes involved in FA biosynthesis, such as PDH2, ACCase, MAT and KAS2, were up-regulated by NaCl-induced stress. Conversely, the genes responsible for the Kennedy pathway were suppressed. The alteration of FA homeostasis was further assessed by overexpressing MAT, the enzyme responsible for the production of malonyl-ACP, a key building block for FA biosynthesis, in the cyanobacterium Synechococcus elongatus PCC 7942. Intracellular FA composition was affected, with a predominant synthesis of SFAs in transformed cells. Owing to the diversity and relative abundance of SFAs, monounsaturated fatty acid (MUFAs) and PUFAs enable the feasibility of using microorganisms as a source of microalgal lipids or valuable nutritional ingredients; salt-induced stress and expression of MAT are useful in providing precursors for enhanced lipid production.

Cochliobolus sp. acts as a biochemical modulator to alleviate salinity stress in okra plants

Salinity stress can severely affect the growth and production of the crop plants. Cheap and reliable actions are needed to enable the crop plants to grow normal under saline conditions. Modification at the molecular level to produce resistant cultivars is one of the promising, yet highly expensive techniques, whereas application of endophytes on the other hand are very cheap. In this regard, the role of Cochliobolus sp. in alleviating NaCl-induced stress in okra has been investigated. The growth and biomass yield, relative water content, chlorophyll content and IAA were decreased, whereas malondialdehyde (MDA) and proline content were increased in okra plants treated with 100 mM NaCl. On the contrary, okra plants inoculated with C. lunatus had higher shoot length, root length, plant dry weight, chlorophyll, carotenoids, xanthophyll, phenolicss, flavonoids, IAA, total soluble sugar and relative water content, while lower MDA. LC-MS/MS analysis of the Cochliobolus sp. extract revealed the presence of pinocembrin, chlorogenic acids, wogonin, calycosin and diadzein as a salinity stress reliever. From the results, it can be concluded that colonization of Cochliobolus sp. improves the NaCl tolerance by ameliorating the physicochemical attributes of the host plants.

Targeted Protection of Mitochondria of Mesophyll Cells in Transgenic CYP11A1 CDNA Expressing Tobacco Plant Leaves After NaCl-Induced Stress Damage

Abstract Recently we have showed that the expression of the mammalian CYP11A1 cDNA in plants confers their resistance to abiotic and biotic stresses. To determine the role of heterologous expression of cytochrome P450scc cDNA in resistance to ROS (radical oxygen species) dependent abiotic stresses, the structural changes of mitochondria and peroxisomes were studied under 150 mM NaCl-induced 14-day salinity treatment on juvenile tobacco plants in in vitro culture. Ultrastructural analysis of mesophyll cells of transgenic tobacco leaves constitutively expressing CYP11A1 cDNA was performed. Under NaCl stress, a change in shape from rounded to elon-gated, reduced section area, formation of branched mitochondria, as well as the emergence of triangular and rhomboid cristae, densification of a mitochondrial matrix, increase in density of contrasting membranes and their thickness were observed in non-transgenic plants. Transgenic plants without stress applied had mitochondria with rounded and elongated shape, twice as small as in non-transgenic plants, with a dense matrix and sinuous cristae. Surprisingly, the effect of NaCl led to increase in size of mitochondria by 1.5 times, decomposition of matrix and the emergence in organelles of light zones presumably containing mitochondrial DNA strands. Thus, the structural organisation of transgenic plant mitochondria under salinity treatment was comparable to that of non-transgenic plants under native conditions. It was also noted that the transgenic plant peroxisomes differed in non-transgenic tobacco both in normal condition and under the action of NaCl. The observed differences in ultrastructural organisation of mitochondria not only support our earlier notion about successful incorporation of the mature P450scc into this organelle, but for the first time demonstrate that the mammalian CYP11A1 signal peptide sequence could be efficiently used in the formation of targeted mitochondria protection of plants from salinity-induced damage.

Efficient rhizobacteria promote growth and alleviate NaCl-induced stress in the plant species Sulla carnosa

The present work aims to characterize native bacteria from the saline rhizosphere of Sulla carnosa and to identify promising rhizobacteria isolates able to ameliorate the salt tolerance of this species. Bacteria were screened in vitro for salt tolerance capacity and plant growth promoting characteristics (PGP). Selected NaCl-tolerant bacteria showing a high PGP potential were further characterized for plant promotion effects on the growth of S. carnosa under salt stress (200 mM NaCl). Three putative salt-tolerant strains that showed multiple PGP-traits identified as Acinetobactersp. (Br3), Pseudomonas putida (Br18) and Curtobacterium sp. (Br20) were selected for inoculation study. In a greenhouse experiment, NaCl significantly disturbed physiological parameters in non-inoculated S. carnosa. In these plants, NaCl reduced growth, increased foliar proline and malondialdehyde concomitant to Na± shoot concentrations. However, bacterial inoculation with selected PGP isolates ameliorated significantly plant growth and alleviated salt-induced physiological disturbances. Hence, as compared to non-inoculated plants, inoculation provided a significant increase in dry biomass and increased photosynthetic efficiency and chlorophyll leaf content under saline condition. Additional analysis showed that microbial inoculation also enhanced total soluble sugars content and antioxidant enzymes activities thereby preventing reactive oxygen species (ROS)-induced oxidative damage in plants. These results suggest that the inoculation of NaCl-stressed plants with selected salt-tolerant PGPR inocula exert beneficial effects on plant growth by alleviating salt-induced toxicity stress on plant growth and development.