Abscisic acid root and leaf concentration in relation to biomass partitioning in salinized tomato plants

Comparing yield, nutrient uptake and water use efficiency of Nasturtium officinale cultivated in aquaponic, hydroponic, and soil systems

Soilless systems have become increasingly popular as effective solutions for regions with infertile soil, low water availability, limited space, and environmental pollution. There is limited information on the role of soilless culture in the production of medicinal plants. While some research has examined growth rates and yields, there is not enough data on how these systems affect nutrient uptake, physiological properties, and water use efficiency (WUE) in medicinal plants. This research investigated soilless systems as alternative techniques for cultivating watercress (Nasturtium officinale). The study was conducted using a completely randomized design with five replications and assessed the impact of different cultivation systems (hydroponic, aquaponic, and soil) on the growth of watercress. The results showed that cultivation systems had significant effects on morphological, physiological and nutrient content of watercress (P < 0.01). When grown using hydroponics and aquaponics, watercress exhibited a 58.2 and 54.3 % increase in height, a 104.7 and 59.2 % increase in root length, a 20.1 and 72.9 % increase in leaves, a 44.3 and 11.4 % increase in lateral branches, a 58.5 and 35.3 % increase in leaf area, and a 46.8 and 81 % increase in yield, respectively, than the soil-based system. The soil-based system promoted higher levels of chlorophyll a and b, while the soilless systems exhibited higher amounts of carotenoids, protein, proline, and relative water content (P < 0.01). The aquaponics demonstrated the highest N, P, Mg, S, and Na, while the soil system displayed the highest Ca, Fe, and Zn concentrations. The higher amount Fe and Zn in soil system can be attributed to soil organic matter, which plays a role in chelating micronutrients and enhancing their accessibility for plant absorption. Different cultivation systems significantly affected the daily water usage and WUE. Daily water decreased by 39 and 34.4 % in the hydroponic and aquaponic, respectively than soil-based system. WUE in the hydroponic and aquaponic was 2.45 and 2.78 higher than in the soil. Overall, soilless systems resulted in faster plant growth and higher yields. This efficiency can lead to reduced inputs and less environmental impact than traditional farming. Further investigation is needed to assess the economic feasibility of growing medicinal plants using soilless methods.

Phlorotannins contribute to the ameliorative bioactivities of Ecklonia maxima-derived bioproduct in salt-stressed Solanumlycopersicum

Seaweed-derived bioproducts are increasingly being deployed as an environmentally friendly and sustainable approach to crop management under stressful growth conditions including salinity. The bioactivities of seaweed-derived extracts are linked to the presence of diverse groups of bioactive compounds. In the present study, the phlorotannins present in the seaweed Ecklonia maxima and Kelpak®, an E. maxima-derived bioproduct, were quantified and identified. Three phlorotannins were identified in E. maxima, namely eckol, 2-phloroeckol, and dibenzodioxin-fucodiphloroethol. Eckol (589.11 - 822.54 μg l-1) and dibenzodioxin-fucodiphloroethol (85 - 895 μg l-1) were present in Kelpak®. Phlorotannin bioactivity was investigated in tomato seedlings grown under NaCl-induced salinity stress. The seedlings treated with either individual phlorotannins (i.e., eckol or a fraction containing 2-phloroeckol and dibenzodioxin-fucodiphloroethol) or Kelpak® resulted in a reprogramming of biomass allocation as indicated by an increased root-to-shoot ratio. Phlorotannin and Kelpak® treatments induced the accumulation of antioxidants with an attendant augmentation of the antioxidant capacities and inhibition of membrane damage in the NaCl-stressed seedlings. Kelpak® treatment induced an increase in abscisic acid (ABA) accumulation and phlorotannin treatments lowered the ABA content of the stressed seedlings. These results demonstrated that phlorotannins contributed to the ameliorative actions of Kelpak®. The more potent effects of Kelpak®, in comparison to phlorotannins, in improving dry matter accumulation, ABA content, antioxidative properties, and inhibiting tissue injury of the salt-stressed tomato seedlings may be attributed to the presence of other bioactive components in the Kelpak® product.

Asymmetric Warming of Day and Night Benefits the Early Growth of Acer mono Seedlings More Than Symmetric Warming

Asymmetric warming refers to the difference between the increase in daytime maximum temperature and the increase in nighttime minimum temperature and has been documented in temperate regions. However, its impacts on seedling growth have been largely ignored. In this study, seedlings of a widely distributed tree species, Acer mono Maxim., were exposed to both symmetric warming (SW) and asymmetric warming scenarios (day warming [DW], night warming [NW] and diurnal asymmetric warming [DAW]). Compared to control, all warming scenarios were found to enhance belowground biomass. DW promoted the seedling growth, while NW reduced the stem biomass. DAW did not impact the total biomass relative to the control. Compared to SW, DAW advanced phenology, increased indole-3-acetic acid content and chlorophyll content, which enhanced total biomass and stored more NSC in the root. Future DAW would be not beneficial to the growth of A. mono seedlings by comparing with the control. This research encourages further exploration of tree growth experiments under asymmetric warming conditions, as most studies tend to underestimate the warming effects on plant growth by focusing on SW. Incorporating the responses of seedling physiology and growth to non-uniform diurnal warming into earth system models is crucial for more accurately predicting carbon and energy balances in a warmer world.

Similar and divergent responses to salinity stress of jamun (Syzygium cumini L. Skeels) genotypes

Background

Genetic variation for salt tolerance remains elusive in jamun (Syzygium cumini).

Methods

Effects of gradually increased salinity (2.0-12.0 dS/m) were examined in 20 monoembryonic and 28 polyembryonic genotypes of jamun. Six genotypes were additionally assessed for understanding salt-induced changes in gas exchange attributes and antioxidant enzymes.

Results

Salt-induced reductions in leaf, stem, root and plant dry mass (PDM) were relatively greater in mono- than in poly-embryonic types. Reductions in PDM relative to control implied more adverse impacts of salinity on genotypes CSJ-28, CSJ-31, CSJ-43 and CSJ-47 (mono) and CSJ-1, CSJ-24, CSJ-26 and CSJ-27 (poly). Comparably, some mono- (CSJ-5, CSJ-18) and poly-embryonic (CSJ-7, CSJ-8, CSJ-14, CSJ-19) genotypes exhibited least reductions in PDM following salt treatment. Most polyembryonic genotypes showed lower reductions in root than in shoot mass, indicating that they may be more adept at absorbing water and nutrients when exposed to salt. The majority of genotypes did not exhibit leaf tip burn and marginal scorch despite significant increases in Na+ and Cl-, suggesting that tissue tolerance existed for storing excess Na+ and Cl- in vacuoles. Jamun genotypes were likely more efficient in Cl- exclusion because leaf, stem and root Cl- levels were consistently lower than those of Na+ under salt treatment. Leaf K+ was particularly little affected in genotypes with high leaf Na+. Lack of discernible differences in leaf, stem and root Ca2+ and Mg2+ contents between control and salt treatments was likely due to their preferential uptake. Correlation analysis suggested that Na+ probably had a greater inhibitory effect on biomass in both mono- and poly-embryonic types. Discriminant analysis revealed that while stem and root Cl- probably accounted for shared responses, root Na+, leaf K+ and leaf Cl- explained divergent responses to salt stress of mono- and poly-embryonic types. Genotypes CSJ-18 and CSJ-19 seemed efficient in fending off oxidative damage caused by salt because of their stronger antioxidant defences.

Conclusions

Polyembryonic genotypes CSJ-7, CSJ-8, CSJ-14 and CSJ-19, which showed least reductions in biomass even after prolonged exposure to salinity stress, may be used as salt-tolerant rootstocks. The biochemical and molecular underpinnings of tissue tolerance to excess Na+ and Cl- as well as preferential uptake of K+, Ca2+, and Mg2+ need to be elucidated.

How Does Zinc Improve Salinity Tolerance? Mechanisms and Future Prospects

Salinity stress (SS) is a serious abiotic stress and a major constraint to agricultural productivity across the globe. High SS negatively affects plant growth and yield by altering soil physio-chemical properties and plant physiological, biochemical, and molecular processes. The application of micronutrients is considered an important practice to mitigate the adverse effects of SS. Zinc (Zn) is an important nutrient that plays an imperative role in plant growth, and it could also help alleviate the effects of salt stress. Zn application improves seed germination, seedling growth, water uptake, plant water relations, nutrient uptake, and nutrient homeostasis, therefore improving plant performance and saline conditions. Zn application also protects the photosynthetic apparatus from salinity-induced oxidative stress and improves stomata movement, chlorophyll synthesis, carbon fixation, and osmolytes and hormone accumulation. Moreover, Zn application also increases the synthesis of secondary metabolites and the expression of stress responsive genes and stimulates antioxidant activities to counter the toxic effects of salt stress. Therefore, to better understand the role of Zn in plants under SS, we have discussed the various mechanisms by which Zn induces salinity tolerance in plants. We have also identified diverse research gaps that must be filled in future research programs. The present review article will fill the knowledge gaps on the role of Zn in mitigating salinity stress. This review will also help readers to learn more about the role of Zn and will provide new suggestions on how this knowledge can be used to develop salt tolerance in plants by using Zn.

Glutathione Transferases Are Involved in the Genotype-Specific Salt-Stress Response of Tomato Plants

Glutathione transferases (GSTs) are one of the most versatile multigenic enzyme superfamilies. In our experiments, the involvement of the genotype-specific induction of GST genes and glutathione- or redox-related genes in pathways regulating salt-stress tolerance was examined in tomato cultivars (Solanum lycopersicum Moneymaker, Mobil, and Elán F1). The growth of the Mobil plants was adversely affected during salt stress (100 mM of NaCl), which might be the result of lowered glutathione and ascorbate levels, a more positive glutathione redox potential (EGSH), and reduced glutathione reductase (GR) and GST activities. In contrast, the Moneymaker and Elán F1 cultivars were able to restore their growth and exhibited higher GR and inducible GST activities, as well as elevated, non-enzymatic antioxidant levels, indicating their enhanced salt tolerance. Furthermore, the expression patterns of GR, selected GST, and transcription factor genes differed significantly among the three cultivars, highlighting the distinct regulatory mechanisms of the tomato genotypes during salt stress. The correlations between EGSH and gene expression data revealed several robust, cultivar-specific associations, underscoring the complexity of the stress response mechanism in tomatoes. Our results support the cultivar-specific roles of distinct GST genes during the salt-stress response, which, along with WRKY3, WRKY72, DREB1, and DREB2, are important players in shaping the redox status and the development of a more efficient stress tolerance in tomatoes.

The Knockdown of AUXIN RESPONSE FACTOR 2 Confers Enhanced Tolerance to Salt and Drought Stresses in Tomato (Solanum lycopersicum L.)

Auxin response factors (ARFs) act as key elements of the auxin-signaling pathway and play important roles in the process of a plant's growth, development, and response to environmental conditions. We studied the implication of the SlARF2 gene in the tomato response to salt (150 mM of NaCl) and drought (15% PEG 20000) stresses. The functional characterization of SlARF2 knockdown tomato mutants revealed that the downregulation of this gene enhanced primary root length and root branching and reduced plant wilting. At the physiological level, the arf2 mutant line displayed higher chlorophyll, soluble sugars, proline, and relative water contents as well as lower stomatal conductance and a decreased malondialdehyde content. Moreover, SlARF2 knockdown tomato mutants demonstrated higher activities of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) under salt and drought stresses than the wild type. Indeed, the stress tolerance of the arf2 mutant was also reflected by the upregulation of stress-related genes involved in ROS scavenging and plant defense, including SOD, CAT, dehydration-responsive element-binding protein, and early responsive to dehydration, which can ultimately result in a better resistance to salt and drought stresses. Furthermore, the transcriptional levels of the Δ1-pyrroline-5-carboxylate synthase (P5CS) gene were upregulated in the arf2 mutant after stress, in correlation with the higher levels of proline. Taken together, our findings reveal that SlARF2 is implicated in salt and drought tolerance in tomato and provides some considerable elements for improving the abiotic stress tolerance and increasing the crop yields of tomato.

Abscisic Acid: A Potential Secreted Effector Synthesized by Phytophagous Insects for Host-Plant Manipulation

Abscisic acid (ABA) is an isoprenoid-derived plant signaling molecule involved in a wide variety of plant processes, including facets of growth and development as well as responses to abiotic and biotic stress. ABA had previously been reported in a wide variety of animals, including insects and humans. We used high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-(ESI)-MS/MS) to examine concentrations of ABA in 17 species of phytophagous insects, including gall- and non-gall-inducing species from all insect orders with species known to induce plant galls: Thysanoptera, Hemiptera, Lepidoptera, Coleoptera, Diptera, and Hymenoptera. We found ABA in insect species in all six orders, in both gall-inducing and non-gall-inducing species, with no tendency for gall-inducing insects to have higher concentrations. The concentrations of ABA in insects often markedly exceeded those typically found in plants, suggesting it is highly improbable that insects obtain all their ABA from their host plant via consumption and sequestration. As a follow-up, we used immunohistochemistry to determine that ABA localizes to the salivary glands in the larvae of the gall-inducing Eurosta solidaginis (Diptera: Tephritidae). The high concentrations of ABA, combined with its localization to salivary glands, suggest that insects are synthesizing and secreting ABA to manipulate their host plants. The pervasiveness of ABA among both gall- and non-gall-inducing insects and our current knowledge of the role of ABA in plant processes suggest that insects are using ABA to manipulate source-sink mechanisms of nutrient allocation or to suppress host-plant defenses. ABA joins the triumvirate of phytohormones, along with cytokinins (CKs) and indole-3-acetic acid (IAA), that are abundant, widespread, and localized to glandular organs in insects and used to manipulate host plants.

Tomato responses to salinity stress: From morphological traits to genetic changes

Tomato is an essential annual crop providing human food worldwide. It is estimated that by the year 2050 more than 50% of the arable land will become saline and, in this respect, in recent years, researchers have focused their attention on studying how tomato plants behave under various saline conditions. Plenty of research papers are available regarding the effects of salinity on tomato plant growth and development, that provide information on the behavior of different cultivars under various salt concentrations, or experimental protocols analyzing various parameters. This review gives a synthetic insight of the recent scientific advances relevant into the effects of salinity on the morphological, physiological, biochemical, yield, fruit quality parameters, and on gene expression of tomato plants. Notably, the works that assessed the salinity effects on tomatoes were firstly identified in Scopus, PubMed, and Web of Science databases, followed by their sifter according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline and with an emphasis on their results. The assessment of the selected studies pointed out that salinity is one of the factors significantly affecting tomato growth in all stages of plant development. Therefore, more research to find solutions to increase the tolerance of tomato plants to salinity stress is needed. Furthermore, the findings reported in this review are helpful to select, and apply appropriate cropping practices to sustain tomato market demand in a scenario of increasing salinity in arable lands due to soil water deficit, use of low-quality water in farming and intensive agronomic practices.

Tomato salt tolerance mechanisms and their potential applications for fighting salinity: A review

One of the most significant environmental factors affecting plant growth, development and productivity is salt stress. The damage caused by salt to plants mainly includes ionic, osmotic and secondary stresses, while the plants adapt to salt stress through multiple biochemical and molecular pathways. Tomato (Solanum lycopersicum L.) is one of the most widely cultivated vegetable crops and a model dicot plant. It is moderately sensitive to salinity throughout the period of growth and development. Biotechnological efforts to improve tomato salt tolerance hinge on a synthesized understanding of the mechanisms underlying salinity tolerance. This review provides a comprehensive review of major advances on the mechanisms controlling salt tolerance of tomato in terms of sensing and signaling, adaptive responses, and epigenetic regulation. Additionally, we discussed the potential application of these mechanisms in improving salt tolerance of tomato, including genetic engineering, marker-assisted selection, and eco-sustainable approaches.

Effects of Salt Stress on the Morphology, Growth and Physiological Parameters of Juglansmicrocarpa L. Seedlings

In this study, to screen for walnut salt-tolerant rootstocks, Juglans microcarpa L. seedlings were treated in different NaCl concentrations (0, 50, 100, 200, and 300 mmol/L), and the growth situation of seedlings was observed. Moreover, we determined the physiological indexes of seedlings on different days (6, 12, 18, and 24 d) after treatment. The results showed that after salt stress, the external morphology of seedlings displayed salt injury, which manifested as yellowing, withering, curling, and falling off of leaves. High concentrations and long-term stress led to more serious damage, with numerous leaves undergoing withering and shedding. Salt stress significantly inhibited the growth of seedlings. With the increase in salt concentration and stress time, the chlorophyll content and photosynthetic parameters of seedlings reduced to varying degrees; the relative electrical conductivity (REC) and malondialdehyde (MDA) increased. Superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities generally increased, followed by a decrease; proline (Pro) accumulated; and soluble sugar (SS) content first increased and then decreased. In addition, it promoted the production of abscisic acid (ABA) and inhibited the synthesis of indole-3-acetic acid (IAA), gibberellic acid 3 (GA3), and zeatin riboside (ZR). It was found that J.microcarpa L. seedlings were more tolerant under 100 mmol/L salt stress, whereas the damage to growth was more severe at 200 mmol/L to 300 mmol/L salt stress.

Removal of total nitrogen from wastewater by a combination of Chlorella sp. and audible sound

In developing countries, nitrogen in the traditional market wastewater is a critical environmental problem. In this study, the microalga Chlorella sp., which was isolated from wastewater, was used to remove the total nitrogen (TN) from conventional market wastewater in combination with audible sound (Vietnamese classical music). In addition, effects of sound exposure on removal efficiency at different initial cell densities were analyzed. Results revealed that music sound control demonstrates potential to improve the removal efficiency. TN removal efficiencies of 96%, 69.5%, and 4.3% were observed for treatments with Chlorella sp./audible sound, Chlorella sp., and without Chlorella sp., respectively. The significance of probability value (p-value) (<0.05) on the paired sample t-test confirmed the critical role of audible sound and Chlorella sp. density on the TN removal in screening experiments. The predicted optimal conditions for TN removal were as follows: a Chlorella sp. density of 4%, an audible sound of 52.5 dB, and a cultivation time of 4.6 days. Results based on statistical analysis revealed that the quadratic models for TN removal are significant at a low p-value (<0.05) and a high predicted coefficient of determination (R² = 0.9452) value. The obtained statistical results also indicated that most of the variables are significant for the abatement of TN from market wastewater using Chlorella sp.

Endophytic halotolerant Bacillus velezensis FMH2 alleviates salt stress on tomato plants by improving plant growth and altering physiological and antioxidant responses

Salinity stress has significant deleterious effects on agricultural lands and plant yields. Plants undergo a series of physiological and molecular changes to reduce salt-induced damage. However, these mechanisms remain insufficient. The inoculation of plant growth promoting bacteria to improve plant health under stress conditions offers promise. Bacillus velezensis FMH2 has been shown to protect tomato fruits against black mold disease and to improve seed tolerance to abiotic stresses. During this study, the major physiological and metabolic changes connected with FMH2 mitigation of abiotic stress tolerance in tomato plants were explored. In presence of different salt levels, FMH2 showed a high potentiality to colonize internal plant tissues and to produce several plant growth promoting metabolites such as siderophores, indole acetic acid, and hydrolytic enzymes. FMH2-treatment promoted plant growth (root structure, plant elongation, leaf emission, fresh and dry weights, water content, etc.) in absence as well as in presence of salt stress. FMH2 treatment decreased endogenous Na⁺ accumulation and increased K⁺ and Ca²⁺ uptake. Furthermore, B. velezensis FMH2-treatment improved chlorophyll contents, membrane integrity and phenol peroxidase concentrations, and reduced malondialdehyde and hydrogen peroxide levels under saline conditions with a significant salinity × strain interaction. The present study suggests the endophytic strain FMH2 involved different mechanisms and regulatory functions to enhance plant oxidative systems and regulate ion uptake mechanisms supporting both growth and stress management.

Halotolerant Microbial Consortia for Sustainable Mitigation of Salinity Stress, Growth Promotion, and Mineral Uptake in Tomato Plants and Soil Nutrient Enrichment

Salinity significantly impacts the growth, development, and reproductive biology of various crops such as vegetables. The cultivable area is reduced due to the accumulation of salts and chemicals currently in use and is not amenable to a large extent to avoid such abiotic stress factors. The addition of microbes enriches the soil without any adverse effects. The effects of microbial consortia comprising Bacillus sp., Delftia sp., Enterobacter sp., Achromobacter sp., was evaluated on the growth and mineral uptake in tomatoes (Solanum Lycopersicum L.) under salt stress and normal soil conditions. Salinity treatments comprising Ec 0, 2, 5, and 8 dS/m were established by mixing soil with seawater until the desired Ec was achieved. The seedlings were transplanted in the pots of the respective pH and were inoculated with microbial consortia. After sufficient growth, these seedlings were transplanted in soil seedling trays. The measurement of soil minerals such as Na, K, Ca, Mg, Cu, Mn, and pH and the Ec were evaluated and compared with the control 0 days, 15 days, and 35 days after inoculation. The results were found to be non-significant for the soil parameters. In the uninoculated seedlings’ (control) seedling trays, salt treatment significantly affected leaf, shoot, root dry weight, shoot height, number of secondary roots, chlorophyll, and mineral contents. While bacterized seedlings sown under saline soil significantly increased leaf (105.17%), shoot (105.62%), root (109.06%) dry weight, leaf number (75.68%), shoot length (92.95%), root length (146.14%), secondary roots (91.23%), and chlorophyll content (−61.49%) as compared to the control (without consortia). The Na and K intake were higher even in the presence of the microbes, but the beneficial effect of the microbe helps plants sustain in the saline environment. The inoculation of microbial consortia produced more secondary roots, which accumulate more minerals and transport substances to the different parts of the plant; thus, it produced higher biomass and growth. Results of the present study revealed that the treatment with microbial consortia could alleviate the deleterious effects of salinity stress and improve the growth of tomato plants under salinity stress. Microbial consortia appear to be the best alternative and cost-effective and sustainable approach for managing soil salinity and improving plant growth under salt stress conditions.

Halotolerant Bacillus spizizenii FMH45 promoting growth, physiological, and antioxidant parameters of tomato plants exposed to salt stress

Bacillus spizizenii is for the first time described as a plant growth salt-tolerant bacterium able to alleviate salt stress in crop plants by improving physiological parameters and antioxidant defense mechanisms. Agricultural soil salinization is a serious issue worldwide affecting agricultural yield. Plant growth promoting bacteria can enhance salt tolerance and plant yield. Bacillus spizizenii FMH45 has been shown to inhibit fungal attacks in tomato fruits and to augment tomato seed germination in presence of abiotic stresses. During this study, we reported for the first time B. spizizenii as a salt-tolerant bacterium able to alleviate salt stress in tomato plants. B. spizizenii FMH45 was examined in vitro for its potential to produce several plant growth promoting characters (siderophores, IAA, and phosphate solubilization) and hydrolytic enzymes (cellulase, glucanase and protease) in the presence of saline conditions. FMH45 was also investigated in vivo in pot experiments to evaluate its ability to promote tomato plant growth under salt stress condition. FMH45 inoculation, enhanced tomato seedling length, vigor index, and plant fresh and dry weights when compared to the non-inoculated controls exposed and not exposed to a regular irrigation with salt solutions containing: 0; 3.5; 7; and 10 g L^-1 of NaCl. FMH45-treated plants also presented improved chlorophyll content, membrane integrity (MI), and phenol peroxidase (POX) concentrations, as well as reduced malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) levels under saline conditions with a significant salinity × strain interaction. Furthermore, FMH45 inoculation significantly decreased endogenous Na⁺ accumulation, increased K⁺ and Ca²⁺ uptake, and thereby improved K⁺/Na⁺ and Ca²⁺/Na⁺ ratios. This study proves that bio-inoculation of FMH45 efficiently increases salt tolerance in tomato plants. This sustainable approach can be applied to other stressed plant species in affected soils.

Untargeted LC-MS-based metabolomics revealed specific metabolic changes in cotyledons and roots of Ricinus communis during early seedling establishment under salt stress

Early seedling development is one of the most crucial period of the plant's life cycle, which is highly susceptible to adverse environmental conditions, especially those impose by salt stress. Castor plant (Ricinus communis) is a famous non-edible oilseed and salt-resistant crop worldwide. However, the specific metabolic responses in the cotyledons and roots of this species during seedling establishment under salt stress are still not clearly understood. In the present study, 16 d castor seedlings were treated with 150 mM NaCl for 6 d, and the metabolite profiling of cotyledons and roots was conducted using liquid chromatography (LC) combined with electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). The Principal Component Analysis (PCA) results showed that the metabolites were great differed in cotyledons and roots under salt stress. There were 38 differential metabolites, mainly including fatty acid, nucleic acid and organic acids in the cotyledons, but only 19 differential metabolites, mainly including fatty acid and organic acids in the roots under such condition. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that flavone and flavonol biosynthesis, pantothenate and CoA biosynthesis, citrate cycle and carotenoid biosynthesis were the common metabolic pathways in response to salt stress in the two organs. Salt stress caused metabolite process alteration mainly on carbon and nitrogen metabolisms, and the carbon allocation from root to cotyledon was increased. Additionally, changes of amino acids and nucleic acids profiles were only found in the cotyledons, and the roots could enhance the activity of antioxidant enzyme systems to scavenge ROS under salinity. In conclusion, the present research provides an improved understanding on specific physiological changes in the cotyledons in castor early seedlings, and explores their interaction under salt stress.

Ethylene and Sulfur Coordinately Modulate the Antioxidant System and ABA Accumulation in Mustard Plants under Salt Stress

This study explored the interactive effect of ethephon (2-chloroethyl phosphonic acid; an ethylene source) and sulfur (S) in regulating the antioxidant system and ABA content and in maintaining stomatal responses, chloroplast structure, and photosynthetic performance of mustard plants (Brassica juncea L. Czern.) grown under 100 mM NaCl stress. The treatment of ethephon (200 µL L⁻¹) and S (200 mg S kg⁻¹ soil) together markedly improved the activity of enzymatic and non-enzymatic components of the ascorbate-glutathione (AsA-GSH) cycle, resulting in declined oxidative stress through lesser content of sodium (Na⁺) ion and hydrogen peroxide (H₂O₂) in salt-stressed plants_. These changes promoted the development of chloroplast thylakoids and photosynthetic performance under salt stress. Ethephon + S also reduced abscisic acid (ABA) accumulation in guard cell, leading to maximal stomatal conductance under salt stress. The inhibition of ethylene action by norbornadiene (NBD) in salt- plus non-stressed treated plants increased ABA and H₂O₂ contents, and reduced stomatal opening, suggesting the involvement of ethephon and S in regulating stomatal conductance. These findings suggest that ethephon and S modulate antioxidant system and ABA accumulation in guard cells, controlling stomatal conductance, and the structure and efficiency of the photosynthetic apparatus in plants under salt stress.

R2R3 MYB-dependent auxin signalling regulates trichome formation, and increased trichome density confers spider mite tolerance on tomato

Unicellular and multicellular tomato trichomes function as mechanical and chemical barriers against herbivores. Auxin treatment increased the formation of II, V and VI type trichomes in tomato leaves. The auxin response factor gene SlARF4, which was highly expressed in II, V and VI type trichomes, positively regulated the auxin-induced formation of II, V and VI type trichomes in the tomato leaves. SlARF4 overexpression plants with high densities of these trichomes exhibited tolerance to spider mites. Two R2R3 MYB genes, SlTHM1 and SlMYB52, were directly targeted and inhibited by SlARF4. SlTHM1 was specifically expressed in II and VI type trichomes and negatively regulated the auxin-induced formation of II and VI type trichomes in the tomato leaves. SlTHM1 down-regulation plants with high densities of II and VI type trichomes also showed tolerance to spider mites. SlMYB52 was specifically expressed in V type trichomes and negatively regulated the auxin-induced formation of V type trichome in the tomato leaves. The regulation of SlARF4 on the formation of II, V and VI type trichomes depended on SlTHM1 and SlMYB52, which directly targeted cyclin gene SlCycB2 and increased its expression. In conclusion, our data indicates that the R2R3 MYB-dependent auxin signalling pathway regulates the formation of II, V and VI type trichomes in tomato leaves. Our study provides an effective method for improving the tolerance of tomato to spider mites.

Wide vessels sustain marginal transpiration flux and do not optimize inefficient gas exchange activity under impaired hydraulic control and salinity

Plants optimize water use and carbon assimilation via transient regulation of stomata resistance and by limiting hydraulic conductivity in a long-term response of xylem anatomy. We postulated that without effective hydraulic regulation plants would permanently restrain water loss and photosynthetic productivity under salt stress conditions. We compared wild-type tomatoes to a transgenic type (TT) with impaired stomatal control. Gas exchange activity, biomass, starch content, leaf area and root traits, mineral composition and main stems xylem anatomy and hydraulic conductivity were analyzed in plants exposed to salinities of 1 and 4 dS m^-1 over 60 days. As the xylem cannot easily readjust to different environmental conditions, shifts in its anatomy and the permanent effect on plant hydraulic conductivity kept transpiration at lower levels under unstressed conditions and maintained it under salt-stress, while sustaining higher but inefficient assimilation rates, leading to starch accumulation and decreased plant biomass, leaf and root area and root length. Narrow conduits in unstressed TT plants were related to permanent restrain of hydraulic conductivity and plant transpiration. Under salinity, TT plants followed the atmospheric water demand, sustained similar transpiration rate from unstressed to salt-stressed conditions and possibly maintained hydraulic integrity, due to likely impaired hydraulic regulation, wider conduits and higher hydraulic conductivity. The accumulation of salts and starch in the TT plants was a strong evidence of salinity tolerance via osmotic regulation, also thought to help to maintain the assimilation rates and transpiration flux under salinity, although it was not translated into higher growth.

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.

Role of Beneficial Microorganisms and Salicylic Acid in Improving Rainfed Agriculture and Future Food Safety

Moisture stress in rainfed areas has significant adverse impacts on plant growth and yield. Plant growth promoting rhizobacteria (PGPR) plays an important role in the revegetation and rehabilitation of rainfed areas by modulating plant growth and metabolism and improving the fertility status of the rhizosphere soils. The current study explored the positive role of PGPR and salicylic acid (SA) on the health of the rhizosphere soil and plants grown under rainfed conditions. Maize seeds of two different varieties, i.e., SWL-2002 (drought tolerant) and CZP-2001 (drought sensitive), were soaked for 4 h prior to sowing in 24-h old culture of Planomicrobium chinense strain P1 (accession no. MF616408) and Bacillus cereus strain P2 (accession no. MF616406). The foliar spray of SA (150 mg/L) was applied on 28-days old seedlings. The combined treatment of the consortium of PGPR and SA not only alleviated the adverse effects of low moisture stress of soil in rainfed area but also resulted in significant accumulation of leaf chlorophyll content (40% and 24%), chlorophyll fluorescence (52% and 34%) and carotenoids (57% and 36%) in the shoot of both the varieties. The PGPR inoculation significantly reduced lipid peroxidation (33% and 23%) and decreased the proline content and antioxidant enzymes activities (32% and 38%) as compared to plants grown in rainfed soil. Significant increases (>52%) were noted in the contents of Ca, Mg, K Cu, Co, Fe and Zn in the shoots of plants and rhizosphere of maize inoculated with the PGPR consortium. The soil organic matter, total nitrogen and C/N ratio were increased (42%), concomitant with the decrease in the bulk density of the rhizosphere. The PGPR consortium, SA and their combined treatment significantly enhanced the IAA (73%) and GA (70%) contents but decreased (55%) the ABA content of shoot. The rhizosphere of plants treated with PGPR, SA and consortium showed a maximum accumulation (>50%) of IAA, GA and ABA contents, the sensitive variety had much higher ABA content than the tolerant variety. It is inferred from the results that rhizosphere soil of treated plants enriched with nutrients content, organic matter and greater concentration of growth promoting phytohormones, as well as stress hormone ABA, which has better potential for seed germination and establishment of seedlings for succeeding crops.

Effect of Arbuscular Mycorrhizal Fungi (AMF) and Plant Growth-Promoting Bacteria (PGPR) Inoculations on Elaeagnus angustifolia L. in Saline Soil

Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) are considered highly-efficient agents for conferring salt tolerance in host plants and improving soil fertility in rhizosphere. However, information about the inoculation of beneficial microbes on halophytes in arid and semi-arid regions remains inadequate. The objective of this study was to evaluate the influence of AMF (Glomus mosseae) inoculation, alone or in combination with PGPR (Bacillus amyloliquefaciens), on biomass accumulation, morphological characteristics, photosynthetic capacity, and rhizospheric soil enzyme activities of Elaeagnus angustifolia L., a typical halophyte in the northwest of China. The results indicate that, for one-year-old seedlings of Elaeagnus angustifolia L., AMF significantly promoted biomass accumulation in aboveground organs, increased the numbers of leaves and branches, and improved the leaf areas, stem diameters and plant height. AMF-mediated morphological characteristics of aboveground organs favored light interception and absorption and maximized the capacities for photosynthesis, transpiration, carbon dioxide assimilation and gas exchange of Elaeagnus angustifolia L. seedlings in saline soil. AMF also promoted root growth, modified root architecture, and enhanced soil enzyme activities. Elaeagnus angustifolia L. was more responsive to specific inoculation by AMF than by a combination of AMF and PGPR or by solely PGPR in saline soils. Therefore, we suggest that G. mosseae can be used in saline soil to enhance Elaeagnus angustifolia L. seedlings growth and improve soil nutrient uptake. This represents a biological technique to aid in restoration of saline-degraded areas.

Stomatal and non-stomatal limitations are responsible in down-regulation of photosynthesis in melon plants grown under the saline condition: Application of carbon isotope discrimination as a reliable proxy

Salinity is one of the most severe environmental stresses limiting agricultural crop production worldwide. Photosynthesis is one of the main biochemical processes getting affected by such stress conditions. Here we investigated the stomatal and non-stomatal factors during photosynthesis in two Iranian melon genotypes "Ghobadlu" and "Suski-e-Sabz", as well as the "Galia" F1 cultivar, with an insight into better understanding the physiological mechanisms involved in the response of melon plants to increasing salinity. After plants were established in the greenhouse, they were supplied with nutrient solutions containing three salinity levels (0, 50, or 100 mM NaCl) for 15 and 30 days. With increasing salinity, almost all of the measured traits (e.g. stomatal conductance, transpiration rate, internal to ambient CO₂ concentration ratio (C_i/C_a), Rubisco and nitrate reductase activity, carbon isotope discrimination (Δ¹³C), chlorophyll content, relative water content (RWC), etc.) significantly decreased after 15 and 30 days of treatments. In contrast, the overall mean of water use efficiency (intrinsic and instantaneous WUE), leaf abscisic acid (ABA) and flavonol contents, as well as osmotic potential (Ψ_S), all increased remarkably with increasing stress, across all genotypes. In addition, notable correlations were found between Δ¹³C and leaf gas exchange parameters as well as most of the measured traits (e.g. leaf area, biomass, RWC, Ψ_S, etc.), encouraging the possibility of using Δ¹³C as an important proxy for indirect selection of melon genotypes with higher photosynthetic capacity and higher salinity tolerance. The overall results suggest that both stomatal and non-stomatal limitations play an important role in reduced photosynthesis rate in melon genotypes studied under NaCl stress. This conclusion is supported by the concurrently increased resistance to CO₂ diffusion, and lower Rubisco activity under NaCl treatments at the two sampling dates, and this was revealed by the appearance of lower C_i/C_a ratios and lower Δ¹³C in the leaves of salt-treated plants.

Effect of soil aeration on root morphology and photosynthetic characteristics of potted tomato plants (Solanum lycopersicum) at different NaCl salinity levels

BACKGROUND

Salt stress is one of the environmental factors that greatly limits crop production worldwide because high salt concentrations in the soil affect morphological responses and physiological and metabolic processes, including root morphology and photosynthetic characteristics. Soil aeration has been reported to accelerate the growth of plants and increase crop yield. The objective of this study was to examine the effects of 3 NaCl salinity levels (28, 74 and 120 mM) and 3 aeration volume levels (2.3, 4.6 and 7.0 L/pot) versus non-aeration and salinity treatments on the root morphology, photosynthetic characteristics and chlorophyll content of potted tomato plants.

RESULTS

The results showed that both aeration volume and salinity level affected the root parameters, photosynthetic characteristics and chlorophyll content of potted tomato plants. The total length, surface area and volume of roots increased with the increase in aeration volume under each NaCl stress level. The effect was more marked in the fine roots (especially in ≤1 mm diameter roots). Under each NaCl stress level, the photosynthetic rate and chlorophyll content of tomato significantly increased in response to the aeration treatments. The net photosynthetic rate and chlorophyll a and t content increased by 39.6, 26.9, and 17.9%, respectively, at 7.0 L/pot aeration volume compared with no aeration in the 28 mM NaCl treatment. We also found that aeration could reduce the death rate of potted tomato plants under high salinity stress conditions (120 mM NaCl).

CONCLUSIONS

The results suggest that the negative effect of NaCl stress can be offset by soil aeration. Soil aeration can promote root growth and increase the photosynthetic rate and chlorophyll content, thus promoting plant growth and reducing the plant death rate under NaCl stress conditions.

Agricultural and Physiological Responses of Tomato Plants Grown in Different Soilless Culture Systems with Saline Water under Greenhouse Conditions

Tomato is the most important horticultural crop in the world. The yields for this crop are highest in Southeastern Spain. In this work we studied a commercial variety of tomato, with different soilless culture systems (deep flow technique, nutrient film technique, and the perlite substrate) and three levels of salinity (2.2, 6.3, and 10.2 dS·m-1) typical of Southeastern Spain. The irrigation management was carried out for optimizing the water use efficiency. Alterations in the water status of the plants, Cl- and Na+ toxicity, and nutritional imbalances altered the vegetative growth and physiology of the plants. The marketable yield was affected by both soilless culture system and salinity. Regarding the soilles culture system, yield decreased in the order: deep flow technique > perlite > nutrient film technique. The salinity treatments improved the fruits quality by increasing the total soluble solids and titratable acidity. Plants cultivated with the nutrient film technique had the highest concentrations of Cl- and Na+ and the highest Na+/K+ ratio. The concentrations of Cl- and Na+ in the plants were not related directly to the yield loss. Therefore, the influence of the toxicity, osmotic effect, and nutritional imbalance seems to have been responsible for the yield loss.

Long-distance electrical signals as a link between the local action of stressors and the systemic physiological responses in higher plants

Our review is devoted to the analysis of the role of long-distance electrical signals in the development of the fast systemic physiological responses in higher plants. The characteristics and mechanisms of basic electrical signals (variation potential, action potential and system potential) are analyzed, and a potential schema of the generation and propagation of the system potential is proposed. The review summarizes the physiological changes induced by the variation potential, action potential and system potential in higher plants, including changes in gene expressions, the production of phytohormones, photosynthesis, phloem mass-flow, respiration, ATP content, transpiration and plant growth. Potential mechanisms of the changes are analyzed. Finally, a hypothetical schema, which describes a hierarchy of the variation potential, action potential and system potential, in the development of the fast systemic non-specific adaptation of plants to stressors, is proposed.

Electrical signals as mechanism of photosynthesis regulation in plants

This review summarizes current works concerning the effects of electrical signals (ESs) on photosynthesis, the mechanisms of the effects, and its physiological role in plants. Local irritations of plants induce various photosynthetic responses in intact leaves, including fast and long-term inactivation of photosynthesis, and its activation. Irritation-induced ESs, including action potential, variation potential, and system potential, probably causes the photosynthetic responses in intact leaves. Probable mechanisms of induction of fast inactivation of photosynthesis are associated with Ca²⁺- and (or) H⁺-influxes during ESs generation; long-term inactivation of photosynthesis might be caused by Ca²⁺- and (or) H⁺-influxes, production of abscisic and jasmonic acids, and inactivation of phloem H⁺-sucrose symporters. It is probable that subsequent development of inactivation of photosynthesis is mainly associated with decreased CO₂ influx and inactivation of the photosynthetic dark reactions, which induces decreased photochemical quantum yields of photosystems I and II and increased non-photochemical quenching of photosystem II fluorescence and cyclic electron flow around photosystem I. However, other pathways of the ESs influence on the photosynthetic light reactions are also possible. One of them might be associated with ES-connected acidification of chloroplast stroma inducing ferredoxin-NADP⁺ reductase accumulation at the thylakoids in Tic62 and TROL complexes. Mechanisms of ES-induced activation of photosynthesis require further investigation. The probable ultimate effect of ES-induced photosynthetic responses in plant life is the increased photosynthetic machinery resistance to stressors, including high and low temperatures, and enhanced whole-plant resistance to environmental factors at least during 1 h after irritation.

The efficient physiological strategy of a tomato landrace in response to short-term salinity stress

Landraces represent an important part of the biodiversity well-adapted under limiting environmental conditions. We investigated the response of two Southern Italy tomato landraces, the well-known San Marzano (our commercial standard) and a local accession called "Ciettaicale", to different levels of sodium chloride in water irrigation (from 0 up to 600 mM) for a short-time exposure (one week). The combination of the chlorophyll a fluorescence and gas exchange analyses suggested that Ciettaicale maintained a higher efficiency of photosystem II (PSII) photochemistry and CO₂ utilization at high salinity concentrations than San Marzano. Stomatal and non-stomatal limitations occurred in San Marzano according to the reduction of maximum efficiency of PSII photochemistry and the increase of intercellular CO₂ concentration. Higher Na⁺/K⁺ ratio and higher concentration of total soluble sugars contributed to non-stomatal limitations in San Marzano leaves. These effects were significantly less evident in Ciettaicale. We also observed changes in total antioxidant capacity and leaf pigment content that emphasized the occurrence of modifications in the photosynthetic apparatus according to salt gradient. The more efficient assimilates supply and an integrated root protection system provided by sugars and antioxidants can explain the significantly higher root/shoot ratio in Ciettaicale. Overall, our results suggest that a comprehensive assessment of salinity tolerance in a genotypes comparison could be also obtained evaluating plant response to high salinity levels at early vegetative stage. In addition, further studies will be carried out in order to evaluate the possibility of using Ciettaicale in tomato improvement programs.

SlDREB2, a tomato dehydration-responsive element-binding 2 transcription factor, mediates salt stress tolerance in tomato and Arabidopsis

To counter environmental cues, cultivated tomato (Solanum lycopersicum L.) has evolved adaptive mechanisms requiring regulation of downstream genes. The dehydration-responsive element-binding protein 2 (DREB2) transcription factors regulate abiotic stresses responses in plants. Herein, we isolated a novel DREB2-type regulator involved in salinity response, named SlDREB2. Spatio-temporal expression profile together with investigation of its promoter activity indicated that SlDREB2 is expressed during early stages of seedling establishment and in various vegetative and reproductive organs of adult plants. SlDREB2 is up-regulated in roots and young leaves following exposure to NaCl, but is also induced by KCl and drought. Its overexpression in WT Arabidopsis and atdreb2a mutants improved seed germination and plant growth in presence of different osmotica. In tomato, SlDREB2 affected vegetative and reproductive organs development and the intronic sequence present in the 5' UTR drives its expression. Physiological, biochemical and transcriptomic analyses showed that SlDREB2 enhanced plant tolerance to salinity by improvement of K(+) /Na(+) ratio, and proline and polyamines biosynthesis. Exogenous hormonal treatments (abscisic acid, auxin and cytokinins) and analysis of WT and 35S::SlDREB2 tomatoes hormonal contents highlighted SlDREB2 involvement in abscisic acid biosynthesis/signalling. Altogether, our results provide an overview of SlDREB2 mode of action during early salt stress response.

A Targeted Management of the Nutrient Solution in a Soilless Tomato Crop According to Plant Needs

The adoption of closed soilless systems is useful in minimizing the environmental impact of the greenhouse crops. Instead, a significant problem in closed soilless systems is represented by the accumulation of ions in the recycled nutrient solution (NS), in particular the unabsorbed or poorly absorbed ones. To overcome such problem, we: (1) studied the effect of several values of the electrical conductivity (EC) of NS in a NFT (Nutrient Film Technique) system on a cherry type tomato crop, and (2) define a NS (called recovery solution), based on the concept of "uptake concentration" and transpiration-biomass ratio, that fits the real needs of the plant with respect to water and nutrients. Three levels of EC set point (SP), above which the NS was completely replaced (SP5, SP7.5, and SP10 for the EC limit of 5, 7.5, and 10 dS m(-1), respectively), were established. The SP10 treatment yield was not different from other treatments, and it allowed a better quality of the berries (for dry matter and total soluble solids) and higher environmental sustainability due to a lower discharge of total nutrients into the environment (37 and 59% with respect to SP7.5 and SP5, respectively). The recovery solution used in the second trial allowed a more punctual NS management, by adapting to the real needs of the crop. Moreover, it allowed a lesser amount of water and nutrients to be discharged into the environment and a better use of brackish water, due to a more accurate management of the EC of the NS. The targeted management, based on transpiration-biomass ratio, indicates that, in some stages of the plant cycle, the NS used can be diluted, in order to save water and nutrients. With such management a closed cycle can be realized without affecting the yield, but improving the quality of the tomato berries.

Hardening with salicylic acid induces concentration-dependent changes in abscisic acid biosynthesis of tomato under salt stress

The role of salicylic acid (SA) in the control of abscisic acid (ABA) biosynthesis is controversial although both plant growth regulators may accumulate in tissues under abiotic and biotic stress conditions. Hardening of tomato plants to salinity stress with 10(-4)M SA ("high SA") resulted in an up-regulation of ABA biosynthesis genes, zeaxanthin epoxidase (SlZEP1), 9-cis-epoxycarotenoid dioxygenase (SlNCED1) and aldehyde oxidases (SlAO1 and SlAO2) in the roots and led to ABA accumulation both in root and leaf tissues. In plants pre-treated with lower concentration of SA (10(-7)M, "low SA"), the up-regulation of SlNCED1 in the roots promoted ABA accumulation in the root tissues but the hormone concentration remained at control level in the leaves. Salt stress induced by 100mM NaCl reduced the transcript abundance of ABA biosynthetic genes and inhibited SlAO activity in plants hardened with "high SA", but the tissues maintained root ABA level over the untreated control. The combined effect of "high SA" and ABA under salt stress led to partially recovered photosynthetic activity, reduced ethylene production in root apices, and restored root growth, which is one of the main features of salt tolerance. Unlike "high SA", hardening with "low SA" had no influence on ethylene production, and led to reduced elongation of roots in plants exposed to 100mM NaCl. The up-regulation of carotenoid cleavage dioxygenases SlCCD1A and SlCCD1B by SA, which produce apocarotenoids, may open new pathways in SA sensing and signalling processes.

Divergences in hormonal and enzymatic antioxidant responses of two Chicory ecotypes to salt stress

To evaluate the effect of salt stress on seed germination, early growth, antioxidant enzymes activity and ABA content of chicory ecotypes (Cichorium intybus) a factorial experiment was conducted at College of Agriculture, Shiraz University in 2014 based on completely randomized design with four replications. The treatments comprised five salinity levels (tapwater, 3, 6, 9, 12 dS m(-1)) of sodium chloride on Shirazi-black and white chicory ecotypes. The results showed that germination characteristics and primary seedling growth were decreased in both ecotypes with increasing in salinity severity. The effects of salinity on radicle and plumule length as well as seedling weight were the same as its effects on seed germination. The effect of salt stress on antioxidant enzymes activity (especially catalase) and ABA content were significant which they were enhanced with increasing salinity level; Black ecotype performs better than the white one under high salinity, as indicated by a lower decreasing in germination characteristics and primary growth and higher antioxidant enzymes activity as well as ABA content. These facts should be taken into consideration in the economic cultivation of this valuable horticultural and medicinal plant and this data would be useful for the crop breeding projects.

The Solanum lycopersicum Zinc Finger2 cysteine-2/histidine-2 repressor-like transcription factor regulates development and tolerance to salinity in tomato and Arabidopsis

The zinc finger superfamily includes transcription factors that regulate multiple aspects of plant development and were recently shown to regulate abiotic stress tolerance. Cultivated tomato (Solanum lycopersicum Zinc Finger2 [SIZF2]) is a cysteine-2/histidine-2-type zinc finger transcription factor bearing an ERF-associated amphiphilic repression domain and binding to the ACGTCAGTG sequence containing two AGT core motifs. SlZF2 is ubiquitously expressed during plant development, and is rapidly induced by sodium chloride, drought, and potassium chloride treatments. Its ectopic expression in Arabidopsis (Arabidopsis thaliana) and tomato impaired development and influenced leaf and flower shape, while causing a general stress visible by anthocyanin and malonyldialdehyde accumulation. SlZF2 enhanced salt sensitivity in Arabidopsis, whereas SlZF2 delayed senescence and improved tomato salt tolerance, particularly by maintaining photosynthesis and increasing polyamine biosynthesis, in salt-treated hydroponic cultures (125 mm sodium chloride, 20 d). SlZF2 may be involved in abscisic acid (ABA) biosynthesis/signaling, because SlZF2 is rapidly induced by ABA treatment and 35S::SlZF2 tomatoes accumulate more ABA than wild-type plants. Transcriptome analysis of 35S::SlZF2 revealed that SlZF2 both increased and reduced expression of a comparable number of genes involved in various physiological processes such as photosynthesis, polyamine biosynthesis, and hormone (notably ABA) biosynthesis/signaling. Involvement of these different metabolic pathways in salt stress tolerance is discussed.

Abscisic acid metabolizing rhizobacteria decrease ABA concentrations in planta and alter plant growth

Although endogenous phytohormones such as abscisic acid (ABA) regulate root growth, and many rhizobacteria can modulate root phytohormone status, hitherto there have been no reports of rhizobacteria mediating root ABA concentrations and growth by metabolising ABA. Using a selective ABA-supplemented medium, two bacterial strains were isolated from the rhizosphere of rice (Oryza sativa) seedlings grown in sod-podzolic soil and assigned to Rhodococcus sp. P1Y and Novosphingobium sp. P6W using partial 16S rRNA gene sequencing and phenotypic patterns by the GEN III MicroPlate test. Although strain P6W had more rapid growth in ABA-supplemented media than strain P1Y, both could utilize ABA as a sole carbon source in batch culture. When rice seeds were germinated on filter paper in association with bacteria, root ABA concentration was not affected, but shoot ABA concentration of inoculated plants decreased by 14% (strain P6W) and 22% (strain P1Y). When tomato (Solanum lycopersicum) genotypes differing in ABA biosynthesis (ABA deficient mutants flacca - flc, and notabilis - not and the wild-type cv. Ailsa Craig, WT) were grown in gnotobiotic cultures on nutrient solution agar, rhizobacterial inoculation decreased root and/or leaf ABA concentrations, depending on plant and bacteria genotypes. Strain P6W inhibited primary root elongation of all genotypes, but increased leaf biomass of WT plants. In WT plants treated with silver ions that inhibit ethylene perception, both ABA-metabolising strains significantly decreased root ABA concentration, and strain P6W decreased leaf ABA concentration. Since these changes in ABA status also occurred in plants that were not treated with silver, it suggests that ethylene was probably not involved in regulating bacteria-mediated changes in ABA concentration. Correlations between plant growth and ABA concentrations in planta suggest that ABA-metabolising rhizobacteria may stimulate growth via an ABA-dependent mechanism.

Abscisic acid and aldehyde oxidase activity in maize ear leaf and grain relative to post-flowering photosynthetic capacity and grain-filling rate under different water/nitrogen treatments

This study investigated changes in leaf abscisic acid (ABA) concentrations and grain ABA concentrations in two maize cultivars and analyzed the following relationships under different water/nitrogen treatments: leaf ABA concentrations and photosynthetic parameters; leaf ABA concentrations and grain ABA concentrations; leaf/grain ABA concentrations and grain-filling parameters; and aldehyde oxidase (AO, EC 1.2.3.1) activities and ABA concentrations. The ear leaf average AO activities and ABA concentrations were lower in the controlled release urea treatments compared with the conventional urea treatments. The average AO activities in the grains were higher in the controlled release urea treatments, and the ABA concentrations were significantly increased at 11-30 DAF. The Pn and ABA concentrations in ear leaves were negatively correlated. And the Gmean were positively correlated with the grain ABA concentrations at 11-30 DAF and negatively correlated with the leaf ABA concentrations at 20 and 40-50 DAF. The grain ABA concentrations and leaf ABA concentrations were positively correlated. Thus, the Gmean were closely related to the AO activities and to the ear leaf and grain ABA concentrations. As compared to other treatments, the subsoiling and controlled release urea treatment promoted the uptake of water and nitrogen by maize, increased the photosynthetic capacity of the ear leaves, increased the grain-filling rate, and improved the movement of photosynthetic assimilates toward the developing grains. In the cultivar Z958, higher ABA concentrations in grains at 11-30 DAF and lower ABA concentrations in ear leaves during the late grain-filling stage, resulted in higher grain-filling rate and increased accumulation of photosynthetic products (relative to the cultivar D3).