Rootstock increases the physiological defence of tomato plants against Pseudomonas syringae pv. tomato infection.

Climate change has intensified the infection of tomato plants by pathogens such as Pseudomonas syringae pv. tomato (Pst). Rootstocks may increase plant tolerance to leaf phytopathogens. The aim of this study was to evaluate the effects of the tolerant Poncho Negro (R) tomato rootstock on physiological defence and the role of hydrogen sulfide (H2S) in susceptible Limachino (L) tomato plant responses to Pst attack. Ungrafted (L), self-grafted (L/L), and grafted (L/R) plants were infected with Pst. Rootstock increased the concentration of antioxidant compounds including ascorbate in the scion. Tolerant rootstock induced an increase of H2S in the scion, which correlated with enhanced expression of the SlAPX2 gene. A high accumulation of salicylic acid was observed in Pst-inoculated grafted L/L and L/R plants, but this was higher in L/R plants. The increase of H2S during Pst infection was associated with a reduction of ethylene in L/R plants. Our study indicates that the Poncho Negro rootstock reduced the symptoms of bacterial speck disease in the Limachino tomato plants, conferring tolerance to Pst infection. This study provides new knowledge about the impact of rootstock in the defence of tomato plants against leaf pathogens that could be used in sustainable management of tomato cultivation.

Evaluating the bio-removal of crude oil by vetiver grass (Vetiveria zizanioides L.) in interaction with bacterial consortium exposed to contaminated artificial soils.

Remediation of crude oil-impacted areas is a major pervasive concern in various environmental conditions. The major aim of this study was to investigate the collaboration of vetiver grass (Vetiveria zizanioides L.) and petroleum hydrocarbon-degrading bacteria to clean up contaminated soils. Vetiver grass and five native bacterial isolates were used in one consortium to remediate contaminated soil by crude oil at various concentrations (2.0, 4.0, 6.0 8.0, 10, and 12.0% woil/wsoil). The presence of isolated bacteria caused a significant (p < 0.05) increment of root-shoot ratio of vetiver in contaminated soils in comparison to non-contaminated soil. The combination of vetiver and bacterial consortium revealed efficient dissipation of more than 30% of low-molecular-weight polycyclic aromatic hydrocarbons (PAHs) and more than 50% of high-molecular-weight PAHs in all crude oil concentrations. The removal of n-alkanes in the simultaneous presence of the bacteria and plant was more than 70.0% at 10.0% of oil concentration, whereas the removals in control were 20.7, 13.7 and 9.2%, respectively. The hydrocarbons dissipation efficiency of applied treatments decreased at 12.0% of contamination. It is concluded that a combination of vetiver grass and the isolated bacteria could be a feasible strategy for remediation of crude oil-polluted soils. Novelty statementDetermination of the responses of vetiver grass under different crude oil concentrations is one of the novelties of the present study, which is helpful for demonstrating plant tolerance on polluted environments. Also, it adds information about the potential of this grass to clean up crude oil-polluted soils solely as well as in the presence of promising selected bacterial strains.

Endogenous Polyamines and Ethylene Biosynthesis in Relation to Germination of Osmoprimed Brassica napus Seeds under Salt Stress.

Currently, seed priming is reported as an efficient and low-cost approach to increase crop yield, which could not only promote seed germination and improve plant growth state but also increase abiotic stress tolerance. Salinity represents one of the most significant abiotic stresses that alters multiple processes in plants. The accumulation of polyamines (PAs) in response to salt stress is one of the most remarkable plant metabolic responses. This paper examined the effect of osmopriming on endogenous polyamine metabolism at the germination and early seedling development of Brassica napus in relation to salinity tolerance. Free, conjugated and bound polyamines were analyzed, and changes in their accumulation were discussed with literature data. The most remarkable differences between the corresponding osmoprimed and unprimed seeds were visible in the free (spermine) and conjugated (putrescine, spermidine) fractions. The arginine decarboxylase pathway seems to be responsible for the accumulation of PAs in primed seeds. The obvious impact of seed priming on tyramine accumulation was also demonstrated. Moreover, the level of ethylene increased considerably in seedlings issued from primed seeds exposed to salt stress. It can be concluded that the polyamines are involved in creating the beneficial effect of osmopriming on germination and early growth of Brassica napus seedlings under saline conditions through moderate changes in their biosynthesis and accumulation.

Salinity differently affects antioxidant content and amino acid profile in two cultivars of Amaranthus cruentus differing in salinity tolerance.

BACKGROUND: Amaranthus cruentus is a promising leafy vegetable with high nutritional value and is able to cope with salt stress but the impact of sodium chloride (NaCl) on its main properties have not been studied in detail. Plants from two contrasting cultivars (Rouge: salt-tolerant and Locale: salt-sensitive) were exposed to NaCl (0, 30, 60 and 90 mmol L-1 ) in nutrient solution for 2 weeks. Plant growth, mineral content, oxidative status and antioxidant concentration, salicylic acid concentration, protein content and amino acid profile were analyzed in the harvested leaves. RESULTS: Low dose (30 mmol L-1 NaCl) increased plant growth while Na+ accumulated to higher extent in salt-sensitive Locale than in salt-tolerant Rouge. A total of 30 mmol L-1 NaCl increased magnesium (Mg), phosphorus (P) and iron (Fe) content, as well as total antioxidant activity, ascorbate, phenolics, α-tocopherol and carotenoids content to higher extent in cultivar (cv.) Rouge than in cv. Locale. Low (30 mmol L-1 ) and moderate salinities (60 mmol L-1 ) increased γ-tocopherol and total protein in cv. Locale. They also increased lysine, valine, methionine and proline concentration as well as chemical score of protein in this cultivar. The highest NaCl (90 mmol L-1 ) dose had a detrimental impact on both cultivars. CONCLUSIONS: It is concluded that A. cruentus is a promising plant species for saline agriculture since moderate doses of salt improve both quantitative and qualitative parameters in cultivar dependent manner. © 2021 Society of Chemical Industry.

Salinity modifies heavy metals and arsenic absorption by the halophyte plant species Kosteletzkya pentacarpos and pollutant leaching from a polycontaminated substrate.

Phytomanagement of polycontaminated soils is challenging, especially in areas simultaneously affected by salinity. The wetland halophyte plant species Kosteletzkya pentacarpos was cultivated in a column device allowing leachate harvest, on a polycontaminated spiked soil containing Cd (6.5 mg kg-1 DW), As (75 mg kg-1 DW), Zn (200 mg kg-1 DW) and Pb (300 mg kg-1 DW) and irrigated with salt water (final soil electrical conductivity 5.0 ms cm-1). Salinity increased Cd bioavailability in the soil and Cd accumulation in the shoots while it had an opposite effect on As. Salinity did not modify Pb and Zn bioavailability and accumulation. Cultivating plants on the polluted soil drastically reduced the volume of leachate. In all cases, salinity reduced the total amounts of heavy metals removed by the leachate and significantly increased the proportion of Cd and Zn removed by the plants. Heavy metal contamination induced a decrease in shoot dry weight and an increase in malondialdehyde (an indicator of oxidative stress); both symptoms were alleviated by the additional presence of NaCl but this positive impact was not related to increase in protecting phytochelatins synthesis. It is concluded i) that bioavailability estimated by the 0.01M CaCl2 extraction procedure is not fully relevant from the heavy metal mobility, ii) that salinity decreased heavy metal percolation, especially in soils cultivated with K. pentacarpos and iii) that salinity improves plant tolerance to heavy metals in K. pentacarpos and that this species is a promising plant material for phytoremediation of polycontaminated soils.

New Insight on Water Status in Germinating Brassica napus Seeds in Relation to Priming-Improved Germination.

Seed priming is a pre-sowing method successfully used to improve seed germination. Since water plays a crucial role in germination, the aim of this study was to investigate the relationship between better germination performances of osmoprimed Brassica napus seeds and seed water status during germination. To achieve this goal, a combination of different kinds of approaches was used, including nuclear magnetic resonance (NMR) spectroscopy, TEM, and SEM as well as semi-quantitative PCR (semi-qPCR). The results of this study showed that osmopriming enhanced the kinetics of water uptake and the total amount of absorbed water during both the early imbibition stage and in the later phases of seed germination. The spin⁻spin relaxation time (T2) measurement suggests that osmopriming causes faster water penetration into the seed and more efficient tissue hydration. Moreover, factors potentially affecting water relations in germinating primed seeds were also identified. It was shown that osmopriming (i) changes the microstructural features of the seed coat, e.g., leads to the formation of microcracks, (ii) alters the internal structure of the seed by the induction of additional void spaces in the seed, (iii) increases cotyledons cells vacuolization, and (iv) modifies the expression pattern of aquaporin genes.

Insights into the molecular regulation of monolignol-derived product biosynthesis in the growing hemp hypocotyl.

BACKGROUND: Lignin and lignans are both derived from the monolignol pathway. Despite the similarity of their building blocks, they fulfil different functions in planta. Lignin strengthens the tissues of the plant, while lignans are involved in plant defence and growth regulation. Their biosyntheses are tuned both spatially and temporally to suit the development of the plant (water conduction, reaction to stresses). We propose to study the general molecular events related to monolignol-derived product biosynthesis, especially lignin. It was previously shown that the growing hemp hypocotyl (between 6 and 20 days after sowing) is a valid system to study secondary growth and the molecular events accompanying lignification. The present work confirms the validity of this system, by using it to study the regulation of lignin and lignan biosynthesis. Microscopic observations, lignin analysis, proteomics, together with in situ laccase and peroxidase activity assays were carried out to understand the dynamics of lignin synthesis during the development of the hemp hypocotyl. RESULTS: Based on phylogenetic analysis and targeted gene expression, we suggest a role for the hemp dirigent and dirigent-like proteins in lignan biosynthesis. The transdisciplinary approach adopted resulted in the gene- and protein-level quantification of the main enzymes involved in the biosynthesis of monolignols and their oxidative coupling (laccases and class III peroxidases), in lignin deposition (dirigent-like proteins) and in the determination of the stereoconformation of lignans (dirigent proteins). CONCLUSIONS: Our work sheds light on how, in the growing hemp hypocotyl, the provision of the precursors needed to synthesize the aromatic biomolecules lignin and lignans is regulated at the transcriptional and proteomic level.

Jasmonic acid to boost secondary growth in hemp hypocotyl.

MAIN CONCLUSION: The application of jasmonic acid results in an increased secondary growth, as well as additional secondary phloem fibres and higher lignin content in the hypocotyl of textile hemp (Cannabis sativa L.). Secondary growth provides most of the wood in lignocellulosic biomass. Textile hemp (Cannabis sativa L.) is cultivated for its phloem fibres, whose secondary cell wall is rich in crystalline cellulose with a limited amount of lignin. Mature hemp stems and older hypocotyls are characterised by large blocks of secondary phloem fibres which originate from the cambium. This study aims at investigating the role of exogenously applied jasmonic acid on the differentiation of secondary phloem fibres. We show indeed that the exogenous application of this plant growth regulator on young hemp plantlets promotes secondary growth, differentiation of secondary phloem fibres, expression of lignin-related genes, and lignification of the hypocotyl. This work paves the way to future investigations focusing on the molecular network underlying phloem fibre development.

Identification of fasciclin-like arabinogalactan proteins in textile hemp (Cannabis sativa L.): in silico analyses and gene expression patterns in different tissues.

BACKGROUND: The fasciclin-like arabinogalactan proteins (FLAs) belong to the arabinogalactan protein (AGP) superfamily and are known to play different physiological roles in plants. This class of proteins was shown to participate in plant growth, development, defense against abiotic stresses and, notably, cell wall biosynthesis. Although some studies are available on the characterization of FLA genes from different species, both woody and herbaceous, no detailed information is available on the FLA family of textile hemp (Cannabis sativa L.), an economically important fibre crop. RESULTS: By searching the Cannabis genome and EST databases, 23 CsaFLAs have been here identified which are divided into four phylogenetic groups. A real-time qPCR analysis performed on stem tissues (isolated bast fibres and shivs sampled at three heights), hypocotyls (6-9-12-15-17-20 days-old), whole seedlings, roots, leaves and female/male flowers of the monoecious fibre variety Santhica 27, indicates that the identified FLA genes are differentially expressed. Interestingly, some hemp FLAs are expressed during early phases of fibre growth (elongation), while others are more expressed in the middle and base of the stem and thus potentially involved in secondary cell wall formation (fibre thickening). The bioinformatic analysis of the promoter regions shows that the FLAs upregulated in the younger regions of the stem share a conserved motif related to flowering control and regulation of photoperiod perception. The promoters of the FLA genes expressed at higher levels in the older stem regions, instead, share a motif putatively recognized by MYB3, a transcriptional repressor belonging to the MYB family subgroup S4. CONCLUSIONS: These results point to the existence of a transcriptional network fine-tuning the expression of FLA genes in the older and younger regions of the stem, as well as in the bast fibres/shivs of textile hemp. In summary, our study paves the way for future analyses on the biological functions of FLAs in an industrially relevant fibre crop.

Phosphorus deficiency modifies As translocation in the halophyte plant species Atriplex atacamensis.

Most arsenic in surface soil and water exists primarily in its oxidized form, as arsenate (As(V); AsO43-), which is an analog of phosphate (PO43-). Arsenate can be taken up by phosphate transporters. Atriplex atacamensis Phil. is native to northern Chile (Atacama Desert), and this species can cope with high As concentrations and low P availability in its natural environment. To determine the impact of P on As accumulation and tolerance in A. atacamensis, the plants were cultivated in a hydroponic system under four treatments: no As(V) addition with 323µM phosphate (control); 1000µM As(V) addition with 323µM phosphate; no As(V) and no phosphate; 1000µM As(V) addition and no phosphate. Phosphate starvation decreased shoot fresh weight, while As(V) addition reduced stem and root fresh weights. Arsenate addition decreased the P concentrations in both roots and leaves, but to a lesser extent than for P starvation. Phosphorus starvation increased the As concentrations in roots, but decreased it in shoots, which suggests that P deficiency reduced As translocation from roots to shoots. Arsenate addition increased total glutathione, but P deficiency decreased oxidized and reduced glutathione in As(V)-treated plants. Arsenate also induced an increase in S accumulation and nonprotein thiol and ethylene synthesis, and a decrease in K concentrations, effects that were similar for the P-supplied and P-starved plants. In contrast, in As(V)-treated plants, P starvation dramatically decreased total soluble protein content and increased lipid peroxidation, compared to plants supplied with P. Phosphorus nutrition thus appears to be an important component of A. atacamensis response to As toxicity.

Germination under Moderate Salinity Increases Phenolic Content and Antioxidant Activity in Rapeseed (Brassica napus var oleifera Del.) Sprouts.

The use of sprouts in the human diet is becoming more and more widespread because they are tasty and high in bioactive compounds and antioxidants, with related health benefits. In this work, we sprouted rapeseed under increasing salinity to investigate the effect on free and bound total phenolics (TP), non-flavonoids (NF), tannins (TAN), phenolic acids (PAs), and antioxidant activity. Seeds were incubated at 0, 25, 50, 100, 200 mM NaCl until early or late sprout stage, i.e., before or after cotyledon expansion, respectively. Sprouting and increasing salinity slightly decreased the bound fractions of TP, NF, TAN, PAs, while it increased markedly the free ones and their antioxidant activity. Further increases were observed in late sprouts. Moderate salinity (25-50 mM NaCl) caused the highest relative increase in phenolic concentration while it slightly affected sprout growth. On the contrary, at higher NaCl concentrations, sprouts grew slowly (100 mM NaCl) or even died before reaching the late sprout stage (200 mM). Overall, moderate salinity was the best compromise to increase phenolic content of rapeseed sprouts. The technique may be evaluated for transfer to other species as a cheap and feasible way to increase the nutritional value of sprouts.

Phenolic Content and Antioxidant Activity in Raw and Denatured Aqueous Extracts from Sprouts and Wheatgrass of Einkorn and Emmer Obtained under Salinity.

Total phenolic content (TPC), reducing power (RP), superoxide radical scavenging (RS), and thiobarbituric acid reactive substances (TBARS) production inhibition were measured in raw and denatured aqueous extracts from sprouts and wheatgrass of einkorn and emmer obtained at increasing salinity. Grains were incubated and kept at 0, 25, 50, and 100 mM NaCl until either sprout or wheatgrass stage. Additionally, a recovery treatment was included, in which sprouts obtained at 100 mM NaCl were then transferred at 0 mM NaCl until wheatgrass stage. All parameters (TPC, RP, RS, and TBARS production inhibition) increased with sprouting and were highest in wheatgrass. Salinity increased all parameters, but the effect varied with NaCl concentration, genotype, developmental stage, and plant material processing (raw or denatured). Overall, given the delay and limitation of growth at high NaCl concentration, the best compromise appears to be the application of a moderate salinity (25 to 50 mM NaCl). In denatured extracts, TPC, RP, and RS slightly decreased, and TBARS was not affected, which means that antioxidant activity was mainly related to compounds other than enzymes and peptides, and thus it can be assumed to remain after digestion. Thus, supplementing the human diet with einkorn or emmer sprouts and wheatgrass can actually benefit health.

Effect of Genotype on the Sprouting of Pomegranate (Punica granatum L.) Seeds as a Source of Phenolic Compounds from Juice Industry by-Products.

Pomegranate (Punica granatum L.) fruits are used mainly by the juice industry, for which seeds are a by-product to be disposed of, though they could potentially be a source of bioactive compounds. In this work, germination (total germination percentage, G; mean germination time, MGT; time to reach 80% of germination, TG80; seedling shoot length, fresh weight and dry matter), and nutritional value (total phenolics, TP; total flavonoids, TF; total non-tannins, TNT; antioxidant activities) of pomegranate seeds and sprouts were determined on four commercial pomegranate cultivars (Akko, Dente di Cavallo, Mollar de Elche and Wonderful). Seeds were removed from ripe fruits and incubated in plastic trays containing sterile cotton wetted with distilled water. Sprout shoots were harvested when they reached the complete cotyledon expansion, i.e., the ready-to-eat stage. Akko showed the best germination performance (G = 98%; MGT = 14 days after sowing, DAS; TG80 = 16 DAS), followed by Mollar de Elche. Sprouting dramatically increased TP, TF, TNT and antioxidant activity in all genotypes, with the highest values recorded in Mollar de Elche and Dente di Cavallo. Overall, based on germination performance, Akko and Mollar de Elche would be the best cultivars for sprouting. Sprouting pomegranate seeds appears to be a suitable way of utilizing by-products of the juice industry to obtain bioactive compounds.

Combining -Omics to Unravel the Impact of Copper Nutrition on Alfalfa (Medicago sativa) Stem Metabolism.

Copper can be found in the environment at concentrations ranging from a shortage up to the threshold of toxicity for plants, with optimal growth conditions situated in between. The plant stem plays a central role in transferring and distributing minerals, water and other solutes throughout the plant. In this study, alfalfa is exposed to different levels of copper availability, from deficiency to slight excess, and the impact on the metabolism of the stem is assessed by a non-targeted proteomics study and by the expression analysis of key genes controlling plant stem development. Under copper deficiency, the plant stem accumulates specific copper chaperones, the expression of genes involved in stem development is decreased and the concentrations of zinc and molybdenum are increased in comparison with the optimum copper level. At the optimal copper level, the expression of cell wall-related genes increases and proteins playing a role in cell wall deposition and in methionine metabolism accumulate, whereas copper excess imposes a reduction in the concentration of iron in the stem and a reduced abundance of ferritins. Secondary ion mass spectrometry (SIMS) analysis suggests a role for the apoplasm as a copper storage site in the case of copper toxicity.

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.

Salicylic acid differently impacts ethylene and polyamine synthesis in the glycophyte Solanum lycopersicum and the wild-related halophyte Solanum chilense exposed to mild salt stress.

This study aimed to determine the effects of exogenous application of salicylic acid (SA) on the toxic effects of salt in relation to ethylene and polyamine synthesis, and to correlate these traits with the expression of genes involved in ethylene and polyamine metabolism in two tomato species differing in their sensitivity to salt stress, Solanum lycopersicum cv Ailsa Craig and its wild salt-resistant relative Solanum chilense. In S. chilense, treatment with 125 mM NaCl improved plant growth, increased production of ethylene, endogenous salicylic acid and spermine. The production was related to a modification of expression of genes involved in ethylene and polyamine metabolism. In contrast, salinity decreased plant growth in S. lycopersicum without affecting endogenous ethylene, salicylic or polyamine concentrations. Exogenous application of salicylic acid at 0.01 mM enhanced shoot growth in both species and affected ethylene and polyamine production in S. chilense. Concomitant application of NaCl and salicylic acid improved osmotic adjustment, thus suggesting that salt and SA may act in synergy on osmolyte synthesis. However, the beneficial impact of exogenous application of salicylic acid was mitigated by salt stress since NaCl impaired endogenous SA accumulation in the shoot and salicylic acid did not improve plant growth in salt-treated plants. Our results thus revealed that both species respond differently to salinity and that salicylic acid, ethylene and polyamine metabolisms are involved in salt resistance in S. chilense.

Implication of citrate, malate and histidine in the accumulation and transport of nickel in Mesembryanthemum crystallinum and Brassica juncea.

Citrate, malate and histidine have been involved in many processes including metal tolerance and accumulation in plants. These molecules have been frequently reported to be the potential nickel chelators, which most likely facilitate metal transport through xylem. In this context, we assess here, the relationship between organics acids and histidine content and nickel accumulation in Mesembryanthemum crystallinum and Brassica juncea grown in hydroponic media added with 25, 50 and 100 µM NiCl2. Results showed that M. crystallinum is relatively more tolerant to Ni toxicity than B. juncea. For both species, xylem transport rate of Ni increased with increasing Ni supply. A positive correlation was established between nickel and citrate concentrations in the xylem sap. In the shoot of B. juncea, citric and malic acids concentrations were significantly higher than in the shoot of M. crystallinum. Also, the shoots and roots of B. juncea accumulated much more histidine. In contrast, a higher root citrate concentration was observed in M. crystallinum. These findings suggest a specific involvement of malic and citric acid in Ni translocation and accumulation in M. crystallinum and B. juncea. The high citrate and histidine accumulation especially at 100µM NiCl2, in the roots of M. crystallinum might be among the important factors associated with the tolerance of this halophyte to toxic Ni levels.

Tomato (Solanum lycopersicum L.) SlIPT3 and SlIPT4 isopentenyltransferases mediate salt stress response in tomato.

BACKGROUND: Cytokinins (CKs) are involved in response to various environmental cues, including salinity. It has been previously reported that enhancing CK contents improved salt stress tolerance in tomato. However, the underlying mechanisms of CK metabolism and signaling under salt stress conditions remain to be deciphered. RESULTS: Two tomato isopentenyltransferases, SlIPT3 and SlIPT4, were characterized in tomato and Arabidopsis. Both proteins displayed isopentenyltransferase (IPT) activity in vitro, while their encoding genes exhibited different spatio-temporal expression patterns during tomato plant development. SlIPT3 and SlIPT4 were affected by the endogenous CK status, tightly connected with CKs feedback regulation, as revealed by hormonal treatements. In response to salt stress, SlIPT3 and SlIPT4 were strongly repressed in tomato roots, and differently affected in young and old leaves. SlIPT3 overexpression in tomato resulted in high accumulation of different CK metabolites, following modifications of CK biosynthesis-, signaling- and degradation-gene expression. In addition, 35S::SlIPT3 tomato plants displayed improved tolerance to salinity consecutive to photosynthetic pigments and K(+)/Na(+) ratio retention. Involvement of SlIPT3 and SlIPT4 in salt stress response was also observed in Arabidopsis ipt3 knock-out complemented plants, through maintenance of CK homeostasis. CONCLUSIONS: SlIPT3 and SlIPT4 are functional IPTs encoded by differently expressed genes, distinctively taking part in the salinity response. The substantial participation of SlIPT3 in CK metabolism during salt stress has been determined in 35S::SlIPT3 tomato transformants, where enhancement of CKs accumulation significantly improved plant tolerance to salinity, underlining the importance of this phytohormone in stress response.

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.

How can we take advantage of halophyte properties to cope with heavy metal toxicity in salt-affected areas?

BACKGROUND: Many areas throughout the world are simultaneously contaminated by high concentrations of soluble salts and by high concentrations of heavy metals that constitute a serious threat to human health. The use of plants to extract or stabilize pollutants is an interesting alternative to classical expensive decontamination procedures. However, suitable plant species still need to be identified for reclamation of substrates presenting a high electrical conductivity. SCOPE: Halophytic plant species are able to cope with several abiotic constraints occurring simultaneously in their natural environment. This review considers their putative interest for remediation of polluted soil in relation to their ability to sequester absorbed toxic ions in trichomes or vacuoles, to perform efficient osmotic adjustment and to limit the deleterious impact of oxidative stress. These physiological adaptations are considered in relation to the impact of salt on heavy metal bioavailabilty in two types of ecosystem: (1) salt marshes and mangroves, and (2) mine tailings in semi-arid areas. CONCLUSIONS: Numerous halophytes exhibit a high level of heavy metal accumulation and external NaCl may directly influence heavy metal speciation and absorption rate. Maintenance of biomass production and plant water status makes some halophytes promising candidates for further management of heavy-metal-polluted areas in both saline and non-saline environments.