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• NaCl stimulates the growth of salt-secreting Reaumuria soongorica. • NaCl assists R. soongorica to maintain leaf morphology structure under drought stress. • Salt secretion helps R. soongorica to keep the better growth under arid-salinity habitat. Reaumuria soongorica, a salt-secreting xerophytic shrub, is a dominant species in arid desert regions of northwest China. To investigate whether NaCl could stimulate the growth and alleviate drought stress in R. soongorica , the seedlings were treated with a range of different concentrations of 0–1.17 g kg−1 NaCl, and also were withheld water for drought stress under without or supplementary 0.59 g kg-1 NaCl. The results showed that 0.59 g kg-1 NaCl (moderate NaCl) significantly stimulated the growth of R. soongorica , and also effectively alleviated deleterious impacts of drought stress on its growth and leaf morphological structure. Further analysis showed that moderate NaCl significantly improved photosynthetic capacity and mitigated light suppression of drought stress on photosystem II in R. soongorica , concomitantly, decreased osmotic potential, enlarged turgor pressure as well as increased the relative water content in leaves under drought stress. Furthermore, moderate NaCl induced an obvious increase of Na+ accumulation in tissues of R. soongorica , which resulted in a significant increase of the contribution of Na+ to leaf osmotic potential from13 to 22% under drought stress. Additionally, moderate NaCl also promoted Na+ secretion via salt glands of leaf. These results suggest that the positive roles of NaCl on the growth and drought resistance of R. soongorica is due to the increase of Na+ accumulating in leaf tissues, facilitating plant to maintain higher photosynthetic activity and better water status in arid environment, simultaneously, salt secretion of salt glands protects plant from excess Na+ toxicity. [ABSTRACT FROM AUTHOR]

Background and aims: Accumulating a great quantity of Na, maintaining the stability of the concentration of important nutrition elements, increasing the activities of enzymes related to ROS-scavenging are crucial strategies for the xerophyte Zygophyllum xanthoxylum surviving under adverse saline and drought environments; besides, actively regulating the photosynthesis is also a main reason for Z. xanthoxylum to adapt to mild salt conditions. However, the possible molecular basis of above physiological mechanisms is poorly understood. Methods: By performing Illumina sequencing combined with a digital gene expression profiling technique, differentially expressed genes in leaves and roots of Z. xanthoxylum under 50 mM NaCl and −0.5 MPa osmotic stress for 6 and 24 h were identified, respectively, mainly focused on genes related to ion transport, ROS-scavenging system and photosynthesis. Results: Under 50 mM NaCl and −0.5 MPa osmotic stress, the transcripts of genes encoding transporters/channels for Na, K, Ca, Mg, nitrogen, phosphate and important micro-elements significantly increased, which is conducive to enhance the uptake and transport of nutrient elements in Z. xanthoxylum; and more importantly, besides Na, genes related to vacuolar compartmentalization of K, Ca, NO in leaves plays vital roles in the adaptation to mild salt condition. Meanwhile, NaCl treatment and osmotic stress significantly increased the transcripts of a number of genes related to ROS-scavenging system, which is beneficial to accelerate the ROS-scavenging under 50 mM NaCl and mitigate the damage of ROS to cell biomembrane system under osmotic stress. In addition, in contrast to osmotic stress, 50 mM NaCl significantly induced the expression of genes encoding proteins participated in photosynthetic electron transport and carbon fixation, while inhibited the expression of genes related to chlorophyll catabolism. Conclusions: The present study identified potential genes underling the principal physiological mechanisms of salt and drought tolerance in Z. xanthoxylum. The results provided abundant genetic resources from desert xerophyte for genetic improvement of stress-resistance of important forage and crop species in arid area. [ABSTRACT FROM AUTHOR]

Salinity and drought are major environmental factors limiting the growth and productivity of alfalfa worldwide as this economically important legume forage is sensitive to these kinds of abiotic stress. In this study, transgenic alfalfa lines expressing both tonoplast NXH and H+- PPase genes, Zx NHX and Zx VP1-1 from the xerophyte Zygophyllum xanthoxylum L., were produced via Agrobacterium tumefaciens-mediated transformation. Compared with wild-type ( WT) plants, transgenic alfalfa plants co-expressing Zx NHX and Zx VP1-1 grew better with greater plant height and dry mass under normal or stress conditions (NaCl or water-deficit) in the greenhouse. The growth performance of transgenic alfalfa plants was associated with more Na+, K+ and Ca2+ accumulation in leaves and roots, as a result of co-expression of Zx NHX and Zx VP1-1. Cation accumulation contributed to maintaining intracellular ions homoeostasis and osmoregulation of plants and thus conferred higher leaf relative water content and greater photosynthesis capacity in transgenic plants compared to WT when subjected to NaCl or water-deficit stress. Furthermore, the transgenic alfalfa co-expressing Zx NHX and Zx VP1-1 also grew faster than WT plants under field conditions, and most importantly, exhibited enhanced photosynthesis capacity by maintaining higher net photosynthetic rate, stomatal conductance, and water-use efficiency than WT plants. Our results indicate that co-expression of tonoplast NHX and H+- PPase genes from a xerophyte significantly improved the growth of alfalfa, and enhanced its tolerance to high salinity and drought. This study laid a solid basis for reclaiming and restoring saline and arid marginal lands as well as improving forage yield in northern China. [ABSTRACT FROM AUTHOR]

Salinisation caused by irrigation is threatening the forage yield of lucerne pasture in the arid and semi-arid areas of west China. To select lucerne cultivars with good salt tolerance, the relative salt tolerance of five lucerne cultivars was assessed based upon shoot dry weight, shoot K+/ Na+ ratio, leaf malondialdehyde (MDA) content and relative membrane permeability (RMP) at the seedling stage. NaCl reduced the shoot dry weight and shoot K+/Na+ ratio, and enhanced the leaf MDA content and RMP in all cultivars, but the degree of either reduction or enhancement differed between these lucerne cultivars. under 200 mM NaCl for 5 days, 'Rambler' had significantly greater shoot dry weight (only dropped 17.2% to 0.17 g plant-1) than other cultivars, and also maintained a better ion status, with higher K+ content, lower Na+ content, and thus a higher relative shoot K+/Na+ ratio. 'Daye' was healthier because neither the MDA content nor the RMP was significantly increased in its leaves. Through combining the relative values of these indicators, the relative salt tolerance of the five cultivars decreased in the order: 'Rambler', 'Daye', 'Sandili', 'Gannong No.3', and 'Longdong'. This study indicated that 'Rambler' and 'Daye' might be suitable for pasture establishment on irrigated land in arid and semi-arid areas of west China. [ABSTRACT FROM AUTHOR]

Abstract: Salinity and drought are two major abiotic factors limiting crop production. To generate the legume forage adapting to saline and arid soils, we had transformed alfalfa (Medicago sativa) with AVP1, a vacuolar H+-pyrophosphatase (H+-PPase) gene from Arabidopsis thaliana. In this paper, we report that overexpression of the AVP1 gene confers enhanced salt and drought tolerance to the transformed alfalfa. Transgenic alfalfa grows well in the presence of 200mM NaCl and also under a water-deprivation condition, while wild-type plants exhibit chlorosis and growth inhibition, even death. Compared with wild-type plants, transgenic plants accumulate more Na+, K+ and Ca2+ in leaves and roots. Moreover, the leaves of transgenic plants retain more water during drought stress than those of wild-type plants due to lower solute potential. Increased solute accumulation and water retention, and steady intracellular ion homeostasis might also confer other phenotypes of salt and drought tolerance in the transgenic plants, which include the higher photosynthesis capacity and the lesser cell membrane damage during salt or water-deficit stress. Furthermore, the increased potassium uptake and root activity in transgenic alfalfa may be the consequences of rhizosphere acidification resulting from expression of the AVP1. These results indicated that the expression of AVP1 confers enhanced salt and drought tolerance on alfalfa, a very important crop. This study provides a way for improving salt and drought tolerance in important legume forages. [Copyright &y& Elsevier]

Revealing the genetic basis for stress-resistant traits in extremophile plants will yield important information for crop improvement. Zygophyllum xanthoxylum, an extant species of the ancient Mediterranean, is a succulent xerophyte that can maintain a favorable water status under desert habitats; however, the genetic basis of this adaptive trait is poorly understood. Furthermore, the phylogenetic position of Zygophyllales, to which Z. xanthoxylum belongs, remains controversial. In this study, we sequenced and assembled the chromosome-level genome of Z. xanthoxylum. Phylogenetic analysis showed that Zygophyllales and Myrtales form a separated taxon as a sister to the clade comprising fabids and malvids, clarifying the phylogenetic position of Zygophyllales at whole-genome scale. Analysis of genomic and transcriptomic data revealed multiple critical mechanisms underlying the efficient osmotic adjustment using Na+ and K+ as "cheap" osmolytes that Z. xanthoxylum has evolved through the expansion and synchronized expression of genes encoding key transporters/channels and their regulators involved in Na+/K+ uptake, transport, and compartmentation. It is worth noting that ZxCNGC1;1 (cyclic nucleotide-gated channels) and ZxCNGC1;2 constituted a previously undiscovered energy-saving pathway for Na+ uptake. Meanwhile, the core genes involved in biosynthesis of cuticular wax also featured an expansion and upregulated expression, contributing to the water retention capacity of Z. xanthoxylum under desert environments. Overall, these findings boost the understanding of evolutionary relationships of eudicots, illustrate the unique water retention mechanism in the succulent xerophyte that is distinct from glycophyte, and thus provide valuable genetic resources for the improvement of stress tolerance in crops and insights into the remediation of sodic lands. Genomic analysis of a desert plant reveals the phylogeny of Zygophyllales and provides elite genes for crop improvement. [ABSTRACT FROM AUTHOR]

Key message: The content of flavonoids could increase in A. canescens under saline conditions. Overexpression of AcCHI in transgenic A. thaliana promotes flavonoid biosynthesis, thereby functioning in the tolerance of transgenic plants to salt and osmotic stress by maintaining ROS homeostasis. Atriplex canescens is a halophytic forage shrub with excellent adaptation to saline environment. Our previous study showed that a large number of genes related to the biosynthesis of flavonoids in A. canescens were significantly up-regulated by NaCl treatments. However, it remains unclear whether flavonoids are involved in A. canescens response to salinity. In this study, we found that the accumulation of flavonoids significantly increased in either the leaves or roots of A. canescens seedling under 100 and 300 mM NaCl treatments. Correspondingly, AcCHS, AcCHI and AcF3H, which encode three key enzymes (chalcone synthases (CHS), chalcone isomerase (CHI), and flavanone 3-hydroxylase (F3H), respectively) of flavonoids biosynthesis, were significantly induced in the roots or leaves of A. canescens by 100 or 300 mM NaCl. Then, we generated the transgenic Arabidopsis thaliana overexpressing AcCHI and found that transgenic plants accumulated more flavonoids through enhancing the pathway of flavonoids biosynthesis. Furthermore, overexpression of AcCHI conferred salt and osmotic stress tolerance in transgenic A. thaliana. Contrasted with wild-type A. thaliana, transgenic lines grew better with greater biomass, less H2O2 content as well as lower relative plasma permeability in either salt or osmotic stress conditions. In conclusion, our results indicate that flavonoids play an important role in A. canescens response to salt stress through reactive oxygen species (ROS) scavenging and the key enzyme gene AcCHI in flavonoids biosynthesis pathway of A. canescens has the potential to improve the stress tolerance of forages and crops. [ABSTRACT FROM AUTHOR]

Background and Aims Desert plants possess excellent water-conservation capacities to survive in extreme environments. Cuticular wax plays a pivotal role in reducing water loss through plant aerial surfaces. However, the role of cuticular wax in water retention by desert plants is poorly understood. Methods We investigated leaf epidermal morphology and wax composition of five desert shrubs from north-west China and characterized the wax morphology and composition for the typical xerophyte Zygophyllum xanthoxylum under salt, drought and heat treatments. Moreover, we examined leaf water loss and chlorophyll leaching of Z. xanthoxylum and analysed their relationships with wax composition under the above treatments. Key Results The leaf epidermis of Z. xanthoxylum was densely covered by cuticular wax, whereas the other four desert shrubs had trichomes or cuticular folds in addition to cuticular wax. The total amount of cuticular wax on leaves of Z. xanthoxylum and Ammopiptanthus mongolicus was significantly higher than that of the other three shrubs. Strikingly, C31 alkane, the most abundant component, composed >71 % of total alkanes in Z. xanthoxylum , which was higher than for the other four shrubs studied here. Salt, drought and heat treatments resulted in significant increases in the amount of cuticular wax. Of these treatments, the combined drought plus 45 °C treatment led to the largest increase (107 %) in the total amount of cuticular wax, attributable primarily to an increase of 122 % in C31 alkane. Moreover, the proportion of C31 alkane within total alkanes remained >75 % in all the above treatments. Notably, the water loss and chlorophyll leaching were reduced, which was negatively correlated with C31 alkane content. Conclusion Zygophyllum xanthoxylum could serve as a model desert plant for study of the function of cuticular wax in water retention because of its relatively uncomplicated leaf surface and because it accumulates C31 alkane massively to reduce cuticular permeability and resist abiotic stressors. [ABSTRACT FROM AUTHOR]

Purpose: Atriplex canescens adapts to saline soils by sequestering excessive Na+ in salt bladders on the surface of aerial tissues, which is a complex comprising epidermal cells (ECs), stalk cells (SCs) and epidermal bladder cells (EBCs). However, the mechanism of how Na+ enters salt bladders of A. canescens is not yet clear. We previously identified two A. canescens HKT1 genes that might be related to Na+ sequestration in salt bladders. The aim of this study was to evaluate the function of AcHKT1 genes in Na+ secretion. Results: Two AcHKT1 genes were cloned; AcHKT1;1 was largely expressed in roots, while AcHKT1;2 was mainly expressed in shoots and strongly induced by NaCl. Heterologous expression of AcHKT1;2 aggravated the Na+-sensitive phenotype in yeast. This result was further confirmed in Xenopus system, in which AcHKT1;2 exerted high selectivity for Na+, indicating that AcHKT1;2 functions as a plasma membrane-localized Na+ transporter and mediates robust Na+ influx at the cellular level. Interestingly, AcHKT1;2 expression in leaves was significantly reduced once salt bladders were removed from the leaf surfaces; in particular, it had the greatest impact on the expression in mature leaves with the strongest activity toward ion secretion, suggesting that AcHKT1;2 was predominantly expressed in the EC-SC-EBC complex of A. canescens leaves. Conclusions: AcHKT1;2 is a key candidate transporter involved in mediating the entry of Na+ into A. canescens EBCs, thereby facilitating continuous Na+ sequestration in EBCs to ensure the survival of plants in harsh saline environments. [ABSTRACT FROM AUTHOR]

Background: Heat stress has adverse effects on the growth and reproduction of plants. Zygophyllum xanthoxylum, a typical xerophyte, is a dominant species in the desert where summer temperatures are around 40 °C. However, the mechanism underlying the thermotolerance of Z. xanthoxylum remained unclear. Results: Here, we characterized the acclimation of Z. xanthoxylum to heat using a combination of physiological measurements and transcriptional profiles under treatments at 40 °C and 45 °C, respectively. Strikingly, moderate high temperature (40 °C) led to an increase in photosynthetic capacity and superior plant performance, whereas severe high temperature (45 °C) was accompanied by reduced photosynthetic capacity and inhibited growth. Transcriptome profiling indicated that the differentially expressed genes (DEGs) were related to transcription factor activity, protein folding and photosynthesis under heat conditions. Furthermore, numerous genes encoding heat transcription shock factors (HSFs) and heat shock proteins (HSPs) were significantly up-regulated under heat treatments, which were correlated with thermotolerance of Z. xanthoxylum. Interestingly, the up-regulation of PSI and PSII genes and the down-regulation of chlorophyll catabolism genes likely contribute to improving plant performance of Z. xanthoxylum under moderate high temperature. Conclusions: We identified key genes associated with of thermotolerance and growth in Z. xanthoxylum, which provide significant insights into the regulatory mechanisms of thermotolerance and growth regulation in Z. xanthoxylum under high temperature conditions. [ABSTRACT FROM AUTHOR]

Atriplex canescens is a representative halophyte with excellent tolerance to salt. Previous studies have revealed certain physiological mechanisms and detected functional genes associated with salt tolerance. However, knowledge on the ROS scavenging system and regulatory mechanisms in this species when adapting to salinity is limited. Therefore, this study further analyzed the transcriptional changes in genes related to the ROS scavenging system and important regulatory mechanisms in A. canescens under saline conditions using our previous RNA sequencing data. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation revealed that the differentially expressed genes (DEGs) were highly enriched in signal transduction- and reactive oxygen species-related biological processes, including "response to oxidative stress", "oxidoreductase activity", "protein kinase activity", "transcription factor activity", and "plant hormone signal transduction". Further analyses suggested that the transcription abundance of many genes involved in SOD, the AsA-GSH cycle, the GPX pathway, PrxR/Trx, and the flavonoid biosynthesis pathway were obviously enhanced. These pathways are favorable for scavenging excessive ROS induced by salt and maintaining the integrity of the cell membrane. Meanwhile, many vital transcription factor genes (WRKY, MYB, ZF, HSF, DREB, and NAC) exhibited increased transcripts, which is conducive to dealing with saline conditions by regulating downstream salt-responsive genes. Furthermore, a larger number of genes encoding protein kinases (RLK, CDPK, MAPK, and CTR1) were significantly induced by saline conditions, which is beneficial to the reception/transduction of salt-related signals. This study describes the abundant genetic resources for enhancing the salt tolerance in salt-sensitive plants, especially in forages and crops. [ABSTRACT FROM AUTHOR]

Atriplex canescens is a C 4 shrub with excellent adaptation to saline and arid environments. Our previous study showed that the secretion of excessive Na+ into leaf salt bladders is a primary strategy in salt tolerance of A. canescens and external 100 mM NaCl can substantially stimulate its growth. To investigate whether NaCl could facilitate Atriplex canescens response to drought stress, five-week-old seedlings were subjected to drought stress (30% of field water capacity) in the presence or absence of additional 100 mM NaCl. The results showed that, under drought stress, the addition of NaCl could substantially improve the growth of A. canescens by increasing leaf relative water content, enhancing photosynthetic activity and inducing a significant declined leaf osmotic potential (Ψs). The addition of NaCl significantly increased Na+ concentration in leaf salt bladders and the Na+ contribution to leaf Ψs , while had no adverse effects on K+ accumulation in leaf laminae. Therefore, the large accumulation of Na+ in salt bladders for enhancing osmotic adjustment (OA) ability is a vital strategy in A. canescens responding to drought stress. In addition, the concentration of free proline, bataine and soluble sugars exhibited a significant increase in the presence of NaCl under drought stress, and the betaine contribution to leaf Ψs was significantly increased by additional NaCl compared with that under drought treatment alone, suggesting that compatible solutes are also involved in OA in addition to functioning as protectants to alleviate water deficit injury. • A. canescens could grow well in drought soils that contain certain salt. • Na+ secretion and K+ retention are vital strategies for A. canescens to cope with water deficit. • NaCl improves photosynthesis and hydration of A. canescens under drought stress. [ABSTRACT FROM AUTHOR]

Background and aims: Uncontrolled uptake of Na+ is the reason that many species are sensitive to salinity. Suberin is a protective barrier found in the walls of root endodermal cells that appears to be important for salt tolerance, yet its specific protective mechanism has not been fully elucidated. Methods: Here we investigated the role of aliphatic suberin in protecting plants against salt stress by using a mutant of Arabidopsis, cyp86a1, which exhibits a significant reduction of root aliphatic suberin. Results: We found that NaCl significantly increased suberization in roots of hydroponic-grown wild-type plants, but not in cyp86a1. Cyp86a1 exhibited a salt-sensitive phenotype. Compared with wild-type, Na+ accumulation in shoots was higher in cyp86a1. We provide evidence that increased Na+ uptake was via the root transcellular pathway. Furthermore, cyp86a1 accumulated less K+ in shoots than wild-type under NaCl stress, which was a consequence of increased K+ efflux from the root vasculature. Additionally, we provide evidence that aliphatic suberin reduces inflow of water across the root endodermis under non-stress conditions but reduces the backflow of water to the medium under salt stress. Conclusions: Finally, we propose a model for the role of aliphatic suberin in restricting Na+ influx, K+ efflux and water backflow in plants under saline conditions. [ABSTRACT FROM AUTHOR]

Background and aims: The Shaker AKT1-like channels are considered to be involved in both high- and low-affinity K uptake and correlated with salt tolerance in glycophytes. Suaeda salsa ( Suaeda maritima subsp. salsa), as a typical salt-accumulating halophyte, is able to absorb K efficiently while growing under saline conditions and taking in a large amount of Na, thus maintaining the K concentration in its cells. In this study, the possible functions of the inward-rectifying K channel SsAKT1 in K uptake and salt tolerance in the halophyte S. salsa were investigated. Methods: SsAKT1 from S. salsa was isolated by RT-PCR and characterized using yeast complementation; the responses of SsAKT1 to various KCl and NaCl treatments were investigated by real-time quantitative PCR. Results: SsAKT1 consisted of 879 amino acid residues and shared high homology (60-67 %) with the identified inward-rectifying K channels AKT1 from other plants. The expression of SsAKT1 rescued the K-uptake-defective phenotype of yeast strain CY162, and also suppressed the salt-sensitive phenotype of yeast strain G19, suggesting SsAKT1 functioned as an inward-rectifying K channel. SsAKT1 was predominantly expressed in roots, and was induced significantly by K starvation; transcript levels increased further on resupply of K (0.1-10 mM for 6 h) by 62 % in 0.1 mM K and 144-174 % in higher K concentrations (1-10 mM). Interestingly, the expression level of SsAKT1 in roots was also induced significantly by short-term treatment (6 h) with NaCl concentrations (25-250 mM). Conclusions: These results demonstrate that the inward-rectifying K channel SsAKT1 might mediate both high- and low-affinity K uptake in S. salsa, but play a greater role in the low-affinity system. Furthermore, SsAKT1 might also be involved in salt tolerance by participating in the maintenance of K nutrition in S. salsa under salinity. [ABSTRACT FROM AUTHOR]

Background and aims: Two major adaptive strategies used by Zygophyllum xanthoxylum, a C succulent xerophyte, against arid environments are absorbing a great quantity of Na from low-salinity soil which is efficiently transported to the leaves, and maintaining the stability of K concentration in those leaves. The plasma membrane Na/H antiporter SOS1 has been suggested to be involved in Na transport and correlated with K nutrition in glycophytes. In this study, we investigated the function of the plasma membrane Na/H antiporter ZxSOS1 in long-distance transport and spatial distribution of Na and K in the xerophyte Z. xanthoxylum. Methods: The responses of ZxSOS1 to NaCl, KCl treatments and osmotic stress were investigated by semi-quantitative RT-PCR, then the role of ZxSOS1 in regulating plant growth and Na, K transport and spatial distribution in Z. xanthoxylum was studied by using post-transcriptional gene silencing. Results: We found that ZxSOS1 was preferentially expressed in roots and was induced and regulated by salt treatments and osmotic stress. Using post-transcriptional gene silencing, we found that ZxSOS1-silenced plants exhibited reduced growth rate compared to wild-type (WT) plants under both normal and saline conditions. ZxSOS1-silenced plants accumulated more Na in their roots but less Na in leaves and stems than WT under 50 mM NaCl. Furthermore, ZxSOS1-silenced plants had a lower net K uptake rate than WT plants under both normal and saline conditions, and more interestingly, accumulated less K in leaves under normal conditions than WT plants. ZxSOS1-silenced plants also showed a decreased concentration and spatial distribution of K in leaves and roots than WT under 50 mM NaCl. In addition, ZxSOS1-silenced plants possessed an increased selective transport (ST) capacity for K over Na from root to stem while a decreased ST value from stem to leaf compared with WT plants when both were grown in 50 mM NaCl. Conclusions: These results demonstrate that ZxSOS1 is not only essential in long-distance transport and spatial distribution of Na and even K, but also vital for regulating K and Na transport system and maintaining Na and K homeostasis in Z. xanthoxylum, thereby regulating its normal growth. [ABSTRACT FROM AUTHOR]

The plasma membrane Na[sup +]/H[sup +] antiporter (SOS1) was shown to be a Na[sup +] efflux protein and also involved in K[sup +] uptake and transport. PtSOS1 was characterised from Puccinellia tenuiflora (Griseb.) Scribn. et Merr., a monocotyledonous halophyte that has a high selectivity for K[sup +] over Na[sup +] by roots under salt stress. To assess the contribution of PtSOS1 to the selectivity for K[sup +] over Na[sup +], the expression levels of PtSOS1 and Na[sup +], K[sup +] accumulations in P. tenuiflora exposed to different concentrations of NaCl, KCl or NaCl plus KCl were analysed. Results showed that the expression levels of PtSOS1 in roots increased significantly with the increase of external NaCl (25-150 mM), accompanied by an increase of selective transport (ST) capacity for K[sup +] over Na[sup +] by roots. Transcription levels of PtSOS1 in roots and ST values increased under 0.1-1 mM KCl, then declined sharply under 5-10 mM KCl. Under 150 mM NaCl, PtSOS1 expression levels in roots and ST values at 0.1 mM KCl was significantly lower than that at 5 mM KCl with the prolonging of treatment time. A significant positive correlation was found between root PtSOS1 expression levels and ST values under various concentrations of NaCl, KCl or 150 mM NaCl plus 0.1 or 5 mM KCl treatments. Therefore, it is proposed that PtSOS1 is the major component of selective transport capacity for K[sup +] over Na[sup +] and hence, salt tolerance of P. tenuiflora. Finally, we hypothesise a function model of SOS1 in regulating K[sup +] and Na[sup +] transport system in the membrane of xylem parenchyma cells by sustaining the membrane integrity; it also appears that this model could reasonably explain the phenomenon of Na[sup +] retrieval from the xylem when plants are exposed to severe salt stress. The halophyte Puccinellia tenuiflora has a high selectivity for K[sup +] over Na[sup +] by roots under salt stress. Our aim was to investigate the molecular basis of this observation: we found that PtSOS1 is the major component of selective transport capacity for K[sup +] over Na[sup +] in P. tenuiflora under salt stress. This result will broaden the understanding of interplay between SOS1 and HKT as a factor depolarising xylem parenchyma, which leads to xylem K[sup +] loading via SKOR. [ABSTRACT FROM AUTHOR]

Zygophyllum xanthoxylum, a C3 woody species, is a succulent xerophyte that is well adapted to arid environments. Our previous investigations showed that Na+ has a positive effect on the growth of Z. xanthoxylum under drought conditions, which was closely related to high Na+ accumulation in leaves. To reveal the physiological mechanisms underlying how Na+ accumulation improves the drought resistance of Z. xanthoxylum, 3-week-old seedlings were treated with a series of additional external NaCl concentrations (5–150 mM) in sand culture experiments. Seedlings were also subjected to water deficit (30% of field water capacity) in the presence or absence of additional NaCl (50 mM) in pot experiments. The results indicated that 50 mM NaCl could mitigate deleterious impacts of water deficit on the growth of Z. xanthoxylum, by improving the relative water content, inducing a significant drop in leaf water potential and, concomitantly, increasing leaf turgor pressure and chlorophyll concentrations resulting in an enhancement of overall plant photosynthetic activity (i.e., photosynthetic rate and water use efficiency). Furthermore, NaCl (50 mM) could alleviate the inhibitory effect of water deficit on the activity of photosystem II in Z. xanthoxylum. The contribution of Na+ to the total osmotic potential varied from 8% in the control to 13% in plants subjected to water deficit and, surprisingly, to 28% in plants grown in the presence of 50 mM NaCl under water deficit; however, the contribution of K+ significantly decreased from 13 to 8%. These findings suggest that, under arid environments, Z. xanthoxylum is able to accumulate a high concentration of Na+ in its leaves and use it directly for osmotic adjustment, which was coupled with an improvement in leaf hydration and photosynthetic activity. [ABSTRACT FROM PUBLISHER]

Abstract: Sodium (Na+) has been found to play important roles in the adaptation of xerophytic species to drought conditions. The tonoplast Na+/H+ antiporter (NHX) proved to be involved in the compartmentalization of Na+ into vacuoles from the cytosol. In this study, a gene (ZxNHX) encoding tonoplast Na+/H+ antiporter was isolated and characterized in Zygophyllum xanthoxylum, a succulent xerophyte growing in desert areas of northwest China. The results revealed that ZxNHX consisted of 532 amino acid residues with a conserved binding domain (78LFFIYLLPPI87) for amiloride and shared high similarity (73–81%) with the identified tonoplast Na+/H+ antiporters in other plant species. Semi-quantitative RT-PCR analysis showed that the mRNA level of ZxNHX was significantly higher in the leaf than in stem or root. The transcript abundance of ZxNHX in Z. xanthoxylum subjected to salt (5–150mM NaCl) or drought (50–15% of field water capacity (FWC)) was 1.4–8.4 times or 2.3–4.4 times that of plants grown in the absence of NaCl or 70% of FWC, respectively. Leaf Na+ concentration in plants exposed to salt or drought was 1.7–5.2 times or 1.5–2.2 times that of corresponding control plants, respectively. It is clear that there is a positive correlation between up-regulation of ZxNHX and accumulation of Na+ in Z. xanthoxylum exposed to salt or drought. Furthermore, Z. xanthoxylum accumulated larger amounts of Na+ than K+ in the leaf under drought conditions, even in low salt soil. In summary, our results suggest that ZxNHX encodes a tonoplast Na+/H+ antiporter and plays important roles in Na+ accumulation and homeostasis of Z. xanthoxylum under salt and drought conditions. [Copyright &y& Elsevier]

• ZxABCG11 was cloned and characterized from the xerophyte Zygophyllum xanthoxylum. • ZxABCG11 was predominantly expressed in young leaves and was induced by salt, drought and heat, especially prominent under combined drought and heat stresses. • Ectopic expression of ZxABCG11 in Arabidopsis increased the density of wax crystals and reduced cuticle permeability. • Expression of ZxABCG11 in Arabidopsis enhanced the drought tolerance of transgenic plants by increasing cuticular wax accumulation. Cuticular waxes, a waterproofing hydrophobic barrier that coats the aerial surfaces of all terrestrial plants, protects plants from various environmental stresses, particularly drought stress. The molecular basis of cuticular wax deposition in xerophytes (e.g. desert plants), including transport mechanisms of waxes to the cell wall, is poorly understood. Here, ZxABCG11 encoding an ATP binding cassette (ABC) transporter was isolated from the xerophyte Zygophyllum xanthoxylum , since we found it was predominantly expressed in young leaves and induced by salt, drought, heat, and combined drought and heat stresses. To ascertain the function of ZxABCG11 , we introduced ZxABCG11 into Arabidopsis thaliana and found an increased abundance of cuticular wax on stems and leaves of the transgenic plants, which also exhibited a thickened cuticle and reduced cuticle permeability. Transcript expression analysis revealed that many genes related to wax biosynthesis and transport were up-regulated in these ZxABCG11 transgenic plants. Furthermore, compared with wild type Arabidopsis, ZxABCG11 transgenic plants displayed a higher biomass and survival rate under drought conditions. Taken together, we propose that the expression of ZxABCG11 in Arabidopsis promotes cuticular wax accumulation and thicker cuticle formation, thereby enhancing drought tolerance. [ABSTRACT FROM AUTHOR]

• ZxNRT1.5 was mainly expressed in the root stele of Zygophyllum xanthoxylum. • ZxNRT1.5 in roots was induced by salt treatments and osmotic stress. • ZxNRT1.5 mediated root-to-shoot NO 3 − transport and enhanced NO 3 − uptake. • ZxNRT1.5 modulated salt and drought tolerance by regulating NO 3 −, Na+, K+ transport. The Nitrate Transporter1/Peptide Transporter family member NPF7.3/NRT1.5 is responsible for long-distance transport of NO 3 − and involved in affecting salt and drought tolerance in plants. However, current studies have only focused on AtNRT1.5 from the stress-sensitive glycophyte Arabidopsis. In this study, the function of the NRT1.5 homolog ZxNRT1.5 from the typical xerophyte Zygophyllum xanthoxylum in ion transport and plants' salt and drought tolerance was analyzed. The results indicated that ZxNRT1.5 was mainly expressed in the root stele, and its expression level was significantly induced by salt treatments and osmotic stress. Overexpression of ZxNRT1.5 in Arabidopsis showed that ZxNRT1.5 mediated root-to-shoot NO 3 − transport and contributed to enhancing NO 3 − uptake. Overexpression of ZxNRT1.5 increased Na+ accumulation by decreasing the expression of AtHKT1;1 in roots, and promoted root-to-shoot transport of K+ probably by changing polarization of cell membrane under salt stress. Meanwhile, ZxNRT1.5 -overexpressing lines exhibited stronger tolerance to mannitol-induced osmotic stress, resulted from an increased accumulation of NO 3 − and the accumulation of a small quantity of Na+ that was beneficial for plant growth. These findings suggest that ZxNRT1.5 is not only essential for long-distance transport and accumulation of NO 3 −, but also involved in regulating Na+ and K+ transport, thereby modulating salt and drought tolerance. [ABSTRACT FROM AUTHOR]

HKT1 and SOS1 are two key Na+ transporters that modulate salt tolerance in plants. Although much is known about the respective functions of HKT1 and SOS1 under salt conditions, few studies have examined the effects of HKT1 and SOS1 mutations on the expression of other important Na+ and K+ transporter genes. This study investigated the physiological parameters and expression profiles of AtHKT1;1, AtSOS1, AtHAK5, AtAKT1, AtSKOR, AtNHX1, and AtAVP1 in wild-type (WT) and athkt1;1 and atsos1 mutants of Arabidopsis thaliana under 25 mM NaCl. We found that AtSOS1 mutation induced a significant decrease in transcripts of AtHKT1;1 (by 56–62% at 6–24 h), AtSKOR (by 36–78% at 6–24 h), and AtAKT1 (by 31–53% at 6–24 h) in the roots compared with WT. This led to an increase in Na+ accumulation in the roots, a decrease in K+ uptake and transportation, and finally resulted in suppression of plant growth. AtHKT1;1 loss induced a 39–76% (6–24 h) decrease and a 27–32% (6–24 h) increase in transcripts of AtSKOR and AtHAK5, respectively, in the roots compared with WT. At the same time, 25 mM NaCl decreased the net selective transport capacity for K+ over Na+ by 92% in the athkt1;1 roots compared with the WT roots. Consequently, Na+ was loaded into the xylem and delivered to the shoots, whereas K+ transport was restricted. The results indicate that AtHKT1;1 and AtSOS1 not only mediate Na+ transport but also control ion uptake and the spatial distribution of Na+ and K+ by cooperatively regulating the expression levels of relevant Na+ and K+ transporter genes, ultimately regulating plant growth under salt stress. [ABSTRACT FROM AUTHOR]