Potassium retention in leaf mesophyll as an element of salinity tissue tolerance in halophytes

How the Ethylene Biosynthesis Pathway of Semi-Halophytes Is Modified with Prolonged Salinity Stress Occurrence?

The mechanism of ethylene (ET)-regulated salinity stress response remains largely unexplained, especially for semi-halophytes and halophytes. Here, we present the results of the multifaceted analysis of the model semi-halophyte Mesembryanthemum crystallinum L. (common ice plant) ET biosynthesis pathway key components' response to prolonged (14 days) salinity stress. Transcriptomic analysis revealed that the expression of 3280 ice plant genes was altered during 14-day long salinity (0.4 M NaCl) stress. A thorough analysis of differentially expressed genes (DEGs) showed that the expression of genes involved in ET biosynthesis and perception (ET receptors), the abscisic acid (ABA) catabolic process, and photosynthetic apparatus was significantly modified with prolonged stressor presence. To some point this result was supported with the expression analysis of the transcript amount (qPCR) of key ET biosynthesis pathway genes, namely ACS6 (1-aminocyclopropane-1-carboxylate synthase) and ACO1 (1-aminocyclopropane-1-carboxylate oxidase) orthologs. However, the pronounced circadian rhythm observed in the expression of both genes in unaffected (control) plants was distorted and an evident downregulation of both orthologs' was induced with prolonged salinity stress. The UPLC-MS analysis of the ET biosynthesis pathway rate-limiting semi-product, namely of 1-aminocyclopropane-1-carboxylic acid (ACC) content, confirmed the results assessed with molecular tools. The circadian rhythm of the ACC production of NaCl-treated semi-halophytes remained largely unaffected by the prolonged salinity stress episode. We speculate that the obtained results represent an image of the steady state established over the past 14 days, while during the first hours of the salinity stress response, the view could be completely different.

Temporal Changes in Biochemical Responses to Salt Stress in Three Salicornia Species

Halophytes adapt to salinity using different biochemical response mechanisms. Temporal measurements of biochemical parameters over a period of exposure to salinity may clarify the patterns and kinetics of stress responses in halophytes. This study aimed to evaluate short-term temporal changes in shoot biomass and several biochemical variables, including the contents of photosynthetic pigments, ions (Na+, K+, Ca2+, and Mg2+), osmolytes (proline and glycine betaine), oxidative stress markers (H2O2 and malondialdehyde), and antioxidant enzymes (superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase) activities of three halophytic Salicornia species (S. persica, S. europaea, and S. bigelovii) in response to non-saline, moderate (300 mM NaCl), and high (500 mM NaCl) salinity treatments at three sampling times. Salicornia plants showed maximum shoot biomass under moderate salinity conditions. The results indicated that high Na+ accumulation in the shoots, coupled with the relative retention of K+ and Ca2+ under salt stress conditions, contributed significantly to ionic and osmotic balance and salinity tolerance in the tested Salicornia species. Glycine betaine accumulation, both constitutive and salt-induced, also seems to play a crucial role in osmotic adjustment in Salicornia plants subjected to salinity treatments. Salicornia species possess an efficient antioxidant enzyme system that largely relies on the ascorbate peroxidase and peroxidase activities to partly counteract salt-induced oxidative stress. The results also revealed that S. persica exhibited higher salinity tolerance than S. europaea and S. bigelovii, as shown by better plant growth under moderate and high salinity. This higher tolerance was associated with higher peroxidase activities and increased glycine betaine and proline accumulation in S. persica. Taking all the data together, this study allowed the identification of the biochemical mechanisms contributing significantly to salinity tolerance of Salicornia through the maintenance of ion and osmotic homeostasis and protection against oxidative stress.

'Against all floods': plant adaptation to flooding stress and combined abiotic stresses

Current climate change brings with it a higher frequency of environmental stresses, which occur in combination rather than individually leading to massive crop losses worldwide. In addition to, for example, drought stress (low water availability), also flooding (excessive water) can threaten the plant, causing, among others, an energy crisis due to hypoxia, which is responded to by extensive transcriptional, metabolic and growth-related adaptations. While signalling during flooding is relatively well understood, at least in model plants, the molecular mechanisms of combinatorial flooding stress responses, for example, flooding simultaneously with salinity, temperature stress and heavy metal stress or sequentially with drought stress, remain elusive. This represents a significant gap in knowledge due to the fact that dually stressed plants often show unique responses at multiple levels not observed under single stress. In this review, we (i) consider possible effects of stress combinations from a theoretical point of view, (ii) summarize the current state of knowledge on signal transduction under single flooding stress, (iii) describe plant adaptation responses to flooding stress combined with four other abiotic stresses and (iv) propose molecular components of combinatorial flooding (hypoxia) stress adaptation based on their reported dual roles in multiple stresses. This way, more future emphasis may be placed on deciphering molecular mechanisms of combinatorial flooding stress adaptation, thereby potentially stimulating development of molecular tools to improve plant resilience towards multi-stress scenarios.

Effect of Na, K and Ca Salts on Growth, Physiological Performance, Ion Accumulation and Mineral Nutrition of Mesembryanthemum crystallinum

Mesembryanthemum crystallinum L. is an obligatory halophyte species showing optimum growth at elevated soil salinity levels, but the ionic requirements for growth stimulation are not known. The aim of the present study was to compare the effects of sodium, potassium and calcium in the form of chloride and nitrate salts on the growth, physiological performance, ion accumulation and mineral nutrition of M. crystallinum plants in controlled conditions. In a paradoxical way, while sodium and potassium had comparable stimulative effect on plant growth, the effect of calcium was strongly negative even at a relatively low concentration, eventually leading to plant death. Moreover, the effect of Ca nitrate was less negative in comparison to that of Ca chloride, but K in the form of nitrate had some negative effects. There were three components of the stimulation of biomass accumulation by NaCl and KCl salinity in M. crsytallinum: the increase in tissue water content, increase in ion accumulation, and growth activation. As optimum growth was in a salinity range from 20 to 100 mM, the increase in the dry biomass of plants at a moderate (200 mM) and high (400 mM) salinity in comparison to control plants was mostly due to ion accumulation. Among physiological indicators, changes in leaf chlorophyll concentration appeared relatively late, but the chlorophyll a fluorescence parameter, Performance Index Total, was the most sensitive to the effect of salts. In conclusion, both sodium and potassium in the form of chloride salts are efficient in promoting the optimum growth of M. crystallinum plants. However, mechanisms leading to the negative effect of calcium on plants need to be assessed further.

Type of Anion Largely Determines Salinity Tolerance in Four Rumex Species

The aim of the present study was to compare the effect of various salts composed of different cations (Na⁺, K⁺) and anions (chloride, nitrate, nitrite) on growth, development and ion accumulation in three Rumex species with accessions from sea coast habitats (Rumex hydrolapathum, Rumex longifolius and Rumex maritimus) and Rumex confertus from an inland habitat. Plants were cultivated in soil in an experimental automated greenhouse during the autumn-winter season. Nitrite salts strongly inhibited growth of all Rumex species, but R. maritimus was the least sensitive. Negative effects of chloride salts were rather little-pronounced, but nitrates resulted in significant growth stimulation, plant growth and development. Effects of Na⁺ and K⁺ at the morphological level were relatively similar, but treatment with K⁺ salts resulted in both higher tissue electrolyte levels and proportion of senescent leaves, especially for chloride salts. Increases in tissue water content in leaves were associated with anion type, and were most pronounced in nitrate-treated plants, resulting in dilution of electrolyte concentration. At the morphological level, salinity responses of R. confertus and R. hydrolapathum were similar, but at the developmental and physiological level, R. hydrolapathum and R. maritimus showed more similar salinity effects. In conclusion, the salinity tolerance of all coastal Rumex species was high, but the inland species R. confertus was the least tolerant to salinity. Similarity in effects between Na⁺ and K⁺ could be related to the fact that surplus Na⁺ and K⁺ has similar fate (including mechanisms of uptake, translocation and compartmentation) in relatively salt-tolerant species. However, differences between various anions are most likely related to differences in physiological functions and metabolic fate of particular ions.

Salt tolerance in relation to elemental concentrations in leaf cell vacuoles and chloroplasts of a C4 monocotyledonous halophyte

Halophytes accumulate and sequester high concentrations of salt in vacuoles while maintaining lower levels of salt in the cytoplasm. The current data on cellular and subcellular partitioning of salt in halophytes are, however, limited to only a few dicotyledonous C₃ species. Using cryo-scanning electron microscopy X-ray microanalysis, we assessed the concentrations of Na, Cl, K, Ca, Mg, P and S in various cell types within the leaf-blades of a monocotyledonous C₄ halophyte, Rhodes grass (Chloris gayana). We also linked, for the first time, elemental concentrations in chloroplasts of mesophyll and bundle sheath cells to their ultrastructure and photosynthetic performance of plants grown in nonsaline and saline (200 mM NaCl) conditions. Na and Cl accumulated to the highest levels in xylem parenchyma and epidermal cells, but were maintained at lower concentrations in photosynthetically active mesophyll and bundle sheath cells. Concentrations of Na and Cl in chloroplasts of mesophyll and bundle sheath cells were lower than in their respective vacuoles. No ultrastructural changes were observed in either mesophyll or bundle sheath chloroplasts, and photosynthetic activity was maintained in saline conditions. Salinity tolerance in Rhodes grass is related to specific cellular Na and Cl distributions in leaf tissues, and the ability to regulate Na and Cl concentrations in chloroplasts.

Early signalling processes in roots play a crucial role in the differential salt tolerance in contrasting Chenopodium quinoa accessions

Significant variation in epidermal bladder cell (EBC) density and salt tolerance (ST) exists amongst quinoa accessions, suggesting that salt sequestration in EBCs is not the only mechanism conferring ST in this halophyte. In order to reveal other traits that may operate in tandem with salt sequestration in EBCs and whether these additional tolerance mechanisms acted mainly at the root or shoot level, two quinoa (Chenopodium quinoa) accessions with contrasting ST and EBC densities (Q30, low ST with high EBC density versus Q68, with high ST and low EBC density) were studied. The results indicate that responses in roots, rather than in shoots, contributed to the greater ST in the accession with low EBC density. In particular, the tolerant accession had improved root plasma membrane integrity and K+ retention in the mature root zone in response to salt. Furthermore, superior ST in the tolerant Q68 was associated with faster and root-specific H2O2 accumulation and reactive oxygen species-induced K+ and Ca2+ fluxes in the root apex within 30 min after NaCl application. This was found to be associated with the constitutive up-regulation of the membrane-localized receptor kinases regulatory protein FERONIA in the tolerant accession. Taken together, this study shows that differential root signalling events upon salt exposure are essential for the halophytic quinoa; the failure to do this limits quinoa adaptation to salinity, independently of salt sequestration in EBCs.

Potassium: A track to develop salinity tolerant plants

Salinity is one of the major constraints to plant growth and development across the globe that leads to the huge crop productivity loss. Salinity stress causes impairment in plant's metabolic and cellular processes including disruption in ionic homeostasis due to excess of sodium (Na⁺) ion influx and potassium (K⁺) efflux. This condition subsequently results in a significant reduction of the cytosolic K⁺ levels, eventually inhibiting plant growth attributes. K⁺ plays a crucial role in alleviating salinity stress by recasting key processes of plants. In addition, K⁺ acquisition and retention also serve as the perquisite trait to establish salt tolerant mechanism. In addition, an intricate network of genes and their regulatory elements are involved in coordinating salinity stress responses. Furthermore, plant growth regulators (PGRs) and other signalling molecules influence K⁺-mediated salinity tolerance in plants. Recently, nanoparticles (NPs) have also been found several implications in plants with respect to their roles in mediating K⁺ homoeostasis during salinity stress in plants. The present review describes salinity-induced adversities in plants and role of K⁺ in mitigating salinity-induced damages. The review also highlights the efficacy of PGRs and other signalling molecules in regulating K⁺ mediated salinity tolerance along with nano-technological perspective for improving K⁺ mediated salinity tolerance in plants.

The influence of transpiration on foliar accumulation of salt and nutrients under salinity in poplar (Populus × canescens)

Increasing salinity is one of the major drawbacks for plant growth. Besides the ion itself being toxic to plant cells, it greatly interferes with the supply of other macronutrients like potassium, calcium and magnesium. However, little is known about how sodium affects the translocation of these nutrients from the root to the shoot. The major driving force of this translocation process is thought to be the water flow through the xylem driven by transpiration. To dissect the effects of transpiration from those of salinity we compared salt stressed, ABA treated and combined salt- and ABA treated poplars with untreated controls. Salinity reduced the root content of major nutrients like K+, Ca2+ and Mg2+. Less Ca2+ and Mg2+ in the roots resulted in reduced leaf Ca2+ and leaf Mg2+ levels due to reduced stomatal conductance and reduced transpiration. Interestingly, leaf K+ levels were positively affected in leaves under salt stress although there was less K+ in the roots under salt. In response to ABA, transpiration was also decreased and Mg2+ and Ca2+ levels decreased comparably to the salt stress treatment, while K+ levels were not affected. Thus, our results suggest that loading and retention of leaf K+ is enhanced under salt stress compared to merely transpiration driven cation supply.

Assessment of Morpho-Physiological, Biochemical and Antioxidant Responses of Tomato Landraces to Salinity Stress

Understanding salt tolerance in tomato (Solanum lycopersicum L.) landraces will facilitate their use in genetic improvement. The study assessed the morpho-physiological variability of Hail tomato landraces in response to different salinity levels at seedling stages and recommended a tomato salt-tolerant landrace for future breeding programs. Three tomato landraces, Hail 548, Hail 747, and Hail 1072 were tested under three salinity levels: 75, 150, and 300 mM NaCl. Salinity stress reduced shoots' fresh and dry weight by 71% and 72%, and roots were 86.5% and 78.6%, respectively. There was 22% reduced chlorophyll content, carotene content by 18.6%, and anthocyanin by 41.1%. Proline content increased for stressed treatments. The 300 mM NaCl treatment recorded the most proline content increases (67.37 mg/g fresh weight), with a percent increase in proline reaching 61.67% in Hail 747. Superoxide dismutase (SOD) activity decreased by 65% in Hail 548, while it relatively increased in Hail 747 and Hail 1072 treated with 300 mM NaCl. Catalase (CAT) activity was enhanced by salt stress in Hail 548 and recorded 7.6%, increasing at 75 and 5.1% at 300 mM NaCl. It revealed a reduction in malondialdehyde (MDA) at the 300 mM NaCl concentration in both Hail 548 and Hail 1072 landraces. Increasing salt concentrations showed a reduction in transpiration rate of 70.55%, 7.13% in stomatal conductance, and 72.34% in photosynthetic rate. K+/Na+ ratios decreased from 56% for 75 mM NaCl to 85% for 300 mM NaCl treatments in all genotypes. The response to salt stress in landraces involved some modifications in morphology, physiology, and metabolism. The landrace Hail 548 may have better protection against salt stress and observed protection against reactive oxygen species (ROS) by increasing enzymatic "antioxidants" activity under salt stress.

Fullerenol regulates oxidative stress and tissue ionic homeostasis in spring wheat to improve net-primary productivity under salt-stress

The effects of fullerenol nanopriming (0, 10, 40, 80 and 120 nM concentration) on salt stressed-wheat (0 and 150 mM NaCl) were investigated under natural conditions. Salinity resulted in a shift in wheat growth pattern in the form of LAR (+ 40.9% increase) and RGR (+ 13.4% increase) while decreased NAR (- 31.7%). It also disturbed shoot and root biomass, ion uptake and reduced chlorophyll contents. Despite increase in enzyme activities, higher ROS generation (+ 48.1% O₂^- anion; and + 62.2% H₂O₂) and lipid peroxidation (+ 40.8% MDA) were detected in salt-stressed wheat plants. Possibly, the increases in enzyme activities were not up to the level to completely counteract the salinity induced oxidative stress. Nanopriming with fullerenol improved NAR (+ 8.77% to 23.2%), ROS metabolism and decreased indicators of oxidative stress. Hydropriming treatment also promoted NAR recovery by 21.9% than control plants. Compared to Na⁺ ions, improvements in shoot relative concentrations of K⁺, Ca²⁺ and P also recorded along with soluble sugars and amino acids, which improved osmotic balance. These biochemical modifications contributed to improvements in grain yield attributes (+11.8% to 18.3% in 100 grain-weight) than salinity stressed control. Hydropriming also contributed to a recovery in grain yield attributes by 12.6%. Above all, the harvested seeds from fullerenol treated plants also showed better germination and seedlings growth traits. Conclusively, we report non-toxic, growth-promoting effects of fullerenol nanoparticles on wheat crop and as a way forward; we suggest its exogenous application to recover crop productivity under saline environments.

Synergistic consequences of salinity and potassium deficiency in quinoa: Linking with stomatal patterning, ionic relations and oxidative metabolism

Quinoa emerged as an ideal food security crop due to its exceptional nutritive profile and stress enduring potential and also deemed as model plant to study the salt-tolerance mechanisms. However to fill the research gaps of this imperative crop, the present work aimed to study the effect of potassium (K) deficiency either separately or in combination with salinity. First, we investigated the stomatal and physiological based variations in quinoa growth under salinity and K, then series of analytical tools were used with model approach to interpret the stomatal aperture (SA) and photosynthesis (Pn) changes. Results revealed that quinoa efficiently deployed antioxidants to scavenge the excessive reactive oxygen species (ROS), had high uptake and retention of K⁺, Ca²⁺, Mg²⁺ with Cl⁻ as charge balancing ion, increased stomata density (SD) and declined the SA to maintain the Pn which resulted the improved growth under salinity. Whereas, K-deficiency caused the stunted growth more severally under salinity due to disruption in ionic homeostasis, excessive ROS production elicited the oxidative damages, SD and SA reduced and ultimately declined in Pn. Our best fitted regression model explored that dependent variables like Pn and SA changed according to theirs signified explanatory variables with quantification per unit based as stomatal conductance (Gs, 51), SD (0.05), ROS (-0.79) and K⁺ (0.08), Cl⁻ (0.34) and Na^{+ (-} 0.52) respectively. Overall, moderate salinity promoted the quinoa growth, while K-deficiency particularly with salinity reduced the quinoa performance by affecting stomatal and non-stomatal factors.

Targeting salt stress coping mechanisms for stress tolerance in Brassica: A research perspective

Brassica genus comprises numerous cultivated brassica species with various economic importance. Salt stress is an overwhelming problem causing serious losses in Brassica species (e.g. B. napus, B. rapa, B. oleracea, B. juncea) growth and grain yield production by inducing ionic and ROS toxicity. Given that a significant variation exists in salt tolerance level in Brassica genus, Brassica species exhibited numerous salt tolerance mechanisms which were either overlooked or given less importance to improve and understand innate salt stress tolerance mechanism in Brassica species. In this review, we tried to highlight the importance and recent findings relating to some overlooked and potential mechanisms such as role of neurotransmitters, and role of cytosolic Ca²⁺ and ROS as signaling elements to enhance salt stress tolerance. Studies revealed that salt tolerant brassica species retained more K⁺ in leaf mesophyll which confers overall salinity tolerance in salt tolerance brassica species. Neurotransmitter such as melatonin, dopamiane and eATP regulates K⁺ and Ca²⁺ permeable ion channels and plays a very crucial role in ionic homeostasis under salinity stress in brassica. At the end, the numerous possible salt stress agronomic strategies were also discussed to mitigate the severity of the salt stress in Brassica species.

Emerging crosstalk between two signaling pathways coordinates K+ and Na+ homeostasis in the halophyte Hordeum brevisubulatum

K+/Na+ homeostasis is the primary core response for plant to tolerate salinity. Halophytes have evolved novel regulatory mechanisms to maintain a suitable K+/Na+ ratio during long-term adaptation. The wild halophyte Hordeum brevisubulatum can adopt efficient strategies to achieve synergistic levels of K+ and Na+ under high salt stress. However, little is known about its molecular mechanism. Our previous study indicated that HbCIPK2 contributed to prevention of Na+ accumulation and K+ reduction. Here, we further identified the HbCIPK2-interacting proteins including upstream Ca2+ sensors, HbCBL1, HbCBL4, and HbCBL10, and downstream phosphorylated targets, the voltage-gated K+ channel HbVGKC1 and SOS1-like transporter HbSOS1L. HbCBL1 combined with HbCIPK2 could activate HbVGKC1 to absorb K+, while the HbCBL4/10-HbCIPK2 complex modulated HbSOS1L to exclude Na+. This discovery suggested that crosstalk between the sodium response and the potassium uptake signaling pathways indeed exists for HbCIPK2 as the signal hub, and paved the way for understanding the novel mechanism of K+/Na+ homeostasis which has evolved in the halophytic grass.

Progress in the Study and Use of Seawater Vegetables

As global soil salinization increases, halophytes that can grow in saline soils are the primary choice for improving soil quality. Some halophytes can even be irrigated with seawater and used as vegetables. These so-called seawater vegetables include those that can be planted on saline and alkali soils and some edible halophytes and ordinary vegetables that are salt-tolerant. The cultivation of seawater vegetables on saline soil has become a matter of increasing interest. In this review, we focus on the salt-tolerance mechanisms and potential applications of some seawater vegetables. We also summarize their value to health, medicine, industry, and the economy as a whole. Further improvement and development to support the use of seawater vegetables will require in-depth research at the cellular and molecular levels.

Mechanisms of Plant Responses and Adaptation to Soil Salinity

Soil salinity is a major environmental stress that restricts the growth and yield of crops. Understanding the physiological, metabolic, and biochemical responses of plants to salt stress and mining the salt tolerance-associated genetic resource in nature will be extremely important for us to cultivate salt-tolerant crops. In this review, we provide a comprehensive summary of the mechanisms of salt stress responses in plants, including salt stress-triggered physiological responses, oxidative stress, salt stress sensing and signaling pathways, organellar stress, ion homeostasis, hormonal and gene expression regulation, metabolic changes, as well as salt tolerance mechanisms in halophytes. Important questions regarding salt tolerance that need to be addressed in the future are discussed.

Mechanisms of Sugar Beet Response to Biotic and Abiotic Stresses

Sugar beet is used not only in the sugar production, but also in a wide range of industries including the production of bioethanol as a source of renewable energy, extraction of pectin and production of molasses. The red beetroot has attracted much attention as health-promoting and disease-preventing functional food. The negative effects of environmental stresses, including abiotic and biotic ones, significantly decrease the cash crop sugar beet productivity. In this paper, we outline the mechanisms of sugar beet response to biotic and abiotic stresses at the levels of physiological change, the genes' functions, transcription and translation. Regarding the physiological changes, most research has been carried out on salt and drought stress. The functions of genes from sugar beet in response to salt, cold and heavy metal stresses were mainly investigated by transgenic technologies. At the transcriptional level, the transcriptome analysis of sugar beet in response to salt, cold and biotic stresses were conducted by RNA-Seq or SSH methods. At the translational level, more than 800 differentially expressed proteins in response to salt, K⁺/Na⁺ ratio, iron deficiency and resupply and heavy metal (zinc) stress were identified by quantitative proteomics techniques. Understanding how sugar beet respond and tolerate biotic and abiotic stresses is important for boosting sugar beet productivity under these challenging conditions. In order to minimize the negative impact of these stresses, studying how the sugar beet has evolved stress coping mechanisms will provide new insights and lead to novel strategies for improving the breeding of stress-resistant sugar beet and other crops.

Involvement of Phosphatidylserine and Triacylglycerol in the Response of Sweet Potato Leaves to Salt Stress

Lipid remodeling plays an important role in the adaptation of plants to environmental factors, but the mechanism by which lipid remodeling mediates salt stress response remains unclear. In this study, we compared the root and leaf lipidome profiles of salt-tolerant and salt-sensitive sweet potato cultivars (Xu 22 and Xu 32, respectively) under salinity stress. After salt treatment, the leaf lipidome showed more significant remodeling than the root lipidome in both cultivars. Compared with Xu 32 leaves, Xu 22 leaves generally maintained higher abundance of phospholipids, glycolipids, sphingolipids, sterol derivatives, and diacylglycerol under salinity conditions. Interestingly, salinity stress significantly increased phosphatidylserine (PS) abundance in Xu 22 leaves by predominantly triggering the increase of PS (20:5/22:6). Furthermore, Xu 32 leaves accumulated higher triacylglycerol (TG) level than Xu 22 leaves under salinity conditions. The exogenous application of PS delayed salt-induced leaf senescence in Xu 32 by reducing salt-induced K+ efflux and upregulating plasma membrane H+-ATPase activity. However, the inhibition of TG mobilization in salinized-Xu 22 leaves disturbed energy and K+/Na+ homeostasis, as well as plasma membrane H+-ATPase activity. These results demonstrate alterations in the leaf lipidome of sweet potato under salinity condition, underscoring the importance of PS and TG in mediating salt-defensive responses in sweet potato leaves.

The elemental composition of halophytes correlates with key morphological adaptations and taxonomic groups

Halophytes are crucial in the light of increasing soil salinization, yet our understanding of their chemical composition and its relationship to key morphological traits such as succulence or salt excretion is limited. This study targets this issue by exploring the relationship between the elemental composition of 108 plant species from saline environments in Iran and their eco-morphological traits and taxonomy. Leaves and/or photosynthetic shoots of individual species and soils were sampled and analyzed for 20 elements in plant samples and 5 major elements plus % gypsum content, pH, and EC in soil samples. Eu-halophytes and leaf- and stem-succulent and salt-recreting plants showed high concentrations of Na, S, and Mg and low concentrations of Ca and K. In contrast, pseudo-halophytes, facultative-halophytes and eury-hygro-halophytes, which often lack succulent shoots, showed low Na, S, and Mg and high Ca and K concentrations in their leaves. Clear patterns were identified among taxonomic families, with Chenopodiaceae and Plumbaginaceae having high Na and Mg and low Ca and K concentrations, Caryophyllaceae having high K, Poaceae having low Na, and Asteraceae, Boraginaceae, and Brassicaceae showing high foliar Ca concentrations. We conclude that the elemental composition of halophytes and pseudo-halophytes is related to salt-tolerance categories, eco-morphological types and respective taxonomic groups.

Shoot chloride translocation as a determinant for NaCl tolerance in Vicia faba L

Faba bean (Vicia faba L.) is sensitive to salinity. While toxic effects of sodium (Na⁺) are well studied, toxicity aspects of chloride (Cl^-) and the underlying tolerance mechanisms to Cl^- are not well understood. For this reason, shoot Cl^- translocation and its effect as potential determinant for tolerance was tested. Diverse V. faba varieties were grown hydroponically and stressed with 100 mM NaCl until necrotic leaf spots appeared. At this point, biomass formation, oxidative damage of membranes as well as Na⁺, Cl^- and potassium concentrations were measured. The V. faba varieties contrasted in the length of the period they could withstand the NaCl stress treatment. More tolerant varieties survived longer without evolving necrosis and were less affected by inhibitory effects on photosynthesis. The concentration of Cl^- at the time point of developing leaf necrosis was in the same range irrespective of the variety, while that of Na⁺ varied. This indicates that Cl^- concentrations, and not Na⁺ concentrations are critical for the formation of salt necrosis in faba bean. Tolerant varieties profited from lower Cl^- translocation to leaves. Therefore, photosynthesis was less affected in those varieties with lower Cl^-. This mechanism is a new trait of interest for salt tolerance in V. faba.

An early ABA-induced stomatal closure, Na+ sequestration in leaf vein and K+ retention in mesophyll confer salt tissue tolerance in Cucurbita species

Tissue tolerance to salinity stress is a complex physiological trait composed of multiple 'sub-traits' such as Na+ compartmentalization, K+ retention, and osmotic tolerance. Previous studies have shown that some Cucurbita species employ tissue tolerance to combat salinity and we aimed to identify the physiological and molecular mechanisms involved. Five C. maxima (salt-tolerant) and five C. moschata (salt-sensitive) genotypes were comprehensively assessed for their salt tolerance mechanisms and the results showed that tissue-specific transport characteristics enabled the more tolerant lines to deal with the salt load. This mechanism was associated with the ability of the tolerant species to accumulate more Na+ in the leaf vein and to retain more K+ in the leaf mesophyll. In addition, C. maxima more efficiently retained K+ in the roots when exposed to transient NaCl stress and it was also able to store more Na+ in the xylem parenchyma and cortex in the leaf vein. Compared with C. moschata, C. maxima was also able to rapidly close stomata at early stages of salt stress, thus avoiding water loss; this difference was attributed to higher accumulation of ABA in the leaf. Transcriptome and qRT-PCR analyses revealed critical roles of high-affinity potassium (HKT1) and intracellular Na+/H+ (NHX4/6) transporters as components of the mechanism enabling Na+ exclusion from the leaf mesophyll and Na+ sequestration in the leaf vein. Also essential was a higher expression of NCED3s (encoding 9-cis-epoxycarotenoid dioxygenase, a key rate-limiting enzyme in ABA biosynthesis), which resulted in greater ABA accumulation in the mesophyll and earlier stomata closure in C. maxima.

Biochar and lignite affect H+-ATPase and H+-PPase activities in root tonoplast and nutrient contents of mung bean under salt stress

This research was conducted to evaluate effects of biochar (50 and 100 g kg^-1 soil) and lignite (50 and 100 g kg^-1 soil) treatments on H⁺-ATPase and H⁺-PPase activity of root tonoplast, nutrient content, and performance of mung bean under salt stress. High saline conditions increased H⁺-ATPase and H⁺-PPase activities in root tonoplast, sodium (Na) content, reactive oxygen species (H₂O₂ and O₂^-) generation, relative electrolyte leakage (REL) and 2,2-Diphenyl-1-picrylhydrazyl (DPPH) activity in root and leaf, but decreased relative water content (RWC), chlorophyll content index, leaf area, potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn) and iron (Fe) content of plant tissues, root and shoot dry weight of mung bean. Lignite and biochar treatments decreased the H⁺-ATPase and H⁺-PPase activities of root tonoplast under salt stress. Moreover, these treatments increased the cation exchange capacity of soil and nutrient values in plant tissues. Biochar and lignite diminished the generation of reactive oxygen species and DPPH activity in root and leaf cells, and these superior effects improved chlorophyll content index, leaf area and growth of mung bean under both conditions. In general, the results of this study demonstrated that biochar and lignite decreased the entry of Na ion into the cells, enriched plant cells with nutrients, and consequently improved mung bean performance under salt toxicity.

Genotypic differences in physiological and biochemical responses to salinity stress in melon (Cucumis melo L.) plants: Prospects for selection of salt tolerant landraces

Melon (Cucumis melo L.) is one of the most important horticultural crops in Iran often cultivated in arid and semiarid regions of the country with salinity problems. The objective of this work was to better understand the mechanisms of physiological and biochemical responses to salinity stress of five Iranian melon landraces "Samsuri", "Kashan", "Khatouni", "Suski-e-Sabz", and "Ghobadlu" from different geographical origins, and "Galia" F1 cultivar. Plants were grown under greenhouse conditions and irrigated with half-strength Hoagland solution containing 0, 30, 60, or 90 mM NaCl for 60 days. Increase in the external salt concentration was accompanied by an obvious depression in leaf relative water content, membrane stability index, chlorophyll a and b and carotenoid contents, stomata and trichome density, leaf area, specific leaf area, biomass, leaf and stem K⁺ concentrations as well as leaf and stem K⁺/Na⁺ ratios in all landraces studied. In contrast, hydrogen peroxide, lipid peroxidation, proline and soluble carbohydrate contents, activity of antioxidant enzymes as well as leaf and stem Na⁺ and Cl^- concentrations, all increased significantly with increasing stress over all plants. Moreover, carbon isotope discrimination (Δ¹³C), determined on leaf organic matter, was found to be associated with evaluated traits. For example, a highly positive correlation between Δ¹³C and both biomass production and salt tolerance index was notable when all saline treatments were averaged (r = 0.998 and 0.998, respectively). Also, scatter plot and clustering analysis showed that "Suski-e-Sabz" and "Ghobadlu" were placed close to "Galia" F1, a salt tolerant cultivar, indicating that their similar behavior under salinity. Overall, the present results indicated a significant genetic variability for most of the traits studied, suggesting that "Suski-e-Sabz" and "Ghobadlu" could be introduced as the superior landraces and the most promising tolerant parents in the future melon breeding programs due to their suitable performance, in terms of responses to salt stress as compared with other landraces. Also, Δ¹³C can be used as a powerful criterion in melon breeding programs aimed at selection of salt tolerant landraces.

Impact of the ion transportome of chloroplasts on the optimization of photosynthesis

Ions play fundamental roles in all living cells, and their gradients are often essential to fuel transport, regulate enzyme activities, and transduce energy within cells. Regulation of their homeostasis is essential for cell metabolism. Recent results indicate that modulation of ion fluxes might also represent a useful strategy to regulate one of the most important physiological processes taking place in chloroplasts, photosynthesis. Photosynthesis is highly regulated, due to its unique role as a cellular engine for growth in the light. Controlling the balance between ATP and NADPH synthesis is a critical task, and availability of these molecules can limit the overall photosynthetic yield. Photosynthetic organisms optimize photosynthesis in low light, where excitation energy limits CO2 fixation, and minimize photo-oxidative damage in high light by dissipating excess photons. Despite extensive studies of these phenomena, the mechanism governing light utilization in plants is still poorly understood. In this review, we provide an update of the recently identified chloroplast-located ion channels and transporters whose function impacts photosynthetic efficiency in plants.