Salt-treated Seedlings Research Articles

Thymol Deploys Multiple Antioxidative Systems to Suppress ROS Accumulation in Chinese Cabbage Seedlings under Saline Stress

Developing biostimulants is a promising approach for sustainable agriculture under a saline environment. Thymol is a plant-derived compound with a potential antioxidative capacity. However, little is known about whether and how the antioxidative property of thymol plays a role in inducing plant tolerance against abiotic stresses. Here, we find that thymol induces saline tolerance in Chinese cabbage seedlings via enhancing the antioxidative capacity. Treatment with NaCl (100 mM) decreased the seedling fresh weight by 59.9% as compared to a control. Thymol at 20 μM showed the greatest effect on promoting seedling growth under saline stress, with the seedling fresh weight being increased by 71.0% as compared to NaCl treatment. Thymol remarkably decreased the overaccumulation of ROS (hydrogen peroxide and a superoxide radical); cell membrane damage (evaluated by lipid oxidation, membrane integrity, and relative conductivity); and cell death in seedlings under saline stress. Thymol induced three antioxidative systems to lower the ROS level in salt-treated seedlings. First, thymol remarkably activated a set of antioxidative enzymes, such as SOD (superoxide dismutase), APX (ascorbate peroxidase), CAT (catalase), and POD (peroxidase). Second, thymol balanced the cellular redox status by increasing the ratio of AsA/DHA (ascorbic acid/dehydroascorbic acid) and GSH/GSSG (glutathione/oxidized glutathione). Third, thymol significantly enhanced the level-two kinds of antioxidants (total phenol and flavonoid). All of these physiological responses were observed in both the shoots and the roots. In sum, thymol deploys multiple antioxidative systems to help Chinese cabbage seedlings against saline stress. Such findings suggest that thymol has great potential to be developed as a novel biostimulant enhancing crop tolerance against saline stress.

Eugenol improves salt tolerance via enhancing antioxidant capacity and regulating ionic balance in tobacco seedlings.

Salt stress inhibits plant growth by disturbing plant intrinsic physiology. The application of exogenous plant growth regulators to improve the plant tolerance against salt stress has become one of the promising approaches to promote plant growth in saline environment. Eugenol (4-allyl-2- methoxyphenol) is the main ingredient in clove oil and it is known for its strong antioxidant and anti-microbial activities. Eugenol also has the ability of inhibiting several plant pathogens, implying the potential use of eugenol as an environmental friendly agrichemical. However, little is known about the possible role of eugenol in the regulation of plant tolerance against abiotic stress. Therefore, here we investigated the effectiveness of phytochemical eugenol in promoting salt tolerance in tobacco seedlings through physiological, histochemical, and biochemical method. The seedling roots were exposed to NaCl solution in the presence or absence of eugenol. Salt stress inhibited seedling growth, but eugenol supplementation effectively attenuated its effects in a dose-dependent manner, with an optimal effect at 20 µM. ROS (reactive oxygen species) accumulation was found in seedlings upon salt stress which was further resulted in the amelioration of lipid peroxidation, loss of membrane integrity, and cell death in salt-treated seedlings. Addition of eugenol highly suppressed ROS accumulation and reduced lipid peroxidation generation. Both enzymatic and non-enzymatic antioxidative systems were activated by eugenol treatment. AsA/DHA and GSH/GSSG were also enhanced upon eugenol treatment, which helped maintain redox homeostasis upon salinity. Eugenol treatment resulted in an increase in the content of osmoprotectants (e.g. proline, soluble sugar and starch) in salt-treated seedlings. Na+ levels decreased significantly in seedlings upon eugenol exposure. This may result from the upregulation of the expression of two ionic transporter genes, SOS1 (salt-hypersensitive 1) and NHX1 (Na+/H+ anti-transporter 1). Hierarchical cluster combined correlation analysis uncovered that eugenol induced salt tolerance was mediated by redox homeostasis and maintaining ionic balance in tobacco seedlings. This work reveals that eugenol plays a crucial role in regulating plant resistant physiology. This may extend its biological function as a novel biostimulant and opens up new possibilities for improving crop productivity in the saline agricultural environment.

Histone Deacetylase Complex 1 and histone 1 epigenetically moderate stress responsiveness of Arabidopsis thaliana seedlings.

Early responses of plants to environmental stress factors prevent damage but can delay growth and development in fluctuating conditions. Optimising these trade-offs requires tunability of plant responsiveness to environmental signals. We have previously reported that Histone Deacetylase Complex 1 (HDC1), which interacts with multiple proteins in histone deacetylation complexes, regulates the stress responsiveness of Arabidopsis seedlings, but the underlying mechanism remained elusive. Here, we show that HDC1 attenuates transcriptome re-programming in salt-treated seedlings, and we identify two genes (LEA and MAF5) that inhibit seedling establishment under salt stress downstream of HDC1. HDC1 attenuates their transcriptional induction by salt via a dual mechanism involving H3K9/14 deacetylation and H3K27 trimethylation. The latter, but not the former, was also abolished in a triple knockout mutant of the linker histone H1, whichpartially mimics the hypersensitivity of the hdc1-1 mutant to salt stress. Although stress-induced H3K27me3 accumulation required both H1 and HDC1, it was not fully recovered by complementing hdc1-1 with a truncated, H1-binding competent HDC1 suggesting other players or independent inputs. The combined findings reveal a dual brake function of HDC1 via regulating both active and repressive epigenetic marks on stress-inducible genes. This natural 'anti-panic' device offers a molecular leaver to tune stress responsiveness in plants.

MeJA-mediated enhancement of salt-tolerance of Populus wutunensis by 5-aminolevulinic acid

Background5-Aminolevulinic acid (ALA) is a natural and environmentally benign multifunctional plant growth regulator involved in the regulation of plant tolerance to various environmental stresses. This research aimed to explore the molecular mechanisms of salt tolerance in Populus wutunensis induced by exogenous ALA using physiological and transcriptomic analyses.ResultsPhysiological results showed that 50 mg·L− 1 ALA-treatment significantly reduced the malondialdehyde (MDA) content and the relative electrical conductivity (REC) and enhanced antioxidant activities of enzymes such as SOD, POD and CAT in salt-stressed P. wutunensis seedlings. Transcriptome analysis identified ALA-induced differentially expressed genes (DEGs) associating with increased salt-tolerance in P. wutunensis. GO and KEGG enrichment analyses showed that ALA activated the jasmonic acid signaling and significantly enhanced the protein processing in endoplasmic reticulum and the flavonoid biosynthesis pathways. Results of the hormone-quantification by LC-MS/MS-based assays showed that ALA could increase the accumulation of methyl jasmonate (MeJA) in salt-stressed P. wutunensis. Induced contents of soluble proteins and flavonoids by exogenous ALA in salt-treated seedlings were also correlated with the MeJA content.Conclusion5-aminolevulinic acid improved the protein-folding efficiency in the endoplasmic reticulum and the flavonoid-accumulation through the MeJA-activated jasmonic acid signaling, thereby increased salt-tolerance in P. wutunensis.

Exogenous SA Applications Alleviate Salinity Stress via Physiological and Biochemical changes in St John’s Wort Plants

The plant St. John's wort contains high levels of melatonin, an important biochemical that has both beneficial and adverse effects on stress. Therefore, a method for increasing melatonin levels in plants without adversely affecting their growth is economically important. In this study, we investigated the regulation of melatonin levels in St. John's wort by exposing samples to salinity stress (150 mM) and salicylic acid (0.25 mM) to augment stress tolerance. The results indicated that salinity stress significantly reduced the plant chlorophyll content and damaged the photosystem, plant growth and development. Additionally, these were reconfirmed with biochemical indicators; the levels of abscisic acid (ABA) and proline were increased and the activities of antioxidants were reduced. However, a significant increase was found in melatonin content under salinity stress through upregulation in the relative expression of tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acetyltransferase (SNAT), and N-acetylserotonin methyltransferase (ASMT). The salicylic acid (SA) treatment considerably improved their photosynthetic activity, the maximum photochemical quantum yield (133%), the potential activity of PSⅡ (294%), and the performance index of electron flux to the final PS I electron acceptors (2.4%). On the other hand, SA application reduced ABA levels (32%); enhanced the activity of antioxidant enzymes, such as superoxide dismutase (SOD) (15.4%) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) (120%); and increased polyphenol (6.4%) and flavonoid (75.4%) levels in salinity-stressed St. John's wort plants. Similarly, SA application under NaCl stress significantly modulated the melatonin content in terms of ion balance; the level of melatonin was reduced after SA application on salt-treated seedlings but noticeably higher than on only SA-treated and non-treated seedlings. Moreover, the proline content was reduced considerably and growth parameters, such as plant biomass, shoot length, and chlorophyll content, were enhanced following treatment of salinity-stressed St. John's wort plants with salicylic acid. These findings demonstrate the beneficial impact of salt stress in terms of a cost-effective approach to extract melatonin in larger quantities from St. John's wort. They also suggest the efficiency of salicylic acid in alleviating stress tolerance and promoting growth of St. John's wort plants.

Physiological and Metabolic Responses of Gac Leaf (Momordica cochinchinensis (Lour.) Spreng.) to Salinity Stress.

Gac is a carotenoid-rich, healthful tropical fruit; however, its productivity is limited by soil salinity, a growing environmental stress. This study aimed to evaluate the effects of salinity stress on key physiological traits and metabolites in 30-day-old gac seedling leaves, treated with 0, 25-, 50-, 100-, and 150-mM sodium chloride (NaCl) for four weeks to identify potential alarm, acclimatory, and exhaustion responses. Electrolyte leakage increased with increasing NaCl concentrations (p < 0.05) indicating loss of membrane permeability and conditions that lead to reactive oxygen species production. At 25 and 50 mM NaCl, superoxide dismutase (SOD) activity, starch content, and total soluble sugar increased. Chlorophyll a, and total chlorophyll increased at 25 mM NaCl but decreased at higher NaCl concentrations indicating salinity-induced thylakoid membrane degradation and chlorophyllase activity. Catalase (CAT) activity decreased (p < 0.05) at all NaCl treatments, while ascorbate peroxidase (APX) and guaiacol peroxidase (GPX) activities were highest at 150 mM NaCl. GC-MS-metabolite profiling showed that 150 mM NaCl induced the largest changes in metabolites and was thus distinct. Thirteen pathways and 7.73% of metabolites differed between the control and all the salt-treated seedlings. Salinity decreased TCA cycle intermediates, and there were less sugars for growth but more for osmoprotection, with the latter augmented by increased amino acids. Although 150 mM NaCl level decreased SOD activity, the APX and GPX enzymes were still active, and some carbohydrates and metabolites also accumulated to promote salinity resistance via multiple mechanisms.

Inhibition of root growth by alkaline salts due to disturbed ion transport and accumulation in Leymus chinensis

Soil alkalization severely affects plant growth and agricultural production. Compared with neutral salts, alkaline salts cause a combined stress of ion toxicity and high pH in plants. The alkali-resistant halophyte Leymus chinensis is a dominant grass growing on soda (NaHCO3 and Na2CO3, pH > 9) saline-alkali soil in northeast China. However, the molecular mechanism of alkaline salt tolerance in L. chinensis roots remains unclear. In this study, the seedling phenotype, ion accumulation, root ion dynamics, and gene expression profiles in L. chinensis under neutral salt (100 mM NaCl), alkaline salt (100 mM NaHCO3 and 50 mM Na2CO3), and high pH (pH = 10) stresses were investigated and compared. Phenotypic analysis showed that alkaline salt more severely inhibited the growth of seedling roots compared to neutral salt and high pH. Ion content detection revealed that alkaline salt-treated seedlings had higher Na+ accumulation and lower nutrient content compared to neutral salt and high pH-treated seedlings. Furthermore, the non-invasive micro-test showed that alkaline salt-induced high pH conditions perturb ion flux in seedling roots, which may be associated with impaired nutrient ion uptake and aggravated Na+ accumulation. Moreover, using full-length transcriptome combined with comparative RNA-seq, the identified alkaline salt-specific response genes were most significantly enriched to the transporter activity term, which contained a large number of genes encoding transporters of nutrient ions. Our results provide new insights into the unique response mechanism of L. chinensis roots to alkaline salt.

Seed-priming with H2O2 alleviates subsequent salt stress by preventing ROS production and amplifying antioxidant defense in cauliflower seeds and seedlings

In the present study, we examined the impact of three seed priming agents; H2O2, GA3 and NaCl on the oxidative stress status in primed seed germination dynamics and growth establishment of cauliflower seedlings subsequently grown under salt stress. Results showed beneficial effect of all priming agents in improving plant responses to salinity. However, specific differences, depending on development stage, organ and priming type were recorded. At the germination stage, GA3 was the most advantageous agent to accelerate seedling emergence. At the seedling stage, seedlings obtained from redried H2O2-primed seeds showed the highest level of seed superoxide anion (5-fold) and H2O2 (4-fold), resulting in higher MDA content (2.4-fold). At the same time, priming seeds with H2O2 triggered the overall seedling antioxidant defense, including enzymatic (SOD, CAT, GPX and APX) and non-enzymatic systems (AsA, GSH and proline). Salinity restricted the growth of both leaves (43%) and roots (60%) of cauliflower seedlings issued from unprimed seeds. Under primed conditions, the relative contribution of GA3 and NaCl was more associated with growth establishment and osmotic adjustment. However, H2O2 role was greatly correlated with the antioxidant defense. Indeed, salt-treated seedlings issued from H2O2-primed seeds showed the lowest levels of superoxide anion, H2O2 and MDA, resulting in the highest activities of the entire antioxidant systems. These findings support the hypothesis that cauliflower plants, when exposed to salt stress benefit from H2O2 seed priming, as a pre-germination stimulus, to prevent itself from subsequent oxidative injuries, which supports the hypothesis of “stress memory” of subsequent salt stress.

Myo‐inositol transport and metabolism participate in salt tolerance of halophyte ice plant seedlings

Myo-inositol and its metabolic derivatives such as pinitol, galactinol, and raffinose affect growth and development and are also involved in stress adaptation. Previous studies have identified myo-inositol transporters (INTs) as transporters of Na+ from root to shoot in the halophyte ice plant (Mesembryanthemum crystallinum). We found that the supply of myo-inositol could alleviate the dehydration effects of salt-stressed ice plant seedlings by decreasing the Na/K ratio in roots and increasing the Na/K ratio in shoots. Analyses of the uptake of exogenous myo-inositol revealed that ice plant seedlings contained intrinsic high-affinity transporters and inducible low-affinity uptake systems. The presence of Na+ facilitated both high- and low-affinity myo-inositol uptake. Six INT genes were identified from the ice plant transcriptome and named McINT1a, 1b, 2, 4a, 4b, and 4c, according to the classification of the Arabidopsis INT family. In seedlings treated with myo-inositol, salt, or myo-inositol plus salt, the expression patterns of all McINT members differed in shoot and root, which indicates organ-specific regulation of McINTs by salt and myo-inositol. The expression of McINT2, 4a, 4b, and 4c was induced by salt stress in shoot and root, but that of McINT1a and 1b was salt-induced only in shoot. The expression of pinitol biosynthesis gene IMT1 was induced by salt and myo-inositol, and their combination had a synergistic effect on the accumulation of pinitol. Supply of myo-inositol to salt-treated seedlings alleviated the detrimental effects by maintaining a low root Na/K ratio and providing precursors for the synthesis of compatible solute to maintain the osmotic balance.

Physiological, biochemical, and molecular responses of wheat seedlings to salinity and plant-derived smoke

There is great interest in developing strategies to reduce the detrimental effects of salinity on plant growth and crop yield. Plant-derived smoke containing many promotive and inhibitory compounds is known to influence seed germination and plant growth in a concentration-dependent manner. It has been suggested that smoke can also alleviate abiotic stress-induced growth inhibition in several plants. However, there is still a lack of comprehensive knowledge regarding smoke-mediated biochemical and molecular changes in plants grown under stress conditions. Here we show that smoke regulates the expression of some genes encoding transcription factors and antioxidant enzymes in wheat seedlings subjected to salt stress (150 mM NaCl). We found that smoke-water (0.1%) increased the expression levels of TaDREB1, TaWRKY2, TaWRKY19, CAT, and Cu/Zn-SOD in salt-treated seedlings. Smoke-water also enhanced the transcription of TaWRKY19 and Cu/Zn-SOD genes under normal growth conditions. In addition, smoke was found to modulate physiological responses of wheat seedlings to salinity. The results demonstrate that smoke-water increases total phenolic content and free radical scavenging activity under salt stress but it leads to a significant decrease in proline accumulation. In conclusion, the current study reveals that smoke, although not having a remarkable effect on growth at the concentration tested, can affect physiological, biochemical, and molecular processes in wheat seedlings exposed to short-term salt stress. Our data also indicate the need for long-term field experiments for a better understanding of the effect of smoke on plant growth in the presence of salinity.

A comparative study of the growth and physiological parameters of two oat (Avena sativa L.) lines under salinity stress

ABSTRACT Salinity degrades the environment, reducing the productive capacity of affected land. This presents a significant challenge in agriculture; however, different crops are known to vary in their tolerance to salt stress. This study investigated the tolerance of two oat (Avena sativa L.) lines, Baiyan2 and Mengnongda1, to salinity stress. Oat lines were subjected to salt treatments (100 mM NaCl) for a two-week period and growth and physiological parameters of the two lines were compared. Salinity did not appear to affect the leaf and root dry weight of Baiyan2. In contrast, the leaf and root dry weight of Mengnongda1 showed a reduction of 42% and 35%, respectively. Additionally, leaf osmotic potential was higher in salt-treated Baiyan2 than in treated Mengnongda1 in all plant organs, suggesting that Baiyan2 is able to maintain better water status in saline conditions. Xylem proline concentration, sheath proline concentration, and proline contribution to sheath osmotic potential were also higher in salt-treated Baiyan2 than in treated Mengnongda1. Results also showed that salt-treated Baiyan2 retained similar levels of root potassium (K+) when compared to control plants, indicating that Baiyan2 has the capacity to maintain ionic homeostasis in root tissues in saline conditions. Contrastingly, salt-treated Mengnongdal seedlings showed a reduction of 34.3% in root K+. The sodium (Na+) and K+ contributions to leaf osmotic potential were also higher in Baiyan2 than in Mengnongda1 under saline conditions, indicating that leaf Na+ and K+ may have a beneficial role in leaf growth of Baiyan2. Our findings suggest that Baiyan2 may have a physiological mechanism that confers a higher salinity tolerance. Accordingly, the Baiyan2 oat line may constitute an important source of germplasm for developing salinity tolerance in oats.

Transcriptome profiling of mild-salt responses in Lycium ruthenicum early seedlings to reveal salinity-adaptive strategies

The traditional Chinese desert shrub Lycium ruthenicum is widely distributed in arid environments such as north-west China, exhibiting ideal salt tolerance to cope with soil desertification, salinity, and alkalinity. However, the salt-tolerance mechanism of L. ruthenicum, especially of its young seedlings at early vegetative stages, remains largely unknown. In the present study, we collected whole-seedling samples from Lycium ruthenicum at a-pair-leaf stage with and without a mild salt (75 mM sodium chloride) treatment, and then performed transcriptome profiling to compare their gene expression patterns. The de novo assembly achieved 94,651 unigenes with 55,156 annotated. Among them, 199 differentially expressed genes (DEGs) were identified between salt-treated seedlings and control, with 41 up-regulated and 158 down-regulated. These DEGs were highly enriched into gene ontology (GO) classifications ‘metabolic process’ and ‘catalytic activity’, into Clusters of Orthologous Groups (COG) function classifications ‘translation, ribosomal structure and biogenesis’ and ‘energy production and conversion’, and into Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways ‘ribosome’ and ‘oxidative phosphorylation’. Specifically, genes involved in energy metabolism (oxidative phosphorylation) and related energy-consuming metabolisms, including ribosome-associated biogenesis and biosynthesis of organic nitrogen-derived compatible solutes (i.e., arginine and proline), were generally down-regulated. Specific genes involved in abscisic acid (ABA) biosynthesis and signaling pathway were simultaneously up-regulated. Changes in the transcript levels of salt-responsive DEGs selected from the transcriptomic profiling were further validated by real-time quantitative polymerase chain reaction (RT-qPCR) analysis. Based on these results, salinity-adaptive strategies for the L. ruthenicum early seedlings are discussed.

Exogenous vanillic acid enhances salt tolerance of tomato: Insight into plant antioxidant defense and glyoxalase systems

We investigated vanillic acid-induced salt tolerance in tomato by exploring the plant defense systems. Ten-d-old tomato (Solanum lycopersicum L. cv. Pusa Ruby) seedlings were treated with salt (NaCl; 150 mM) and vanillic acid (VA; 40 and 50 μM) separately and in combination with salt. Salinity restricted seedlings growth, biomass accumulation, chlorophyll and carotenoid contents. Salt-induced osmotic stress was indicated by lower leaf relative water content (RWC) and elevated proline (Pro) content, where higher Na+/K+ ratio indicated the ionic toxicity. Tomato seedlings went through oxidative damage due to acute reactive oxygen species (ROS) production and lipoxygenase (LOX) activity and confirmed by higher lipid peroxidation and membrane damage under salinity. Conversely, exogenous VA reduced osmotic and ionic toxicity in stressed-seedlings by enhancing the RWC and Pro level, and lowering Na+/K+ ratio, respectively. Exogenous VA up-regulated the components of antioxidant defense system in salt-treated seedlings resulted in the reduction of ROS production, LOX activity and membrane damage in stressed-seedlings. Additionally, VA application caused the reduction of toxic methylglyoxal accumulation under salt stress through the enhancement of glyoxalase system. Thus, VA-induced alleviation of osmotic, ionic and oxidative stresses leading to improve plant growth and chlorophyll synthesis in stressed-seedlings. So, VA significantly improves salinity tolerance and plant growth performance by involving the actions of plant antioxidant defense and glyoxalase systems.

Physiological and Proteomic Analyses Reveal Adaptive Mechanisms of Ryegrass (Annual vs. Perennial) Seedlings to Salt Stress

Ryegrass has a relatively high salt tolerance and is considered to be a promising species for both foraging and turf purposes in salt-affected soils in China. While annual ryegrass and perennial ryegrass are two different species, they have similar genomes. However, little is known about their physiological and molecular response mechanisms to salinity stress. Here, biomass, chlorophyll fluorescence, and inorganic ion and organic solute content were measured. 2-DE-based proteomic technology was then used to identify the differentially expressed proteins in the salt-treated seedlings. The results showed that salt stress reduced growth and photosynthesis in the seedlings of both species, but much more so in annual ryegrass. With increasing salinity, the Na+ concentration increased while the K+ concentration decreased in both species, and the sugars and proline increased as the primary organic solutes used to cope with osmotic stress. Additionally, proteomic analysis revealed 33 and 37 differentially expressed proteins in annual and perennial ryegrass, respectively. Most of the identified proteins were involved in carbohydrate and energy metabolism, photosynthesis, genetic information processes, amino acid metabolism, stress defense, and protein synthesis and folding. The results suggest that the two-ryegrass species had different physiological and proteomic responses. These findings can provide new insights into physiological mechanisms by which ryegrass species respond to salt stress.

Transcriptomic reprogramming in soybean seedlings under salt stress

To obtain a comprehensive understanding of transcriptomic reprogramming under salt stress, we performed whole-transcriptome sequencing on the leaf and root of soybean seedlings subjected to salt treatment in a time-course experiment (0, 1, 2, 4, 24, and 48hr). This time series dataset enabled us to identify important hubs and connections of gene expressions. We highlighted the analysis on phytohormone signaling pathways and their possible crosstalks. Differential expressions were also found among those genes involved in carbon and nitrogen metabolism. In general, the salt-treated seedlings slowed down their photosynthetic functions and ramped up sugar catabolism to provide extra energy for survival. Primary nitrogen assimilation was shut down whereas nitrogen resources were redistributed. Overall, the results from the transcriptomic analyses indicate that the plant uses a multipronged approach to overcome salt stress, with both fast-acting, immediate physiological responses, and longer term reactions that may involve metabolic adjustment.

A differential tolerance to mild salt stress conditions among six Italian rice genotypes does not rely on Na+ exclusion from shoots

Rice is very sensitive to salt stress at the seedling level, with consequent poor crop establishment. A natural variability in susceptibility to moderate saline environments was found in a group of six Italian temperate japonica rice cultivars, and the physiological determinants for salt tolerance were investigated. Cation (Na+, K+ and Mg++) levels were determined in shoots from individual rice plantlets grown in the absence or in the presence of inhibitory, yet sublethal salt levels, and at increasing time after salt treatments. Significant variations were found among genotypes, but these were unrelated to the relative tolerance, which seems to result from neither mechanism(s) for reduced Na+ translocation to the aerial part, nor its increased retrieval from the xylem mediating Na+ exclusion from leaves. Accordingly, thiobarbituric acid reactive substance levels raised in leaf tissues of salt-treated seedlings, and osmo-induced proline accumulation was found in all genotypes. Data suggest that the difference in salt tolerance most likely depends on mechanisms for osmotic adjustment and/or antioxidative defence.

Salinity Has no Effect on Polysomatic Pattern in Seedlings of Trifolium pratense and T. repens

AbstractEndopolyploidy is a condition of a cell containing reduplicated genetic material in its nucleus. Cells with the nuclei of different ploidy levels are often present within a single polysomatic organism. Endoreduplication is thus a modified cell cycle that omits cytokinesis and leads to chromatin replication in the endopolyploid cells. This study aimed to research the effect of salinity on endopolyploidy ofTrifolium pratenseandT. repens. Both species are important pasture legumes and belong to the genusFabaceaewith the well documented endopolyploidy occurence. Endopolyploidy levels in the seedlings treated with 0, 30, 60, 90 and 120 mM NaCl were investigated by flow cytometry. The seedling organs were evaluated during three ontogeny stages. The cytometric data plotted on a histogram showed the presence of 2C-16C nuclei inT. pratenseand 2C-8C inT. repens. The hypothesis that salinity induces additional endocycles was not confirmed. Our results show that the distribution of nuclei among ploidy levels does not differ markedly between the treatment groups and the control ones. Additionally, only minor changes were observed among the endoreduplication indexes (EI) of plant organs after exposure to various salt concentrations. Endopolyploidy patterns within the salt-treated seedlings during ontogeny are similar to the controls. We suggest that endopolyploidy inTrifoliumspecies is a conserved genetic trait, rather than an adaptation to salinity stress. The analyses of the roots ofT. pratenseat stage III show that with the increased concentrations of NaCl the length of roots decreased, but no evident changes in endopolyploidy occured.

A bioassay-guided fractionation system to identify endogenous small molecules that activate plasma membrane H+-ATPase activity in Arabidopsis.

Plasma membrane (PM) H+-ATPase is essential for plant growth and development. Various environmental stimuli regulate its activity, a process that involves many protein cofactors. However, whether endogenous small molecules play a role in this regulation remains unknown. Here, we describe a bio-guided isolation method to identify endogenous small molecules that regulate PM H+-ATPase activity. We obtained crude extracts from Arabidopsis seedlings with or without salt treatment and then purified them into fractions based on polarity and molecular mass by repeated column chromatography. By evaluating the effect of each fraction on PM H+-ATPase activity, we found that fractions containing the endogenous, free unsaturated fatty acids oleic acid (C18:1), linoleic acid (C18:2), and linolenic acid (C18:3) extracted from salt-treated seedlings stimulate PM H+-ATPase activity. These results were further confirmed by the addition of exogenous C18:1, C18:2, or C18:3 in the activity assay. The ssi2 mutant, with reduced levels of C18:1, C18:2, and C18:3, displayed reduced PM H+-ATPase activity. Furthermore, C18:1, C18:2, and C18:3 directly bound to the C-terminus of the PM H+-ATPase AHA2. Collectively, our results demonstrate that the binding of free unsaturated fatty acids to the C-terminus of PM H+-ATPase is required for its activation under salt stress. The bio-guided isolation model described in this study could enable the identification of new endogenous small molecules that modulate essential protein functions, as well as signal transduction, in plants.

Anatomical and Physiological Responses of Four Quinoa Cultivars to Salinity at Seedling Stage

Objectives: Salinity is one of the most important environmental stress factors that limits both seed germination and seedling develop. Seedling stage is the most susceptible stage of plants to salt stress. The aim of this work is to study the effect of salt stress on anatomical and physiological features of cotyledons and roots of the seedlings of four quinoa cultivars (Witulla, Wariponcho, Pasankalla and CICA). Methods/ Statistical Analysis: Seed germination and seedling growth was carried out under 0 and 200 mM NaCl during 10 days. Root length and diameter, and root proton extrusion were measured. Soluble sugars and proline concentrations were determined in both cotyledons and roots. Anatomical attributes of cotyledons (adaxial and abaxial stomatal area and density, palisade and spongy cell layers, palisade cell density) and roots (stele diameter and surface, metaxylem vessel diameter) were also analyzed. Findings: Salt stress caused physiological and anatomical changes in cotyledons and roots. Sucrose, glucose and fructose concentrations were more affected in cotyledons than in roots of salt-treated seedlings. Proline accumulation was more affected in roots. Saline stress affected differentially the anatomical attributes of quinoa cultivars. Application/Improvements: Quinoa seedlings when subjected to salt stress are able to develop a set of anatomical, physiological and biochemical adaptive mechanisms which seem to occur at different combinations among quinoa cultivars, but giving similar abilities to cope with the excess of salt and survive under extreme conditions.

Tetraploidy enhances the ability to exclude chloride from leaves in carrizo citrange seedlings

Tetraploid citrus seedlings are more tolerant to salt stress than diploid genotypes. To provide insight into the causes of differences in salt tolerance due to ploidy and thus to better understand Cl− exclusion mechanisms in citrus, diploid and tetraploid seedlings of Carrizo citrange (CC) were grown at 0 (control) and 40mM NaCl (salt-treated) medium for 20 days. Chloride uptake and root-to-shoot translocation rates were on average 1.4-fold higher in diploid than in tetraploid salt-treated plants, which resulted in a greater (1.6-fold) Cl− build up in the leaves of the former. Root hydraulic conductance and leaf transpiration rate were 58% and 17% lower, respectively, in tetraploid than in diploid control plants. Differences remained after salt treatment which reduced these parameters by 30–40% in both genotypes. Morphology of the root system was significantly influenced by ploidy. Tetraploid roots were less branched and with lower number of root tips than those of diploid plants. The cross-section diameter and area were lower in the diploid, and consequently specific root length was higher (1.7-fold) than in tetraploid plants. The exodermis in sections close to the root apex was broader and with higher deposition of suberin in cell walls in the tetraploid than in the diploid genotype. Net CO2 assimilation rate in tetraploid salt-treated seedlings was 1.5-fold higher than in diploid salt-treated plants, likely due to the loss of photosynthetic capacity of diploid plants induced by Cl− toxicity. Leaf damage was much higher, in terms of burnt area and defoliation, in diploid than in tetraploid salt-treated plants (8- and 6-fold, respectively). Salt treatment significantly reduced (37%) the dry weight of the diploid plants, but did not affect the tetraploids. In conclusion, tetraploid CC plants appear more tolerant to salinization and this effect seems mainly due to differences in morphological and histological traits of roots affecting hydraulic conductance and transpiration rate. These results may suggest that tetraploid CC used as rootstock could improve salt tolerance in citrus trees.