Cross-species transcriptomic analyses reveals common and opposite responses in Arabidopsis, rice and barley following oxidative stress and hormone treatment.

BACKGROUND: For translational genomics, a roadmap is needed to know the molecular similarities or differences between species, such as model species and crop species. This knowledge is invaluable for the selection of target genes and pathways to alter downstream in response to the same stimuli. Here, the transcriptomic responses to six treatments including hormones (abscisic acid - ABA and salicylic acid - SA); treatments that cause oxidative stress (3-amino-1,2,4-triazole - 3AT, methyl viologen - MV); inhibit respiration (antimycin A - AA) or induce genetic damage (ultraviolet radiation -UV) were analysed and compared between Arabidopsis (Arabidopsis thaliana), barley (Hordeum vulgare) and rice (Oryza sativa). RESULTS: Common and opposite responses were identified between species, with the number of differentially expressed genes (DEGs) varying greatly between treatments and species. At least 70% of DEGs overlapped with at least one other treatment within a species, indicating overlapping response networks. Remarkably, 15 to 34% of orthologous DEGs showed opposite responses between species, indicating diversity in responses, despite orthology. Orthologous DEGs with common responses to multiple treatments across the three species were correlated with experimental data showing the functional importance of these genes in biotic/abiotic stress responses. The mitochondrial dysfunction response was revealed to be highly conserved in all three species in terms of responsive genes and regulation via the mitochondrial dysfunction element. CONCLUSIONS: The orthologous DEGs that showed a common response between species indicate conserved transcriptomic responses of these pathways between species. However, many genes, including prominent salt-stress responsive genes, were oppositely responsive in multiple-stresses, highlighting fundamental differences in the responses and regulation of these genes between species. This work provides a resource for translation of knowledge or functions between species.

Timing-dependent effects of salicylic acid treatment on phytohormonal changes, ROS regulation, and antioxidant defense in salinized barley (Hordeum vulgare L.).

Cross-talk between exogenous salicylic acid (SA) and endogenous phytohormone pathways affects the antioxidant defense system and its response to salt stress. The study presented here investigated the effects of SA treatment before and during salt stress on the levels of endogenous plant growth regulators in three barley cultivars with different salinity tolerances: Hordeum vulgare L. cvs. Akhisar (sensitive), Erginel (moderate), and Kalayci (tolerant). The cultivars' relative leaf water contents, growth parameters, proline contents, chlorophyll a/b ratios, and lipid peroxidation levels were measured, along with the activities of enzymes involved in detoxifying reactive oxygen species (ROS) including superoxide-dismutase, peroxidase, catalase, ascorbate-peroxidase, and glutathione-reductase. In addition, levels of several endogenous phytohormones (indole-3-acetic-acid, cytokinins, abscisic acid, jasmonic acid, and ethylene) were measured. Barley is known to be more salt tolerant than related plant species. Accordingly, none of the studied cultivars exhibited changes in membrane lipid peroxidation under salt stress. However, they responded differently to salt-stress with respect to their accumulation of phytohormones and antioxidant enzyme activity. The strongest and weakest increases in ABA and proline accumulation were observed in Kalayci and Akhisar, respectively, suggesting that salt-stress was more effectively managed in Kalayci. The effects of exogenous SA treatment depended on both the timing of the treatment and the cultivar to which it was applied. In general, however, where SA helped mitigate salt stress, it appeared to do so by increasing ROS scavenging capacity and antioxidant enzyme activity. SA treatment also induced changes in phytohormone levels, presumably as a consequence of SA-phytohormone salt-stress cross-talk.

Plastid differentiation during microgametogenesis determines green plant regeneration in barley microspore culture.

Developing plants from in vitro culture of microspores or immature pollen grains (androgenesis) is a highly genotype-dependent process whose effectiveness in cereals is significantly reduced by occurrence of albino regenerants. Here, we examined a hypothesis that the molecular differentiation of plastids in barley microspores prior to in vitro culture affects the genotype ability to regenerate green plants in culture. At the mid-to-late uninucleate (ML) stage, routinely used to initiate microspore culture, the expression of most genes involved in plastid transcription, translation and starch synthesis was significantly higher in microspores of barley cv. 'Mercada' producing 90% albino regenerants, than in cv. 'Jersey' that developed 90% green regenerants. The ML microspores of cv. 'Mercada' contained a large proportion of amyloplasts filled with starch, while in cv. 'Jersey' there were only proplastids. Using additional spring barley genotypes that differed in their ability to regenerate green plants we confirmed the correlation between plastid differentiation prior to culture and albino regeneration in culture. The expression of GBSSI gene (Granule-bound starch synthaseI) in early-mid (EM) microspores was a good marker of a genotype potential to produce green regenerants during androgenesis. Initiating culture from EM microspores that significantly improved regeneration of green plants may overcome the problem of albinism.

A laser ablation technique maps differences in elemental composition in roots of two barley cultivars subjected to salinity stress.

In saline soils, high levels of sodium (Na+ ) and chloride (Cl- ) ions reduce root growth by inhibiting cell division and elongation, thereby impacting on crop yield. Soil salinity can lead to Na+ toxicity of plant cells, influencing the uptake and retention of other important ions [i.e. potassium (K+ )] required for growth. However, measuring and quantifying soluble ions in their native, cellular environment is inherently difficult. Technologies that allow in situ profiling of plant tissues are fundamental for our understanding of abiotic stress responses and the development of tolerant crops. Here, we employ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to quantify Na, K and other elements [calcium (Ca), magnesium (Mg), sulphur (S), phosphorus (P), iron (Fe)] at high spatial resolution in the root growth zone of two genotypes of barley (Hordeum vulgare) that differ in salt-tolerance, cv. Clipper (tolerant) and Sahara (sensitive). The data show that Na+ was excluded from the meristem and cell division zone, indicating that Na+ toxicity is not directly reducing cell division in the salt-sensitive genotype, Sahara. Interestingly, in both genotypes, K+ was strongly correlated with Na+ concentration, in response to salt stress. In addition, we also show important genetic differences and salt-specific changes in elemental composition in the root growth zone. These results show that LA-ICP-MS can be used for fine mapping of soluble ions (i.e. Na+ and K+ ) in plant tissues, providing insight into the link between Na+ toxicity and root growth responses to salt stress.

Root plasticity and Pi recycling within plants contribute to low-P tolerance in Tibetan wild barley.

BACKGROUND: Barley is a low phosphorus (P) demand cereal crop. Tibetan wild barley, as a progenitor of cultivated barley, has revealed outstanding ability of tolerance to low-P stress. However, the underlying mechanisms of low-P adaption and the relevant genetic controlling are still unclear. RESULTS: We identified low-P tolerant barley lines in a doubled-haploid (DH) population derived from an elite Tibetan wild barley accession and a high-yield cultivar. The tolerant lines revealed greater root plasticity in the terms of lateral root length, compared to low-P sensitive lines, in response to low-P stress. By integrating the QTLs associated with root length and root transcriptomic profiling, candidate genes encoding isoflavone reductase, nitrate reductase, nitrate transporter and transcriptional factor MYB were identified. The differentially expressed genes (DEGs) involved the growth of lateral root, Pi transport within cells as well as from roots to shoots contributed to the differences between low-P tolerant line L138 and low-P sensitive lines L73 in their ability of P acquisition and utilization. CONCLUSIONS: The plasticity of root system is an important trait for barley to tolerate low-P stress. The low-P tolerance in the elite DH line derived from a cross of Tibetan wild barley and cultivated barley is characterized by enhanced growth of lateral root and Pi recycling within plants under low-P stress.

Inhibition of TNFα-induced interleukin-6 gene expression by barley (Hordeum vulgare) ethanol extract in BV-2 microglia.

BACKGROUND: Inflammation in the central nervous system is closely associated with pathological neurodegenerative diseases as well as psychiatric disorders. Prolonged activation of microglia can produce many inflammatory mediators, which may result in pathological neurotoxic side effects. Interleukin (IL)-6 serves as a hallmark of the injured brain. OBJECTIVE: Whole grains are known to contain many bioactive components. However, little information is available about anti-neuroinflammatory effects of grains in the CNS. This study aims to investigate the effect of Hordeum vulgare ethanol extract (HVE) on the suppression of IL-6 expression in BV2 microglia. METHODS: Inhibitory effects of HVE on IL-6 expression were analyzed by immunoblot anaysis, immunofluoresce microscopic analysis, reverse transcription-polymerase chain reaction, and luciferase promoter reporter assay. RESULTS: HVE inhibited TNFα-induced phosphorylation of IKKα/ß, IκB, and p65/RelA NF-κB. TNFα-induced IL-6 mRNA expression and promoter activity were reduced by HVE. Point mutation of NF-κB-binding site within the IL-6 gene promoter abolished TNFα-induced reporter activity, whereas exogenous expression of p65 NF-κB enhanced IL-6 promoter activity. CONCLUSION: NF-κB-binding site within the IL-6 promoter region is a HVE target element involved in the inhibition of TNFα-induced IL-6 gene transcription. HVE inhibits TNFα-induced IL-6 expression via suppression of NF-κB signaling in BV2 microglial cells.

Ethylene modulates root cortical senescence in barley.

Background and Aims: Root cortical senescence (RCS) is a poorly understood phenomenon with implications for adaptation to edaphic stress. It was hypothesized that RCS in barley (Hordeum vulgare L.) is (1) accelerated by exogenous ethylene exposure; (2) accompanied by differential expression of ethylene synthesis and signalling genes; and (3) associated with differential expression of programmed cell death (PCD) genes. Methods: Gene expression of root segments from four barley genotypes with and without RCS was evaluated using quantitative real-time PCR (qRT-PCR). The progression of RCS was manipulated with root zone ethylene and ethylene inhibitor applications. Key Results: The results demonstrate that ethylene modulates RCS. Four genes related to ethylene synthesis and signalling were upregulated during RCS in optimal, low nitrogen and low phosphorus nutrient regimes. RCS was accelerated by root zone ethylene treatment, and this effect was reversed by an ethylene action inhibitor. Roots treated with exogenous ethylene had 35 and 46 % more cortical senescence compared with the control aeration treatment in seminal and nodal roots, respectively. RCS was correlated with expression of two genes related to programmed cell death (PCD). Conclusions: The development of RCS is similar to root cortical aerenchyma formation with respect to ethylene modulation of the PCD process.

Root Engineering in Barley: Increasing Cytokinin Degradation Produces a Larger Root System, Mineral Enrichment in the Shoot and Improved Drought Tolerance.

Root size and architecture are important crop plant traits, as they determine access to water and soil nutrients. The plant hormone cytokinin is a negative regulator of root growth and branching. Here, we generated transgenic barley (Hordeum vulgare) plants with an enlarged root system by enhancing cytokinin degradation in roots to explore the potential of cytokinin modulations in improving root functions. This was achieved through root-specific expression of a CYTOKININ OXIDASE/DEHYDROGENASE gene. Enhanced biomass allocation to roots did not penalize shoot growth or seed yield, indicating that these plants were not source limited. In leaves of transgenic lines, the concentrations of several macroelements and microelements were increased, particularly those with low soil mobility (phosphorus, manganese, and zinc). Importantly, seeds contained up to 44% more zinc, which is beneficial for human nutrition. Transgenic lines also demonstrated dampened stress responses to long-term drought conditions, indicating lower drought sensitivity. Taken together, this work demonstrates that root engineering of cereals is a promising strategy to improve nutrient efficiency, biofortification, and drought tolerance.

Autophagy is activated and involved in cell death with participation of cathepsins during stress-induced microspore embryogenesis in barley.

Microspores are reprogrammed towards embryogenesis by stress. Many microspores die after this stress, limiting the efficiency of microspore embryogenesis. Autophagy is a degradation pathway that plays critical roles in stress response and cell death. In animals, cathepsins have an integral role in autophagy by degrading autophagic material; less is known in plants. Plant cathepsins are papain-like C1A cysteine proteases involved in many physiological processes, including programmed cell death. We have analysed the involvement of autophagy in cell death, in relation to cathepsin activation, during stress-induced microspore embryogenesis in Hordeum vulgare. After stress, reactive oxygen species (ROS) and cell death increased and autophagy was activated, including HvATG5 and HvATG6 up-regulation and increase of ATG5, ATG8, and autophagosomes. Concomitantly, cathepsin L/F-, B-, and H-like activities were induced, cathepsin-like genes HvPap-1 and HvPap-6 were up-regulated, and HvPap-1, HvPap-6, and HvPap-19 proteins increased and localized in the cytoplasm, resembling autophagy structures. Inhibitors of autophagy and cysteine proteases reduced cell death and promoted embryogenesis. The findings reveal a role for autophagy in stress-induced cell death during microspore embryogenesis, and the participation of cathepsins. Similar patterns of activation, expression, and localization suggest a possible connection between cathepsins and autophagy. The results open up new possibilities to enhance microspore embryogenesis efficiency with autophagy and/or cysteine protease modulators.

Circadian and Light Regulated Expression of CBFs and their Upstream Signalling Genes in Barley.

CBF (C-repeat binding factor) transcription factors show high expression levels in response to cold; moreover, they play a key regulatory role in cold acclimation processes. Recently, however, more and more information has led to the conclusion that, apart from cold, light-including its spectra-also has a crucial role in regulating CBF expression. Earlier, studies established that the expression patterns of some of these regulatory genes follow circadian rhythms. To understand more of this complex acclimation process, we studied the expression patterns of the signal transducing pathways, including signal perception, the circadian clock and phospholipid signalling pathways, upstream of the CBF gene regulatory hub. To exclude the confounding effect of cold, experiments were carried out at 22 °C. Our results show that the expression of genes implicated in the phospholipid signalling pathway follow a circadian rhythm. We demonstrated that, from among the tested CBF genes expressed in Hordeumvulgare (Hv) under our conditions, only the members of the HvCBF4-phylogenetic subgroup showed a circadian pattern. We found that the HvCBF4-subgroup genes were expressed late in the afternoon or early in the night. We also determined the expression changes under supplemental far-red illumination and established that the transcript accumulation had appeared four hours earlier and more intensely in several cases. Based on our results, we propose a model to illustrate the effect of the circadian clock and the quality of the light on the elements of signalling pathways upstream of the HvCBFs, thus integrating the complex regulation of the early cellular responses, which finally lead to an elevated abiotic stress tolerance.

Early generation of nitric oxide contributes to copper tolerance through reducing oxidative stress and cell death in hulless barley roots.

The objective of this study was to investigate the specific role of nitric oxide (NO) in the early response of hulless barley roots to copper (Cu) stress. We used the fluorescent probe diaminofluorescein-FM diacetate to establish NO localization, and hydrogen peroxide (H2O2)-special labeling and histochemical procedures for the detection of reactive oxygen species (ROS) in the root apex. An early production of NO was observed in Cu-treated root tips of hulless barley, but the detection of NO levels was decreased by supplementation with a NO scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO). Application of sodium nitroprusside (a NO donor) relieved Cu-induced root inhibition, ROS accumulation and oxidative damage, while c-PTIO treatment had a synergistic effect with Cu and further enhanced ROS levels and oxidative stress. In addition, the Cu-dependent increase in activities of superoxide dismutase, peroxidase and ascorbate peroxidase were further enhanced by exogenous NO, but application of c-PTIO decreased the activities of catalase and ascorbate peroxidase in Cu-treated roots. Subsequently, cell death was observed in root tips and was identified as a type of programed cell death (PCD) by terminal deoxynucleotidyl transferase dUTP nick end labeling assay. The addition of NO prevented the increase of cell death in root tips, whereas inhibiting NO accumulation further increased the number of cells undergoing PCD. These results revealed that NO production is an early response of hulless barley roots to Cu stress and that NO contributes to Cu tolerance in hulless barley possibly by modulating antioxidant defense, subsequently reducing oxidative stress and PCD in root tips.

Stimulation of Phenolics, Antioxidant and α-Glucosidase Inhibitory Activities During Barley (Hordeum vulgare L.) Seed Germination.

The rationale of this study was to enhance the nutritional quality of dry barley seeds. In this study we are evaluating the effect of germination on barley seeds relevant to total phenolic contents, antioxidant activity (in terms of DPPH free-radical scavenging) and the in vitro α-glucosidase inhibitory activities. Barley seeds were germinated for 18.5, 24, 30, 48, and 67 h and then extracted in water. The total phenolic contents, antioxidant activities and α-glucosidase inhibitory activities changed with germination time. More specifically, within the first 48 h of germination the total phenolic content increased from 1.1 mg/g fresh weight (0 h) to 3.4 mg/g fresh weight (48 h) and then slightly reduced by 67 h. Similarly, α-glucosidase inhibitory activity was significantly increased from an IC50 128.82 mg/mL (0 h) to an IC50 18.88 mg/mL (48 h) and then slightly reduced by 67 h. Significant maltase inhibitory activity was observed only with 48 h-germinated extract. Antioxidant activities increased continuously from an IC50 15.72 mg/mL at 0 h to and IC50 5.72 mg/mL after 48 h of germination. Based on our observations, barley seed germination was over after 48 h. During the progress of germination phenolic compounds are becoming available and are more easily extracted. After 48 h, lignification is initiated resulting to the decreased total phenolic content and observed antioxidant and carbohydrate hydrolyzing enzyme inhibition activities. The above results indicate the positive effect of germination in barley seeds for enhanced antioxidant and α-glucosidase inhibitory activities.

Transcriptome analysis reveals translational regulation in barley microspore-derived embryogenic callus under salt stress.

KEY MESSAGE: Transcriptome analysis of barley embryogenic callus from isolated microspore culture under salt stress uncovered a role of translation inhibition and selective activation of stress-specific proteins in cellular defense. Soil salinity is one of the major abiotic stresses which constrains the plant growth and reduces the productivity of field crops. In this study, it was observed that the salt stress in barley isolated microspore culture impacted not only on the quantity of embryogenic callus but also on the quality for later differentiation. The barley microspore-derived embryogenic callus, a transient intermediate form linked cells and plants, was employed for a global transcriptome analysis by RNA sequencing to provide new insights into the cellular adaptation or acclimation to stress. A total of 596 differentially expressed genes (DEGs) were identified, in which 123 DEGs were up-regulated and 473 DEGs were down-regulated in the embryogenic callus produced from microspore culture under salt stress as compared to the control conditions. KEGG pathway analysis identified 'translation' (27 DEGs; 12.56 %) as the largest group and followed by 'folding, sorting and degradation' (25 DEGs; 11.63 %) in 215 mapped metabolic pathways. The results of RNA-Seq data and quantitative real-time polymerase chain reaction validation showed that the genes related to translation regulation (such as eIF1A, RPLP0, RPLP2, VARS) were down-regulated to control general protein synthesis, and the genes related to endoplasmic reticulum stress response (such as small heat shock protein genes) were selectively up-regulated against protein denaturing during microspore embryogenesis under continuous salt stress. These transcriptional remodeling might affect the essential protein synthesis for the cell development to fulfill totipotency under salt stress.

Physiological relevance of plant 2-Cys peroxiredoxin overoxidation level and oligomerization status.

Peroxiredoxins are ubiquitous thioredoxin-dependent peroxidases presumed to display, upon environmental constraints, a chaperone function resulting from a redox-dependent conformational switch. In this work, using biochemical and genetic approaches, we aimed to unravel the factors regulating the redox status and the conformation of the plastidial 2-Cys peroxiredoxin (2-Cys PRX) in plants. In Arabidopsis, we show that in optimal growth conditions, the overoxidation level mainly depends on the availability of thioredoxin-related electron donors, but not on sulfiredoxin, the enzyme reducing the 2-Cys PRX overoxidized form. We also observed that upon various physiological temperature, osmotic and light stress conditions, the overoxidation level and oligomerization status of 2-Cys PRX can moderately vary depending on the constraint type. Further, no major change was noticed regarding protein conformation in water-stressed Arabidopsis, barley and potato plants, whereas species-dependent up- and down-variations in overoxidation were observed. In contrast, both 2-Cys PRX overoxidation and oligomerization were strongly induced during a severe oxidative stress generated by methyl viologen. From these data, revealing that the oligomerization status of plant 2-Cys PRX does not exhibit important variation and is not tightly linked to the protein redox status upon physiologically relevant environmental constraints, the possible in planta functions of 2-Cys PRX are discussed.

The identification of new cytosolic glutamine synthetase and asparagine synthetase genes in barley (Hordeum vulgare L.), and their expression during leaf senescence.

Glutamine synthetase and asparagine synthetase are two master enzymes involved in ammonium assimilation in plants. Their roles in nitrogen remobilization and nitrogen use efficiency have been proposed. In this report, the genes coding for the cytosolic glutamine synthetases (HvGS1) and asparagine synthetases (HvASN) in barley were identified. In addition to the three HvGS1 and two HvASN sequences previously reported, two prokaryotic-like HvGS1 and three HvASN cDNA sequences were identified. Gene structures were then characterized, obtaining full genomic sequences. The response of the five HvGS1 and five HvASN genes to leaf senescence was then studied. Developmental senescence was studied using primary and flag leaves. Dark-exposure or low-nitrate conditions were also used to trigger stress-induced senescence. Well-known senescence markers such as the chlorophyll and Rubisco contents were monitored in order to characterize senescence levels in the different leaves. The three eukaryotic-like HvGS1_1, HvGS1_2, and HvGS1_3 sequences showed the typical senescence-induced reduction in gene expression described in many plant species. By contrast, the two prokaryotic-like HvGS1_4 and HvGS1_5 sequences were repressed by leaf senescence, similar to the HvGS2 gene, which encodes the chloroplast glutamine synthetase isoenzyme. There was a greater contrast in the responses of the five HvASN and this suggested that these genes are needed for N remobilization in senescing leaves only when plants are well fertilized with nitrate. Responses of the HvASN sequences to dark-induced senescence showed that there are two categories of asparagine synthetases, one induced in the dark and the other repressed by the same conditions.

Evolutionary relationships among barley and Arabidopsis core circadian clock and clock-associated genes.

The circadian clock regulates a multitude of plant developmental and metabolic processes. In crop species, it contributes significantly to plant performance and productivity and to the adaptation and geographical range over which crops can be grown. To understand the clock in barley and how it relates to the components in the Arabidopsis thaliana clock, we have performed a systematic analysis of core circadian clock and clock-associated genes in barley, Arabidopsis and another eight species including tomato, potato, a range of monocotyledonous species and the moss, Physcomitrella patens. We have identified orthologues and paralogues of Arabidopsis genes which are conserved in all species, monocot/dicot differences, species-specific differences and variation in gene copy number (e.g. gene duplications among the various species). We propose that the common ancestor of barley and Arabidopsis had two-thirds of the key clock components identified in Arabidopsis prior to the separation of the monocot/dicot groups. After this separation, multiple independent gene duplication events took place in both monocot and dicot ancestors.

Bayesian inference of baseline fertility and treatment effects via a crop yield-fertility model.

To effectively manage soil fertility, knowledge is needed of how a crop uses nutrients from fertilizer applied to the soil. Soil quality is a combination of biological, chemical and physical properties and is hard to assess directly because of collective and multiple functional effects. In this paper, we focus on the application of these concepts to agriculture. We define the baseline fertility of soil as the level of fertility that a crop can acquire for growth from the soil. With this strict definition, we propose a new crop yield-fertility model that enables quantification of the process of improving baseline fertility and the effects of treatments solely from the time series of crop yields. The model was modified from Michaelis-Menten kinetics and measured the additional effects of the treatments given the baseline fertility. Using more than 30 years of experimental data, we used the Bayesian framework to estimate the improvements in baseline fertility and the effects of fertilizer and farmyard manure (FYM) on maize (Zea mays), barley (Hordeum vulgare), and soybean (Glycine max) yields. Fertilizer contributed the most to the barley yield and FYM contributed the most to the soybean yield among the three crops. The baseline fertility of the subsurface soil was very low for maize and barley prior to fertilization. In contrast, the baseline fertility in this soil approximated half-saturated fertility for the soybean crop. The long-term soil fertility was increased by adding FYM, but the effect of FYM addition was reduced by the addition of fertilizer. Our results provide evidence that long-term soil fertility under continuous farming was maintained, or increased, by the application of natural nutrients compared with the application of synthetic fertilizer.

Relative importance of an arbuscular mycorrhizal fungus (Rhizophagus intraradices) and root hairs in plant drought tolerance.

Both arbuscular mycorrhizal (AM) fungi and root hairs play important roles in plant uptake of water and mineral nutrients. To reveal the relative importance of mycorrhiza and root hairs in plant water relations, a bald root barley (brb) mutant and its wild type (wt) were grown with or without inoculation of the AM fungus Rhizophagus intraradices under well-watered or drought conditions, and plant physiological traits relevant to drought stress resistance were recorded. The experimental results indicated that the AM fungus could almost compensate for the absence of root hairs under drought-stressed conditions. Moreover, phosphorus (P) concentration, leaf water potential, photosynthetic rate, transpiration rate, stomatal conductance, and water use efficiency were significantly increased by R. intraradices but not by root hairs, except for shoot P concentration and photosynthetic rate under the drought condition. Root hairs even significantly decreased root P concentration under drought stresses. These results confirm that AM fungi can enhance plant drought tolerance by improvement of P uptake and plant water relations, which subsequently promote plant photosynthetic performance and growth, while root hairs presumably contribute to the improvement of plant growth and photosynthetic capacity through an increase in shoot P concentration.

Understanding the genetic control and physiological traits associated with rhizosheath production by barley (Hordeum vulgare).

There is an urgent need for simple rapid screens of root traits that improve the acquisition of nutrients and water. Temperate cereals produce rhizosheaths of variable weight, a trait first noted on desert species sampled by Tansley over 100 yr ago. This trait is almost certainly important in tolerance to abiotic stress. Here, we screened association genetics populations of barley for rhizosheath weight and derived quantitative trait loci (QTLs) and candidate genes. We assessed whether rhizosheath weight was correlated with plant performance and phosphate uptake under combined drought and phosphorus deficiency. Rhizosheath weight was investigated in relation to root hair length, and under both laboratory and field conditions. Our data demonstrated that rhizosheath weight was correlated with phosphate uptake under dry conditions and that the differences in rhizosheath weight between genotypes were maintained in the field. Rhizosheath weight also varied significantly within barley populations, was correlated with root hair length and was associated with a genetic locus (QTL) on chromosome 2H. Putative candidate genes were identified. Rhizosheath weight is easy and rapid to measure, and is associated with relatively high heritability. The breeding of cereal genotypes for beneficial rhizosheath characteristics is achievable and could contribute to agricultural sustainability in nutrient- and water-stressed environments.

Evaluating contribution of ionic, osmotic and oxidative stress components towards salinity tolerance in barley.

BACKGROUND: Salinity tolerance is a physiologically multi-faceted trait attributed to multiple mechanisms. Three barley (Hordeum vulgare) varieties contrasting in their salinity tolerance were used to assess the relative contribution of ionic, osmotic and oxidative stress components towards overall salinity stress tolerance in this species, both at the whole-plant and cellular levels. In addition, transcriptional changes in the gene expression profile were studied for key genes mediating plant ionic and oxidative homeostasis (NHX; RBOH; SOD; AHA and GORK), to compare a contribution of transcriptional and post-translational factors towards the specific components of salinity tolerance. RESULTS: Our major findings are two-fold. First, plant tissue tolerance was a dominating component that has determined the overall plant responses to salinity, with root K(+) retention ability and reduced sensitivity to stress-induced hydroxyl radical production being the main contributing tolerance mechanisms. Second, it was not possible to infer which cultivars were salinity tolerant based solely on expression profiling of candidate genes at one specific time point. For the genes studied and the time point selected that transcriptional changes in the expression of these specific genes had a small role for barley's adaptive responses to salinity. CONCLUSIONS: For better tissue tolerance, sodium sequestration, K(+) retention and resistance to oxidative stress all appeared to be crucial. Because these traits are highly interrelated, it is suggested that a major progress in crop breeding for salinity tolerance can be achieved only if these complementary traits are targeted at the same time. This study also highlights the essentiality of post translational modifications in plant adaptive responses to salinity.