Mechanism of kinetin-induced death of Vicia faba ssp. minor root cortex cells

Cell death (CD) may be induced by endogenous or exogenous factors and contributes to all the steps of plant development. This paper presents results related to the mechanism of CD regulation induced by kinetin (Kin) in the root cortex of Vicia faba ssp. minor. To explain the process, 6-(2-hydroxy-3-methylbenzylamino)purine (PI-55), adenine (Ad), 5'-amine-5'-deoxyadenosine (Ado) and N-(2-chloro-4-piridylo)-N'-phenylurea (CPPU) were applied to (i) block cytokinin receptors (CKs) and inhibit the activities of enzymes of CK metabolism, i.e., (ii) phosphoribosyltransferase, (iii) kinases, and (iv) oxidases, respectively. Moreover, ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), lanthanum chloride (LaCl3), ruthenium red (RRed) and cyclosporine A (CS-A) were applied to (i) chelate extracellular calcium ions (Ca2+) as well as blocks of (ii) plasma-, (iii) endoplasmic reticulum- (ER) membrane Ca2+ ion channels and (iv) mitochondria- (MIT) Ca2+ ions release by permeability transition por (PTP), respectively. The measured physiological effectiveness of these factors was the number of living and dying cortex cells estimated with orange acridine (OA) and ethidium bromide (EB), the amounts of cytosolic Ca2+ ions with chlortetracycline (CTC) staining and the intensity of chromatin and Ca2+-CTC complex fluorescence, respectively. Moreover, the role of sorafenib, an inhibitor of RAF kinase, on the vitality of cortex cells and ethylene levels as well as the activities of RAF-like kinase and MEK2 with Syntide-2 and Mek2 as substrates were studied. The results clarified the previously presented suggestion that Kin is converted to appropriate ribotides (5'-monophosphate ribonucleotides), which cooperate with the ethylene and Ca2+ ion signalling pathways to transduce the signal of kinetin-programmed cell death (Kin-PCD). Based on the present and previously published results related to Kin-PCD, the crosstalk between ethylene and MAP kinase signalling, as well as inhibitors of CK receptors and enzymes of their metabolism, is proposed.

The cropping system matters - Contrasting responses of winter faba bean (Vicia faba L.) genotypes to drought stress

Intercropping of legumes and cereals provides many ecological advantages and contributes to a sustainable agriculture. These agricultural systems face ongoing shifts in precipitation patterns and seasonal drought. Although the effect of drought stress on legumes has been frequently studied, knowledge about water deficits influencing legumes under different cropping systems is still limited. Therefore, we investigated the impact of water deficit and re-irrigation on two winter faba bean genotypes (S_004 and S_062) and winter wheat (var. Genius) in pure and intercropped stands under greenhouse conditions. Various physiological and biochemical parameters, such as canopy surface temperature, leaf relative water content and proline content, were collected at three time points (beginning of water deficit, end of water deficit, after re-irrigation). In addition, water use efficiency (WUE) was analyzed at the end of the experiment. The overall drought stress tolerance was determined as conceptual analysis of all measured parameters. Water deficit significantly affected WUE, surface temperature and proline content of both winter faba bean genotypes. Interestingly, intercropping with wheat resulted in an overall high drought tolerance of genotype S_004, while genotype S_062 had a high drought tolerance in pure stands. Under water deficit, pure stands of S_062 substantially increased WUE by 30.5%. Intercropping of genotype S_004 increased the dry matter per plant by 31.7% compared to pure stands under water deficit. Contrary, intercropping of genotype S_062 did not improve the dry matter production. Our findings indicate that genotype S_004 benefits from resource complementarity in intercropping systems with wheat, whereas S_062 is better suitable for pure stands due to competitive effects. Thus, our study highlights that the drought tolerance of winter faba bean genotypes depends on the cropping system, leading to a demand for drought-adapted cultivars specifically selected for intercropping.

Stomatal morphology and physiology explain varied sensitivity to abscisic acid across vascular plant lineages

Abscisic acid (ABA) can induce rapid stomatal closure in seed plants, but the action of this hormone on the stomata of fern and lycophyte species remains equivocal. Here, ABA-induced stomatal closure, signaling components, guard cell K+ and Ca2+ fluxes, vacuolar and actin cytoskeleton dynamics, and the permeability coefficient of guard cell protoplasts (Pf) were analyzed in species spanning the diversity of vascular land plants including 11 seed plants, 6 ferns, and 1 lycophyte. We found that all 11 seed plants exhibited ABA-induced stomatal closure, but the fern and lycophyte species did not. ABA-induced hydrogen peroxide elevation was observed in all species, but the signaling pathway downstream of nitric oxide production, including ion channel activation, was only observed in seed plants. In the angiosperm faba bean (Vicia faba), ABA application caused large vacuolar compartments to disaggregate, actin filaments to disintegrate into short fragments and Pf to increase. None of these changes was observed in the guard cells of the fern Matteuccia struthiopteris and lycophyte Selaginella moellendorffii treated with ABA, but a hypertonic osmotic solution did induce stomatal closure in fern and the lycophyte. Our results suggest that there is a major difference in the regulation of stomata between the fern and lycophyte plants and the seed plants. Importantly, these findings have uncovered the physiological and biophysical mechanisms that may have been responsible for the evolution of a stomatal response to ABA in the earliest seed plants.

Acclimatisation of guard cell metabolism to long-term salinity

Stomatal movements are enabled by changes in guard cell turgor facilitated via transient accumulation of inorganic and organic ions imported from the apoplast or biosynthesized within guard cells. Under salinity, excess salt ions accumulate within plant tissues resulting in osmotic and ionic stress. To elucidate whether (a) Na⁺ and Cl^- concentrations increase in guard cells in response to long-term NaCl exposure and how (b) guard cell metabolism acclimates to the anticipated stress, we profiled the ions and primary metabolites of leaves, the apoplast and isolated guard cells at darkness and during light, that is, closed and fully opened stomata. In contrast to leaves, the primary metabolism of guard cell preparations remained predominantly unaffected by increased salt ion concentrations. Orchestrated reductions of stomatal aperture and guard cell osmolyte synthesis were found, but unlike in leaves, no increases of stress responsive metabolites or compatible solutes occurred. Diverging regulation of guard cell metabolism might be a prerequisite to facilitate the constant adjustment of turgor that affects aperture. Moreover, the photoperiod-dependent sucrose accumulation in the apoplast and guard cells changed to a permanently replete condition under NaCl, indicating that stress-related photosynthate accumulation in leaves contributes to the permanent closing response of stomata under stress.

Investigating the underlying mechanism of cadmium-induced plant adaptive response to genotoxic stress

Plants as sessile organisms have developed some unique strategies to withstand environmental stress and adaptive response (AR) is one of them. In the present study Cadmium (Cd)-induced AR was evaluated to ameliorate the genotoxicity of a known chemical mutagen ethyl methanesulphonate (EMS) based on cytotoxicity, genotoxicity and oxidative stress in two model plant systems Allium cepa L. and Vicia faba L. Priming the plants with cadmium chloride (CdCl₂, 25 and 50 μM) reduced the genotoxicity of EMS (0.25 mM). Cd-induced AR was evident by the magnitude of adaptive response (MAR) values calculated for cytotoxicity, genotoxicity and biochemical parameters. In addition the involvement of some major metabolic pathways and epigenetic modifications in AR was investigated. Metabolic blockers of protein kinase cascades, DNA repair, oxidative stress and de novo translation interfered with the adaptive response implying their role in AR whereas, inhibitors involved in post-replication repair and autophagy were ineffective implicating that they probably have no role in the AR studied. Moreover to find the role of DNA methylation in AR, methylation-sensitive comet assay was carried out. Simultaneously 5-methyl- 2'-deoxycytidine (5mdC) levels were quantified by HPLC (high performance liquid chromatography). AR was eliminated in cells treated with a demethylating agent, 5-aza- 2'deoxycytidine (AZA). Results implied a contribution of DNA hypermethylation. To the best of our knowledge this is a first report correlating DNA methylation to Cd-induced adaptive response in plants undergoing genotoxic stress.

Potential risks of nicotine on the germination, growth, and nutritional properties of broad bean

This study evaluated the allelopathy, uptake and accumulation, and potential agricultural and food safety risks of nicotine in broad bean (Vicia faba L.) during seed germination and seedling growth. Nicotine stress has an allelopathic inhibitory effect on seeds and a hormesis effect on germinated seeds and seedlings, which has an enhancement effect (<50 mg kg^-1) and an inhibition effect (>100 mg kg^-1) on the germinated seeds and an enhancement effect (<100 mg kg^-1) and an inhibition effect (>200 mg kg^-1) on the seedlings. Exogenous nicotine can be absorbed by broad bean roots from nicotine-contaminated soil and accumulated in the main organs of the seedlings, especially the leaves, which exceeded the maximum residue level (0.03 mg kg^-1 DW) at 50 mg kg^-1. Moreover, nicotine resulted in a bitter taste in the edible broad bean leaves, disrupting the balance of basic nutritional properties, decreasing sucrose, and increasing bitter substances such as choline and procyanidin. These results demonstrated that residual nicotine in the soil not only poses potential risks to sustainable agricultural development but also a food safety risk for consumers. The present study provides insight into the potential risks of nicotine in agroecosystems.

Earthworm Eisenia andrei modulates oxidative stress in bean plants Vicia faba irrigated with treated wastewater

With respect to reducing the pressure on freshwater resources, treated wastewater (TWW) irrigation represents a sustainable alternative in agriculture. Due to their low quality and variable composition, TWW could entail harmful consequences for living organisms in terrestrial ecosystems. This study aims to evaluate how earthworm (Eisenia andrei) can modulate oxidative stress in bean plants (Vicia faba) that are irrigated over a course of 60 days with two doses of TWW (50 and 100%) in addition to a control condition (0%) irrigated with distilled water. This is achieved by measuring glutathione-S-transferase (GST) activity and malondialdehyde accumulation (MDA) in plants. Furthermore, catalase (CAT), GST, MDA, and acetylcholinesterase (AChE) activities of the earthworms are also assessed. Our results show that growth and physiological parameters are modified when applying TWW irrigation. Moreover, oxidative stress apprehended by GST activity and MDA accumulation is exacerbated in V. faba plants after exposure to increased TWW doses. Similarly, TWW irrigation enhances oxidative stress parameters in earthworms with a crucial decrease in AChE activity. In addition, the presence of earthworms increases growth and physiological parameters; it also results in a significant reduction in GST activity and MDA rate in V. faba plants. Our results provide new insights into the impact of TWW irrigation on soil organisms and the importance of earthworms in the reduction of oxidative stress in plants.

Using advanced vibrational molecular spectroscopy (ATR-Ft/IRS) to study heating process induced changes on protein molecular structure of biodegradation residues in cool-climate adapted faba bean seeds: Relationship with rumen and intestinal protein digestion in ruminant systems

The objective of this study was to evaluate the effects of heating process on protein molecular structure from ruminal degradation residues in cool-climate adapted faba bean seeds in relation to crude protein (CP), in situ degradation kinetics, rumen protein degradation and intestinal protein digestion parameters in dairy cows. Seeds of six faba bean varieties with low (Snowbird, Snowdrop, 219_16) and normal tannin (Fatima, 346_10, SSNS_1) were collected from three different locations, and were heated 3 min by microwave irradiation (MI, dry heating) or heated 1 h by steam pressure toasting (SP, moist heating) or kept raw as a control. Heat treated samples were used for rumen incubating 24, 12, 8, 4, 2, 0 h(s) in two replicate runs and then residues from 12 h of rumen degradation were used for three steps in vitro technique for determining intestinal protein digestion. Attenuated total reflectance Fourier transforms infrared spectroscopy (ATR-Ft/IRS) was used for analyzing protien molecular structure of residual faba bean seeds. The results showed that SP increased the intensities of amide I, amide II, α-helix and β-sheet but decreased amide I to amide II height and area ratio, α-helix to β-sheet height ratio from 12 and 24 h of ruminal degradation, and MI decreased all the intensities of amide I, amide II, α-helix and β-sheet and ratios except amide I to amide II area ratio of residues from 24 h of ruminal degradation. Additionally, the intensities of amide I, amide II, α-helix and β-sheet had a unique pattern of increasing first and then decreasing with the increasing ruminal digestion time for SP treatment, while amide I to amide II height and area ratio, α-helix to β-sheet height ratio were declining. For the MI groups, this pattern was not observed and the intensities were rather consistent across the digestion process. Rumen protein degradation parameters including rumen bypass crude protein (BCP) or rumen undegradable protein (RUP) and rumen degradable protein (RDP) closely correlated with protein molecular structure of to peak heights, areas and ratios. Regression equations based on residual protein molecular structure presented a good estimation power for soluble fraction (S, R² = 0.79), degradable fraction (D, R² = 0.805), BCP (R² = 0.941), RUP (R² = 0.941) and RDP (R² = 0.811). Overall, heat-induced changes in rumen residual protein molecular structures were related to CP, in situ degradation kinetics, rumen protein degradation and rumen protein digestion parameters.

The transgenerational effects of solar short-UV radiation differed in two accessions of Vicia faba L. from contrasting UV environments

BACKGROUND AND AIMS

UVB radiation can rapidly induce gene regulation leading to cumulative changes for plant physiology and morphology. We hypothesized that a transgenerational effect of chronic exposure to solar short UV modulates the offspring's responses to UVB and blue light, and that the transgenerational effect is genotype dependent.

METHODS

We established a factorial experiment combining two Vicia faba L. accessions, two parental UV treatments (full sunlight and exclusion of short UV, 290-350 nm), and four offspring light treatments from the factorial combination of UVB and blue light. The accessions were Aurora from southern Sweden, and ILB938 from Andean region of Colombia and Ecuador.

KEY RESULTS

The transgenerational effect influenced morphological responses to blue light differently in the two accessions. In Aurora, when UVB was absent, blue light increased shoot dry mass only in plants whose parents were protected from short UV. In ILB938, blue light increased leaf area and shoot dry mass more in plants whose parents were exposed to short UV than those that were not. Moreover, when the offspring was exposed to UVB, the transgenerational effect decreased in ILB938 and disappeared in Aurora. For flavonoids, the transgenerational effect was detected only in Aurora: parental exposure to short UV was associated with a greater induction of total quercetin in response to UVB. Transcript abundance was higher in Aurora than in ILB938 for both CHALCONE SYNTHASE (99-fold) and DON-GLUCOSYLTRANSFERASE 1 (19-fold).

CONCLUSIONS

The results supported both hypotheses. Solar short UV had transgenerational effects on progeny responses to blue and UVB radiation, and they differed between the accessions. These transgenerational effects could be adaptive by acclimation of slow and cumulative morphological change, and by early build-up of UV protection through flavonoid accumulation on UVB exposure. The differences between the two accessions aligned with their adaptation to contrasting UV environments.

Sodium nitroprusside (SNP) improves tolerance to arsenic (As) toxicity in Vicia faba through the modifications of biochemical attributes, antioxidants, ascorbate-glutathione cycle and glyoxalase cycle

The present study was conducted to evaluate the effect of arsenic (As) toxicity and the mitigating role of nitric oxide (NO) donor sodium nitroprusside (SNP) on Vicia faba. Arsenics stress decreased the growth and biomass yield, and photosynthetic pigments, but it enhanced As accumulation. Supplementation of NO enhanced the afore-mentioned parameters except As accumulation which decreased in both shoot and root. Supplementation of NO enhanced the shoot tolerance index (Shoot TI%), root tolerance index (Root TI%) but it declined the As translocation factor (TF). Application of NO alleviated the As-induced decline in net assimilation rate, stomatal conductance, transpiration and leaf relative water content. The levels of proline and glycine betaine (GB) further increased due to NO application, whereas malondialdehyde (MDA), hydrogen peroxide (H₂O₂), electrolyte leakage (EL) and methylglyoxal (MG) declined considerably. Activities of enzymatic antioxidants such as superoxide dismutase (SOD) and catalase (CAT) increased under As stress. Supplementation of NO up-regulated the enzymes involved in Asc-Glu cycle and glyoxalase cycle under As toxicity. Another experiment was setup to authenticate whether NO was certainly able to alleviate As toxicity. For this purpose, the NO scavenger [2-(4-carboxy-2 phenyl)-4,4,5,5-tertamethylimidazoline-1-oxyl-3-oxide (cPTIO)] was added to As and NO supplemented plants. Addition of cPTIO to NO supplemented As-treated plants showed the same effect when As alone was supplied to plants. In conclusion, addition of NO to the growth medium maintained the plant performance under As toxicity through modulation of physio-biochemical attributes, antioxidant enzymes, and the Asc-Glu and glyoxalase systems.

Metabolomics of red-light-induced stomatal opening in Arabidopsis thaliana: Coupling with abscisic acid and jasmonic acid metabolism

Environmental stimuli-triggered stomatal movement is a key physiological process that regulates CO₂ uptake and water loss in plants. Stomata are defined by pairs of guard cells that perceive and transduce external signals, leading to cellular volume changes and consequent stomatal aperture change. Within the visible light spectrum, red light induces stomatal opening in intact leaves. However, there has been debate regarding the extent to which red-light-induced stomatal opening arises from direct guard cell sensing of red light versus indirect responses as a result of red light influences on mesophyll photosynthesis. Here we identify conditions that result in red-light-stimulated stomatal opening in isolated epidermal peels and enlargement of protoplasts, firmly establishing a direct guard cell response to red light. We then employ metabolomics workflows utilizing gas chromatography mass spectrometry and liquid chromatography mass spectrometry for metabolite profiling and identification of Arabidopsis guard cell metabolic signatures in response to red light in the absence of the mesophyll. We quantified 223 metabolites in Arabidopsis guard cells, with 104 found to be red light responsive. These red-light-modulated metabolites participate in the tricarboxylic acid cycle, carbon balance, phytohormone biosynthesis and redox homeostasis. We next analyzed selected Arabidopsis mutants, and discovered that stomatal opening response to red light is correlated with a decrease in guard cell abscisic acid content and an increase in jasmonic acid content. The red-light-modulated guard cell metabolome reported here provides fundamental information concerning autonomous red light signaling pathways in guard cells.

Phytotoxicity of silver nanoparticles on Vicia faba: Evaluation of particle size effects on photosynthetic performance and leaf gas exchange

Nanotechnology is an emerging field in science and engineering, which presents significant impacts on the economy, society and the environment. The nanomaterials' (NMs) production, use, and disposal is inevitably leading to their release into the environment where there are uncertainties about its fate, behaviour, and toxicity. Recent works have demonstrated that NMs can penetrate, translocate, and accumulate in plants. However, studies about the effects of the NMs on plants are still limited because most investigations are carried out in the initial stage of plant development. The present study aimed to evaluate and characterize the photochemical efficiency of photosystem II (PSII) of broad bean (Vicia faba) leaves when subjected to silver nanoparticles (AgNPs) with diameters of 20, 51, and 73 nm as well as to micrometer-size Ag particles (AgBulk). The AgNPs were characterized by transmission electron microscopy and dynamic light scattering. The analyses were performed by injecting the leaves with 100 mg L^-1 aqueous solution of Ag and measuring the chlorophyll fluorescence imaging, gas exchange, thermal imaging, and reactive oxygen species (ROS) production. In addition, silver ion (Ag⁺) release from Ag particles was determined by dialysis. The results revealed that AgNPs induce a decrease in the photochemical efficiency of photosystem II (PSII) and an increase in the non-photochemical quenching. The data also revealed that AgNPs affected the stomatal conductance (g_s) and CO₂ assimilation. Further, AgNPs induced an overproduction of ROS in Vicia faba leaves. Finally, all observed effects were particle diameter-dependent, increasing with the reduction of AgNPs diameter and revealing that AgBulk caused only a small or no changes on plants. In summary, the results point out that AgNPs may negatively affect the photosynthesis process when accumulated in the leaves, and that the NPs themselves were mainly responsible since negligible Ag⁺ release was detected.

Is nitric oxide a critical key factor in ABA-induced stomatal closure?

The role of nitric oxide (NO) in abscisic acid (ABA)-induced stomatal closure is a matter of debate. We conducted experiments in Vicia faba leaves using NO gas and sodium nitroprusside (SNP), a NO-donor compound, and compared their effects to those of ABA. In epidermal strips, stomatal closure was induced by ABA but not by NO, casting doubt on the role of NO in ABA-mediated stomatal closure. Leaf discs and intact leaves showed a dual dose response to NO: stomatal aperture widened at low dosage and narrowed at high dosage. Overcoming stomatal resistance by means of high CO2 concentration ([CO2]) restored photosynthesis in ABA-treated leaf discs but not in those exposed to NO. NO inhibited photosynthesis immediately, causing an instantaneous increase in intercellular [CO2] (Ci), followed by stomatal closure. However, lowering Ci by using low ambient [CO2] showed that it was not the main factor in NO-induced stomatal closure. In intact leaves, the rate of stomatal closure in response to NO was about one order of magnitude less than after ABA application. Because of the different kinetics of photosynthesis and stomatal closure that were observed, we conclude that NO is not likely to be the key factor in ABA-induced rapid stomatal closure, but that it fine-tunes stomatal aperture via different pathways.

Genotoxicity response of Vicia faba seedlings to cadmium in soils as characterized by direct soil exposure and micronucleus test

To overcome the drawbacks of the Vicia faba root tip micronucleus test in soil using the solution extract method, we conducted a potting experiment by direct soil exposure. Cadmium was spiked into 3 typical soils (brown soil, red soil, and black soil) to simulate environmental concentrations (0.625, 1.25, 2.5, 5, and 10 mg kg^-1). Multiple Vicia faba tissues (primary root tips, secondary root tips, and leaf tips) were sampled, and mitotic index (MI), chromosome aberration frequency (CA), and micronucleus frequency (MN) were used as endpoints after a seedling period of 5 days. The results showed a response between Cd concentrations and multiple sampling tissues of Vicia faba, and the secondary root tips responded to Cd stress the most, followed by primary root tips and leaf tips. Soil physicochemical properties (e.g., pH, total phosphorus, total organic carbon, etc.) influenced the genotoxicity of Cd, and pH was the dominant factor, which resulted in the genetic toxicity response of Cd in soils in the order: red soil > brown soil > black soil. The lowest observable effect concentration (LOEC) of Cd was 1.25 mg kg^-1 for both brown soil and red soil and 2.5 mg kg^-1 for black soil. In view of this, we suggested that soil properties should be considered in evaluating genotoxicity risk of Cd in soil, especially with soil pH range, and the secondary root tips should be taken as suitable test tissues in the MN test due to its more sensible response feature to Cd stress in soil.

Enzymes contributing to the hydrogen peroxide signal dynamics that regulate wall labyrinth formation in transfer cells

Transfer cells are characterized by an amplified plasma membrane area supported on a wall labyrinth composed of a uniform wall layer (UWL) from which wall ingrowth (WI) papillae arise. Adaxial epidermal cells of developing Vicia faba cotyledons, when placed in culture, undergo a rapid (hours) trans-differentiation to a functional epidermal transfer cell (ETC) phenotype. The trans-differentiation event is controlled by a signalling cascade comprising auxin, ethylene, apoplasmic reactive oxygen species (apoROS), and cytosolic Ca2+. Apoplasmic hydrogen peroxide (apoH2O2) was confirmed as the apoROS regulating UWL and WI papillae formation. Informed by an ETC-specific transcriptome, a pharmacological approach identified a temporally changing cohort of H2O2 biosynthetic enzymes. The cohort contained a respiratory burst oxidase homologue, polyamine oxidase, copper amine oxidase, and a suite of class III peroxidases. Collectively these generated two consecutive bursts in apoH2O2 production. Spatial organization of biosynthetic/catabolic enzymes was deduced from responses to pharmacologically blocking their activities on the cellular and subcellular distribution of apoH2O2. The findings were consistent with catalase activity constraining the apoH2O2 signal to the outer periclinal wall of the ETCs. Strategic positioning of class III peroxidases in this outer domain shaped subcellular apoH2O2 signatures that differed during assembly of the UWL and WI papillae.

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.

Ecotoxicological Evaluation of Municipal Sludge

Municipal wastes originating from urban and industrial areas have become a major source of soil, ground and surface water pollution. These undesirable agents in our environment significantly interact with our flora and fauna. The aim of this study was to test samples of municipal sludge (MS) for their ecotoxicological potential by using sensitive bioassays involving a plant, Vicia faba, and the earthworm, Eisenia foetida. A 10% leachate of MS was prepared for the experiments, and V. faba seedlings were exposed to three leachate concentrations (2.5%, 5% and 10%) for 5 days. The findings revealed chromosome aberrations during the metaphase as well as the anaphase of cell division, and inhibition of the mitotic index, which reflects that MS originating from domestic and other human activities may be genotoxic to the living organisms of the ecosystem. Abnormalities in chlorophyll content, plant growth, root length, shoot length and root/shoot length ratio in V. faba clearly indicated the toxicity of the sludge. Behavioural and reproduction studies with E. foetida also provided evidence for the toxic nature of the MS.

Limited effects of the maternal rearing environment on the behaviour and fitness of an insect herbivore and its natural enemy

The maternal rearing environment can affect offspring fitness or phenotype indirectly via 'maternal effects' and can also influence a mother's behaviour and fecundity directly. However, it remains uncertain how the effects of the maternal rearing environment cascade through multiple trophic levels, such as in plant-insect herbivore-natural enemy interactions. Pea aphids (Acyrthosiphon pisum) show differential fitness on host legume species, while generalist aphid parasitoids can show variable fitness on different host aphid species, suggesting that maternal effects could operate in a plant-aphid-parasitoid system. We tested whether the maternal rearing environment affected the behaviour and fitness of aphids by rearing aphids on two plant hosts that were either the same as or different from those experienced by the mothers. A similar approach was used to test the behaviour and fitness of parasitoid wasps in response to maternal rearing environment. Here, the host environment was manipulated at the plant or plant and aphid trophic levels for parasitoid wasps. We also quantified the quality of host plants for aphids and host aphids for parasitoid wasps. In choice tests, aphids and parasitoid wasps had no preference for the plant nor plant and aphid host environment on which they were reared. Aphid offspring experienced 50.8% higher intrinsic rates of population growth, 43.4% heavier offspring and lived 14.9% longer when feeding on bean plants compared to aphids feeding on pea plants, with little effect of the maternal rearing environment. Plant tissue nitrogen concentration varied by 21.3% in response to aphid mothers' rearing environment, and these differences correlated with offspring fitness. Maternal effects in parasitoid wasps were only observed when both the plant and aphid host environment was changed: wasp offspring were heaviest by 10.9-73.5% when both they and their mothers developed in bean-reared pea aphids. Also, parasitoid wasp fecundity was highest by 38.4% when offspring were oviposited in the maternal rearing environment. These findings indicate that maternal effects have a relatively small contribution towards the outcome of plant-aphid-parasitoid interactions.

Ion-dependent metabolic responses of Vicia faba L. to salt stress

Salt-affected farmlands are increasingly burdened by chlorides, carbonates, and sulfates of sodium, calcium, and magnesium. Intriguingly, the underlying physiological processes are studied almost always under NaCl stress. Two faba bean cultivars were subjected to low- and high-salt treatments of NaCl, Na₂ SO₄ , and KCl. Assimilation rate and leaf water vapor conductance were reduced to approximately 25-30% without biomass reduction after 7 days salt stress, but this did not cause severe carbon shortage. The equimolar treatments of Na⁺ , K⁺ , and Cl^- showed comparable accumulation patterns in leaves and roots, except for SO₄^2- which did not accumulate. To gain a detailed understanding of the effects caused by the tested ion combinations, we performed nontargeted gas chromatography-mass spectrometry-based metabolite profiling. Metabolic responses to various salts were in part highly linearly correlated, but only a few metabolite responses were common to all salts and in both cultivars. At high salt concentrations, only myo-inositol, allantoin, and glycerophosphoglycerol were highly significantly increased in roots under all tested conditions. We discovered several metabolic responses that were preferentially associated with the presence of Na⁺ , K⁺ , or Cl^- . For example, increases of leaf proline and decreases of leaf fumaric acid and malic acid were apparently associated with Cl^- accumulation.

Root traits of European Vicia faba cultivars-Using machine learning to explore adaptations to agroclimatic conditions

Faba bean (Vicia faba L.) is an important source of protein, but breeding for increased yield stability and stress tolerance is hampered by the scarcity of phenotyping information. Because comparisons of cultivars adapted to different agroclimatic zones improve our understanding of stress tolerance mechanisms, the root architecture and morphology of 16 European faba bean cultivars were studied at maturity. Different machine learning (ML) approaches were tested in their usefulness to analyse trait variations between cultivars. A supervised, that is, hypothesis-driven, ML approach revealed that cultivars from Portugal feature greater and coarser but less frequent lateral roots at the top of the taproot, potentially enhancing water uptake from deeper soil horizons. Unsupervised clustering revealed that trait differences between northern and southern cultivars are not predominant but that two cultivar groups, independently from major and minor types, differ largely in overall root system size. Methodological guidelines on how to use powerful ML methods such as random forest models for enhancing the phenotypical exploration of plants are given.

Comparison of intracellular location and stimulus reaction times of forisomes in sieve tubes of four legume species

Forisomes in legumes are responsible for fast sieve-element occlusion in response to injury to the vascular system. This prevents uncontrolled leakage of phloem sap and protects against invasion of pathogens. Here we compared forisomes of four different legumes (Pisum sativum, Vicia faba, Trifolium pratense and Medicago sativa) by their location (basal, central, apical) in the sieve element and reactivity to a distant heat stimulus. In each species, the majority of forisomes was located basally. Yet, we found differences in intracellular location: forisomes are distributed more evenly in the sieve elements of Pisum. After burning, basally located forisomes of the four species reacted with dispersion, followed by a spontaneous recondensation with similar reaction times. The results suggest universal forisome behaviour in fabacean species.

Ambient aerosol increases minimum leaf conductance and alters the aperture-flux relationship as stomata respond to vapor pressure deficit (VPD)

Aerosols are important components of the global plant environment, with beneficial and deleterious impacts. The direct effects of aerosol deposition on plant-water relationships remain poorly characterized but potentially important. Vicia faba was grown in ambient urban air and in the same air with aerosol excluded, in a moderately polluted environment using two exposure protocols. Simultaneous measurement of gas exchange and stomatal pore aperture was combined with leaf dehydration kinetics and microscopic evaluation of leaf wetness formation and aerosol deposition patterns. The ambient aerosol was shown to be hygroscopic. Aerosol exposure increased minimum leaf conductance, shown by dehydration kinetics, and nocturnal water vapor flux, shown by dark-adapted gas exchange. Aerosol exposure decreased stomatal apertures at each level of vapor pressure deficit (VPD) and increased stomatal conductance at comparable levels of aperture. Overall, these effects were modest, and largest when stomata were wide open. The uncoupling of conductance (flux-based) from aperture (directly measured microscopically) implies that aerosol-induced water loss is not fully under stomatal control. This reduces drought tolerance and may provide a mechanism by which deposited aerosol plays a direct role in stomatal response to VPD.

Proteomic analysis dissects the impact of nodulation and biological nitrogen fixation on Vicia faba root nodule physiology

Symbiotic nitrogen fixation in root nodules of legumes is a highly important biological process which is only poorly understood. Root nodule metabolism differs from that of roots. Differences in root and nodule metabolism are expressed by altered protein abundances and amenable to quantitative proteome analyses. Differences in the proteomes may either be tissue specific and related to the presence of temporary endosymbionts (the bacteroids) or related to nitrogen fixation activity. An experimental setup including WT bacterial strains and strains not able to conduct symbiotic nitrogen fixation as well as root controls enables identification of tissue and nitrogen fixation specific proteins. Root nodules are specialized plant organs housing and regulating the mutual symbiosis of legumes with nitrogen fixing rhizobia. As such, these organs fulfill unique functions in plant metabolism. Identifying the proteins required for the metabolic reactions of nitrogen fixation and those merely involved in sustaining the rhizobia:plant symbiosis, is a challenging task and requires an experimental setup which allows to differentiate between these two physiological processes. Here, quantitative proteome analyses of nitrogen fixing and non-nitrogen fixing nodules as well as fertilized and non-fertilized roots were performed using Vicia faba and Rhizobium leguminosarum. Pairwise comparisons revealed altered enzyme abundance between active and inactive nodules. Similarly, general differences between nodules and root tissue were observed. Together, these results allow distinguishing the proteins directly involved in nitrogen fixation from those related to nodulation. Further observations relate to the control of nodulation by hormones and provide supportive evidence for the previously reported correlation of nitrogen and sulfur fixation in these plant organs. Additionally, data on altered protein abundance relating to alanine metabolism imply that this amino acid may be exported from the symbiosomes of V. faba root nodules in addition to ammonia. Data are available via ProteomeXchange with identifier PXD008548.

A computational approach for inferring the cell wall properties that govern guard cell dynamics

Guard cells dynamically adjust their shape in order to regulate photosynthetic gas exchange, respiration rates and defend against pathogen entry. Cell shape changes are determined by the interplay of cell wall material properties and turgor pressure. To investigate this relationship between turgor pressure, cell wall properties and cell shape, we focused on kidney-shaped stomata and developed a biomechanical model of a guard cell pair. Treating the cell wall as a composite of the pectin-rich cell wall matrix embedded with cellulose microfibrils, we show that strong, circumferentially oriented fibres are critical for opening. We find that the opening dynamics are dictated by the mechanical stress response of the cell wall matrix, and as the turgor rises, the pectinaceous matrix stiffens. We validate these predictions with stomatal opening experiments in selected Arabidopsis cell wall mutants. Thus, using a computational framework that combines a 3D biomechanical model with parameter optimization, we demonstrate how to exploit subtle shape changes to infer cell wall material properties. Our findings reveal that proper stomatal dynamics are built on two key properties of the cell wall, namely anisotropy in the form of hoop reinforcement and strain stiffening.

Elevated temperature drives a shift from selfing to outcrossing in the insect-pollinated legume, faba bean (Vicia faba)

Climate change can threaten the reproductive success of plants, both directly, through physiological damage during increasingly extreme weather events, and indirectly, through disruption of plant-pollinator interactions. To explore how plant-pollinator interactions are modified by extreme weather, we exposed faba bean (Vicia faba) plants to elevated temperature for 5 d during flowering, simulating a heatwave. We then moved the plants to flight cages with either bumblebees or no pollinators, or to two field sites, where plants were enclosed in mesh bags or pollinated by wild insect communities. We used a morphological marker to quantify pollen movement between experimental plants. There was a substantial increase in the level of outcrossing by insect pollinators following heat stress. Proportion outcrossed seed increased from 17 % at control temperature, to 33 % following heat stress in the flight cages, and from 31 % to 80 % at one field site, but not at the other (33 % to 32 %). Abiotic stress can dramatically shift the relative contributions of cross- and self-pollination to reproduction in an insect pollinated plant. The resulting increases in gene flow have broad implications for genetic diversity and functioning of ecosystems, and may increase resilience by accelerating the selection of more stress-tolerant genotypes.

Early changes of the pH of the apoplast are different in leaves, stem and roots of Vicia faba L. under declining water availability

Changes in pH of the apoplast have recently been discussed as an important factor in adjusting transpiration and water relations under conditions of drought via modulatory effect on abscisic acid (ABA) concentration. Using Vicia faba L., we investigated whether changes in the root, shoot and leaf apoplastic pH correlated with (1) a drought-induced reduction in transpiration and with (2) changes in ABA concentration. Transpiration, leaf water potential and ABA in leaves were measured and correlated with root and shoot xylem pH, determined by a pH microelectrode, and pH of leaf apoplast quantified by microscopy-based in vivo ratiometric analysis. Results revealed that a reduction in transpiration rate in the early phase of soil drying could not be linked with changes in the apoplastic pH via effects on the stomata-regulating hormone ABA. Moreover, drought-induced increase in pH of xylem or leaf apoplast was not the remote effect of an acropetal transport of alkaline sap from root, because root xylem acidified during progressive soil drying, whereas the shoot apoplast alkalized. We reason that other, yet unknown signalling mechanism was responsible for reduction of transpiration rate in the early phase of soil drying.

Genetic Diversity and Symbiotic Efficiency of Nodulating Rhizobia Isolated from Root Nodules of Faba Bean in One Field

Thirty-one nodulating rhizobium strains were collected from root nodules of spring and winter type faba bean cultivars grown in micro ecoarea, i.e. the same field in Chengdu plain, China. The symbiotic efficiency and phylogeny of these strains were studied. Effectively nitrogen fixing strains were isolated from both winter type and spring type cultivars. Based on phylogenetic analysis of 16S rRNA gene and concatenated sequence of atpD, glnII and recA genes, the isolates were assigned as Rhizobium anhuiense and a potential new Rhizobium species. The isolates were diverse on symbiosis related gene level, carrying five, four and three variants of nifH, nodC and nodD, respectively. Strains carrying similar gene combinations were trapped by both winter and spring cultivars, disagreeing with the specificity of symbiotic genotypes to reported earlier faba bean ecotypes.

Herbivore-Triggered Electrophysiological Reactions: Candidates for Systemic Signals in Higher Plants and the Challenge of Their Identification

In stressed plants, electrophysiological reactions (elRs) are presumed to contribute to long-distance intercellular communication between distant plant parts. Because of the focus on abiotic stress-induced elRs in recent decades, biotic stress-triggered elRs have been widely ignored. It is likely that the challenge to identify the particular elR types (action potential [AP], variation potential, and system potential [SP]) was responsible for this course of action. Thus, this survey focused on insect larva feeding (Spodoptera littoralis and Manduca sexta) that triggers distant APs, variation potentials, and SPs in monocotyledonous and dicotyledonous plant species (Hordeum vulgare, Vicia faba, and Nicotiana tabacum). APs were detected only after feeding on the stem/culm, whereas SPs were observed systemically following damage to both stem/culm and leaves. This was attributed to the unequal vascular innervation of the plant and a selective electrophysiological connectivity of the plant tissue. However, striking variations in voltage patterns were detected for each elR type. Further analyses (also in Brassica napus and Cucurbita maxima) employing complementary electrophysiological approaches in response to different stimuli revealed various reasons for these voltage pattern variations: an intrinsic plasticity of elRs, a plant-specific signature of elRs, a specific influence of the applied (a)biotic trigger, the impact of the technical approach, and/or the experimental setup. As a consequence, voltage pattern variations, which are not irregular but rather common, need to be included in electrophysiological signaling analysis. Due to their widespread occurrence, systemic propagation, and respective triggers, elRs should be considered as candidates for long-distance communication in higher plants.

Glucose- and mannose-induced stomatal closure is mediated by ROS production, Ca(2+) and water channel in Vicia faba

Sugars act as vital signaling molecules that regulate plant growth, development and stress responses. However, the effects of sugars on stomatal movement have been unclear. In our study, we explored the effects of monosaccharides such as glucose and mannose on stomatal aperture. Here, we demonstrate that glucose and mannose trigger stomatal closure in a dose- and time-dependent manner in epidermal peels of broad bean (Vicia faba). Pharmacological studies revealed that glucose- and mannose-induced stomatal closure was almost completely inhibited by two reactive oxygen species (ROS) scavengers, catalase (CAT) and reduced glutathione (GSH), was significantly abolished by an NADPH oxidase inhibitor, diphenylene iodonium chloride (DPI), whereas they were hardly affected by a peroxidase inhibitor, salicylhydroxamic acid (SHAM). Furthermore, glucose- and mannose-induced stomatal closure was strongly inhibited by a Ca(2+) channel blocker, LaCl3 , a Ca(2+) chelator, ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) and two water channel blockers, HgCl2 and dimethyl sulfoxide (DMSO); whereas the inhibitory effects of the water channel blockers were essentially abolished by the reversing agent β-mercaptoethanol (β-ME). These results suggest that ROS production mainly via NADPH oxidases, Ca(2+) and water channels are involved in glucose- and mannose-induced stomatal closure.

Shift from complementarity to facilitation on P uptake by intercropped wheat neighboring with faba bean when available soil P is depleted

Rhizosphere processes stimulate overyielding and facilitative phosphorus (P) uptake in cereal/legume intercropping systems. However, little is known about when and how rhizosphere alteration of legumes plays a role in improving P uptake by cereals. Wheat was grown isolated, monocropped or intercropped with faba bean in pots with low-P soil. The biomass, P content, carboxylates and phosphatases activity were measured in 15 destructive samplings. Intraspecific competition of the biomass and P uptake of monocropped wheat was not significant before 40 and 36 days after sowing (DAS), whereas there was interspecific competition of biomass of intercropped wheat before 66 DAS. However, afterwards, the increments of the biomass and P uptake of the intercropped wheat were 1.3-1.9 and 1.9-2.3 times of increment of monocropped wheat. Meanwhile, the concentrations of malate and citrate and the acid phosphatase activity in the rhizospheres of intercropped wheat were significantly increased, which suggested that wheat/faba bean intercropping is efficient in P utilization due to complementary P uptake in the early growth stage and the positive interactions of the rhizosphere processes when the soil P was depleted.

Glutamate functions in stomatal closure in Arabidopsis and fava bean

Guard cells are indispensable for higher plants because they control gas exchange and water balance to maintain photosynthetic activity. The signaling processes that govern their movement are controlled by several factors, such as abscisic acid (ABA), blue light, pathogen-associated molecular patterns (PAMPs), and carbon dioxide. Herein, we demonstrated that the amino acid glutamate (Glu), a well-known mammalian neurotransmitter, functions as a novel signaling molecule in stomatal closure in both Arabidopsis and fava bean (Vicia faba L.). Pharmacological and electrophysiological analyses provided important clues for the participation of Glu-receptors, Ca(2+), and protein phosphorylation during the signaling process. Genetic analyses using Arabidopsis ABA-deficient (aba2-1) and ABA-insensitive (abi1-1 and abi2-1) mutants showed that ABA is not required for Glu signaling. However, loss-of-function of the Arabidopsis gene encoding Slow Anion Channel-Associated 1 (SLAC1) and Calcium-Dependent Protein Kinase 6 (CPK6) impaired the Glu response. Moreover, T-DNA knockout mutations of the Arabidopsis Glu receptor-like gene (GLR), GLR3.5, lost their sensitivity to Glu-dependent stomatal closure. Our results strongly support functional Glu-signaling in stomatal closure and the crucial roles of GLRs in this signaling process.

Rapid modulation of ultraviolet shielding in plants is influenced by solar ultraviolet radiation and linked to alterations in flavonoids

The accumulation of ultraviolet (UV)-absorbing compounds (flavonoids and related phenylpropanoids) and the resultant decrease in epidermal UV transmittance (TUV ) are primary protective mechanisms employed by plants against potentially damaging solar UV radiation and are critical components of the overall acclimation response of plants to changing solar UV environments. Whether plants can adjust this UV sunscreen protection in response to rapid changes in UV, as occurs on a diurnal basis, is largely unexplored. Here, we use a combination of approaches to demonstrate that plants can modulate their UV-screening properties within minutes to hours, and these changes are driven, in part, by UV radiation. For the cultivated species Abelmoschus esculentus, large (30-50%) and reversible changes in TUV occurred on a diurnal basis, and these adjustments were associated with changes in the concentrations of whole-leaf UV-absorbing compounds and several quercetin glycosides. Similar results were found for two other species (Vicia faba and Solanum lycopersicum), but no such changes were detected in Zea mays. These findings reveal a much more dynamic UV-protection mechanism than previously recognized, raise important questions concerning the costs and benefits of UV-protection strategies in plants and have practical implications for employing UV to enhance crop vigor and quality in controlled environments.

Increased soil phosphorus availability induced by faba bean root exudation stimulates root growth and phosphorus uptake in neighbouring maize

Root growth is influenced by soil nutrients and neighbouring plants, but how these two drivers affect root interactions and regulate plant growth dynamics is poorly understood. Here, interactions between the roots of maize (Zea mays) and faba bean (Vicia faba) are characterized. Maize was grown alone (maize) or with maize (maize/maize) or faba bean (maize/faba bean) as competitors under five levels of phosphorus (P) supply, and with homogeneous or heterogeneous P distribution. Maize had longer root length and greater shoot biomass and P content when grown with faba bean than with maize. At each P supply rate, faba bean had a smaller root system than maize but greater exudation of citrate and acid phosphatase, suggesting a greater capacity to mobilize P in the rhizosphere. Heterogeneous P availability enhanced the root-length density of maize but not faba bean. Maize root proliferation in the P-rich patches was associated with increased shoot P uptake. Increased P availability by localized P application or by the presence of faba bean exudation stimulated root morphological plasticity and increased shoot growth in maize in the maize/faba bean mixture, suggesting that root interactions of neighbouring plants can be modified by increased P availability.

Morphological and physiological changes in esterase and lipid peroxidation of two bean cultivars pre-soaked with potassium nitrate under salt stress

Two broad bean cultivars (Vicia faba CV Nobaria3 and Vicia faba CV Sakha3) were obtained from Mallwi Agriculture Research Center, El Minia Governorate, Egypt. The seeds were divided into two groups, the first group soaked with distilled water, while the second group were soaked with 3 mM KNO₃, respectively, for 4 hours. Seeds were sown and left to grow for 3 weeks then treated with different concentrations of NaCl (0.0, 40, 80, 120 and 160 mM) by top irrigation, then they left to grow further for 65 days from sowing. Plant samples were collected for some measurements: leaf area, plant height, root length, fresh and dry weight, photosynthetic pigments, carotenoids, soluble sugars, soluble proteins, total free amino acids, esterase enzyme, as well as MDA (malondialdehyde) content. Salinity reduced both fresh and dry weight in two broad bean cultivars, this reduction were more pronounced in Sakha3 than Nobaria3. Seed pre-soaking with KNO₃resulted in enhancement of fresh and dry weight production in both cultivars especially at 40 mM NaCl. Photosynthetic pigments were substantially affected by salt treatment while the carotenoids were increased, seed pre-soaking with KNO₃improved these components. The soluble sugars, amino acids as well as soluble proteins showed various responses with increasing salinity in the cultivars, seed pre-soaking with KNO₃has improved these parameters to some extent. The shoots of two cultivars exhibited significant accumulation of MDA, compared to roots exposed to the highest salinity levels. Pre-soaking seeds with KNO₃did not improve MDA in shoots but enhanced it in roots, however, in most cases still lower than the absolute control. The assessment of the esterase isozyme profiles on 7.5% native polyacrylamide gel revealed the presence of 13 isoforms in two faba bean plants in response to KNO₃pre-soaking and treatments with different concentrations of NaCl.

Chloride-inducible transient apoplastic alkalinizations induce stomata closure by controlling abscisic acid distribution between leaf apoplast and guard cells in salt-stressed Vicia faba

Chloride stress causes the leaf apoplast transiently to alkalize, an event that is presumed to contribute to the ability of plants to adapt to saline conditions. However, the initiation of coordinated processes downstream of the alkalinization is unknown. We hypothesize that chloride-inducible pH dynamics are a key chemical feature modulating the compartmental distribution of abscisic acid (ABA) and, as a consequence, affecting stomata aperture. Apoplastic pH and stomata aperture dynamics in intact Vicia faba leaves were monitored by microscopy-based ratio imaging and porometric measurements of stomatal conductance. ABA concentrations in leaf apoplast and guard cells were compared with pH dynamics by gas-chromatography-mass-spectrometry (GC-MS) and liquid-chromatography-tandem-mass spectrometry (LC-MS/MS). Results demonstrate that, upon chloride addition to roots, an alkalizing factor that initiates the pH dynamic propagates from root to leaf in a way similar to xylem-distributed water. In leaves, it induces a systemic transient apoplastic alkalinization that causes apoplastic ABA concentration to increase, followed by an elevation of endogenous guard cell ABA. We conclude that the transient alkalinization, which is a remote effect of chloride stress, modulates the compartmental distribution of ABA between the leaf apoplast and the guard cells and, in this way, is instrumental in inducing stomata closure during the beginning of salinity.

Parasitic Wasps Aphidius ervi are More Attracted to a Blend of Host-Induced Plant Volatiles than to the Independent Compounds

Arthropodal natural enemies respond to volatiles from plants infested by their prey/host herbivores (herbivore-induced plant volatiles; HIPVs). However, the relative importance of HIPV blends vs. each compound in the blend in attracting natural enemies is not fully understood. In this study, we investigated the response of a parasitic wasp, Aphidius ervi, to HIPVs that were specific or nonspecific to infestations by its host aphid, Acyrthosiphon pisum. To select such compounds, we compared the volatiles emitted from broad bean plants infested by either A. pisum (host) or by Aphis craccivora (nonhost), and selected the host-specific HIPVs β-myrcene, n-octanal, and α-phellandrene, and host-nonspecific HIPVs (E)-β-ocimene, γ-terpinene, and linalool as test compounds. For each compound, we used a range that covered the amounts emitted from infested broad bean plants for bioassays. Female wasps preferred n-octanal and (E)-β-ocimene at 10-ng and 30-ng doses over clean air. Interestingly, the wasps preferred α-phellandrene at 0.1-ng and 30-ng doses, but not at 1-ng and 10-ng doses. The wasps repelled linalool over clean air at 1-ng and 0.1-ng doses. We then mixed the equivalent amounts of the six compounds to test the effect of the blend. The wasps responded to a blend of six HIPV components at all concentrations tested (0.001 ng each to 5 ng each). These results suggested that the blend provided more useful information for female wasps than the individual compounds. The possible use of the single component and the blend for the biological control of A. ervi is discussed.

Faba bean forisomes can function in defence against generalist aphids

Phloem sieve elements have shut-off mechanisms that prevent loss of nutrient-rich phloem sap when the phloem is damaged. Some phloem proteins such as the proteins that form forisomes in legume sieve elements are one such mechanism and in response to damage, they instantly form occlusions that stop the flow of sap. It has long been hypothesized that one function of phloem proteins is defence against phloem sap-feeding insects such as aphids. This study provides the first experimental evidence that aphid feeding can induce phloem protein occlusion and that the aphid-induced occlusions inhibit phloem sap ingestion. The great majority of phloem penetrations in Vicia faba by the generalist aphids Myzus persicae and Macrosiphum euphorbiae triggered forisome occlusion and the aphids eventually withdrew their stylets without ingesting phloem sap. This contrasts starkly with a previous study on the legume-specialist aphid, Acyrthosiphon pisum, where penetration of faba bean sieve elements did not trigger forisome occlusion and the aphids readily ingested phloem sap. Next, forisome occlusion was demonstrated to be the cause of failed phloem ingestion attempts by M. persicae: when occlusion was inhibited by the calcium channel blocker lanthanum, M. persicae readily ingested faba bean phloem sap.

Stomatal malfunctioning under low VPD conditions: induced by alterations in stomatal morphology and leaf anatomy or in the ABA signaling?

Exposing plants to low VPD reduces leaf capacity to maintain adequate water status thereafter. To find the impact of VPD on functioning of stomata, stomatal morphology and leaf anatomy, fava bean plants were grown at low (L, 0.23 kPa) or moderate (M, 1.17 kPa) VPDs and some plants that developed their leaves at moderate VPD were then transferred for 4 days to low VPD (M→L). Part of the M→L-plants were sprayed with ABA (abscisic acid) during exposure to L. L-plants showed bigger stomata, larger pore area, thinner leaves and less spongy cells compared with M-plants. Stomatal morphology (except aperture) and leaf anatomy of the M→L-plants were almost similar to the M-plants, while their transpiration rate and stomatal conductance were identical to that of L-plants. The stomatal response to ABA was lost in L-plants, but also after 1-day exposure of M-plants to low VPD. The level of foliar ABA sharply decreased within 1-day exposure to L, while the level of ABA-GE (ABA-glucose ester) was not affected. Spraying ABA during the exposure to L prevented loss of stomatal closing response thereafter. The effect of low VPD was largely depending on exposure time: the stomatal responsiveness to ABA was lost after 1-day exposure to low VPD, while the responsiveness to desiccation was gradually lost during 4-day exposure to low VPD. Leaf anatomical and stomatal morphological alterations due to low VPD were not the main cause of loss of stomatal closure response to closing stimuli.

Resistance of Faba Bean and Pea Germplasm to Callosobruchus chinensis (Coleoptera: Bruchidae) and Its Relationship With Quality Components

In total, 339 faba bean (Vicia faba L.) and 100 pea (Pisum sativum L.) accessions were screened for their ability to resist Callosobruchus chinensis L. in free choice laboratory tests. Four, 15, and 43 faba bean varieties were highly resistant, resistant, and moderately resistant to C. chinensis, respectively. Three immune, three highly resistant, and six resistant accessions were discovered among the pea germplasm. The faba bean and pea varieties presented a hundred-kernel weight reduction varied from 0.18 to 35.36% for faba bean varieties and 0 to 56.53% for pea varieties. Varieties with brown and black seed color had significantly fewer wormholes and higher C. chinensis resistance than varieties with light-color seeds. Resistance to C. chinensis showed a significant, positive correlation with catechin, total polyphenol, and γ-aminobutyric acid contents, but a significant, negative correlation with oligosaccharide content. Correlation coefficients (r) between infestation rate of faba bean and total phenol, catechin, and oligosaccharide contents were -0.9723, -0.8071, and 0.7631, respectively. The values of r for pea resistance and total phenol, catechin, and oligosaccharide content were -0.8846, -0.7666, and 0.8308, respectively. The results suggest that quality components in faba bean and pea have a great role in resistance against C. chinensis.

Low strigolactone root exudation: a novel mechanism of broomrape (Orobanche and Phelipanche spp.) resistance available for faba bean breeding

Faba bean yield is severely constrained in the Mediterranean region and Middle East by the parasitic weeds Orobanche crenata, O. foetida, and Phelipanche aegyptiaca. Seed germination of these weeds is triggered upon recognition of host root exudates. Only recently faba bean accessions have been identified with resistance based in low induction of parasitic seed germination, but the underlying mechanism was not identified. Strigolactones are a group of terpenoid lactones involved in the host recognition by parasitic plants. Our LC-MS/MS analysis of root exudates of the susceptible accession Prothabon detected orobanchol, orobanchyl acetate, and a novel germination stimulant. A time course analysis indicated that their concentration increased with plant age. However, low or undetectable amounts of these germination stimulants were detected in root exudates of the resistant lines Quijote and Navio at all plant ages. A time course analysis of seed germination induced by root exudates of each faba bean accession indicated important differences in the ability to stimulate parasitic germination. Results presented here show that resistance to parasitic weeds based on low strigolactone exudation does exist within faba bean germplasm. Therefore, selection for this trait is feasible in a breeding program. The remarkable fact that low induction of germination is similarly operative against O. crenata, O. foetida, and P. aegyptiaca reinforces the value of this resistance.

Stomata prioritize their responses to multiple biotic and abiotic signal inputs

Stomata are microscopic pores in leaf epidermis that regulate gas exchange between plants and the environment. Being natural openings on the leaf surface, stomata also serve as ports for the invasion of foliar pathogenic bacteria. Each stomatal pore is enclosed by a pair of guard cells that are able to sense a wide spectrum of biotic and abiotic stresses and respond by precisely adjusting the pore width. However, it is not clear whether stomatal responses to simultaneously imposed biotic and abiotic signals are mutually dependent on each other. Here we show that a genetically engineered Escherichia coli strain DH5α could trigger stomatal closure in Vicia faba, an innate immune response that might depend on NADPH oxidase-mediated ROS burst. DH5α-induced stomatal closure could be abolished or disguised under certain environmental conditions like low [CO₂], darkness, and drought, etc. Foliar spraying of high concentrations of ABA could reduce stomatal aperture in high humidity-treated faba bean plants. Consistently, the aggressive multiplication of DH5α bacteria in Vicia faba leaves under high humidity could be alleviated by exogenous application of ABA. Our data suggest that a successful colonization of bacteria on the leaf surface is correlated with stomatal aperture regulation by a specific set of environmental factors.

Protein Kinase Cascade Involved in Rapid ABA-signaling in Guard Cells of Vicia faba

Protein kinases are involved in signal transduction for environmental stress responses. In response to drought and salinity, a 48-kDa protein kinase (AAPK; abscisic acid-activated protein kinase (AAPK) in guard cells is activated by abscisic acid (ABA) and phosphorylates several targets such as the carboxy-terminus of inward-rectifying K+ channel and heterogeneous mRNA binding protein to adopt to the changing environment. The AAPK expressed specifically in guard cells, and recombinant AAPK was phosphorylated only with the extract from ABA-treated guard cells but not from untreated cells. This indicates the presence of an AAPK kinase (AAPKK), which is activated by ABA and phosphorylates AAPK preceding the activation of AAPK. Both AAPK and AAPKK are involved in the protein kinase cascade for the rapid ABA-signaling.

Genomics-assisted breeding in four major pulse crops of developing countries: present status and prospects

KEY MESSAGE

Given recent advances in pulse molecular biology, genomics-driven breeding has emerged as a promising approach to address the issues of limited genetic gain and low productivity in various pulse crops. The global population is continuously increasing and is expected to reach nine billion by 2050. This huge population pressure will lead to severe shortage of food, natural resources and arable land. Such an alarming situation is most likely to arise in developing countries due to increase in the proportion of people suffering from protein and micronutrient malnutrition. Pulses being a primary and affordable source of proteins and minerals play a key role in alleviating the protein calorie malnutrition, micronutrient deficiencies and other undernourishment-related issues. Additionally, pulses are a vital source of livelihood generation for millions of resource-poor farmers practising agriculture in the semi-arid and sub-tropical regions. Limited success achieved through conventional breeding so far in most of the pulse crops will not be enough to feed the ever increasing population. In this context, genomics-assisted breeding (GAB) holds promise in enhancing the genetic gains. Though pulses have long been considered as orphan crops, recent advances in the area of pulse genomics are noteworthy, e.g. discovery of genome-wide genetic markers, high-throughput genotyping and sequencing platforms, high-density genetic linkage/QTL maps and, more importantly, the availability of whole-genome sequence. With genome sequence in hand, there is a great scope to apply genome-wide methods for trait mapping using association studies and to choose desirable genotypes via genomic selection. It is anticipated that GAB will speed up the progress of genetic improvement of pulses, leading to the rapid development of cultivars with higher yield, enhanced stress tolerance and wider adaptability.

Microscopic and macroscopic monitoring of adaxial-abaxial pH gradients in the leaf apoplast of Vicia faba L. as primed by NaCl stress at the roots

The pH is a basic chemical requirement in cellular and apoplastic compartments that influences various physiological processes in plants. Apoplastic pH shifts can modulate the apoplastic and symplastic distribution of plant hormones or influence proton motive force-driven uptake processes over the plasma-membrane. Changing environments are known to effect on the apoplastic H(+)-concentration in leaves and roots. The onset of NaCl-stress at the roots for instance primes a chloride-specific systemic alkalinization of the leaf apoplast. By means of microscopy- and macroscopy-based in planta ratio-imaging we surprisingly found that large adaxial-abaxial pH gradients were established throughout the leaf apoplast during the formation of the NaCl-induced alkalinization. Moreover, the root system is necessary to ensure the transient nature of the leaf apoplastic alkalinization.

Single-bilayer graphene oxide sheet impacts and underlying potential mechanism assessment in germinating faba bean (Vicia faba L.)

This study investigates the impact of different single-bilayer graphene oxide sheet (hereafter 'graphene oxide', GO; size: 0.5-5 μm) concentrations (0, 100, 200, 400, 800 and 1,600 mg L(-1)) and underlying potential mechanisms in germinating faba bean (Vicia faba L.) seedlings. The study revealed both positive and negative concentration-dependent GO-effects on V. faba. Significant negative impacts of GO concentrations (ordered by magnitude of effect: 1600>200>100 mg GO L(-1)) were indicated by decreases in growth parameters and the activity of H2O2-decomposing enzymes (ascorbate peroxidase, APX; catalase, CAT), and by increases in the levels of electrolyte leakage (EL), H2O2, and lipid and protein oxidation. The positive impacts of 400 and 800 mg GO L(-1) included significant improvements in V. faba health status indicated by decreased levels of EL, H2O2, and lipid and protein oxidation, and by enhanced H2O2-decomposing APX and CAT activity, and increased proline and seed-relative water content. V. faba seedlings-polypeptide patterns strongly substantiated these GO-concentration effects. Overall, the positive effects of these two GO concentrations (800>400 mg L(-1)) on V. faba seedlings indicate their safe nature and allow to suggest further studies.

Legume seed exudates and Physcomitrella patens extracts influence swarming behavior in Rhizobium leguminosarum

Plants are known to secrete chemical compounds that can change the behavior of rhizosphere-inhabiting bacteria. We investigated the effects of extracts from legume host plants on the swarming behavior of Rhizobium leguminosarum bv. viciae. We also investigated the effects on swarming when Rhizobium is exposed to extracts from an ancestor to vascular plants, the model bryophyte Physcomitrella patens. Lentil and faba bean seed exudates enhanced and inhibited swarming motility, respectively, whereas pea seed exudates had no observable effect on swarming. Swarming was also enhanced by the moss extracts. Exposure to lentil seed exudates and the moss extract increased flaA expression 2-fold, while faba bean seed exudates exposure decreased expression 3-fold, suggesting that the swarming effect could, in part, be due to regulation of flagellin gene expression. However, the exudates and extracts did not significantly affect flaA gene expression in planktonic motile cells, indicating that the response to flagellar regulation is specific to a physiology unique to the swarming cell. Transmission electron microscopy demonstrated that addition of the lentil seed exudate and the moss extract results in earlier differentiation into swarmer cells, which could contribute to the development of a larger swarming surface area. To gain further mechanistic insight into the effect of the moss extract on swarming, a moss strigolactone-deficient mutant (Ppccd8Δ) was tested. A reduction in the promotive effect was observed, suggesting that the plant hormone strigolactone may be a signalling molecule activating swarming motility in R. leguminosarum.

ABA induces H2O2 production in guard cells, but does not close the stomata on Vicia faba leaves developed at high air humidity

Plants developed under constant high (> 85%) relative air humidity (RH) have larger stomata that are unable to close completely. One of the hypotheses for the less responsive stomata is that the plants have reduced sensitivity to abscisic acid (ABA). Both ABA and darkness are signals for stomatal closure and induce the production of the secondary messenger hydrogen peroxide (H2O2). In this study, the ability of Vicia faba plants developed in moderate or high RH to close the stomata in response to darkness, ABA and H2O2 was investigated. Moreover, the ability of the plants to produce H2O2 when treated with ABA or transferred to darkness was also assessed. Our results show that the ABA concentration in moderate RH is not increased during darkness even though the stomata are closing. This indicates that stomatal closure in V. faba during darkness is independent of ABA production. ABA induced both H2O2 production and stomatal closure in stomata formed at moderate RH. H2O2 production, as a result of treatment with ABA, was also observed in stomata formed at high RH, though the closing response was considerably smaller as compared with moderate RH. In either RH, leaf ABA concentration was not affected by darkness. Similarly to ABA treatment, darkness elicited both H2O2 production and stomatal closure following plant cultivation at moderate RH. Contrary to this, neither H2O2 production nor stomatal closure took place when stomata were formed at high RH. These results suggest that the reduced stomatal response in plants developed in continuous high RH is caused by one or more factors downstream of H2O2 in the signaling pathway toward stomatal closure.

Response of bean (Vicia faba L.) plants to low sink demand by measuring the gas exchange rates and chlorophyll a fluorescence kinetics

Background

The decline of photosynthesis in plants under low sink demand is well known. Previous studies focused on the relationship between stomatal conductance (g_s) and net photosynthetic rate (P_n). These studies investigated the effect of changes in Photosystem II (PSII) function on the P_n decline under low sink demand. However, little is known about its effects on different limiting steps of electron transport chain in PSII under this condition.

Methodology/Principal Finding

Two-month-old bean plants were processed by removing pods and flowers (low sink demand). On the 1^st day after low sink demand treatment, a decline of P_n was accompanied by a decrease in g_s and internal-to-ambient CO₂ concentration ratio (C_i/C_a). From the 3^rd to 9^th day, P_n and g_s declined continuously while C_i/C_a ratio remained stable in the treatment. Moreover, these values were lower than that of control. W_k (a parameter reflecting the damage to oxygen evolving complex of the donor side of PSII) values in the treatment were significantly higher than their corresponding control values. However, RC_QA (a parameter reflecting the number of active RCs per excited cross-section of PSII) values in the treatment were significantly lower than control from the 5^th day. From the 11^th to 21^st day, P_n and g_s of the treatment continued to decline and were lower than control. This was accompanied by a decrease of RC_QA, and an increase of W_k. Furthermore, the quantum yield parameters φ_Po, φ_Eo and ψ_Eo in the treatment were lower than in control; however, C_i/C_a values in the treatment gradually increased and were significantly higher than control on the 21^st day.

Conclusions

Stomatal limitation during the early stage, whereas a combination of stomatal and non-stomatal limitation during the middle stage might be responsible for the reduction of P_n under low sink demand. Non-stomatal limitation during the late stages after the removal of the sink of roots and pods may also cause P_n reduction. The non-stomatal limitation was associated with the inhibition of PSII electron transport chain. Our data suggests that the donor side of PSII was the most sensitive to low sink demand followed by the reaction center of PSII. The acceptor side of PSII may be the least sensitive.

Does aphid salivation affect phloem sieve element occlusion in vivo?

To protect against loss of photo-assimilate-rich phloem sap, plants have evolved several mechanisms to plug phloem sieve tubes in response to damage. In many Fabaceae, each sieve element contains a discrete proteinaceous body called a forisome, which, in response to damage, rapidly transforms from a condensed configuration that does not impede the flow of sap to a dispersed configuration that plugs the sieve element. Aphids and other specialized phloem sap feeders can ingest phloem sap from a single sieve element for hours or days, and to do this, they must be able to suppress or reverse phloem plugging. A recent study provided in vitro evidence that aphid saliva can reverse forisome plugs. The present study tested this hypothesis in vivo by inducing forisome plugs which triggered aphids to switch behaviour from phloem sap ingestion to salivation into the sieve element. After salivating into the sieve element for various periods of time, the aphids were instantaneously cryofixed (freeze fixed) in situ on their leaf. The state of the forisome was then determined in the penetrated sieve element and in nearby non-penetrated sieve elements which served as controls for sieve elements not subjected to direct aphid salivation. Forisomes were almost always in close contact with the stylet tips and thus came into direct contact with the saliva. Nonetheless, forisome plugs in the penetrated sieve element did not revert back to a non-plugging state any faster than those in neighbouring sieve elements that were not subjected to direct aphid salivation.

Adjustments in epidermal UV-transmittance of leaves in sun-shade transitions

Epidermal UV transmittance (TUV ) and UV-absorbing compounds were measured in sun and shade leaves of Populus tremuloides and Vicia faba exposed to contrasting light environments under field conditions to evaluate UV acclimation potentials and regulatory roles of photosynthetically active radiation (PAR) and UV in UV-shielding. Within a natural canopy of P. tremuloides, TUV ranged from 4 to 98% and showed a strong nonlinear relationship with mid-day horizontal fluxes of PAR [photon flux density (PFD) = 6-1830 µmol m⁻²  s⁻¹]; similar patterns were found for V. faba leaves that developed under a comparable PFD range. A series of field transfer experiments using neutral-density shade cloth and UV blocking/transmitting films indicated that PAR influenced TUV during leaf development to a greater degree than UV, and shade leaves of both species increased their UV-shielding when exposed to full sun; however, this required the presence of UV, with both UV-A and UV-B required for full acclimation. TUV of sun leaves of both species was largely unresponsive to shade either with or without UV. In most, but not all cases, changes in TUV were associated with alterations in the concentration of whole-leaf UV-absorbing compounds. These results suggest that, (1) moderate-to-high levels of PAR alone during leaf development can induce substantial UV-protection in field-grown plants, (2) mature shade leaves have the potential to adjust their UV-shielding which may reduce the detrimental effects of UV that could occur following sudden exposures to high light and (3) under field conditions, PAR and UV play different roles in regulating UV-shielding during and after leaf development.