Physiological and biochemical responses involved in water deficit tolerance of nitrogen-fixing Vicia faba

Phenotyping revealed tolerance traits and genotypes for acidity and aluminum toxicity in European Vicia faba L

Soil acidity is a global issue; soils with pH <4.5 are widespread in Europe. This acidity adversely affects nutrient availability to plants; pH levels <5.0 lead to aluminum (Al3+) toxicity, a significant problem that hinders root growth and nutrient uptake in faba bean (Vicia faba L.) and its symbiotic relationship with Rhizobium. However, little is known about the specific traits and tolerant genotypes among the European faba beans. This study aimed to identify response traits associated with tolerance to root zone acidity and Al3+ toxicity and potentially tolerant genotypes for future breeding efforts. Germplasm survey was conducted using 165 genotypes in a greenhouse aquaponics system. Data on the root and shoot systems were collected. Subsequently, 12 genotypes were selected for further phenotyping in peat medium, where data on physiological and morphological parameters were recorded along with biochemical responses in four selected genotypes. In the germplasm survey, about 30% of genotypes showed tolerance to acidity and approximately 10% exhibited tolerance to Al3+, while 7% showed tolerance to both. The phenotyping experiment indicated diverse morphological and physiological responses among treatments and genotypes. Acid and Al3+ increased proline concentration. Interaction between genotype and environment was observed for ascorbate peroxidase activity, malondialdehyde, and proline concentrations. Genomic markers associated with acidity and acid+Al3+-toxicity tolerances were identified using GWAS analysis. Four faba bean genotypes with varying levels of tolerance to acidity and Al3+ toxicity were identified.

Strong Invasive Mechanism of Wedelia trilobata via Growth and Physiological Traits under Nitrogen Stress Condition

Nitrogen (N) is one of the most crucial elements for plant growth. However, a deficiency of N affects plant growth and development. Wedelia trilobata is a notorious invasive plant species that exhibits superior tolerance to adapt to environmental stresses. Yet, research on the growth and antioxidant defensive system of invasive Wedelia under low N stress, which could contribute to understanding invasion mechanisms, is still limited. Therefore, this study aims to investigate and compare the tolerance capability of invasive and native Wedelia under low and normal N conditions. Native and invasive Wedelia species were grown in normal and low-N conditions using a hydroponic nutrient solution for 8 weeks to assess the photosynthetic parameters, antioxidant activity, and localization of reactive oxygen species (ROS). The growth and biomass of W. trilobata were significantly (p < 0.05) higher than W. chinensis under low N. The leaves of W. trilobata resulted in a significant increase in chlorophyll a, chlorophyll b, and total chlorophyll content by 40.2, 56.2, and 46%, respectively, compared with W. chinensis. W. trilobata significantly enhanced antioxidant defense systems through catalase, peroxidase, and superoxide dismutase by 18.6%, 20%, and 36.3%, respectively, providing a positive response to oxidative stress caused by low N. The PCA analysis showed that W. trilobata was 95.3% correlated with physiological traits by Dim1 (79.1%) and Dim2 (16.3%). This study provides positive feedback on W. trilobata with respect to its comprehensive invasion mechanism to improve agricultural systems via eco-friendly approaches in N deficit conditions, thereby contributing to the reclamation of barren land.

Comparative transcriptome analysis of two contrasting genotypes provides new insights into the drought response mechanism in pigeon pea (Cajanus cajan L. Millsp.)

BACKGROUND

Despite plant's ability to adapt and withstand challenging environments, drought poses a severe threat to their growth and development. Although pigeon pea is already quite resistant to drought, the prolonged dehydration induced by the aberrant climate poses a serious threat to their survival and productivity.

OBJECTIVE

Comparative physiological and transcriptome analyses of drought-tolerant (CO5) and drought-sensitive (CO1) pigeon pea genotypes subjected to drought stress were carried out in order to understand the molecular basis of drought tolerance in pigeon pea.

METHODS

The transcriptomic analysis allowed us to examine how drought affects the gene expression of C. cajan. Using bioinformatics tools, the unigenes were de novo assembled, annotated, and functionally evaluated. Additionally, a homology-based sequence search against the droughtDB database was performed to identify the orthologs of the DEGs.

RESULTS

1102 potential drought-responsive genes were found to be differentially expressed genes (DEGs) between drought-tolerant and drought-sensitive genotypes. These included Abscisic acid insensitive 5 (ABI5), Nuclear transcription factor Y subunit A-7 (NF-YA7), WD40 repeat-containing protein 55 (WDR55), Anthocyanidin reductase (ANR) and Zinc-finger homeodomain protein 6 (ZF-HD6) and were highly expressed in the tolerant genotype. Further, GO analysis revealed that the most enriched classes belonged to biosynthetic and metabolic processes in the biological process category, binding and catalytic activity in the molecular function category and nucleus and protein-containing complex in the cellular component category. Results of KEGG pathway analysis revealed that the DEGs were significantly abundant in signalling pathways such as plant hormone signal transduction and MAPK signalling pathways. Consequently, in our investigation, we have identified and validated by qPCR a group of genes involved in signal reception and propagation, stress-specific TFs, and basal regulatory genes associated with drought response.

CONCLUSION

In conclusion, our comprehensive transcriptome dataset enabled the discovery of candidate genes connected to pathways involved in pigeon pea drought response. Our research uncovered a number of unidentified genes and transcription factors that could be used to understand and improve susceptibility to drought.

Bioinoculants as a means of increasing crop tolerance to drought and phosphorus deficiency in legume-cereal intercropping systems

Ensuring plant resilience to drought and phosphorus (P) stresses is crucial to support global food security. The phytobiome, shaped by selective pressures, harbors stress-adapted microorganisms that confer host benefits like enhanced growth and stress tolerance. Intercropping systems also offer benefits through facilitative interactions, improving plant growth in water- and P-deficient soils. Application of microbial consortia can boost the benefits of intercropping, although questions remain about the establishment, persistence, and legacy effects within resident soil microbiomes. Understanding microbe- and plant-microbe dynamics in drought-prone soils is key. This review highlights the beneficial effects of rhizobacterial consortia-based inoculants in legume-cereal intercropping systems, discusses challenges, proposes a roadmap for development of P-solubilizing drought-adapted consortia, and identifies research gaps in crop-microbe interactions.

Assessment of drought tolerance indices in faba bean genotypes under different irrigation regimes

Drought stress has devastating impacts on faba bean production, particularly with the current abrupt climate changes in arid environments. Hence, it is essential to identify drought-tolerant genotypes. The present study aimed at assessing six faba bean genotypes under three irrigation levels during two winter successive growing seasons (2018/2019 and 2019/2020). The applied irrigation levels were well-watered (every 4 days (D1), moderate drought every 8 days (D2), and severe drought 12 days (D3)) regimes. The analysis of variance exhibited highly significant differences among genotypes, irrigation treatments, and their interactions for all studied traits, except the number of pods plant−1 in the first season. Yield traits of all assessed genotypes decreased significantly with increasing drought stress. Otherwise, proline content (Pro) increased significantly with increasing drought stress. The genotypes Giza.843, Nubaria.2, and Nubaria.3 recorded the highest values of plant height, number of branches/plant, pods/plant, pods weight/plant, 100 seed weight, seed yield/plant, and seed yield/kg under drought stress. Similarly, the highest Pro was displayed by Giza.843 and Nubaria.3 under drought stress in both seasons. Furthermore, Giza.843, Nubaria.2, and Nubaria.3 genotypes had the highest values for most tolerant indices. Accordingly, these genotypes could be exploited in developing drought-tolerant and high-yielding faba bean genotypes in arid environments through breeding programs.

Wild Vicia Species Possess a Drought Tolerance System for Faba Bean Improvement

Faba bean (Vicia faba L.), a drought-sensitive crop, is drastically affected by drought stresses compromising its growth and yield. However, wild relatives of faba bean are considered a reservoir of potential genetic resources for tolerance against abiotic stresses. This study was conducted to characterize wild relatives of faba bean for identification of a specific tolerance system required for its improvement against drought stress. The study focused on physiological, biochemical, and anatomical responses of wild Vicia species under drought stress conditions. The experiment was carried out under various levels of drought stress imposed through different field capacities (FC) which included 80% FC ie (well-watered condition), 55% FC (moderate stress), and 30% FC (severe stress). When compared to plants grown in a control environment, drought stress significantly reduced the studied physiological attributes including soluble sugars (21.3% and 15.8%), protein contents (14.7 and 14.6%), and chlorophyll (8.4 and 28.6%) under moderate (55% FC) and severe drought stress (30% FC), respectively. However, proline content increased by 20.5% and 27.6%, peroxidase activity by 48.5% and 57.1%, and superoxide dismutase activity by 72.6% and 64.8% under moderate and severe stress, respectively. The studied anatomical attributes were also affected under drought stress treatments, including diameter of stem xylem vessels (9.1% and 13.7%), leaf lower epidermal thickness (8.05% and 13.34%), and leaf phloem width (5.3% and 10.1%) under moderate and severe stress, respectively. Wild Vicia spp. showed better tolerance to water-deficit conditions as compared to cultivated Vicia L. The observed potential diversity for drought tolerance in wild Vicia spp. may assist in improvement of faba bean and may also help in understanding the mechanisms of adaptations in drought-prone environments.

Physiological Responses to Drought, Salinity, and Heat Stress in Plants: A Review

On the world stage, the increase in temperatures due to global warming is already a reality that has become one of the main challenges faced by the scientific community. Since agriculture is highly dependent on climatic conditions, it may suffer a great impact in the short term if no measures are taken to adapt and mitigate the agricultural system. Plant responses to abiotic stresses have been the subject of research by numerous groups worldwide. Initially, these studies were concentrated on model plants, and, later, they expanded their studies in several economically important crops such as rice, corn, soybeans, coffee, and others. However, agronomic evaluations for the launching of cultivars and the classical genetic improvement process focus, above all, on productivity, historically leaving factors such as tolerance to abiotic stresses in the background. Considering the importance of the impact that abiotic stresses can have on agriculture in the short term, new strategies are currently being sought and adopted in breeding programs to understand the physiological, biochemical, and molecular responses to environmental disturbances in plants of agronomic interest, thus ensuring the world food security. Moreover, integration of these approaches is bringing new insights on breeding. We will discuss how water deficit, high temperatures, and salinity exert effects on plants.

Impact of Two Strains of Rhizobium leguminosarum on the Adaptation to Terminal Water Deficit of Two Cultivars Vicia faba

Drought stress has become one of the most uncontrolled and unpredictable constraints on crop production. The purpose of this study was to evaluate the impacts of two different Rhizobium leguminosarum strains on terminal drought tolerance induction in two faba bean genotypes cultivated in Algeria, Aquadulce and Maltais. To this end, we measured physiological parameters—osmoprotectants accumulation, oxidative stress markers and enzyme activities—to assess the effect of R. leguminosarum inoculation on V. faba under terminal water deficiency conditions in greenhouse trials. Upregulation of anti-oxidative mechanisms and production of compatible solutes were found differentially activated according to Rhizobium strain. Drought stress resilience of the Maltais variety was improved using the local Rhizobium strain OL13 compared to the common strain 3841. Symbiosis with OL13 strain leads in particular to a much better production of proline and soluble sugar in nodules but also in roots and leaves of Maltais plant. Even if additional work is still necessary to decipher the mechanism by which a Rhizobium strain can affect the accumulation of osmoprotectants or cellular redox status in all the plants, inoculation with selected Rhizobium could be a promising strategy for improving water stress management in the forthcoming era of climate change.

Chemical composition and reproductive functionality of contrasting faba bean genotypes in response to water deficit

Water deficit (WD), a major contributor to yield reductions in faba bean (Vicia faba), is a complex phenomenon that varies across daily to seasonal cycles. Several studies have identified various morphological and physiological indicators of WD tolerance, which generally show limited water use during WD. Limited information is available on the impact of WD on nutrient content and reproductive biology of the faba bean. We studied carbohydrates, amino acids, mineral nutrients and the abundance of naturally occurring carbon isotopes (δ¹³ C) in leaf and grain tissues of faba bean genotypes grown under well-watered (WW) and WD conditions. δ¹³ C of leaf tissues were found to indicate changes in water use due to WD but this was not reflected in grain tissues. Nutrient concentrations with regard to amino acids and minerals were not influenced by WD. However, carbohydrate accumulation was found to be significant for WD, specifically through the presence of a higher concentration of myo-inositol in WD leaf tissues. Alternatively, sucrose concentration in grain tissues was reduced under WD treatment. WD hampered reproductive functionality by reducing pollen viability and germination with the severity and duration of stress and this reduction was less prominent in the drought-tolerant genotype (AC0805#4912) compared to the sensitive one (11NF010c-4). It was also demonstrated that WD caused developmental impairment in the stamen and pistil, where the pistil appeared more sensitive than stamen. These findings suggest that WD impairs pollen viability and pistil function reducing yield volume, but the nutrient content of the resulting yield is not significantly affected.

Root Exudates Alter the Expression of Diverse Metabolic, Transport, Regulatory, and Stress Response Genes in Rhizosphere Pseudomonas

Plants live in association with microorganisms that positively influence plant development, vigor, and fitness in response to pathogens and abiotic stressors. The bulk of the plant microbiome is concentrated belowground at the plant root-soil interface. Plant roots secrete carbon-rich rhizodeposits containing primary and secondary low molecular weight metabolites, lysates, and mucilages. These exudates provide nutrients for soil microorganisms and modulate their affinity to host plants, but molecular details of this process are largely unresolved. We addressed this gap by focusing on the molecular dialog between eight well-characterized beneficial strains of the Pseudomonas fluorescens group and Brachypodium distachyon, a model for economically important food, feed, forage, and biomass crops of the grass family. We collected and analyzed root exudates of B. distachyon and demonstrated the presence of multiple carbohydrates, amino acids, organic acids, and phenolic compounds. The subsequent screening of bacteria by Biolog Phenotype MicroArrays revealed that many of these metabolites provide carbon and energy for the Pseudomonas strains. RNA-seq profiling of bacterial cultures amended with root exudates revealed changes in the expression of genes encoding numerous catabolic and anabolic enzymes, transporters, transcriptional regulators, stress response, and conserved hypothetical proteins. Almost half of the differentially expressed genes mapped to the variable part of the strains’ pangenome, reflecting the importance of the variable gene content in the adaptation of P. fluorescens to the rhizosphere lifestyle. Our results collectively reveal the diversity of cellular pathways and physiological responses underlying the establishment of mutualistic interactions between these beneficial rhizobacteria and their plant hosts.

Biochemical and Genetic Responses of Tea (Camellia sinensis (L.) Kuntze) Microplants under Mannitol-Induced Osmotic Stress In Vitro

Osmotic stress is a major factor reducing the growth and yield of many horticultural crops worldwide. To reveal reliable markers of tolerant genotypes, we need a comprehensive understanding of the responsive mechanisms in crops. In vitro stress induction can be an efficient tool to study the mechanisms of responses in plants to help gain a better understanding of the physiological and genetic responses of plant tissues against each stress factor. In the present study, the osmotic stress was induced by addition of mannitol into the culture media to reveal biochemical and genetic responses of tea microplants. The contents of proline, threonine, epigallocatechin, and epigallocatechin gallate were increased in leaves during mannitol treatment. The expression level of several genes, namely DHN2, LOX1, LOX6, BAM, SUS1, TPS11, RS1, RS2, and SnRK1.3, was elevated by 2–10 times under mannitol-induced osmotic stress, while the expression of many other stress-related genes was not changed significantly. Surprisingly, down-regulation of the following genes, viz. bHLH12, bHLH7, bHLH21, bHLH43, CBF1, WRKY2, SWEET1, SWEET2, SWEET3, INV5, and LOX7, was observed. During this study, two major groups of highly correlated genes were observed. The first group included seven genes, namely CBF1, DHN3, HXK2,SnRK1.1, SPS, SWEET3, and SWEET1. The second group comprised eight genes, viz. DHN2, SnRK1.3, HXK3, RS1, RS2,LOX6, SUS4, and BAM5. A high level of correlation indicates the high strength connection of the genes which can be co-expressed or can be linked to the joint regulons. The present study demonstrates that tea plants develop several adaptations to cope under osmotic stress in vitro; however, some important stress-related genes were silent or downregulated in microplants.

Alleviation of drought stress in faba bean (Vicia faba L.) by exogenous application of β-aminobutyric acid (BABA)

Drought stress is one of the most prevalent environmental factors limiting faba bean (Vicia faba L.) crop productivity. β-aminobutyric acid (BABA) is a non-protein amino acid that may be involved in the regulation of plant adaptation to drought stress. The effect of exogenous BABA application on physiological, biochemical and molecular responses of faba bean plants grown under 18% PEG-induced drought stress were investigated. The results showed that the application of 1 mM of BABA improved the drought tolerance of faba bean. The application of BABA increased the leaf relative water content, leaf photosynthesis rate (A), transpiration rate (E), and stomatal conductance (gs), thereby decreased the water use efficiency. Furthermore, exogenous application of BABA decreased production of hydrogen peroxide (H₂O₂), malondialdehyde and electrolyte leakage levels, leading to less cell membrane damage due to oxidative stress. Regarding osmoprotectants, BABA application enhanced the accumulation of proline, and soluble sugars, which could improve the osmotic adjustment ability of faba bean under drought challenge. Interestingly, mended antioxidant enzyme activities like catalase, guaiacol peroxidase, ascorbate peroxidase and superoxide dismutase and their transcript levels may lead to counteract the damaging effects of oxidative stress and reducing the accumulation of harmful substances in BABA-treated faba bean plants. In addition, exogenous BABA significantly induced the accumulation of drought tolerance-related genes like VfMYB, VfDHN, VfLEA, VfERF, VfNCED, VfWRKY, VfHSP and VfNAC in leaves and roots, suggesting that BABA might act as a signal molecule to regulate the expression of drought tolerance-related genes.

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.

Morphophysiological and biochemical response of mungbean [Vigna radiata (L.) Wilczek] varieties at different developmental stages under drought stress

The present study was conducted to assess the morphophysiological and biochemical responses during different developmental stages in mungbean varieties subjected to drought stress, and to screen the varieties for drought tolerance. A field experiment was performed according to a completely randomized design on 25 mungbean varieties with 3 replicates per variety. Stress treatment was applied at 3 levels: control (no stress), vegetative stage (25 days after sowing), and reproductive stage (35 days after sowing). According to combined analysis of variance, there were significant effects from drought stress on relative water content (RWC), membrane stability index (MSI), protein and proline content of leaves, leaf area, plant height, and yield traits. MSI, RWC, protein content, leaf area, plant height, and yield traits were decreased during drought stress, while proline content was increased under drought stress conditions. The results showed that the vegetative stage was more sensitive to drought stress, which was further supported by correlation analysis. Taken together, Vigna sublobata, MCV-1, PLM-32, LGG-407, LGG-450, TM-96-2, and Sattya varieties were identified as drought tolerant as they maintained the higher values of RWC, MSI, protein, proline content, leaf area, plant height, and yield traits. These varieties could be used in breeding programs for better physiological drought tolerance traits.

L-DOPA Trends in Different Tissues at Early Stages of Vicia faba Growth: Effect of Tyrosine Treatment

The nonprotein amino acid Levo-3,4-dihydroxyphenylalanine (L-DOPA) has insecticidal, allelochemical, and antiparkinsonian effects. The aim of this research was to assess L-DOPA content in different tissues of Vicia faba (cv. Super Agua Dulce), and to verify if treatment with the phenolic amino acid L-4-hydroxyphenylalanine (tyrosine) had an effect on such content. Under light germination, control and tyrosine-treated early seedling stages of V. faba were studied and L-DOPA was quantified spectrophotometrically (Arnow’s method) and by high-performance thin-layer chromatography (HPTLC), as well. Additionally, tyrosinase (TYROX) and guaiacol peroxidase (GPX) activities (considered markers of a phenolic compounds metabolism) were quantified as germination proceeded. Different organs (roots, sprouts, and seeds) and different developmental stages were considered. Steady high L-DOPA concentrations were found in untreated sprouts and roots compared to seeds, as time progressed. While TYROX activity was not detected in these experiments, GPX had diverse trends. In control tissues, GPX increased in seed tissue as germination progressed, whereas in roots and sprouts, a decreasing GPX activity was observed. Tyrosine exposure decreased L-DOPA content, and decreased or did not change GPX activity (depending on the organ). Both Arnow’s and HPTLC methods were consistent in terms of tendencies, except for the scarce contents found in seeds, in which HPTLC was more sensitive. The richest source of L-DOPA was found in shoots (untreated), reaching as high as 125 mg g−1 DW (12% in DW) (the highest content reported in fava bean seedlings until now), whereas the smallest L-DOPA content was found in seeds. The importance of light germination conditions is discussed in terms of L-DOPA yield and from a physiological perspective. It is concluded that V. faba (cv. Super Agua Dulce) shoots are a good source of L-DOPA and that tyrosine addition (0.55 mM) decreases L-DOPA content in actively growing tissues (shoots and roots).