Changes in Ecophysiology, Osmolytes, and Secondary Metabolites of the Medicinal Plants of Mentha piperita and Catharanthus roseus Subjected to Drought and Heat Stress

Mitigation of salinity stress in yarrow (Achillea millefolium L.) plants through spermidine application

This study investigated the mitigating effects of spermidine on salinity-stressed yarrow plants (Achillea millefolium L.), an economically important medicinal crop. Plants were treated with four salinity levels (0, 30, 60, 90 mM NaCl) and three spermidine concentrations (0, 1.5, 3 μM). Salinity induced electrolyte leakage in a dose-dependent manner, increasing from 22% at 30 mM to 56% at 90 mM NaCl without spermidine. However, 1.5 μM spermidine significantly reduced leakage across salinities by 1.35-11.2% relative to untreated stressed plants. Photosynthetic pigments (chlorophyll a, b, carotenoids) also exhibited salinity- and spermidine-modulated responses. While salinity decreased chlorophyll a, both spermidine concentrations increased chlorophyll b and carotenoids under most saline conditions. Salinity and spermidine synergistically elevated osmoprotectants proline and total carbohydrates, with 3 μM spermidine augmenting proline and carbohydrates up to 14.4% and 13.1% at 90 mM NaCl, respectively. Antioxidant enzymes CAT, POD and APX displayed complex regulation influenced by treatment factors. Moreover, salinity stress and spermidine also influenced the expression of linalool and pinene synthetase genes, with the highest expression levels observed under 90 mM salt stress and the application of 3 μM spermidine. The findings provide valuable insights into the responses of yarrow plants to salinity stress and highlight the potential of spermidine in mitigating the adverse effects of salinity stress.

Heat Stress and Microbial Stress Induced Defensive Phenol Accumulation in Medicinal Plant Sparganium stoloniferum

An approach based on the heat stress and microbial stress model of the medicinal plant Sparganium stoloniferum was proposed to elucidate the regulation and mechanism of bioactive phenol accumulation. This method integrates LC-MS/MS analysis, 16S rRNA sequencing, RT-qPCR, and molecular assays to investigate the regulation of phenolic metabolite biosynthesis in S. stoloniferum rhizome (SL) under stress. Previous research has shown that the metabolites and genes involved in phenol biosynthesis correlate to the upregulation of genes involved in plant-pathogen interactions. High-temperature and the presence of Pseudomonas bacteria were observed alongside SL growth. Under conditions of heat stress or Pseudomonas bacteria stress, both the metabolites and genes involved in phenol biosynthesis were upregulated. The regulation of phenol content and phenol biosynthesis gene expression suggests that phenol-based chemical defense of SL is stimulated under stress. Furthermore, the rapid accumulation of phenolic substances relied on the consumption of amino acids. Three defensive proteins, namely Ss4CL, SsC4H, and SsF3'5'H, were identified and verified to elucidate phenol biosynthesis in SL. Overall, this study enhances our understanding of the phenol-based chemical defense of SL, indicating that bioactive phenol substances result from SL's responses to the environment and providing new insights for growing the high-phenol-content medicinal herb SL.

Surviving a Double-Edged Sword: Response of Horticultural Crops to Multiple Abiotic Stressors

Climate change-induced weather events, such as extreme temperatures, prolonged drought spells, or flooding, pose an enormous risk to crop productivity. Studies on the implications of multiple stresses may vary from those on a single stress. Usually, these stresses coincide, amplifying the extent of collateral damage and contributing to significant financial losses. The breadth of investigations focusing on the response of horticultural crops to a single abiotic stress is immense. However, the tolerance mechanisms of horticultural crops to multiple abiotic stresses remain poorly understood. In this review, we described the most prevalent types of abiotic stresses that occur simultaneously and discussed them in in-depth detail regarding the physiological and molecular responses of horticultural crops. In particular, we discussed the transcriptional, posttranscriptional, and metabolic responses of horticultural crops to multiple abiotic stresses. Strategies to breed multi-stress-resilient lines have been presented. Our manuscript presents an interesting amount of proposed knowledge that could be valuable in generating resilient genotypes for multiple stressors.

Plant secondary metabolism in a fluctuating world: climate change perspectives

Climate changes have unpredictable effects on ecosystems and agriculture. Plants adapt metabolically to overcome these challenges, with plant secondary metabolites (PSMs) being crucial for plant-environment interactions. Thus, understanding how PSMs respond to climate change is vital for future cultivation and breeding strategies. Here, we review PSM responses to climate changes such as elevated carbon dioxide, ozone, nitrogen deposition, heat and drought, as well as a combinations of different factors. These responses are complex, depending on stress dosage and duration, and metabolite classes. We finally identify mechanisms by which climate change affects PSM production ecologically and molecularly. While these observations provide insights into PSM responses to climate changes and the underlying regulatory mechanisms, considerable further research is required for a comprehensive understanding.

DNA methylation regulates the secondary metabolism of saponins to improve the adaptability of Eleutherococcus senticosus during drought stress

Plant growth and development can be significantly impacted by drought stress. Plants will adjust the synthesis and accumulation of secondary metabolites to improve survival in times of water constraint. Simultaneously, drought stress can lead to modifications in the DNA methylation status of plants, and these modifications can directly impact gene expression and product synthesis by changing the DNA methylation status of functional genes involved in secondary metabolite synthesis. However, further research is needed to fully understand the extent to which DNA methylation modifies the content of secondary metabolites to mediate plants' responses to drought stress, as well as the underlying mechanisms involved. Our study found that in Eleutherococcus senticosus (E. senticosus), moderate water deprivation significantly decreased DNA methylation levels throughout the genome and at the promoters of EsFPS, EsSS, and EsSE. Transcription factors like EsMYB-r1, previously inhibited by DNA methylation, can re-bind to the EsFPS promotor region following DNA demethylation. This process promotes gene expression and, ultimately, saponin synthesis and accumulation. The increased saponin levels in E. senticosus acted as antioxidants, enhancing the plant's adaptability to drought stress.

Identification of Metabolites from Catharanthus roseus Leaves and Stem Extract, and In Vitro and In Silico Antibacterial Activity against Food Pathogens

The plant produced powerful secondary metabolites and showed strong antibacterial activities against food-spoiling bacterial pathogens. The present study aimed to evaluate antibacterial activities and to identify metabolites from the leaves and stems of Catharanthus roseus using NMR spectroscopy. The major metabolites likely to be observed in aqueous extraction were 2,3-butanediol, quinic acids, vindoline, chlorogenic acids, vindolinine, secologanin, and quercetin in the leaf and stem of the Catharanthus roseus. The aqueous extracts from the leaves and stems of this plant have been observed to be most effective against food spoilage bacterial strains, followed by methanol and hexane. However, leaf extract was observed to be most significant in terms of the content and potency of metabolites. The minimum inhibitory concentration (20 µg/mL) and bactericidal concentrations (35 g/mL) of leaf extract were observed to be significant as compared to the ampicillin. Molecular docking showed that chlorogenic acid and vindolinine strongly interacted with the bacterial penicillin-binding protein. The docking energies of chlorogenic acid and vindolinine also indicated that these could be used as food preservatives. Therefore, the observed metabolite could be utilized as a potent antibacterial compound for food preservation or to treat their illness, and further research is needed to perform.

Plant hormones and secondary metabolites under environmental stresses: Enlightening defense molecules

The climatic changes have great threats to sustainable agriculture and require efforts to ensure global food and nutritional security. In this regard, the plant strategic responses, including the induction of plant hormones/plant growth regulators (PGRs), play a substantial role in boosting plant immunity against environmental stress-induced adversities. In addition, secondary metabolites (SMs) have emerged as potential 'stress alleviators' that help plants to adapt against environmental stressors imposing detrimental impacts on plant health and survival. The introduction of SMs in plant biology has shed light on their beneficial effects in mitigating environmental crises. This review explores SMs-mediated plant defense responses and highlights the crosstalk between PGRs and SMs under diverse environmental stressors. In addition, genetic engineering approaches are discussed as a potential revenue to enhance plant hormone-mediated SM production in response to environmental cues. Thus, the present review aims to emphasize the significance of SMs implications with PGRs association and genetic approachability, which could aid in shaping the future strategies that favor agro-ecosystem compatibility under unpredictable environmental conditions.

Allelopathy and allelobiosis: efficient and economical alternatives in agroecosystems

Chemical interactions in plants often involve plant allelopathy and allelobiosis. Allelopathy is an ecological phenomenon leading to interference among organisms, while allelobiosis is the transmission of information among organisms. Crop failures and low yields caused by inappropriate management can be related to both allelopathy and allelobiosis. Therefore, research on these two phenomena and the role of chemical substances in both processes will help us to understand and upgrade agroecosystems. In this review, substances involved in allelopathy and allelobiosis in plants are summarized. The influence of environmental factors on the generation and spread of these substances is discussed, and relationships between allelopathy and allelobiosis in interspecific, intraspecific, plant-micro-organism, plant-insect, and mechanisms, are summarized. Furthermore, recent results on allelopathy and allelobiosis in agroecosystem are summarized and will provide a reference for the future application of allelopathy and allelobiosis in agroecosystem.

Study of the genetic variability of durum wheat (Triticum durum Desf.) in the face of combined stress: water and heat

The devastating effects and extent of abiotic stress on cereal production continue to increase globally, affecting food security in several countries, including Tunisia. Heat waves and the scarcity of rainfall strongly affect durum wheat yields. The present study aims to screen for tolerance to combined water and heat stresses in durum wheat at the juvenile stage. Three combined treatments were tested, namely: T0 (100% field capacity (FC) at 24 °C), T1 (50% FC at 30 °C), and T2 (25% FC at 35 °C). The screening was carried out based on morphological, physiological, and biochemical criteria. The results showed that the combined stress significantly affected all the measured parameters. The relative water content (RWC) decreased by 37.6% under T1 compared to T0. Quantum yield (Fv/m) and photosynthetic efficiency (Fv/0) decreased under severe combined stress (T2) by 37.15% and 37.22%, respectively. Under T2 stress, LT increased by 63.7%. A significant increase in osmoprotective solutes was also observed, including proline, which increased by 154.6% under T2. Correlation analyses of the combination of water and heat stress confirm that the traits RWC, chlorophyll b content, Fv/m, proline content, Fv/0 and leaf temperature can be used as reliable screening criteria for the two stresses combined. The principal component analysis highlighted that Aouija tolerates the two levels of stresses studied, while the genotypes Karim and Hmira are the most sensitive. The results show that the tolerance of durum wheat to combined water and heat stress involves several adaptation mechanisms proportional to the stress intensity.

The effect of environmental stressors on the anticancer potential of Amaranthus hypochondriacus aqueous extracts and fractions

Some Amaranthus species have been shown to have pharmacological properties such as activity against cancer, and it is also used as a traditional herbal medicine in many rural parts of the world. The (3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide assay was used as a screening tool to determine the approximate cell viability inhibitory concentrations of methanol and aqueous crude extracts of Amaranthus spp. The extracts were screened using small-cell lung cancer (H69V), hepatocellular carcinoma (HepG2/C3A) and non-cancerous kidney cells (Vero) cell lines. Viability was assessed following exposure to a series of concentrations of each extract and A. hypochondriacus showed cytotoxicity of 70.55 µg/mL against H69V with a Si index of 1.8. The fractionated aqueous extract of 40 °C-treated A. hypochondriacus under well-watered conditions had a higher viability inhibition on H69V and Vero cell lines compared to the A. caudatus, A. cruentus and A. spinosus crude extracts. In conclusion, A. hypochondriacus could serve as a potential source of anticancer phytoconstituents for drug development.

Sophora tonkinensis: response and adaptation of physiological characteristics, functional traits, and secondary metabolites to drought stress

The medicinal plant Sophora tonkinensis is a characteristic Chinese shrub of karst areas. The arid climate in karst areas produces high-quality S. tonkinensis; however, the mechanisms of drought tolerance are not clear, which restricts sustainable plantings of S. tonkinensis. This study involved a 20-day drought stress experiment with potted S. tonkinensis and threee soil water regimes: control (CK), mild drought (MDT), and severe drought (SDT). Plant morphology, biomass, physiological indicators, alkaloid content, and other changes under drought stress were monitored. The content of soluble sugars and proteins, and activity of antioxidant enzymes in leaves and roots were higher under drought than CK, indicating that S. tonkinensis is tolerant to osmotic stress in early drought stages. Content of matrine and oxymatrine increased gradually with increasing drought duration in the short term. The epidermis of S. tonkinensis leaves have characteristics of desert plants, including upper epidermal waxy layer, lower epidermal villi, and relatively sunken stomata, suggesting that S. tonkinensis has strong drought tolerance. In conclusion, drought stress changed the cell structure of S. tonkinensis, induced antioxidant enzyme activity and increased its resistance to drought.

The synergy of halotolerant PGPB and mauran mitigates salt stress in tomato (Solanum lycopersicum) via osmoprotectants accumulation

Salinity stress is one of the major abiotic factors limiting sustainable agriculture. Halotolerant plant growth-promoting bacteria (PGPB) increased salt stress tolerance in plants, but the mechanisms underlying the tolerance are poorly understood. This study investigated the PGP activity of four halotolerant bacteria under salinity stress and the tomato salt-tolerance mechanisms induced by the synergy of these bacteria with the exopolysaccharide (EPS) mauran. All PGPB tested in this study were able to offer a significant improvement of tomato plant biomass under salinity stress; Peribacillus castrilensis N3 being the most efficient one. Tomato plants treated with N3 and the EPS mauran showed greater tolerance to NaCl than the treatment in the absence of EPS and PGPB. The synergy of N3 with mauran confers salt stress tolerance in tomato plants by increasing sodium transporter genes' expression and osmoprotectant content, including soluble sugars, polyols, proline, GABA, phenols and the polyamine putrescine. These osmolytes together with the induction of sodium transporter genes increase the osmotic adjustment capacity to resist water loss and maintain ionic homeostasis. These findings suggest that the synergy of the halotolerant bacterium N3 and the EPS mauran could enhance tomato plant growth by mitigating salt stress and could have great potential as an inductor of salinity tolerance in the agriculture sector.

Synergistic effect of β-sitosterol and biochar application for improving plant growth of Thymus vulgaris under heat stress

Climate change has become the global concern due to its drastic effects on the environment. Agriculture sector is the backbone of food security which remains at the disposal of climate change. Heat stress is the is the most concerning effect of climate change which negatively affect the plant growth and potential yields. The present experiment was conducted to assess the effects of exogenously applied β-sitosterol (Bs at 100 mg/L) and eucalyptus biochar (Eb at 5%) on the antioxidants and nutritional status in Thymus vulgaris under heat stressed conditions. The pot experiment was conducted in completely randomize design in which thymus plants were exposed to heat stress (33 °C) and as a result, plants showed a substantial decline in morpho-physiological and biochemical parameters e.g., a reduction of 59.46, 75.51, 100.00, 34.61, 22.65, and 38.65% was found in plant height, shoot fresh weight, root fresh weight, dry shoot weight, dry root weight and leaf area while in Bs + Eb + heat stress showed 21.16, 56.81, 67.63, 23.09, 12.84, and 35.89% respectively as compared to control. In the same way photosynthetic pigments, transpiration rate, plant nutritional values and water potential increased in plants when treated with Bs and Eb in synergy. Application of Bs and Eb significantly decreased the electrolytic leakage of cells in heat stressed thymus plants. The production of reactive oxygen species was significantly decreased while the synthesis of antioxidants increased with the application of Bs and Eb. Moreover, the application Bs and Eb increased the concentration of minerals nutrients in the plant body under heat stress. Our results suggested that application of Bs along with Eb decreased the effect of heat stress by maintaining nutrient supply and enhanced tolerance by increasing the production of photosynthetic pigments and antioxidant activity.

Algal Bio-Stimulants Enhance Salt Tolerance in Common Bean: Dissecting Morphological, Physiological, and Genetic Mechanisms for Stress Adaptation

Salinity adversely affects the plant's morphological characteristics, but the utilization of aqueous algal extracts (AE) ameliorates this negative impact. In this study, the application of AE derived from Chlorella vulgaris and Dunaliella salina strains effectively reversed the decline in biomass allocation and water relations, both in normal and salt-stressed conditions. The simultaneous application of both extracts in salt-affected soil notably enhanced key parameters, such as chlorophyll content (15%), carotene content (1%), photosynthesis (25%), stomatal conductance (7%), and transpiration rate (23%), surpassing those observed in the application of both AE in salt-affected as compared to salinity stress control. Moreover, the AE treatments effectively mitigated lipid peroxidation and electrolyte leakage induced by salinity stress. The application of AE led to an increase in GB (6%) and the total concentration of free amino acids (47%) by comparing with salt-affected control. Additionally, salinity stress resulted in an elevation of antioxidant enzyme activities, including superoxide dismutase, ascorbate peroxidase, catalase, and glutathione reductase. Notably, the AE treatments significantly boosted the activity of these antioxidant enzymes under salinity conditions. Furthermore, salinity reduced mineral contents, but the application of AE effectively counteracted this decline, leading to increased mineral levels. In conclusion, the application of aqueous algal extracts, specifically those obtained from Chlorella vulgaris and Dunaliella salina strains, demonstrated significant efficacy in alleviating salinity-induced stress in Phaseolus vulgaris plants.

Unlocking secrets of nature's chemists: Potential of CRISPR/Cas-based tools in plant metabolic engineering for customized nutraceutical and medicinal profiles

Plant species have evolved diverse metabolic pathways to effectively respond to internal and external signals throughout their life cycle, allowing adaptation to their sessile and phototropic nature. These pathways selectively activate specific metabolic processes, producing plant secondary metabolites (PSMs) governed by genetic and environmental factors. Humans have utilized PSM-enriched plant sources for millennia in medicine and nutraceuticals. Recent technological advances have significantly contributed to discovering metabolic pathways and related genes involved in the biosynthesis of specific PSM in different food crops and medicinal plants. Consequently, there is a growing demand for plant materials rich in nutrients and bioactive compounds, marketed as "superfoods". To meet the industrial demand for superfoods and therapeutic PSMs, modern methods such as system biology, omics, synthetic biology, and genome editing (GE) play a crucial role in identifying the molecular players, limiting steps, and regulatory circuitry involved in PSM production. Among these methods, clustered regularly interspaced short palindromic repeats-CRISPR associated protein (CRISPR/Cas) is the most widely used system for plant GE due to its simple design, flexibility, precision, and multiplexing capabilities. Utilizing the CRISPR-based toolbox for metabolic engineering (ME) offers an ideal solution for developing plants with tailored preventive (nutraceuticals) and curative (therapeutic) metabolic profiles in an ecofriendly way. This review discusses recent advances in understanding the multifactorial regulation of metabolic pathways, the application of CRISPR-based tools for plant ME, and the potential research areas for enhancing plant metabolic profiles.

The phenotypic variation mechanisms of Atractylodes lancea post-cultivation revealed by conjoint analysis of rhizomic transcriptome and metabolome

The wild Atractylodes lancea rhizomes have been traditionally used as herbal medicine. As the increasingly exhaustion of wild A. lancea, the artificial cultivation mainly contributed to the medicinal material production. However, besides the phenotypic variation of rhizome phenotypic trait alteration, the qualities of cultivated A. lancea decrease compared with the wild counterpart. To unveil the physiological and molecular mechanism beneath the phenotypic variation, GC-MS-based volatile organic compounds (VOCs) profiling and RNAseq-based transcriptome analysis were conducted. The volatile metabolomics profiling revealed 65 differentially accumulated metabolites (DAMs) while the transcriptomic profiling identified 12 009 differentially expressed unigenes (DEGs) post-cultivation. The volatile active compounds including atractylone, and eudesmol accumulated more in wild rhizome than in the cultivated counterpart, and several unigenes in terpene synthesis were downregulated under cultivated condition. Compared with the wild A. lancea rhizome, the contents of bioactive Jasmonic Acid (JAs) in cultivated A. lancea rhizome were higher, and evidences that JAs negatively regulate the terpenes biosynthesis in the cultivated A. lancea rhizome were also provided. The combinational omics analysis further indicated the high correlation between the ten cultivation-suppressed VOCs and the cultivation-altered genes for sesquiterpenoids biosynthesis in A. lancea. The network of the cultivation-altered transcription factors (TFs) and the ten VOCs suggested TFs (e.g. Arabidopsis ERF13 homologs and WRKY50) are involved in the regulation of terpenes biosynthesis. These results laid a theoretical basis for developing geo-herbalism medicinal plants with "high quality and optimal shape".

Investigating high throughput phenotyping based morpho-physiological and biochemical adaptations of indian pennywort (Centella asiatica L. urban) in response to different irrigation regimes

Indian pennywort (Centella asiatica L. Urban; Apiaceae) is a herbaceous plant used as traditional medicine in several regions worldwide. An adequate supply of fresh water in accordance with crop requirements is an important tool for maintaining the productivity and quality of medicinal plants. The objective of this study was to find a suitable irrigation schedule for improving the morphological and physiological characteristics, and crop productivity of Indian pennywort using high-throughput phenotyping. Four treatments were considered based on irrigation schedules (100, 75, 50, and 25% of field capacity denoted by I100 [control], I75, I50, and I25, respectively). The number of leaves, plant perimeter, plant volume, and shoot dry weight were sustained in I75 irrigated plants, whereas adverse effects on plant growth parameters were observed when plants were subjected to I25 irrigation for 21 days. Leaf temperature (Tleaf) was also retained in I75 irrigated plants, when compared with control. An increase of 2.0 °C temperature was detected in the Tleaf of plants under I25 irrigation treatment when compared with control. The increase in Tleaf was attributed to a decreased transpiration rate (R2 = 0.93), leading to an elevated crop water stress index. Green reflectance and leaf greenness remained unchanged in plants under I75 irrigation, while significantly decreased under I50 and I25 irrigation. These decreases were attributed to declined leaf osmotic potential, increased non-photochemical quenching, and inhibition of net photosynthetic rate (Pn). The asiatic acid and total centellosides in the leaf tissues, and centellosides yield of plants under I75 irrigation were retained when compared with control, while these parameters were regulated to maximal when exposed to I50 irrigation. Based on the results, I75 irrigation treatment was identified as the optimum irrigation schedule for Indian pennywort in terms of sustained biomass and a stable total centellosides. However, further validation in the field trials at multiple locations and involving different crop rotations is recommended to confirm these findings.

The biochemical properties of Rosmarinus officinalis L. affected by irrigation water amount and quality

Water deficiency, especially in the arid and semi-arid areas, necessitates the proper water use and recycling. The objective was to investigate the effects of deficit irrigation as well as treated wastewater on the biochemical properties of Rosmarinus officinalis L., grown in the arid area of Iranshahr, Iran. A split-split plot design on the basis of a complete randomized block design with three replicates was conducted in 2017. Irrigation water treatments of (I1 = 100% of field capacity, FC), 75% of FC (I2), and 50% of FC (I3) as main plots, reduced (S1), and partial irrigation (S2), as sub-plots, and well water (Q1), treated wastewater (Q2), and the combination of Q1 and Q2 (Q3, 50% + 50%), as sub-sub plots, were tested. Plant biochemical properties including proline (Pr), soluble sugars (SS), and essential oil volume (V) and yield (Y) as well as water use efficiency (WUE) were determined. The I2, treatment, compared with I1, increased Pr, SS, V, Y and WUE by 34.4, 31.9, 52.6, 34.3, and 48.1%, respectively. The S2 treatment also increased plant biochemical properties more than 45% related to S1, and Q2 significantly enhanced the measured parameters compared with Q1 and Q3. Treated wastewater improved the essential oil yield of the plant in water deficit conditions. Accordingly, under deficit water conditions, treatment I2S2, and in the case of unfavorable water sources and deficit water conditions, treatment I2Q2 are recommendable to alleviate water stress and improve the biochemical properties of Rosmarinus officinalis L. in the arid areas.

When drought meets heat - a plant omics perspective

Changes in weather patterns with emerging drought risks and rising global temperature are widespread and negatively affect crop growth and productivity. In nature, plants are simultaneously exposed to multiple biotic and abiotic stresses, but most studies focus on individual stress conditions. However, the simultaneous occurrence of different stresses impacts plant growth and development differently than a single stress. Plants sense the different stress combinations in the same or in different tissues, which could induce specific systemic signalling and acclimation responses; impacting different stress-responsive transcripts, protein abundance and modifications, and metabolites. This mini-review focuses on the combination of drought and heat, two abiotic stress conditions that often occur together. Recent omics studies indicate common or independent regulators involved in heat or drought stress responses. Here, we summarize the current research results, highlight gaps in our knowledge, and flag potential future focus areas.

Influence of drought stress and mycorrhizal (Funneliformis mosseae) symbiosis on growth parameters, chlorophyll fluorescence, antioxidant activity, and essential oil composition of summer savory (Satureja hortensis L.) plants

Introduction

Drought stress unfavorably influences the growth and physiological traits of plants in the arid and semi-arid regions of the world. This study aimed to determine the effects of arbuscular mycorrhiza fungi (AMF; Funneliformis mosseae) inoculation on the physiological and biochemical responses of summer savory (Satureja hortensis L.) under different irrigation regimes.

Methods

The first factor was different irrigation regimes, including no drought stress (100% field capacity; FC), moderate drought stress (60% FC), and severe drought stress (30% FC); the second factor included the plants without AMF (AMF₀) and with AMF inoculation (AMF₁).

Results

The results showed that better values, higher plant height, shoot mass (fresh and dry weight), relative water content (RWC), membrane stability index (MSI), photosynthesis pigments, Fv, Fm, Fv/Fm, and total soluble proteins were obtained in the plants inoculated with AMF. The highest values were obtained for plants with no drought stress, then the plants subjected to AMF₁ under 60% FC, and the lowest ones for plants under 30% FC without AMF inoculation. Thus, these properties are reduced under moderate and severe drought stress. At the same time, the utmost activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and the highest malondialdehyde (MDA), H₂O₂, proline, and antioxidant activity (TAA) were achieved for 30% FC + AMF₀. It was also found that AMF inoculation improved essential oil (EO) composition, also as EO obtained from plants under drought stress. Carvacrol (50.84-60.03%) was the dominant component in EO; γ-terpinene (19.03-27.33%), p-cymene, α-terpinene, and myrcene, were recognized as other important components in EO. The higher carvacrol and γ-terpinene contents were obtained from summer savory plants with AMF inoculation and the lowest for plants without AMF and under 30% FC.

Conclusion

According to the present findings, using AMF inoculation could be a sustainable and eco-friendly approach to improve physiological and biochemical characteristics and the essential oil quality of summer savory plants under water shortage conditions.

Conferring of Drought and Heat Stress Tolerance in Wheat (Triticum aestivum L.) Genotypes and Their Response to Selenium Nanoparticles Application

In this study, the role of selenium nanoparticles (SeNPs, 10 mg·L^-1) has been investigated in modulating the negative effects of drought and heat stresses on eight bread wheat (Triticum aestivum L.) genotype seedlings. Those genotypes included Giza-168, Giza-171, Misr-1, Misr-3, Shandweel-1, Sids-1, Sids-12, and Sids-14. The study included six treatments as follows: regular irrigation with 100% Field Capacity (FC) at a temperature of 23 ± 3 °C (T1), drought stress with 60% FC (T2), heat stress of 38 °C for 5 h·day^-1 (T3), foliar spray of 10 mg·L^-1 of SeNPs only (T4), a combination of drought stress with foliar spray of 10 mg·L^-1 of SeNPs (T5), and heat stress with foliar spray of 10 mg·L^-1 of SeNPs (T6). The experiment continued for 31 days. Foliar application of SeNPs improved the plant growth, morpho-physiological and biochemical responses, and expression of stress-responsive genes in wheat (T. aestivum L.) seedlings. Overall, morpho-physiological traits such as plant height (PH), shoot fresh weight (SFW), shoot dry weight (SDW), root fresh weight (RFW), and root dry weight (RDW) of wheat genotypes grown under different conditions ranged from 25.37-51.51 cm, 3.29-5.15 g, 0.50-1.97 g, 0.72-4.21 g, and 0.11-1.23 g, respectively. From the morpho-physiological perspective, drought stress had a greater detrimental impact on wheat plants than heat stress, whereas heat stress significantly impacted the expression of stress-responsive genes. Stress responses to drought and heat varied between wheat genotypes, suggesting that different genotypes are more resilient to stress. Exogenous spraying of 10 mg·L^-1 of SeNPs improved the photosynthetic pigments, photosynthetic rate, gas exchange, and transpiration rate of wheat plants and enhanced drought and heat tolerance by increasing the activity of antioxidant enzymes including catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) and the expression level of stress-responsive genes. Our results showed that spraying wheat seedlings with 10 mg·L^-1 of SeNPs enhanced SOD activity for all genotypes as compared to the control, with the Sids-12 genotype having the highest value (196.43 U·mg^-1 FW·min^-1) and the Giza-168 genotype having the lowest (152.30 U·mg^-1 FW·min^-1). The expression of PIP1, LEA-1, HSP70, and HSP90 stress-responsive genes was more significant in tolerant genotypes (Giza-171 and Giza-168) than in sensitive ones (Misr-1 and Misr-3) in response to drought and heat stresses. Under stress conditions, the shoot and root fresh weights, photosynthetic pigment content, stomatal conductance (SC), and transpiration rate (TR) were positively correlated with plant height (PH), while root and shoot dry weights, malondialdehyde (MDA), proline, hydrogen peroxide (H₂O₂), and APX were negatively correlated. Multivariate analysis and biplot results revealed that genotypes Giza-168, Giza-171, Sids-12, and Sids-14 performed well in both stress situations and were classified as stress-tolerant genotypes. These best genotypes may be employed in future breeding projects as tools to face climate change. This study concluded that various physio-biochemicals and gene expression attributes under drought and heat stress could be modulated by foliar application of SeNPs in wheat genotypes, potentially alleviating the adverse effects of drought and heat stress.

Influence of Drought and Heat Stress on Mineral Content, Antioxidant Activity and Bioactive Compound Accumulation in Four African Amaranthus Species

Drought and heat stress is known to influence the accumulation of mineral content, antioxidant activity, phenolics, flavonoids and other bioactive compounds in many tolerant leafy vegetables. Amaranthus plants can tolerate adverse weather conditions, especially drought and heat. Therefore, evaluating the influence of drought and heat stress on commercially and medically important crop species like Amaranthus is important to grow the crop for optimal nutritional and medicinal properties. This study investigated the influence of drought and heat stress and a combination of both on the accumulation of phenolic and flavonoid compounds and the antioxidant capacity of African Amaranthus caudatus, A. hypochondriacus, A. cruentus and A. spinosus. Phenolic and flavonoid compounds were extracted with methanol and aqueous solvents and were quantified using liquid chromatography with tandem mass spectrometry (LC-MS/MS). Caffeic acid was the main phenolic compound identified in aqueous extracts of A. caudatus and A. hypochondriacus. Rutin was the most abundant flavonoid compound in all the Amaranthus species tested, with the highest concentration found in A. caudatus. The results suggest a strong positive, but species and compound-specific effect of drought and heat stress on bioactive compounds accumulation. We concluded that heat stress at 40 °C under well-watered conditions and combined drought and heat stress (at 30 °C and 35 °C) appeared to induce the accumulation of caffeic acid and rutin. Hence, cultivation of these species in semi-arid and arid areas is feasible.

Plant secondary metabolic responses to global climate change: A meta-analysis in medicinal and aromatic plants

Plant secondary metabolites (SMs) play crucial roles in plant-environment interactions and contribute greatly to human health. Global climate changes are expected to dramatically affect plant secondary metabolism, yet a systematic understanding of such influences is still lacking. Here, we employed medicinal and aromatic plants (MAAPs) as model plant taxa and performed a meta-analysis from 360 publications using 1828 paired observations to assess the responses of different SMs levels and the accompanying plant traits to elevated carbon dioxide (eCO₂ ), elevated temperature (eT), elevated nitrogen deposition (eN) and decreased precipitation (dP). The overall results showed that phenolic and terpenoid levels generally respond positively to eCO₂ but negatively to eN, while the total alkaloid concentration was increased remarkably by eN. By contrast, dP promotes the levels of all SMs, while eT exclusively exerts a positive influence on the levels of phenolic compounds. Further analysis highlighted the dependence of SM responses on different moderators such as plant functional types, climate change levels or exposure durations, mean annual temperature and mean annual precipitation. Moreover, plant phenolic and terpenoid responses to climate changes could be attributed to the variations of C/N ratio and total soluble sugar levels, while the trade-off supposition contributed to SM responses to climate changes other than eCO₂ . Taken together, our results predicted the distinctive SM responses to diverse climate changes in MAAPs and allowed us to define potential moderators responsible for these variations. Further, linking SM responses to C-N metabolism and growth-defence balance provided biological understandings in terms of plant secondary metabolic regulation.

Interactions between hydrogen sulphide and rhizobia modulate the physiological and metabolism process during water deficiency-induced oxidative defense in soybean

Hydrogen sulphide (H₂ S), a new gas signal molecule, participates in the regulation of various abiotic stresses in plants. However, how the tandem working of H₂ S and rhizobia affects the adaptation of soybean to water deficiency is still unclear. In this study, we investigated the adaptation mechanism of H₂ S and rhizobia in soybean to water deficiency. Our results revealed that H₂ S and rhizobia jointly enhanced the leaf chlorophyll content and relative water content in plants, and caused an increase in the biomass of soybean seedlings under water deficiency. Besides, in the absence of water, H₂ S enhanced the biomass by affecting the number of nodules and nitrogenase activity during vegetative growth. The expression of nodulation marker genes including early nodulin 40 (GmENOD40), ERF required for nodulation (GmERN) and nodulation inception genes (GmNIN1a, GmNIN2a and GmNIN2b) were upregulated by H₂ S and rhizobia in the nodules. Moreover, the combined effect of H₂ S and rhizobia was proved to affect the enzyme activities and gene expression level of antioxidants, as well as osmotic protective substance content and related gene expression levels under water deficiency in soybean seedlings. In addition, the metabolomic results suggested that the combined effect of H₂ S and rhizobia remarkably promoted the contents of lipids and lipid-like molecules. Our results indicated that H₂ S and rhizobia synergistically reduced the oxidative damage caused by water deficiency through increasing the accumulation of metabolites and strengthening the plant antioxidant capacity.

Versatile roles of polyamines in improving abiotic stress tolerance of plants

In recent years, extreme environmental cues such as abiotic stresses, including frequent droughts with irregular precipitation, salinity, metal contamination, and temperature fluctuations, have been escalating the damage to plants' optimal productivity worldwide. Therefore, yield maintenance under extreme events needs improvement in multiple mechanisms that can minimize the influence of abiotic stresses. Polyamines (PAs) are pivotally necessary for a defensive purpose under adverse abiotic conditions, but their molecular interplay in this remains speculative. The PAs' accretion is one of the most notable metabolic responses of plants under stress challenges. Recent studies reported the beneficial roles of PAs in plant development, including metabolic and physiological processes, unveiling their potential for inducing tolerance against adverse conditions. This review presents an overview of research about the most illustrious and remarkable achievements in strengthening plant tolerance to drought, salt, and temperature stresses by the exogenous application of PAs. The knowledge of underlying processes associated with stress tolerance and PA signaling pathways was also summarized, focusing on up-to-date evidence regarding the metabolic and physiological role of PAs with exogenous applications that protect plants under unfavorable climatic conditions. Conclusively, the literature proposes that PAs impart an imperative role in abiotic stress tolerance in plants. This implies potentially important feedback on PAs and plants' stress tolerance under unfavorable cues.

Advances in Plant Metabolomics and Its Applications in Stress and Single-Cell Biology

In the past two decades, the post-genomic era envisaged high-throughput technologies, resulting in more species with available genome sequences. In-depth multi-omics approaches have evolved to integrate cellular processes at various levels into a systems biology knowledge base. Metabolomics plays a crucial role in molecular networking to bridge the gaps between genotypes and phenotypes. However, the greater complexity of metabolites with diverse chemical and physical properties has limited the advances in plant metabolomics. For several years, applications of liquid/gas chromatography (LC/GC)-mass spectrometry (MS) and nuclear magnetic resonance (NMR) have been constantly developed. Recently, ion mobility spectrometry (IMS)-MS has shown utility in resolving isomeric and isobaric metabolites. Both MS and NMR combined metabolomics significantly increased the identification and quantification of metabolites in an untargeted and targeted manner. Thus, hyphenated metabolomics tools will narrow the gap between the number of metabolite features and the identified metabolites. Metabolites change in response to environmental conditions, including biotic and abiotic stress factors. The spatial distribution of metabolites across different organs, tissues, cells and cellular compartments is a trending research area in metabolomics. Herein, we review recent technological advancements in metabolomics and their applications in understanding plant stress biology and different levels of spatial organization. In addition, we discuss the opportunities and challenges in multiple stress interactions, multi-omics, and single-cell metabolomics.

Toxicity analysis of TNT to alfalfa's mineral nutrition and secondary metabolism

Alfalfa has the ability to degrade TNT. TNT exposure caused root disruption of mineral nutrient metabolism. The exposure of TNT imbalanced basal cell energy metabolism. The mechanism of 2,4,6-trinitrotoluene (TNT) toxicity effects was analyzed in alfalfa (Medicago sativa L.) seedlings by examining the mineral nutrition and secondary metabolism of the plant roots. Exposure to 25-100 mg·L^-1 TNT in a hydroponic solution for 72 h resulted in a TNT absorption rate of 26.8-63.0%. The contents of S, K, and B in root mineral nutrition metabolism increased significantly by 1.70-5.46 times, 1.38-4.01 times, and 1.40-4.03 times, respectively, after TNT exposure. Non-targeted metabolomics analysis of the roots identified 189 significantly upregulated metabolites and 420 significantly downregulated metabolites. The altered metabolites were primarily lipids and lipid-like molecules, and the most significant enrichment pathways were alanine, aspartate, and glutamate metabolism and glycerophospholipid metabolism. TNT itself was transformed in the root system into several intermediate products, including 4-hydroxylamino-2,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene, 2-hydroxylamino-4,6-dinitrotoluene, 2,4',6,6'-tetranitro-2',4-azoxytoluene, 4,4',6,6'-tetranitro-2,2'-azoxytoluene, and 2,4-dinitrotoluene. Overall, TNT exposure disturbed the mineral metabolism balance, and significantly interfered with basic plant metabolism.

Ultraviolet-B Irradiation Increases Antioxidant Capacity of Pakchoi (Brassica rapa L.) by Inducing Flavonoid Biosynthesis

As an important abiotic stress factor, ultraviolet-B (UV-B) light can stimulate the accumulation of antioxidants in plants. In this study, the possibility of enhancing antioxidant capacity in pakchoi (Brassica rapa L.) by UV-B supplementation was assessed. Irradiation with 4 µmol·m⁻²·s⁻¹ UV-B for 4 h or 2 µmol·m⁻²·s⁻¹ UV-B for 24 h significantly increased the 1,1–diphenyl–2–picrylhydrazyl (DPPH) scavenging activity and total reductive capacity, as a result of inducing a greater accumulation of total polyphenols and flavonoids without affecting the plant biomass. A high performance liquid chromatography (HPLC) analysis showed that the concentrations of many flavonoids significantly increased in response to UV-B treatment. The activities of three enzymes involved in the early steps of flavonoid biosynthesis, namely phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxylase (C4H), and 4-coumarate: coenzyme A (CoA) ligase (4CL), were significantly increased after the corresponding UV-B treatment. Compared with the control, the expression levels of several flavonoid biosynthesis genes (namely BrPAL, BrC4H, Br4CL, BrCHS, BrF3H, BrF3′H, BrFLS, BrDFR, BrANS, and BrLDOX) were also significantly up–regulated in the UV-B treatment group. The results suggest that appropriate preharvest UV-B supplementation could improve the nutritional quality of greenhouse-grown pakchoi by promoting the accumulation of antioxidants.

Improvement of Phytopharmaceutical and Alkaloid Production in Periwinkle Plants by Endophyte and Abiotic Elicitors

Periwinkle plant represents a major source of immensely vital terpenoid indole alkaloids and natural antioxidants which are widely used in cancer chemotherapy. A pot experiment was done to evaluate the role of two periwinkle endophytes (Streptomyces sp. and Bacillus sp.) with or without abiotic elicitors (aluminum chloride, tryptophan, and chitosan) on plant biomass, physio-biochemical attributes, phytopharmaceutical constituents, and alkaloid production. Inoculation with endophyte microbes significantly increased plant growth, nitrogen, phosphorus, potassium, carotenoids, ascorbic acid, and alkaloid yield. It also decreased oxidative biomarkers (hydrogen peroxide and malondialdehyde) and had no significant effects on flavonoids and anthocyanin. In this regard, Streptomyces sp. was more effective than Bacillus sp. Foliar spraying with chitosan significantly increased plant growth, chlorophyll, ions, antioxidant capacity, phytopharmaceutical constituents (total soluble phenols, flavonoids, and anthocyanin), and alkaloid yield, associated with a decline in oxidative biomarkers. Conversely, aluminum chloride application generally increased oxidative biomarkers, which was associated with a decreasing effect on plant growth, chlorophyll, and ions. Application of either tryptophan or chitosan with endophyte microbes increased plant growth, chlorophyll, ions, antioxidants, and alkaloid; meanwhile, it decreased oxidative biomarkers. On the contrary, aluminum chloride with endophytes evoked oxidative damage that was associated with a reduction in plant growth, chlorophyll, ions, and phytopharmaceutical constituents. The current study provides a proof-of-concept of the use of the endophyte Streptomyces sp. with chitosan for enhancing periwinkle plant biomass, phytopharmaceuticals accumulation, and alkaloid production.

Exogenous citric acid enhances drought tolerance in tobacco (Nicotiana tabacum)

Organic acids play a pivotal role in improving plant response to long-term drought stress. External application of organic acids has been reported to improve drought resistance in several species. However, whether organic acids have similar effects in tobacco remains unknown. A screening study of the protective function of organic acids in tobacco and understanding the underlying molecular mechanism would be useful in developing a strategy for drought tolerance. Several physiological and molecular adaptations to drought including abscisic acid, stomatal closure, reactive oxygen species homeostasis, amino acid accumulation, and drought-responsive gene expression were observed by exogenous citric acid in tobacco plants. Exogenous application of 50 mm citric acid to tobacco plants resulted in higher chlorophyll content, net photosynthesis, relative water content, abscisic acid content and lower stomatal conductance, transpiration and water loss under drought conditions. Moreover, reactive oxygen species homeostasis was better maintained through increasing activity of antioxidant enzymes and decreasing hydrogen peroxide content after citric acid pretreatment under drought. Amino acids involved in the TCA cycle accumulated after external application of citric acid under drought stress. Furthermore, several drought stress-responsive genes also dramatically changed after application of citric acid. These data support the idea that external application of citric acid enhances drought resistance by affecting physiological and molecular regulation in tobacco. This study provides clear insights into mechanistic details of regulation of amino acid and stress-responsive gene expression by citric acid in tobacco in response to drought, which is promising for minimizing growth inhibition in agricultural fields.

'Omics' approaches in developing combined drought and heat tolerance in food crops

Global climate change will significantly increase the intensity and frequency of hot, dry days. The simultaneous occurrence of drought and heat stress is also likely to increase, influencing various agronomic characteristics, such as biomass and other growth traits, phenology, and yield-contributing traits, of various crops. At the same time, vital physiological traits will be seriously disrupted, including leaf water content, canopy temperature depression, membrane stability, photosynthesis, and related attributes such as chlorophyll content, stomatal conductance, and chlorophyll fluorescence. Several metabolic processes contributing to general growth and development will be restricted, along with the production of reactive oxygen species (ROS) that negatively affect cellular homeostasis. Plants have adaptive defense strategies, such as ROS-scavenging mechanisms, osmolyte production, secondary metabolite modulation, and different phytohormones, which can help distinguish tolerant crop genotypes. Understanding plant responses to combined drought/heat stress at various organizational levels is vital for developing stress-resilient crops. Elucidating the genomic, proteomic, and metabolic responses of various crops, particularly tolerant genotypes, to identify tolerance mechanisms will markedly enhance the continuing efforts to introduce combined drought/heat stress tolerance. Besides agronomic management, genetic engineering and molecular breeding approaches have great potential in this direction.

Expression profiling of rosmarinic acid biosynthetic genes and some physiological responses from Mentha piperita L. under salinity and heat stress

Peppermint is of great economic importance, mainly due to its valuable essential oils. The present study aimed to compare the expression level of genes coding for proteins involved in the rosmarinic acid biosynthesis pathway and some physiological responses in peppermint under three levels of salinity (0, 60 and 120 mM) and two levels of thermal stresses (at 25 °C, optimal plant heat, and 35 °C, for thermal stress). The results showed that salinity at 25 °C resulted in an increased relative level of phenolic compounds, proline and antioxidant activity by 1.88, 1.92 and 2.58 times after 72 h respectively at salinity of 120 mM. Rosmarinic acid as well as soluble sugar, chlorophyll and K⁺/N⁺ ratio showed a decreasing trend by 3.2, 1.8, 4.6 and 9 times after 72 h respectively at salinity of 120 mM at 35 °C. Gene expression analysis showed a significant increase in HPPR and C4H expression and a significant decrease in RAS expression in plants subjected to simultaneous stresses. The higher levels of C4H and HPPR expression indicate the roles of these genes in defense processes and the effects of phenolic compounds in inhibiting oxidative stress. Our results may help increase knowledge about the stress-dependent alterations in gene expression profiles and physiological patterns in plants. This information may be used for medicinal plant improvement programs aimed at increasing rosmarinic acid production.

Specialized metabolites: Physiological and biochemical role in stress resistance, strategies to improve their accumulation, and new applications in crop breeding and management

Specialized plant metabolites (SPMs), traditionally referred to as 'secondary metabolites', are chemical compounds involved in a broad range of biological functions, including plant responses to abiotic and biotic stresses. Moreover, some of them have a role in end-product quality with potential health benefits in humans. For this reason, they became an important target of studies focusing on their mechanisms of action and use in crop breeding and management. In this review we summarize the specific role of SPMs in physiological processes and in plant resistance to abiotic and biotic stresses, and the different strategies to enhance their production/accumulation in plant tissues under stress, including genetic approaches (marker-assisted selection and biotechnological tools) and agronomic management (fertilizer applications, cultivation method and beneficial microorganisms). New crop management strategies based on the direct application of the most promising compounds in form of plant residuals or liquid formulations are also described.

Generous Hosts: 'Candidatus Liberibacter asiaticus' Growth in Madagascar Periwinkle (Catharanthus roseus) Highlights Its Nutritional Needs

'Candidatus Liberibacter asiaticus', the putative causal agent of citrus greening, is not available in pure culture yet. In addition to trees of citrus and citrus relatives, 'Ca. L. asiaticus' can grow in Madagascar periwinkle (Catharanthus roseus). Using gas chromatography-mass spectrometry, we compared the phloem sap composition in sweet orange 'Valencia' (Citrus sinensis) and periwinkle plants after the infection with 'Ca. L. asiaticus'. Interestingly, in contrast to our previous studies of total leaf metabolites, we found that, compared with uninfected phloem sap, the organic acids implicated in the tricarboxylic acid cycle (TCA) cycle including citrate, isocitrate, succinate, fumarate, and malate were reduced significantly in the infected phloem saps of both species. As a result of the reduction of organic acids content, the pH of infected phloem saps was increased. We hypothesize that the bacterial growth induces the mitochondrial TCA cycle in parenchyma cells to produce more of these compounds to be used as a bacterial carbon source. Once these compounds reach a low level in the phloem sap, the bacterium may send a signal, yet to be identified, to initiate a feedback loop to further induce the TCA cycle. Phloem blockage might be another reason behind the reduced translocation of TCA cycle intermediates within the phloem. The net result, localized availability of organic acids, likely benefits bacterial growth and may explain the unequal distribution of 'Ca. L. asiaticus' within infected trees. These findings may help in designing media for the pure culturing of 'Ca. L. asiaticus'.

Protective role of antifusarial eco-friendly agents (Trichoderma and salicylic acid) to improve resistance performance of tomato plants

Fusarium wilt triggered great losing in tomato plants quality and quantity in all worlds. In the recent experiment, physiological resistance performance in tomato seedlings using Trichoderma harzianum and salicylic acid (SA) either (individual or combination) anti Fusarium had been studied. In vitro antifungal prospective of T. harzianum and SA against F. oxysporum were also examined. A noticeable antifungal capacity with highest activity of 10 and 8 mm ZOI after the treatment with the T. harzianum and SA. Also, Trichoderma have great ability to decreasing Fusarium growth by 25% inhibition at dual culture method. The MIC of SA was 1.5 mM to reduce Fusarium growth. For more ultrastructure by TEM of Fusarium treated with SA and Trichoderma showed alteration of cell wall as well as cytoplasmic components of mycelium, macroconidia and microconida. In the current experiment, ameliorative potentials of T. harzianum and SA either (individual or combination) via soil or foliar application were administered to the Fusarium- infected tomato plants and then disease index, growth indicators, photosynthetic pigments, metabolic markers, and antioxidant isozymes were assessed. The achieved result indicates that T. harzianum and SA through two modes (foliar and soil) lowered PDI by 12.50 and 20.83% and produced great protecting ability by 86.36 and 72.2%. The results revealed, infected seedlings exhibited high decrement in all tested growth characters, photosynthetic pigment contents, contents of total carbohydrate and protein, whereas proline, phenols and enzymes’ activity were elevated under Fusarium infectivity. It was concluded that use of combination (T. harzianum and SA) acted as a commercially eco-friendly instrument for intensifying the defense system of tomato plants against Fusarium wilt.

Joint transcriptomic and metabolomic analysis reveals the mechanism of low-temperature tolerance in Hosta ventricosa

Hosta ventricosa is a robust ornamental perennial plant that can tolerate low temperatures, and which is widely used in urban landscaping design in Northeast China. However, the mechanism of cold-stress tolerance in this species is unclear. A combination of transcriptomic and metabolomic analysis was used to explore the mechanism of low-temperature tolerance in H. ventricosa. A total of 12 059 differentially expressed genes and 131 differentially expressed metabolites were obtained, which were mainly concentrated in the signal transduction and phenylpropanoid metabolic pathways. In the process of low-temperature signal transduction, possibly by transmitting Ca²⁺ inside and outside the cell through the ion channels on the three cell membranes of COLD, CNGCs and CRLK, H. ventricosa senses temperature changes and stimulates SCRM to combine with DREB through the MAPK signal pathway and Ca²⁺ signal sensors such as CBL, thus strengthening its low-temperature resistance. The pathways of phenylpropanoid and flavonoid metabolism represent the main mechanism of low-temperature tolerance in this species. The plant protects itself from low-temperature damage by increasing its content of genistein, scopolentin and scopolin. It is speculated that H. ventricosa can also adjust the content ratio of sinapyl alcohol and coniferyl alcohol and thereby alter the morphological structure of its cell walls and so increase its resistance to low temperatures.When subjected to low-temperature stress, H. ventricosa perceives temperature changes via COLD, CNGCs and CRLK, and protection from low-temperature damage is achieved by an increase in the levels of genistein, scopolentin and scopolin through the pathways of phenylpropanoid biosynthesis and flavonoid biosynthesis.

Roles of Exogenous α-Lipoic Acid and Cysteine in Mitigation of Drought Stress and Restoration of Grain Quality in Wheat

Cysteine (Cys) and α-lipoic acid (ALA) are naturally occurring antioxidants (sulfur-containing compounds) that can protect plants against a wide spectrum of environmental stresses. However, up to now, there are no conclusive data on their integrative roles in mitigation of drought stress in wheat plants. Here, we studied the influence of ALA at 0.02 mM (grain dipping pre-cultivation treatment) and Cys (25 and 50 ppm as a foliar application) under well watered and deficit irrigation (100% and 70% of recommended dose). The results showed that deficit irrigation markedly caused obvious cellular oxidative damage as indicated by elevating the malondialdehyde (MDA) and hydrogen peroxide content (H₂O₂). Moreover, water stressed plants exhibited multiple changes in physiological metabolism, which affected the quantitative and qualitative variables of grain yield. The enzymatic antioxidants, including superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and peroxidase (POX) were improved by Cys application. SOD and APX had the same response when treated with ALA, but CAT and POX did not. Moreover, both studied molecules stimulated chlorophyll (Chl) and osmolytes' biosynthesis. In contrast, the Chl a/b ratio was decreased, while flavonoids were not affected by either of the examined molecules. Interestingly, all above-mentioned changes were associated with an improvement in the scavenging capacity of reactive oxygen species (ROS), leaf relative water content (RWC), grain number, total grain yield, weight of 1000 kernels, gluten index, falling number, and alveographic parameters (P, W, and P/L values). Furthermore, heatmap plot analysis revealed several significant correlations between different studied parameters, which may explore the importance of applied Cys and ALA as effective compounds in wheat cultivation under water deficit conditions.

Elucidating the relevance of high temperature and elevated CO2 in plant secondary metabolites (PSMs) production

Plant secondary metabolites (PSMs) are plant products that are discontinuously distributed throughout the plant kingdom. These secondary compounds have various chemical groups and are named according to their chemical constituents. For their ability to defend biotic and abiotic stresses they are considered as plants' defensive compounds. These metabolites take part in plant protection from insects, herbivores, and extreme environmental conditions. They are indirectly involved in plants’ growth and development. Secondary metabolites are also used by people in the form of medicines, pharmaceuticals, agrochemicals, colors, fragrances, flavorings, food additives, biopesticides, and drugs development. However, the increase in atmospheric temperature by several anthropogenic activities majorly by the combustion of hydrocarbons is a great issue now. On the other hand, climate change leaves an impact on the quality and quantity of plant secondary metabolites. It is measured that several greenhouse gases (GHGs) are present in the atmosphere, like Chlorofluorocarbons (CFCs), nitrous oxides (NO_x), Carbon dioxide (CO₂), Methane (CH₄) and Ozone (O₃), etc. CO₂, the major greenhouse gas is essential for photosynthesis. On the other hand, CO₂ plays a significant role in the up-regulation of atmospheric temperature. Plants produce various types of primary metabolites such as carbohydrates, proteins, fats, membrane lipids, nucleic acids, and chlorophyll as well as a variety of secondary metabolites from photosynthesis. The high temperature in the atmosphere creates heat stress for plants. As a matter of fact many morphological, physiological and biochemical changes occur in the plant. The high temperature invariably elicits the production of several secondary metabolites within plants. Various strategies have been universally documented to improve the production of PSMs. With this objective, the focus of the current review is to further investigate and discuss futuristic scenarios the effect of elevated CO₂ and high temperature on PSMs production which may perhaps beneficial for pharmaceutical industries, biotechnology industries, and also in climate change researches.

Exogenously Applied Gibberellic Acid Enhances Growth and Salinity Stress Tolerance of Maize through Modulating the Morpho-Physiological, Biochemical and Molecular Attributes

Soil salinity is the major limiting factor restricting plant growth and development. Little is known about the comparative and combined effects of gibberellic acid (GA3) seed priming and foliar application on maize under salt stress. The current study determined the impact of different application methods of GA3 on morpho-physiological, biochemical and molecular responses of maize seedlings under three salinity stress treatments (no salinity, moderate salinity-6 dS m-1, and severe salinity-12 dS m-1). The GA3 treatments consisted of control, hydro-priming (HP), water foliar spray (WFS), HP + WFS, seed priming with GA3 (GA3P, 100 mg L-1), foliar spray with GA3 (GA3FS, 100ppm) and GA3P + GA3FS. Salt stress particularly at 12 dS m-1 reduced the length of shoots and roots, fresh and dry weights, chlorophyll, and carotenoid contents, K+ ion accumulation and activities of antioxidant enzymes, while enhanced the oxidative damage and accumulation of the Na+ ion in maize plants. Nevertheless, the application of GA3 improved maize growth, reduced oxidative stress, and increased the antioxidant enzymes activities, antioxidant genes expression, and K+ ion concentration under salt stress. Compared with control, the GA3P + GA3FS recorded the highest increase in roots and shoots length (19-37%), roots fresh and dry weights (31-43%), shoots fresh and dry weights (31-47%), chlorophyll content (21-70%), antioxidant enzymes activities (73.03-150.74%), total soluble protein (13.05%), K+ concentration (13-23%) and antioxidants genes expression levels under different salinity levels. This treatment also reduced the H2O2 content, and Na+ ion concentration. These results indicated that GA3P + GA3FS could be used as an effective tool for improving the maize growth and development, and reducing the oxidative stress in salt-contaminated soils.

Physiological and metabolic changes in two Himalayan medicinal herbs under drought, heat and combined stresses

Valeriana jatamansi Jones and Hedychium spicatum Ham-ex-Smith are important medicinal herbs of the Himalayan region, which are highly demanded by pharmaceutical industries. Climatic variability especially increasing temperature and water deficit affects the growth and productivity of these species. In addition, increased temperature and water deficit may trigger the biosynthesis of medicinally important bioactive metabolites, which influence the quality of raw plant material and finished products. Therefore, V. jatamansi and H. spicatum plants were undertaken and subjected to different levels of drought (no irrigation), heat (35 °C), and combined stresses for investigating their physiological and metabolic responses. Both the treatments (individually and in combination) reduced relative water content, photosynthesis, carboxylation efficiency, chlorophyll content, while increased intracellular CO₂, malondialdehyde and H₂O₂ content in both the species. Transpiration and stomatal conductance increased under heat and reduced under drought stress as compared to control. Water use efficiency was found to be increased under drought, while reduced under heat stress. Protein, proline, carotenoid content and antioxidant enzymes activities (superoxide dismutase, peroxidise, catalase) initially increased and thereafter decreased during late stages of stress. Exposure of plants to combined stress was more detrimental than individual stress. In V. jatamansi, exposure to drought stress significantly (p < 0.05) increased valerenic acid content in all plant parts (1.0-6.9 fold) with maximum increase after 20 days of exposure, while under heat stress, valerenic acid content increased (1.0-1.2 fold) in belowground part of V. jatamansi, and decreased (1.1-1.3 fold) in aerial part as compared to control. In H. spicatum, exposure of individual heat stress for 25-30 days and combined stress for 5-15 days significantly (p < 0.05) increased linalool content to 6.2-6.5 fold and 8.3-19.6 fold, respectively, as compared to control. Higher accumulation of bioactive compounds after exposure to mild stress provides encouraging prospects for enhancing pharmaceutical properties of these Himalayan herbs.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01027-w.

How to improve CHMs quality: Enlighten from CHMs ecological cultivation

Chinese herbal medicines (CHMs) are one of the important bioresources of medicine, which works by unlocking nature's ability to prevent diseases and recover from illnesses. Recently, it has ascended to the world stage and become a global icon. Nowadays, a considerable of researches have focused on the quality evaluation of CHMs. However, it is difficult to meet the reasonable needs of human beings for safe drug use to evaluate the quality of a huge number of inferior goods for the CHMs contaminated by pesticides and heavy metals. Hence to explore an eligible medicinal plant cultivation pattern, which can provide high quality CHMs sustainably, is most promising. This review analyzed the situation and characteristics of medicinal plant resources in different periods, including wild-harvested and cultivated resources during different stages, putting forward that ecological cultivation must be the way to develop medicinal plant cultivation and to obtain high quality CHMs.

Morpho-Physio-Biochemical and Molecular Responses of Maize Hybrids to Salinity and Waterlogging during Stress and Recovery Phase

Maize is one of the most economically important cereal crops worldwide. Salinity coupled with waterlogging is a major challenge for successful crop production. Understanding the underlying mechanisms and impacts of individual and combined salinity and waterlogging stress on the morpho-physio-biochemical and molecular responses and oxidative metabolism of maize during stress and recovery periods is essential. The present study was carried out to assess the response of four hybrid maize cultivars viz. DK-6142, FH-1231, FH-949, and MALKA-2016 under individual and combined salinity and waterlogging conditions. The treatments comprised the control (no stress), NaCl (salinity with 10 dSm⁻¹), WL (waterlogged conditions with 3 cm flooding), and NaCl + WL (combined salinity and waterlogging stress). The data regarding morpho-physiological attributes were collected at 22 days after sowing (DAS; stress phase) and 30 DAS (recovery phase). The results revealed that both stresses, either individually or in combination, substantially reduced the root-shoot length, root-shoot fresh and dry weights, leaf width, and the number of leaves per plant as well as the leaf chlorophyll (Chl) and carotenoids contents; however, the inhibitory effects were more severe in combined stresses than for individual stress factors in many cultivars. Both individual and combined stress conditions enhanced hydrogen peroxide (H₂O₂) accumulation, whereas the antioxidant enzyme activities, i.e., superoxide dismutase (SOD), peroxidase (POD) catalase (CAT), and ascorbate peroxidase (APX), remained higher under stress conditions compared to the control. The expression levels of antioxidant genes (CAT and POD) were also upregulated under stress conditions. All of the cultivars recovered better from individual stresses than combined stress conditions; however, the hybrid DK-6142 performed better than the other maize hybrids under stress conditions and showed faster recovery.

Ex-foliar application of glycine betaine and its impact on protein, carbohydrates and induction of ROS scavenging system during drought stress in flax (Linum usitatissimum)

Crop plants have an innate capacity to acclimatize and survive myriad stresses in field conditions. This acclimatization to stress enhances crop stand in field and productivity of plant. Inter alia field crops withstand drought stress (hydropenia) by inducing synthesis or accumulation of osmolytes such as (i) proline and other amino acids, (ii) glycine betaine (GB), (iii) soluble carbohydrates, and (iv) reactive oxygen species (ROS) scavenging system as intrinsic drought antagonizing molecules. Precise in vivo induction of osmolytes and their effect on ROS scavenging system in flax/linseed has not been elucidated. The investigation was carried out to identify a tolerant and susceptible cultivar of flax from a core collection of 53 core accessions and evaluate the role of compatible osmolytes in Linum usitatissimum under hydropenia. We screened eight morphometrically diverse flax genotypes in field under irrigated and un-irrigated condition and classified them as tolerant and susceptible genotypes. Further, we examined the effect of ex-foliar glycine betaine application - a signature molecule involved in drought tolerance, on selected tolerant and susceptible varieties. Our results showed stimulatory impact of glycine betaine on accumulation of ROS scavenging antioxidants, total soluble protein and on its own accumulation. While the ex-foliar application had no inhibitory effect on the growth of plants; accumulation of free proline, amino acids and carbohydrates are inhibited par se in flax. Our findings reveal, flax is a non-accumulator of glycine betaine and exogenous application of glycine betaine enhances its own levels during drought stress.

Diversity in Chemical Structures and Biological Properties of Plant Alkaloids

Phytochemicals belonging to the group of alkaloids are signature specialized metabolites endowed with countless biological activities. Plants are armored with these naturally produced nitrogenous compounds to combat numerous challenging environmental stress conditions. Traditional and modern healthcare systems have harnessed the potential of these organic compounds for the treatment of many ailments. Various chemical entities (functional groups) attached to the central moiety are responsible for their diverse range of biological properties. The development of the characterization of these plant metabolites and the enzymes involved in their biosynthesis is of an utmost priority to deliver enhanced advantages in terms of biological properties and productivity. Further, the incorporation of whole/partial metabolic pathways in the heterologous system and/or the overexpression of biosynthetic steps in homologous systems have both become alternative and lucrative methods over chemical synthesis in recent times. Moreover, in-depth research on alkaloid biosynthetic pathways has revealed numerous chemical modifications that occur during alkaloidal conversions. These chemical reactions involve glycosylation, acylation, reduction, oxidation, and methylation steps, and they are usually responsible for conferring the biological activities possessed by alkaloids. In this review, we aim to discuss the alkaloidal group of plant specialized metabolites and their brief classification covering major categories. We also emphasize the diversity in the basic structures of plant alkaloids arising through enzymatically catalyzed structural modifications in certain plant species, as well as their emerging diverse biological activities. The role of alkaloids in plant defense and their mechanisms of action are also briefly discussed. Moreover, the commercial utilization of plant alkaloids in the marketplace displaying various applications has been enumerated.

Scrutinizing the impact of water deficit in plants: Transcriptional regulation, signaling, photosynthetic efficacy, and management

Suboptimal availability of water limits plant growth, development, and performance. Drought is one of the leading factors responsible for worldwide crop yield reduction. In the future, owing to climate changes, more agricultural land will be affected by prolonged periods of water deficit. Thus, understanding the fundamental mechanism of drought response is a major scientific concern for improvement of crop production. To combat drought stress, plants deploy varied mechanistic strategies and alter their morphological, physiochemical, and molecular attributes. This helps plant to enhance water uptake and storage, reduce water loss and avoid wilting. Induction of several transcription factors and drought responsive genes leads to synthesis of stress proteins, regulation of water channels i.e. aquaporins and production of osmolytes that are essential for maintenance of osmotic balance at the cellular level. Self- and hormone-regulated signaling pathways are often stimulated by plants after receiving drought stress signals via secondary messengers, mitogen-activated protein kinases, and stress hormones. These signaling cascades often leads to stomatal closure and reduction in transpiration rates. Reduced carbon dioxide diffusion in chloroplast, lowered efficacy of photosystems, and other metabolic constraints limits the key regulatory photosynthetic process during water deficit. The impact of these stomatal and nonstomatal limitations varies with stress intensity, superimposed stresses and plant species. A clear understanding of the drought resistance process is thus important before adopting strategies for imparting drought tolerance in plants. These management practices at present include exogenous hormone application, breeding, and genetic engineering techniques for combating the water deficit issues.

γ-Aminobutyric acid (GABA) mitigates drought and heat stress in sunflower (Helianthus annuus L.) by regulating its physiological, biochemical and molecular pathways

Drought and heat stress are two dominant abiotic stress factors that often occur simultaneously in nature causing oxidative damage in plants and thus decline in yield. The present study was conducted to examine the γ-aminobutyric acid (GABA)-induced heat and drought tolerance in sunflower through physiological, biochemical and molecular analysis. The results showed that drought and heat stress triggered oxidative stress as revealed by enhanced level in hydrogen peroxide, malondialdehyde and electrolyte leakage. Moreover, the photosynthetic attributes such as photosynthetic rate, stomatal conductance and quantum efficiency declined when subjected to drought and heat stress. In this study, GABA treatment effectively alleviated the drought and heat-induced stress as reflected by significantly higher levels of proline, soluble sugar and total protein content. Besides, the data also revealed the direct relationship between antioxidant enzyme activities (superoxide dismutase, peroxidase, glutathione reductase, monodehydroascorbate peroxidase, ascorbate peroxidase) and the relative expression of genes (Heat Shock Proteins, Dehydrin, Osmotin, Aquaporin, Leaf Embryogenesis Protein), under drought and heat stress. Moreover, a significant increase in gene expression was observed upon GABA treatment with respect to control. This data suggest that GABA-induced drought and heat tolerance in sunflower could involve the improvement in osmolyte metabolism, gene expression and antioxidant enzyme activities and thus a rise in the GABA shunt which in turn provides intermediates during long-term drought and heat stress, thus maintaining homeostasis.

Growing and Flowering in a Changing Climate: Effects of Higher Temperatures and Drought Stress on the Bee-Pollinated Species Impatiens glandulifera Royle

Drought and higher temperatures caused by climate change are common stress conditions affecting plant growth and development. The reproductive phase is particularly sensitive to stress, but plants also need to allocate their limited resources to produce floral traits and resources to attract pollinators. We investigated the physiological and floral consequences of abiotic stress during the flowering period of Impatiens glandulifera, a bee-pollinated species. Plants were exposed to three temperatures (21, 24, 27 °C) and two watering regimes (well-watered, water stress) for 3 weeks. Not all parameters measured responded in the same manner to drought and/or heat stress. Drought stress induced leaf senescence, decreasing leaf number by 15-30% depending on growth temperature. Drought also reduced photosynthetic output, while temperature rise affected stomatal conductance. The number of flowers produced dropped 40-90% in response to drought stress, while higher temperatures shortened flower life span. Both stresses affected floral traits, but flower resources diminished in response to higher temperatures, with lower nectar volume and pollen protein content. We conclude that increased temperatures and drought stress, which are becoming more frequent with climate change, can negatively affect flowering, even if plants deploy physiological resistance strategies.

Wuxal amino (Bio stimulant) improved growth and physiological performance of tomato plants under salinity stress through adaptive mechanisms and antioxidant potential

In the present study, ameliorative capabilities of wuxal amino (bio stimulant) under salt stress has been investigated through adaptive mechanisms and antioxidant potential in tomato plants. In the experiment, two different concentrations (2 cm L^-1 and 3 cm L^-1) of wuxal amino through foliar application and soil irrigation were applied to the salt (150 mM) treated tomato plants and then morphological traits, photosynthetic pigments, osmolytes, secondary metabolites, oxidative stress and antioxidant enzymes activity were assessed at 60 days after planting. The results revealed that salt stress decreased the growth parameters, photosynthetic pigments, soluble sugars and soluble protein whereas, content of proline, ascorbic acid, total phenols, malondialdehyde, hydrogen peroxide and the activity of antioxidant enzymes activity increased under salt stress. Moreover, Wuxal amino application through foliar or soil to salt stressed plants improved morphological traits, photosynthetic pigments, osmolytes, total phenol and antioxidant enzymes activity. Interestingly, the deleterious impact of salinity on tomato plants were significantly reduced and it can be evident from reduced MDA and H₂O₂ levels. These responses varied with the mode (foliar or soil) of application of Wuxal amino under different concentrations (2 cm L^-1 and 3 cm L^-1). It was concluded that application of Wuxal amino (2 cm L^-1, foliar) and (3 cm L^-1; soil) proved best and could be commercially used as eco-friendly tool for the protection of tomato plants grown under salinity stress.

Physiological and Gene Expression Changes of Clematis crassifolia and Clematis cadmia in Response to Heat Stress

Clematis is a superior perennial ornamental vine known for varied colors and shapes of its flowers. Clematis crassifolia is sensitive to high temperature, whereas Clematis cadmia has a certain temperature adaptability. Here we analyzed the potential regulatory mechanisms of C. crassifolia and C. cadmia in response to heat stress by studying the photosynthesis, antioxidant parameters, amino acids, and gene expression patterns under three temperature treatments. Heat stress caused the fading of leaves; decreased net photosynthetic rate, stomatal conductance, superoxide dismutase, and catalase activity; increased 13 kinds of amino acids content; and up-regulated the expression of seven genes, including C194329_G3, C194434_G1, and C188817_g1, etc., in C. crassifolia plants. Under the treatments of heat stress, the leaf tips of C. cadmia were wilted, and the net photosynthetic rate and soluble protein content decreased, with the increase of 12 amino acids content and the expression of c194329_g3, c194434_g1, and c195983_g1. Our results showed that C. crassifolia and C. cadmia had different physiological and molecular response mechanisms to heat stress during the ecological adaptation.

Exogenous γ-aminobutyric acid (GABA)-induced signaling events and field performance associated with mitigation of drought stress in Phaseolus vulgaris L

Not much information is available to substantiate the possible role of γ -aminobutyric acid (GABA) signaling in mitigating water-deficit stress in snap bean (Phaseolus vulgaris L.) plants under semiarid conditions. Present work aims to investigate the role of exogenous GABA (foliar application; 0.5, 1 and 2 mM) in amelioration of drought stress and improvement of field performance on snap bean plants raised under two drip irrigation regimes (100% and 70% of water requirements). Water stress led to significant reduction in plant growth, leaf relative water content (RWC), cell membrane stability index (CMSI), nutrient uptake (N, P, K, Ca, Fe and Zn), pod yield and its content from protein and total soluble solids (TSS). Meanwhile, lipid peroxidation (malondialdehyde content- MDA), osmolyte content (free amino acids- FAA, proline, soluble sugars) antioxidative defense (activity of superoxide dismutase- SOD, catalase- CAT, peroxidase- POX and ascorbate peroxidase- APX) and the pod fiber content exhibited significantly increase due to water stress. Exogenous GABA application (especially at 2 mM) revealed partial normalization of the effects of drought stress in snap bean plants. GABA-induced mitigation of drought stress was manifested by improvement in growth, water status, membrane integrity, osmotic adjustment, antioxidant defense and nutrient acquisition. Furthermore, GABA application during water stress in snap bean plants resulted in improvement of field performance being manifested by increased pod yield and its quality attributes. To sum up, exogenous GABA appears to function as an effective priming molecule to alleviate drought stress in snap bean plants under semiarid conditions.