Comparison of ROS formation and antioxidant enzymes in Cleome gynandra (C₄) and Cleome spinosa (C₃) under drought stress

Association between Reactive Oxygen Species, Transcription Factors, and Candidate Genes in Drought-Resistant Sorghum

Drought stress is one of the most severe natural disasters in terms of its frequency, length, impact intensity, and associated losses, making it a significant threat to agricultural productivity. Sorghum (Sorghum bicolor), a C4 plant, shows a wide range of morphological, physiological, and biochemical adaptations in response to drought stress, paving the way for it to endure harsh environments. In arid environments, sorghum exhibits enhanced water uptake and reduced dissipation through its morphological activity, allowing it to withstand drought stress. Sorghum exhibits physiological and biochemical resistance to drought, primarily by adjusting its osmotic potential, scavenging reactive oxygen species, and changing the activities of its antioxidant enzymes. In addition, certain sorghum genes exhibit downregulation capabilities in response to drought stress. Therefore, in the current review, we explore drought tolerance in sorghum, encompassing its morphological characteristics and physiological mechanisms and the identification and selection of its functional genes. The use of modern biotechnological and molecular biological approaches to improving sorghum resistance is critical for selecting and breeding drought-tolerant sorghum varieties.

The cold-responsive C-repeat binding factors in Betula platyphylla Suk. positively regulate cold tolerance

Cold stress is one of the most destructive abiotic stresses limiting plant growth and development. CBF (C-repeat binding factor) transcription factors and their roles in cold response have been identified in Arabidopsis as well as several other plant species. However, the biological functions and related molecular mechanisms of CBFs in birch (Betula platyphylla Suk.) remain undetermined. In this study, five cold-responsive BpCBF genes, BpCBF1, BpCBF2, BpCBF7, BpCBF10 and BpCBF12 were cloned. Via protoplast transformation, BpCBF7 was found to be localized in nucleus. The result of yeast one hybrid assay validated the binding of BpCBF7 to the CRT/DRE (C-repeat/dehydration responsive element) elements in the promoter of BpERF1.1 gene. By overexpressing and repressing BpCBFs in birch plants, it was proven that BpCBFs play positive roles in the cold tolerance. At the metabolic level, BpCBFs OE lines had lower ROS accumulation, as well as higher activities of antioxidant enzymes (SOD, POD and CAT) and higher accumulation of protective substances (soluble sugar, soluble protein and proline). Via yeast one hybrid and co-transformation of effector and reporter vectors assay, it was proven that BpCBF7 can regulate the expression of BpERF5 and BpZAT10 genes by directly binding to their promoters. An interacting protein of BpCBF7, BpWRKY17, was identified by yeast two hybrid library sequencing and the interaction was validated with in vivo methods. These results indicates that BpCBFs can increase the cold tolerance of birch plants, partly by gene regulation and protein interaction. This study provides a reference for the research on CBF transcription factors and genetic improvement of forest trees upon abiotic stresses.

A meta-analysis highlights the cross-resistance of plants to drought and salt stresses from physiological, biochemical, and growth levels

In nature, drought and salt stresses often occur simultaneously and affect plant growth at multiple levels. However, the mechanisms underlying plant responses to drought and salt stresses and their interactions are still not fully understood. We performed a meta-analysis to compare the effects of drought, salt, and combined stresses on plant physiological, biochemical, morphological and growth traits, analyze the different responses of C3 and C4 plants, as well as halophytes and non-halophytes, and identify the interactive effects on plants. There were numerous similarities in plant responses to drought, salt, and combined stresses. C4 plants had a more effective antioxidant defense system, and could better maintain above-ground growth. Halophytes could better maintain photosynthetic rate (Pn) and relative water content (RWC), and reduce growth as an adaptation strategy. The responses of most traits (Pn, RWC, chlorophyll content, soluble sugar content, H2O2 content, plant dry weight, etc.) to combined stress were less-than-additive, indicating cross-resistance rather than cross-sensitivity of plants to drought and salt stresses. These results are important to improve our understanding of drought and salt cross-resistance mechanisms and further induce resistance or screen-resistant varieties under stress combination.

A comprehensive analysis of transcriptomic data for comparison of plants with different photosynthetic pathways in response to drought stress

The main factor leading to a decrease in crop productivity is abiotic stresses, particularly drought. Plants with C4 and CAM photosynthesis are better adapted to drought-prone areas than C3 plants. Therefore, it is beneficial to compare the stress response of plants with different photosynthetic pathways. Since most crops are C3 and C4 plants, this study focused on conducting an RNA-seq meta-analysis to investigate and compare how C3 and C4 plants respond to drought stress at the gene expression level in their leaves. Additionally, the accuracy of the meta-analysis results was confirmed with RT-qPCR. Based on the functional enrichment and network analysis, hub genes related to ribosomal proteins and photosynthesis were found to play a potential role in stress response. Moreover, our findings suggest that the low abundant amino acid degradation pathway, possibly through providing ATP source for the TCA cycle, in both groups of plants and the activation of the OPPP pathway in C4 plants, through providing the electron source required by this plant, can help to improve drought stress tolerance.

Achieving abiotic stress tolerance in plants through antioxidative defense mechanisms

Climate change has increased the overall impact of abiotic stress conditions such as drought, salinity, and extreme temperatures on plants. Abiotic stress adversely affects the growth, development, crop yield, and productivity of plants. When plants are subjected to various environmental stress conditions, the balance between the production of reactive oxygen species and its detoxification through antioxidant mechanisms is disturbed. The extent of disturbance depends on the severity, intensity, and duration of abiotic stress. The equilibrium between the production and elimination of reactive oxygen species is maintained due to both enzymatic and non-enzymatic antioxidative defense mechanisms. Non-enzymatic antioxidants include both lipid-soluble (α-tocopherol and β-carotene) and water-soluble (glutathione, ascorbate, etc.) antioxidants. Ascorbate peroxidase (APX), superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) are major enzymatic antioxidants that are essential for ROS homeostasis. In this review, we intend to discuss various antioxidative defense approaches used to improve abiotic stress tolerance in plants and the mechanism of action of the genes or enzymes involved.

Drought tolerance of Aspergillus violaceofuscus and Bacillus licheniformis and their influence on tomato growth and potassium uptake in mica amended tropical soils under water-limiting conditions

Drought is a significant abiotic stress that alters plant physiology and ultimately affects crop productivity. Among essential plant nutrients, potassium (K) is known to mitigate the deleterious effect of drought on plant growth. If so, K addition or inoculation of potassium solubilizing microorganisms (KSMs) that are tolerant to drought should promote plant growth during water stress. Therefore, in this study, K solubilizing Aspergillus violaceofuscus and Bacillus licheniformis, isolated from saxicolous environments, were tested for their capacity to tolerate drought using different molecular weights (~4000, 6000, and 8000 Da), and concentrations (0, 250, 500, 750, 1000, and 1250 mg/L) of polyethylene glycol (PEG) under in vitro conditions. The results showed that high concentrations (750 and 1000 mg/L) of PEG with different molecular weight considerably improved bacterial cell numbers/fungal biomass and catalase (CAT) and proline activities. Moreover, the ability of KSMs alone or in combination to impart drought tolerance and promote plant growth in the presence and absence of mica (9.3% K₂O) supplementation was tested in Alfisol and Vertisol soil types under greenhouse conditions. The results revealed that the tomato plants inoculated with KSMs individually or dually with/without mica improved the physiological and morphological traits of the tomato plants under drought. Generally, tomato plants co-inoculated with KSMs and supplemented with mica were taller (2.62 and 3.38-fold) and had more leaf area (2.03 and 1.98-fold), total root length (3.26 and 8.86-fold), shoot biomass (3.87 and 3.93-fold), root biomass (9.00 and 7.24-fold), shoot K content (3.08 and 3.62-fold), root K content (3.39 and 2.03-fold), relative water content (1.51 and 1.27-fold), CAT activity (2.11 and 2.14-fold), proline content (3.41 and 3.28-fold), and total chlorophyll content (1.81 and 1.90-fold), in unsterilized Alfisol and Vertisol soil types, respectively, than uninoculated ones. Dual inoculation of the KSMs along with mica amendment, also improved the endorrhizal symbiosis of tomato plants more than their individual inoculation or application in both soil types. These findings imply that the A. violaceofuscus and B. licheniformis isolates are promising as novel bioinoculants for improving crop growth in water-stressed and rainfed areas of the tropics in the future.

Differential regulation of reactive oxygen species in dimorphic chloroplasts of single cell C4 plant Bienertia sinuspersici during drought and salt stress

Single cell C₄ (SCC₄) plants, discovered around two decades ago, are promising materials for efforts for genetic engineering of C₄ photosynthesis into C₃ crops. Unlike C₄ plants with Kranz anatomy, they exhibit a fully functional C₄ photosynthesis in just a single cell and do not require mesophyll and bundle sheath cell spatial separation. Bienertia sinuspersici is one such SCC₄ plant, with NAD-malic enzyme (NAD-ME) subtype C₄ photosynthesis. Its chlorenchyma cell consist of two compartments, peripheral compartment (PC), analogous to mesophyll cell, and central compartment (CC), analogous to bundle sheath cell. Since oxidative stress creates an important constraint for plants under salinity and drought, we comparatively examined the response of enzymatic antioxidant system, H₂O₂ and TBARS contents, peroxiredoxin Q, NADPH thioredoxin reductase C, and plastid terminal oxidase protein levels of PC chloroplasts (PCC) and CC chloroplasts (CCC). Except for protein levels, these parameters were also examined on the whole leaf level, as well as catalase and NADPH oxidase activities, water status and growth parameters, and levels of C₄ photosynthesis related transcripts. Many C₄ photosynthesis related transcript levels were elevated, especially under drought. Activities of dehydroascorbate reductase and especially peroxidase were elevated under drought in both compartments (CCC and PCC). Even though decreases of antioxidant enzyme activities were more prevalent in PCC, and the examined redox regulating protein levels, especially of peroxiredoxin Q, were elevated in CCC under both stresses, PCC was less damaged by either stress. These suggest PCC is more tolerant and has other means of preventing or alleviating oxidative damage.

A meta-analysis on morphological, physiological and biochemical responses of plants with PGPR inoculation under drought stress

Plant growth-promoting rhizobacteria (PGPR) can help plants to resist drought stress. However, the mechanisms of how PGPR inoculation affect plant status under drought remain incompletely understood. We performed a meta-analysis of plant response to PGPR inoculation by compiling data from 57 PGPR-inoculation studies, including 2, 387 paired observations on morphological, physiological and biochemical parameters under drought and well-watered conditions. We compare the PGPR effect on plants performances among different groups of controls and treatments. Our results reveal that PGPR enables plants to restore themselves from drought-stressed to near a well-watered state, and that C4 plants recover better from drought stress than C3 plants. Furthermore, PGPR is more effective underdrought than well-watered conditions in increasing plant biomass, enhancing photosynthesis and inhibiting oxidant damage, and the responses of C4 plants to the PGPR effect was stronger than that of C3 plants under drought conditions. Additionally, PGPR belonging to different taxa and PGPR with different functional traits have varying degrees of drought-resistance effects on plants. These results are important to improve our understanding of the PGPR beneficial effects on enhanced drought-resistance of plants.

Physiological Adaptation Mechanisms to Drought and Rewatering in Water-Saving and Drought-Resistant Rice

Water-saving and drought-resistant rice (WDR) has high a yield potential in drought. However, the photosynthetic adaptation mechanisms of WDR to drought and rehydration have yet to be conclusively determined. Hanyou 73 (HY73, WDR) and Huanghuazhan (HHZ, drought-sensitive cultivar) rice cultivars were subjected to drought stress and rewatering when the soil water potential was −180 KPa in the booting stage. The leaf physiological characteristics were dynamically determined at 0 KPa, −30 KPa, −70 KPa, −180 KPa, the first, the fifth, and the tenth day after rewatering. It was found that the maximum net photosynthetic rate (Amax) and light saturation point were decreased under drought conditions in both cultivars. The change in dark respiration rate (Rd) in HY73 was not significant, but was markedly different in HHZ. After rewatering, the photosynthetic parameters of HY73 completely returned to the initial state, while the indices in HHZ did not recover. The antioxidant enzyme activities and osmoregulatory substance levels increased with worsening drought conditions and decreased with rewatering duration. HY73 had higher peroxidase (POD) activity as well as proline levels, and lower catalase (CAT) activity, ascorbate peroxidase (APX) activity, malondialdehyde (MDA) level, and soluble protein (SP) content during all of the assessment periods compared with HHZ. In addition, Amax was markedly negatively correlated with superoxide dismutase (SOD), POD, CAT, and SP in HY73 (p < 0.001), while in HHZ, it was negatively correlated with SOD, CAT, APX, MDA, Pro, and SP, and positively correlated with Rd (p < 0.001). These results suggest that WDR has a more simplified adaptation mechanism to protect photosynthetic apparatus from damage in drought and rehydration compared with drought-sensitive cultivars. The high POD activity and great SP content would be considered as important physiological bases to maintain high photosynthetic production potential in WDR.

Molecular Regulation and Evolution of Redox Homeostasis in Photosynthetic Machinery

The recent advances in plant biology have significantly improved our understanding of reactive oxygen species (ROS) as signaling molecules in the redox regulation of complex cellular processes. In plants, free radicals and non-radicals are prevalent intra- and inter-cellular ROS, catalyzing complex metabolic processes such as photosynthesis. Photosynthesis homeostasis is maintained by thiol-based systems and antioxidative enzymes, which belong to some of the evolutionarily conserved protein families. The molecular and biological functions of redox regulation in photosynthesis are usually to balance the electron transport chain, photosystem II, photosystem I, mesophyll and bundle sheath signaling, and photo-protection regulating plant growth and productivity. Here, we review the recent progress of ROS signaling in photosynthesis. We present a comprehensive comparative bioinformatic analysis of redox regulation in evolutionary distinct photosynthetic cells. Gene expression, phylogenies, sequence alignments, and 3D protein structures in representative algal and plant species revealed conserved key features including functional domains catalyzing oxidation and reduction reactions. We then discuss the antioxidant-related ROS signaling and important pathways for achieving homeostasis of photosynthesis. Finally, we highlight the importance of plant responses to stress cues and genetic manipulation of disturbed redox status for balanced and enhanced photosynthetic efficiency and plant productivity.

The Developmental Delay of Seedlings With Cotyledons Only Confers Stress Tolerance to Suaeda aralocaspica (Chenopodiaceae) by Unique Performance on Morphology, Physiology, and Gene Expression

Cotyledons play an important role in seedling establishment, although they may just exist for a short time and become senescent upon the emergence of euphylla. So far, the detailed function of cotyledons has not been well understood. Suaeda aralocaspica is an annual halophyte distributed in cold deserts; its cotyledons could exist for a longer time, even last until maturity, and they must exert a unique function in seedling development. Therefore, in this study, we conducted a series of experiments to investigate the morphological and physiological performances of cotyledons under salt stress at different developmental stages. The results showed that the cotyledons kept growing slowly to maintain the normal physiological activities of seedlings by balancing phytohormone levels, accumulating osmoprotectants and antioxidants, and scavenging reactive oxygen species (ROS). Salt stress activated the expression of osmoprotectant-related genes and enhanced the accumulation of related primary metabolites. Furthermore, differentially expressed transcriptional profiles of the cotyledons were also analyzed by cDNA-AFLP to gain an understanding of cotyledons in response to development and salt stress, and the results revealed a progressive increase in the expression level of development-related genes, which accounted for a majority of the total tested TDFs. Meanwhile, key photosynthetic and important salt stress-related genes also actively responded. All these performances suggest that "big cotyledons" are experiencing a delayed but active developmental process, by which S. aralocaspica may survive the harsh condition of the seedling stage.

Bacillus amyloliquefaciens Rescues Glycyrrhizic Acid Loss Under Drought Stress in Glycyrrhiza uralensis by Activating the Jasmonic Acid Pathway

Drought is a major factor limiting the production of the perennial medicinal plant Glycyrrhiza uralensis Fisch. (Fabaceae) in Northwest China. In this study, 1-year-old potted plants were inoculated with the strain Bacillus amyloliquefaciens FZB42, using a gradient of concentrations (CFU), to test for microbe-induced host tolerance to drought condition treatments in a greenhouse experiment. At the concentration of 10⁸ CFU ml^-1, FZB42 had significant growth-promoting effect on G. uralensis: the root biomass was 1.52, 0.84, 0.94, and 0.38 times that under normal watering and mild, moderate, and severe drought stress conditions, respectively. Under moderate drought, the positive impact of FZB42 on G. uralensis growth was most pronounced, with both developing axial and lateral roots strongly associated with indoleacetic acid (IAA) accumulation. An untargeted metabolomic analysis and physiological measurements of mature roots revealed that FZB42 improved the antioxidant system of G. uralensis through the accumulation of proline and sucrose, two osmotic adjustment solutes, and by promoting catalase (CAT) activity under moderate drought stress. Furthermore, significantly higher levels of total flavonoids, liquiritin, and glycyrrhizic acid (GA), the pharmacologically active substances of G. uralensis, were found in the roots of inoculated plants after FZB42 inoculation under all imposed drought conditions. The jasmonic acid (JA) content, which is closely related to plant defense responses and secondary metabolites' production, was greatly increased in roots after the bacterial inoculations, indicating that FZB42 activated the JA pathway. Taken together, our results demonstrate that inoculation with FZB42 alleviates the losses in production and pharmacological metabolites of G. uralensis caused by drought via the JA pathway's activation. These results provide a developed prospect of a microbial agent to improve the yield and quality of medical plants in arid and semi-arid regions.

Assessment of the Photosynthetic Apparatus Functions by Chlorophyll Fluorescence and P700 Absorbance in C3 and C4 Plants under Physiological Conditions and under Salt Stress

Functions of the photosynthetic apparatus of C3 (Pisum sativum L.) and C4 (Zea mays L.) plants under physiological conditions and after treatment with different NaCl concentrations (0-200 mM) were investigated using chlorophyll a fluorescence (pulse-amplitude-modulated (PAM) and JIP test) and P700 photooxidation measurement. Data revealed lower density of the photosynthetic structures (RC/CSo), larger relative size of the plastoquinone (PQ) pool (N) and higher electron transport capacity and photosynthetic rate (parameter RFd) in C4 than in C3 plants. Furthermore, the differences were observed between the two studied species in the parameters characterizing the possibility of reduction in the photosystem (PSI) end acceptors (REo/RC, REo/CSo and δRo). Data revealed that NaCl treatment caused a decrease in the density of the photosynthetic structures and relative size of the PQ pool as well as decrease in the electron transport to the PSI end electron acceptors and the probability of their reduction as well as an increase in the thermal dissipation. The effects were stronger in pea than in maize. The enhanced energy losses after high salt treatment in maize were mainly from the increase in the regulated energy losses (ΦNPQ), while in pea from the increase in non-regulated energy losses (ΦNO). The reduction in the electron transport from QA to the PSI end electron acceptors influenced PSI activity. Analysis of the P700 photooxidation and its decay kinetics revealed an influence of two PSI populations in pea after treatment with 150 mM and 200 mM NaCl, while in maize the negligible changes were registered only at 200 mM NaCl. The experimental results clearly show less salt tolerance of pea than maize.

Climate change regulated abiotic stress mechanisms in plants: a comprehensive review

Global climate change is identified as a major threat to survival of natural ecosystems. Climate change is a dynamic, multifaceted system of alterations in environmental conditions that affect abiotic and biotic components of the world. It results in alteration in environmental conditions such as heat waves, intensity of rainfall, CO₂ concentration and temperature that lead to rise in new pests, weeds and pathogens. Climate change is one of the major constraints limiting plant growth and development worldwide. It impairs growth, disturbs photosynthesis, and reduces physiological responses in plants. The variations in global climate have gained the attention of researchers worldwide, as these changes negatively affect the agriculture by reducing crop productivity and food security. With this background, this review focuses on the effects of elevated atmospheric CO₂ concentration, temperature, drought and salinity on the morphology, physiology and biochemistry of plants. Furthermore, this paper outlines an overview on the reactive oxygen species (ROS) production and their impact on the biochemical and molecular status of plants with increased climatic variations. Also additionally, different tolerance strategies adopted by plants to combat environmental adversities have been discussed.

Comparison of photosynthetic activity and heat tolerance between near isogenic lines of wheat with different photosynthetic rates

Wheat (Triticum aestivum L.) is one of the most important crops in the world, but the yield and quality of wheat are highly susceptible to heat stress, especially during the grain-filling stage. Therefore, it is crucial to select high-yield and high-temperature-resistant varieties for food cultivation. There is a positive correlation between the yield and photosynthetic rate of wheat during the entire grain-filling stage, but few studies have shown that lines with high photosynthetic rates can maintain higher thermotolerance at the same time. In this study, two pairs of wheat near isogenic lines (NILs) with different photosynthetic rates were used for all experiments. Our results indicated that under heat stress, lines with a high photosynthetic rate could maintain the activities of photosystem II (PSII) and key Calvin cycle enzymes in addition to their higher photosynthetic rates. The protein levels of D1 and HSP70 were significantly increased in the highly photosynthetic lines, which contributed to maintaining high photosynthetic rates and ensuring the stability of the Calvin cycle under heat stress. Furthermore, we found that lines with a high photosynthetic rate could maintain high antioxidant enzyme activity to scavenge reactive oxygen species (ROS) and reduce ROS accumulation better than lines with a low photosynthetic rate under high-temperature stress. These findings suggest that lines with high photosynthetic rates can maintain a higher photosynthetic rate despite heat stress and are more thermotolerant than lines with low photosynthetic rates.

Biochemical response and nutrient uptake of two arbuscular mycorrhiza-inoculated chamomile varieties under different osmotic stresses

BACKGROUND

Water-deficit stress is known as one of the most severe environmental stresses affecting the growth of plants through marked reduction of water uptake, which leads to osmotic stress by lowering water potential. Adopting appropriate varieties using soil microorganisms, such as arbuscular mycorrhiza (AM) fungi, can significantly reduce the adverse effects of water deficiency. This study aimed to evaluate the role of Funneliformis mosseae on nutrient uptake and certain physiological traits of two chamomile varieties, namely Bodgold (Bod) and Soroksári (Sor) under osmotic stress. For pot culture, a factorial experiment was performed in a completely randomized design with three factors: osmotic stress (PEG 6000) was applied along with Hoagland solution at three levels (0, -0.4 and -0.8 MPa), two German chamomile varieties (Bodgold (Bod) and Soroksari (Sor)), and AM inoculation (Funneliformis mosseae species (fungal and non-fungal)) at four replications in perlite substrate.

RESULTS

Osmotic stress significantly reduced the uptake of macro-nutrients (N and P) and micro-nutrients (Fe, Cu, Mn, and Zn) in the shoots and roots. Moreover, the level of osmolytes (total soluble sugars and proline) and the activity of antioxidant enzymes in the shoots of both varieties increased under osmotic stress. Regarding the Sor variety, the level of these compounds was more satisfactory. AM improved plant nutrition uptake and osmolyte contents while enhancing antioxidant enzymes and reducing the adverse effects of osmotic stress. Under osmotic stress, the growth and total dry weight were improved upon AM inoculation.

CONCLUSIONS

In general, inoculation of chamomile with AM balanced the uptake of nutrients and increased the level of osmolytes and antioxidant enzymes; hence, it improved plant characteristics under osmotic stress in both varieties. However, it was found to be more effective in reducing stress damages in the Sor variety.

Antioxidant gene expression analysis and evaluation of total phenol content and oxygen-scavenging system in tea accessions under normal and drought stress conditions

BACKGROUND

Abiotic and biotic stresses induce oxidative processes in plant cells that this process starts with the production of ROSs which cause damage to the proteins. Therefore, plants have increased their antioxidant activity to defend against this oxidative stress to be able to handle stress better. In this research, 14 different tea accessions in a randomized complete block design with two replications were evaluated in two normal and drought stress conditions, and their antioxidant activity was measured by DPPH-free radicals' assay and gene expression analysis.

RESULTS

The results of gene expression analysis showed that the 100 and 399 accessions and Bazri cultivar had high values for most of the antioxidant enzymes, ascorbate peroxidase, superoxide dismutase, catalase, and peroxidase under drought stress conditions while the 278 and 276 accessions had the lowest amount of antioxidant enzymes in the same situation. Results showed that the IC50 of the BHT combination was 90.12 μg/ ml. Also, The IC50 of accessions ranged from 218 to 261 μg/ml and 201-264 μg/ml at normal and drought stress conditions, respectively. The 100 and 399 accessions showed the lowest IC50 under normal and drought stress conditions, while 278 and 276 accessions had the highest value for IC50. The antioxidant activity of tea accession extracts under normal conditions was ranged from 25 to 69% for accessions 278 and 100, respectively. While, the antioxidant activities of extracts under drought stress condition was 12 to 83% for accessions 276 and 100, respectively. So, according to the results, 100 and 399 accessions exhibited the least IC50 and more antioxidant activity under drought stress conditions and were identified as stress-tolerant accessions. However, 278 and 276 accessions did not show much antioxidant activity and were recognized as sensitive accessions under drought stress conditions.

CONCLUSIONS

These results demonstrate that total phenol content, antioxidant activity, and the oxygen-scavenging system can be used as a descriptor for identifying drought-tolerant accessions.

Research on the drought tolerance mechanism of Pennisetum glaucum (L.) in the root during the seedling stage

BACKGROUND

Drought is one of the major environmental stresses resulting in a huge reduction in crop growth and biomass production. Pearl millet (Pennisetum glaucum L.) has excellent drought tolerance, and it could be used as a model plant to study drought resistance. The root is a very crucial part of plant that plays important roles in plant growth and development, which makes it a focus of research.

RESULTS

In this study, we explored the mechanism of drought tolerance of pearl millet by comparing physiological and transcriptomic data under normal condition and drought treatment at three time points (1 h, 3 h and 7 h) in the root during the seedling stage. The relative electrical conductivity went up from 1 h to 7 h in both control and drought treatment groups while the content of malondialdehyde decreased. A total of 2004, 1538 and 605 differentially expressed genes were found at 1 h, 3 h and 7 h respectively and 12 genes showed up-regulation at all time points. Some of these differentially expressed genes were significantly enriched into 'metabolic processes', 'MAPK signaling pathway' and 'plant hormone signal transduction' such as the ABA signal transduction pathway in GO and KEGG enrichment analysis.

CONCLUSIONS

Pearl millet was found to have a quick drought response, which may occur before 1 h that contributes to its tolerance against drought stress. These results can provide a theoretical basis to enhance the drought resistance in other plant species.

Soil arsenic toxicity differentially impacts C3 (barley) and C4 (maize) crops under future climate atmospheric CO2

Soil arsenic (As) contamination limits global agricultural productivity. Anthropogenic emissions are causing atmospheric CO₂ levels to rise. Elevated CO₂ (eCO₂) boosts plant growth both under optimal and suboptimal growth conditions. However, the crop-specific interaction between eCO₂ and soil arsenic exposure has not been investigated at the whole plant, physiological and biochemical level. Here, we tested the effects of eCO₂ (620 ppm) and soil As exposure (mild and severe treatments, 25 and 100 mg As/Kg soil) on growth, photosynthesis and redox homeostasis in barley (C3) and maize (C4). Compared to maize, barley was more susceptible to soil As exposure at ambient CO₂ levels. Barley plants accumulated more As, particularly in roots. As accumulation inhibited plant growth and induced oxidative damage in a species-specific manner. As-exposed barley experienced severe oxidative stress as illustrated by high H₂O₂ and protein oxidation levels. Interestingly, eCO₂ differentially mitigated As-induced stress in barley and maize. In barley, eCO₂ exposure reduced photorespiration, H₂O₂ production, and lipid/protein oxidation. In maize eCO₂ exposure led to an upregulation of the ascorbate-glutathione (ASC/GSH)-mediated antioxidative defense system. Combined, this work highlights how ambient and future eCO₂ levels differentially affect the growth, physiology and biochemistry of barley and maize crops exposed to soil As pollution.

Different physiological responses of C3 and C4 plants to nanomaterials

Several studies have previously reported that nanomaterial uptake and toxicity in plants are species dependent. However, the differences between photosynthetic pathways, C3 and C4, following nanomaterial exposure are poorly understood. In the current work, wheat and rice, two C3 pathway species are compared to amaranth and maize, which utilize the C4 photosynthetic mechanism. These plants were cultured in soils which were spiked with CuO, Ag, TiO₂, MWCNT, and FLG nanomaterials. Overall, the C4 plant exhibited higher resilience to NM stress than C3 plants. In particular, significant differences were observed in chlorophyll contents with rice returning a 40.9-54.2% decrease compared to 3.5-15.1% for maize. Fv/Fm levels were significantly reduced by up to 51% in rice whereas no significant reductions were observed in amaranth and maize. Furthermore, NM uptake in the C3 species was greater than that in C4 plants, a trend that was also seen in metal concentration. TEM results showed that CuO NPs altered the chloroplast thylakoid structure in rice leaves and a large number of CuO NPs were observed in the vascular sheath cells. In contrast, there were no significant changes in the chloroplasts in the vascular sheath and no significant CuO NPs were found in maize leaves. This study was the first to systematically characterize the effect of metal and carbon-based nanomaterials in soil on C3 and C4 plants, providing a new perspective for understanding the impact of nanomaterials on plants.

Regulation of ROS Metabolism in Plants under Environmental Stress: A Review of Recent Experimental Evidence

Various environmental stresses singly or in combination generate excess amounts of reactive oxygen species (ROS), leading to oxidative stress and impaired redox homeostasis. Generation of ROS is the obvious outcome of abiotic stresses and is gaining importance not only for their ubiquitous generation and subsequent damaging effects in plants but also for their diversified roles in signaling cascade, affecting other biomolecules, hormones concerning growth, development, or regulation of stress tolerance. Therefore, a good balance between ROS generation and the antioxidant defense system protects photosynthetic machinery, maintains membrane integrity, and prevents damage to nucleic acids and proteins. Notably, the antioxidant defense system not only scavenges ROS but also regulates the ROS titer for signaling. A glut of studies have been executed over the last few decades to discover the pattern of ROS generation and ROS scavenging. Reports suggested a sharp threshold level of ROS for being beneficial or toxic, depending on the plant species, their growth stages, types of abiotic stresses, stress intensity, and duration. Approaches towards enhancing the antioxidant defense in plants is one of the vital areas of research for plant biologists. Therefore, in this review, we accumulated and discussed the physicochemical basis of ROS production, cellular compartment-specific ROS generation pathways, and their possible distressing effects. Moreover, the function of the antioxidant defense system for detoxification and homeostasis of ROS for maximizing defense is also discussed in light of the latest research endeavors and experimental evidence.

CaHsfA1d Improves Plant Thermotolerance via Regulating the Expression of Stress- and Antioxidant-Related Genes

Heat shock transcription factor (Hsf) plays an important role in regulating plant thermotolerance. The function and regulatory mechanism of CaHsfA1d in heat stress tolerance of pepper have not been reported yet. In this study, phylogenetic tree and sequence analyses confirmed that CaHsfA1d is a class A Hsf. CaHsfA1d harbored transcriptional function and predicted the aromatic, hydrophobic, and acidic (AHA) motif mediated function of CaHsfA1d as a transcription activator. Subcellular localization assay showed that CaHsfA1d protein is localized in the nucleus. The CaHsfA1d was transcriptionally up-regulated at high temperatures and its expression in the thermotolerant pepper line R9 was more sensitive than that in thermosensitive pepper line B6. The function of CaHsfA1d under heat stress was characterized in CaHsfA1d-silenced pepper plants and CaHsfA1d-overexpression Arabidopsis plants. Silencing of the CaHsfA1d reduced the thermotolerance of the pepper, while CaHsfA1d-overexpression Arabidopsis plants exhibited an increased insensitivity to high temperatures. Moreover, the CaHsfA1d maintained the H2O2 dynamic balance under heat stress and increased the expression of Hsfs, Hsps (heat shock protein), and antioxidant gene AtGSTU5 (glutathione S-transferase class tau 5) in transgenic lines. Our findings clearly indicate that CaHsfA1d improved the plant thermotolerance via regulating the expression of stress- and antioxidant-related genes.

Physiological and molecular mechanisms governing the effect of virus-free chewing cane seedlings on yield and quality

The effects of increasing yield and quality of virus-free chewing cane seedlings and their physiological and molecular basis were studied in this study. Results showed that compared with infected seedlings (the control), the yield of chewing cane stems grown from virus-free seedlings increased by 21.81-29.93%, stem length increased by 28.66-34.49 cm, internode length increased by 2.16-2.68 cm, the single stem weight increased by 20.10-27.68%, the reducing sugar increased by 0.91-1.15% (absolute value), and sucrose increased by - 0.06-1.33% (absolute value). The decrease in sucrose content did not reach significant level, but all other parameters were reached significant level. The chlorophyll content, photosynthetic parameters such as stomatal conductance (Gs), net photosynthetic rate (Pn) and transpiration rate (Tr), the activity of photosynthetic key enzymes ribulose-1,5-bisphosphate carboxylase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC), and gene (pepc, rbcS, and rbcL) expression levels were all greater in virus-free seedlings than infected seedlings. The content of superoxide anion (O2-) and malondialdehyde (MDA) in virus-free seedlings was lower than infected seedlings at the main growth stage. With increased development, the activities of the antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were gradually higher in virus-free seedlings than infected seedlings. Our results indicate that virus-free seedlings may improve photosynthesis efficiency and promote photosynthesis by increasing chlorophyll content, photosynthetic key enzyme activity, and the gene expression levels in leaves. By increasing the activity of antioxidant enzymes, reducing the degree of membrane lipid peroxidation, and improving the stress resistance of chewing cane, the virus-free chewing cane seedlings increased yield and quality. Our findings provide a scientific and theoretical basis for the promotion and application of virus-free chewing cane seedlings.

Nitrogen supply enhances the physiological resistance of Chinese fir plantlets under polyethylene glycol (PEG)-induced drought stress

Water and nitrogen stresses are major constraints for agricultural and forest productivity. Although the effects of water scarcity or nitrogen stress on plant growth, physiology, and yield have been widely studied, few studies have assessed the combined effects of both stresses. In the present study, we investigated the effects of different nitrogen forms (NO3-N, NH4+-N, and a combination of NO3-N + NH4+-N) on antioxidant enzyme activity, osmotic regulatory substances, and nitrogen assimilation in Chinese fir (Cunninghamia lanceolata) plantlets under drought stress (induced by 10% polyethylene glycol). We found that different N ionic forms had different effects on drought-stressed plantlets. Nitrogen supply greatly increased the activities of superoxide dismutase (SOD), peroxidase (POD) and polyphenol oxidase (PPO) when plantlets were exposed to water stress. The malondialdehyde (MDA) contents significantly decreased under the NH4+ + water stress treatment. The proline (Pr) contents significantly increased in both the NO3-N and NH4+-N + water stress treatment. The nitrate reductase (NR) increased by 7.1% in the NO3- + water stress treatment, and the glutamine synthetase (GS), and the glutamate synthase (GOGAT) activity increased in all the nitrogen + water stress treatments. These results suggested that nitrogen supply could alleviate the adverse effects of drought stress on plants by enhancing antioxidant defense and improving nitrogen assimilation, while the effects on plant tolerance to drought stress varied with nitrogen ionic forms.

Physiological and Biochemical Responses of four cassava cultivars to drought stress

The antioxidant mechanism is crucial for resisting oxidative damage induced by drought stress in plants. Different antioxidant mechanisms may contribute to the tolerance of cassava to drought stress, but for a specific genotype, the response is still unknown. The objective of this study was to investigate antioxidant response and physiological changes of four cassava genotypes under water stress conditions, by keeping the soil moisture content as 80% (control), 50% (medium), 20% (severe) of field capacity for a week. Genotypes RS01 and SC124 were keeping higher relative water content (RWC) and relative chlorophyll content (SPAD value) and less affected by oxidative stress than SC205 and GR4 under drought stress. RS01 just showed slight membrane damage and oxidative stress even under severe drought conditions. A principal component analysis showed that cassava plant water status was closely related to the antioxidant mechanism. Antioxidant response in genotypes RS01 and SC124 under drought stress might attribute to the increased accumulation of ascorbate (AsA) and glutathione (GSH) content and higher superoxide dismutase (SOD) and catalase (CAT) activities, which explained by the up-regulation of Mn-SOD and CAT genes. However, Genotypes SC205 and GR4 mainly depended on the accumulation of total phenolics (TP) and increased glutathione reductase (GR) activity, which attribute to the up-regulation of the GR gene. Our findings could provide vital knowledge for refining the tactics of cultivation and molecular breeding with drought avoidance in cassava.

Influence of drought stress on pistil physiology and reproductive success of two Gossypium hirsutum cultivars differing in drought tolerance

The causes of reproductive failure under drought stress (DS) are poorly understood. We hypothesized that reproductive failure was related to drought-induced changes in pistil biochemistry. To address this hypothesis, a water deficit-induced experiment was conducted with two cotton cultivars (Dexiamian 1, drought tolerant; Yuzaomian 9110, drought sensitive). Results showed that DS decreased the photosynthesis of subtending leaf and downregulated sucrose transporter gene (GhSUT-1) expression in pistil for both cultivars, resulting in lower pistil carbon accumulation which was reflected in the decreased starch accumulation. Lower starch, as potential energy, and adenosine triphosphate (ATP), as direct energy, in droughted pistils suggested less energy for pollen tube entrance into ovules, reducing the fertilized ovule number and fertilization efficiency. Further, although pistil peroxidase activity increased under DS, a higher hydrogen peroxide (H₂ O₂ ) level still was measured in droughted pistils than well-watered pistils, damaging reproductive activities. Moreover, larger decreases in photosynthesis, pistil GhSUT-1 expression, carbon accumulation, starch and ATP contents caused by DS for Yuzaomian 9110 than Dexiamian 1, and different responses of superoxide dismutase and catalase activities, and ascorbic acid and H₂ O₂ contents to DS between the two cultivars might be the reasons causing a greater decrease in fertilization efficiency for Yuzaomian 9110 than Dexiamian 1 under DS. Thus, we suggest that decreased ovule fertilization under DS was related to the disorganized carbohydrate metabolism and inefficient antioxidant defense in droughted pistils, and the effects of DS on pistil carbohydrate metabolism and antioxidant defense were more significant for drought-sensitive cultivars than drought-tolerant cultivars.

The CaChiVI2 Gene of Capsicum annuum L. Confers Resistance Against Heat Stress and Infection of Phytophthora capsici

Extreme environmental conditions seriously affect crop growth and development, resulting in substantial reduction in yield and quality. However, chitin-binding proteins (CBP) family member CaChiVI2 plays a crucial role in eliminating the impact of adverse environmental conditions, such as cold and salt stress. Here, for the first time it was discovered that CaChiVI2 (Capana08g001237) gene of pepper (Capsicum annuum L.) had a role in resistance to heat stress and physiological processes. The full-length open-reading frame (ORF) of CaChiVI2 (606-bp, encoding 201-amino acids), was cloned into TRV2:CaChiVI2 vector for silencing. The CaChiVI2 gene carries heat shock elements (HSE, AAAAAATTTC) in the upstream region, and thereby shows sensitivity to heat stress at the transcriptional level. The silencing effect of CaChiVI2 in pepper resulted in increased susceptibility to heat and Phytophthora capsici infection. This was evident from the severe symptoms on leaves, the increase in superoxide (O2 -) and hydrogen peroxide (H2O2) accumulation, higher malondialdehyde (MDA), relative electrolyte leakage (REL) and lower proline contents compared with control plants. Furthermore, the transcript level of other resistance responsive genes was also altered. In addition, the CaChiIV2-overexpression in Arabidopsis thaliana showed mild heat and drought stress symptoms and increased transcript level of a defense-related gene (AtHSA32), indicating its role in the co-regulation network of the plant. The CaChiVI2-overexpressed plants also showed a decrease in MDA contents and an increase in antioxidant enzyme activity and proline accumulation. In conclusion, the results suggest that CaChiVI2 gene plays a decisive role in heat and drought stress tolerance, as well as, provides resistance against P. capsici by reducing the accumulation of reactive oxygen species (ROS) and modulating the expression of defense-related genes. The outcomes obtained here suggest that further studies should be conducted on plants adaptation mechanisms in variable environments.

A comparative study of the physiological and biochemical properties of tomato (Lycopersicon esculentum M.) and maize (Zea mays L.) under palladium stress

There is great concern about the environmental impact and toxicity of palladium (Pd) because of its widespread use in automotive catalytic converters and other applications. Pd migrates and transforms in the environment and is absorbed by plant roots where it affects plant growth and eventually enters the food chain. Here we explored the effects of Pd on the physicochemical and biochemical characteristics of C3 (tomato) and C4 (maize) plants. We measured physicochemical and biochemical properties, including chlorophyll, protein, soluble sugar, antioxidant enzymes, malondialdehyde, proline, and root activity, in tomato and maize seedlings after cultivation in different concentrations of PdCl₂ solution (0, 0.2, 0.5, and 1 mM) in order to observe how Pd stresses them. Results showed that, with increasing Pd concentration, chlorophyll a and chlorophyll b contents and root activity decreased. Meanwhile, malondialdehyde, proline, protein, and soluble sugar contents increased. After cultivation in 1 mM PdCl₂, the Pd contents in the roots, stems, and leaves of tomato seedlings were 12.389, 1.132, and 0.206 mg/g, respectively. In general, Pd has significant effects on the physiological and biochemical properties of both tomato and maize. Additionally, tomato seedlings were more sensitive to Pd stress, photosynthesis in maize was less inhibited by Pd and the antioxidant capability of maize was stronger. These results indicated that maize (C4 plant) exhibited a higher tolerance to Pd than tomato (C3 plant). Pd migration in tomato was observed and the translocation factor (TF) was calculated. The values of TF_stem/root, TF_leaf/root, TF_leaf/stem, and TF_shoot/root were 0.09, 0.02, 0.18, and 0.11 in tomato seedlings, respectively. Pd accumulated most in the roots, followed in turn by stems, leaves, and only trace amount of Pd was transferred into shoots.

Arbuscular Mycorrhizal Fungi Mediate Drought Tolerance and Recovery in Two Contrasting Carob (Ceratonia siliqua L.) Ecotypes by Regulating Stomatal, Water Relations, and (In)Organic Adjustments

Irregular precipitation and drought caused an increase in tree mortality rates in multiple forest biomes with alterations in both ecosystem services and carbon balance. Carob (Ceratonia siliqua) growth and production in arid and semi-arid ecosystems are likely affected by climate change-induced droughts. Understanding the physiological responses of drought-induced early-stage tree death and strategies to enhance drought tolerance and optimize growth will help tree improvement programs. Mycorrhizal inoculation has a pronounced impact on plant growth, water absorption, mineral nutrition, and protection from abiotic stresses. However, a better understanding of these complex interconnected cellular processes and arbuscular mycorrhizal fungi (AMF)-mediated mechanisms regulating drought tolerance in plants will enhance its potential application as an efficient approach for bio-amelioration of stresses. The objectives of this work were to elucidate the different effects of autochthone AMF on inorganic solute and water content uptakes, organic adjustments (sugar and proteins content), leaf gas exchange (stomatal conductance and efficiency of photosystems I and II), and oxidative damage of two contrasting ecotypes of carob seedlings: coastal (southern ecotype (SE)) and in-land (northern ecotype (NE)) under control (C), drought (by cessation of irrigation for 15 days (15D)), and recovery (R) conditions. Our findings showed that AMF promoted growth, nutrient content, and physiological and biochemical parameters in plants of both ecotypes during C, 15D, and R conditions. After four days of recovery, stomatal conductance (gs), the maximum photochemical efficiency of PSII (Fv/Fm), water content, and plant uptake of mineral nutrients (P, K, Na, and Ca) were significantly higher in shoots of mycorrhizal (AM) than non-mycorrhizal (NM) control plants. Consequently, AMF reduced to a greater degree the accumulation of hydrogen peroxide (H2O2) and oxidative damage to lipid (malondialdehyde (MDA)) content in AM than NM plants in NE and SE, after recovery. Altogether, our findings suggest that AMF can play a role in drought resistance of carob trees at an early stage by increasing the inorganic solutes (P, K, Na, and Ca), water content uptake, organic solutes (soluble sugars and protein content), stomatal conductance, and defense response against oxidative damage during re-watering after drought stress.

Flavonoid Naringenin Alleviates Short-Term Osmotic and Salinity Stresses Through Regulating Photosynthetic Machinery and Chloroplastic Antioxidant Metabolism in Phaseolus vulgaris

The current study was conducted to demonstrate the possible roles of exogenously applied flavonoid naringenin (Nar) on the efficiency of PSII photochemistry and the responses of chloroplastic antioxidant of salt and osmotic-stressed Phaseolus vulgaris (cv. Yunus90). For this aim, plants were grown in a hydroponic culture and were treated with Nar (0.1 mM and 0.4 mM) alone or in a combination with salt (100 mM NaCl) and/or osmotic (10% Polyethylene glycol, -0.54 MPa). Both caused a reduction in water content (RWC), osmotic potential (Ψ_Π), chlorophyll fluorescence (F_v/F_m), and potential photochemical efficiency (F_v/F_o). Nar reversed the changes on these parameters. The phenomenological fluxes (TR_o/CS and ET_o/CS) altered by stress were induced by Nar and Nar led to a notable increase in the performance index (PI_ABS) and the capacity of light reaction [ΦP_o/(1-ΦP_o)]. Besides, Nar-applied plants exhibited higher specific fluxes values [ABS/RC, ET_o/RC, and ΨE_o/(1-ΨE_o)] and decreasing controlled dissipation of energy (DI_o/CS_o and DI_o/RC). The transcripts levels of psbA and psbD were lowered in stress-treated bean but upregulated in Nar-treated plants after stress exposure. Nar also alleviated the changes on gas exchange parameters [carbon assimilation rate (A), stomatal conductance (g_s), intercellular CO₂ concentrations (C_i), transpiration rate (E), and stomatal limitation (L_s)]. By regulating the antioxidant metabolism of the isolated chloroplasts, Nar was able to control the toxic levels of hydrogen peroxide (H₂O₂) and TBARS (lipid peroxidation) produced by stresses. Chloroplastic superoxide dismutase (SOD) activity reduced by stresses was increased by Nar. In response to NaCl, Nar increased the activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR), as well as peroxidase (POX). Nar protected the bean chloroplasts by minimizing disturbances caused by NaCl exposure via the ascorbate (AsA) and glutathione (GSH) redox-based systems. Under Nar plus PEG, Nar maintained the AsA regeneration by the induction of MDHAR and DHAR, but not GSH recycling by virtue of no induction in GR activity and the reduction in GSH/GSSG and GSH redox state. Based on these advances, Nar protected in bean chloroplasts by minimizing disturbances caused by NaCl or PEG exposure via the AsA or GSH redox-based systems and POX activity.

Insights into Drought Stress Signaling in Plants and the Molecular Genetic Basis of Cotton Drought Tolerance

Drought stress restricts plant growth and development by altering metabolic activity and biological functions. However, plants have evolved several cellular and molecular mechanisms to overcome drought stress. Drought tolerance is a multiplex trait involving the activation of signaling mechanisms and differentially expressed molecular responses. Broadly, drought tolerance comprises two steps: stress sensing/signaling and activation of various parallel stress responses (including physiological, molecular, and biochemical mechanisms) in plants. At the cellular level, drought induces oxidative stress by overproduction of reactive oxygen species (ROS), ultimately causing the cell membrane to rupture and stimulating various stress signaling pathways (ROS, mitogen-activated-protein-kinase, Ca2+, and hormone-mediated signaling). Drought-induced transcription factors activation and abscisic acid concentration co-ordinate the stress signaling and responses in cotton. The key responses against drought stress, are root development, stomatal closure, photosynthesis, hormone production, and ROS scavenging. The genetic basis, quantitative trait loci and genes of cotton drought tolerance are presented as examples of genetic resources in plants. Sustainable genetic improvements could be achieved through functional genomic approaches and genome modification techniques such as the CRISPR/Cas9 system aid the characterization of genes, sorted out from stress-related candidate single nucleotide polymorphisms, quantitative trait loci, and genes. Exploration of the genetic basis for superior candidate genes linked to stress physiology can be facilitated by integrated functional genomic approaches. We propose a third-generation sequencing approach coupled with genome-wide studies and functional genomic tools, including a comparative sequenced data (transcriptomics, proteomics, and epigenomic) analysis, which offer a platform to identify and characterize novel genes. This will provide information for better understanding the complex stress cellular biology of plants.

Knockdown of CaHSP60-6 confers enhanced sensitivity to heat stress in pepper (Capsicum annuum L.)

HSP60 gene family in pepper was analyzed through bioinformatics along with transcriptional regulation against multiple abiotic and hormonal stresses. Furthermore, the knockdown of CaHSP60-6 increased sensitivity to heat stress. The 60 kDa heat shock protein (HSP60) also known as chaperonin (cpn60) is encoded by multi-gene family that plays an important role in plant growth, development and in stress response as a molecular chaperone. However, little is known about the HSP60 gene family in pepper (Capsicum annuum L.). In this study, 16 putative pepper HSP60 genes were identified through bioinformatic tools. The phylogenetic tree revealed that eight of the pepper HSP60 genes (50%) clustered into group I, three (19%) into group II, and five (31%) into group III. Twelve (75%) CaHSP60 genes have more than 10 introns, while only a single gene contained no introns. Chromosomal mapping revealed that the tandem and segmental duplication events occurred in the process of evolution. Gene ontology enrichment analysis predicted that CaHSP60 genes were responsible for protein folding and refolding in an ATP-dependent manner in response to various stresses in the biological processes category. Multiple stress-related cis-regulatory elements were found in the promoter region of these CaHSP60 genes, which indicated that these genes were regulated in response to multiple stresses. Tissue-specific expression was studied under normal conditions and induced under 2 h of heat stress measured by RNA-Seq data and qRT-PCR in different tissues (roots, stems, leaves, and flowers). The data implied that HSP60 genes play a crucial role in pepper growth, development, and stress responses. Fifteen (93%) CaHSP60 genes were induced in both, thermo-sensitive B6 and thermo-tolerant R9 lines under heat treatment. The relative expression of nine representative CaHSP60 genes in response to other abiotic stresses (cold, NaCl, and mannitol) and hormonal applications [ABA, methyl jasmonate (MeJA), and salicylic acid (SA)] was also evaluated. Knockdown of CaHSP60-6 increased the sensitivity to heat shock treatment as documented by a higher relative electrolyte leakage, lipid peroxidation, and reactive oxygen species accumulation in silenced pepper plants along with a substantial lower chlorophyll content and antioxidant enzyme activity. These results suggested that HSP60 might act as a positive regulator in pepper defense against heat and other abiotic stresses. Our results provide a basis for further functional analysis of HSP60 genes in pepper.

Understanding the Role of the Antioxidant System and the Tetrapyrrole Cycle in Iron Deficiency Chlorosis

Iron deficiency chlorosis (IDC) is an abiotic stress often experienced by soybean, owing to the low solubility of iron in alkaline soils. Here, soybean lines with contrasting Fe efficiencies were analyzed to test the hypothesis that the Fe efficiency trait is linked to antioxidative stress signaling via proper management of tissue Fe accumulation and transport, which in turn influences the regulation of heme and non heme containing enzymes involved in Fe uptake and ROS scavenging. Inefficient plants displayed higher oxidative stress and lower ferric reductase activity, whereas root and leaf catalase activity were nine-fold and three-fold higher, respectively. Efficient plants do not activate their antioxidant system because there is no formation of ROS under iron deficiency; while inefficient plants are not able to deal with ROS produced under iron deficiency because ascorbate peroxidase and superoxide dismutase are not activated because of the lack of iron as a cofactor, and of heme as a constituent of those enzymes. Superoxide dismutase and peroxidase isoenzymatic regulation may play a determinant role: 10 superoxide dismutase isoenzymes were observed in both cultivars, but iron superoxide dismutase activity was only detected in efficient plants; 15 peroxidase isoenzymes were observed in the roots and trifoliate leaves of efficient and inefficient cultivars and peroxidase activity levels were only increased in roots of efficient plants.

Toxicological risks of Acid Bordeaux B on duckweed and the plant potential for effective remediation of dye-polluted waters

In the present study, the ability of duckweed (Lemna minor L.) in the decolorization of Acid Bordeaux B (ABB), as an aminoazo benzene dye, from polluted waters was evaluated. It was found that the rise of temperature and enhancement of the plant initial weight led to increasing the dye removal efficiency, but raising the initial dye concentration and pH reduced it. However, in the optimum conditions, the plant exhibited a considerable potential for the phytoremediation of ABB by 94%. The comparison of the experimental dye removal efficiency with its predicted amounts from ANN (R² = 0.99) showed that ANN supplied the appropriate predictive performance. Inhibition of the plant growth and reduction of the chlorophyll (Chl) a, b, and a+b content (around 26%, 32.4%, and 28.6%, respectively) after plant treatment with 40 mg/L of ABB confirmed its toxic effects on the plant in high concentrations. Antioxidant enzyme activities and contents of malondialdehyde, phenol, and flavonoids were also raised by the augmentation of the ABB concentration. As a result of the ABB biodegradation pathway, seven intermediate compounds were identified using GC-MS analysis.

A small heat shock protein CaHsp25.9 positively regulates heat, salt, and drought stress tolerance in pepper (Capsicum annuum L.)

Extreme environmental conditions seriously affect crop growth and development, resulting in a decrease in crop yield and quality. However, small heat shock proteins (Hsp20s) play an important role in helping plants to avoid these negative impacts. In this study, we identified the expression pattern of the CaHsp25.9 gene in a thermo-tolerance pepper line R9 and thermo-sensitive line B6. The transcription of CaHsp25.9 was strongly induced by heat stress in both R9 and B6. The expression of CaHsp25.9 was induced by salt and drought stress in R9. Additionally, the CaHsp25.9 protein was localized in the cell membrane and cytoplasm. When silencing the CaHsp25.9 gene in the R9 line, the accumulation of malonaldehyde (MDA), relative electrolytic leakage, hydrogen peroxide, superoxide anion were increased, while total chlorophyll decreased under heat, salt, and drought stress. Over-expression of CaHsp25.9 in Arabidopsis resulted in decreased MDA, while proline, superoxide dismutase activity, germination, and root length increased under heat, salt, and drought stress. However, peroxidase activity was higher in drought stress but lower in heat and salt stress in transgenic Arabidopsis compared to the wild type (WT). Furthermore, the transcription of stress related genes was more highly induced in transgenic lines than WT. Our results indicated that CaHsp25.9 confers heat, salt, and drought stress tolerance to plants by reducing the accumulation of reactive oxygen species, enhancing the activity of antioxidant enzymes, and regulating the expression of stress-related genes. Therefore, these results may provide insight into plant adaption mechanisms developed in variable environments.

Using intervarietal substitution lines for the identification of wheat chromosomes involved in early responses to water-deficit stress

Water deficit induces reactive oxygen species (ROS) overproduction, which in turn inhibits plant growth and development. High concentrations of ROS disrupt the osmotic balance in plant cells and alter membrane integrity. Chromosomes carrying structural or regulatory genes must be detected to better understand plant response mechanisms to stress. The aim of our study was to identify Triticum aestivum L. chromosomes involved in early responses to short-term water-deficit stress (1, 3 and 6 h). In the present study, intervarietal substitution lines of drought-tolerant 'Saratovskaya 29' and sensitive 'Janetzkis Probat' wheat cultivars were examined. We studied the biochemical plant response system and conducted an analysis of catalase, ascorbate peroxidase and guaiacol peroxidase activities, levels of lipid peroxidation and changes in relative water content. Our results determined that the first reaction was a significant increase in guaiacol peroxidase (GPX) activity. However, the strongest impact on plant responses was found for catalase (CAT), which caused a significant decrease in lipid peroxidation (LPO) levels. Our findings indicate that chromosomes 5A, 4B, 6B and 7D are associated with early responses to short-term osmotic stress in wheat.

Arbuscular Mycorrhizal Fungi Alleviate Drought Stress in C3 (Leymus chinensis) and C4 (Hemarthria altissima) Grasses via Altering Antioxidant Enzyme Activities and Photosynthesis

As one of the most important limiting factors of grassland productivity, drought is predicted to increase in intensity and frequency. Greenhouse studies suggest that arbuscular mycorrhizal fungi (AMF) can improve plant drought resistance. However, whether AMF can improve plant drought resistance in field conditions and whether the effects of AMF on drought resistance differ among plants with different photosynthetic pathways remain unclear. To evaluate the effect of indigenous AMF on plant drought resistance, an in situ rainfall exclusion experiment was conducted in a temperate meadow in northeast China. The results showed that AMF significantly reduced the negative effects of drought on plant growth. On average, AMF enhanced plant biomass, photosynthetic rate (A), stomatal conductance (g s), intrinsic water use efficiency (iWUE), and superoxide dismutase (SOD) activity of the C3 species Leymus chinensis by 58, 63, 38, 15, and 45%, respectively, and reduced levels of malondialdehyde (MDA) by 32% under light and moderate drought (rainfall exclusion of 30 and 50%, respectively). However, under extreme drought (rainfall exclusion of 70%), AMF elevated only aboveground biomass and catalase (CAT) activities. Averagely, AMF increased the aboveground biomass, A, and CAT activity of Hemarthria altissima (C4) by 37, 28, and 30%, respectively, under light and moderate droughts. The contribution of AMF to plant drought resistance was higher for the C3 species than that for the C4 species under both light and moderate drought conditions. The results highlight potential photosynthetic type differences in the magnitude of AMF-associated enhancement in plant drought resistance. Therefore, AMF may determine plant community structure under future climate change scenarios by affecting the drought resistance of different plant functional groups.

The Role of the Plant Antioxidant System in Drought Tolerance

Water deficiency compromises plant performance and yield in many habitats and in agriculture. In addition to survival of the acute drought stress period which depends on plant-genotype-specific characteristics, stress intensity and duration, also the speed and efficiency of recovery determine plant performance. Drought-induced deregulation of metabolism enhances generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) which in turn affect the redox regulatory state of the cell. Strong correlative and analytical evidence assigns a major role in drought tolerance to the redox regulatory and antioxidant system. This review compiles current knowledge on the response and function of superoxide, hydrogen peroxide and nitric oxide under drought stress in various species and drought stress regimes. The meta-analysis of reported changes in transcript and protein amounts, and activities of components of the antioxidant and redox network support the tentative conclusion that drought tolerance is more tightly linked to up-regulated ascorbate-dependent antioxidant activity than to the response of the thiol-redox regulatory network. The significance of the antioxidant system in surviving severe phases of dehydration is further supported by the strong antioxidant system usually encountered in resurrection plants.

Analysis of wheat gene expression related to the oxidative stress response and signal transduction under short-term osmotic stress

Water shortage is a major environmental stress that causes the generation of reactive oxygen species (ROS). The increase in ROS production induces molecular responses, which are key factors in determining the level of plant tolerance to stresses, including drought. The aim of this study was to determine the expression levels of genes encoding MAPKs (MAPK3 and MAPK6), antioxidant enzymes (CAT, APX and GPX) and enzymes involved in proline biosynthesis (P5CS and P5CR) in Triticum aestivum L. seedlings in response to short-term drought conditions. A series of wheat intervarietal substitution lines (ISCSLs) obtained by the substitution of single chromosomes from a drought-sensitive cultivar into the genetic background of a drought-tolerant cultivar was used. This source material allowed the chromosomal localization of the genetic elements involved in the response to the analyzed stress factor (drought). The results indicated that the initial plant response to drought stress resulted notably in changes in the expression of MAPK6 and CAT and both the P5CS and P5CR genes. Our results showed that the substitution of chromosomes 3B, 5A, 7B and 7D had the greatest impact on the expression level of all tested genes, which indicates that they contain genetic elements that have a significant function in controlling tolerance to water deficits in the wheat genome.

Chlorophyll Fluorescence, Photoinhibition and Abiotic Stress: Does it Make Any Difference the Fact to Be a C3 or C4 Species?

Chlorophyll fluorescence analysis is one of the most powerful and widely used techniques to study the effect of stresses on the photosynthetic process. From the first utilization, the F v/F m ratio has been largely used as a sensitive indicator of plant photosynthetic performance. Decreases of this index are indicative of the reduction of photosystem II (PSII) efficiency, namely photoinhibition. In the last 20 years, application of chlorophyll fluorescence has been largely improved, and many other informative parameters have been established to detect PSII photochemical efficiency and the partitioning of light energy to alternative dissipative mechanisms (qE, energy-dependent quenching; qZ, zeaxanthin-dependent quenching and qI, photoinhibitory quenching; qH, sustained photoprotective antenna quenching; qM, quenching dependent to chloroplast movement; qT, light harvesting complexes II-I state-transition) such as the recently developed "photoprotective power" of non-photochemical quenching (pNPQ). This review reports a brief description of the main chlorophyll fluorescence parameters and a wide analysis of the current bibliography on the use of different parameters which are useful to detect events of PSII photoinhibition. In addition, in view of the inherent differences in morpho-anatomical, physiological and biochemical features between C3 and C4 metabolism, possible differences in terms of photoinhibition between C3 and C4 plant species under stress conditions are proposed. The attempt is to highlight the limits of their comparison in terms of susceptibility to photoinhibition and to propose direction of future research which, assisted by chlorophyll fluorescence, should improve the knowledge of the different sensitivity of C3 and C4 to abiotic stressors.

CaHSP16.4, a small heat shock protein gene in pepper, is involved in heat and drought tolerance

Environmental stress affects growth and development of crops, and reduces yield and quality of crops. To cope with environmental stressors, plants have sophisticated defense mechanisms, including the HSF/HSP pathway. Here, we identify the expression pattern of CaHSP16.4 in thermo-tolerant and thermo-sensitive pepper (Capsicum annuum L.) lines. Under heat stress, R9 thermo-tolerant line had higher CaHSP16.4 expression level than the B6 thermo-sensitive line. Under drought stress, expression pattern of CaHSP16.4 was dynamic. Initially, CaHSP16.4 was downregulated then CaHSP16.4 significantly increased. Subcellular localization assay showed that CaHSP16.4 localizes in cytoplasm and nucleus. In the R9 line, silencing of CaHSP16.4 resulted in a significant increase in malonaldehyde content and a significant reduction in total chlorophyll content, suggesting that silencing of CaHSP16.4 reduces heat and drought stresses tolerance. Overexpression of CaHSP16.4 enhances tolerance to heat stress in Arabidopsis. Under heat stress, the survival rate of CaHSP16.4 overexpression lines was significantly higher than wild type. Furthermore, under heat, drought, and combined stress conditions, the CaHSP16.4-overexpression lines had lower relative electrolytic leakage and malonaldehyde content, higher total chlorophyll content, and higher activity levels of superoxide dismutase, catalase, ascorbic acid peroxidase, and glutathione peroxidase compared to wild type. Furthermore, the expression levels of the stress response genes in the overexpression lines were higher than the wild type. These results indicate that the overexpression of CaHSP16.4 enhances the ability of reactive oxygen species scavenging under heat and drought stress.

Coping with drought: stress and adaptive mechanisms, and management through cultural and molecular alternatives in cotton as vital constituents for plant stress resilience and fitness

Increased levels of greenhouse gases in the atmosphere and associated climatic variability is primarily responsible for inducing heat waves, flooding and drought stress. Among these, water scarcity is a major limitation to crop productivity. Water stress can severely reduce crop yield and both the severity and duration of the stress are critical. Water availability is a key driver for sustainable cotton production and its limitations can adversely affect physiological and biochemical processes of plants, leading towards lint yield reduction. Adaptation of crop husbandry techniques suitable for cotton crop requires a sound understanding of environmental factors, influencing cotton lint yield and fiber quality. Various defense mechanisms e.g. maintenance of membrane stability, carbon fixation rate, hormone regulation, generation of antioxidants and induction of stress proteins have been found play a vital role in plant survival under moisture stress. Plant molecular breeding plays a functional role to ascertain superior genes for important traits and can offer breeder ready markers for developing ideotypes. This review highlights drought-induced damage to cotton plants at structural, physiological and molecular levels. It also discusses the opportunities for increasing drought tolerance in cotton either through modern gene editing technology like clustered regularly interspaced short palindromic repeat (CRISPR/Cas9), zinc finger nuclease, molecular breeding as well as through crop management, such as use of appropriate fertilization, growth regulator application and soil amendments.

A return to the genetic heritage of durum wheat to cope with drought heightened by climate change

The objective of this work was to perform a comparative analysis of the physiological, biochemical and agronomical parameters of recent and heritage durum wheat cultivars (Triticum durum Desf.) under water-deficit conditions. Five cultivars were grown under irrigated (control) and rainfall (stressed) conditions. Different agro-physiological and biochemical parameters were studied: electrolyte leakage, relative water content, chlorophyll fluorescence, proline, soluble sugars, specific peroxidase activity, yield and drought stress indices. It was revealed that a water deficit increased proline content, electrolyte leakage, soluble sugars and specific peroxidase activity and decreased relative water content, fluorescence and grain yield. According to these parameters and drought stress indices, our investigation indicated that old cultivars are the best-adapted to local conditions and showed characteristics of drought tolerance, while recent cultivars showed more drought susceptibility. Therefore, local cultivars of each country should be kept by farmers and plant breeders to preserve their genetic heritage.

Antioxidant enzymes responses in shoots of arsenic hyperaccumulator, Isatis cappadocica Desv., under interaction of arsenate and phosphate

The present study investigated the effects of arsenate and phosphate interaction on growth, lipid peroxidation, arsenic (As) accumulation, phosphorus (P) accumulation, and the activities of some antioxidant enzymes in Isatis cappadocica. Plants were exposed to (50-1200 μmol L^-1) arsenate and (5-1600 μmol L^-1) phosphate for 28 days in a hydroponic system. At a phosphate concentration of 1600 µM, biomass production and chlorophyll content increased, demonstrating clearly that phosphate was able to provide protection against As toxicity. In case of joint application of 1600 µM phosphate with arsenate, the As accumulation and then lipid peroxidation were decreased when compared to samples treated with arsenate and 5 µM phosphate. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) increased with increasing arsenate supply levels. Addition of P decreased activities of SOD, APX and CAT, while high phosphate treatments had a positive effect on GR activity, which may be due to regulation of glutathione biosynthesis within the plants. In conclusion, high arsenate treatment (800-1200 µM) could cause an increasing oxidative stress, which can be scavenged by the antioxidant enzyme. Furthermore, P may affect As-induced oxidative stress through nutrient condition and As accumulation.

Changes in redox regulation during transition from C3 to single cell C4 photosynthesis in Bienertia sinuspersici

Bienertia sinuspersici performs single cell C₄ photosynthesis without Kranz anatomy. Peripheral and central cytoplasmic compartments in a single chlorenchyma cell act as mesophyll cells and bundle sheath cells. Development of this specialized mechanism is gradual during plant development. Young leaves perform C₃ photosynthesis, while mature leaves have complete C₄ cycle. The aim of this work was to investigate changes in redox regulation and antioxidant defence during transition from C₃ to single cell C₄ photosynthesis in B. sinuspersici leaves. First, we confirmed gradual development of C₄ with protein blot and qRT-PCR analysis of C₄ enzymes. After this activities and isoenzymes of superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and H₂O₂ and TBARS and glutathione pool and redox status (GSH/GSSG) were determined in young, developing and mature leaves during transition from C₃ to single cell C₄ photosynthesis. Activities of SOD, APX and POX decrease, while GR and DHAR were increased. However, most striking results were the changes in isoenzyme patterns of SOD, CAT and GR which were gradual through transition to C₄ photosynthesis.

Molecular responses to recurrent drought in two contrasting rice genotypes

The set of variables analyzed as integrated by multivariate analysis of principal components consistently showed a memory effect induced by the drought pre-treatment in AN Cambará plants. The effects of drought can vary ddepending on many factors. Among these the occurrence of a previous water stress may leave a residual effect (memory), influencing the future performance of a plant in response to a new drought event. This study tested the hypothesis that plants experiencing recurrent drought would show more active mechanisms of water deficit tolerance, mainly plants of the genotype that is cultivated often experiencing water shortages periods. Additionally, all the plants subjected to water deficit were rehydrated by 24 h and the expression of transcription factors related to drought responses was re-evaluated. To this end, the water status of two rice genotypes, BRS Querência (flooded) and AN Cambará (dryland), was evaluated to identify molecular alterations likely underpinning drought-memory. In growth stage V5, some plants were exposed to water stress (10% VWC soil moisture-pre-treatment). Thereafter, the pots were rehydrated at the same level as the control pots and maintained under this condition until drought was reapplied (10% VWC) at the reproductive stage (R1-R2). Then, the plants were rehydrated and maintained at pot capacity for 24 h. Overall, the set of variables analyzed integrally by multivariate analysis of principal components consistently showed a memory effect induced by the drought pre-treatment in AN Cambará plants (the dryland genotype). This conclusion, based on data of the biochemical and molecular analyses, was supported by the greater capacity of maintenance of the water status by stomatal regulation of the pre-treated and rehydrated plants after the second drought stimulus.

Integrating High-Resolution and Solid-State Magic Angle Spinning NMR Spectroscopy and a Transcriptomic Analysis of Soybean Tissues in Response to Water Deficiency

INTRODUCTION

Solid-state NMR (SSNMR) spectroscopy methods provide chemical environment and ultrastructural details that are not easily accessible by other non-destructive, high-resolution spectral techniques. High-resolution magic angle spinning (HR-MAS) has been widely used to obtain the metabolic profile of a heterogeneous sample, combining the resolution enhancement provided by MAS in SSNMR with the shimming and locking procedures in liquid-state NMR.

OBJECTIVE

In this work, we explored the feasibility of using the HR-MAS and SSNMR techniques to identify metabolic changes in soybean leaves subjected to water-deficient conditions.

METHODOLOGY

Control and water-deficient soybean leaves were analysed using one-dimensional (1D) HR-MAS and SSNMR. Total RNA was extracted from the leaves for the transcriptomic analysis.

RESULTS

The 1 H HR-MAS and CP-MAS 13 C{1 H} spectra of soybean leaves grown with and without water deficiency stress revealed striking differences in metabolites. A total of 30 metabolites were identified, and the impact of water deficiency on the metabolite profile of soybean leaves was to induce amino acid synthesis. High expression levels of genes required for amino acid biosynthesis were highly correlated with the compounds identified by 1 H HR-MAS.

CONCLUSIONS

The integration of the 1 H HR-MAS and SSNMR spectra with the transcriptomic data provided a complete picture of the major changes in the metabolic profile of soybeans in response to water deficiency. Copyright © 2017 John Wiley & Sons, Ltd.

Assessment on cadmium and lead in soil based on a rhizosphere microbial community

The soil ecosystem is easily polluted by heavy metals. Cadmium (Cd) and lead (Pb), as the main pollutants of heavy metals, cause much harm to the soil ecosystem. However, the impact of the two chemicals on rhizosphere microorganisms remains almost unknown. The change of catalase (CAT) activity was consistent with the microbial biomass. 16S rRNA gene sequencing was performed on soil samples to study the toxic effect of heavy metals. On performing sequence analysis at the phylum and family taxonomic levels, 32 identified phyla and 303 families were observed. The dominant phylum was Proteobacteria followed by Bacteroidetes, Acidobacteria, and Actinobacteria. The relative abundance of the dominant phyla was obviously changed under the stress of Cd and Pb, suggesting that the heavy metal input had affected the microbial community structure. At the Order and Family levels, there was different variation of richness and diversity in Cd and Pb group as compared to those in the control group. Furthermore, abundance and similarity analysis showed the differences between Cd and Pb, indicating different toxicology effect on rhizosphere microbial communities because of the unique properties. This study provided a novel insight into the composition of microbial communities of rhizosphere, which could be used to evaluate the soil environment.