ROS-mediated abiotic stress-induced programmed cell death in plants

The early hormone signaling network underlying wound-induced de novo root regeneration

Plants possess a remarkable capability to regenerate new organs after wounding. De novo root regeneration (DNRR) from aboveground tissues after physical wounding is observed in a wide range of plant species. Here, we provide an overview of recent progress in the elucidation of the molecular mechanisms that govern DNRR, with a particular emphasis on the early signaling components. Wound-inducible chemicals and hormones such as jasmonic acid, ethylene, and salicylic acid, which were originally identified as defense hormones, influence DNRR. Ongoing work elucidating the molecular network underlying DNRR provides insight into the coactivating regeneration and defense responses at the early stages of the wound response in plants.

Cellular nitro-oxidative burden and survival through regulated cell death in the plants

Throughout the life of a plant, generations of different forms of reactive oxygen (ROS) and nitrogen species (RNS) are derived as a by-product of metabolic events. The quantum of ROS and RNS becomes higher once a plant encounters a perturbed situation either through biotic or abiotic factor. As each of reactive species is harmful to the cells beyond certain optimal level, it requires a mechanism to detoxify RONS induced cellular toxicity. For the purpose cell has instituted highly organized multi-layered defense mechanisms. In the first layer of defense, cell produces different antioxidant enzymes and non-enzyme molecules. Once generated, ROS and RNS become beyond the detoxification capacity of cellular antioxidant pool, another strategy comes into the operation wherein a few targeted cells undergo self-autolysis progression known as programmed cell death (PCD). The process of PCD has been partially dissected in plants emphasizing either under amplified ROS or RNS condition. However, there are evidences for reaction between species of ROS and RNS. It is unequivocally evident that superoxide has tendency to react with nitric oxide giving rise to a very potential oxidant called peroxynitrite that has ability to nitrosylate several biomolecules thus, altering cellular fate. This suggests that cellular damage caused by reactive species of nitrogen and oxygen is not only an outcome of accumulation of individual species of ROS and RNS, but a combinatorial product of ROS and RNS may have a key role to play. In this review, we intend to advocate role of cellular nitro-oxidative condition in PCD in plants.

Melanaphis sacchari/sorghi complex: current status, challenges and integrated strategies for managing the invasive sap-feeding insect pest of sorghum

Melanaphis sacchari (Zehntner;Hemiptera: Aphididae), sugarcane aphid (SCA), is an invasive phloem-feeder found worldwide with a wide host range of economically important plants including sorghum and sugarcane. Given its high reproductive capacity and ability to rapidly spread over long distances, SCA presents challenges for effective control, leading to substantial economic losses. Recent studies have identified two multiloci SCA genotypes specialized in feeding on sugarcane (MLL-D) and sorghum (MLL-F) in the USA, which raises concerns as the USA is the second largest sorghum-producing country. This has encouraged research towards identifying these two biotypes where some research has stated them as two species; MLL-D clade to be M. sacchari and MLL-F clade to be M. sorghi Theobald (Hemiptera: Aphididae), sorghum aphid (SA). This review aims at compiling research progress that has been made on understanding the SCA/SA species complex. Furthermore, this review also highlights a wide range of management strategies against SCA/SA that includes both biological and chemical methods. In addition, the review emphasizes studies examining host plant resistance to understand and evaluate the role of R-genes and phytohormones such as jasmonic acid, salicylic acid and ethylene against SCA. Beside this, plant volatiles and other secondary metabolites such as flavonoids, terpenes and phytanes are also explored as potential control agents. Being an invasive pest, a single management tactic is inadequate to control SCA population and hence, integrated pest management practices incorporating physical, cultural and biological control methods should be implemented with exclusive chemical control as a last resort, which this review examines in detail. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Arabidopsis CIRP1 E3 ligase modulates drought and oxidative stress tolerance and reactive oxygen species homeostasis by directly degrading catalases

Reactive oxygen species (ROS) plays critical roles in modulating plant growth and stress response and its homeostasis is fine tuned using multiple peroxidases. H2O2, a major kind of ROS, is removed rapidly and directly using three catalases, CAT1, CAT2, and CAT3, in Arabidopsis. Although the activity regulations of catalases have been well studied, their degradation pathway is less clear. Here, we report that CAT2 and CAT3 protein abundance was partially controlled using the 26S proteasome. To further identify candidate proteins that modulate the stability of CAT2, we performed yeast-two-hybrid screening and recovered several clones encoding a protein with RING and vWA domains, CIRP1 ( CAT2 Interacting RING Protein 1). Drought and oxidative stress downregulated CIRP1 transcripts. CIRP1 harbored E3 ubiquitination activity and accelerated the degradation of CAT2 and CAT3 by direct interaction and ubiquitination. The cirp1 mutants exhibited stronger drought and oxidative stress tolerance, which was opposite to the cat2 and cat3 mutants. Genetic analysis revealed that CIRP1 acts upstream of CAT2 and CAT3 to negatively regulate drought and oxidative stress tolerance. The increased drought and oxidative stress tolerance of the cirp1 mutants was due to enhanced catalase (CAT) activities and alleviated ROS levels. Our data revealed that the CIRP1-CAT2/CAT3 module plays a vital role in alleviating ROS levels and balancing growth and stress responses in Arabidopsis.

Comparative analysis of HKT genes in Ipomoea pes-caprae unveils conserved Na+/K+ symporter functions within the gene family

The HKT protein family plays a vital role in plant responses to salt stress by mediating sodium (Na+) and potassium (K+) transport and maintaining Na+-K+ balance. Ipomoea pes-caprae (IPC), a pantropical creeping plant distributed along coastal regions in tropical and subtropical zones, exhibits exceptional salt tolerance. Understanding its salt tolerance mechanisms provides valuable insights for developing salt-tolerant crops and identifying candidate genes for genetic engineering. In this study, we identified two HKT genes, IpcHKT1;1 and IpcHKT1;2, in IPC. Phylogenetic analysis with HKT genes from other Ipomoea species revealed that all analyzed species contain two HKT genes located adjacently on the same chromosome. Comparative analysis of conserved motifs and intron-exon structures indicated that, despite their close evolutionary relationship, the HKT genes in IPC may exhibit functional divergence. Promoter analysis showed that their regulatory regions are enriched with cis-elements associated with responses to biotic and abiotic stresses, hormonal signaling, and growth, highlighting functional diversity within the HKT family. Subcellular localization experiments demonstrated that IpcHKT1;1 and IpcHKT1;2 are ion transporters localized to the plasma membrane. Heterologous expression in yeast confirmed their role in Na+/K+ symporter. Furthermore, RT-qPCR analysis revealed distinct expression patterns under salt stress: IpcHKT1;2 was significantly upregulated in roots, while IpcHKT1;1 expression was transitionally downregulated at 400 mM NaCl treatment. Prolonged high expression of IpcHKT1;2 in roots suggests its critical role in sustained salt stress tolerance. These findings provide new insights into the molecular mechanisms of salt tolerance in IPC. The identification of IpcHKT1;1 and IpcHKT1;2 as key players in salt stress responses offers promising genetic resources for enhancing crop resilience to soil salinity, addressing challenges associated with global salinization.

Promoting effects of NaCl and KCl stresses on astaxanthin yield in Microcystis flos-aquae

This study was to uncover the astaxanthin accumulation mechanism of Microcystis flos-aquae stressed by NaCl and KCl and select the optimal condition for astaxanthin production. Both of NaCl and KCl stresses showed inhibiting effects on M. flos-aquae growth by reducing photosynthetic abilities and causing reactive oxygen species accumulation. With raising the two salt concentrations, astaxanthin content and yield gradually increased, and the highest accumulation was under 300 mM for each salt, which should result from the up-regulation of 6 related genes promoting the precursor (β-carotene and zeaxanthin) transformation. KCl stress was more effective for improving astaxanthin yield than NaCl stress, which was strongly related with the salt concentration and astaxanthin content. Compared with other potential suitable conditions (35°C and purple light), 300 mM KCl also exhibited maximum effect on astaxanthin accumulation. Therefore, M. flos-aquae is first identified to synthesize astaxanthin, and KCl stress is more favorable to the compound production.

The Antifungal Activity and Mechanism of Dehydroabietic Acid Against Alternaria alternata Causing Poplar Leaf Spot

Dehydroabietic acid (DHA) is a secondary metabolite isolated from rosin, which has certain antifungal activity, but its inhibitory effects against Alternaria alternata are unclear. In the present study, we found that DHA inhibited the mycelial growth of A. alternata, Botrytis cinerea, Valsa mali, Pestalotiopsis neglecta, and Fusarium oxysporum in a concentration-dependent manner, with the best inhibitory effect against A. alternata. Moreover, DHA can also inhibit the spore germination of A. alternata. Then, in vivo inoculation experiments showed that the leaf lesions of Populus alba gradually decreased with the increase in DHA concentration. The disease of P. alba leaves inoculated with A. alternata was not obvious after treatment with 800 mg/L DHA. The scanning electron microscopy showed that the mycelial morphology was abnormal, with crinkles and depressions. Meanwhile, the relative conductivity, soluble protein content, malondialdehyde content and hydrogen peroxide content of A. alternata were significantly increased after DHA treatment, which affected the integrity of the cell membrane and increased the permeability of A. alternata, resulting in a large leakage of intracellular substances, exacerbating the degree of lipid peroxidation of the cell membrane of A. alternata and causing oxidative damage to cells. The enzyme activity assay showed that treatment with 56.015 mg/L (EC50) DHA significantly reduced the activities of antioxidant enzymes (superoxide dismutase, catalase, peroxidase) and cell-wall-degrading enzymes (endoglucanase, polygalacturonase, pectin lyase) in A. alternata (p < 0.05), resulting in a decrease in the activity of pathogenic fungi, as well as a reduction in the ability of the A. alternata to degrade the cell wall of the host plant, which led to a decrease in the ability of the A. alternata to infest the host plant. Moreover, the decrease in the relative expression of defense-related enzyme genes (AaSOD, AaPOD, AaCAT) and pathogenicity-related enzyme genes (AaPL, AaPG) was consistent with the enzyme activity results. Thus, the present study revealed the fungicidal activity and mechanism of DHA against A. alternata and the potential of DHA to be developed as a plant-derived antifungal agent was established.

Harnessing phosphate-solubilizing microorganisms for mitigation of nutritional and environmental stresses, and sustainable crop production

MAIN CONCLUSION

Phosphate-solubilizing microorganisms enhance nutrients availability, mitigate environmental stresses, and increase plant growth. The bioengineering of phosphate-solubilizing microbes and host plants may further improve their efficacy for increasing crop yield. Unsustainable agricultural practices are followed in current crop production systems worldwide for resolving food demand issues of ever-increasing human population. In addition, global food crop production is further affected due to continuous climatic change, erratic rains, and environmental stresses during the recent past causing threat to microbial as well as plant biodiversity. The application of plant beneficial microorganisms into agricultural practices has emerged recently as an innovative and sustainable approach to increase crop yield with limited resources and in vulnerable environment. These beneficial microbes improve crop productivity by enhancing nutrients' availability and mitigation of abiotic stresses along with suppression of plant diseases. However, there have been limited studies on the stress ameliorative role of phosphate-solubilizing microorganisms (PSMs), and there is still a need to elucidate the contribution of PSMs in improving plant health and crop productivity under harsh environmental conditions. This review summarizes the role of PSMs in improving phosphorus availability in soil through solubilization or mineralization of organic phosphate, and by assisting plants in amelioration of environmental stresses. Other beneficial activities of PSMs, such as release of phytohormones, production of ACC deaminase, strengthening of antioxidant system, and induction of systemic resistance, also contribute toward stress mitigation and plant growth promotion under stressful environments. Improvement in efficacy of PSMs and host plants using genetic engineering techniques has been discussed leading to increases in crop yields. However, further research is needed to develop sustainable climate-resilient approach by improving plant growth-promoting activities of PSMs even under environmental stresses to increase soil fertility and crop production in different agroecosystems.

Magnetic Nanoparticles in Agriculture: Unraveling the Impact of Nickel Ferrite Nanoparticles on Peanut Growth and Seed Nutritional Quality

Nanotechnology has been a source of innovation in various fields in recent years, and its application in agriculture has attracted much attention, particularly for its potential to enhance crop growth and optimize nutritional quality. This study systematically investigated the effects of nickel ferrite nanoparticles (NiFe2O4 NPs) on peanut (Arachis hypogaea L.) growth, nutrient dynamics, and biochemical responses, highlighting their potential as sustainable alternatives to conventional fertilizers. The results showed that an optimum concentration of 50 mg/kg soil significantly improved photosynthetic efficiency, biomass accumulation, seed yield, and nutritional quality, with 1000 seed weight and total yield increasing by 12.3% and 15.6%, respectively. In addition, we hypothesized that NiFe2O4 NPs would activate the antioxidant system and increase plant resistance. According to the risk assessment, the target hazard quotient (THQ = 0.081) is well below the safety threshold of 1. These findings provide strong evidence for the application of NiFe2O4 NPs as next-generation nano-fertilizers, offering a dual advantage of improved agronomic performance and biosafety. However, further research is needed to optimize their application strategies and assess potential long-term environmental impacts.

Alleviating lanthanum stress in tomato plants using MnO nanoparticles and triacontanol: Impacts on growth, photosynthesis, and antioxidant defense

The present study evaluated the synthesis, characterization, and ameliorative potential of manganese oxide nanoparticles (MnO NPs) against lanthanum (La)-induced stress in tomato plants. Biosynthesized MnO NPs exhibited a characteristic UV-Vis absorption peak at 276 nm and a cubic crystalline structure with an average crystallite size of 13 nm, as determined by XRD. TEM images confirmed pseudo-spherical morphology and homogenous distribution. Under La stress, tomato plants showed a significant reduction in shoot length (54.90 %), root length (62.39 %), shoot dry weight (49.71 %), and root dry weight (37.17 %). Application of MnO NPs and triacontanol (TRIA) mitigated these effects, with combined treatments enhanced shoot and root lengths by 155.81 % and 216.66 %, respectively, and dry weights by 116.58 % (shoot) and 173.06 % (root). La stressed plants demonstrated decreased accumulation of La in roots and shoots by about 36.64 % and 32.21 %, respectively, upon synergistic application of MnO NPs and TRIA. La stress decreased photosynthetic pigments, including chlorophyll a (53.56 %), chlorophyll b (51.28 %), total chlorophyll (53.10 %), and carotenoids (26.36 %). Combined MnO NPs and TRIA treatment significantly increased these pigments by 110.23 %, 263.15 %, 142.27 %, and 266.66 %, respectively. Photosynthetic efficiency parameters, such as net photosynthetic rate, stomatal conductance, and transpiration rate, also improved by up to 74.44 %, 119.00 %, and 89.44 %, respectively, under combined treatments. Relative water content (RWC) decreased by 49.83 % under La stress but increased by 84.75 % following combined treatments. Osmolytes like proline and glycine betaine were elevated by 20.13 % and 38.47 %, respectively. Reactive oxygen species (ROS)-related markers, including H₂O₂, malondialdehyde, and electrolyte leakage, were significantly reduced by 58.14 %, 28.46 %, and 39.81 %, respectively, with MnO NPs and TRIA. Antioxidant enzyme activities were enhanced, with combined treatments elevating SOD (27.02 %), CAT (15.38 %), APX (90.37 %), and GR (90.38 %). Moreover, activities of DHAR and MDHAR, previously suppressed by La, increased by 91.64 % and 81.75 %, respectively. The findings highlight the synergistic role of MnO NPs and TRIA in alleviating La toxicity by enhancing growth, photosynthetic efficiency, antioxidant defense, and reducing ROS, offering a sustainable approach for crop improvement under metal stress conditions.

Selenium Improves Yield and Quality in Prunella vulgaris by Regulating Antioxidant Defense, Photosynthesis, Growth, Secondary Metabolites, and Gene Expression Under Acid Stress

Prunella vulgaris, an essential component of traditional Chinese medicine, is suitable for growing in soil with a pH value ranging from 6.5 to 7.5. However, it is primarily cultivated in acidic soil regions of China, where its growth is frequently compromised by acidic stress. Selenium (Se) has been recognized for its potential to enhance stress tolerance in plants. However, its role in acid-stress-induced oxidative stress is not clear. In this study, the effects of varying Se concentrations on the growth and quality of P. vulgaris under acidic stress were investigated. The results showed that acid stress enhanced antioxidant enzyme activities, non-enzymatic antioxidant substances, and osmolyte content, accompanied by an increase in oxidant production and membrane damage. Furthermore, it decreased the photosynthetic capacity, inhibited root and shoot growth, and diminished the yield of P. vulgaris. In contrast, exogenous application of Se, particularly at 5 mg L-1, markedly ameliorated these adverse effects. Compared to acid-stressed plants, 5 mg L-1 Se treatment enhanced superoxide dismutase, peroxidase, ascorbate peroxidase, and glutathione peroxidase activities by 150.19%, 54.94%, 43.43%, and 45.55%, respectively. Additionally, soluble protein, soluble sugar, and proline contents increased by 11.75%, 23.32%, and 40.39%, respectively. Se application also improved root architecture and alleviated membrane damage by reducing hydrogen peroxide, superoxide anion, malondialdehyde, and electrolyte leakage levels. Furthermore, it significantly enhanced the photosynthetic capacity by elevating pigment levels, the performance of PSI and PSII, electron transfer, and the coordination of PSI and PSII. Consequently, plant growth and spica weight were significantly promoted, with a 12.50% increase in yield. Moreover, Se application upregulated key genes involved in flavonoid and phenolic acid metabolic pathways, leading to elevated levels of total flavonoids, caffeic acid, ferulic acid, rosmarinic acid, and hyperoside by 31.03%, 22.37%, 40.78%, 15.11%, and 20.84%, respectively, compared to acid-stressed plants. In conclusion, exogenous Se effectively alleviated the adverse effects of acid stress by improving the antioxidant system, growth, and photosynthetic capacity under acid stress, thus enhancing the yield and quality of P. vulgaris.

Arabidopsis thaliana Plants' Overexpression of the MYB Transcription Factor VhMYB60 in the Face of Stress Hazards Enhances Salt and Cold Tolerance

'Beta' (Vitisriparia × V. labrusca) is a vine fruit tree of the genus Vitis which is a cross between American and riparian grapes. In the current situation of grape production in northern regions, cold, drought, and salinity are important bottlenecks restricting its development, while some grape rootstocks with excellent traits show the disadvantage of poor resilience. 'Beta' (Vitis riparia × V. labrusca), one of the most extensively utilized rootstocks in viticulture, has demonstrated remarkable resilience to adverse conditions. However, the mechanisms by which 'Beta' rootstocks resist abiotic stresses are unknown and need to be further investigated. In this study, we successfully isolated and cloned a novel MYB transcription factor, VhMYB60, from the 'Beta' grapevine. This factor spans 972 base pairs and encodes a protein comprising 323 amino acids. Subcellular localization studies revealed that VhMYB60 is predominantly expressed within the nucleus. Furthermore, tissue-specific expression analysis demonstrated that VhMYB60 is more abundantly expressed in the mature leaves and roots of the grape plant. Further studies showed that salt and cold stress notably increased VhMYB60 gene expression in both mature leaves and grape roots. Compared with the control, Arabidopsis thaliana (Arabidopsis) plants molecularly modified to overexpress VhMYB60 exhibited enhanced salt and cold resistance and improved survival rates. Moreover, notable changes were detected in chlorophyll, malondialdehyde (MDA), proline, peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) levels. Concurrently, the expression levels of structural genes that are positively correlated with resistance to adversity stress were markedly elevated in Arabidopsis plants that overexpress VhMYB60. Consequently, VhMYB60 may serve as a pivotal transcription factor in the regulation of 'Beta' resistance.

Unraveling the role of autophagy and antioxidants in anther and pistil responses to heat stress in rapeseed (Brassica napus L.)

KEY MESSAGE

Enhanced antioxidant enzymes activity, particularly superoxide dismutase and catalase, along with autophagy process in reproductive organs, can improve the resilience of rapeseed to heat stress, thereby securing crop yield in the face of global warming. Climate change and global warming have increasingly influenced yield and quality of rapeseed (Brassica napus) almost all across the world. The response of reproductive organs to high-temperature stress was studied in two rapeseed varieties, SAFI5 and DH13 with contrasting levels of heat stress tolerance. Pollen germination, viability, and seed set showed a significant reduction in the heat-sensitive variety (DH13). Superoxide quantification revealed higher accumulation in heat-sensitive variety, leading to decreased seed formation and floret fertility most probably due to declined pollen viability and stigma receptivity. Further microscopic analysis of the anther and pistil demonstrated a significant overlay between the damaged areas and the location of O2- accumulation. The sensitive variety showed higher O2- accumulation and a wider damage area than the tolerant one, suggesting that superoxide could incapacitate anther and pistil due to structural injury. Moreover, the activity levels and expression of superoxide dismutase and catalase antioxidant enzymes were significantly higher in the anther and pistil of the tolerant variety. Histochemical analysis also indicated markedly higher autophagosome formation in tolerant variety's anther and pistil. Consistently, the expression levels of autophagy and ubiquitin-proteasome system (UPS)-related genes including BnATG8d, BnEXO70B, BnATl1 4A, and BnNBR1, as well as ubiquitin-activating enzyme E1, were higher in both reproductive organs of the tolerant variety. Interestingly, the areas of autophagosome formation overlapped with the areas in which higher superoxide accumulation and structural changes happened, suggesting a specific role of autophagy in oxidative stress response.

The impact of fruit size on internal browning in pineapples

A typical symptom of post-harvest pineapple (Ananas comosus L.) internal browning is influenced by multiple factors. However, the precise mechanism through which fruit size influences the occurrence of browning remains unclear. Therefore, this study aimed to investigate the impacts of fruit size in browning and its possible mechanisms in harvested pineapple fruit using physical and biochemical analysis and RNA-seq. Disease incidence was assessed in four groups of fruits (1, 1.5, 2, and 2.5 ± 0.2 kg), with the two most significant groups (1 and 2.5 ± 0.2 kg) selected for detailed analysis. The results showed that the large pineapple fruits had faster browning senescence and membrane lipid peroxidation, higher respiration intensity, more reactive oxygen species accumulation, and higher malondialdehyde content. Likewise, lower antioxidant capacity such as ascorbic acid, ascorbate peroxidase, catalase, and superoxide dismutase and higher polyphenol oxidase activity, peroxidase activity, phenylalanine ammonia-lyase activity, and lipoxygenase activity. It can be concluded that the large pineapple fruits were severely subjected to oxygen stress and membrane lipid peroxidation during storage. Gene ontology enrichment reveals that this relates mainly to oxidoreductase and glutathione metabolism. The large pineapple fruits accelerated AsA-GSH cycle pathway metabolism. Real-time quantitative PCR shows downregulated expression of AcAPX1, AcAPX6, AcAPX6 × 1, AcCAT2, AcSOD[Fe]2, and AcSODX2 in large pineapple fruits, whereas AcPPO and AcLOX upregulated expression. This study offers insights into fruit size and browning. Future molecular techniques may reduce fruit browning.

Do different wheat ploidy levels respond differently against stripe rust infection: Interplay between reactive oxygen species (ROS) and the antioxidant defense system?

Wheat stripe rust (Puccinia striiformis f. sp. tritici, Pst) is the most damaging wheat disease, causing substantial losses in global wheat production and productivity. Our study aimed to unravel the complex reciprocity between reactive oxygen species and the antioxidant defense system as a source of resistance against stripe rust in diploid, tetraploid and hexaploid wheat genotypes. The significant genetic variability for stripe rust in the materials under study was evident as the genotypes showed contrasting responses during both the adult and seedling stages. Our thorough perspective on the biochemical responses of wheat genotypes to stripe rust infection revealed distinct patterns in oxidative damage, antioxidant enzymes and photosynthetic pigments. Principal component analysis revealed inverse correlations between antioxidants and ROS, underscoring their key function in maintaining the cellular redox balance and protecting plants against oxidative damage. Diploid (Ae. tauschii) wild wheat exhibited a better biochemical defense system and greater resistance to stripe rust than the tetraploid (T. durum) and hexaploid (Triticum aestivum) wheat genotypes. The antioxidant enzyme activity of durum wheat was moderate compared to diploid and hexaploid wheat genotypes. The hexaploid wheat genotypes exhibited increased ROS production, reduced antioxidant enzyme activity and decreased photosynthetic pigment levels. This study enhances understanding of the antioxidant defense system across different wheat ploidies facing stripe rust, serving as a valuable strategy for improving crop disease resistance. This study validated the biochemical response of stripe rust-resistant and susceptible candidate genotypes, which will be used to develop genetic resources for discovering stripe rust resistance genes in wheat.

Crosstalk Between Abiotic and Biotic Stresses Responses and the Role of Chloroplast Retrograde Signaling in the Cross-Tolerance Phenomena in Plants

In the natural environment, plants are simultaneously exposed to multivariable abiotic and biotic stresses. Typical abiotic stresses are changes in temperature, light intensity and quality, water stress (drought, flood), microelements availability, salinity, air pollutants, and others. Biotic stresses are caused by other organisms, such as pathogenic bacteria and viruses or parasites. This review presents the current state-of-the-art knowledge on programmed cell death in the cross-tolerance phenomena and its conditional molecular and physiological regulators, which simultaneously regulate plant acclimation, defense, and developmental responses. It highlights the role of the absorbed energy in excess and its dissipation as heat in the induction of the chloroplast retrograde phytohormonal, electrical, and reactive oxygen species signaling. It also discusses how systemic- and network-acquired acclimation and acquired systemic resistance are mutually regulated and demonstrates the role of non-photochemical quenching and the dissipation of absorbed energy in excess as heat in the cross-tolerance phenomenon. Finally, new evidence that plants evolved one molecular system to regulate cell death, acclimation, and cross-tolerance are presented and discussed.

Nitric oxide in plants: an insight on redox activity and responses toward abiotic stress signaling

Plants, as sessile organisms, are subjected to diverse abiotic stresses, including salinity, desiccation, metal toxicity, thermal fluctuations, and hypoxia at different phases of plant growth. Plants can activate messenger molecules to initiate a signaling cascade of response toward environmental stresses that results in either cell death or plant acclimation. Nitric oxide (NO) is a small gaseous redox-active molecule that exhibits a plethora of physiological functions in growth, development, flowering, senescence, stomata closure and responses to environmental stresses. It can also facilitate alteration in protein function and reprogram the gene profiling by direct or indirect interaction with different target molecules. The bioactivity of NO can be manifested through different redox-based protein modifications including S-nitrosylation, protein nitration, and metal nitrosylation in plants. Although there has been considerable progress in the role of NO in regulating stress signaling, still the physiological mechanisms regarding the abiotic stress tolerance in plants remain unclear. This review summarizes recent advances in understanding the emerging knowledge regarding NO function in plant tolerance against abiotic stresses. The manuscript also highlighted the importance of NO as an abiotic stress modulator and developed a rational design for crop cultivation under a stress environment.

γ-Aminobutyric Acid Alleviates Programmed Cell Death in Two Brassica Species Under Cadmium Stress

Previous studies have demonstrated that γ-Aminobutyric acid (GABA) effectively alleviates heavy metal stresses by maintaining the redox balance and reducing the accumulation of reactive oxygen species (ROS). However, little is known about the role of GABA on programmed cell death (PCD) under Cd treatments in plants. The present study investigated the effects of GABA on Cd-induced PCD in two Brassica species, oilseed rape (Brassica napus, Bn), and black mustard (Brassica juncea, Bj). We observed that GABA significantly alleviated Cd-induced PCD by enhancing antioxidant systems, inhibiting chromatin condensation in the nucleus, and reducing DNA fragmentation under Cd stress. Moreover, GABA may not only reduce caspase-3-like activity by repressing gene expression, but also regulate transcription of PCD-related genes. Bn showed lower Cd accumulation and lower tolerance, with more pronounced PCD, compared with Bj. Our results provide new insights into the mechanism that GABA enhances Cd tolerance in plants.

A mechanistic integration of hypoxia signaling with energy, redox, and hormonal cues

Oxygen deficiency (hypoxia) occurs naturally in many developing plant tissues but can become a major threat during acute flooding stress. Consequently, plants as aerobic organisms must rapidly acclimate to hypoxia and the associated energy crisis to ensure cellular and ultimately organismal survival. In plants, oxygen sensing is tightly linked with oxygen-controlled protein stability of group VII ETHYLENE-RESPONSE FACTORs (ERFVII), which, when stabilized under hypoxia, act as key transcriptional regulators of hypoxia-responsive genes (HRGs). Multiple signaling pathways feed into hypoxia signaling to fine-tune cellular decision-making under stress. First, ATP shortage upon hypoxia directly affects the energy status and adjusts anaerobic metabolism. Secondly, altered redox homeostasis leads to reactive oxygen and nitrogen species (ROS and RNS) accumulation, evoking signaling and oxidative stress acclimation. Finally, the phytohormone ethylene promotes hypoxia signaling to improve acute stress acclimation, while hypoxia signaling in turn can alter ethylene, auxin, abscisic acid, salicylic acid, and jasmonate signaling to guide development and stress responses. In this Update, we summarize the current knowledge on how energy, redox, and hormone signaling pathways are induced under hypoxia and subsequently integrated at the molecular level to ensure stress-tailored cellular responses. We show that some HRGs are responsive to changes in redox, energy, and ethylene independently of the oxygen status, and we propose an updated HRG list that is more representative for hypoxia marker gene expression. We discuss the synergistic effects of hypoxia, energy, redox, and hormone signaling and their phenotypic consequences in the context of both environmental and developmental hypoxia.

Untargeted mutagenesis of brassinosteroid receptor SbBRI1 confers drought tolerance by altering phenylpropanoid metabolism in Sorghum bicolor

Drought is a critical issue in modern agriculture; therefore, there is a need to create crops with drought resilience. The complexity of plant responses to abiotic stresses, particularly in the field of brassinosteroid (BR) signalling, has been the subject of extensive research. In this study, we unveil compelling insights indicating that the BRASSINOSTEROID-INSENSITIVE 1 (BRI1) receptor in Arabidopsis and Sorghum plays a critical role as a negative regulator of drought responses. Introducing untargeted mutation in the sorghum BRI1 receptor (SbBRI1) effectively enhances the plant's ability to withstand osmotic and drought stress. Through DNA Affinity Purification sequencing (DAP-seq), we show that the sorghum BRI1-EMS-SUPPRESSOR 1 (SbBES1) transcription factor, a downstream player of the BR signalling, binds to a conserved G-box binding motif, and it is responsible for regulating BR homeostasis, as its Arabidopsis ortholog AtBES1. We further characterized the drought tolerance of sorghum bri1 mutants and decipher SbBES1-mediated regulation of phenylpropanoid pathway. Our findings suggest that SbBRI1 signalling serves a dual purpose: under normal conditions, it regulates lignin biosynthesis by SbBES1, but during drought conditions, BES1 becomes less active, allowing the activation of the flavonoid pathway. This adaptive shift improves the photosynthetic rate and photoprotection, reinforcing crop adaptation to drought.

Regulating programmed cell death in plant cells: Intracellular acidification plays a pivotal role together with calcium signaling

Programmed cell death (PCD) occurs in different tissues in response to a number of different signals in plant cells. Drawing from work in several different contexts, including root-cap cell differentiation, plant response to biotic and abiotic stress, and some self-incompatibility (SI) systems, the data suggest that, despite differences, there are underlying commonalities in the early decision-making stages of PCD. Here, we focus on how 2 cellular events, increased [Ca2+]cyt levels and cytosolic acidification, appear to act as early signals involved in regulating both developmental and stimulus-induced PCD in plant cells.

Selenium dynamics in plants: Uptake, transport, toxicity, and sustainable management strategies

Selenium (Se) plays crucial roles in human, animal, and plant physiology, but its varied plant functions remain complex and not fully understood. While Se deficiency affects over a billion people worldwide, excessive Se levels can be toxic, presenting substantial risks to ecosystem health and public safety. The delicate balance between Se's beneficial and harmful effects necessitates a deeper understanding of its speciation dynamics and how different organisms within ecosystems respond to Se. Since humans primarily consume Se through Se-rich foods, exploring Se's behavior, uptake, and transport within agroecosystems is critical to creating effective management strategies. Traditional physicochemical methods for Se remediation are often expensive and potentially harmful to the environment, pushing the need for more sustainable solutions. In recent years, phytotechnologies have gained traction as a promising approach to Se management by harnessing plants' natural abilities to absorb, accumulate, metabolize, and volatilize Se. These strategies range from boosting Se uptake and tolerance in plants to releasing Se as less toxic volatile compounds or utilizing it as a biofortified supplement, opening up diverse possibilities for managing Se, offering sustainable pathways to improve crop nutritional quality, and protecting human health in different environmental contexts. However, closing the gaps in our understanding of Se dynamics within agricultural systems calls for a united front of interdisciplinary collaboration from biology to environmental science, agriculture, and public health, which has a crucial role to play. Phytotechnologies offer a sustainable bridge between Se deficiency and toxicity, but further research is needed to optimize these methods and explore their potential in various agricultural and environmental settings. By shedding light on Se's multifaceted roles and refining management strategies, this review contributes to developing cost-effective and eco-friendly approaches for Se management in agroecosystems. It aims to lead the way toward a healthier and more sustainable future by balancing the need to address Se deficiency and mitigate the risks of Se toxicity.

Nano-Fe3O4: Enhancing the tolerance of Elymus nutans to Cd stress through regulating programmed cell death

Cadmium (Cd) poses a significant threat to plant growth and the environment. Nano-Fe3O4 is effective in alleviating Cd stress in plants. Elymus nutans Griseb. is an important fodder crop on the Qinghai-Tibetan Plateau (QTP). However, the potential mechanism by which nano-Fe3O4 alleviates Cd stress in E. nutans is not well understood. E. nutans were subjected to single Cd, single nano-Fe3O4, and co-treatment with nano-Fe3O4 and Cd, and the effects on morphology, Cd uptake, antioxidant enzyme activity, reactive oxygen species (ROS) levels and programmed cell death (PCD) were studied to clarify the regulatory mechanism of nano-Fe3O4. The results showed that Cd stress significantly decreased the germination percentage and biomass of E. nutans. The photosynthetic pigment content decreased significantly under Cd stress. Cd stress also caused oxidative stress and lipid peroxidation, accumulation of excessive ROS, resulting in PCD, but the effect of nano-Fe3O4 was different. Seed germination, seedling growth, and physiological processes were analyzed to elucidate the regulatory role of nano-Fe3O4 nanoparticles in promoting photosynthesis, reducing Cd accumulation, scavenging ROS, and regulating PCD, to promote seed germination and seedling growth in E. nutans. This report provides a scientific basis for improving the tolerance of Elymus to Cd stress by using nano-Fe3O4.

Athyrium yokoscense, a cadmium-hypertolerant fern, exhibits two cadmium stress mitigation strategies in its roots and aerial parts

Athyrium yokoscense is hypertolerant to cadmium (Cd) and can grow normally under a high Cd concentration despite Cd being a highly toxic heavy metal. To mitigate Cd stress in general plant species, Cd is promptly chelated with a thiol compound and is isolated into vacuoles. Generated active oxygen species (ROS) in the cytoplasm are removed by reduced glutathione. However, we found many differences in the countermeasures in A. yokoscense. Thiol compounds accumulated in the stele of the roots, although a long-term Cd exposure induced Cd accumulation in the aerial parts. Synchrotron radiation-based X-ray fluorescence (SR-XRF) analysis indicated that a large amount of Cd was localized in the cell walls of the roots. Overexpression of AyNramp5a, encoding a representative Fe and Mn transporter of A. yokoscense, increased both Cd uptake and Fe and Mn uptake in rice calli under the Cd exposure conditions. Organic acids are known to play a key role in reducing Cd availability to the plants by forming chelation and preventing its entry in free form into the roots. In A. yokoscense roots, Organic acids were abundantly detected. Investigating the chemical forms of the Cd molecules by X-ray absorption fine structure (XAFS) analysis detected many compounds with Cd-oxygen (Cd-O) binding in A. yokoscense roots, whereas in the aerial parts, the ratio of the compounds with Cd-sulfur (Cd-S) binding was increased. Together, our results imply that the strong Cd tolerance of A. yokoscense is an attribute of the following two mechanisms: Cd-O compound formation in the cell wall is a barrier to reduce Cd uptake into aerial parts. Thiol compounds in the region of root stele are involved in detoxication of Cd by formation of Cd-S compounds.

Surviving the desert's grasp: Decipherment phreatophyte Tamarix aphylla (L.) Karst. Adaptive strategies for arid resilience

Phreatophytes play an important role in maintaining the ecological services in arid and semi-arid areas. Characterizing the interaction between groundwater and phreatophytes is critical for the land and water management in such areas. Therefore, the identification of key traits related to mitigating desertification in differently adapted T. aphylla populations was the focus. Fifteen naturally adapted populations of the prominent phreatophyte T. aphylla from diverse ecological regions of Punjab, Pakistan were selected. Key structural and functional modifications involved in ecological success and adaptations against heterogeneous environments for water conservation include widened metaxylem vessels in roots, enlarged brachy sclereids in stems/leaves, tissues succulence, and elevated organic osmolytes and antioxidants activity for osmoregulation and defense mechanism. Populations from hot and dry deserts (Dratio: 43.17-34.88) exhibited longer roots and fine-scaled leaves, along with enlarged vascular bundles and parenchyma cells in stems. Populations inhabiting saline deserts (Dratio: 38.59-33.29) displayed enhanced belowground biomass production, larger root cellular area, broadest phloem region in stems, and numerous large stomata in leaves. Hyper-arid populations (Dratio: 33.54-23.07) excelled in shoot biomass production, stem cellular area, epidermal thickness, pith region in stems, and lamina thickness in leaves. In conclusion, this research highlights T. aphylla as a vital model for comprehending plant resilience to environmental stresses, with implications for carbon sequestration and ecosystem restoration.

Endogenous γ-Aminobutyric Acid Accumulation Enhances Salinity Tolerance in Rice

Rice is an important food crop worldwide but is usually susceptible to saline stress. When grown on soil with excessive salt, rice plants experience osmotic, ionic, and oxidative stresses that adversely affect growth performance. γ-Aminobutyric acid (GABA) is a nonproteinogenic amino acid that plays an important role in the metabolic activities of organisms. Glutamate decarboxylase (GAD) is the rate-limiting enzyme in GABA metabolism. Here, we genetically modified rice GAD by overexpression or CRISPR-mediated genome editing. These lines, named gad3-ox1 and gad3-ox2 or gad1/3-ko, were used to explore the effects of endogenous GABA accumulation on salt tolerance in rice. Both the gad3-ox1 and gad3-ox2 lines exhibited significant accumulation of the GABA content, whereas the gad1/3-ko line presented a reduced GABA content in vivo. Notably, the two overexpression lines were markedly resistant to salt stress compared with the wild-type and knockout lines. Furthermore, our results demonstrated that endogenous GABA accumulation in the gad3-ox1 and gad3-ox2 lines increased the contents of antioxidant substances and osmotic regulators, decreased the content of membrane lipid peroxidation products and the Na+ content, and resulted in strong tolerance to salt stress. Together, these data provide a theoretical basis for cultivating rice varieties with strong salt tolerance.

Evaluation of growth, physiological response, and drought resistance of different flue-cured tobacco varieties under drought stress

Background

In recent years, more severe droughts have occurred frequently in many parts of the world, drought stress is the primary abiotic stress factor restricting the growth and quality of flue-cured tobacco. Therefore, screening dryland cultivation-compatible flue-cured tobacco varieties will help reduce the negative impact of drought.

Methods

Tobacco varieties were selected: Qinyan 96 (Q96), Zhongyan 101 (Z101), Yunyan 87 (Y87), and Yunyan 116 (Y116). A pot experiment was conducted with four water supply gradients: sufficient, mild stress, moderate stress, and severe stress. The aim was to analyze inter-varietal differences in agronomic traits, photosynthetic traits, reactive oxygen species (ROS) metabolism, and antioxidant enzyme system under drought stress. Additionally, the drought resistance of four flue-cured tobacco varieties was evaluated using principal component analysis and membership function analysis.

Results

The results showed that drought intensification inhibited seedling growth and development across all varieties, with Q96 showing the least decrease and Y116 the greatest. With the increasing degree of drought stress, photosynthetic rates (Pn), transpiration rate (Tr), and stomatal conduction (Gs) have shown gradually decreasing trends, while substomatal cavity CO2 concentration (Ci) showed a growing trend. Severe drought corresponded with lower chlorophyll content and decreased the maximal photochemical efficiency (Fv/Fm), photosystem II (PSII), and photochemical quenching coefficient (qP) in all varieties, while steady-state non-photochemical quenching (NPQ) increased. Increased drought stress led to significantly higher reactive oxygen species (ROS) and malondialdehyde (MDA) content accumulation in tobacco seedlings. The antioxidant enzyme activities in, Q96, Z101, and Y87 increased under mild drought stress, whereas Y116 showed decreased activity.

Conclusion

The drought resistance ranking among the four varieties is as follows: Q96 > Z101 > Y87 > Y116. Therefore, Q96 is a promising drought-tolerant breeding material that can be used as a reference for dryland cultivation of flue-cured tobacco.

Vacuolar degradation of plant organelles

Plants continuously remodel and degrade their organelles due to damage from their metabolic activities and environmental stressors, as well as an integral part of their cell differentiation programs. Whereas certain organelles use local hydrolytic enzymes for limited remodeling, most of the pathways that control the partial or complete dismantling of organelles rely on vacuolar degradation. Specifically, selective autophagic pathways play a crucial role in recognizing and sorting plant organelle cargo for vacuolar clearance, especially under cellular stress conditions induced by factors like heat, drought, and damaging light. In these short reviews, we discuss the mechanisms that control the vacuolar degradation of chloroplasts, mitochondria, endoplasmic reticulum, Golgi, and peroxisomes, with an emphasis on autophagy, recently discovered selective autophagy receptors for plant organelles, and crosstalk with other catabolic pathways.

PlPOD45 positively regulates high-temperature tolerance of herbaceous peony by scavenging reactive oxygen species

Herbaceous peony (Paeonia lactiflora Pall.) is a widely used famous traditional flower in China. It prefers cold and cool climate, but is not resistant to high temperature during summer in the middle and lower reaches of the Yangtze River. Previously, we found peroxidase (POD) is an important antioxidant enzyme that played an important role in high-temperature tolerance of P. lactiflora. The present study isolated the candidate gene PlPOD45 and verified its function in resisting high-temperature stress. And the results showed that PlPOD45 had an open reading frame of 978 bp that encoded 325 amino acids. Its protein was localized to the cell membrane and cytoplasm. High-temperature stress induced PlPOD45 expression. Heterologous overexpression of PlPOD45 improved plant tolerance to high-temperature stress, decreased reactive oxygen species (ROS) accumulation, relative electrical conductivity and malondialdehyde content, and increased the ratio of variable fluorescence to highest fluorescence and POD activity. Conversely, silencing PlPOD45 in P. lactiflora could decrease POD activity, ROS scavenging capability and cell membrane stability when these plants were exposed to high-temperature stress. These results suggest that PlPOD45 positively regulates high-temperature tolerance through ROS scavenging, which would provide a theoretical basis for improving high-temperature tolerance in P. lactiflora.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01505-x.

Nanobiotechnology-mediated regulation of reactive oxygen species homeostasis under heat and drought stress in plants

Global warming causes heat and drought stress in plants, which affects crop production. In addition to osmotic stress and protein inactivation, reactive oxygen species (ROS) overaccumulation under heat and drought stress is a secondary stress that further impairs plant performance. Chloroplasts, mitochondria, peroxisomes, and apoplasts are the main ROS generation sites in heat- and drought-stressed plants. In this review, we summarize ROS generation and scavenging in heat- and drought-stressed plants and highlight the potential applications of plant nanobiotechnology for enhancing plant tolerance to these stresses.

6-Methyl-5-hepten-2-one promotes programmed cell death during superficial scald development in pear

Plants possess the ability to induce programmed cell death (PCD) in response to abiotic and biotic stresses; nevertheless, the evidence on PCD initiation during pear scald development and the involvement of the scald trigger 6-methyl-5-hepten-2-one (MHO) in this process is rudimentary. Pyrus bretschneideri Rehd. cv. 'Dangshansuli' pear was used to validate such hypothesis. The results showed that superficial scald occurred after 120-d chilling exposure, which accompanied by typical PCD-associated morphological alterations, such as plasmolysis, cell shrinkage, cytosolic and nuclear condensation, vacuolar collapse, tonoplast disruption, subcellular organelle swelling, and DNA fragmentation. These symptoms were aggravated after MHO fumigation but alleviated by diphenylamine (DPA) dipping. Through transcriptome assay, 24 out of 146 PCD-related genes, which were transcribed during cold storage, were identified as the key candidate members responsible for these cellular biological alternations upon scald development. Among these, PbrCNGC1, PbrGnai1, PbrACD6, and PbrSOBIR1 were implicated in the MHO signaling pathway. Additionally, PbrWRKY2, 34 and 39 could bind to the W-box element in the promoter of PbrGnai1 or PbrSOBIR1 and activate their transcription, as confirmed by dual-luciferase, yeast one-hybrid, and transient overexpression assays. Hence, our study confirms the PCD initiation during scald development and explores the critical role of MHO in this process.

Cell death in bryophytes: emerging models to study core regulatory modules and conserved pathways

This review summarizes recent progress in our current understanding of the mechanisms underlying the cell death pathways in bryophytes, focusing on conserved pathways and particularities in comparison to angiosperms. Regulated cell death (RCD) plays key roles during essential processes along the plant life cycle. It is part of specific developmental programmes and maintains homeostasis of the organism in response to unfavourable environments. Bryophytes could provide valuable models to study developmental RCD processes as well as those triggered by biotic and abiotic stresses. Some pathways analogous to those present in angiosperms occur in the gametophytic haploid generation of bryophytes, allowing direct genetic studies. In this review, we focus on such RCD programmes, identifying core conserved mechanisms and raising new key questions to analyse RCD from an evolutionary perspective.

Spermine and spermidine inhibit or induce programmed cell death in Arabidopsis thaliana in vitro and in vivo in a dose-dependent manner

Polyamines are ubiquitous biomolecules with a number of established functions in eukaryotic cells. In plant cells, polyamines have previously been linked to abiotic and biotic stress tolerance, as well as to the modulation of programmed cell death (PCD), with contrasting reports on their pro-PCD and pro-survival effects. Here, we used two well-established platforms for the study of plant PCD, Arabidopsis thaliana suspension cultures cells and the root hair assay, to examine the roles of the polyamines spermine and spermidine in the regulation of PCD. Using these systems for precise quantification of cell death rates, we demonstrate that both polyamines can trigger PCD when applied exogenously at higher doses, whereas at lower concentrations they inhibit PCD induced by both biotic and abiotic stimuli. Furthermore, we show that concentrations of polyamines resulting in inhibition of PCD generated a transient ROS burst in our experimental system, and activated the expression of oxidative stress- and pathogen response-associated genes. Finally, we examined PCD responses in existing Arabidopsis polyamine synthesis mutants, and identified a subtle PCD phenotype in Arabidopsis seedlings deficient in thermo-spermine. The presented data show that polyamines can have a role in PCD regulation; however, that role is dose-dependent and consequently they may act as either inhibitors, or inducers, of PCD in Arabidopsis.

What can reactive oxygen species (ROS) tell us about the action mechanism of herbicides and other phytotoxins?

Reactive oxygen species (ROS) are formed in plant cells continuously. When ROS production exceeds the antioxidant capacity of the cells, oxidative stress develops which causes damage of cell components and may even lead to the induction of programmed cell death (PCD). The levels of ROS production increase upon abiotic stress, but also during pathogen attack in response to elicitors, and upon application of toxic compounds such as synthetic herbicides or natural phytotoxins. The commercial value of many synthetic herbicides is based on weed death as result of oxidative stress, and for a number of them, the site and the mechanism of ROS production have been characterized. This review summarizes the current knowledge on ROS production in plants subjected to different groups of synthetic herbicides and natural phytotoxins. We suggest that the use of ROS-specific fluorescent probes and of ROS-specific marker genes can provide important information on the mechanism of action of these toxins. Furthermore, we propose that, apart from oxidative damage, elicitation of ROS-induced PCD is emerging as one of the important processes underlying the action of herbicides and phytotoxins.

Mitochondrial pathway of programmed cell death in Paeonia lactiflora pollen cryopreservation

Programmed cell death (PCD) is an important factor to reduces the viability of plant germplasm after cryopreservation. However, the pathways by which PCD occurs is not fully understood. To investigate whether there is a mitochondrial pathway for pollen PCD after cryopreservation, the pollen of Paeonia lactiflora two cultivars with different PCD levels after cryopreservation was used as test material and the changes of mitochondrial calcium ions (Ca2+), structure, function and their relationship with PCD were compared. The results showed that compared with fresh pollen, the PCD of 'Feng Huang Nie Pan' was significantly reduced after cryopreservation. Their mitochondrial Ca2+ content decreased by 74.27%, mitochondrial permeability transition pore (MPTP) opening reduced by 25.41%, mitochondrial membrane potential slightly decreased by 5.02%, cardiolipin oxidation decreased by 65.31%, and oxygen consumption remained stable, with a slightly ATP production increase. On the contrary, compared with fresh pollen, 'Zi Feng Chao Yang' showed severe PCD after cryopreservation. The decline in mitochondrial Ca2+-ATPase activity led to an accumulation of excessive Ca2+ within mitochondria, triggering widespread opening of MPTP, significantly affecting mitochondrial respiration and energy synthesis. These results suggest the mitochondrial pathway of PCD exists in pollen cryopreservation.

Heat stress and sexual reproduction in maize: unveiling the most pivotal factors and the greatest opportunities

The escalation in the intensity, frequency, and duration of high-temperature (HT) stress is currently unparalleled, which aggravates the challenges for crop production. Yet, the stage-dependent responses of reproductive organs to HT stress at the morphological, physiological, and molecular levels remain inadequately explored in pivotal staple crops. This review synthesized current knowledge regarding the mechanisms by which HT stress induces abnormalities and aberrations in reproductive growth and development, as well as by which it alters the morphology and function of florets, flowering patterns, and the processes of pollination and fertilization in maize (Zea mays L.). We identified the stage-specific sensitivities to HT stress and accurately defined the sensitive period from a time scale of days to hours. The microspore tetrad phase of pollen development and anthesis (especially shortly after pollination) are most sensitive to HT stress, and even brief temperature spikes during these stages can lead to significant kernel loss. The impetuses behind the heat-induced impairments in seed set are closely related to carbon, reactive oxygen species, phytohormone signals, ion (e.g. Ca2+) homeostasis, plasma membrane structure and function, and others. Recent advances in understanding the genetic mechanisms underlying HT stress responses during maize sexual reproduction have been systematically summarized.

Dynamic interplay of reactive oxygen and nitrogen species (ROS and RNS) in plant resilience: unveiling the signaling pathways and metabolic responses to biotic and abiotic stresses

KEY MESSAGE

Plants respond to environmental challenges by producing reactive species such as ROS and RNS, which play critical roles in signaling pathways that lead to adaptation and survival strategies. Understanding these pathways, as well as their detection methods and effects on plant development and metabolism, provides insight into increasing crop tolerance to combined stresses. Plants encounter various environmental stresses (abiotic and biotic) that affect plant growth and development. Plants sense biotic and abiotic stresses by producing different molecules, including reactive species, that act as signaling molecules and stimulate secondary messengers and subsequent gene transcription. Reactive oxygen and nitrogen species (ROS and RNS) are produced in both physiological and pathological conditions in the plasma membranes, chloroplasts, mitochondria, and endoplasmic reticulum. Various techniques, including spectroscopy, chromatography, and fluorescence methods, are used to detect highly reactive, short-half-life ROS and RNS either directly or indirectly. In this review, we highlight the roles of ROS and RNS in seed germination, root development, senescence, mineral nutrition, and post-harvest control. In addition, we provide information on the specialized metabolism involved in plant growth and development. Secondary metabolites, including alkaloids, flavonoids, and terpenoids, are produced in low concentrations in plants for signaling and metabolism. Strategies for improving crop performance under combined drought and pathogen stress conditions are discussed in this review.

The role of reactive oxygen species in plant-virus interactions

Reactive oxygen species (ROS) play a complex role in interactions between plant viruses and their host plants. They can both help the plant defend against viral infection and support viral infection and spread. This review explores the various roles of ROS in plant-virus interactions, focusing on their involvement in symptom development and the activation of plant defense mechanisms. The article discusses how ROS can directly inhibit viral infection, as well as how they can regulate antiviral mechanisms through various pathways involving miRNAs, virus-derived small interfering RNAs, viral proteins, and host proteins. Additionally, it examines how ROS can enhance plant resistance by interacting with hormonal pathways and external substances. The review also considers how ROS might promote viral infection and transmission, emphasizing their intricate role in plant-virus dynamics. These insights offer valuable guidance for future research, such as exploring the manipulation of ROS-related gene expression through genetic engineering, developing biopesticides, and adjusting environmental conditions to improve plant resistance to viruses. This framework can advance research in plant disease resistance, agricultural practices, and disease control.

Functional analysis of a novel endo-β-1,6-glucanase MoGlu16 and its application in detecting cell wall β-1,6-glucan of Magnaporthe oryzae

As an essential component of the fungal cell wall, β-1,6-glucan has an important role in the growth and development of fungi, but its distribution has not been investigated in Magnaporthe oryzae. Here, a novel β-1,6-glucanase from M. oryzae, MoGlu16, was cloned and expressed in Pichia pastoris. The enzyme was highly active on pustulan, with a specific activity of 219.0 U/mg at pH 5.0 and 50°C, and showed great selectivity for continuous β-1,6-glycosidic bonding polysaccharides. Based on this, β-1,6-glucan was selectively visualized in the vegetative hyphae, conidia and bud tubes of M. oryzae using a hydrolytically inactive GFP-tagged MoGlu16 with point mutations at the catalytic position (His-MoGlu16E236A-Gfp). The spore germination and appressorium formation were significantly inhibited after incubation of 105/ml conidia with 0.03 μg/μl MoGlu16. Mycelia treated with MoGlu16 produced reactive oxygen species and triggered the cell wall integrity pathway, increasing the expression levels of genes involved in cell wall polysaccharide synthesis. These results revealed that MoGlu16 participated in the remodeling of cell wall in M. oryzae, laying a foundation for the analysis of cell wall structure.

Exploring Aluminum Tolerance Mechanisms in Plants with Reference to Rice and Arabidopsis: A Comprehensive Review of Genetic, Metabolic, and Physiological Adaptations in Acidic Soils

Aluminum (Al) makes up a third of the Earth's crust and is a widespread toxic contaminant, particularly in acidic soils. It impacts crops at multiple levels, from cellular to whole plant systems. This review delves into Al's reactivity, including its cellular transport, involvement in oxidative redox reactions, and development of specific metabolites, as well as the influence of genes on the production of membrane channels and transporters, alongside its role in triggering senescence. It discusses the involvement of channel proteins in calcium influx, vacuolar proton pumping, the suppression of mitochondrial respiration, and the initiation of programmed cell death. At the cellular nucleus level, the effects of Al on gene regulation through alterations in nucleic acid modifications, such as methylation and histone acetylation, are examined. In addition, this review outlines the pathways of Al-induced metabolic disruption, specifically citric acid metabolism, the regulation of proton excretion, the induction of specific transcription factors, the modulation of Al-responsive proteins, changes in citrate and nucleotide glucose transporters, and overall metal detoxification pathways in tolerant genotypes. It also considers the expression of phenolic oxidases in response to oxidative stress, their regulatory feedback on mitochondrial cytochrome proteins, and their consequences on root development. Ultimately, this review focuses on the selective metabolic pathways that facilitate Al exclusion and tolerance, emphasizing compartmentalization, antioxidative defense mechanisms, and the control of programmed cell death to manage metal toxicity.

Combined Ascorbic Acid and Mild Heat Treatment to Improve the Quality of Fresh-Cut Carrots

Mild heat (MH) treatment and ascorbic acid (AsA) addition can improve the quality of fresh-cut produce when used individually; however, their combined effect remains unclear. Herein, fresh-cut carrots were used as models to explore the effects of MH (50 °C)-AsA (0.5%) on quality properties including reactive oxygen species (ROS) metabolism, antioxidants, lignin metabolism, naturally present microbes, and inoculated pathogens (Escherichia coli O157: H7 and Salmonella Typhimurium) during storage (0-5 d, 4 °C). The results indicate that the antioxidant properties in the MH-AsA group were consistent with those of single treatments, resulting in a consistent ROS-scavenging effect. From day 3-5, lignin synthesis was significantly inhibited by MH-AsA as compared with single treatments, probably because the two enzymes (phenylalanine ammonia-lyase and peroxidase) responsible for lignin synthesis exhibited lower expressions. Microbial analysis revealed that MH-AsA treatment led to the lowest counts of both pathogens and aerobic mesophilic bacteria at 0-5 d. Conversely, the inhibitory effect of MH-AsA treatment on mold and yeast was consistent with the single treatments. These results suggest that MH-AsA is a low-cost and safe approach to improve the physiological characteristics of fresh-cut produce while reducing microbial risk.

Effects of Different Cutting Styles on Physiological Properties in Fresh-Cut Carrots

With the internationalization of Chinese culture, ready-to-cook Chinese food has become popular. Vegetables in Chinese preparations are usually cut into slices, cubes, and shreds. Carrots, as a typical Chinese side dish, were selected as the model in this work. The polyphenol content, antioxidant capacity, O2-, hydrogen peroxide, malondialdehyde, lignin, antioxidant enzymes, and other enzymes activities were analyzed. The results indicated that these parameters were insignificantly different between three cutting styles. Therefore, metabolomics is further employed. Pathway enrichment indicated that glyceollin II and 6″-malonylgenistin were metabolites particularly expressed in the isoflavonoid biosynthesis pathway; (+)-gallocatechin, trans-chlorogenic acid, and (-)-epiafzelechin were specifically identified in the flavonoid biosynthesis pathway after slicing; and shredding caused the expression of coniferyl aldehyde and eugenol, which were specifically expressed in the phenylpropanoid biosynthesis pathway. These results indicate that different cutting styles do not change the physiological indicators of carrots but induce the expression of specific metabolites.

PtWRKY2, a WRKY transcription factor from Pinellia ternata confers heat tolerance in Arabidopsis

High temperatures are a major stress factor that limit the growth of Pinellia ternata. WRKY proteins widely distribute in plants with the important roles in plant growth and stress responses. However, WRKY genes have not been identified in P. ternata thus far. In this study, five PtWRKYs with four functional subgroups were identified in P. ternata. One group III WRKY transcription factor, PtWRKY2, was strongly induced by high temperatures, whereas the other four PtWRKYs were suppressed. Analysis of transcription factor characteristics revealed that PtWRKY2 localized to the nucleus and specifically bound to W-box elements without transcriptional activation activity. Overexpression of PtWRKY2 increased the heat tolerance of Arabidopsis, as shown by the higher percentage of seed germination and survival rate, and the longer root length of transgenic lines under high temperatures compared to the wild-type. Moreover, PtWRKY2 overexpression significantly decreased reactive oxygen species accumulation by increasing the catalase, superoxide dismutase, and peroxidase activities. Furthermore, the selected heat shock-associated genes, including five transcription factors (HSFA1A, HSFA7A, bZIP28, DREB2A, and DREB2B), two heat shock proteins (HSP70 and HSP17.4), and three antioxidant enzymes (POD34, CAT1, and SOD1), were all upregulated in transgenic Arabidopsis. The study identifies that PtWRKY2 functions as a key transcriptional regulator in the heat tolerance of P. ternata, which might provide new insights into the genetic improvement of P. ternata.

Pepper vein yellow virus P0 protein triggers NbHERC3, NbBax, and NbCRR mediated hypersensitive response

P0 proteins encoded by the pepper vein yellow virus (PeVYV) are pathogenic factors that cause hypersensitive response (HR). However, the host gene expression related to PeVYV P0-induced HR has not been thoroughly studied. Transcriptomic technology was used to investigate the host pathways mediated by the PeVYV P0 protein to explore the molecular mechanisms underlying its function. We found 12,638 differentially expressed genes (DEGs); 6784 and 5854 genes were significantly upregulated and downregulated, respectively. Transcriptomic and reverse-transcription quantitative polymerase chain reaction (RT-qPCR) analyses revealed that salicylic acid (SA) and jasmonic acid (JA) synthesis-related gene expression was upregulated, and ethylene synthesis-related gene expression was downregulated. Ultrahigh performance liquid chromatography-tandem mass spectrometry was used to quantify SA and JA concentrations in Nicotiana benthamiana, and the P0 protein induced SA and JA biosynthesis. We then hypothesized that the pathogenic activity of the P0 protein might be owing to proteins related to host hormones in the SA and JA pathways, modulating host resistance at different times. Viral gene silencing suppression technology was used in N. benthamiana to characterize candidate proteins, and downregulating NbHERC3 (Homologous to E6-AP carboxy-terminus domain and regulator of choromosome condensation-1 dmain protein 3) accelerated cell necrosis in the host. The downregulation of NbCRR reduced cell death, while that of NbBax induced necrosis and curled heart leaves. Our findings indicate that NbHERC3, NbBax, and NbCRR are involved in P0 protein-driven cell necrosis.

Superoxide Dismutase Premodulates Oxidative Stress in Plastids for Protection of Tobacco Plants from Cold Damage Ultrastructure Damage

ROS-dependent induction of oxidative damage can be used as a trigger initiating genetically determined non-specific protection in plant cells and tissues. Plants are potentially able to withstand various specific (toxic, osmotic) factors of abiotic effects, but do not have sufficient or specific sensitivity to form an adequate effective response. In this work, we demonstrate one of the possible approaches for successful cold acclimation through the formation of effective protection of photosynthetic structures due to the insertion of the heterologous FeSOD gene into the tobacco genome under the control of the constitutive promoter and equipped with a signal sequence targeting the protein to plastid. The increased enzymatic activity of superoxide dismutase in the plastid compartment of transgenic tobacco plants enables them to tolerate the oxidative factor of environmental stresses scavenging ROS. On the other hand, the cost of such resistance is quite high and, when grown under normal conditions, disturbs the arrangement of the intrachloroplastic subdomains leading to the modification of stromal thylakoids, probably significantly affecting the photosynthesis processes that regulate the efficiency of photosystem II. This is partially compensated for by the fact that, at the same time, under normal conditions, the production of peroxide induces the activation of ROS detoxification enzymes. However, a violation of a number of processes, such as the metabolism of accumulation, and utilization and transportation of sugars and starch, is significantly altered, which leads to a shift in metabolic chains. The expected step for further improvement of the applied technology could be both the use of inducible promoters in the expression cassette, and the addition of other genes encoding for hydrogen peroxide-scavenging enzymes in the genetic construct that are downstream in the metabolic chain.

Oxidative Stress Response Mechanisms Sustain the Antibacterial and Antioxidant Activity of Quercus ilex

The development of new natural antibiotics is considered as the heart of several investigations in the nutraceutical field. In this work, leaves of Quercus ilex L. treated by tropospheric ozone (O3) and nitrogen (N) deposition, exhibited a clear antimicrobial efficacy against five multi-drug resistant (MDR) bacterial strains (two gram-positive and three gram-negative). Under controlled conditions, it was studied how simulated N deposition influences the response to O3 and the antibacterial and antioxidant activity, and antioxidant performance. The extraction was performed by ultra-pure acetone using two different steps. A higher antioxidant activity was measured in the presence of interaction between O3 and N treatments on Quercus leaves. At the same time, all organic extracts tested have shown bacteriostatic activity against all the tested strains with a MIC comprised between 9 and 4 micrograms/mL, and a higher antioxidant efficacy shown by spectrophotometric assay. Stronger antimicrobial activity was found in the samples treated with O3, whereas N-treated plants exhibited an intermediate antibacterial performance. This performance is related to the stimulation of the non-enzymatic antioxidant system induced by the oxidative stress, which results in an increase in the production of antimicrobial bioactive compounds.

PuNDH9, a subunit of ETC Complex I regulates plant defense by interacting with PuPR1

NAD+ and NADH play critical roles in energy metabolism, cell death, and gene expression. The NADH-ubiquinone oxidoreductase complex (Complex I) has been long known as a key enzyme in NAD+ and NADH metabolism. In the present study, we found and analyzed a new subunit of Complex I (NDH9), which was isolated from Pyrus ussuriensis combined with RT-PCR. Following infection with A. alternata, RT-qPCR analysis demonstrated an increase in the expression of PuNDH9. Genetic manipulation of PuNDH9 levels suggested that PuNDH9 plays key roles in NADH/NAD+ homeostasis, defense enzyme activities, ROS generation, cell death, gene expression, energy metabolism, and mitochondrial functions during the pear- A. alternata interaction. Furthermore, Y2H, GST-pull down, and a split-luciferase complementation imaging assays revealed that PuNDH9 interacts with PuPR1. We discover that PuNDH9 and PuPR1 synergistically activate defense enzyme activities, ROS accumulation, cell death, and plant defenses. Collectively, our findings reveal that PuNDH9 is likely important for plant defenses.

UMAMIT44 is a key player in glutamate export from Arabidopsis chloroplasts

Selective partitioning of amino acids among organelles, cells, tissues, and organs is essential for cellular metabolism and plant growth. Nitrogen assimilation into glutamine and glutamate and de novo biosynthesis of most protein amino acids occur in chloroplasts; therefore, various transport mechanisms must exist to accommodate their directional efflux from the stroma to the cytosol and feed the amino acids into the extraplastidial metabolic and long-distance transport pathways. Yet, Arabidopsis (Arabidopsis thaliana) transporters functioning in plastidial export of amino acids remained undiscovered. Here, USUALLY MULTIPLE ACIDS MOVE IN AND OUT TRANSPORTER 44 (UMAMIT44) was identified and shown to function in glutamate export from Arabidopsis chloroplasts. UMAMIT44 controls glutamate homeostasis within and outside of chloroplasts and influences nitrogen partitioning from leaves to sinks. Glutamate imbalances in chloroplasts and leaves of umamit44 mutants impact cellular redox state, nitrogen and carbon metabolism, and amino acid (AA) and sucrose supply of growing sinks, leading to negative effects on plant growth. Nonetheless, the mutant lines adjust to some extent by upregulating alternative pathways for glutamate synthesis outside the plastids and by mitigating oxidative stress through the production of other amino acids and antioxidants. Overall, this study establishes that the role of UMAMIT44 in glutamate export from chloroplasts is vital for controlling nitrogen availability within source leaf cells and for sink nutrition, with an impact on growth and seed yield.

Investigating the effects of tauroursodeoxycholic acid (TUDCA) in mitigating endoplasmic reticulum stress and cellular responses in Pak choi

The accumulation of misfolded proteins in the endoplasmic reticulum (ER) within plant cells due to unfavourable conditions leads to ER stress. This activates interconnected pathways involving reactive oxygen species (ROS) and unfolded protein response (UPR), which play vital roles in regulating ER stress. The aim of this study is to investigate the underlying mechanisms of tunicamycin (TM) induced ER stress and explore the potential therapeutic applications of tauroursodeoxycholic acid (TUDCA) in mitigating cellular responses to ER stress in Pak choi (Brassica campestris subsp. chinensis). The study revealed that ER stress in Pak choi leads to detrimental effects on plant morphology, ROS levels, cellular membrane integrity, and the antioxidant defence system. However, treatment with TUDCA in TM-induced ER stressed Pak choi improved morphological indices, pigment contents, ROS accumulation, cellular membrane integrity, and antioxidant defence system restoration. Additionally, TUDCA also modulates the transcription levels of ER stress sensors genes, ER chaperone genes, and ER-associated degradation (ERAD) genes during ER stress in Pak choi. Furthermore, TUDCA has demonstrated its ability to alleviate ER stress, stabilize the UPR, reduce oxidative stress, prevent apoptosis, and positively influence plant growth and development. These results collectively comprehend TUDCA as a promising agent for mitigating ER stress-induced damage in Pak choi plants and provide valuable insights for further research and potential applications in crop protection and stress management.

A scientific version of understanding "Why did the chickens cross the road"? - A guided journey through Bacillus spp. towards sustainable agriculture, circular economy and biofortification

The world, a famished planet with an overgrowing population, requires enormous food crops. This scenario compelled the farmers to use a high quantity of synthetic fertilizers for high food crop productivity. However, prolonged usage of chemical fertilizers results in severe adverse effects on soil and water quality. On the other hand, the growing population significantly consumes large quantities of poultry meats. Eventually, this produces a mammoth amount of poultry waste, chicken feathers. Owing to the protein value of the chicken feathers, these wastes are converted into protein hydrolysate and further extend their application as biostimulants for sustained agriculture. The protein profile of chicken feather protein hydrolysate (CFPH) produced through Bacillus spp. was the maximum compared to physical and chemical protein extraction methods. Several studies proved that the application of CFPH and active Bacillus spp. culture to soil and plants results in enhanced plant growth, phytochemical constituents, crop yield, soil nutrients, fertility, microbiome and resistance against diverse abiotic and biotic stresses. Overall, "CFPH - Jack of all trades" and "Bacillus spp. - an active camouflage to the surroundings where they applied showed profound and significant benefits to the plant growth under the most adverse conditions. In addition, Bacillus spp. coheres the biofortification process in plants through the breakdown of metals into metal ions that eventually increase the nutrient value of the food crops. However, detailed information on them is missing. This can be overcome by further real-world studies on rhizoengineering through a multi-omics approach and their interaction with plants. This review has explored the best possible and efficient strategy for managing chicken feather wastes into protein-rich CFPH through Bacillus spp. bioconversion and utilizing the CFPH and Bacillus spp. as biostimulants, biofertilizers, biopesticides and biofortificants. This paper is an excellent report on organic waste management, circular economy and sustainable agriculture research frontier.