Nitric oxide modulates the expression of cell cycle regulatory genes during lateral root formation in tomato

Exogenous Sodium Nitroprusside Affects the Redox System of Wheat Roots Differentially Regulating the Activity of Antioxidant Enzymes under Short-Time Osmotic Stress

Nitric oxide (NO) is a multifunctional signalling molecule involved in the regulation of plant ontogenesis and adaptation to different adverse environmental factors, in particular to osmotic stress. Understanding NO-induced plant protection is important for the improvement of plant stress tolerance and crop productivity under global climate changes. The root system is crucial for plant survival in a changeable environment. Damages that it experiences under water deficit conditions during the initial developmental periods seriously affect the viability of the plants. This work was devoted to the comparative analysis of the pretreatment of wheat seedlings through the root system with NO donor sodium nitroprusside (SNP) for 24 h on various parameters of redox homeostasis under exposure to osmotic stress (PEG 6000, 12%) over 0.5-24 h. The active and exhausted solutions of SNP, termed as (SNP/+NO) and (SNP/-NO), respectively, were used in this work at a concentration of 2 × 10-4 M. Using biochemistry and light microscopy methods, it has been revealed that osmotic stress caused oxidative damages and the disruption of membrane cell structures in wheat roots. PEG exposure increased the production of superoxide (O2•-), hydrogen peroxide (H2O2), malondialdehyde (MDA), and the levels of electrolyte leakage (EL) and lipid peroxidation (LPO). Stress treatment enhanced the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), the excretion of proline, and the rate of cell death and inhibited their division. Pretreatment with (SNP/+NO) decreased PEG-induced root damages by differently regulating the antioxidant enzymes under stress conditions. Thus, (SNP/+NO) pretreatment led to SOD, APX, and CAT inhibition during the first 4 h of stress and stimulated their activity after 24 h of PEG exposure when compared to SNP-untreated or (SNP/-NO)-pretreated and stress-subjected plants. Osmotic stress triggered the intense excretion of proline by roots into the external medium. Pretreatment with (SNP/+NO) in contrast with (SNP/-NO) additionally increased stress-induced proline excretion. Our results indicate that NO is able to mitigate the destructive effects of osmotic stress on the roots of wheat seedlings. However, the mechanisms of NO protective action may be different at certain periods of stress exposure.

Melatonin Modulates Tomato Root Morphology by Regulating Key Genes and Endogenous Hormones

Melatonin plays a vital role in plant growth and development. In this study, we treated hydroponically grown tomato roots with various concentrations of exogenous melatonin (0, 10, 30, and 50 μmol·L-1). We utilized root scanning and microscopy to examine alterations in root morphology and cell differentiation and elucidated the mechanism by which melatonin regulates these changes through the interplay with endogenous hormones and relevant genes. The results showed that for melatonin at concentrations ranging between 10 and 30 μmol·L-1, the development of lateral roots were significantly stimulated, the root hair growth was enhanced, and biomass accumulation and root activity were increased. Furthermore, we elucidated that melatonin acts as a mediator for the expression of genes, such as SlCDKA1, SlCYCA3;1, SlARF2, SlF3H, and SlKT1, which are involved in the regulation of root morphology changes. Additionally, we observed that melatonin influences the levels of endogenous hormones, including ZT, GA3, IAA, ABA, and BR, which subsequently impact the root morphology development of tomato roots. In summary, this study shows that tomato root morphology can be promoted by the optimal concentration of exogenous melatonin (10-30 μmol·L-1).

Multiple Ways of Nitric Oxide Production in Plants and Its Functional Activity under Abiotic Stress Conditions

Nitric oxide (NO) is an endogenous signaling molecule that plays an important role in plant ontogenesis and responses to different stresses. The most widespread abiotic stress factors limiting significantly plant growth and crop yield are drought, salinity, hypo-, hyperthermia, and an excess of heavy metal (HM) ions. Data on the accumulation of endogenous NO under stress factors and on the alleviation of their negative effects under exogenous NO treatments indicate the perspectives of its practical application to improve stress resistance and plant productivity. This requires fundamental knowledge of the NO metabolism and the mechanisms of its biological action in plants. NO generation occurs in plants by two main alternative mechanisms: oxidative or reductive, in spontaneous or enzymatic reactions. NO participates in plant development by controlling the processes of seed germination, vegetative growth, morphogenesis, flower transition, fruit ripening, and senescence. Under stressful conditions, NO contributes to antioxidant protection, osmotic adjustment, normalization of water balance, regulation of cellular ion homeostasis, maintenance of photosynthetic reactions, and growth processes of plants. NO can exert regulative action by inducing posttranslational modifications (PTMs) of proteins changing the activity of different enzymes or transcriptional factors, modulating the expression of huge amounts of genes, including those related to stress tolerance. This review summarizes the current data concerning molecular mechanisms of NO production and its activity in plants during regulation of their life cycle and adaptation to drought, salinity, temperature stress, and HM ions.

Application of Data Modeling, Instrument Engineering and Nanomaterials in Selected Medid the Scientific Recinal Plant Tissue Culture

At present, most precious compounds are still obtained by plant cultivation such as ginsenosides, glycyrrhizic acid, and paclitaxel, which cannot be easily obtained by artificial synthesis. Plant tissue culture technology is the most commonly used biotechnology tool, which can be used for a variety of studies such as the production of natural compounds, functional gene research, plant micropropagation, plant breeding, and crop improvement. Tissue culture material is a basic and important part of this issue. The formation of different plant tissues and natural products is affected by growth conditions and endogenous substances. The accumulation of secondary metabolites are affected by plant tissue type, culture method, and environmental stress. Multi-domain technologies are developing rapidly, and they have made outstanding contributions to the application of plant tissue culture. The modes of action have their own characteristics, covering the whole process of plant tissue from the induction, culture, and production of natural secondary metabolites. This paper reviews the induction mechanism of different plant tissues and the application of multi-domain technologies such as artificial intelligence, biosensors, bioreactors, multi-omics monitoring, and nanomaterials in plant tissue culture and the production of secondary metabolites. This will help to improve the tissue culture technology of medicinal plants and increase the availability and the yield of natural metabolites.

Nitric Oxide Acts as a Key Signaling Molecule in Plant Development under Stressful Conditions

Nitric oxide (NO), a colorless gaseous molecule, is a lipophilic free radical that easily diffuses through the plasma membrane. These characteristics make NO an ideal autocrine (i.e., within a single cell) and paracrine (i.e., between adjacent cells) signalling molecule. As a chemical messenger, NO plays a crucial role in plant growth, development, and responses to biotic and abiotic stresses. Furthermore, NO interacts with reactive oxygen species, antioxidants, melatonin, and hydrogen sulfide. It regulates gene expression, modulates phytohormones, and contributes to plant growth and defense mechanisms. In plants, NO is mainly produced via redox pathways. However, nitric oxide synthase, a key enzyme in NO production, has been poorly understood recently in both model and crop plants. In this review, we discuss the pivotal role of NO in signalling and chemical interactions as well as its involvement in the mitigation of biotic and abiotic stress conditions. In the current review, we have discussed various aspects of NO including its biosynthesis, interaction with reactive oxygen species (ROS), melatonin (MEL), hydrogen sulfide, enzymes, phytohormones, and its role in normal and stressful conditions.

Auxin Crosstalk with Reactive Oxygen and Nitrogen Species in Plant Development and Abiotic Stress

The phytohormone auxin acts as an important signaling molecule having regulatory functions during the growth and development of plants. Reactive oxygen species (ROS) are also known to perform signaling functions at low concentrations; however, over-accumulation of ROS due to various environmental stresses damages the biomolecules and cell structures and leads to cell death, and therefore, it can be said that ROS act as a double-edged sword. Nitric oxide (NO), a gaseous signaling molecule, performs a wide range of favorable roles in plants. NO displays its positive role in photomorphogenesis, root growth, leaf expansion, seed germination, stomatal closure, senescence, fruit maturation, mitochondrial activity and metabolism of iron. Studies have revealed the early existence of these crucial molecules during evolution. Moreover, auxin, ROS and NO together show their involvement in various developmental processes and abiotic stress tolerance. Redox signaling is a primary response during exposure of plants to stresses and shows a link with auxin signaling. This review provides updated information related to crosstalk between auxin, ROS and NO starting from their evolution during early Earth periods and their interaction in plant growth and developmental processes as well as in the case of abiotic stresses to plants.

Absence of Arabidopsis Polyamine Oxidase 5 Influences the Cytokinin-Induced Shoot Meristem Formation from Lateral Root Primordia

Lateral root primordia (LRPs) of Arabidopsis can be directly converted to shoot meristems (SMs) by the application of exogenous cytokinin. Here, we report that Arabidopsis POLYAMINE OXIDASE 5 (AtPAO5) contributes to this process, since the rate of SM formation from LRPs was significantly lower in the pao5-2 knockout mutant. Furthermore, the presented experiments showed that AtPAO5 influences SM formation via controlling the thermospermine (T-Spm) level. Gene expression analyses supported the view that the pao5-2 mutation as well as exogenous T-Spm downregulate the expression of the class 3 haemoglobin coding genes AtGLB1 and AtGLB2. AtGLB1 and 2 have been reported to augment cytokinin sensitivity, indirectly inhibiting the expression of type-A ARABIDOPSIS RESPONSE REGULATORs (ARRs). In agreement, the same ARR-coding genes were found to be upregulated in the pao5-2 mutant. Although GLB proteins might also control cytokinin-induced nitric oxide (NO) accumulation, we could not find experimental evidence for it. Rather, the negative effect of NO-donor treatment on AtPAO5 gene expression and SM formation was seen. Nevertheless, a hypothetical pathway is set up explaining how AtPAO5 may affect direct shoot meristem formation, controlling cytokinin sensitivity through T-Spm and GLBs.

New Paradigms in Brassinosteroids, Strigolactones, Sphingolipids, and Nitric Oxide Interaction in the Control of Lateral and Adventitious Root Formation

The root system is formed by the primary root (PR), which forms lateral roots (LRs) and, in some cases, adventitious roots (ARs), which in turn may produce their own LRs. The formation of ARs is also essential for vegetative propagation in planta and in vitro and for breeding programs. Root formation and branching is coordinated by a complex developmental network, which maximizes the plant's ability to cope with abiotic stress. Rooting is also a response caused in a cutting by wounding and disconnection from the donor plant. Brassinosteroids (BRs) are steroid molecules perceived at the cell surface. They act as plant-growth-regulators (PGRs) and modulate plant development to provide stress tolerance. BRs and auxins control the formation of LRs and ARs. The auxin/BR interaction involves other PGRs and compounds, such as nitric oxide (NO), strigolactones (SLs), and sphingolipids (SPLs). The roles of these interactions in root formation and plasticity are still to be discovered. SLs are carotenoid derived PGRs. SLs enhance/reduce LR/AR formation depending on species and culture conditions. These PGRs possibly crosstalk with BRs. SPLs form domains with sterols within cellular membranes. Both SLs and SPLs participate in plant development and stress responses. SPLs are determinant for auxin cell-trafficking, which is essential for the formation of LRs/ARs in planta and in in vitro systems. Although little is known about the transport, trafficking, and signaling of SPLs, they seem to interact with BRs and SLs in regulating root-system growth. Here, we review the literature on BRs as modulators of LR and AR formation, as well as their crosstalk with SLs and SPLs through NO signaling. Knowledge on the control of rooting by these non-classical PGRs can help in improving crop productivity and enhancing AR-response from cuttings.

Small Heat Shock Protein (sHSP) Gene Family from Sweet Pepper (Capsicum annuum L.) Fruits: Involvement in Ripening and Modulation by Nitric Oxide (NO)

Small heat shock proteins (sHSPs) are usually upregulated in plants under diverse environmental stresses. These proteins have been suggested to function as molecular chaperones to safeguard other proteins from stress-induced damage. The ripening of pepper (Capsicum annuum L.) fruit involves important phenotypic, physiological, and biochemical changes, which have associated endogenous physiological nitro-oxidative stress, but they can also be significantly affected by environmental conditions, such as temperature. Based on the available pepper genome, a total of 41 sHSP genes were identified in this work, and their distributions in the 12 pepper chromosomes were determined. Among these genes, only 19 sHSP genes were found in the transcriptome (RNA-Seq) of sweet pepper fruits reported previously. This study aims to analyze how these 19 sHSP genes present in the transcriptome of sweet pepper fruits are modulated during ripening and after treatment of fruits with nitric oxide (NO) gas. The time-course expression analysis of these genes during fruit ripening showed that 6 genes were upregulated; another 7 genes were downregulated, whereas 6 genes were not significantly affected. Furthermore, NO treatment triggered the upregulation of 7 sHSP genes and the downregulation of 3 sHSP genes, whereas 9 genes were unchanged. These data indicate the diversification of sHSP genes in pepper plants and, considering that sHSPs are important in stress tolerance, the observed changes in sHSP expression support that pepper fruit ripening has an associated process of physiological nitro-oxidative stress, such as it was previously proposed.

Molecular hydrogen positively influences lateral root formation by regulating hydrogen peroxide signaling

Although a previous study discovered that exogenous molecular hydrogen (H₂) supplied with hydrogen-rich water (HRW) can mediate lateral root (LR) development, whether or how endogenous H₂ influences LR formation is still elusive. In this report, mimicking the induction responses in tomato seedlings achieved by HRW or exogenous hydrogen peroxide (H₂O₂; a positive control), transgenic Arabidopsis that overexpressed the hydrogenase1 gene (CrHYD1) from Chlamydomonas reinhardtii not only stimulated endogenous hydrogen peroxide (H₂O₂) production, but also markedly promoted LR formation. Above H₂ and H₂O₂ responses were abolished by the removal of endogenous H₂O₂. Moreover, the changes in transcriptional patterns of representative cell cycle genes and auxin signaling-related genes during LR development in both tomato and transgenic Arabidopsis thaliana matched with above phenotypes. The alternations in the levels of GUS transcripts driven by the CYCB1 promoter and expression of PIN1 protein further indicated that H₂O₂ synthesis was tightly linked to LR formation achieved by endogenous H₂, and cell cycle regulation and auxin-dependent pathway might be their targets. There results might provide a reference for molecular mechanism underlying the regulation of root morphogenesis by H₂.

Biological Functions of Hydrogen Sulfide in Plants

Hydrogen sulfide (H₂S), which is a gasotransmitter, can be biosynthesized and participates in various physiological and biochemical processes in plants. H₂S also positively affects plants' adaptation to abiotic stresses. Here, we summarize the specific ways in which H₂S is endogenously synthesized and metabolized in plants, along with the agents and methods used for H₂S research, and outline the progress of research on the regulation of H₂S on plant metabolism and morphogenesis, abiotic stress tolerance, and the series of different post-translational modifications (PTMs) in which H₂S is involved, to provide a reference for future research on the mechanism of H₂S action.

Nitric oxide: A core signaling molecule under elevated GHGs (CO2, CH4, N2O, O3)-mediated abiotic stress in plants

Nitric oxide (NO), an ancient molecule with multiple roles in plants, has gained momentum and continues to govern plant biosciences-related research. NO, known to be involved in diverse physiological and biological processes, is a central molecule mediating cellular redox homeostasis under abiotic and biotic stresses. NO signaling interacts with various signaling networks to govern the adaptive response mechanism towards stress tolerance. Although diverging views question the role of plants in the current greenhouse gases (GHGs) budget, it is widely accepted that plants contribute, in one way or another, to the release of GHGs (carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and ozone (O3)) to the atmosphere, with CH4 and N2O being the most abundant, and occur simultaneously. Studies support that elevated concentrations of GHGs trigger similar signaling pathways to that observed in commonly studied abiotic stresses. In the process, NO plays a forefront role, in which the nitrogen metabolism is tightly related. Regardless of their beneficial roles in plants at a certain level of accumulation, high concentrations of CO2, CH4, and N2O-mediating stress in plants exacerbate the production of reactive oxygen (ROS) and nitrogen (RNS) species. This review assesses and discusses the current knowledge of NO signaling and its interaction with other signaling pathways, here focusing on the reported calcium (Ca2+) and hormonal signaling, under elevated GHGs along with the associated mechanisms underlying GHGs-induced stress in plants.

Involvement of Calcium and Calmodulin in NO-Alleviated Salt Stress in Tomato Seedlings

Salt stress is an adverse impact on the growth and development of plants, leading to yield losses in crops. It has been suggested that nitric oxide (NO) and calcium ion (Ca2+) act as critical signals in regulating plant growth. However, their crosstalk remains unclear under stress condition. In this study, we demonstrate that NO and Ca2+ play positive roles in the growth of tomato (Lycopersicum esculentum) seedlings under salt stress. Our data show that Ca2+ channel inhibitor lanthanum chloride (LaCl3), Ca2+ chelator ethylene glycol-bis (2-aminoethylether)-N,N,N,N-tetraacetic acid (EGTA), or calmodulin (CaM) antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfona-mide hydrochloride (W-7) significantly reversed the effect of NO-promoted the growth of tomato seedlings under salt stress. We further show that NO and Ca2+ significantly decreased reactive oxygen accumulation, increased proline content, and increased the activity of antioxidant enzymes, as well as increased expression of antioxidant enzymes related genes. However, LaCl3, EGTA, and W-7 prevented the positive roles of NO. In addition, the activity of downstream target enzymes related to Ca2+/CaM was increased by NO under salt stress, while LaCl3, EGTA, and W-7 reversed this enhancement. Taken together, these results demonstrate that Ca2+/CaM might be involved in NO-alleviate salt stress.

Auxin regulates growth, photosynthetic efficiency and mitigates copper induced toxicity via modulation of nutrient status, sugar metabolism and antioxidant potential in Brassica juncea

The involvement of auxin (IAA) in growth and development of plants is well known, but its role in the mitigation of metal stress, especially copper (Cu), is not fully understood; therefore, it is time to explore its involvement in minimizing the stress. A pot experiment was conducted to assess the protective function of IAA, applied to the foliage, on photosynthetic machinery, carbohydrate metabolism, and growth of Brassica juncea, grown with Cu (30 or 60 mg kg^-1 of soil). Among the different concentrations (10^-10, 10^-8, or 10^-6 M), 10^-8 M of IAA alone enhanced the photosynthetic characteristics, sugar accumulation and vegetative growth with minimal cellular oxidative stress level. Moreover, the same concentration of auxin was most effective in decreasing the stress levels generated by Cu and maintained it nearly to that of the control in terms of photosynthetic attributes, gas exchange parameters, PSII activity, electron transport rate, and growth attributes. Auxin also maintained the membrane stability and ultrastructure of chloroplast, stomatal morphology with a reduction in malondialdehyde (MDA), electrolyte leakage (EL) and cell death in test plants even under Cu stress. IAA also improved the translocation of Cu from root to the aerial parts, thus enhanced the Cu-reclamation in metal contaminated soils. Our findings suggest that the application of 10^-8 M of IAA maintains the overall growth of plants and may be used as an effective agent to improve growth, photosynthesis and phyto-remediation potential of B. juncea in Cu contaminated soil.

Thiol Modifications in the Extracellular Space—Key Proteins in Inflammation and Viral Infection

Posttranslational modifications (PTMs) allow to control molecular and cellular functions in response to specific signals and changes in the microenvironment of cells. They regulate structure, localization, stability, and function of proteins in a spatial and temporal manner. Among them, specific thiol modifications of cysteine (Cys) residues facilitate rapid signal transduction. In fact, Cys is unique because it contains the highly reactive thiol group that can undergo different reversible and irreversible modifications. Upon inflammation and changes in the cellular microenvironment, many extracellular soluble and membrane proteins undergo thiol modifications, particularly dithiol–disulfide exchange, S-glutathionylation, and S-nitrosylation. Among others, these thiol switches are essential for inflammatory signaling, regulation of gene expression, cytokine release, immunoglobulin function and isoform variation, and antigen presentation. Interestingly, also the redox state of bacterial and viral proteins depends on host cell-mediated redox reactions that are critical for invasion and infection. Here, we highlight mechanistic thiol switches in inflammatory pathways and infections including cholera, diphtheria, hepatitis, human immunodeficiency virus (HIV), influenza, and coronavirus disease 2019 (COVID-19).

Prohibitin 3 gives birth to a new lateral root primordium

This article comments on: Li S, Li Q, Tian X, Mu L, Ji M, Wang X, Li N, Liu F, Shu J, Crawford NM, Wang Y. 2022. PHB3 regulates lateral root primordia formation via NO-mediated degradation of AUXIN/INDOLE-3-ACETIC ACID proteins. Journal of Experimental Botany 73,4034–4045.

COE2 Is Required for the Root Foraging Response to Nitrogen Limitation

There are numerous exchanges of signals and materials between leaves and roots, including nitrogen, which is one of the essential nutrients for plant growth and development. In this study we identified and characterized the Chlorophyll A/B-Binding Protein (CAB) (named coe2 for CAB overexpression 2) mutant, which is defective in the development of chloroplasts and roots under normal growth conditions. The phenotype of coe2 is caused by a mutation in the Nitric Oxide Associated (NOA1) gene that is implicated in a wide range of chloroplast functions including the regulation of metabolism and signaling of nitric oxide (NO). A transcriptome analysis reveals that expression of genes involved in metabolism and lateral root development are strongly altered in coe2 seedlings compared with WT. COE2 is expressed in hypocotyls, roots, root hairs, and root caps. Both the accumulation of NO and the growth of lateral roots are enhanced in WT but not in coe2 under nitrogen limitation. These new findings suggest that COE2-dependent signaling not only coordinates gene expression but also promotes chloroplast development and function by modulating root development and absorption of nitrogen compounds.

Glutathione produced by γ-glutamyl cysteine synthetase acts downstream of hydrogen to positively influence lateral root branching

Hydrogen gas (H₂) mediation of lateral root (LR) branching was previously described. However, related signaling pathway is largely unexplored. In this study, we discovered that application with H₂ using hydrogen-rich water, mimicking the responses of exogenous glutathione (GSH), not only enhanced GSH synthesis, but also induced tomato LR development. The changes in the transcripts of auxin signaling-related genes and cell cycle regulatory genes were matched with above phenotypes. The addition of H₂ could trigger higher transcript levels of SlGSH1 and SlGSH2, encoding γ-glutamylcysteine synthetase (γ-ECS) and glutathione synthetase (GS), confirming the stimulation of GSH synthesis. These responses were greatly abolished when the inhibitor of γ-ECS was applied. The inhibition in lateral root primordium development, especially in emergence stage, was also observed. Genetic evidence revealed that the defects in GSH production and lateral rooting in Arabidopsis cad2-1, a γ-ECS defective mutant, were obviously abolished in the presence of GSH compared to those in the presence of H₂. Further evidence revealed that mRNA levels of target genes elicited by H₂ in wild-type, were differentially impaired in mutant plants. Together, above data clearly demonstrated that γ-ECS-dependent GSH production might be closely associated with H₂ control of LR branching.

Molecular Mechanisms of Nitric Oxide (NO) Signaling and Reactive Oxygen Species (ROS) Homeostasis during Abiotic Stresses in Plants

Abiotic stressors, such as drought, heavy metals, and high salinity, are causing huge crop losses worldwide. These abiotic stressors are expected to become more extreme, less predictable, and more widespread in the near future. With the rapidly growing human population and changing global climate conditions, it is critical to prevent global crop losses to meet the increasing demand for food and other crop products. The reactive gaseous signaling molecule nitric oxide (NO) is involved in numerous plant developmental processes as well as plant responses to various abiotic stresses through its interactions with various molecules. Together, these interactions lead to the homeostasis of reactive oxygen species (ROS), proline and glutathione biosynthesis, post-translational modifications such as S-nitrosylation, and modulation of gene and protein expression. Exogenous application of various NO donors positively mitigates the negative effects of various abiotic stressors. In view of the multidimensional role of this signaling molecule, research over the past decade has investigated its potential in alleviating the deleterious effects of various abiotic stressors, particularly in ROS homeostasis. In this review, we highlight the recent molecular and physiological advances that provide insights into the functional role of NO in mediating various abiotic stress responses in plants.

Cross-Talk between Hydrogen Peroxide and Nitric Oxide during Plant Development and Responses to Stress

Nitric oxide (NO) and hydrogen peroxide (H₂O₂) are gradually becoming established as critical regulators in plants under physiological and stressful conditions. Strong spatiotemporal correlations in their production and distribution have been identified in various plant biological processes. In this context, NO and H₂O₂ act synergistically or antagonistically as signals or stress promoters depending on their respective concentrations, engaging in processes such as the hypersensitive response, stomatal movement, and abiotic stress responses. Moreover, proteins identified as potential targets of NO-based modifications include a number of enzymes related to H₂O₂ metabolism, reinforcing their cross-talk. In this review, several processes of well-characterized functional interplay between H₂O₂ and NO are discussed with respect to the most recent reported evidence on hypersensitive response-induced programmed cell death, stomatal movement, and plant responses to adverse conditions and, where known, the molecular mechanisms and factors underpinning their cross-talk.

Silicon induces adventitious root formation in rice under arsenate stress with involvement of nitric oxide and indole-3-acetic acid

Arsenic (As) negatively affects plant development. This study evaluates how the application of silicon (Si) can favor the formation of adventitious roots in rice under arsenate stress (AsV) as a mechanism to mitigate its negative effects. The simultaneous application of AsV and Si up-regulated the expression of genes involved in nitric oxide (NO) metabolism, cell cycle progression, auxin (IAA, indole-3-acetic acid) biosynthesis and transport, and Si uptake which accompanied adventitious root formation. Furthermore, Si triggered the expression and activity of enzymes involved in ascorbate recycling. Treatment with L-NAME (NG-nitro L-arginine methyl ester), an inhibitor of NO generation, significantly suppressed adventitious root formation, even in the presence of Si; however, supplying NO in the growth media rescued its effects. Our data suggest that both NO and IAA are essential for Si-mediated adventitious root formation under AsV stress. Interestingly, TIBA (2,3,5-triiodobenzoic acid), a polar auxin transport inhibitor, suppressed adventitious root formation even in the presence of Si and SNP (sodium nitroprusside, an NO donor), suggesting that Si is involved in a mechanism whereby a cellular signal is triggered and that first requires NO formation, followed by IAA biosynthesis.

Ethylene and Nitric Oxide Involvement in the Regulation of Fe and P Deficiency Responses in Dicotyledonous Plants

Iron (Fe) and phosphorus (P) are two essential elements for plant growth. Both elements are abundant in soils but with poor availability for plants, which favor their acquisition by developing morphological and physiological responses in their roots. Although the regulation of the genes related to these responses is not totally known, ethylene (ET) and nitric oxide (NO) have been involved in the activation of both Fe-related and P-related genes. The common involvement of ET and NO suggests that they must act in conjunction with other specific signals, more closely related to each deficiency. Among the specific signals involved in the regulation of Fe- or P-related genes have been proposed Fe-peptides (or Fe ion itself) and microRNAs, like miR399 (P), moving through the phloem. These Fe- or P-related phloem signals could interact with ET/NO and confer specificity to the responses to each deficiency, avoiding the induction of the specific responses when ET/NO increase due to other nutrient deficiencies or stresses. Besides the specificity conferred by these signals, ET itself could confer specificity to the responses to Fe- or P-deficiency by acting through different signaling pathways in each case. Given the above considerations, there are preliminary results suggesting that ET could regulate different nutrient responses by acting both in conjunction with other signals and through different signaling pathways. Because of the close relationship among these two elements, a better knowledge of the physiological and molecular basis of their interaction is necessary to improve their nutrition and to avoid the problems associated with their misuse. As examples of this interaction, it is known that Fe chlorosis can be induced, under certain circumstances, by a P over- fertilization. On the other hand, Fe oxides can have a role in the immobilization of P in soils. Qualitative and quantitative assessment of the dynamic of known Fe- and P-related genes expression, selected ad hoc and involved in each of these deficiencies, would allow us to get a profound knowledge of the processes that regulate the responses to both deficiencies. The better knowledge of the regulation by ET of the responses to these deficiencies is necessary to properly understand the interactions between Fe and P. This will allow the obtention of more efficient varieties in the absorption of P and Fe, and the use of more rational management techniques for P and Fe fertilization. This will contribute to minimize the environmental impacts caused by the use of P and Fe fertilizers (Fe chelates) in agriculture and to adjust the costs for farmers, due to the high prices and/or scarcity of Fe and P fertilizers. This review aims to summarize the latest advances in the knowledge about Fe and P deficiency responses, analyzing the similarities and differences among them and considering the interactions among their main regulators, including some hormones (ethylene) and signaling substances (NO and GSNO) as well as other P- and Fe-related signals.

Nitric oxide (NO) and salicylic acid (SA): A framework for their relationship in plant development under abiotic stress

The free radical nitric oxide (NO) and the phenolic phytohormone salicylic acid (SA) are signal molecules which exert key functions at biochemical and physiological levels. Abiotic stresses, especially in early plant development, impose the biggest threats to agricultural systems and crop yield. These stresses impair plant growth and subsequently cause a reduction in root development, affecting nutrient uptake and crop productivity. The molecules NO and SA have been identified as robust tools for efficiently mitigating the negative effects of abiotic stress in plants. SA is engaged in an array of tasks under adverse environmental situations. The function of NO depends on its cellular concentration; at a low level, it acts as a signal molecule, while at a high level, it triggers nitro-oxidative stress. The crosstalk between NO and SA involving different signalling molecules and regulatory factors modulate plant function during stressful situations. Crosstalk between these two signalling molecules induces plant tolerance to abiotic stress and needs further investigation. This review aims to highlight signalling aspects of NO and SA in higher plants and critically discusses the roles of these two molecules in alleviating abiotic stress.

Nitric Oxide Alters the Pattern of Auxin Maxima and PIN-FORMED1 During Shoot Development

Hormone patterns tailor cell fate decisions during plant organ formation. Among them, auxins and cytokinins are critical phytohormones during early development. Nitric oxide (NO) modulates root architecture by the control of auxin spatial patterns. However, NO involvement during the coordination of shoot organogenesis remains unclear. Here, we explore the effect of NO during shoot development by using a phenotypic, cellular, and genetic analysis in Arabidopsis thaliana and get new insights into the characterization of NO-mediated leaf-related phenotypes. NO homeostasis mutants are impaired in several shoot architectural parameters, including phyllotactic patterns, inflorescence stem elongation, silique production, leaf number, and margin. Auxin distribution is a key feature for tissue differentiation and need to be controlled at different levels (i.e., synthesis, transport, and degradation mechanisms). The phenotypes resulting from the introduction of the cue1 mutation in the axr1 auxin resistant and pin1 backgrounds exacerbate the relationship between NO and auxins. Using the auxin reporter DR5:GUS, we observed an increase in auxin maxima under NO-deficient mutant backgrounds and NO scavenging, pointing to NO-ASSOCIATED 1 (NOA1) as the main player related to NO production in this process. Furthermore, polar auxin transport is mainly regulated by PIN-FORMED 1 (PIN1), which controls the flow along leaf margin and venations. Analysis of PIN1 protein levels shows that NO controls its accumulation during leaf development, impacting the auxin mediated mechanism of leaf building. With these findings, we also provide evidence for the NO opposite effects to determine root and shoot architecture, in terms of PIN1 accumulation under NO overproduction.

Molecular functions of nitric oxide and its potential applications in horticultural crops

Nitric oxide (NO) regulates plant growth, enhances nutrient uptake, and activates disease and stress tolerance mechanisms in most plants, making NO a potential tool for use in improving the yield and quality of horticultural crop species. Although the use of NO in horticulture is still in its infancy, research on NO in model plant species has provided an abundance of valuable information on horticultural crop species. Emerging evidence implies that the bioactivity of NO can occur through many potential mechanisms but occurs mainly through S-nitrosation, the covalent and reversible attachment of NO to cysteine thiol. In this context, NO signaling specifically affects crop development, immunity, and environmental interactions. Moreover, NO can act as a fumigant against a wide range of postharvest diseases and pests. However, for effective use of NO in horticulture, both understanding and exploring the biological significance and potential mechanisms of NO in horticultural crop species are critical. This review provides a picture of our current understanding of how NO is synthesized and transduced in plants, and particular attention is given to the significance of NO in breaking seed dormancy, balancing root growth and development, enhancing nutrient acquisition, mediating stress responses, and guaranteeing food safety for horticultural production.

Transcription Factors as the "Blitzkrieg" of Plant Defense: A Pragmatic View of Nitric Oxide's Role in Gene Regulation

Plants are in continuous conflict with the environmental constraints and their sessile nature demands a fine-tuned, well-designed defense mechanism that can cope with a multitude of biotic and abiotic assaults. Therefore, plants have developed innate immunity, R-gene-mediated resistance, and systemic acquired resistance to ensure their survival. Transcription factors (TFs) are among the most important genetic components for the regulation of gene expression and several other biological processes. They bind to specific sequences in the DNA called transcription factor binding sites (TFBSs) that are present in the regulatory regions of genes. Depending on the environmental conditions, TFs can either enhance or suppress transcriptional processes. In the last couple of decades, nitric oxide (NO) emerged as a crucial molecule for signaling and regulating biological processes. Here, we have overviewed the plant defense system, the role of TFs in mediating the defense response, and that how NO can manipulate transcriptional changes including direct post-translational modifications of TFs. We also propose that NO might regulate gene expression by regulating the recruitment of RNA polymerase during transcription.

Physiological significance of pedospheric nitric oxide for root growth, development and organismic interactions

Nitric oxide (NO) is essential for plant growth and development, as well as interactions with abiotic and biotic environments. Its importance for multiple functions in plants means that tight regulation of NO concentrations is required. This is of particular significance in roots, where NO signalling is involved in processes, such as root growth, lateral root formation, nutrient acquisition, heavy metal homeostasis, symbiotic nitrogen fixation and root-mycorrhizal fungi interactions. The NO signal can also be produced in high levels by microbial processes in the rhizosphere, further impacting root processes. To explore these interesting interactions, in the present review, we firstly summarize current knowledge of physiological processes of NO production and consumption in roots and, thereafter, of processes involved in NO homeostasis in root cells with particular emphasis on root growth, development, nutrient acquisition, environmental stresses and organismic interactions.

Crosstalk among hydrogen sulfide (H2S), nitric oxide (NO) and carbon monoxide (CO) in root-system development and its rhizosphere interactions: A gaseous interactome

Root development in higher plants is achieved by a precise intercellular communication which determines cell fate in the primary embryonic meristem where the gasotransmitters H₂S, NO and CO participate dynamically. Furthermore, the rhizosphere interaction of these molecules with microbial and soil metabolism also affects root development. NO regulates root growth and architecture in association with several other biomolecules like auxin indole-3-acetic acid (IAA), ethylene, jasmonic acid (JA), strigolactones, alkamides and melatonin. The CO-mediated signal transduction pathway in roots is closely linked to the NO-mediated signal cascades. Interestingly, H₂S acts also as an upstream component in IAA and NO-mediated crosstalk during root development. Heme oxygenase (HO) 1 generates CO and functions as a downstream component in H₂S-mediated adventitious rooting and H₂S-CO crosstalk. Likewise, reactive oxygen species (ROS), H₂S and NO crosstalk are important components in the regulation of root architecture. Deciphering these interactions will be a potential biotechnological tool which could provide benefits in crop management in soils, especially under adverse environmental conditions. This review aims to provide a comprehensive update of the complex networks of these gasotransmitters during the development of roots.

Enhanced Nitric Oxide Synthesis Through Nitrate Supply Improves Drought Tolerance of Sugarcane Plants

Nitric oxide (NO) is an important signaling molecule associated with many biochemical and physiological processes in plants under stressful conditions. Nitrate reductase (NR) not only mediates the reduction of NO3 - to NO2 - but also reduces NO2 - to NO, a relevant pathway for NO production in higher plants. Herein, we hypothesized that sugarcane plants supplied with more NO3 - as a source of N would produce more NO under water deficit. Such NO would reduce oxidative damage and favor photosynthetic metabolism and growth under water limiting conditions. Sugarcane plants were grown in nutrient solution and received the same amount of nitrogen, with varying nitrate:ammonium ratios (100:0 and 70:30). Plants were then grown under well-watered or water deficit conditions. Under water deficit, plants exhibited higher root [NO3 -] and [NO2 -] when supplied with 100% NO3 -. Accordingly, the same plants also showed higher root NR activity and root NO production. We also found higher photosynthetic rates and stomatal conductance in plants supplied with more NO3 -, which was associated with increased root growth. ROS accumulation was reduced due to increases in the activity of catalase in leaves and superoxide dismutase and ascorbate peroxidase in roots of plants supplied with 100% NO3 - and facing water deficit. Such positive responses to water deficit were offset when a NO scavenger was supplied to the plants, thus confirming that increases in leaf gas exchange and plant growth were induced by NO. Concluding, NO3 - supply is an interesting strategy for alleviating the negative effects of water deficit on sugarcane plants, increasing drought tolerance through enhanced NO production. Our data also provide insights on how plant nutrition could improve crop tolerance against abiotic stresses, such as drought.

An Update on Nitric Oxide Production and Role Under Phosphorus Scarcity in Plants

Phosphate (P) is characterized by its low availability and restricted mobility in soils, and also by a high redistribution capacity inside plants. In order to maintain P homeostasis in nutrient restricted conditions, plants have developed mechanisms which enable P acquisition from the soil solution, and an efficient reutilization of P already present in plant cells. Nitric oxide (NO) is a bioactive molecule with a plethora of functions in plants. Its endogenous synthesis depends on internal and environmental factors, and is closely tied with nitrogen (N) metabolism. Furthermore, there is evidence demonstrating that N supply affects P homeostasis and that P deficiency impacts on N assimilation. This review will provide an overview on how NO levels in planta are affected by P deficiency, the interrelationship with N metabolism, and a summary of the current understanding about the influence of this reactive N species over the processes triggered by P starvation, which could modify P use efficiency.

A Novel Mechanism Underlying Multi-walled Carbon Nanotube-Triggered Tomato Lateral Root Formation: the Involvement of Nitric Oxide

Abundant studies revealed that multi-walled carbon nanotubes (MWCNTs) are toxic to plants. However, whether or how MWCNTs influence lateral root (LR) formation, which is an important component of the adaptability of the root system to various environmental cues, remains controversial. In this report, we found that MWCNTs could enter into tomato seedling roots. The administration with MWCNTs promoted tomato LR formation in an approximately dose-dependent fashion. Endogenous nitric oxide (NO) production was triggered by MWCNTs, confirmed by Greiss reagent method, electron paramagnetic resonance (EPR), and laser scanning confocal microscopy (LSCM), together with the scavenger of NO. A cause-effect relationship exists between MWCNTs and NO in the induction of LR development, since MWCNT-triggered NO synthesis and LR formation were obviously blocked by the removal of endogenous NO with its scavenger. The activity of NO generating enzyme nitrate reductase (NR) was increased in response to MWCNTs. Tungstate inhibition of NR not only impaired NO production, but also abolished LR formation triggered by MWCNTs. The addition of NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of mammalian nitric oxide synthase (NOS)-like enzyme, failed to influence LR formation. Collectively, we proposed that NO might act as a downstream signaling molecule in MWCNT control of LR development, at least partially via NR.

Methane-induced lateral root formation requires the participation of nitric oxide signaling

Although methane (CH₄)-induced lateral root (LR) formation has been discovered, the identification of downstream signaling compounds has yet to be fully elucidated. Here, we report a unique mechanism for the involvement of nitric oxide (NO) in the above CH₄-mediated pathway in tomato (Solanum lycopersicum L.) and Arabidopsis thaliana. NO was produced rapidly in the root tissues of tomato seedlings when CH₄ was administrated exogenously. The scavenging of NO with its scavengers prevented lateral root primordia formation and thereafter lateral rooting triggered by CH₄. Gene expression analysis revealed that similar to the responses of sodium nitroprusside (SNP; a NO-releasing compound), CH₄-induced SlCYCA2;1, SlCYCA3;1, and SlCDKA1 transcripts, and -downregulated SlKRP2 mRNA, were differentially abolished when endogenous NO was removed by its scavengers. Changes in the lateral root-related miRNA genes (SlmiR160 and SlmiR390a) and their target genes (SlARF16 and SlARF4), exhibited similar tendencies. Similar to those results in tomato, the addition of CH₄ and SNP could obviously induce NO production and LR formation in Arabidopsis seedlings, which were correlated with the transcriptional profiles of representative LR-related genes. Combine with these findings in tomato and Arabidopsis thaliana, our results showed that NO might act, at least partially, as the downstream signaling molecule for CH₄ control of lateral rooting.

Revealing on hydrogen sulfide and nitric oxide signals co-ordination for plant growth under stress conditions

In the recent times, plants are facing certain types of environmental stresses, which give rise to formation of reactive oxygen species (ROS) such as hydroxyl radicals, hydrogen peroxides, superoxide anions and so on. These are required by the plants at low concentrations for signal transduction and at high concentrations, they repress plant root growth. Apart from the ROS activities, hydrogen sulfide (H₂ S) and nitric oxide (NO) have major contributions in regulating growth and developmental processes in plants, as they also play key roles as signaling molecules and act as chief plant immune defense mechanisms against various biotic as well as abiotic stresses. H₂ S and NO are the two pivotal gaseous messengers involved in growth, germination and improved tolerance in plants under stressed and non-stress conditions. H₂ S and NO mediate cell signaling in plants as a response to several abiotic stresses like temperature, heavy metal exposure, water and salinity. They alter gene expression levels to induce the synthesis of antioxidant enzymes, osmolytes and also trigger their interactions with each other. However, research has been limited to only cross adaptations and signal transductions. Understanding the change and mechanism of H₂ S and NO mediated cell signaling will broaden our knowledge on the various biochemical changes that occur in plant cells related to different stresses. A clear understanding of these molecules in various environmental stresses would help to confer biotechnological applications to protect plants against abiotic stresses and to improve crop productivity.

Present knowledge and controversies, deficiencies, and misconceptions on nitric oxide synthesis, sensing, and signaling in plants

After 30 years of intensive work, nitric oxide (NO) has just started to be characterized as a relevant regulatory molecule on plant development and responses to stress. Its reactivity as a free radical determines its mode of action as an inducer of posttranslational modifications of key target proteins through cysteine S-nitrosylation and tyrosine nitration. Many of the NO-triggered regulatory actions are exerted in tight coordination with phytohormone signaling. This review not only summarizes and updates the information accumulated on how NO is synthesized, sensed, and transduced in plants but also makes emphasis on controversies, deficiencies, and misconceptions that are hampering our present knowledge on the biology of NO in plants. The development of noninvasive accurate tools for the endogenous NO quantitation as well as the implementation of genetic approaches that overcome misleading pharmacological experiments will be critical for getting significant advances in better knowledge of NO homeostasis and regulatory actions in plants.

Visible light-controlled NO generation for photoreceptor-mediated plant root growth regulation

Nitric oxide (NO) is an essential redox-signaling molecule free radical, contributes a significant role in a diverse range of physiological processes. Photo-triggered NO donors have significant potential compared to other NO donors because it releases NO in the presence of light. Hence, an efficient visible light-triggered NO donor is designed and synthesized by coupling 2,6-dimethyl nitrobenzene moiety at the peri-position of 1, 8-naphthalimide. The NO-releasing ability is validated using various spectroscopic techniques, the photoproduct is characterized, and finally, the NO generation quantum yield is also determined. Furthermore, the photo-generated NO has been employed to Arabidopsis thaliana as a model plant to examine the effect of photoreceptor-mediated NO uptake on plant root growth regulation molecule.

Melatonin facilitates lateral root development by coordinating PAO-derived hydrogen peroxide and Rboh-derived superoxide radical

Melatonin, a phytochemical, can regulate lateral root (LR) formation, but the downstream signaling of melatonin remains elusive. Here we investigated the roles of hydrogen peroxide (H2O2) and superoxide radical (O2•‾) in melatonin-promoted LR formation in tomato (Solanum lycopersicum) roots by using physiological, histochemical, bioinformatic, and biochemical approaches. The increase in endogenous melatonin level stimulated reactive oxygen species (ROS)-dependent development of lateral root primordia (LRP) and LR. Melatonin promoted LRP/LR formation and modulated the expression of cell cycle genes (SlCDKA1, SlCYCD3;1, and SlKRP2) by stimulating polyamine oxidase (PAO)-dependent H2O2 production and respiratory burst oxidase homologue (Rboh)-dependent O2•‾ production, respectively. Screening of SlPAOs and SlRbohs gene family combined with gene expression analysis suggested that melatonin-promoted LR formation was correlated to the upregulation of SlPAO1, SlRboh3, and SlRboh4 in LR-emerging zone. Transient expression analysis confirmed that SlPAO1 was able to produce H2O2 while SlRboh3 and SlRboh4 were capable of producing O2•‾. Melatonin-ROS signaling cassette was also found in the regulation of LR formation in rice root and lateral hyphal branching in fungi. These results suggested that SlPAO1-H2O2 and SlRboh3/4-O2•‾ acted as downstream of melatonin to regulate the expression of cell cycle genes, resulting in LRP initiation and LR development. Such findings uncover one of the regulatory pathways for melatonin-regulated LR formation, which extends our knowledge for melatonin-regulated plant intrinsic physiology.

Nitric oxide and hydrogen sulfide in plants: which comes first?

Nitric oxide (NO) is a signal molecule regarded as being involved in myriad functions in plants under physiological, pathogenic, and adverse environmental conditions. Hydrogen sulfide (H2S) has also recently been recognized as a new gasotransmitter with a diverse range of functions similar to those of NO. Depending on their respective concentrations, both these molecules act synergistically or antagonistically as signals or damage promoters in plants. Nevertheless, available evidence shows that the complex biological connections between NO and H2S involve multiple pathways and depend on the plant organ and species, as well as on experimental conditions. Cysteine-based redox switches are prone to reversible modification; proteomic and biochemical analyses have demonstrated that certain target proteins undergo post-translational modifications such as S-nitrosation, caused by NO, and persulfidation, caused by H2S, both of which affect functionality. This review provides a comprehensive update on NO and H2S in physiological processes (seed germination, root development, stomatal movement, leaf senescence, and fruit ripening) and under adverse environmental conditions. Existing data suggest that H2S acts upstream or downstream of the NO signaling cascade, depending on processes such as stomatal closure or in response to abiotic stress, respectively.

Nitric oxide accelerates germination via the regulation of respiration in chickpea

Seed germination is crucial for the plant life cycle. We investigated the role of nitric oxide (NO) in two chickpea varieties that differ in germination capacity: Kabuli, which has a low rate of germination and germinates slowly, and Desi, which shows improved germination properties. Desi produced more NO than Kabuli and had lower respiratory rates. As a result of the high respiration rates, Kabuli had higher levels of reactive oxygen species (ROS). Treatment with the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP) reduced respiration in Kabuli and decreased ROS levels, resulting in accelerated germination rates. These findings suggest that NO plays a key role in the germination of Kabuli. SNAP increased the levels of transcripts encoding enzymes involved in carbohydrate metabolism and the cell cycle. Moreover, the levels of amino acids and organic acids were increased in Kabuli as a result of SNAP treatment. 1H-nuclear magnetic resonance analysis revealed that Kabuli has a higher capacity for glucose oxidation than Desi. An observed SNAP-induced increase in 13C incorporation into soluble alanine may result from enhanced oxidation of exogenous [13C]glucose via glycolysis and the pentose phosphate pathway. A homozygous hybrid that originated from a recombinant inbred line population of a cross between Desi and Kabuli germinated faster and had increased NO levels and a reduced accumulation of ROS compared with Kabuli. Taken together, these findings demonstrate the importance of NO in chickpea germination via the control of respiration and ROS accumulation.

Nitric oxide and plant mineral nutrition: current knowledge

Plants under conditions of essential mineral deficiency trigger signaling mechanisms that involve common components. Among these components, nitric oxide (NO) has been identified as a key participant in responses to changes in nutrient availability. Usually, nutrient imbalances affect the levels of NO in specific plant tissues, via modification of its rate of synthesis or degradation. Changes in the level of NO affect plant morphology and/or trigger responses associated with nutrient homeostasis, mediated by its interaction with reactive oxygen species, phytohormones, and through post-translational modification of proteins. NO-related events constitute an exciting field of research to understand how plants adapt and respond to conditions of nutrient shortage. This review summarizes the current knowledge on NO as a component of the multiple processes related to plant performance under conditions of deficiency in mineral nutrients, focusing on macronutrients such as nitrogen, phosphate, potassium, and magnesium, as well as micronutrients such as iron and zinc.

Nitric oxide alters nitrogen metabolism and PIN gene expressions by playing protective role in arsenic challenged Brassica juncea L

Plants have ability to adapt themselves through altering their growth process. In the present study, we examined exogenous application of nitric oxide (NO) on nitrogen metabolism and auxin (PIN) gene expression, and its possible role in alleviation of arsenic (As) toxicity in Brassica juncea seedlings. Seven days old hydroponically grown B. juncea seedlings were exposed to As^III (150 μM), Sodium nitroprusside (NO donor, 100 μM), As^III + SNP and control (without metal)for 48 h. Experimental results revealed that As^III stress: enhanced the level of nitrite, NiR activity, NO₃^- and NH₄⁺content as well as NADH-GOGAT activity; but GDH level decreased; enhanced content of amino acids; upregulated gene expression level of N metabolism and downregulated polar auxin transporter genes (PIN); inhibited plant growth and morphological parameters; increased MDA, H₂O_2, cysteine, proline content, enzymatic antioxidants (SOD, CAT, APX; GSH, TT, NPT); and decreased nutrient content. As^III + SNP combination reduced the accumulation of As; improved growth; chlorophyll, protein and mineral nutrient content by scavenging ROS generation; maintained amino acids content; downregulated expression of N metabolism genes and upregulated expression of auxin transporter (PIN) genes . Additional biochemical data depicts reduction in the level of nitrogen related enzymatic activities, and other stress related parameters. Overall, this study provides an integrated view that exogenous SNP (NO donor) supplementation alleviated the inhibitory role of As^III in B. juncea seedlings by altering nutrients, amino acids and auxin redistribution via expression of nitrogen and PIN gene profiling.

Hydrogen peroxide is involved in methane-induced tomato lateral root formation

Pharmacological and molecular evidence reveals a novel role of methane (CH₄) gas in root organogenesis, the induction of lateral root (LR) formation, and this response might require hydrogen peroxide (H₂O₂) synthesis. Although plants can produce CH₄ and release this to atmosphere, the beneficial role(s) of CH₄ are not fully elucidated. In this study, the fumigation with CH₄ not only increased NADPH oxidase activity and H₂O₂ production, but also induced tomato lateral root primordial formation and thereafter LR development. However, exogenously applied argon and nitrogen failed to influence LR formation. Above responses triggered by CH₄ were sensitive to the removal of endogenous H₂O₂ with dimethylthiourea (DMTU; a membrane-permeable scavenger of H₂O₂), suggesting the hypothesis that CH₄'s effect on LR formation could be mediated by endogenous H₂O₂. Diphenylene iodonium (DPI) inhibition of the H₂O₂ generating enzyme NADPH oxidase attenuated H₂O₂ synthesis and impaired LR formation in response to CH₄, confirming the requirement of NADPH oxidase-dependent H₂O₂. Meanwhile, the alterations of endogenous H₂O₂ concentrations failed to influence CH₄ production in tomato seedlings. Molecular evidence revealed that CH₄-induced SlCDKA1, SlCYCA2;1, and SlCYCA3;1 transcripts, and -decreased SlKRP2 mRNA were impaired by DMTU or DPI. Contrasting changes in LR formation-related miR390a and miR160 transcripts and their target genes, including SlARF4 and SlARF16, were observed. Together, our pharmacological and molecular evidence suggested the requirement of H₂O₂ synthesis in CH₄-triggered tomato LR formation, partially via the regulation of cell cycle regulatory genes, miRNA-, and tasiRNA-modulated gene expression.

Strigolactone-nitric oxide interplay in plants: The story has just begun

Both strigolactones (SLs) and nitric oxide (NO) are regulatory signals with diverse roles during plant development and stress responses. This review aims to discuss the so far available data regarding SLs-NO interplay in plant systems. The majority of the few articles dealing with SL-NO interplay focuses on the root system and it seems that NO can be an upstream negative regulator of SL biosynthesis or an upstream positive regulator of SL signaling depending on the nutrient supply. From the so far published results it is clear that NO modifies the activity of target proteins involved in SL biosynthesis or signaling which may be a physiologically relevant interaction. Therefore, in silico analysis of NO-dependent posttranslational modifications in SL-related proteins was performed using computational prediction tools and putative NO-target proteins were specified. The picture is presumably more complicated, since also SL is able to modify NO levels. As a confirmation, author detected NO levels in different organs of max1-1 and max2-1 Arabidopsis and compared to the wild-type these mutants showed enhanced NO levels in their root tips indicating the negative effect of endogenous SLs on NO metabolism. Exogenous SL analogue-triggered NO production seems to contradict the results of the genetic study, which is an inconsistency should be taken into consideration in the future. In the coming years, the link between SL and NO signaling in further physiological processes should be examined and the possibilities of NO-dependent posttranslational modifications of SL biosynthetic and signaling proteins should be looked more closely.

A novel function of N-signaling in plants with special reference to Trichoderma interaction influencing plant growth, nitrogen use efficiency, and cross talk with plant hormones

Trichoderma spp. is considered as a plant growth promoter and biocontrol fungal agents. They colonize on the surface of root in most of the agriculture crops. They secrete different secondary metabolites and enzymes which promote different physiological processes as well as protect plants from various environmental stresses. This is part of their vital functions. They are widely exploited as a biocontrol agent and plant growth promoter in agricultural fields. Colonization of Trichoderma with roots can enhance nutrient acquisition from surrounding soil to root and can substantially increase nitrogen use efficiency (NUE) in crops and linked with activation of plant signaling cascade. Among Trichoderma species, only some Trichoderma species were well characterized which help in the uptake of nitrogen-containing compound (especially nitrate form) and induced nitric oxide (NO) in plants. Both nitrate and NO are known as a signaling agent, involved in plant growth and development and disease resistance. Activation of these signaling molecules may crosstalk with other signaling molecule (Ca²⁺) and phytohormone (auxin, gibberellins, cytokinin and ethylene). This ability of Trichoderma is important to agriculture not only for increased plant growth but also to control plant diseases. Recently, Trichoderma strains have been shown to encompass the ability to regulate transcripts level of high-affinity nitrate transporters and probably it was positively regulated by NO. This review aims to focus the usage of Trichoderma strains on crops by their abilities to regulate transcript levels, probably through activation of plant N signaling transduction that improve plant health.

Visible light-triggered NO generation from Naphthalimide-based probe for photoreceptor-mediated plant root growth regulation.. [DOI: 10.1101/550004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

An efficient visible light-triggered nitric oxide (NO) releasing fluorescent molecule is designed and synthesized by coupling 2,6-dimethyl nitrobenzene moiety at the peri-position of 1, 8-naphthalimide through an alkene bond. The NO-releasing ability is investigated in details using various spectroscopic techniques, and the photoproduct was also characterized. Further, the photo-generated NO has been employed to examine the effect of photoreceptor-mediated NO uptake on plant root growth regulation.