Jasmonates, Ethylene and Brassinosteroids Control Adventitious and Lateral Rooting as Stress Avoidance Responses to Heavy Metals and Metalloids

Regulatory Mechanisms of Phytohormones in Thiocyanate-Exposed Rice Plants: Integrating Multi-Omics Profiling with Mathematical Modeling

Plants experience various abiotic stresses, among which pollutant stress is one of the most damaging, threatening plant productivity and survival. Thiocyanate (SCN-), a recalcitrant byproduct of industrial processes, poses escalating threats to agroecosystems by disrupting plant hormonal homeostasis, which is critical for stress adaptation. Here, we dissect the regulatory interplay of phytohormones in rice (Oryza sativa L.) under SCN- stress (4.80-124.0 mg SCN/L) through integrated transcriptomic and metabolomic profiling. Quantitative hormonal assays revealed dose- and tissue-specific perturbations in phytohormone homeostasis, with shoots exhibiting higher sensitivity than roots. Transcriptomic analysis revealed that a number of differentially expressed genes (DEGs) mapped in different phytohormone pathways in SCN--treated rice seedlings, and their transcript abundances are tissue-specific. To identify the phytohormones governing rice's sensitivity to SCN- stress, we developed a Total Hormonal Sensitivity Index (THSI) through an integrative multivariate framework, which combines Modified Variable Importance in Projection (VIP(m)) scores to quantify hormonal fluctuations and Total Weighted Contribution Scores (TWCS) at the gene-level from hormonal pathways. This study establishes a system-level understanding of how phytohormonal crosstalk mediates rice's adaptation to SCN- stress, providing biomarkers for phytoremediation strategies in contaminated paddies.

Phytohormone and Amino Acid Changes in Cherry Radish as Metabolic Adaptive Response to Arsenic Single and Multi-Contamination

This study investigated the metabolic adaptive responses to As contamination and As co-contamination with cadmium, lead, and zinc in the leaves and tubers of cherry radish (Raphanus sativus var. sativus Pers.). The response was assessed by measuring malondialdehyde levels, total phenolic content (TPC), total anthocyanin pigment (TAC), growth and stress phytohormone concentration, and free amino acid content. The characteristic As accumulation of single contamination resulted in a decrease in tuber growth. However, in the case of co-contamination, As uptake was influenced by the presence of other potentially toxic elements (PTEs), mainly zinc, with no significant effect on growth. Both contaminated treatments exhibited significant differences in metabolite levels among the organs, along with notable changes in their contents. Increases in malondialdehyde, TPC, and TAC indicated induced oxidative stress and an antioxidant response that was more pronounced by As co-contamination. Also, the results for phytohormones, which showed both increases and decreases, along with selected free amino acids (which showed increases), demonstrated a more significant influence of As co-contamination. Based on these findings, it can be concluded that the response of cherry radish to contaminated treatments exhibited significant differences in the studied parameters, along with variability in the results, reflecting the extent of the effects of PTEs that induce oxidative stress.

Brassinosteroids in Micronutrient Homeostasis: Mechanisms and Implications for Plant Nutrition and Stress Resilience

Brassinosteroids (BRs) are crucial plant hormones that play a significant role in regulating various physiological processes, including micronutrient homeostasis. This review delves into the complex roles of BRs in the uptake, distribution, and utilization of essential micronutrients such as iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), and boron (B). BRs influence the expression of key transporter genes responsible for the absorption and internal distribution of these micronutrients. For iron, BRs enhance the expression of genes related to iron reduction and transport, improve root architecture, and strengthen stress tolerance mechanisms. Regarding zinc, BRs regulate the expression of zinc transporters and support root development, thereby optimizing zinc uptake. Manganese homeostasis is managed through the BR-mediated regulation of manganese transporter genes and chlorophyll production, essential for photosynthesis. For copper, BRs influence the expression of copper transporters and maintain copper-dependent enzyme activities crucial for metabolic functions. Finally, BRs contribute to boron homeostasis by regulating its metabolism, which is vital for cell wall integrity and overall plant development. This review synthesizes recent findings on the mechanistic pathways through which BRs affect micronutrient homeostasis and discusses their implications for enhancing plant nutrition and stress resilience. Understanding these interactions offers valuable insights into strategies for improving micronutrient efficiency in crops, which is essential for sustainable agriculture. This comprehensive analysis highlights the significance of BRs in micronutrient management and provides a framework for future research aimed at optimizing nutrient use and boosting plant productivity.

Toxicity of copper oxide nanoparticles in barley: induction of oxidative stress, hormonal imbalance, and systemic resistances

BACKGROUND

Over the years, nanoparticles have emerged as a promising approach for improving crop growth, yield, and overall agricultural sustainability. However, there has been growing concern about the potential adverse effects of nanoparticles in the agricultural sector and the environment. The present study aimed to investigate the detrimental effects of high (1000 mg L-1) concentrations of copper oxide nanoparticles (CuO NPs) on barley seedlings. The equivalent concentrations of CuO bulk and the ionic form of copper were also used in the experiments for comparative analysis. CuO NPs were characterized by Field Emission-Scanning Electron Microscopy, Dynamic Light Scattering, Zeta Potential analysis, and X-ray Diffraction prior to the application. Barley seedlings were subjected to the foliar application of CuO NP, CuO bulk, ionic Cu, and control group. The presence of CuO NPs in barley leaves was confirmed 72 hours after treatment by energy-dispersive X-ray analysis.

RESULTS

The results showed a CuO NPs treatment led to an impairment of nutrient balance in barley leaves. An increase in hydrogen peroxide content followed by the higher specific activity of catalase and ascorbate peroxidase was also observed in response to CuO NPs, CuO bulk, and Cu2+ ions. The profile of phytohormones including auxins (IAA and IBA), Gibberellins (GA1, GA4, and GA9), abscisic acid (ABA), ethylene (ET), and jasmonic acid (JA) significantly affected by CuO NPs, CuO bulk, and Cu2+ ions. The transcripts of the PR1 gene involved in systemic acquired resistance (SAR) and LOX-1 and PAL involved in induced systemic resistance (ISR) were significantly upregulated in response to CuO NPs treatment.

CONCLUSION

Our findings suggest that the systemic resistances in barley seedlings were induced by higher accumulation of ABA, ET, and JA under CuO NPs treatment. The activation of systemic resistances indicated the involvement of both SAR and SAR pathways in the response to CuO NPs in barley.

Methyl jasmonate induced tolerance effect of Pinus koraiensis to Bursaphelenchus xylophilus

BACKGROUND

Methyl jasmonate (MeJA) can affect the balance of hormones and regulate the disease resistance of plants. Exploring the application and mechanism of MeJA in inducing the tolerance of Pinus koraiensis to pine wood nematode (PWN) infection is of great significance for developing new strategies for pine wilt disease control.

RESULTS

Different concentrations (0.1, 1, 5 and 10 mm) of MeJA treatment groups showed differences in relative tolerance index and relative anti-nematode index of P. koraiensis seedlings to PWN infection. The treatment of 5 mm MeJA solution induced the best tolerance effect, followed by the 1 mm MeJA solution. Transcriptome analysis indicated that many plant defense-related genes upregulated after treatment with 1, 5 and 10 mm MeJA solutions. Among them, genes such as jasmonate ZIM domain-containing protein, phenylalanine ammonia-lyase and peroxidase also continuously upregulated after PWN infection. Metabolome analysis indicated that jasmonic acid (JA) was significantly increased at 7 days postinoculation with PWN, and after treatment with both 1 and 5 mm MeJA solutions. Integrated analysis of transcriptome and metabolome indicated that differences in JA accumulation might lead to ubiquitin-mediated proteolysis, and expression changes in trans-caffeic acid and trans-cinnamic acid-related genes, leading to the abundance differences of these two metabolisms and the formation of multiple lignin and glucosides.

CONCLUSIONS

MeJA treatment could activate the expression of defense-related genes that correlated with JA, regulate the abundance of defense-related secondary metabolites, and improve the tolerance of P. koraiensis seedlings to PWN infection. © 2024 Society of Chemical Industry.

Plastid dynamism integrates development and environment

In land plants plastid type differentiation occurs concomitantly with cellular differentiation and the transition from one type to another is under developmental and environmental control. Plastid dynamism is based on a bilateral communication between plastids and nucleus through anterograde and retrograde signaling. Signaling occurs through the interaction with specific phytohormones (abscisic acid, strigolactones, jasmonates, gibberellins, brassinosteroids, ethylene, salicylic acid, cytokinin and auxin). The review is focused on the modulation of plastid capabilities at both transcriptional and post-translational levels at the crossroad between development and stress, with a particular attention to the chloroplast, because the most studied plastid type. The role of plastid-encoded and nuclear-encoded proteins for plastid development and stress responses, and the changes of plastid fate through the activity of stromules and plastoglobules, are discussed. Examples of plastid dynamism in response to soil stress agents (salinity, lead, cadmium, arsenic, and chromium) are described. Albinism and root greening are described based on the modulation activities of auxin and cytokinin. The physiological and functional responses of the sensory epidermal and vascular plastids to abiotic and biotic stresses along with their specific roles in stress sensing are described together with their potential modulation of retrograde signaling pathways. Future research perspectives include an in-depth study of sensory plastids to explore their potential for establishing a transgenerational memory to stress. Suggestions about anterograde and retrograde pathways acting at interspecific level and on the lipids of plastoglobules as a novel class of plastid morphogenic agents are provided.

Transcriptomics combined with physiological analysis provided new insights into the Zn enrichment capacity and tolerance mechanism of Dendrobium denneanum Kerr

In this study, we investigated the tolerance and accumulation capacity of Dendrobium denneanum Kerr (D.denneanum) by analyzing the growth and physiological changes of D.denneanum under different levels of Zn treatments, and further transcriptome sequencing of D.denneanum leaves to screen and analyze the differentially expressed genes. The results showed that Zn400 treatment (400 mg·kg-1) promoted the growth of D.denneanum while both Zn800 (800 mg·kg-1) and Zn1600 treatment (1600 mg·kg-1) caused stress to D.denneanum. Under Zn800 treatment (800 mg·kg-1), the resistance contribution of physiological indexes was the most obvious: antioxidant system, photosynthetic pigment, osmoregulation, phytochelatins, and ASA-GSH cycle (Ascorbic acid-Glutathione cycle). D.denneanum leaves stored the most Zn, followed by stems and roots. The BCF(Bioconcentration Factor) of the D.denneanum for Zn were all more than 1.0 under different Zn treatments, with the largest BCF (1.73) for Zn400. The transcriptome revealed that there were 1500 differentially expressed genes between Zn800 treatment and group CK, of which 842 genes were up-regulated and 658 genes were down-regulated. The genes such as C4H, PAL, JAZ, MYC2, PP2A, GS, and GST were significantly induced under the Zn treatments. The differentially expressed genes were associated with phenylpropane biosynthesis, phytohormone signaling, and glutathione metabolism. There were three main pathways of response to Zn stress in Dendrobium: antioxidant action, compartmentalization, and cellular chelation. This study provides new insights into the response mechanisms of D.denneanum to Zn stress and helps to evaluate the phytoremediation potential of D.denneanum in Zn-contaminated soils.

Ethylene Modulates Rice Root Plasticity under Abiotic Stresses

Plants live in constantly changing environments that are often unfavorable or stressful. Root development strongly affects plant growth and productivity, and the developmental plasticity of roots helps plants to survive under abiotic stress conditions. This review summarizes the progress being made in understanding the regulation of the phtyohormone ethylene in rice root development in response to abiotic stresses, highlighting the complexity associated with the integration of ethylene synthesis and signaling in root development under adverse environments. Understanding the molecular mechanisms of ethylene in regulating root architecture and response to environmental signals can contribute to the genetic improvement of crop root systems, enhancing their adaptation to stressful environmental conditions.

Synergistic effect of silicon and arbuscular mycorrhizal fungi reduces cadmium accumulation by regulating hormonal transduction and lignin accumulation in maize

Cadmium (Cd) stress causes serious damage to plants, inducing various physiological and biochemical disruptions that lead to reduced plant biomass and compromised growth. The study investigated the combined effects of silicon (Si) and arbuscular mycorrhizal fungi (AMF) on mitigating Cd stress in plants, revealing promising results in enhancing plant tolerance to Cd toxicity. Under Cd stress, plant biomass was significantly reduced (-33% and -30% shoot and root dry weights) as compared to control. However, Si and AMF application ameliorated this effect, leading to increased shoot and root dry weights (+47% and +39%). Furthermore, Si and AMF demonstrated their potential in reducing the relative Cd content (-43% and -36% in shoot and root) in plants and positively influencing plant colonization (+648%), providing eco-friendly and sustainable strategies to combat Cd toxicity in contaminated soils. Additionally, the combined treatment in the Cd-stressed conditions resulted in notable increases in saccharide compounds and hormone levels in both leaf and root tissues, further enhancing the plant's resilience to Cd-induced stress. Si and AMF also played a vital role in positively regulating key lignin biosynthesis genes and altering lignin-related metabolites, shedding light on their potential to fortify plants against Cd stress. These findings underscore the significance of Si and AMF as promising tools in addressing Cd toxicity and enhancing plant performance in Cd-contaminated environments.

Silicon inhibits cadmium uptake by regulating the genes associated with the lignin biosynthetic pathway and plant hormone signal transduction in maize plants

Cadmium (Cd) contamination in soil poses a severe threat to plant growth and development. In contrast, silicon (Si) has shown promise in enhancing plant resilience under Cd-induced stress. In this study, we conducted an integrated investigation employing morphological studies, gene expression analysis, and metabolomics to unravel the molecular mechanisms underlying Cd tolerance in maize plants. Our results demonstrate that Si biofortification significantly mitigated Cd stress by reducing Cd accumulation in plant tissues, increasing Si content, and enhancing maize biomass in Cd-stressed plants resulted in a substantial enhancement in shoot dry weight (+ 75%) and root dry weight (+ 30%). Notably, Si treatment upregulated key lignin-related genes (TaPAL, TaCAD, Ta4CL, and TaCOMT) and promoted the accumulation of metabolites (sinapyl alcohol, phenylalanine, p-coumaryl alcohol, cafeyl alcohol, and coniferaldehyde) essential for cell wall strength, particularly under Cd stress conditions. Si application enriched the signal transduction by hormones and increased resistance by induction of biosynthesis genes (TaBZR1, TaLOX3, and TaNCDE1) and metabolites (brassinolide, abscisic acid, and jasmonate) in the roots and leaves under Cd stress. Furthermore, our study provides a comprehensive view of the intricate molecular crosstalk between Si, Cd stress, and plant hormonal responses. We unveil a network of genetic and metabolic interactions that culminate in a multifaceted defense system, enabling maize plants to thrive even in the presence of Cd-contaminated soil. This knowledge not only advances our understanding of the protective role of Si but also highlights the broader implications for sustainable agricultural practices. By harnessing the insights gained from this research, we may pave the way for innovative strategies to fortify crops against environmental stressors, ultimately contributing to the goal of food security in an ever-changing world. In summary, our research offers valuable insights into the protective mechanisms facilitated by Si, which enhance plants' ability to withstand environmental stress, and holds promise for future applications in sustainable agriculture.

24-Epibrassinolide Facilitates Adventitious Root Formation by Coordinating Cell-Wall Polyamine Oxidase- and Plasma Membrane Respiratory Burst Oxidase Homologue-Derived Reactive Oxygen Species in Capsicum annuum L

Adventitious root (AR) formation is a critical process in cutting propagation of horticultural plants. Brassinosteroids (BRs) have been shown to regulate AR formation in several plant species; however, little is known about their exact effects on pepper AR formation, and the downstream signaling of BRs also remains elusive. In this study, we showed that treatment of 24-Epibrassinolide (EBL, an active BR) at the concentrations of 20-100 nM promoted AR formation in pepper (Capsicum annuum). Furthermore, we investigated the roles of apoplastic reactive oxygen species (ROS), including hydrogen peroxide (H₂O₂) and superoxide radical (O₂^•-), in EBL-promoted AR formation, by using physiological, histochemical, bioinformatic, and biochemical approaches. EBL promoted AR formation by modulating cell-wall-located polyamine oxidase (PAO)-dependent H₂O₂ production and respiratory burst oxidase homologue (RBOH)-dependent O₂^•- production, respectively. Screening of CaPAO and CaRBOH gene families combined with gene expression analysis suggested that EBL-promoted AR formation correlated with the upregulation of CaPAO1, CaRBOH2, CaRBOH5, and CaRBOH6 in the AR zone. Transient expression analysis confirmed that CaPAO1 was able to produce H₂O₂, and CaRBOH2, CaRBOH5, and CaRBOH6 were capable of producing O₂^•-. The silencing of CaPAO1, CaRBOH2, CaRBOH5, and CaRBOH6 in pepper decreased the ROS accumulation and abolished the EBL-induced AR formation. Overall, these results uncover one of the regulatory pathways for BR-regulated AR formation, and extend our knowledge of the functions of BRs and of the BRs-ROS crosstalk in plant development.

Transcriptome analysis reveals that auxin promotes strigolactone-induced adventitious root growth in the hypocotyl of melon seedlings

Introduction

Strigolactone (SL) and auxin are two important phytohormones involved in plant root development, but whether they show synergistic or mutual promotion effects during adventitious root (AR) formation has not been adequately explored.

Methods

In this study, we investigated the mechanisms of GR24 (synthetic SL) and indole-3-acetic acid (IAA; a type of auxin) in the formation of ARs using melon as the study material.

Results

Morphological measurements showed that the AR number, length, superficial area, and volume under the GR24 treatment were 1.60-3.27, 1.58-3.99, 2.06-3.42, and 3.00-6.11 times greater than those of the control group, respectively, at 6-10 days; the GR24+IAA treatment further promoted AR formation in melon seedlings, and the AR number, length, superficial area, and volume under the GR24+IAA treatment were 1.44-1.51, 1.28-1.73, 1.19-1.83, and 1.31-1.87 times greater than those obtained with the GR24 treatment, respectively. Transcriptome analysis revealed 2,742, 3,352, and 2,321 differentially expressed genes (DEGs) identified from the GR24 vs. control, GR24+IAA vs. control, and GR24+IAA vs. GR24 comparisons, respectively. The GR24 treatment and GR24+IAA treatment affected auxin and SL synthesis as well as components of the phytohormone signal transduction pathway, such as auxin, brassinosteroid (BR), ethylene (ETH), cytokinin (CK), gibberellin (GA), and abscisic acid (ABA). The concentrations of auxin, GA, zeatin (ZT), and ABA were evaluated using high-performance liquid chromatography (HPLC). From 6 to 10 days, the auxin, GA, and ZT contents in the GR24 treatment group were increased by 11.48%-15.34%, 11.83%-19.50%, and 22.52%-66.17%, respectively, compared to the control group, and these features were increased by 22.00%-31.20%, 21.29%-25.75%, 51.76%-98.96%, respectively, in the GR24+IAA treatment group compared with the control group. Compared to that in the control, the ABA content decreased by 10.30%-11.83% in the GR24 treatment group and decreased by 18.78%-24.00% in the GR24+IAA treatment group at 6-10 days.

Discussion

Our study revealed an interaction between strigolactone and auxin in the induction of AR formation in melon seedlings by affecting the expression of genes related to plant hormone pathways and contents.

Effect of Foliar Spraying of Gibberellins and Brassinolide on Cadmium Accumulation in Rice

Cadmium (Cd) is one of the heavy metals that contaminate rice cultivation, and reducing Cd contamination in rice through agronomic measures is a hot research topic. In this study, foliar sprays of gibberellins (GA) and brassinolide (BR) were applied to rice under Cd stress in hydroponic and pot experiments. After foliar spraying of GR and BR, the biomass of rice plants grown in either hydroponics or soil culture was significantly higher or even exceeded that in the absence of Cd stress. In addition, photosynthetic parameters (maximum fluorescence values), root length and root surface area, and CAT, SOD and POD activities were significantly improved. The MDA content decreased in the shoots, suggesting that the application of GR and BA may have enhanced photosynthesis and antioxidant function to alleviate Cd stress. Furthermore, the BR and GA treatments decreased the Cd content of rice roots, shoots and grains as well as the Cd transfer coefficient. Cd chemical morphology analysis of rice roots and shoots showed that the proportion of soluble Cd (Ethanol-Cd and Water-Cd) decreased, whereas the proportion of NaCl-Cd increased. Analysis of the subcellular distribution of Cd in rice roots and above ground showed that the proportion of Cd in the cell wall increased after foliar spraying of GA and BR. The results indicate that after foliar application of GA and BR, more of the Cd in rice was transformed into immobile forms and was fixed in the cell wall, thus reducing the amount in the seeds. In summary, foliar sprays of GA and BR can reduce the toxic effects of Cd on rice plants and reduce the Cd content in rice grains, with GA being more effective.

Transcriptome modulation by endophyte drives rice seedlings response to Pb stress

This study investigated the growth, SPAD value, chlorophyll fluorescence and transcriptome response of endophyte uninoculated and inoculated rice seedlings under Pb stress after treatment of 1 d and 5 d. Inoculation of endophytes significantly improved the plant height, SPAD value, F_v/F_0, F_v/F_m and PI_ABS by 1.29, 1.73, 0.16, 1.25 and 1.90 times on the 1 d, by 1.07, 2.45, 0.11, 1.59 and 7.90 times on the 5 d, respectively, however, decreased the root length by 1.11 and 1.65 times on the 1 d and 5 d, respectively under Pb stress. Analysis of rice seedlings leaves by RNA-seq, there were 574 down-regulated and 918 up-regulated genes after treatment of 1 d, 205 down-regulated and 127 up-regulated genes after treatment of 5 d, of which 20 genes (11 up-regulated and 9 down-regulated) exhibited the same changing pattern after treatment of 1 d and 5 d. Using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) to annotate these DEGs, and it was found that many of DEGs involved in photosynthesis, oxidative detoxification, hormone synthesis and signal transduction, protein phosphorylation/kinase and transcription factors. These findings provide new insights into the molecular mechanism of interaction between endophyte and plants under heavy metal stress, and contribute to agricultural production in limited environments.

Early lateral root formation in response to calcium and nickel shows variation within disjunct populations of Arabidopsis lyrata spp. lyrata

Root architecture is important in nutrient uptake and avoidance of toxic compounds within the soil. Arabidopsis lyrata spp. lyrata has widespread distribution in disjunct environments that encounter unique stressors starting at germination. Five populations of A. lyrata spp. lyrata show local adaptation to Nickel (Ni) but cross-tolerance to variations in Calcium (Ca) concentration within the soil. Differentiation among the populations begins early in development and appears to impact timing of lateral root formation; therefore the purpose of the study was to understand changes in root architecture and root exploration in response to Ca and Ni within the first three weeks of growth. Lateral root formation was first characterized under one concentration of Ca and Ni. Lateral root formation and tap root length were reduced in all five populations in response to Ni compared to Ca, with the least reduction in the three serpentine populations. When the populations were exposed to a gradient (either Ca or Ni) there were differences in population response based on the nature of the gradient. Start side was the greatest determinant of root exploration and lateral root formation under a Ca gradient, while population was the greatest determinant of root exploration and lateral root formation under a Ni gradient. All populations exhibited about the same frequency of root exploration under a Ca gradient, while the serpentine populations exhibited much higher levels of root exploration under a Ni gradient compared to the two non-serpentine populations. Differences among populations in response to Ca and Ni demonstrate the importance of stress responses early in development, particularly in species that have widespread distribution among disparate habitats.

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.

24-epibrassinolide improves cadmium tolerance and lateral root growth associated with regulating endogenous auxin and ethylene in Kentucky bluegrass

The application of phytohormones is a viable technique to increase the efficiency of phytoremediation in heavy metal-contaminated soils. The objective of this study was to determine how the application of 24-epibrassinolide (EBR), a brassinosteroid analog, could regulate root growth and tolerance to cadmium (Cd) stress in Kentucky bluegrass. As a result, the number of lateral root primordia and total root length in the Cd-treated seedlings decreased by 33.1 % and 56.5 %, respectively. After the application of EBR, Cd accumulation in roots and leaves, and the negative effect of Cd on root growth were reduced under Cd stress. Additionally, the expression of the brassinosteroid signaling gene PpBRI1 was significantly upregulated by exogenous EBR. Moreover, exogenous EBR upregulated the expression of genes encoding antioxidant enzymes and improved the activity of antioxidant enzymes, thereby reduced oxidative stress in roots. Finally, targeted hormonomics analysis highlighted the utility of the application of EBR to alleviate the effect of Cd on the reduction in auxin (IAA) content and the increase in ethylene (ACC) content. These were known to be associated with the upregulation in the expression of auxin biosynthesis gene PpYUCCA1 and downregulation in the expression of ethylene biosynthesis gene PpACO1 in the roots treated with Cd stress. Overall, the application of EBR alleviated Cd-induced oxidative stress in addition to improving root elongation and lateral root growth crosstalk with auxin and ethylene in Kentucky bluegrass subjected to Cd stress. This study further highlights the potential role of brassinosteroids in improving the efficiency of phytoremediation for Cd-contaminated soils.

Convergence between Development and Stress: Ectopic Xylem Formation in Arabidopsis Hypocotyl in Response to 24-Epibrassinolide and Cadmium

Ectopic xylary element (EXE) formation in planta is a poorly investigated process, and it is unknown if it occurs as a response to the soil pollutant Cadmium (Cd). The pericycle cells of Arabidopsis thaliana hypocotyl give rise to EXEs under specific hormonal inputs. Cadmium triggers pericycle responses, but its role in EXE formation is unknown. Brassinosteroids (BRs) affect numerous developmental events, including xylogenesis in vitro, and their exogenous application by 24-epibrassinolide (eBL) helps to alleviate Cd-stress by increasing lateral/adventitious rooting. Epibrassinolide's effects on EXEs in planta are unknown, as well as its relationship with Cd in the control of the process. The research aims to establish an eBL role in pericycle EXE formation, a Cd role in the same process, and the possible interaction between the two. Results show that 1 nM eBL causes an identity reversal between the metaxylem and protoxylem within the stele, and its combination with Cd reduces the event. All eBL concentrations increase EXEs, also affecting xylary identity by changing from protoxylem to metaxylem in a concentration-dependent manner. Cadmium does not affect EXE identity but increases EXEs when combined with eBL. The results suggest that eBL produces EXEs to form a mechanical barrier against the pollutant.

Arsenic as hazardous pollutant: Perspectives on engineering remediation tools

Arsenic (As) is highly toxic metal (loid) that impairs plant growth and proves fatal towards human population. It disrupts physiological, biochemical and molecular attributes of plants associated with water/nutrient uptake, redox homeostasis, photosynthetic machineries, cell/membrane damage, and ATP synthesis. Numerous transcription factors are responsive towards As through regulating stress signaling, toxicity and resistance. Additionally, characterization of specific genes encoding uptake, translocation, detoxification and sequestration has also explained their underlying mechanisms. Arsenic within soil enters the food chain and cause As-poisoning. Plethora of conventional methods has been used since decades to plummet As-toxicity, but the success rate is quite low due to environmental hazards. Henceforth, exploration of effective and eco-friendly methods is aimed for As-remediation. With the technological advancements, we have enumerated novel strategies to address this concern for practicing such techniques on global scale. Novel strategies such as bioremediation, phytoremediation, mycorrhizae-mediated remediation, biochar, algal-remediation etc. possess extraordinary results. Moreover, nitric oxide (NO), a signaling molecule has also been explored in relieving As-stress through reducing oxidative damages and triggering antioxidative responses. Other strategies such as role of plant hormones (salicylic acid, indole-3-acetic acid, jasmonic acid) and micro-nutrients such as selenium have also been elucidated in As-remediation from soil. This has been observed through stimulated antioxidant activities, gene expression of transporters, defense genes, cell-wall modifications along with the synthesis of chelating agents such as phytochelatins and metallothioneins. This review encompasses the updated information about As toxicity and its remediation through novel techniques that serve to be the hallmarks for stress revival. We have summarised the genetic engineering protocols, biotechnological as well as nanotechnological applications in plants to combat As-toxicity.

Chromium toxicity induced oxidative damage in two rice cultivars and its mitigation through external supplementation of brassinosteroids and spermine

The chromium (Cr) induced phytotoxicity avowed the scientific community to develop stress mitigation strategies to restrain the Cr accumulation inside the food chain. Whereas, brassinosteroids (BRs), and spermine (SPM) are well-known growth-promoting phytohormones, which enhance the plants health, and resilient the toxic effects under stress conditions. Until now, their interactive role against Cr-mitigation is poorly known. Hence, we conducted the hydroponic experiment to perceive the behavior of seed primed with BRs, or/and SPM treatment against Cr disclosure in two different rice cultivars (CY927; sensitive, YLY689; tolerant). Our findings delineated that BRs (0.01 μM), or/and SPM (0.01 mM) remarkably alleviated Cr-induced phytotoxicity by improving the seed germination ratio, chlorophyll pigments, PSII system, total soluble sugar, and minimizing the MDA contents level, ROS extra generation, and electrolyte leakage through restricting the Cr accretion in roots, and shoots of both rice cultivars under Cr stress. Additionally, the BRs, or/and SPM modulated the antioxidant enzyme, and non-enzyme activities to reduce the Cr-induced cellular oxidative damage as well as maintained the ionic hemostasis in both rice cultivars, especially in YLY689. Concisely, enhanced the plants biomass and growth. Overall, our outcomes revealed that BRs and SPM interact positively to alleviate the Cr-induced damages in rice seedlings on the above-mentioned indices, and combine treatment is much more efficient than solely. Moreover, the effect of BRs, or/and SPM was more obvious in YLY689 than CY927 to hamper the oxidative stress, and boost the antioxidant capacity.

Molecular insight into arsenic uptake, transport, phytotoxicity, and defense responses in plants: a critical review

A critical investigation into arsenic uptake and transportation, its phytotoxic effects, and defense strategies including complex signaling cascades and regulatory networks in plants. The metalloid arsenic (As) is a leading pollutant of soil and water. It easily finds its way into the food chain through plants, more precisely crops, a common diet source for humans resulting in serious health risks. Prolonged As exposure causes detrimental effects in plants and is diaphanously observed through numerous physiological, biochemical, and molecular attributes. Different inorganic and organic As species enter into the plant system via a variety of transporters e.g., phosphate transporters, aquaporins, etc. Therefore, plants tend to accumulate elevated levels of As which leads to severe phytotoxic damages including anomalies in biomolecules like protein, lipid, and DNA. To combat this, plants employ quite a few mitigation strategies such as efficient As efflux from the cell, iron plaque formation, regulation of As transporters, and intracellular chelation with an array of thiol-rich molecules such as phytochelatin, glutathione, and metallothionein followed by vacuolar compartmentalization of As through various vacuolar transporters. Moreover, the antioxidant machinery is also implicated to nullify the perilous outcomes of the metalloid. The stress ascribed by the metalloid also marks the commencement of multiple signaling cascades. This whole complicated system is indeed controlled by several transcription factors and microRNAs. This review aims to understand, in general, the plant-soil-arsenic interaction, effects of As in plants, As uptake mechanisms and its dynamics, and multifarious As detoxification mechanisms in plants. A major portion of this article is also devoted to understanding and deciphering the nexus between As stress-responsive mechanisms and its underlying complex interconnected regulatory networks.

Brassinosteroids Mitigate Cadmium Effects in Arabidopsis Root System without Any Cooperation with Nitric Oxide

The heavy metal cadmium (Cd) affects root system development and quiescent center (QC)-definition in Arabidopsis root-apices. The brassinosteroids-(BRs)-mediated tolerance to heavy metals has been reported to occur by a modulation of nitric oxide (NO) and root auxin-localization. However, how BRs counteract Cd-action in different root types is unknown. This research aimed to find correlations between BRs and NO in response to Cd in Arabidopsis’s root system, monitoring their effects on QC-definition and auxin localization in root-apices. To this aim, root system developmental changes induced by low levels of 24-epibrassinolide (eBL) or by the BR-biosynthesis inhibitor brassinazole (Brz), combined or not with CdSO₄, and/or with the NO-donor nitroprusside (SNP), were investigated using morpho-anatomical and NO-epifluorescence analyses, and monitoring auxin-localization by the DR5::GUS system. Results show that eBL, alone or combined with Cd, enhances lateral (LR) and adventitious (AR) root formation and counteracts QC-disruption and auxin-delocalization caused by Cd in primary root/LR/AR apices. Exogenous NO enhances LR and AR formation in Cd-presence, without synergism with eBL. The NO-signal is positively affected by eBL, but not in Cd-presence, and BR-biosynthesis inhibition does not change the low NO-signal caused by Cd. Collectively, results show that BRs ameliorate Cd-effects on all root types acting independently from NO.

PIN3-mediated auxin transport contributes to blue light-induced adventitious root formation in Arabidopsis

Adventitious rooting is a heritable quantitative trait that is influenced by multiple endogenous and exogenous factors in plants, and one important environmental factor required for efficient adventitious root formation is light signaling. However, the physiological significance and molecular mechanism of light underlying adventitious root formation are still largely unexplored. Here, we report that blue light-induced adventitious root formation is regulated by PIN-FORMED3 (PIN3)-mediated auxin transport in Arabidopsis. Adventitious root formation is significantly impaired in the loss-of-function mutants of the blue light receptors, PHOTOROPIN1 (PHOT1) and PHOTOROPIN2 (PHOT2), as well as the phototropic transducer, NON-PHOTOTROPIC HYPOCOTYL3 (NPH3). In addition, blue light enhanced the auxin content in the adventitious root, and the pin3 loss-of-function mutant had a reduced adventitious rooting response under blue light compared to the wild type. The PIN3 protein level was higher in plants treated with blue light than in those in darkness, especially in the hypocotyl pericycle, while PIN3-GFP failed to accumulate in nph3 PIN3::PIN3-GFP. Furthermore, the results showed that PIN3 physically interacted with NPH3, a key transducer in phototropic signaling. Taken together, our study demonstrates that blue light induces adventitious root formation through the phototropic signal transducer, NPH3, which regulates adventitious root formation by affecting PIN3-mediated auxin transport.

Nanoselenium transformation and inhibition of cadmium accumulation by regulating the lignin biosynthetic pathway and plant hormone signal transduction in pepper plants

Selenium (Se) can promote the growth and resistance of agricultural crops as fertilizers, while the role of nano-selenium (nano-Se) against Cd remains unclear in pepper plants (Capsicum annuum L.). Biofortification with nano-Se observably restored Cd stress by decreasing the level of Cd in plant tissues and boosting the accumulation in biomass. The Se compounds transformed by nano-Se were primarily in the form of SeMet and MeSeCys in pepper tissues. Differential metabolites and the genes of plant signal transduction and lignin biosynthesis were measured by employing transcriptomics and determining target metabolites. The number of lignin-related genes (PAL, CAD, 4CL, and COMT) and contents of metabolites (sinapyl alcohol, phenylalanine, p-coumaryl alcohol, caffeyl alcohol, and coniferaldehyde) were remarkably enhanced by treatment with Cd1Se0.2, thus, maintaining the integrity of cell walls in the roots. It also enhanced signal transduction by plant hormones and responsive resistance by inducing the biosynthesis of genes (BZR1, LOX3, and NCDE1) and metabolites (brassinolide, abscisic acid, and jasmonic acid) in the roots and leaves. In general, this study can enable a better understanding of the protective mechanism of nano-Se in improving the capacity of plants to resist environmental stress.

Peroxisomal PEX7 Receptor Affects Cadmium-Induced ROS and Auxin Homeostasis in Arabidopsis Root System

Peroxisomes are important in plant physiological functions and stress responses. Through the production of reactive oxygen and nitrogen species (ROS and RNS), and antioxidant defense enzymes, peroxisomes control cellular redox homeostasis. Peroxin (PEX) proteins, such as PEX7 and PEX5, recognize peroxisome targeting signals (PTS1/PTS2) important for transporting proteins from cytosol to peroxisomal matrix. pex7-1 mutant displays reduced PTS2 protein import and altered peroxisomal metabolism. In this research we analyzed the role of PEX7 in the Arabidopsis thaliana root system exposed to 30 or 60 μM CdSO₄. Cd uptake and translocation, indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) levels, and reactive oxygen species (ROS) and reactive nitrogen species (RNS) levels and catalase activity were analyzed in pex7-1 mutant primary and lateral roots in comparison with the wild type (wt). The peroxisomal defect due to PEX7 mutation did not reduce Cd-uptake but reduced its translocation to the shoot and the root cell peroxisomal signal detected by 8-(4-Nitrophenyl) Bodipy (N-BODIPY) probe. The trend of nitric oxide (NO) and peroxynitrite in pex7-1 roots, exposed/not exposed to Cd, was as in wt, with the higher Cd-concentration inducing higher levels of these RNS. By contrast, PEX7 mutation caused changes in Cd-induced hydrogen peroxide (H₂O₂) and superoxide anion (O₂^●-) levels in the roots, delaying ROS-scavenging. Results show that PEX7 is involved in counteracting Cd toxicity in Arabidopsis root system by controlling ROS metabolism and affecting auxin levels. These results add further information to the important role of peroxisomes in plant responses to Cd.

Role of miR164 in the growth of wheat new adventitious roots exposed to phenanthrene

Polycyclic aromatic hydrocarbons (PAHs), ubiquitous organic pollutants in the environment, can accumulate in humans via the food chain and then harm human health. MiRNAs (microRNAs), a kind of non-coding small RNAs with a length of 18-30 nucleotides, regulate plant growth and development and respond to environmental stress. In this study, it is demonstrated that miR164 can regulate root growth and adventitious root generation of wheat under phenanthrene exposure by targeting NAC (NAM/ATAF/CUC) transcription factor. We observed that phenanthrene treatment accelerated the senescence and death of wheat roots, and stimulated the occurrence of new roots. However, it is difficult to compensate for the loss caused by old root senescence and death, due to the slower growth of new roots under phenanthrene exposure. Phenanthrene accumulation in wheat roots caused to generate a lot of reactive oxygen species, and enhanced lipoxygenase activity and malonaldehyde concentration, meaning that lipid peroxidation is the main reason for root damage. MiR164 was up-regulated by phenanthrene, enhancing the silence of NAC1, weakening the association with auxin signal, and inhibiting the occurrence of adventitious roots. Phenanthrene also affected the expression of CDK (the coding gene of cyclin-dependent kinase) and CDC2 (a gene regulating cell division cycle), the key genes in the cell cycle of pericycle cells, thereby affecting the occurrence and growth of lateral roots. In addition, NAM (a gene regulating no apical meristem) and NAC23 may also be related to the root growth and development in wheat exposed to phenanthrene. These results provide not only theoretical basis for understanding the molecular mechanism of crop response to PAHs accumulation, but also knowledge support for improving phytoremediation of soil or water contaminated by PAHs.

An update on redox signals in plant responses to biotic and abiotic stress crosstalk: insights from cadmium and fungal pathogen interactions

Complex signalling pathways are involved in plant protection against single and combined stresses. Plants are able to coordinate genome-wide transcriptional reprogramming and display a unique programme of transcriptional responses to a combination of stresses that differs from the response to single stresses. However, a significant overlap between pathways and some defence genes in the form of shared and general stress-responsive genes appears to be commonly involved in responses to multiple biotic and abiotic stresses. Reactive oxygen and nitrogen species, as well as redox signals, are key molecules involved at the crossroads of the perception of different stress factors and the regulation of both specific and general plant responses to biotic and abiotic stresses. In this review, we focus on crosstalk between plant responses to biotic and abiotic stresses, in addition to possible plant protection against pathogens caused by previous abiotic stress. Bioinformatic analyses of transcriptome data from cadmium- and fungal pathogen-treated plants focusing on redox gene ontology categories were carried out to gain a better understanding of common plant responses to abiotic and biotic stresses. The role of reactive oxygen and nitrogen species in the complex network involved in plant responses to changes in their environment is also discussed.