Nitric oxide acts as an inducer of Strategy-I responses to increase Fe availability and mobilization in Fe-starved broccoli (Brassica oleracea var. oleracea).

Iron (Fe) deficiency causes reduced growth and yield in broccoli. This study elucidates how sodium nitroprusside (SNP), known as nitric oxide (NO) donor, mitigates the retardation caused by Fe deficiency in broccoli. The SNP caused substantial nitric oxide accumulation in the roots of Fe-deficient plants, which resulted in a significant improvement in chlorophyll levels, photosynthetic efficiency, and morphological growth parameters, showing that it has a favorable influence on recovering broccoli health. Ferric reductase activity and the expression of BoFRO1 (ferric chelate reductase) gene in roots were consistently increased by SNP under Fe deficiency, which likely resulted in increased Fe mobilization. Furthermore, proton (H+) extrusion and BoHA2 (H+-ATPase 2) expression were significantly increased, suggesting that they may be involved in lowering rhizospheric pH to restore Fe mobilization in roots of bicarbonate-treated broccoli plants. The levels of Fe in root and shoot tissues and the expression of BoIRT1 (Fe-regulated transporter) both increased dramatically after SNP supplementation under Fe deprivation. Furthermore, SNP-induced increase in citrate and malate concentrations suggested a role of NO in improved Fe chelation in Fe-deficient broccoli. A NO scavenger (cPTIO) ceased the elevated FCR activity and IAA (indole-3-acetic acid) concentration in Fe-starved plants treated with SNP. These findings suggest that SNP may play a role in initiating Fe availability by elevated IAA concentration and BoEIR1 (auxin efflux carrier) expression in the roots of broccoli during Fe shortage. Therefore, SNP may improve Fe availability and mobilization by increasing Strategy-I Fe uptake pathways, which may help broccoli tolerate Fe deficiency.

Regulation of Na+/H+ exchangers, Na+/K+ transporters, and lignin biosynthesis genes, along with lignin accumulation, sodium extrusion, and antioxidant defense, confers salt tolerance in alfalfa.

Accumulation of high sodium (Na+) leads to disruption of metabolic processes and decline in plant growth and productivity. Therefore, this study was undertaken to clarify how Na+/H+ exchangers and Na+/K+ transporter genes contribute to Na+ homeostasis and the substantial involvement of lignin biosynthesis genes in salt tolerance in alfalfa (Medicago sativa L.), which is poorly understood. In this study, high Na+ exhibited a substantial reduction of morphophysiological indices and induced oxidative stress indicators in Xingjiang Daye (XJD; sensitive genotype), while Zhongmu (ZM; tolerant genotype) remained unaffected. The higher accumulation of Na+ and the lower accumulation of K+ and K+/(Na+ + K+) ratio were found in roots and shoots of XJD compared with ZM under salt stress. The ZM genotype showed a high expression of SOS1 (salt overly sensitive 1), NHX1 (sodium/hydrogen exchanger 1), and HKT1 (high-affinity potassium transporter 1), which were involved in K+ accumulation and excess Na+ extrusion from the cells compared with XJD. The lignin accumulation was higher in the salt-adapted ZM genotype than the sensitive XJD genotype. Consequently, several lignin biosynthesis-related genes including 4CL2, CCoAOMT, COMT, CCR, C4H, PAL1, and PRX1 exhibited higher mRNA expression in salt-tolerant ZM compared with XJD. Moreover, antioxidant enzyme (catalase, superoxide dismutase, ascorbate peroxidase, and glutathione reductase) activity was higher in ZM relative to XJD. This result suggests that high antioxidant provided the defense against oxidative damages in ZM, whereas low enzyme activity with high Na+ triggered the oxidative damage in XJD. These findings together illustrate the ion exchanger, antiporter, and lignin biosysthetic genes involving mechanistic insights into differential salt tolerance in alfalfa.

Potassium in plant physiological adaptation to abiotic stresses.

Potassium (K) is an integral part of plant nutrition, playing essential roles in plant growth and development. Despite its abundance in soils, the limitedly available form of K ion (K+) for plant uptake is a critical factor for agricultural production. Plants have evolved complex transport systems to maintain appropriate K+ levels in tissues under changing environmental conditions. Adequate stimulation and coordinated actions of multiple K+-channels and K+-transporters are required for nutrient homeostasis, reproductive growth, cellular signaling and stress adaptation responses in plants. Various contemporary studies revealed that K+-homeostasis plays a substantial role in plant responses and tolerance to abiotic stresses. The beneficial effects of K+ in plant responses to abiotic stresses include its roles in physiological and biochemical mechanisms involved in photosynthesis, osmoprotection, stomatal regulation, water-nutrient absorption, nutrient translocation and enzyme activation. Over the last decade, we have seen considerable breakthroughs in K research, owing to the advances in omics technologies. In this aspect, omics investigations (e.g., transcriptomics, metabolomics, and proteomics) in systems biology manner have broadened our understanding of how K+ signals are perceived, conveyed, and integrated for improving plant physiological resilience to abiotic stresses. Here, we update on how K+-uptake and K+-distribution are regulated under various types of abiotic stress. We discuss the effects of K+ on several physiological functions and the interaction of K+ with other nutrients to improve plant potential against abiotic stress-induced adverse consequences. Understanding of how K+ orchestrates physiological mechanisms and contributes to abiotic stress tolerance in plants is essential for practicing sustainable agriculture amidst the climate crisis in global agriculture.

Mechanistic assessment of tolerance to iron deficiency mediated by Trichoderma harzianum in soybean roots.

AIMS: Iron (Fe) deficiency in soil is a continuing problem for soybean (Glycine max L.) production, partly as a result of continuing climate change. This study elucidates how Trichoderma harzianum strain T22 (TH) mitigates growth retardation associated with Fe-deficiency in a highly sensitive soybean cultivar. METHODS AND RESULTS: Soil TH supplementation led to mycelial colonization and the presence of UAOX1 gene in roots that caused substantial improvement in chlorophyll score, photosynthetic efficiency and morphological parameters, indicating a positive influence on soybean health. Although rhizosphere acidification was found to be a common feature of Fe-deficient soybean, the upregulation of Fe-reductase activity (GmFRO2) and total phenol secretion were two of the mechanisms that substantially increased the Fe availability by TH. Heat-killed TH applied to soil caused no improvement in photosynthetic attributes and Fe-reductase activity, confirming the active role of TH in mitigating Fe-deficiency. Consistent increases in tissue Fe content and increased Fe-transporter (GmIRT1, GmNRAMP2a, GmNRAMP2b and GmNRAMP7) mRNA levels in roots following TH supplementation were observed only under Fe-deprivation. Root cell death, electrolyte leakage, superoxide (O2 •- ) and hydrogen peroxide (H2 O2 ) substantially declined due to TH in Fe-deprived plants. Further, the elevation of citrate and malate concentration along with the expression of citrate synthase (GmCs) and malate synthase (GmMs) caused by TH suggest improved chelation of Fe in Fe-deficient plants. Results also suggest that TH has a role in triggering antioxidant defence by increasing the activity of glutathione reductase (GR) along with elevated S-metabolites (glutathione and methionine) to stabilize redox status under Fe-deficiency. CONCLUSIONS: TH increases the availability and mobilization of Fe by inducing Fe-uptake pathways, which appears to help provide resistance to oxidative stress associated with Fe-shortage in soybean. SIGNIFICANCE AND IMPACT OF THE STUDY: These findings indicate that while Fe deficiency does not affect the rate or degree of TH hyphal association in soybean roots, the beneficial effects of TH alone may be Fe deficiency-dependent.

Changes in physiological responses and MTP (metal tolerance protein) transcripts in soybean (Glycine max) exposed to differential iron availability.

Members of MTP (metal tolerance protein) family are potential metal ion transporters, but little is known about how their responses and expression are altered in response to the deficiency and excess of Fe in soybean. In this study, root and shoot length and biomass in addition to leaf chlorophyll score, PSII efficiency and photosynthetic performance index were adversely affected by Fe-deficiency and excess Fe. Fe and S concentrations in the root and shoot, as well as the increased root FCR activity, consistently decreased and increased, respectively, accompanied by elevated Zn levels under Fe deficiency and Fe toxicity. This implies that Fe-uptake of plants subjected to differential Fe availability are likely determined by S and Zn nutritional status. In qPCR analysis, GmMTP5, GmMTP7, GmMTP8, and GmMTP10 genes showed downregulation under Fe shortage, whereas GmMTP6 and GmMTP11 were significantly upregulated due to Fe-toxicity. Further, GmMTP1, GmMTP3, GmMTP6, GmMTP7, and GmMTP10 were significantly induced in response to Fe toxicity, indicating their potential role in metal tolerance. Bioinformatics analysis showed that soybean MTP genes possessed a close relationship with certain Arabidopsis genes (i.e. ZAT, MTPB1) involved in solute transport and metal sequestration. Furthermore, top five motifs of soybean MTP protein correspond to the cation efflux family exhibited strong amino acid and evolutionary similarities with Arabidopsisthaliana. These findings shed light on Fe homeostasis mechanisms in soybean and could be used to regulate Fe uptake through breeding or transgenic manipulations of MTP genes.

Nitric Oxide Prevents Fe Deficiency-Induced Photosynthetic Disturbance, and Oxidative Stress in Alfalfa by Regulating Fe Acquisition and Antioxidant Defense.

Iron (Fe) deficiency impairs photosynthetic efficiency, plant growth and biomass yield. This study aimed to reveal the role of nitric oxide (NO) in restoring Fe-homeostasis and oxidative status in Fe-deficient alfalfa. In alfalfa, a shortage of Fe negatively affected the efficiency of root andshoot length, leaf greenness, maximum quantum yield PSII (Fv/Fm), Fe, S, and Zn accumulation, as well as an increase in H2O2 accumulation. In contrast, in the presence of sodium nitroprusside (SNP), a NO donor, these negative effects of Fe deficiency were largely reversed. In response to the SNP, the expression of Fe transporters (IRT1, NRAMP1) and S transporter (SULTR1;2) genes increased in alfalfa. Additionally, the detection of NO generation using fluorescence microscope revealed that SNP treatment increased the level of NO signal, indicating that NO may act as regulatory signal in response to SNP in plants. Interestingly, the increase of antioxidant genes and their related enzymes (Fe-SOD, APX) in response to SNP treatment suggests that Fe-SOD and APX are key contributors to reducing ROS (H2O2) accumulation and oxidative stress in alfalfa. Furthermore, the elevation of Ascorbate-glutathione (AsA-GSH) pathway-related genes (GR and MDAR) Fe-deficiency with SNP implies that the presence of NO relates to enhanced antioxidant defense against Fe-deficiency stress.

Early-stage iron deficiency alters physiological processes and iron transporter expression, along with photosynthetic and oxidative damage to sorghum.

Iron (Fe) starvation in Strategy II plants is a major nutritional problem causing severe visual symptoms and yield reductions. This prompted us to investigate the physiological and molecular consequences of Fe deficiency responses at an early stage in sorghum plants. The Fe-starved sorghum did not show shoot biomass reduction, but the root length, biomass, and chlorophyll synthesis were severely affected. The chlorophyll a fluorescence analysis showed that the quantum yield efficiency of PSII (Fv/Fm) and photosynthesis performance index (Pi_ABS) in young leaves significantly reduced in response to low Fe. Besides, Fe concentration in root and shoot significantly declined in Fe-starved plants relative to Fe-sufficient plants. Accordingly, this Fe reduction in tissues was accompanied by a marked decrease in PS-release in roots. The qPCR experiment showed the downregulation of SbDMAS2 (deoxymugineic acid synthase 2), SbNAS3 (nicotianamine synthase 3), and SbYSL1 (Fe-phytosiderophore transporter yellow stripe 1) in Fe-deprived roots, suggesting that decreased rhizosphere mobilization of Fe(III)-PS contributes to reduced uptake and long-distance transport of Fe. The cis-acting elements of these gene promoters are commonly responsive to abscisic acid and methyl jasmonate, while SbYSL1 additionally responsive to salicylic acid. Further, antioxidant defense either through metabolites or antioxidant enzymes is not efficient in counteracting oxidative damage in Fe-deprived sorghum. These findings may be beneficial for the improvement of sorghum genotypes sensitive to Fe-deficiency through breeding or transgenic approaches.

Molecular characterization and bioinformatics analysis of transporter genes associated with Cd-induced phytotoxicity in rice (Oryza sativa L.).

Cadmium (Cd) adversely affects the yield and quality of rice. It is, therefore, crucial to elucidate the consequences of Cd toxicity. Plant height, biomass, SPAD score, PSII efficiency, and photosynthetic performance index were all significantly reduced in Cd-stressed rice. Cd stress resulted in a simultaneous increase in Cd and Fe concentrations in both the roots and the shoots, accompanied by the significant upregulation of heavy metal ATPase (OsHMA2, OsHMA3), natural resistance-associated macrophage proteins (OsNramp1, OsNramp5), Fe-regulated transporters (OsIRT1), Fe-reductase oxidase (OsFRO1) genes, and FCR activity in roots. This implies that Cd uptake may be closely associated with Fe transporters resulted in physiological and photosynthetic damages in Cd-stressed rice. In silico analysis suggested that the localization of Cd-uptake proteins in the plasma membrane exhibiting transporter activity, among which two motifs were linked to the pfam_fs: Nramp domain. In a phylogenetic tree, HMA and Nramp genes were consistently positioned in the same cluster, while OsIRT1 and OsFRO1 were independently located. The key cis-acting elements were abscisic acid-responsiveness, methyl jasmonate-responsiveness, zein metabolism regulation, stress-responsiveness, salicylic acid-responsiveness, and gibberellin-responsiveness. An interactome map revealed the diverse functional partners of Cd-uptake genes, including MTP1 (metal tolerance protein 1), YSL6 (metal-nicotianamine transporter), IRO2 (Fe-regulated transcription factor 2), OsJ_16707 (a vacuolar Fe transporter homolog), YSL15 (an Fe-phytosiderophore transporter), and NAS2 (nicotianamine synthase), which were predominantly linked to Fe homeostasis. These findings greatly elucidate the Cd uptake mechanism in rice plants and can help to regulate Cd uptake either by breeding or silencing these transporters.

The Cd-induced morphological and photosynthetic disruption is related to the reduced Fe status and increased oxidative injuries in sugar beet.

Cadmium (Cd) toxicity is a form of soil contamination that causes losses in plant growth and yield. Understanding the effects of Cd-induced changes in physiological and cellular processes will help scientists develop better scientific strategies for sugar beet plant improvement. Cd toxicity triggered a substantial decrease in morphological parameters and total soluble protein in sugar beets, as well as membrane damage and cell death. Furthermore, the SPAD score and photosynthetic OJIP parameters in leaves were severely affected due to Cd stress. This was correlated with the decreased FCR activity and BvIRT1 expression in roots, suggesting the adverse effect of Cd in Fe acquisition in sugar beet. Our findings also revealed that BvHMA3 and BvNRAMP3 were upregulated in Cd-exposed roots, indicating that these genes might be involved in Cd uptake in sugar beet. In silico analysis of BvHMA3 and BvNRAMP3 proteins showed close partnerships with several Arabidopsis genes mainly linked to metal tolerance protein, cation diffusion facilitator, vacuolar metal transporter, and vacuolar Fe transporter. Subsequently, Cd-exposed sugar beet showed severe sensitivity to oxidative damages resulted in elevated H2O2 and O2.- without possessed efficient antioxidant defense. Finally, growth retardation in Cd-exposed sugar beets is linked to photosynthetic inefficiency caused by low Fe levels and oxidative stress in cells. These results may be used to improve Cd-sensitive sugar beet plants by breeding or transgenic programs.

Silicon induces metallochaperone-driven cadmium binding to the cell wall and restores redox status through elevated glutathione in Cd-stressed sugar beet.

Cadmium (Cd) is toxic; however, whether silicon (Si) alleviates Cd toxicity was never studied in sugar beet. The study was conducted on 2-week-old sugar beet cultivated in the presence or absence of Cd (10 µM CdSO4 ) and Si (1 mM Na2 SiO3 ) in hydroponic conditions. The morphological impairment and cellular damages observed in sugar beet upon Cd toxicity were entirely reversed due to Si. Si substantially restored the energy-providing ability, absorbed energy flux, and electron transport toward PSII, which might be correlated with the upregulation of BvIRT1 and ferric chelate reductase activity leading to the restoration of Fe status in Cd-stressed sugar beet. Although Si caused a reduction of shoot Cd, the root Cd substantially increased under Cd stress, a significant part of which was retained in the cell wall rather than in the root vacuole. While the concentration of phytochelatin and the expression of BvPCS3 (PHYTOCHELATIN SYNTHASE 3) showed no changes upon Si exposure, Si induced the expression of BvHIPP32 (HEAVY METAL-ASSOCIATED ISOPRENYLATED PLANT PROTEIN 32) in the Cd-exposed root. The BvHIPP32 and AtHIPP32 metallochaperone proteins are localized in the cell wall and they share similar sequence alignment, physiochemical properties, secondary structure, cellular localization, motif locations, domain association, and metal-binding site (cd00371) linked to the metallochaperone-like protein. It suggests that Si reduces the Cd level in shoot by retaining the excess Cd in the cell wall of roots due to the induction of BvHIPP32 gene. Also, Si stimulates glutathione-related antioxidants along with the BvGST23 expression, inferring an ascorbate-glutathione ROS detoxification pathway in Cd-exposed plants.

Impact of LFGD (Ar+O2) plasma on seed surface, germination, plant growth, productivity and nutritional composition of maize (Zea mays L.).

In this present study conducted with the LFGD (Low-Frequency Glow Discharge) (Ar + O2) plasma treated maize seeds, to inspect the effect on seed surface modifications, seed germination, growth, development, productivity and nutritional compositions of maize plants. This study reported that LFGD (Ar + O2) plasma treated maize seeds have a potential effect to change its smooth seed surfaces and, it becomes rougher. It also enhances the seed germination rate up to (15.88%), which might help to increase the shoot length (33.42%), root length (10.67%), stem diameter (13.37%), total chlorophyll content (46.93%), total soluble protein (52.48%), total soluble phenol (21.68%) and sugar (1.62%) concentrations in respect controls of our experimental plants. For this reason, the acceptable treatment duration for maize seeds were 30sec, 60sec, 90sec and 120sec. After treatment, the plants exhibited a significant increase in CAT, SOD, APX and GR activities in the leaves and roots, and also significantly changes in H2O2 (208.33 ± 5.87µ molg-1 FW) in the leaves and (61.13 ± 1.72µ molg-1 FW) in the roots, NO was (369.24 ± 213.19µ molg-1FW) and (1094.23 ± 135.44µ molg-1FW) in the leaves and roots. LFGD plasma treatment also contributed to enhancement of productivity (1.27%), nutritional (moisture, ash, fat, and crude fiber) compositions, and iron and zinc micro-nutrition concentrations of maize. From this research, LFGD (Ar + O2) plasma treatment showed a potential impact on the maize cultivation system, which is very effective tools and both in nationally and internationally alter the conventional cultivation system of maize. Because it promotes seed surface modification, improved germination rate, shoot length, root length, chlorophyll content, some of the growths related enzymatic activity, nutrient composition, iron, and zinc micro-nutrients and the productivity of maize.

Molecular characterization of Fe-acquisition genes causing decreased Fe uptake and photosynthetic inefficiency in Fe-deficient sunflower.

Iron (Fe) deficiency in plants hinders growth and yield. Thus, this study aims to elucidate the responses and molecular characterization of genes in Fe-deficient sunflower. The study was conducted on 14 days-old sunflower plants cultivated in hydroponic culture under Fe-sufficient and Fe-deficient conditions. The Fe-starved sunflower showed substantial decrease in plant biomass, SPAD score, quantum yield efficiency of PSII (Fv/Fm), photosynthetic performance index (Pi_ABS). Further, Fe shortage reduced Fe and Zn concentrations in roots and shoots, accompanied by a marked decrease of HaNramp1 and HaZIP1 expression in roots, suggesting the association of Zn status contributing to photosynthetic inefficiency in sunflower. The ferric chelate reductase (FCR) activity, along with HaFRO2 and HaIRT1 transcripts, were constitutively expressed, suggesting that sunflower plants can regulate FCR activity, although the lack of bioavailable Fe in the rhizosphere strongly corresponds to the limited Fe uptake in sunflower. The substantial increase of proton extrusion in roots and the localization of Fe-related genes in the plasma membrane are also evident in sunflower as common responses to Fe-deficiency by this Strategy I plant species. Analysis showed that three motifs of Fe-related proteins were linked to the ZIP zinc transporter. The interactome map revealed the close partnership of these Fe-related genes in addition to FRU gene encoding putative transcription factor linked to Fe uptake response. The cis-regulatory analysis of promoter suggested the involvement of auxin, salicylic acid, and methyl jasmonate-responsive elements in the regulatory process in response to Fe deficiency. These findings may be beneficial to develop Fe-efficient sunflower plants through breeding or genome editing approaches.

Physiological responses and genome-wide characterization of TaNRAMP1 gene in Mn-deficient wheat.

Manganese (Mn) is an essential micronutrient for plants. This study elucidates the physiological consequences and characterization of TaNRAMP1 transporter in Mn-starved wheat. The cellular integrity, redox status, chlorophyll score, and Fv/Fm were severely affected, accompanied by decreased Mn concentration in root and shoot in Mn-deficient wheat. However, Fe concentration and root phytosiderophore release were not affected, contradicting the interactions of Fe status with Mn under Mn shortage. The genome-wide identification of TaNRAMP1 (natural resistance-associated macrophage protein 1), known as high-affinity Mn transporter, showed several polymorphisms within genome A, B, and D. The expression of TaNRAMP1 significantly decreased in roots of genome A and B but was constitutively expressed in genome D due to Mn-deficiency. The TaNRAMP1 was located in the plasma membrane and showed six motifs matched to Nramp (divalent metal transport). Further, TaNRAMP1 showed a close partnership with cation transporter associated with P-type ATPase/cation transport network. In the RNASeq platform, TaNRAMP1, located in all three genomes, showed the highest expression potential in microspore. Besides, only TaNRAMP1 in genome D was upregulated due to heat and drought stress but showed downregulation in response to excess sulfur and Puccinia triticina infection in all three genomes. The cis-regulatory analysis implies the transcriptional regulation of TaNRAMP1 linked to methyl jasmonate and abscisic acid synthesis. Furthermore, TaNRAMP1 proteins showed similar physicochemical properties, but the C-terminus position of genome D was different than genome A and B. This is the first study on the responses and genome-wide characterization of TaNRAMP1 in Mn-starved wheat.

Downregulation of Zn-transporters along with Fe and redox imbalance causes growth and photosynthetic disturbance in Zn-deficient tomato.

Zinc (Zn) deficiency hinders growth and development in tomato. This study unveils the responses of how Zn starvation affects physiological and molecular processes in tomato. Zn deficiency negatively affected the biomass, cellular integrity, and chlorophyll synthesis in tomato. Also, Zn deficiency decreased the maximum yield of PSII, photosynthesis performance index and dissipation energy per active reaction center, although the antenna size, trapping energy efficiency and electron transport flux were stable in Zn-starved leaves. Further, Zn shortage caused a substantial reduction in Zn and Fe concentrations in both roots and shoots along with decreased root Fe-reductase activity accompanied by the downregulation of Fe-regulated transporter 1, Zn transporter-like (LOC100037509), and Zn transporter (LOC101255999) genes predicted to be localized in the root plasma membrane. The interactome partners of these Zn transporters are predominantly associated with root-specific metal transporter, ferric-chelate reductase, BHLH transcriptional regulator, and Zn metal ion transporters, suggesting that Zn homeostasis may be tightly linked to the Fe status along with BHLH transcription factor in Zn-deficient tomato. We also noticed elevated O2.- and H2O2 due to Zn deficiency which was consistent with the inefficient antioxidant properties. These findings will be useful in the downstream approach to improve vegetable crops sensitive to Zn-deficiency.

Sulfur triggers glutathione and phytochelatin accumulation causing excess Cd bound to the cell wall of roots in alleviating Cd-toxicity in alfalfa.

Although Cd is threatening to the environment, animal, and human, the eco-friendly approach to mitigate the Cd-toxicity in alfalfa was barely studied. Therefore, this study aims at elucidating the role of S, a crucial macroelement, in alleviating Cd toxicity in alfalfa plants. The supplementation of S in Cd-stressed alfalfa reversed the detrimental effect on plant biomass, chlorophyll synthesis, and protein concentration. Interestingly, S surplus restored the photosynthetic kinetics, such as Fv/Fm, Pi_ABS, and Mo values in leaves of Cd-stressed alfalfa. Further, Cd-induced adverse effect on membrane stability, cell viability, and redox status was restored due to S under Cd stress. The exogenous S not only increased S status and the expression of sulfate transporters (MsSULRT1;2 and MsSULTR1;3), but also decreased the Cd concentration in the shoot by retaining elevated Cd in root tissue. Further analysis revealed the upregulation of MsGS (glutathione synthetase) and MsPCS1 (phytochelatin synthase) genes along with the increased concentration of glutathione and phytochelatin, predominantly in roots subjected to S surplus under Cd stress. The subcellular Cd analysis showed elevated Cd in the cell wall but not in the vacuole. It suggests that S-induced elevated glutathione enables the phytochelatin to bind with excess Cd leading to subcellular sequestration in the cell wall of roots. Also, S stimulates the S-metabolites and GR enzyme that coordinately counteracts Cd-induced oxidative damage. These findings can be utilized to popularize the application of S and to perform breeding/transgenic experiments to develop Cd-free forage crops.

Glutathione Restores Hg-Induced Morpho-Physiological Retardations by Inducing Phytochelatin and Oxidative Defense in Alfalfa.

Mercury (Hg) is toxic to plants, but the effect of glutathione in Hg alleviation was never studied in alfalfa, an important forage crop. In this study, Hg toxicity showed morphological retardation, chlorophyll reduction, and PSII inefficiency, which was restored due to GSH supplementation in alfalfa plants treated with Hg. Results showed a significant increase of Hg, but Fe and S concentrations substantially decreased in root and shoot accompanied by the downregulation of Fe (MsIRT1) and S (MsSultr1;2 and MsSultr1;3) transporters in roots of Hg-toxic alfalfa. However, GSH caused a significant decrease of Hg in the shoot, while the root Hg level substantially increased, accompanied by the restoration of Fe and S status, relative to Hg-stressed alfalfa. The subcellular analysis showed a substantial deposition of Hg in the root cell wall accompanied by the increased GSH and PC and the upregulation of MsPCS1 and MsGSH1 genes in roots. It suggests the involvement of GSH in triggering PC accumulation, causing excess Hg bound to the cell wall of the root, thereby reducing Hg translocation in alfalfa. Bioinformatics analysis showed that the MsPCS1 protein demonstrated one common conserved motif linked to the phytochelatin synthase domain (CL0125) with MtPCS1 and AtMCS1 homologs. These in silico analysis further confirmed the detoxification role of MsPCS1 induced by GSH in Hg-toxic alfalfa. Additionally, GSH induces GSH and GR activity to counteract oxidative injuries provoked by Hg-induced H2O2 and lipid peroxidation. These findings may provide valuable knowledge to popularize GSH-derived fertilizer or to develop Hg-free alfalfa or other forage plants.

Morpho-physiological retardations due to iron toxicity involve redox imbalance rather than photosynthetic damages in tomato.

Iron (Fe) toxicity is a major nutritional disorder that affects growth and yield in plants. Understanding the responses or damages due to Fe-toxicity may provide useful knowledge to improve tomato varieties. This study investigates the physiological and molecular responses in Fe-toxic tomato plants. The tomato plants were grown in separate hydroponic containers with two concentrations of Fe-EDTA (25 µM and 5 mM) in addition to the other nutrient elements. Fe-toxicity showed a severe reduction in growth parameters, which was accompanied by the increased electrolyte leakage and cell death in tomato. However, the SPAD score, quantum efficiency of PSII, and photosynthesis performance index did not show any changes in leaves, suggesting that damages due to Fe-toxicity are not related to the photosynthetic disturbance in tomato. The FCR (ferric chelate reductase) activity in root along with the Fe concentration in root and shoot significantly increased, being consistent with the upregulation of Fe-related genes (SlNramp1 and SlFRO1) in roots. It suggests that inefficiency to cope with elevated Fe is closely linked to Fe mobilization and uptake in roots of tomato. Consequently, this sensitive genotype was more prone to oxidative damages because of the inefficient antioxidant defense linked to antioxidant enzymes and metabolites. In conclusion, the growth retardation in Fe-toxic tomato is not related to photosynthetic inefficiency but highly associated with oxidative injuries in cells. These findings could be targeted in breeding or transgenic program to improve tomato plants sensitive to Fe toxicity.

Arbuscular mycorrhizal fungi mitigate Fe deficiency symptoms in sorghum through phytosiderophore-mediated Fe mobilization and restoration of redox status.

Sustainable management of iron (Fe) deficiency through the microbial association is highly desirable to ensure crop yield. This study elucidates whether and how arbuscular mycorrhizal fungi (AMF) ameliorate Fe deficiency symptoms in sorghum. AMF inoculation showed a significant improvement in plant biomass, chlorophyll score, Fv/Fm (quantum efficiency of photosystem II), and Pi_ABS (photosynthesis performance index), suggesting its potentiality to diminish Fe deficiency symptoms in sorghum. This AMF-driven prevention of Fe deficiency was further supported by the improvement of biochemical stress indicators, such as cell death, electrolyte leakage, hydrogen peroxide, and superoxide anion. In this study, AMF showed a significant increase in phytosiderophore (PS) release as well as Fe and S concentrations in sorghum under Fe deficiency. Quantitative real-time PCR analysis demonstrated the consistent upregulation of SbDMAS2 (deoxymugineic acid synthase 2), SbNAS2 (nicotianamine synthase 2), and SbYS1 (Fe-phytosiderophore transporter yellow stripe) in roots due to AMF with Fe deficiency. It suggests that the enhancement of Fe due to AMF is related to the mobilization of Fe(III)-PS in the rhizosphere supported by the long-distance transport of Fe by SbYS1 transporter in sorghum. Our study further showed that the elevation of S mainly in the presence of AMF possibly enhances the S-containing antioxidant metabolites (Met, Cys, and GSH) as well as enzymes (CAT, SOD, and GR) to counteract H2O2 and O2- for the restoration of redox status in Fe-deprived sorghum. Moreover, S possibly participates in Strategy II responses revealing its crucial role as a signaling molecule for Fe homeostasis in sorghum.

Arbuscular Mycorrhizal Symbiosis Mitigates Iron (Fe)-Deficiency Retardation in Alfalfa (Medicago sativa L.) Through the Enhancement of Fe Accumulation and Sulfur-Assisted Antioxidant Defense.

Iron (Fe)-deficiency is one of the major constraints affecting growth, yield and nutritional quality in plants. This study was performed to elucidate how arbuscular mycorrhizal fungi (AMF) alleviate Fe-deficiency retardation in alfalfa (Medicago sativa L.). AMF supplementation improved plant biomass, chlorophyll score, Fv/Fm (quantum efficiency of photosystem II), and Pi_ABS (photosynthesis performance index), and reduced cell death, electrolyte leakage, and hydrogen peroxide accumulation in alfalfa. Moreover, AMF enhanced ferric chelate reductase activity as well as Fe, Zn, S and P in alfalfa under Fe-deficiency. Although Fe-transporters (MsIRT1 and MsNramp1) did not induce in root but MsFRO1 significantly induced by AMF under Fe deficiency in roots, suggesting that AMF-mediated Fe enhancement is related to the bioavailability of Fe at rhizosphere/root apoplast rather than the upregulation of Fe transporters under Fe deficiency in alfalfa. Several S-transporters (MsSULTR1;1, MsSULTR1;2, MsSULTR1;3, and MsSULTR3;1) markedly increased following AMF supplementation with or without Fe-deficiency alfalfa. Our study further suggests that Fe uptake system is independently influenced by AMF regardless of the S status in alfalfa. However, the increase of S in alfalfa is correlated with the elevation of GR and S-metabolites (glutathione and cysteine) associated with antioxidant defense under Fe deficiency.

Arbuscular mycorrhizal fungi alleviate Fe-deficiency symptoms in sunflower by increasing iron uptake and its availability along with antioxidant defense.

Iron (Fe)-deficiency causes chlorosis and growth inhibition in sunflower, an important commercial crop. This study examines whether and how arbuscular mycorrhizal fungi (AMF) ameliorate Fe-deficiency symptoms in Fe-deficiency sensitive sunflower plants. AMF supplementation showed a significant improvement in plant biomass, chlorophyll score, Fv/Fm (quantum efficiency of photosystem II), and Pi_ABS (photosynthesis performance index), suggesting its beneficial effect under Fe deficiency. This AM-driven amelioration of Fe deficiency was further supported by the improvement of biochemical stress indicators, such as cell death, electrolyte leakage, superoxide anion, and hydrogen peroxide. In this study, the AMF supplementations resulted in significant improvement in Fe as well as Zn concentrations in root and shoot of sunflower under Fe deficiency. One of the primary Strategy-I responses, ferric reductase activity along with the expression of its respective gene (HaFRO1), significantly increased in roots due to AMF ensuring Fe availability in the rhizosphere under Fe deficiency. Our qPCR analysis also showed a significant upregulation of HaIRT1, HaNramp1, and HaZIP1 in roots of sunflower in the presence of AMF, suggesting that Fe and Zn transporters are concurrently involved with AMF-mediated alleviation of Fe deficiency. Further, AMF accelerates the activities of CAT and SOD, predominantly in roots to protect sunflower plants from Fe-deficiency reactive oxygen species (ROS). This study unveils the mechanistic basis of AMF to limit Fe deficiency retardation in sunflower.