Manganese in Plants: From Acquisition to Subcellular Allocation

Regulatory role of microRNAs (miRNAs) in the recent development of abiotic stress tolerance of plants

MicroRNAs (miRNAs) are a distinct groups of single-stranded non-coding, tiny regulatory RNAs approximately 20-24 nucleotides in length. miRNAs negatively influence gene expression at the post-transcriptional level and have evolved considerably in the development of abiotic stress tolerance in a number of model plants and economically important crop species. The present review aims to deliver the information on miRNA-mediated regulation of the expression of major genes or Transcription Factors (TFs), as well as genetic and regulatory pathways. Also, the information on adaptive mechanisms involved in plant abiotic stress responses, prediction, and validation of targets, computational tools, and databases available for plant miRNAs, specifically focus on their exploration for engineering abiotic stress tolerance in plants. The regulatory function of miRNAs in plant growth, development, and abiotic stresses consider in this review, which uses high-throughput sequencing (HTS) technologies to generate large-scale libraries of small RNAs (sRNAs) for conventional screening of known and novel abiotic stress-responsive miRNAs adds complexity to regulatory networks in plants. The discoveries of miRNA-mediated tolerance to multiple abiotic stresses, including salinity, drought, cold, heat stress, nutritional deficiency, UV-radiation, oxidative stress, hypoxia, and heavy metal toxicity, are highlighted and discussed in this review.

Bio-Priming with Compatible Rhizospheric Microbes Enhances Growth and Micronutrient Uptake of Red Cabbage

Red cabbage is known as the millennium’s functional food, which has a lot of importance in our diet because of the health-promoting ingredients present in it. The current study investigated the synergistic relationship of rhizospheric-competent microbial agents (Trichoderma harzianum, Pseudomonas fluorescens, and Bacillus subtilis) in modulating the performance of red cabbage under the field conditions of Middle Gangetic Plains, India. Growth parameters were studied at three developmental stages, viz., pre-cupping, early head formation, and maturity. Our results suggested that the dual application of T. harzianum + P. fluorescens along with the 75% recommended dose of fertilizers (RDF) increased the number of leaves (24.6), leaf area (537.2 cm2), root length (19.8 cm), and micronutrient uptake (Fe, Mn, and Cu) by head of the crop, whereas the co-inoculation of P. fluorescens and B. subtilis along with 75% RDF enhanced plant spread (39.0 cm), earliness (95.2 days), and Zn uptake. Maximum plant height (28.7 cm) and chlorophyll (SPAD, 77.3) were recorded in 100% RDF (120:60:60 kg ha−1) and the combination of T. harzianum + B. subtilis along with 75% RDF, respectively. Interestingly, consortium (T. harzianum + P. fluorescens) bio-primed plants recorded about 14% higher root length in comparison to plants receiving sole fertilizers. The regression analysis revealed a significant relationship of Fe and Mn uptake with chlorophyll (SPAD) and between Zn uptake and the earliness of the crop. The present study indicated that seedling bio-priming with the dual consortium of efficient bio-agents is a viable strategy to lessen our dependence on chemical fertilizers for improving red cabbage production.

Leaf microscopy applications in photosynthesis research: identifying the gaps

Leaf imaging via microscopy has provided critical insights into research on photosynthesis at multiple junctures, from the early understanding of the role of stomata, through elucidating C4 photosynthesis via Kranz anatomy and chloroplast arrangement in single cells, to detailed explorations of diffusion pathways and light utilization gradients within leaves. In recent decades, the original two-dimensional (2D) explorations have begun to be visualized in three-dimensional (3D) space, revising our understanding of structure-function relationships between internal leaf anatomy and photosynthesis. In particular, advancing new technologies and analyses are providing fresh insight into the relationship between leaf cellular components and improving the ability to model net carbon fixation, water use efficiency, and metabolite turnover rate in leaves. While ground-breaking developments in imaging tools and techniques have expanded our knowledge of leaf 3D structure via high-resolution 3D and time-series images, there is a growing need for more in vivo imaging as well as metabolite imaging. However, these advances necessitate further improvement in microscopy sciences to overcome the unique challenges a green leaf poses. In this review, we discuss the available tools, techniques, challenges, and gaps for efficient in vivo leaf 3D imaging, as well as innovations to overcome these difficulties.

Liming and tillering application of manganese alleviates iron manganese plaque reduction and cadmium accumulation in rice (Oryza sativa L.)

The application time and soil pH are key to manganese (Mn) bioavailability, which may influence Mn effects on cadmium (Cd) accumulation in rice. Accordingly, this study investigated the effects of Mn application at different stages, alone or with basal liming, on Cd accumulation in rice through pot and field experiments. The results showed that basal Mn application maximally elevated soil dissolved Mn, and increasing Mn accumulation in rice by 140%-367% compared to the control. Additionally, basal or tillering applications had better effects on enhancing iron manganese plaque (IMP) and inhibiting CaCl₂-extractable Cd than later applications. Therefore, basal and tillering Mn reduced brown rice Cd by 24.6% and 18.9% compared to the control, respectively. Liming reduced CaCl₂-extractable Cd by 83.3% compared to the control but inhibited soil dissolved Mn (25.8%-76.6%) and IMP (28.9%-29.7%), resulting in only a 41.7% reduction in brown rice Cd. Liming combined with tillering Mn maximally reduced brown rice Cd by 67.4%, structural equation modeling revealed CaCl₂-extractable Cd and manganese plaque played the greatest positive and negative roles, respectively. Therefore, basal liming and tillering application of Mn is most effective at reducing rice Cd through inhibition of Cd bioavailability and alleviation of IMP reduction.

Yield and Compositional Profile of Eggplant Fruits as Affected by Phosphorus Supply, Genotype and Grafting

The present experiment addressed the effects of two phosphorus regimes (30 and 90 kg ha−1, hereafter P30 and P90) on yield and composition of eggplant fruits in ‘Birgah’ and ‘Dalia’, whether or not these cultivars were grafted onto Solanum torvum ‘Espina’. The P30 regime did not reduce yield, and promoted fruits’ dry matter and total phenols content, along with their concentrations of macronutrients, mesonutrients (S and Na) and micronutrients (mostly Cu, B, Zn); however, their Fe concentrations were depressed. The rootstock ‘Espina’ increased fruit yield, dry matter content, epicarp chroma (in ‘Birgah’) and Ca content, together with their concentrations of B and Zn (especially at P30), but reduced their Fe content, mostly under P30. Thus, the reduced P supply and grafting proved to be effective tools to enhance fruit yield, carpometric and almost all nutritional traits in eggplant, in a framework of more sustainable crop management. However, the reduced fruit concentration of Fe suggests that the affinity of the rootstock with specific micro minerals should be taken into account, along with the option to adopt complementary practices (e.g., targeted micronutrient fertilizations) to manage the micro mineral composition of eggplants.

The rice heavy-metal transporter OsNRAMP1 regulates disease resistance by modulating ROS homoeostasis

Crop diseases threaten food security and sustainable agriculture. Consumption of crops containing nonessential toxic metals leads to health risks for humans. Therefore, cultivation of disease-resistant and toxic metal-safe crops is a double-gain strategy that can contribute to food security. Here, we show that rice heavy-metal transporter OsNRAMP1 plays an important role in plant immunity by modulating metal ion and reactive oxygen species (ROS) homoeostasis. OsNRAMP1 expression was induced after pathogenic bacteria and fungi infections. The osnramp1 mutants had an increased content of H₂ O₂ and activity of superoxide dismutase, but decreased activity of catalase, showing enhanced broad-spectrum resistance against bacterial and fungal pathogens. RNA-seq analysis identified a number of differentially expressed genes that were involved in metal ion and ROS homoeostasis. Altered expression of metal ion-dependent ROS-scavenging enzymes genes and lower accumulation of cations such as Mn together induced compromised metal ion-dependent enzyme-catalysing activity and modulated ROS homoeostasis, which together contributed towards disease resistance in osnramp1 mutants. Furthermore, the osnramp1 mutants contained lower levels of toxic heavy metals Cd and Pb and micronutrients Ni and Mn in leaves and grains. Taken together, a proof of concept was achieved that broad-spectrum disease-resistant and toxic heavy-metal-safe rice was engineered by removal of the OsNRAMP1 gene.

Novel approach to enhance Bradyrhizobium diazoefficiens nodulation through continuous induction of ROS by manganese ferrite nanomaterials in soybean

BACKGROUND

The study of symbiotic nitrogen fixation between (SNF) legumes and rhizobia has always been a hot frontier in scientific research. Nanotechnology provides a new strategy for biological nitrogen fixation research. However, how to construct abiotic nano-structure-biological system, using the special properties of nanomaterials, to realize the self-enhancement of biological nitrogen fixation capacity is important.

RESULTS

In order to construct a more efficient SNF system, in this study, we applied manganese ferrite nanoparticles (MF-NPs) with sustainable diatomic catalysis to produce reactive oxygen species (ROS), thus regulating the nodulation pathway and increasing the number of nodules in soybean (Glycine max), eventually enhancing symbiotic nitrogen fixation. Symbiosis cultivation of MF-NPs and soybean plants resulted in 50.85% and 61.4% increase in nodule weight and number, respectively, thus inducing a 151.36% nitrogen fixation efficiency increase, finally leading to a 25.70% biomass accumulation increase despite no substantial effect on the nitrogenase activity per unit. Transcriptome sequencing analysis showed that of 36 differentially expressed genes (DEGs), 31 DEGs related to soybean nodulation were upregulated in late rhizobium inoculation stage (12 d), indicating that the increase of nodules was derived from nodule-related genes (Nod-R) continuous inductions by MF-NPs.

CONCLUSIONS

Our results indicated that the nodule number could be effectively increased by extending the nodulation period without threatening the vegetative growth of plants or triggering the autoregulation of nodulation (AON) pathway. This study provides an effective strategy for induction of super-conventional nodulation.

Geo-Accumulation Index of Manganese in Soils Due to Flooding in Boac and Mogpog Rivers, Marinduque, Philippines with Mining Disaster Exposure

This paper presents the effects of flooding on the accumulation of manganese (Mn) in soils within proximity of the Boac and Mogpog rivers in Marinduque of The Philippines. Marinduque, an island province in the Philippines, experienced two catastrophic tailings storage facility (TSF) failures in the 1990s that released sulfide-rich tailings into the two major rivers. The Philippines experiences 21–23 typhoons every year, 11 of which pass thru Marinduque that causing inundation of floodplain areas in the province. A flood hazard map developed using LiDAR DEM was utilized for the Boac and Mogpog rivers for an accurate representation of flooding events. A portable X-ray fluorescence spectrometer (pXRF) and a Hannah multi-parameter device were used for the on-site analyses of Mn concentration and water physico-chemical properties, respectively. Spatial grid mapping with zonal statistics was employed for a comprehensive analysis of all the data collected and processed. Correlation analysis was carried out on Mn concentrations in soil and surface water, electrical conductivity (EC), total dissolved solids (TDS), pH, temperature, curve number (CN), and flood heights. The curve number indicates the runoff response characteristic of the Mogpog-Boac River basin. The results show that 40% of the total floodplain area of Boac and Mogpog were subjected to high hazards with flood heights above 1.5 m. The Mn content of soils had a statistically significant moderate positive correlation with flood height (r = 0.458) and a moderate negative correlation with pH (r = −0.438). This condition suggested that more extensive flooding promotes Mn contamination of floodplain soils in the two rivers, the source of which includes the mobilization of Mn-bearing silt, sediments, and mine drainage from the abandoned mine pits and TSFs. There is also a strong negative correlation between pH and Mn concentrations in surface water, a relationship attributed to the solubilization of Mn-bearing precipitates based on geochemical modeling results. Using Muller’s geo-accumulation index, 77.5% of the total floodplain of the two rivers was identified as “moderately contaminated” with an average Mn soil content of 3.4% by weight (34,000 mg/kg). The Mn contamination map of floodplain soils in the Mogpog and Boac rivers described in this study could guide relevant regional, national, and local government agencies in planning appropriate intervention, mitigation, remediation, and rehabilitation strategies to limit human exposure to highly contaminated areas.

Effects of Fe and Mn Deficiencies on the Root Protein Profiles of Tomato (Solanum lycopersicum) Using Two-Dimensional Electrophoresis and Label-Free Shotgun Analyses

Iron (Fe) and manganese (Mn) are two essential elements for plants that compete for the same uptake transporters and show conflicting interactions at the regulatory level. In order to understand the differential response to both metal deficiencies in plants, two proteomic techniques (two-dimensional gel electrophoresis and label-free shotgun) were used to study the proteome profiles of roots from tomato plants grown under Fe or Mn deficiency. A total of 119 proteins changing in relative abundance were confidently quantified and identified, including 35 and 91 in the cases of Fe deficiency and Mn deficiency, respectively, with 7 of them changing in both deficiencies. The identified proteins were categorized according to function, and GO-enrichment analysis was performed. Data showed that both deficiencies provoked a common and intense cell wall remodelling. However, the response observed for Fe and Mn deficiencies differed greatly in relation to oxidative stress, coumarin production, protein, nitrogen, and energy metabolism.

Soil application of manganese sulfate effectively reduces Cd bioavailability in Cd-contaminated soil and Cd translocation and accumulation in wheat

Cadmium (Cd) pollution in wheat fields has caused serious food safety issues in China. Manganese (Mn)-containing materials have been widely used in paddy fields to reduce Cd accumulation in rice. However, the remediation effects of MnSO₄ in wheat fields have not been well studied and the underlying mechanisms are poorly understood. Our field experiment showed that the application of 0.1% and 0.2% MnSO₄ in soil reduced Cd concentrations significantly in wheat root, stem, leaf, and grain by 26.67-30.76%, 15.78-29.30%, 22.03-30.66%, and 30.57-50.55%, respectively, while increasing Mn concentrations significantly in these wheat tissues. MnSO₄ application significantly increased soil available Mn content by 3.78-6.19 times, the free Mn oxides and amorphous Mn oxides by 1.72-10.38 times, and Mn oxides bound Cd contents by 10.23-39.55%, resulting in a reduction of Cd availability by 30.11-40.78%. Simultaneously, MnSO₄ treatment altered the chemical forms of Cd and Mn, promoted the soluble protein concentration, and decreased the malondialdehyde (MDA) content in wheat roots. Additionally, soil application of MnSO₄ down-regulated the expression of TaNramp5, TaHMA2, and TaLCT1 in wheat roots, mediating the reduction of wheat root Cd concentration, and increased the sequestration of Cd into vacuoles by up-regulating the expression of TaHMA3. These findings add to the current knowledge of how MnSO₄ affects Cd mobilization and absorption via different mechanisms occurring both in the soil medium and at the plant level. This research indicates that soil application of MnSO₄ has great potential to remediate Cd-contaminated wheat fields.

Essential trace metals in plant responses to heat stress

Essential trace metals function as structural components or cofactors in many proteins involved in a wide range of physiological processes in plants. Hence, trace metal deficiency can significantly hamper plant growth and development. On the other hand, excess concentrations of trace metals can also induce phytotoxicity, for example via an enhanced production of reactive oxygen species. Besides their roles in plant growth under favourable environmental conditions, trace metals also contribute to plant responses to biotic and abiotic stresses. Heat is a stress factor that will become more prevalent due to increasing climate change and is known to negatively affect crop yield and quality, posing a severe threat to food security for future generations. Gaining insight into heat stress responses is essential to develop strategies to optimize plant growth and quality under unfavourable temperatures. In this context, trace metals deserve particular attention as they contribute to defence responses and are important determinants of plant nutritional value. Here, we provide an overview of heat-induced effects on plant trace metal homeostasis and the involvement of trace metals and trace metal-dependent enzymes in plant responses to heat stress. Furthermore, avenues for future research on the interactions between heat stress and trace metals are discussed.

Micronutrient homeostasis in plants for more sustainable agriculture and healthier human nutrition

The provision of sustainable, sufficient, and nutritious food to the growing population is a major challenge for agriculture and the plant research community. In this respect, the mineral micronutrient content of food crops deserves particular attention. Micronutrient deficiencies in cultivated soils and plants are a global problem that adversely affects crop production and plant nutritional value, as well as human health and well-being. In this review, we call for awareness of the importance and relevance of micronutrients in crop production and quality. We stress the need for better micronutrient nutrition in human populations, not only in developing but also in developed nations, and describe strategies to identify and characterize new varieties with high micronutrient content. Furthermore, we explain how adequate nutrition of plants with micronutrients impacts metabolic functions and the capacity of plants to express tolerance mechanisms against abiotic and biotic constraints. Finally, we provide a brief overview and a critical discussion on current knowledge, future challenges, and specific technological needs for research on plant micronutrient homeostasis. Research in this area is expected to foster the sustainable development of nutritious and healthy food crops for human consumption.

Ca2+-dependent successive phosphorylation of vacuolar transporter MTP8 by CBL2/3-CIPK3/9/26 and CPK5 is critical for manganese homeostasis in Arabidopsis

Manganese (Mn) is an essential micronutrient for all living organisms. However, excess Mn supply that can occur in acid or waterlogged soils has toxic effects on plant physiology and development. Although a variety of Mn transporter families have been characterized, we have only a rudimentary understanding of how these transporters are regulated to uphold and adjust Mn homeostasis in plants. Here, we demonstrate that two calcineurin-B-like proteins, CBL2/3, and their interacting kinases, CIPK3/9/26, are key regulators of plant Mn homeostasis. Arabidopsis mutants lacking CBL2 and 3 or their interacting protein kinases CIPK3/9/26 exhibit remarkably high Mn tolerance. Intriguingly, CIPK3/9/26 interact with and phosphorylate the tonoplast-localized Mn and iron (Fe) transporter MTP8 primarily at Ser35, which is conserved among MTP8 proteins from various species. Mn transport complementation assays in yeast combined with multiple physiological assays indicate that CBL-CIPK-mediated phosphorylation of MTP8 negatively regulates its transport activity from the cytoplasm to the vacuole. Moreover, we show that sequential phosphorylation of MTP8, initially at Ser31/32 by the calcium-dependent protein kinase CPK5 and subsequently at Ser35 by CIPK26, provides an activation/deactivation fine-tuning mechanism for differential regulation of Mn transport. Collectively, our findings define a two-tiered calcium-controlled mechanism for dynamic regulation of Mn homeostasis under conditions of fluctuating Mn supply.

Pulp Mineral Content of Passion Fruit Germplasm Grown in Ecuador and Its Relationship with Fruit Quality Traits

There are several species of passion fruit grown in South America. However, there is a lack of information about the mineral content in their pulp. Thus, the objective of the present research was to determine the mineral content in the pulp of different germplasms of passion fruit [Passiflora edulis f. flavicarpa (INIAP 2009 and P10), P. alata (Sweet passion fruit), P. edulis f. edulis (Gulupa) and Passiflora sp. (Criollo POR1 and Criollo PICH1)] grown in Ecuador and to determine their relationship with relevant fruit quality traits. The results showed that high Mg content was associated with less peel thickness, soluble solids was negatively related to K and B content, and vitamin C was negatively related to S content. INIAP 2009 had high titratable acidity and fruit weight but low N and Na; P10 showed the highest contents of N, K, Na, Mn and fruit weight but less P, Mg, and Fe; sweet passion fruit showed high S, Zn, Cu, soluble solids, and peel thickness but low K, Ca, B, and titratable acidity; Gulupa had high Mg, B, and Zn but low S, Fe, and Mn; Criollo POR1 showed high N and Fe but low Zn; and Criollo PICH1 showed high P, Ca, Mg, and Cu but low soluble solids and peel thickness. These results provide additional information on passion fruit germplasm grown in Ecuador and constitutes a reference for further breeding programs.

Mineral Content and Volatile Profiling of Prunus avium L. (Sweet Cherry) By-Products from Fundão Region (Portugal)

Large amounts of Prunus avium L. by-products result from sweet cherry production and processing. This work aimed to evaluate the mineral content and volatile profiling of the cherry stems, leaves, and flowers of the Saco cultivar collected from the Fundão region (Portugal). A total of 18 minerals were determined by ICP-MS, namely 8 essential and 10 non-essential elements. Phosphorus (P) was the most abundant mineral, while lithium (Li) was detected in trace amounts. Three different preparations were used in this work to determine volatiles: hydroethanolic extracts, crude extracts, and aqueous infusions. A total of 117 volatile compounds were identified using HS-SPME/GC-MS, distributed among different chemical classes: 31 aldehydes, 14 alcohols, 16 ketones, 30 esters, 4 acids, 4 monoterpenes, 3 norisoprenoids, 4 hydrocarbons, 7 heterocyclics, 1 lactone, 1 phenol, and 2 phenylpropenes. Benzaldehyde, 4-methyl-benzaldehyde, hexanal, lilac aldehyde, and 6-methyl-5-hepten-2-one were the major volatile compounds. Differences in the types of volatiles and their respective amounts in the different extracts were found. This is the first study that describes the mineral and volatile composition of Portuguese sweet cherry by-products, demonstrating that they could have great potential as nutraceutical ingredients and natural flavoring agents to be used in the pharmaceutical, cosmetic, and food industries.

Phosphorus confers tolerance against manganese toxicity in Prunus persica by reducing oxidative stress and improving chloroplast ultrastructure

In this study, we evaluated the mitigative role of phosphorus (P) in terms of manganese (Mn) toxicity in peach (Prunus persica L.) plants. Ten-day-old seedlings were treated with excess Mn (1 mM MnSO₄) alone and in combination with different P levels (100, 150, 200 and 250 μM KH₂PO₄) in half-strength Hoagland medium. The results demonstrated that Mn toxicity plants accumulated a significant amount of Mn in their tissues, and the concentration was higher in roots than in leaves. The accumulated Mn led to a considerable reduction in plant biomass, water status, chlorophyll content, photosynthetic rate, and disrupted the chloroplast ultrastructure by increasing oxidative stress (H₂O₂ and O₂^•-). However, P supplementation dramatically improved plant biomass, leaf relative water and chlorophyll contents, upregulating the ascorbate-glutathione pool and increasing the activities of antioxidant enzymes (superoxide dismutase; peroxidase dismutase; ascorbate peroxidase; monodehydroascorbate reductase; dehydroascorbate reductase), thus reducing oxidative damage as evidenced by lowering H₂O₂ and O₂^•- staining intensity. Moreover, P application markedly restored stomatal aperture and improved chloroplast ultrastructure, as indicated by the improved performance of photosynthetic machinery. Altogether, our findings suggest that P (250 μM) has a great potential to induce tolerance against Mn toxicity by limiting Mn accumulation in tissues, upregulating antioxidant defense mechanisms, alleviating oxidative damage, improving chloroplast ultrastructure and photosynthetic performance in peach plants.

MicroRNA Mediated Plant Responses to Nutrient Stress

To complete their life cycles, plants require several minerals that are found in soil. Plant growth and development can be affected by nutrient shortages or high nutrient availability. Several adaptations and evolutionary changes have enabled plants to cope with inappropriate growth conditions and low or high nutrient levels. MicroRNAs (miRNAs) have been recognized for transcript cleavage and translational reduction, and can be used for post-transcriptional regulation. Aside from regulating plant growth and development, miRNAs play a crucial role in regulating plant’s adaptations to adverse environmental conditions. Additionally, miRNAs are involved in plants’ sensory functions, nutrient uptake, long-distance root transport, and physiological functions related to nutrients. It may be possible to develop crops that can be cultivated in soils that are either deficient in nutrients or have extreme nutrient supplies by understanding how plant miRNAs are associated with nutrient stress. In this review, an overview is presented regarding recent advances in the understanding of plants’ responses to nitrogen, phosphorus, potassium, sulfur, copper, iron, boron, magnesium, manganese, zinc, and calcium deficiencies via miRNA regulation. We conclude with future research directions emphasizing the modification of crops for improving future food security.

Impacts of Mn, Fe, and Oxidative Stressors on MnSOD Activation by AtMTM1 and AtMTM2 in Arabidopsis

It has been reported that the mitochondrial carrier family proteins of AtMTM1 and AtMTM2 are necessary for manganese superoxide dismutase (MnSOD) activation in Arabidopsis, and are responsive to methyl viologen (MV)-induced oxidative stress. In this study, we showed that MnSOD activity was enhanced specifically by Mn treatments. By using AtMnSOD-overexpressing and AtMnSOD-knockdown mutant plants treated with the widely used oxidative stressors including MV, NaCl, H₂O₂, and tert-butyl hydroperoxide (t-BH), we revealed that Arabidopsis MnSOD was crucial for root-growth control and superoxide scavenging ability. In addition, it has been reported that E. coli MnSOD activity is inhibited by Fe and that MTM1-mutated yeast cells exhibit elevated Fe content and decreased MnSOD activity, which can be restored by the Fe²⁺-specific chelator, bathophenanthroline disulfonate (BPS). However, we showed that BPS inhibited MnSOD activity in AtMTM1 and AtMTM2 single- and double-mutant protoplasts, implying that altered Fe homeostasis affected MnSOD activation through AtMTM1 and AtMTM2. Notably, we used inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis to reveal an abnormal Fe/Mn ratio in the roots and shoots of AtMTM1 and AtMTM2 mutants under MV stress, indicating the importance of AtMTM1 in roots and AtMTM2 in shoots for maintaining Fe/Mn balance.

Impact of nanoparticles and their ionic counterparts derived from heavy metals on the physiology of food crops

Heavy metals and their engineered nanoparticle (NP) counterparts are emerging contaminants in the environment that have captured the attention of researchers worldwide. Although copper, iron, zinc and manganese are essential micronutrients for food crops, higher concentrations provoke several physiological and biochemical alterations that in extreme cases can lead to plant death. The effects of heavy metals on plants have been studied but the influence of nanoparticles (NPs) derived from these heavy metals, and their comparative effect is less known. In this critical review, we have found similar impacts for copper and manganese ionic and NP counterparts; in contrast, iron and zinc NPs seem less toxic for food crops. Although these nutrients are metals that can be dissociated in water, few authors have conducted joint ionic state and NP assays to evaluate their comparative effect. More efforts are thus required to fully understand the impact of NPs and their ion counterparts at the physiological, metabolic and molecular dimensions in crop plants.

Integrated Nutrient Management Improves the Growth and Yield of Rice and Greengram in a Rice-Greengram Cropping System under the Coastal Plain Agro-Climatic Condition

Continuous mono-cropping of rice has resulted in decline or stagnation of yield output due to the occurrence of multiple nutrient deficiencies and worsening of soil physicochemical properties accompanying increased pressure of insect pests and diseases. The basic concept of integrated nutrient management (INM) is maintenance or adjustment of soil fertility and supply of plant nutrients to an optimum level for sustaining the desired crop productivity through optimisation of benefits from all possible sources of plant nutrients in an integrated way. Augmenting a rice-based cropping system with pulses is a prevalent and indigenous cropping system under rainfed conditions. Considering the above facts, experiments were conducted to evaluate the impacts of integrated nutrient management on productivity of aromatic rice-greengram cropping system and nutrient balance of the post-harvest soil for agricultural sustainability under rainfed conditions in two consecutive years (2017-2018 and 2018-2019) with six main plots and three subplots. The experimental findings revealed that the treatment comprised of 50% recommended dose of fertiliser (RDF) through chemicals + 50% recommended dose of nitrogen (RDN) through farmyard manure (FYM) increased the plant height, tillers, dry matter accumulation, leaf area and leaf area duration, and yield parameters in short grain aromatic rice. Similarly, preceding application of 50% RDF + 50% RDN through FYM to rice and further application 75% RDF + Rhizobium+ phosphate solubilizing bacteria (PSB) to greengram increased the growth characteristics and yield parameters-such as pods/plant, seeds/pod, grain yield, stover yield, and harvest index-in greengram. It was concluded that the treatment consisting of 50% RDF (chemical fertiliser) + 50% RDN (FYM) to rice and 75% RDF + Rhizobium + PSB to greengram increased the productivity of the rice-greengram cropping system. Furthermore, the adoption of INM has positively impacted post-harvest soil nutrient balance.

Switching to nanonutrients for sustaining agroecosystems and environment: the challenges and benefits in moving up from ionic to particle feeding

The worldwide agricultural enterprise is facing immense pressure to intensify to feed the world's increasing population while the resources are dwindling. Fertilizers which are deemed as indispensable inputs for food, fodder, and fuel production now also represent the dark side of the intensive food production system. With most crop production systems focused on increasing the quantity of produce, indiscriminate use of fertilizers has created havoc for the environment and damaged the fiber of the biogeosphere. Deteriorated nutritional quality of food and contribution to impaired ecosystem services are the major limiting factors in the further growth of the fertilizer sector. Nanotechnology in agriculture has come up as a better and seemingly sustainable solution to meet production targets as well as maintaining the environmental quality by use of less quantity of raw materials and active ingredients, increased nutrient use-efficiency by plants, and decreased environmental losses of nutrients. However, the use of nanofertilizers has so far been limited largely to controlled environments of laboratories, greenhouses, and institutional research experiments; production and availability on large scale are still lagging yet catching up fast. Despite perceivable advantages, the use of nanofertilizers is many times debated for adoption at a large scale. The scenario is gradually changing, worldwide, towards the use of nanofertilizers, especially macronutrients like nitrogen (e.g. market release of nano-urea to replace conventional urea in South Asia), to arrest environmental degradation and uphold vital ecosystem services which are in critical condition. This review offers a discussion on the purpose with which the nanofertilizers took shape, the benefits which can be achieved, and the challenges which nanofertilizers face for further development and real-world use, substantiated with the significant pieces of scientific evidence available so far.

Genome-Wide Characterization and Abiotic Stresses Expression Analysis of Annexin Family Genes in Poplar

Poplar is an illustrious industrial woody plant with rapid growth, providing a range of materials, and having simple post-treatment. Various kinds of environmental stresses limit its output. Plant annexin (ANN) is a calcium-dependent phospholipid-binding protein involved in plant metabolism, growth and development, and cooperatively regulating drought resistance, salt tolerance, and various stress responses. However, the features of the PtANN gene family and different stress responses remain unknown in poplar. This study identified 12 PtANN genes in the P. trichocarpa whole-genome and PtANNs divided into three subfamilies based on the phylogenetic tree. The PtANNs clustered into the same clade shared similar gene structures and conserved motifs. The 12 PtANN genes were located in ten chromosomes, and segmental duplication events were illustrated as the main duplication method. Additionally, the PtANN4 homogenous with AtANN1 was detected localized in the cytoplasm and plasma membrane. In addition, expression levels of PtANNs were induced by multiple abiotic stresses, which indicated that PtANNs could widely participate in response to abiotic stress. These results revealed the molecular evolution of PtANNs and their profiles in response to abiotic stress.

Inorganic Compounds that Aid in Obtaining Somatic Embryos

Somatic embryogenesis (SE) is a process that allows formation of embryos from somatic cells; this biological process has different stages that first require micropropagation and conditioning of explant, and then induction, multiplication, development, and germination of somatic embryos (SoE), to obtain seedlings that will be acclimatized and grown in a greenhouse to further be cultivated in the field. Inorganic compounds are supplemented by macro- and micronutrients that can conform different culture media, and with other compounds such as a carbon source, vitamins, and plant growth regulators (PGRs), will direct the fate of the plant cells to obtain SoE that will regenerate into plants. The concentration of these inorganic compounds must be optimized, since at very high concentrations they can cause toxicity and at low concentrations they may not induce the desired response. The objective of this chapter is to describe the most significant advances in the use of inorganic elements during the different stages of SE, starting with the description of the most used basal media and later describing the use of the main studied mineral elements during establishment of SE.

Sauropus androgynus (L.) Merr.: a multipurpose plant with multiple uses in traditional ethnic culinary and ethnomedicinal preparations

Various plants form the basis of multiple traditional ethnic cuisines and ethnomedicinal practices across the globe. The ethnic cuisines cater to the nutritional, dietary and medicinal requirements of the tribal and rural communities even today. Using literature from various scholarly databases, this study was conducted to consolidate a comprehensive review on the use of Sauropus androgynus (L.) Merr. in various traditional ethnic cuisines and ethnomedicinal preparations across the globe. The survey shows that it is used in multiple ethnic cuisines and is variously known in different countries and among the communities. Further, it possesses multiple nutritional and ethnomedicinal properties. Considering its importance in ethnic foods and ethnomedicinal preparations, it is important to investigate the nutritional composition, phytochemical constitution and pharmacological basis of ethnomedicinal uses. Therefore, we further compiled this information and found that it is a rich source of both micro- and macronutrients and packed with several bioactive compounds. Survey of pharmacological studies on its traditional medicinal uses supports its ethnomedicinal properties. Despite its importance in traditional food and ethnomedicinal systems, it remains underexplored. Limited information on the toxicity of its various extracts shows that further studies should be conducted to understand its safety aspects. Further clinical studies to prospect possible drug candidates from it should be attempted.

Overexpression of METAL TOLERANCE PROTEIN8 reveals new aspects of metal transport in Arabidopsis thaliana seeds

METAL TOLERANCE PROTEIN8 (MTP8) of Arabidopsis thaliana is a member of the CATION DIFFUSION FACILITATOR (CDF) family of proteins that transports primarily manganese (Mn), but also iron (Fe). MTP8 mediates Mn allocation to specific cell types in the developing embryo, and Fe re-allocation as well as Mn tolerance during imbibition. We analysed if an overexpression of MTP8 driven by the CaMV 35S promoter has an effect on Mn tolerance during imbibition and on Mn and Fe storage in seeds, which would render it a biofortification target. Fe, Mn and Zn concentrations in MTP8-overexpressing lines in wild type and vit1-1 backgrounds were analysed by ICP-MS. Distribution of metals in intact seeds was determined by synchrotron µXRF tomography. MTP8 overexpression led to a strongly increased Mn tolerance of seeds during imbibition, supporting its effectiveness in loading excess Mn into the vacuole. In mature seeds, MTP8 overexpression did not cause a consistent increase in Mn and Fe accumulation, and it did not change the allocation pattern of these metals. Zn concentrations were consistently increased in bulk samples. The results demonstrate that Mn and Fe allocation is not determined primarily by the MTP8 expression pattern, suggesting either a cell type-specific provision of metals for vacuolar sequestration by upstream transport processes, or the determination of MTP8 activity by post-translational regulation.

Impact of Plasma-Activated Water (PAW) on Seed Germination of Soybean

The present study reports the generation of plasma-activated water (PAW) using dielectric barrier discharge (DBD), its physicochemical properties, and its potential impact on the seed germination and seedling growth of soybean. The results revealed significant changes in physical parameters, such as pH, total dissolved solids, total suspended solids, turbidity, conductivity, dissolved oxygen, and chemical parameters, such as calcium, chromium, sodium, manganese, nitrate, nitrites, phosphorus, and sulfur and biological parameter such as E. coli in water after plasma treatment. The concentration of dissolved oxygen, conductivity, nitrate, nitrite, and sulfur was increased with an increase in water treatment time, and the amounts of the other analyzed parameters decreased with the increase in water treatment time. The effects of untreated water and plasma-activated water treated for 20 minutes on soybean germination and growth were studied. The germination rate was found to be higher with plasma-treated water. Shoot lengths, seedlings length, vigor index, and germination rates were increased as compared to those germinated by normal water irrigation. The seedlings irrigated with PAW responded to the abundance of nitrogen by producing intensely green leaves because of their increased chlorophyll a as compared to seedlings irrigated with normal water. However, the content of chlorophyll b and carotenoids was found to decrease in the case of seedlings irrigated with PAW. Based on this report, we conclude that PAW could be used to substantially enhance seed germination and seedling growth.

Bioinoculants-Natural Biological Resources for Sustainable Plant Production

Agricultural sustainability is of foremost importance for maintaining high food production. Irresponsible resource use not only negatively affects agroecology, but also reduces the economic profitability of the production system. Among different resources, soil is one of the most vital resources of agriculture. Soil fertility is the key to achieve high crop productivity. Maintaining soil fertility and soil health requires conscious management effort to avoid excessive nutrient loss, sustain organic carbon content, and minimize soil contamination. Though the use of chemical fertilizers have successfully improved crop production, its integration with organic manures and other bioinoculants helps in improving nutrient use efficiency, improves soil health and to some extent ameliorates some of the constraints associated with excessive fertilizer application. In addition to nutrient supplementation, bioinoculants have other beneficial effects such as plant growth-promoting activity, nutrient mobilization and solubilization, soil decontamination and/or detoxification, etc. During the present time, high energy based chemical inputs also caused havoc to agriculture because of the ill effects of global warming and climate change. Under the consequences of climate change, the use of bioinputs may be considered as a suitable mitigation option. Bioinoculants, as a concept, is not something new to agricultural science, however; it is one of the areas where consistent innovations have been made. Understanding the role of bioinoculants, the scope of their use, and analysing their performance in various environments are key to the successful adaptation of this technology in agriculture.

Pre-Harvest MeJA Application Counteracts the Deleterious Impact of Al and Mn Toxicity in Highbush Blueberry Grown in Acid Soils

Volcanic ash-derived soils are characterized by low pH (pH ≤ 5.5) with increased concentrations of aluminum (Al³⁺) and manganese (Mn²⁺), which decreases plant growth, fruit quality, and yield. Methyl jasmonate (MeJA) improves abiotic stress tolerance. Our work aimed to evaluate the application of MeJA's impact on the growth, antioxidant defense, and fruit quality of highbush blueberry grown under Al and Mn toxicity. A field assay was conducted with four-year-old bushes of highbush blueberry cultivar Legacy under eight treatments (Control, Al (87% of Al saturation), Mn (240 mg kg^-1), and Al-Mn with and without MeJA application). Physiological, biochemical, and fruit quality parameters were measured. Growth rate significantly decreased with Al (20%), Mn (45%), and Al-Mn (40%). MeJA application recovered the growth rate. Photosynthetic parameters were not affected. Antioxidant activity increased under all treatments compared with controls, being higher with MeJA application. Total phenols (TP) were decreased in plants under Al (43%) and Mn (20%) compared with controls. MeJA application increased TP in all treatments. Fruits of bushes under Al and Mn toxicity with MeJA applications exhibited an increase in fruit firmness and weight, maintaining suitable contents of soluble solids. Our results provide insights about the beneficial effect of MeJA application on growth, antioxidant properties, and fruit quality of highbush blueberry plants grown in acid soils under Al and Mn toxicity.

Manganese distribution in the Mn-hyperaccumulator Grevillea meisneri from New Caledonia

New Caledonian endemic Mn-hyperaccumulator Grevillea meisneri is useful species for the preparation of ecocatalysts, which contain Mn–Ca oxides that are very difficult to synthesize under laboratory conditions. Mechanisms leading to their formation in the ecocatalysts are unknown. Comparing tissue-level microdistribution of these two elements could provide clues. We studied tissue-level distribution of Mn, Ca, and other elements in different tissues of G. meisneri using micro-X-Ray Fluorescence-spectroscopy (μXRF), and the speciation of Mn by micro-X-ray Absorption Near Edge Structure (µXANES), comparing nursery-grown plants transplanted into the site, and similar-sized plants growing naturally on the site. Mirroring patterns in other Grevillea species, Mn concentrations were highest in leaf epidermal tissues, in cortex and vascular tissues of stems and primary roots, and in phloem and pericycle–endodermis of parent cluster roots. Strong positive Mn/Ca correlations were observed in every tissue of G. meisneri where Mn was the most concentrated. Mn foliar speciation confirmed what was already reported for G. exul, with strong evidence for carboxylate counter-ions. The co-localization of Ca and Mn in the same tissues of G. meisneri might in some way facilitate the formation of mixed Ca–Mn oxides upon preparation of Eco-CaMnOx ecocatalysts from this plant. Grevillea meisneri has been successfully used in rehabilitation of degraded mining sites in New Caledonia, and in supplying biomass for production of ecocatalysts. We showed that transplanted nursery-grown seedlings accumulate as much Mn as do spontaneous plants, and sequester Mn in the same tissues, demonstrating the feasibility of large-scale transplantation programs for generating Mn-rich biomass.

Bioaccumulation of Cu, Fe, Mn and Zn in native Brachystegia longifolia naturally growing in a copper mining environment of Mufulira, Zambia

Heavy metal contamination in the soil and the subsequent accumulation in Brachystegia longifolia were investigated as a function of the wind direction and distance from a copper mine in Mufulira, Zambia. Soil and leaves of B. longifolia were collected along transects up to 12 km downwind and 19 km upwind. The total concentration of trace elements in the soil and leaves was determined through _pXRF. Plant-available Cu, Fe, Mn, and Zn were extracted in a Mehlich III solution and analyzed using ICP-AES. The degree of soil contamination illustrates that Cu and Fe from the copper mine strongly pollute Mufulira and the surrounding forests. Bioavailable Cu, Fe, Mn, and Zn reduced with increasing distance from the mine. An average of 296 mg/kg Cu, 2337 mg/kg Fe, 1101 mg/kg Mn, and 109 mg/kg Zn were recorded in leaves at the most polluted site. Similarly, 55.21 mg/kg Cu, 516.4 mg/kg Fe, 3196 mg/kg Mn, and 154 mg/kg Zn were recorded at an unpolluted site 19 km upwind. The concentration of Cu and Fe reduced significantly with increasing distance, while Mn and Zn increased significantly. It was further established that B. longifolia leaves accumulated Mn (× 38) and Zn (× 15) more than their respective total concentration in the soil. The concentrations of Cu and Fe found in leaves near the mine, as well as the Mn concentration in leaves across the study sites, could be stressful for B. longifolia tree growth.

Transport, functions, and interaction of calcium and manganese in plant organellar compartments

Calcium (Ca2+) and manganese (Mn2+) are essential elements for plants and have similar ionic radii and binding coordination. They are assigned specific functions within organelles, but share many transport mechanisms to cross organellar membranes. Despite their points of interaction, those elements are usually investigated and reviewed separately. This review takes them out of this isolation. It highlights our current mechanistic understanding and points to open questions of their functions, their transport, and their interplay in the endoplasmic reticulum (ER), vesicular compartments (Golgi apparatus, trans-Golgi network, pre-vacuolar compartment), vacuoles, chloroplasts, mitochondria, and peroxisomes. Complex processes demanding these cations, such as Mn2+-dependent glycosylation or systemic Ca2+ signaling, are covered in some detail if they have not been reviewed recently or if recent findings add to current models. The function of Ca2+ as signaling agent released from organelles into the cytosol and within the organelles themselves is a recurrent theme of this review, again keeping the interference by Mn2+ in mind. The involvement of organellar channels [e.g. glutamate receptor-likes (GLR), cyclic nucleotide-gated channels (CNGC), mitochondrial conductivity units (MCU), and two-pore channel1 (TPC1)], transporters (e.g. natural resistance-associated macrophage proteins (NRAMP), Ca2+ exchangers (CAX), metal tolerance proteins (MTP), and bivalent cation transporters (BICAT)], and pumps [autoinhibited Ca2+-ATPases (ACA) and ER Ca2+-ATPases (ECA)] in the import and export of organellar Ca2+ and Mn2+ is scrutinized, whereby current controversial issues are pointed out. Mechanisms in animals and yeast are taken into account where they may provide a blueprint for processes in plants, in particular, with respect to tunable molecular mechanisms of Ca2+ versus Mn2+ selectivity.

Characterization of Metal Tolerance Proteins and Functional Analysis of GmMTP8.1 Involved in Manganese Tolerance in Soybean

Manganese is an essential micronutrient for plant growth but can be toxic to plants when it reaches excessive levels. Although metal tolerance proteins (MTPs), which belong to the cation diffusion facilitator (CDF) family, have been demonstrated to play critical roles in manganese (Mn) tolerance in plants, the characteristics and functions of GmMTP members in the response of soybean (Glycine max) to Mn toxicity have not been documented. In this study, growth inhibition was observed in soybean plants that were exposed to a toxic level of Mn in hydroponics, as reflected by the generation of brown spots, and decreased leaf chlorophyll concentration and plant fresh weight. Subsequent genome-wide analysis resulted in the identification of a total of 14 GmMTP genes in the soybean genome. Among these GmMTPs, 9 and 12 were found to be regulated by excess Mn in leaves and roots, respectively. Furthermore, the function of GmMTP8.1, a Mn-CDF homologue of ShMTP8 identified in the legume Stylosanthes hamata that is involved in Mn detoxification, was characterized. Subcellular localization analysis showed that GmMTP8.1 was localized to the endoplasmic reticulum (ER). Heterologous expression of GmMTP8.1 led to the restoration of growth of the Mn-hypersensitive yeast (Saccharomyces cerevisiae) mutant Δpmr1, which is made defective in Mn transport into the Golgi apparatus by P-type Ca/Mn-ATPase. Furthermore, GmMTP8.1 overexpression conferred tolerance to the toxic level of Mn in Arabidopsis (Arabidopsis thaliana). Under excess Mn conditions, concentrations of Mn in shoots but not roots were decreased in transgenic Arabidopsis, overexpressing GmMTP8.1 compared to the wild type. The overexpression of GmMTP8.1 also led to the upregulation of several transporter genes responsible for Mn efflux and sequestration in Arabidopsis, such as AtMTP8/11. Taken together, these results suggest that GmMTP8.1 is an ER-localized Mn transporter contributing to confer Mn tolerance by stimulating the export of Mn out of leaf cells and increasing the sequestration of Mn into intracellular compartments.

Visualising the ionome in resistant and susceptible plant-pathogen interactions

At the morphological and anatomical levels, the ionome, or the elemental composition of an organism, is an understudied area of plant biology. In particular, the ionomic responses of plant-pathogen interactions are scarcely described, and there are no studies on immune reactions. In this study we explored two X-ray fluorescence (XRF)-based ionome visualisation methods (benchtop- and synchrotron-based micro-XRF [µXRF]), as well as the quantitative inductively coupled plasma optical emission spectroscopy (ICP-OES) method, to investigate the changes that occur in the ionome of compatible and incompatible plant-pathogen interactions. We utilised the agronomically important and comprehensively studied interaction between potato (Solanum tuberosum) and the late blight oomycete pathogen Phytophthora infestans as an example. We used one late blight-susceptible potato cultivar and two resistant transgenic plant lines (only differing from the susceptible cultivar in one or three resistance genes) both in control and P. infestans-inoculated conditions. In the lesions from the compatible interaction, we observed rearrangements of several elements, including a decrease of the mobile macronutrient potassium (K) and an increase in iron (Fe) and manganese (Mn), compared with the tissue outside the lesion. Interestingly, we observed distinctly different distribution patterns of accumulation at the site of inoculation in the resistant lines for calcium (Ca), magnesium (Mg), Mn and silicon (Si) compared to the susceptible cultivar. The results reveal different ionomes in diseased plants compared to resistant plants. Our results demonstrate a technical advance and pave the way for deeper studies of the plant-pathogen ionome in the future.

Manganese toxicity disrupts indole acetic acid homeostasis and suppresses the CO2 assimilation reaction in rice leaves

Despite the essentiality of Mn in terrestrial plants, its excessive accumulation in plant tissues can cause growth defects, known as Mn toxicity. Mn toxicity can be classified into apoplastic and symplastic types depending on its onset. Symplastic Mn toxicity is hypothesised to be more critical for growth defects. However, details of the relationship between growth defects and symplastic Mn toxicity remain elusive. In this study, we aimed to elucidate the molecular mechanisms underlying symplastic Mn toxicity in rice plants. We found that under excess Mn conditions, CO₂ assimilation was inhibited by stomatal closure, and both carbon anabolic and catabolic activities were decreased. In addition to stomatal dysfunction, stomatal and leaf anatomical development were also altered by excess Mn accumulation. Furthermore, indole acetic acid (IAA) concentration was decreased, and auxin-responsive gene expression analyses showed IAA-deficient symptoms in leaves due to excess Mn accumulation. These results suggest that excessive Mn accumulation causes IAA deficiency, and low IAA concentrations suppress plant growth by suppressing stomatal opening and leaf anatomical development for efficient CO₂ assimilation in leaves.

Demonstration gardens with EDTA-washed soil. Part III: Plant growth, soil physical properties and production of safe vegetables

In previous reports large-scale EDTA-based soil washing using ReSoil® technology was demonstrated. In the current study, we established a vegetable garden with nine raised beds (4 × 1 × 0.5 m), three with original (contaminated) soil, three with remediated soil, and three with remediated soil vitalized by addition of vermicompost, earthworms, and rhizosphere inoculum. The garden was managed in 6 rotations between July 2018 and November 2019. Buckwheat was sown first as a green manure followed by spinach, lamb's lettuce, chicory, garlic, onion, leek, lettuce, carrot, kohlrabi and spinach again. Buckwheat growth on the remediated soil was reduced by half. Throughout the gardening process there were no remarkable differences in bulk density, hydraulic conductivity, available water capacity, and aggregate stability of the original and remediated soil. Biomass yield and plant performance, as measured by NDVI, also remained similar regardless of soil treatment. Remediation reduced Pb concentration in edible parts of vegetables from 76 (garlic) to 95% (kohlrabi), Zn concentration from 14 (lettuce) to 76% (first cutting of chicory), and Cd concentration from 33% (carrot) to 91% (leek and second cutting of chicory). The transfer of metals from soil to root and from root to shoot occurred in the order: Pb < Zn < Cd. The bioconcentration of toxic metals in edible plant parts was generally lower in the remediated soils. Application of ReSoil® technology and growing vegetables that exclude metals, especially Cd, has potential for safe food production on remediated soils. Vitalization had little effect on the properties of the remediated soil.

Hysteresis of heavy metals uptake induced in Taraxacum officinale by thiuram

Dandelion (Taraxacum officinale) yields active substances frequently used in herbal medicinal preparations. Its plantations are exposed to fungal plagues which pose a threat to herbal crops. The aim of this study was to evaluate the long time effects of a fungicide thiuram on dandelion growth and photosynthesis. Additionally, the manganese, iron, copper, zinc, cadmium, and lead uptake and transport were also investigated. Plants were cultivated under greenhouse conditions by the pot method in a universal flowering soil. The elements content in soil and plants were determined by the HR-CS FAAS spectrometer. Thiuram concentrations were established by the HPLC. Those analyses showed that almost 80% of thiuram decomposed within two weeks of its application. The photosynthesis indicators suggested, that plants were in good conditions and the fungicide supplementation facilitated plant growth. The latter could be prompted by thiuram acting as a sulfur rich chemical micro fertilizer. The hypothesis, that thiuram significantly affects heavy metals interactions in dandelion was proved by the one-way analysis of variance. Notable, metals uptake did not completely recover after fungicide decomposition for all investigated elements except iron We suggest to define this chemically induced, time-dependent heavy metals migrations in the soil-plant system as hysteresis of heavy metals uptake.

Macrophytes as wastewater treatment agents: Nutrient uptake and potential of produced biomass utilization toward circular economy initiatives

Macrophytes have been widely used as agents in wastewater treatment. The involvement of plants in wastewater treatment cannot be separated from wetland utilization. As one of the green technologies in wastewater treatment plants, wetland exhibits a great performance, especially in removing nutrients from wastewater before the final discharge. It involves the use of plants and consequently produces plant biomasses as treatment byproducts. The produced plant biomasses can be utilized or converted into several valuable compounds, but related information is still limited and scattered. This review summarizes wastewater's nutrient content (macro and micronutrient) that can support plant growth and the performance of constructed wetland (CW) in performing nutrient uptake by using macrophytes as treatment agents. This paper further discusses the potential of the utilization of the produced plant biomasses as bioenergy production materials, including bioethanol, biohydrogen, biogas, and biodiesel. This paper also highlights the conversion of plant biomasses into animal feed, biochar, adsorbent, and fertilizer, which may support clean production and circular economy efforts. The presented review aims to emphasize and explore the utilization of plant biomasses and their conversion into valuable products, which may solve problems related to plant biomass handling during the adoption of CW in wastewater treatment plants.

Analytical Assessment of Bioelements in Various Types of Black Teas from Different Geographical Origins in View of Chemometric Approach

A comprehensive approach to the mineral composition of black teas of different origins was studied using the Flame Atomic Absorption Spectrometry (FAAS) method, supported by chemometric tools including Principal Component Analysis PCA) and Classification and Regression Trees (CART). Significant differences between the teas from seven countries (Japan, Nepal, Kenya, Iran, Sri Lanka, India, and China) were shown. K was the main element determined in all teas, with an average concentration of 11,649 mg/kg, followed by Ca, Mg and Mn. In general, regarding all investigated black teas, the element content was ranked in the following order: K > Ca > Mg > Mn > Fe > Na > Zn > Cu. The applied chemometric methods allowed us to recognize black tea clusters based on their mineral composition and place of cultivation, and allowed us to find correlations between particular elements in black teas. The performed analyses revealed interesting correlations between the concentration of various elements in black teas: K was negatively correlated with Na, Fe, Mn and Cu; K was positively correlated with the content of Ca and Mg. Significant positive correlations between Mn and Fe and Mn and Zn in the studied black tea samples were also revealed. It was shown that mineral composition may be a significant factor regarding the origin of the black tea, not only considering the country, but also the region or province.

A path toward concurrent biofortification and cadmium mitigation in plant-based foods

Millions of people are anemic due to inadequate consumption of foods rich in iron and zinc. Plant-based foods provide most of our dietary nutrients but may also contain the toxic heavy metal cadmium (Cd). A low level of Cd silently enters the body through the diet. Once ingested, Cd may remain for decades. Hence, prolonged intake of Cd-containing foods endangers human health. Research that leads towards micronutrient enrichment and mitigation of Cd in foods has therefore dual significance for human health. The breeding of Cd-tolerant cultivars may enable them to grow on Cd-polluted soils; however, they may not yield Cd-free foods. Conversely, sequestration of Cd in roots can prevent its accumulation in grains, but this mechanism also retains nutrients, hence counteracting biofortification efforts. A specific restriction of the Cd absorption capacity of crops would prevent Cd entry into the plant system while maintaining micronutrient accumulation and may thus be a solution to the dilemma. After recapitulating existing strategies employed for the development of Cd-tolerant and biofortified cultivars, this Viewpoint elaborates alternative approaches based on directed evolution and genome editing strategies for excluding Cd while enriching micronutrients in plant foods, which will concurrently help to eradicate malnutrition and prevent Cd intoxication.

Cotyledon loss of Astragalus membranaceus hindered seedling establishment through mineral element reallocation and carbohydrate depletion

Tissue loss of plants caused by herbivores is very common in nature. As the storage and first photosynthetic organ, the loss of cotyledon severely impacts dicot seedling establishment and the subsequent growth. However, it is still not clear how plants adjust their metabolic strategy in response to cotyledon loss. In this study, we employed ICP-OES, GC and LC-MS to examine the effects of cotyledon removal (RC1: remove one cotyledon, RC2: remove two cotyledon) on mineral element distribution and metabolite changes in a traditional Chinese herbal plant, Astragalus membranaceus. The results showed that cotyledon removal had a greater effect on shoot than root growth. Specifically, RC2 revealed a more serious impact on shoot growth than RC1. Microelement Mn and Na in shoot increased more in RC2 than RC1. Macroelement K and microelement B in root increased in RC2. The metabolite results in shoot showed that sugars related to galactose metabolism reduced while amino acids significantly increased in RC2. In root, sugars related to fructose and mannose metabolism decreased in both RC1 and RC2 while most flavonoids increased in RC2. It can be concluded that cotyledon removal triggered different metabolic strategies in both root and shoot. In shoot, more Mn was absorbed to improve the lowered photosynthetic efficiency. Meanwhile, increased Na may have promoted carbohydrate consumption and amino acid synthesis, thereby maintaining shoot growth. In root, K and B participation in cell division and expansion increased, as well as the delivery and metabolism of carbohydrates, to maintain root system growth.

Metal transporters in organelles and their roles in heavy metal transportation and sequestration mechanisms in plants

Heavy metal toxicity is one of the major concerns for agriculture and health. Accumulation of toxic heavy metals at high concentrations in edible parts of crop plants is the primary cause of disease in humans and cattle. A dramatic increase in industrialization, urbanization, and other high anthropogenic activities has led to the accumulation of heavy metals in agricultural soil, which has consequently disrupted soil conditions and affected crop yield. By now, plants have developed several mechanisms to cope with heavy metal stress. However, not all plants are equally effective in dealing with the toxicity of high heavy metal concentrations. Plants have modified their anatomy, morphophysiology, and molecular networks to survive under changing environmental conditions. Heavy metal sequestration is one of the essential processes evolved by some plants to deal with heavy metals' toxic concentration. Some plants even have the ability to accumulate metals in high quantities in the shoots/organelles without toxic effects. For intercellular and interorganeller metal transport, plants harbor spatially distributed various transporters which mainly help in uptake, translocation, and redistribution of metals. This review discusses different heavy metal transporters in different organelles and their roles in metal sequestration and redistribution to help plants cope with heavy metal stress. A good understanding of the processes at stake helps in developing more tolerant crops without affecting their productivity.

Golgi-localised manganese transporter PML3 regulates Arabidopsis growth through modulating Golgi glycosylation and cell wall biosynthesis

Golgi is a critical compartment for both the reutilisation of the essential micronutrient manganese (Mn) and its detoxification. However, whether Mn plays a role in the Golgi remains to be demonstrated in plants. We characterised the function of PML3, a member of the Unknown Protein Family UPF0016, in Mn transport and the regulation of plant growth, Golgi glycosylation and cell wall biosynthesis in Arabidopsis. We also investigated the relationship of PML3 with NRAMP2, a trans-Golgi network localised Mn transporter. PML3-GFP is preferentially localised in the cis-Golgi. PML3 can transport Mn to rescue the hypersensitivity of yeast mutant Δpmr1 to excess Mn. Two mutant alleles of PML3 displayed reduced plant growth and impaired seed development under Mn-deficient conditions. The pml3 mutants also showed impaired Golgi glycosylation and cell wall biosynthesis under Mn deficiency. Double mutations of PML3 and NRAMP2 showed improved plant growth compared with that of single mutants under Mn deficiency, implying that PML3 and NRAMP2 play opposite roles in the regulation of Golgi Mn levels. Our results suggest that PML3 mediates Mn uptake into the Golgi compartments, which is required for proper protein glycosylation and cell wall biosynthesis under Mn-deficient conditions.

Biophenolic Profile Modulations in Olive Tissues as Affected by Manganese Nutrition

Manganese (Mn) is an essential element that intervenes in several plant metabolic processes. The olive tree, and its fruits and leaves, are known as a source of nutraceuticals since they are rich in biophenols. However, there is still a serious lack of data about biophenolic distribution in olive stems and roots under Mn fertilisation. In this context, our study aimed to examine the effects of Mn fertilisation on the biophenolic profile in the leaves, stems, and roots of the ‘Istarska bjelica’ olive cultivar. The experiment was set up in a greenhouse, during a period of five months, as a random block design consisting of three treatments with varying Mn concentrations in full-strength Hoagland’s nutrient solution (0.2 µM Mn, 12 µM Mn, and 24 µM Mn). The obtained results indicate that the amount of Mn in the examined olive plant tissues was significantly higher under 12 µM Mn and 24 µM Mn treatments compared to that of the 0.2 µM Mn treatment. While the concentration of biophenols varied in roots depending on the compound in question, a strong positive impact of the increased Mn concentration in nutrient solution (12 µM Mn and 24 µM Mn) on the concentrations of the main biophenolic compounds was observed in stems. The concentration of oleuropein in leaves almost doubled at 24 µM Mn, with the highest Mn concentration, as compared to the 0.2 µM Mn treatment. The obtained results led to the conclusion that the supply of Mn could enhance the concentration of some biologically active compounds in olives grown hydroponically, implying a critical need for further investigation of Mn fertilisation practices in the conventional olive farming system.

Polymer-coated manganese fertilizer and its combination with lime reduces cadmium accumulation in brown rice (Oryza sativa L.)

Manganese (Mn) has the potential to reduce cadmium (Cd) uptake by rice; however, the efficiency depends on its soil availability. Therefore, this study designed a slow-release Mn fertilizer by employing a polyacrylate coating. Pot trials were conducted to study the effects of coated-Mn and uncoated-Mn alone or in combination with lime on the dynamics of soil dissolved-Mn and available Cd, and the transportation of Mn and Cd within rice. The results showed that coated-Mn declined the release of Mn until the 7th day of application; however, it consistently supplied more dissolved-Mn than uncoated-Mn. As a result, coated-Mn induced a greater Cd reduction (45.8%) in brown rice than uncoated-Mn (9.7%). The total Cd of rice and its proportion in brown rice were greatly reduced by coated-Mn, indicating the inhibition of root uptake and interior transport of Cd. Additionally, lime addition prominently increased the soil pH and decreased the CaCl₂-extractable Cd (90.1-93.9%). However, since lime reduced the soil dissolved-Mn, downregulated the OsHMA3 expression and upregulated the OsNramp5 expression, brown rice Cd was reduced by only 43.0%. The combined addition of lime and coated-Mn alleviated the liming effect on soil Mn and gene expression in roots, thereby reducing brown rice Cd by 71.5%.

A Test of the Inadvertent Uptake Hypothesis Using Plant Species Adapted to Serpentine Soil

Serpentine soils are a stressful growing environment for plants, largely due to nutrient deficiencies and high concentrations of toxic heavy metals (e.g., Ni). Plants have evolved various adaptations for tolerating these extreme environments, including metal hyperaccumulation into above-ground tissues. However, the adaptive significance of metal hyperaccumulation is a topic of debate, with several non-mutually-exclusive hypotheses under study. For example, the inadvertent uptake hypothesis (IUH) states that heavy metal accumulation is a consequence of an efficient nutrient-scavenging mechanism for plants growing in nutrient-deficient soils. Thus, it is possible that metal hyperaccumulation is simply a byproduct of non-specific ion transport mechanisms allowing plants to grow in nutrient-deficient soils, such as serpentine soils, while simultaneously tolerating other potentially toxic heavy metals. Furthermore, some nutrient needs are tissue-specific, and heavy metal toxicity can be more pronounced in reproductive tissues; thus, studies are needed that document nutrient and metal uptake into vegetative and reproductive plant tissues across species of plants that vary in the degree to which they accumulate soil metals. To test these ideas, we grew nine plant species that are variously adapted to serpentine soils (i.e., Ni-hyperaccumulating endemic, non-hyperaccumulating endemic, indicator, or indifferent) in a common garden greenhouse experiment. All species were grown in control soils, as well as those that were amended with the heavy metal Ni, and then analyzed for macronutrient (Ca, Mg, K, and P), micronutrient (Cu, Fe, Zn, Mn, and Mo), and heavy metal (Cr and Co) concentrations in their vegetative and reproductive organs (leaves, anthers, and pistils). In accordance with the IUH, we found that hyperaccumulators often accumulated higher concentrations of nutrients and metals compared to non-hyperaccumulating species, although these differences were often organ-specific. Specifically, while hyperaccumulators accumulated significantly more K and Co across all organs, Cu was higher in leaves only, while Mn and Zn were higher in anthers only. Furthermore, hyperaccumulators accumulated significantly more Co and Mo across all organs when Ni was added to the soil environment. Our work provides additional evidence in support of the IUH, and contributes to our understanding of serpentine adaptation in plants.

Identifying General Stress in Commercial Tomatoes Based on Machine Learning Applied to Plant Electrophysiology

Automated monitoring of plant health is becoming a crucial component for optimizing agricultural production. Recently, several studies have shown that plant electrophysiology could be used as a tool to determine plant status related to applied stressors. However, to the best of our knowledge, there have been no studies relating electrical plant response to general stress responses as a proxy for plant health. This study models general stress of plants exposed to either biotic or abiotic stressors, namely drought, nutrient deficiencies or infestation with spider mites, using electrophysiological signals acquired from 36 plants. Moreover, in the signal processing procedure, the proposed workflow reuses information from the previous steps, therefore considerably reducing computation time regarding recent related approaches in the literature. Careful choice of the principal parameters leads to a classification of the general stress in plants with more than 80% accuracy. The main descriptive statistics measured together with the Hjorth complexity provide the most discriminative information for such classification. The presented findings open new paths to explore for improved monitoring of plant health.