Iron in leaves: chemical forms, signalling, and in-cell distribution

Tuber quality enhancement via grafting potato onto a wooden goji rootstock through vitalizing multi-pathways

Grafting is applied in Solanaceae to improve growth and quality traits. However, grafting potato onto a wooden goji rootstock is rare. Our study introduces a novel distant grafting technique to investigate potato scion responses, specifically regarding photosynthetic and tuber nutritional quality. The physiological and transcriptomic findings reveal an increase in photosynthesis ratio and carbon fixation in potato leaves after 45 days of grafting due to the upregulation of pivotal genes (PsbA, PPC1, rbcl, and GAPDH). After 95 days of long-term growth, the leaf redox balance was maintained with intensified chlorophyll synthesis, facilitated by the enrichment of crucial genes (GUN4, CHLH, CHLP, CAO) and several light-harvesting proteins (Lhca and Lhcb) in potato leaves. The tubers of grafted plants showed a 6.5% increase in crude protein, 51% in anthocyanin, and lower carbohydrate content. Goji altered the expression of tubers genes involved in assimilatory sulfate reduction, which subsequently affects cysteine-methionine biosynthesis. Furthermore, the tuber transcriptome shows ABA signaling and transcription factors regulate the expression of key biosynthetic genes involved in inducing the secondary metabolites, such as scopoletin and anthocyanin accumulation, which are primary polyphenols in goji. Our innovative grafting approach offers valuable insights into the interactions between woody and herbaceous plants for developing future strategies to modulate growth efficiency and tuber quality in the face of climate challenges and to meet the demand for nutritious food.

In Vitro Collection for the Safe Storage of Grapevine Hybrids and Identification of the Presence of Plasmopara viticola Resistance Genes

This paper focuses on the creation of an in vitro collection of grapevine hybrids from the breeding program of the Kazakh Scientific Research Institute of Fruit Growing and Viticulture and investigates the presence of Plasmopara viticola resistance mediated by Rpv3 and Rpv12 loci. We looked at the optimization of in vitro establishment using either shoots taken directly from field-grown plants or from budwood cuttings forced indoors. We further screened for the presence of endophyte contamination in the initiated explants and optimized the multiplication stage. Finally, the presence of the resistance loci against P. viticola was studied. The shoots initiated from the field-sourced explants were the more effective method of providing plant sources for in vitro initiation once all plant accessions met the goal of in vitro establishment. The concentration of phytohormones and the acidity of the culture medium have a great effect on the multiplication rate and the quality of in vitro stock cultures. Out of 17 grapevine accessions, 16 showed the presence of single or combined resistance loci against P. viticola. The grapevine accessions identified as carrying Rpv3 and Rpv12 alleles represent important genetic resources for disease resistance breeding programs. These accessions may further contribute to the creation of new elite cultivars of economic interest.

Revealing the nuclearity of iron citrate complexes at biologically relevant conditions

Citric acid plays an ubiquitous role in the complexation of essential metals like iron and thus it has a key function making them biologically available. For this, iron(III) citrate complexes are considered among the most significant coordinated forms of ferric iron that take place in biochemical processes of all living organisms. Although these systems hold great biological relevance, their coordination chemistry has not been fully elucidated yet. The current study aimed to investigate the speciation of iron(III) citrate using Mössbauer and electron paramagnetic resonance spectroscopies. Our aim was to gain insights into the structure and nuclearity of the complexes depending on the pH and iron to citrate ratio. By applying the frozen solution technique, the results obtained directly reflect the iron speciation present in the aqueous solution. At 1:1 iron:citrate molar ratio, polynuclear species prevailed forming most probably a trinuclear structure. In the case of citrate excess, the coexistence of several monoiron species with different coordination environments was confirmed. The stability of the polynuclear complexes was checked in the presence of organic solvents.

Iron Nutrition and Its Biochemical Interactions in Plants: Iron Uptake, Biofortification, Bacteria, and Fungi in Focus

Microelements are vital for plant growth and development [...].

Plant Growth Regulation in Cell and Tissue Culture In Vitro

Precise knowledge of all aspects controlling plant tissue culture and in vitro plant regeneration is crucial for plant biotechnologists and their correlated industry, as there is increasing demand for this scientific knowledge, resulting in more productive and resilient plants in the field. However, the development and application of cell and tissue culture techniques are usually based on empirical studies, although some data-driven models are available. Overall, the success of plant tissue culture is dependent on several factors such as available nutrients, endogenous auxin synthesis, organic compounds, and environment conditions. In this review, the most important aspects are described one by one, with some practical recommendations based on basic research in plant physiology and sharing our practical experience from over 20 years of research in this field. The main aim is to help new plant biotechnologists and increase the impact of the plant tissue culture industry worldwide.

Diversification of Plastid Structure and Function in Land Plants

Plastids represent a largely diverse group of organelles in plant and algal cells that have several common features but also a broad spectrum of morphological, ultrastructural, biochemical, and physiological differences. Plastids and their structural and metabolic diversity significantly contribute to the functionality and developmental flexibility of the plant body throughout its lifetime. In addition to the multiple roles of given plastid types, this diversity is accomplished in some cases by interconversions between different plastids as a consequence of developmental and environmental signals that regulate plastid differentiation and specialization. In addition to basic plastid structural features, the most important plastid types, the newly characterized peculiar plastids, and future perspectives in plastid biology are also provided in this chapter.

Plant Iron Research in African Countries: Current "Hot Spots", Approaches, and Potentialities

Plant iron (Fe) nutrition and metabolism is a fascinating and challenging research topic; understanding the role of Fe in the life cycle of plants requires knowledge of Fe chemistry and biochemistry and their impact during development. Plant Fe nutritional status is dependent on several factors, including the surrounding biotic and abiotic environments, and influences crop yield and the nutritional quality of edible parts. The relevance of plant Fe research will further increase globally, particularly for Africa, which is expected to reach 2.5 billion people by 2050. The aim of this review is to provide an updated picture of plant Fe research conducted in African countries to favor its dissemination within the scientific community. Three main research hotspots have emerged, and all of them are related to the production of plants of superior quality, i.e., development of Fe-dense crops, development of varieties resilient to Fe toxicity, and alleviation of Fe deficiency, by means of Fe nanoparticles for sustainable agriculture. An intensification of research collaborations between the African research groups and plant Fe groups worldwide would be beneficial for the progression of the identified research topics.

PSI Photoinhibition and Changing CO2 Levels Initiate Retrograde Signals to Modify Nuclear Gene Expression

Photosystem I (PSI) is a critical component of the photosynthetic machinery in plants. Under conditions of environmental stress, PSI becomes photoinhibited, leading to a redox imbalance in the chloroplast. PSI photoinhibition is caused by an increase in electron pressure within PSI, which damages the iron-sulfur clusters. In this study, we investigated the susceptibility of PSI to photoinhibition in plants at different concentrations of CO2, followed by global gene expression analyses of the differentially treated plants. PSI photoinhibition was induced using a specific illumination protocol that inhibited PSI with minimal effects on PSII. Unexpectedly, the varying CO2 levels combined with the PSI-PI treatment neither increased nor decreased the likelihood of PSI photodamage. All PSI photoinhibition treatments, independent of CO2 levels, upregulated genes generally involved in plant responses to excess iron and downregulated genes involved in iron deficiency. PSI photoinhibition also induced genes encoding photosynthetic proteins that act as electron acceptors from PSI. We propose that PSI photoinhibition causes a release of iron from damaged iron-sulfur clusters, which initiates a retrograde signal from the chloroplast to the nucleus to modify gene expression. In addition, the deprivation of CO2 from the air initiated a signal that induced flavonoid biosynthesis genes, probably via jasmonate production.

Iron transport mechanisms and their evolution focusing on chloroplasts

Iron (Fe) is an essential element for photosynthetic organisms, required for several vital biological functions. Photosynthesis, which takes place in the chloroplasts of higher plants, is the major Fe consumer. Although the components of the root Fe uptake system in dicotyledonous and monocotyledonous plants have been extensively studied, the Fe transport mechanisms of chloroplasts in these two groups of plants have received little attention. This review focuses on the comparative analysis of Fe transport processes in the evolutionary ancestors of chloroplasts (cyanobacteria) with the processes in embryophytes and green algae (Viridiplantae). The aim is to summarize how chloroplasts are integrated into cellular Fe homeostasis and how Fe transporters and Fe transport mechanisms have been modified by evolution.

Iron uptake of etioplasts is independent from photosynthesis but applies the reduction-based strategy

Introduction

Iron (Fe) is one of themost important cofactors in the photosynthetic apparatus, and its uptake by chloroplasts has also been associated with the operation of the photosynthetic electron transport chain during reduction-based plastidial Fe uptake. Therefore, plastidial Fe uptake was considered not to be operational in the absence of the photosynthetic activity. Nevertheless, Fe is also required for enzymatic functions unrelated to photosynthesis, highlighting the importance of Fe acquisition by non-photosynthetic plastids. Yet, it remains unclear how these plastids acquire Fe in the absence of photosynthetic function. Furthermore, plastids of etiolated tissues should already possess the ability to acquire Fe, since the biosynthesis of thylakoid membrane complexes requires a massive amount of readily available Fe. Thus, we aimed to investigate whether the reduction-based plastidial Fe uptake solely relies on the functioning photosynthetic apparatus.

Methods

In our combined structure, iron content and transcript amount analysis studies, we used Savoy cabbage plant as a model, which develops natural etiolation in the inner leaves of the heads due to the shading of the outer leaf layers.

Results

Foliar and plastidial Fe content of Savoy cabbage leaves decreased towards the inner leaf layers. The leaves of the innermost leaf layers proved to be etiolated, containing etioplasts that lacked the photosynthetic machinery and thus were photosynthetically inactive. However, we discovered that these etioplasts contained, and were able to take up, Fe. Although the relative transcript abundance of genes associated with plastidial Fe uptake and homeostasis decreased towards the inner leaf layers, both ferric chelate reductase FRO7 transcripts and activity were detected in the innermost leaf layer. Additionally, a significant NADP(H) pool and NAD(P)H dehydrogenase activity was detected in the etioplasts of the innermost leaf layer, indicating the presence of the reducing capacity that likely supports the reduction-based Fe uptake of etioplasts.

Discussion

Based on these findings, the reduction-based plastidial Fe acquisition should not be considered exclusively dependent on the photosynthetic functions.

Beyond iron-storage pool: functions of plant apoplastic iron during stress

Iron (Fe) is an essential micronutrient for plants, and its storage in the apoplast represents an important Fe pool. Plants have developed various strategies to reutilize this apoplastic Fe pool to adapt to Fe deficiency. In addition, growing evidence indicates that the dynamic changes in apoplastic Fe are critical for plant adaptation to other stresses, including ammonium stress, phosphate deficiency, and pathogen attack. In this review, we discuss and scrutinize the relevance of apoplastic Fe for plant behavior changes in response to stress cues. We mainly focus on the relevant components that modulate the actions and downstream events of apoplastic Fe in stress signaling networks.

Dopamine Inhibits Arabidopsis Growth through Increased Oxidative Stress and Auxin Activity

Like some bacterial species and all animals, plants synthesize dopamine and react to its exogenous applications. Despite dopamine’s widespread presence and activity in plants, its role in plant physiology is still poorly understood. Using targeted experimentation informed by the transcriptomic response to dopamine exposure, we identify three major effects of dopamine. First, we show that dopamine causes hypersensitivity to auxin indole-3-acetic acid by enhancing auxin activity. Second, we show that dopamine increases oxidative stress, which can be mitigated with glutathione. Third, we find that dopamine downregulates iron uptake mechanisms, leading to a decreased iron content—a response possibly aimed at reducing DA-induced oxidative stress. Finally, we show that dopamine-induced auxin sensitivity is downstream of glutathione biosynthesis, indicating that the auxin response is likely a consequence of DA-induced oxidative stress. Collectively, our results show that exogenous dopamine increases oxidative stress, which inhibits growth both directly and indirectly by promoting glutathione-biosynthesis-dependent auxin hypersensitivity.

Functional Analysis of Chloroplast Iron Uptake and Homeostasis

Iron has a crucial role in plastid biology. Iron is a required cofactor for the operation of the photosynthetic functions and other metabolic pathways. Despite the importance of the iron homeostasis in chloroplasts, the functional analysis of the plastidial iron uptake and homeostasis still lack a consensus methodology. Here, we describe a sequence of subsequent techniques that can be applied in functional characterization of proteins involved in iron uptake and incorporation into chloroplasts as well as of the non-transport protein members of the chloroplast iron homeostasis. Since the ferrous iron ligation of bathophenantroline disulfonate is specific and not disrupted by the presence of other transition metals, it offers a simple way for iron quantification both in solubilized chloroplast samples as well as in ferric chelate reductase activity measurements.

The ferroxidases LPR1 and LPR2 control iron translocation in the xylem of Arabidopsis plants

Iron (Fe) deficiency is common in agricultural crops and affects millions of people worldwide. Translocation of Fe in the xylem is a key step for Fe distribution in plants. The mechanism controlling this process remains largely unknown. Here, we report that two Arabidopsis ferroxidases, LPR1 and LPR2, play a crucial and redundant role in controlling Fe translocation in the xylem. LPR1 and LPR2 are mainly localized in the cell walls of xylem vessels and the surrounding cells in roots, leaves, and stems. Knockout of both LPR1 and LPR2 increased the proportion of Fe(II) in the xylem sap, and caused Fe deposition along the vascular bundles especially in the petioles and main veins of leaves, which was alleviated by blocking blue light. The lpr1 lpr2 double mutant displayed constitutive expression of Fe deficiency response genes and overaccumulation of Fe in the roots and mature leaves under Fe-sufficient supply, but Fe deficiency chlorosis in the new leaves and inflorescences under low Fe supply. Moreover, the lpr1 lpr2 double mutant showed lower Fe concentrations in the xylem and phloem saps, and impaired ⁵⁷Fe translocation along the xylem. In vitro assays showed that Fe(III)-citrate, the main form of Fe in xylem sap, is easily photoreduced to Fe(II)-citrate, which is unstable and prone to adsorption by cell walls. Taken together, these results indicate that LPR1 and LPR2 are required to oxidize Fe(II) and maintain Fe(III)-citrate stability and mobility during xylem translocation against photoreduction. Our study not only uncovers an essential physiological role of LPR1 and LPR2 but also reveals a new mechanism by which plants maintain Fe mobility during long-distance translocation in the xylem.

The ferroxidases are critical for Fe(II) oxidation in xylem to ensure a healthy Fe allocation in Arabidopsis thaliana

The long-distance transport of iron (Fe) in the xylem is critical for maintaining systemic Fe homeostasis in plants. The loading form of Fe(II) into the xylem and the long-distance translocation form of Fe(III)-citrate have been identified, but how Fe(II) is oxidized to Fe(III) in the xylem remains unknown. Here, we showed that the cell wall-resided ferroxidases LPR1 and LPR2 (LPRs) were both specifically expressed in the vascular tissues of Arabidopsis thaliana, while disruption of both of them increased Fe(II) in the xylem sap and caused excessive Fe deposition in the xylem vessel wall under Fe-sufficient conditions. As a result, a large amount of Fe accumulated in both roots and shoots, hindering plant growth. Moreover, under low-Fe conditions, LPRs were preferentially induced in old leaves, but the loss of LPRs increased Fe deposition in the vasculature of older leaves and impeded Fe allocation to younger leaves. Therefore, disruption of both LPRs resulted in severer chlorosis in young leaves under Fe-deficient conditions. Taken together, the oxidation of Fe(II) to Fe(III) by LPRs in the cell wall of vasculature plays an important role in xylem Fe allocation, ensuring healthy Fe homeostasis for normal plant growth.

Iron Source and Medium pH Affect Nutrient Uptake and Pigment Content in Petunia hybrida ‘Madness Red’ Cultured In Vitro

Deficiency or excess of iron (Fe) and improper medium pH will inhibit the growth and development of plants, reduce the transfer and utilization of energy from the root to the leaf, and affect the utilization efficiency of inorganic nutrients. The most common symptom of Fe deficiency in plants is chlorosis of the young leaves. In this study, the effects of the iron source, in combination with the medium pH, on plant growth and development, plant pigment synthesis, and nutrient uptake in a model plant Petunia hybrida cultured in vitro were investigated. Iron sulfate (FeSO4·7H2O) or iron chelated with ethylenediaminetetraacetic acid (Fe-EDTA) were supplemented to the MNS (a multipurpose nutrient solution) medium at a concentration of 2.78 mg·L−1 Fe, and the treatment without any Fe was used as the control. The pH of the agar-solidified medium was adjusted to either 4.70, 5.70, or 6.70 before autoclaving. The experiment was carried out in an environmentally controlled culture room with a temperature of 24 °C with 100 µmol·m−2·s−1 photosynthetic photon flux density (PPFD) supplied by white light emitting diodes (LEDs) during a photoperiod of 16 h a day, 18 °C for 8 h a day in the dark, and 70% relative humidity. Regardless of the Fe source including the control, the greatest number of leaves was observed at pH 4.70. However, the greatest lengths of the leaf and root were observed in the treatment with Fe-EDTA combined with pH 5.70. The contents of the chlorophyll, carotenoid, and anthocyanin decreased with increasing medium pH, and contents of these plant pigments were positively correlated with the leaf color. The highest soluble protein content and activities of APX and CAT were observed in the Fe-EDTA under pH 5.70. However, the GPX activity was the highest in the control under pH 4.70. In addition, the highest contents of ammonium (NH4+) and nitrate (NO3−) were measured in the FeSO4-4.7 and EDTA-5.7, respectively. More than that, the treatment of Fe-EDTA combined with pH 5.70 (EDTA-5.7) enhanced nutrient absorption, as proven by the highest tissue contents of P, K, Ca, Mg, Fe, and Mn. The genes’ ferric reduction oxidase 1 and 8 (PhFRO1 and PhFRO8), iron-regulated transporter 1 (PhIRT1), nitrate transporter 2.5 (PhNRT2.5), and deoxyhypusine synthase (PhDHS) were expressed at the highest levels in this treatment as well. In the treatment of EDTA-5.7, the reduction and transport of chelated iron in P. hybrida leaves were enhanced, which also affected the transport of nitrate and catalyzed chlorophyll level in leaves. In conclusion, when the medium pH was adjusted to 5.70, supplementation of chelated Fe-EDTA was more conducive to promoting the growth and development of, and absorption of mineral nutrients by, the plant and the expression of related genes in the leaves.