From element to development: the power of the essential micronutrient boron to shape morphological processes in plants

Boric Acid in Milk Replacer as a Health Enhancer and Growth Promoter for Lambs in the Suckling Period

This study was performed to investigate the effects of boric acid supplementation in milk replacer of lambs in the suckling period on performance, biochemical parameters, the antioxidant system, fecal culture, and expression of some genes. During the suckling period, 60 lambs (4 days old) were randomly given four levels of boric acid (0, 30, 60, and 90 mg/kg body weight) via milk replacer for 57 days. The lambs supplemented with boric acid had a higher weight gain and better feed conversion ratio. Boric acid supplementation quadratically increased serum triglyceride, total protein, alkaline phosphatase, serum antioxidant activity and oxidative stress biomarkers, and fecal flora and decreased IL1β, IL10, iNOS, NF-kB, and TNF-α gene expressions. The effect of boric acid on rumen papilla development could not be determined since the animals were not slaughtered. In conclusion, the use of boric acid to lambs in the suckling period improved the average weekly body weight gain and feed conversion efficiency, positively affected some biochemical parameters, antioxidant system, and intestinal flora, and also affected gene expressions related to the immune system. Boric acid supplementation had a beneficial effect on the health and growth of suckling lambs.

Linking the key physiological functions of essential micronutrients to their deficiency symptoms in plants

In this review, we untangle the physiological key functions of the essential micronutrients and link them to the deficiency responses in plants. Knowledge of these responses at the mechanistic level, and the resulting deficiency symptoms, have improved over the last decade and it appears timely to review recent insights for each of them. A proper understanding of the links between function and symptom is indispensable for an accurate and timely identification of nutritional disorders, thereby informing the design and development of sustainable fertilization strategies. Similarly, improved knowledge of the molecular and physiological functions of micronutrients will be important for breeding programmes aiming to develop new crop genotypes with improved nutrient-use efficiency and resilience in the face of changing soil and climate conditions.

Boron-mediated amelioration of copper toxicity in Citrus sinensis seedlings involved reduced concentrations of copper in leaves and roots and their cell walls rather than increased copper fractions in their cell walls

Little information is available on how boron (B) supplementation affects plant cell wall (CW) remodeling under copper (Cu) excess. 'Xuegan' (Citrus sinensis) seedlings were submitted to 0.5 or 350 µM Cu × 2.5 or 25 µM B for 24 weeks. Thereafter, we determined the concentrations of CW materials (CWMs) and CW components (CWCs), the degree of pectin methylation (DPM), and the pectin methylesterase (PME) activities and PME gene expression levels in leaves and roots, as well as the Cu concentrations in leaves and roots and their CWMs (CWCs). Additionally, we analyzed the Fourier transform infrared (FTIR) and X-ray diffraction (XRD) spectra of leaf and root CWMs. Our findings suggested that adding B reduced the impairment of Cu excess to CWs by reducing the Cu concentrations in leaves and roots and their CWMs and maintaining the stability of CWs, thereby improving leaf and root growth. Cu excess increased the Cu fractions in leaf and root pectin by decreasing DPM due to increased PME activities, thereby contributing to citrus Cu tolerance. FTIR and XRD indicated that the functional groups of the CW pectin, hemicellulose, cellulose, and lignin could bind and immobilize Cu, thereby reducing Cu cytotoxicity in leaves and roots.

Foliar application of iron-lysine to boost growth attributes, photosynthetic pigments and biochemical defense system in canola (Brassica napus L.) under cadmium stress

In the current industrial scenario, cadmium (Cd) as a metal is of great importance but poses a major threat to the ecosystem. However, the role of micronutrient - amino chelates such as iron - lysine (Fe - lys) in reducing Cr toxicity in crop plants was recently introduced. In the current experiment, the exogenous applications of Fe - lys i.e., 0 and10 mg L - 1, were examined, using an in vivo approach that involved plant growth and biomass, photosynthetic pigments, oxidative stress indicators and antioxidant response, sugar and osmolytes under the soil contaminated with varying levels of Cd i.e., 0, 50 and 100 µM using two different varieties of canola i.e., Sarbaz and Pea - 09. Results revealed that the increasing levels of Cd in the soil decreased plant growth and growth-related attributes and photosynthetic apparatus and also the soluble protein and soluble sugar. In contrast, the addition of different levels of Cd in the soil significantly increased the contents of malondialdehyde (MDA) and hydrogen peroxide (H2O2), which induced oxidative damage in both varieties of canola i.e., Sarbaz and Pea - 09. However, canola plants increased the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and non-enzymatic compounds such as phenolic, flavonoid, proline, and anthocyanin, which scavenge the over-production of reactive oxygen species (ROS). Cd toxicity can be overcome by the supplementation of Fe - lys, which significantly increased plant growth and biomass, improved photosynthetic machinery and sugar contents, and increased the activities of different antioxidative enzymes, even in the plants grown under different levels of Cd in the soil. Research findings, therefore, suggested that the Fe - lys application can ameliorate Cd toxicity in canola and result in improved plant growth and composition under metal stress.

Regulation on copper-tolerance in Citrus sinensis seedlings by boron addition: Insights from root exudates, related metabolism, and gene expression

Boron (B) can alleviate Citrus copper (Cu)-toxicity. However, the underlying mechanism by which B mitigates Cu-toxicity is unclear. 'Xuegan' (Citrus sinensis) seedlings were exposed to 0.5 (control) or 350 (Cu-toxicity) µM Cu and 2.5 or 25 µM B for 24 weeks. Thereafter, we investigated the secretion of low molecular weight compounds [LMWCs; citrate, malate, total soluble sugars (TSS), total phenolics (TP), and total free amino acids (TFAA)] by excised roots and their concentrations in roots and leaves, as well as related enzyme gene expression and activities in roots and leaves. Cu-stress stimulated root release of malate and TFAA, which might contribute to citrus Cu-tolerance. However, B-mediated-mitigation of Cu-stress could not be explained in this way, since B addition failed to further stimulate malate and TFAA secretion. Indeed, B addition decreased Cu-stimulated-secretion of malate. Further analysis suggested that Cu-induced-exudation of malate and TFAA was not regulated by their levels in roots. By contrast, B addition increased malate, citrate, and TFAA concentrations in Cu-toxic roots. Cu-toxicity increased TP concentration in 25 μM B-treated leaves, but not in 2.5 μM B-treated leaves. Our findings suggested that the internal detoxification of Cu by LMWCs played a role in B-mediated-alleviation of Cu-toxicity.

Silicon Enhances Brassica napus Tolerance to Boron Deficiency by the Remobilisation of Boron and by Changing the Expression of Boron Transporters

Boron (B) is an essential micronutrient for plants, and its deficiency is a widespread nutritional disorder, particularly in high-demanding crops like Brassica napus. Over the past few decades, silicon (Si) has been shown to mitigate plant nutrient deficiencies of different macro- and micro-nutrients. However, the work on B and Si cross-talk has mostly been focused on the alleviation of B toxicity by Si application. In the present study, we investigated the effect of Si application on rapeseed plants grown hydroponically under long-term B deficiency (20 days at 0.1 µM B). In addition, a B-uptake labelling experiment was conducted, and the expression of the genes involved in B uptake were monitored between 2 and 15 days of B shortage. The results showed that Si significantly improved rapeseed plant growth under B deficiency by 34% and 49% in shoots and roots, respectively. It also increased the expression level of BnaNIP5;1 and BOR1;2c in both young leaves and roots. The uptake labelling experiment showed the remobilization of previously fixed ¹¹B from old leaves to new tissues. This study provides additional evidence of the beneficial effects of Si under conditions lacking B by changing the expression of the BnaNIP5;1 gene and by remobilizing ¹¹B to young tissues.

What Can Boron Deficiency Symptoms Tell Us about Its Function and Regulation?

On the eve of the 100th anniversary of Dr. Warington's discovery of boron (B) as a nutrient essential for higher plants, "boronists" have struggled to demonstrate a role beyond its structural function in cell walls dimerizing pectin molecules of rhamnogalacturonan II (RGII). In this regard, B deficiency has been associated with a plethora of symptoms in plants that include macroscopic symptoms like growth arrest and cell death and biochemical or molecular symptoms that include changes in cell wall pore size, apoplast acidification, or a steep ROS production that leads to an oxidative burst. Aiming to shed light on B functions in plant biology, we proposed here a unifying model integrating the current knowledge about B function(s) in plants to explain why B deficiency can cause such remarkable effects on plant growth and development, impacting crop productivity. In addition, based on recent experimental evidence that suggests the existence of different B ligands other than RGII in plant cells, namely glycolipids, and glycoproteins, we proposed an experimental pipeline to identify putative missing ligands and to determine how they would integrate into the above-mentioned model.

Loss of LEUCINE CARBOXYL METHYLTRANSFERASE 1 interferes with metal homeostasis in Arabidopsis and enhances susceptibility to environmental stresses

The biochemical function of LEUCINE CARBOXYL METHYLTRANSFERASE 1 (LCMT1) is to transfer a methyl group from the methyl donor S-adenosylmethionine (SAM) to the catalytic subunits of PROTEIN PHOSPHATASE 2A (PP2Ac), PP4 and PP6. This post-translational modification by LCMT1 is found throughout eukaryotes from yeast to animals and plants, indicating that its function is essential. However, Arabidopsis with knocked out LCMT1 still grows and develops almost normally, at least under optimal growth conditions. We therefore proposed that the presence of LCMT1 would be important under non-optimal growth conditions and favoured plant survival during evolution. To shed light on the physiological functions of plant LCMT1, phenotypes of the lcmt1 mutant and wild type Arabidopsis were compared under various conditions including exposure to heavy metals, variable chelator concentrations, and increased temperature. The lcmt1 mutant was found to be more susceptible to these environmental changes than wild type and resulted in poor growth of seedlings and rosette stage plants. Element analysis of rosette stage plants mainly showed a difference between the lcmt1 mutant and wild type regarding concentrations of sodium and boron, two-fold up or halved, respectively. In both lcmt1 and wild type, lack of EDTA in the growth medium resulted in enhanced concentration of copper, manganese, zinc and sulphur, and especially lcmt1 growth was hampered by these conditions. The altered phenotype in response to stress, the element and mRNA transcript analysis substantiate that LCMT1 has an important role in metal homeostasis and show that functional LCMT1 is necessary to prevent damages from heat, heavy metals or lack of chelator.

Mineral nutrient dynamics in pecans (Carya illinoensis) 'Mahan' grown in southern China

It is of great significance to study the nutritional characteristics of plants. Further understanding of plant mineral nutrient dynamics can provide theoretical basis for scientific fertilization to improve fruit quality and yield. In this study, eight mineral elements (N, P, K, Ca, Mg, Mn, Zn, B) were measured at regular intervals in leaves and kernels of the pecan "Mahan" planted in southern China. The study discussed the characteristics of mineral nutrient dynamics of pecan through the indicators of concentration, accumulation and cumulative relative rate, a new first proposed indicator, and focused on critical time, intensity, amount of mineral nutrients required in pecan during the fruit developing period, as well as the transfer information of the elements in leaves and kernels. The results show that the mineral nutrient requirements of the leaves and kernels are not identical, with an upward trend in nutrient accumulation within the kernel. The most abundant mineral nutrients in the leaves and kernels were N, K and Ca with Ca being greater than N in leaves. In particular, the concentration of Mn in pecan 'Mahan' is higher than that of other plants, and its Mg content is also higher than that of P in kernels. The dynamic changes of mineral nutrients in walnut showed obvious stages, with a trend of "slow (before mid-July) - fast (mid-July to late August) - slow (late August to late September) - fast (late September to harvest)". The "critical period" of kernels was before mid-July, during which the cumulative relative rates increased rapidly, indicating that the kernels had a great potential to absorb mineral nutrients. Significant accumulation of mineral nutrients occurred from mid-July to late August and late September to the end.

Involvement of NGATHA-Like 1 Transcription Factor in Boron Transport under Low and High Boron Conditions

NGATHA-Like 1 (NGAL1) transcription factor has been identified as a gene regulated through AUG-stop-mediated boron (B)-dependent translation stall; however, its function in B response remains unknown. Here, we show that NGAL1 plays an important role in the maintenance of B transport under both low- and high-B conditions in Arabidopsis thaliana. NGAL1 mRNA is accumulated predominantly in shoots in response to B stress. Independent ngal1 mutants carrying transferred DNA (T-DNA) and Ds-transposon insertions exhibit reduced B concentrations in aerial tissues and produce shortened and reduced number of siliques when B supply is limited. Furthermore, the expression of B transporter genes including nodulin 26-like intrinsic protein 6; 1 (NIP6;1), NIP5;1, NIP7;1 and borate exporter 1 (BOR1) is significantly decreased in ngal1 mutants under low-B condition, suggesting that NGAL1 is required for the transcript accumulation of B transporter genes to facilitate B transport and distribution under B limitation. Under high-B condition, ngal1 mutants exhibit reduced growth and increased B concentration in their shoots. The accumulation of BOR4 mRNA, a B transporter required for B efflux to soil, is significantly reduced in roots of ngal1 plants under high-B condition, suggesting that NGAL1 is involved in the upregulation of BOR4 in response to excess B. Together, our results indicate that NGAL1 is involved in the transcriptional regulation of B transporter genes to facilitate B transport and distribution under both low- and high-B conditions.

Effect of boron toxicity on pollen tube cell wall architecture and the relationship of cell wall components of Castanea mollissima Blume

Boron (B) is essential to plant development. However, excessive B is toxic to plants. This research was performed to evaluate the effects of B toxicity on cell wall architecture of Chinese chestnut (Castanea mollissima Blume) pollen tubes with emphasis on the relationship among pectins, cellulose, and callose. Results showed that 0.8 mM H₃BO₃ inhibited pollen germination and led to abnormal morphology of the pollen tubes. B toxicity also affected the distribution of cell wall components of the pollen tube. In control pollen tube, esterified and acid pectins were distributed unevenly, with the former mainly at the tip and the latter on the distal region. Cellulose was distributed uniformly on the surface with less at the tip; callose reduced gradually from base to sub-tip of the pollen tubes and no callose at the tip of the tube was detected. B toxicity led to the deposition of esterified and acid pectins, cellulose, and callose at the tip of the pollen tube. Results from scanning electron microscopy and transmission electron microscopy showed that B toxicity also altered pollen tube wall ultrastructure. The results from enzymatic treatment illustrated that there existed a close relationship among pectins, cellulose, and callose. B toxicity also altered the relationship. In a word, B toxicity altered deposition and relationship of pectins, cellulose, and callose of pollen tube wall.

Aquaporin-mediated transport: Insights into metalloid trafficking

Metalloids in plants have diverse physiological effects. From being essential to beneficial to toxic, they have significant effects on many physiological processes, influencing crop yield and quality. Aquaporins are a group of membrane channels that have several physiological substrates along with water. Metalloids have emerged as one of their important substrates and they are found to have a substantial role in regulating plant metalloid homeostasis. The present review comprehensively details the multiple isoforms of aquaporins having specificity for metalloids and being responsible for their influx, distribution or efflux. In addition, it also highlights the usage of aquaporin-mediated transport as a selection marker in toxic screens and as tracer elements for closely related metalloids. Therefore, aquaporins, with their imperative contribution to the regulation of plant growth, development and physiological processes, need more research to unravel the metalloid trafficking mechanisms and their future applications.

Mechanistic insight on boron-mediated toxicity in plant vis-a-vis its mitigation strategies: a review

Boron (B) is an essential micronutrient, crucial for the growth and development of crop plants. However, the essential to a toxic range of B in the plant is exceptionally narrow, and symptoms develop with a slight change in its concentration in soil. The morphological and anatomical response, such as leaf chlorosis, stunted growth, and impairment in the xylem and phloem development occurs under B-toxicity. The transport of B in the plant occurs via transpiration stream with the involvement of B-channels and transporter in the roots. The higher accumulation of B in source and sink tissue tends to have lower photosynthetic, chlorophyll content, infertility, failure of pollen tube formation and germination, impairment of cell wall formation, and disruption of membrane systems. Excess B in the plant hinders the uptake of other micronutrients, hormone transport, and metabolite partitioning. B-mediated reactive oxygen species production leads to the synthesis of antioxidant enzymes which help to scavenge these molecules and prevent the plant from further oxidative damage. This review highlights morpho-anatomical, physiological, biochemical, and molecular responses of the plant under B toxicity and thereby might help the researchers to understand the related mechanism and design strategies to develop B tolerant cultivars.

Boron uptake in rice is regulated post-translationally via a clathrin-independent pathway

Uptake of boron (B) in rice (Oryza sativa) is mediated by the Low silicon rice 1 (OsLsi1) channel, belonging to the NOD26-like intrinsic protein III subgroup, and the efflux transporter B transporter 1 (OsBOR1). However, it is unknown how these transporters cooperate for B uptake and how they are regulated in response to B fluctuations. Here, we examined the response of these two transporters to environmental B changes at the transcriptional and posttranslational level. OsBOR1 showed polar localization at the proximal side of both the exodermis and endodermis of mature root region, forming an efficient uptake system with OsLsi1 polarly localized at the distal side of the same cell layers. Expression of OsBOR1 and OsLsi1 was unaffected by B deficiency and excess. However, although OsLsi1 protein did not respond to high B at the protein level, OsBOR1 was degraded in response to high B within hours, which was accompanied with a significant decrease of total B uptake. The high B-induced degradation of OsBOR1 was inhibited in the presence of MG-132, a proteasome inhibitor, without disturbance of the polar localization. In contrast, neither the high B-induced degradation of OsBOR1 nor its polarity was affected by induced expression of dominant-negative mutated dynamin-related protein 1A (OsDRP1AK47A) or knockout of the mu subunit (AP2M) of adaptor protein-2 complex, suggesting that clathrin-mediated endocytosis is not involved in OsBOR1 degradation and polar localization. These results indicate that, in contrast to Arabidopsis thaliana, rice has a distinct regulatory mechanism for B uptake through clathrin-independent degradation of OsBOR1 in response to high B.

Defects in meristem maintenance, cell division, and cytokinin signaling are early responses in the boron deficient maize mutant tassel-less1

Meristems house the stem cells needed for the developmental plasticity observed in adverse environmental conditions and are crucial for determining plant architecture. Meristem development is particularly sensitive to deficiencies of the micronutrient boron, yet how boron integrates into meristem development pathways is unknown. We addressed this question using the boron-deficient maize mutant, tassel-less1 (tls1). Reduced boron uptake in tls1 leads to a progressive impairment of meristem development that manifests in vegetative and reproductive defects. We show, that the tls1 tassel phenotype (male reproductive structure) was partially suppressed by mutations in the CLAVATA1 (CLV1)-ortholog, thick tassel dwarf1 (td1), but not by other mutants in the well characterized CLV-WUSCHEL pathway, which controls meristem size. The suppression of tls1 by td1 correlates with altered signaling of the phytohormone cytokinin. In contrast, mutations in the meristem maintenance gene knotted1 (kn1) enhanced both vegetative and reproductive defects in tls1. In addition, reduced transcript levels of kn1 and cell cycle genes are early defects in tls1 tassel meristems. Our results show that specific meristem maintenance and hormone pathways are affected in tls1, and suggest that reduced boron levels induced by tls1 are the underlying cause of the observed defects. We, therefore, provide new insights into the molecular mechanisms affected by boron deficiency in maize, leading to a better understanding of how genetic and environmental factors integrate during shoot meristem development.

Carbon-11 Radiotracing Reveals Physiological and Metabolic Responses of Maize Grown under Different Regimes of Boron Treatment

In agriculture, boron is known to play a critical role in healthy plant growth. To dissect the role of boron in maize metabolism, radioactive carbon-11 (t_½ 20.4 min) was used to examine the physiological and metabolic responses of 3-week-old B73 maize plants to different levels of boron spanning 0 mM, 0.05 mM, and 0.5 mM boric acid (BA) treatments. Growth behavior, of both shoots and roots, was recorded and correlated to plant physiological responses. ¹¹CO₂ fixation, leaf export of [¹¹C]-photosynthates, and their rate of transport increased systematically with increasing BA concentrations, while the fraction of [¹¹C]-photosynthates delivered to the roots under 0 mM and 0.5 mM BA treatments was lower than under 0.05 mM BA treatment, likely due to changes in root growth. Additionally, solid-phase extraction coupled with gamma counting, radio-fluorescence thin layer chromatography, and radio-fluorescence high-performance liquid chromatography techniques applied to tissue extracts provided insight into the effects of BA treatment on 'new' carbon (as ¹¹C) metabolism. Most notable was the strong influence reducing boron levels had on raising ¹¹C partitioning into glutamine, aspartic acid, and asparagine. Altogether, the growth of maize under different regimes of boron affected ¹¹CO₂ fixation, its metabolism and allocation belowground, and altered root growth. Finally, inductively coupled plasma mass spectrometry provided insight into the effects of BA treatment on plant uptake of other essential nutrients. Here, levels of boron and zinc systematically increased in foliar tissues with increasing BA concentration. However, levels of magnesium, potassium, calcium, manganese, and iron remained unaffected by treatment. The rise in foliar zinc levels with increased BA concentration may contribute to improved ¹¹CO₂ fixation under these conditions.

Microbial enhancement of plant nutrient acquisition

Nutrient availability is a determining factor for crop yield and quality. While fertilization is a major approach for improving plant nutrition, its efficacy can be limited and the production and application of fertilizers frequently bring problems to the environment. A large number of soil microbes are capable of enhancing plant nutrient acquisition and thereby offer environmentally benign solutions to meet the requirements of plant nutrition. Herein we provide summations of how beneficial microbes enhance plant acquisition of macronutrients and micronutrients. We also review recent studies on nutrition-dependent plant-microbe interactions, which highlight the plant's initiative in establishing or deterring the plant-microbe association. By dissecting complex signaling interactions between microbes within the root microbiome, a greater understanding of microbe-enhanced plant nutrition under specific biotic and abiotic stresses will be possible.

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.

Boron Contents of German Mineral and Medicinal Waters and Their Bioavailability in Drosophila melanogaster and Humans

SCOPE

Boron is a trace element that naturally occurs in soil, making mineral and medicinal water important contributors to overall intake. Thus, in a systematic screening, the mean boron concentrations of 381 German mineral and medicinal waters are determined.

METHODS AND RESULTS

Boron concentrations in mineral and medicinal waters are analyzed by inductively coupled mass spectrometry (ICP-MS). Highest boron values find in waters from the southwest of Germany. The boron content of the waters is positively correlated with the concentration of most other analyzed bulk elements, including calcium, potassium, magnesium, and sodium. Mineral waters with either low (7.9 µg L^-1 ), medium (113.9 µg L^-1 ), or high (2193.3 µg L^-1 ) boron content are chosen for boron exposure experiments in fruit flies (Drosophila melanogaster) and humans. In flies, boron-rich mineral water significantly increases boron accumulation, with the accumulation predominantly occurring in the exoskeleton. In humans, serum boron and 24-h urinary boron excretion significantly increase only in response to the intake of boron-rich mineral water.

CONCLUSION

Overall, the current data demonstrate that mineral and medicinal waters vary substantially in the content of boron and that boron-rich mineral water can be used to elevate the boron status, both in flies and humans.

Assessment of trace element concentrations in sediment and vegetation of mesic and arid African savannahs as indicators of ecosystem health

The savannah biome supports unique biodiversity and provides a multitude of ecosystem services. Defining background concentrations for trace elements in the environment is beneficial for the determination of nutrient deficiencies/hotspots and for the management of pollution. Sediment and corresponding vegetation samples were collected around 48 surface water points in two savannah wildlife areas for assessment and comparison of 20 trace elements using ICP-MS. Site-specific and matrix-specific differences were evident for essential B, Co, Cu, Fe, Mn, Mo, Ni, Se and Zn, potentially toxic As, Cd, Cr, Hg, Pb and V and additional elements Al, Ba, Sb, Sn and Sr analysed. Sediment and vegetation from all sampled locations at both sites contained single or multiple potentially toxic elements at various concentrations. Although the presence of all elements can be linked to underlying geology and geochemistry specific to each site, evidence of anthropogenic cause was also evident at both sites. This paper covers the widest range of trace elements assessed in protected terrestrial wildlife reserves in the South African savannah biome to date and highlights the potential for deleterious consequences of trace element contamination of the environment.

Boron: More Than an Essential Element for Land Plants?

Although boron (B) is an element that has long been assumed to be an essential plant micronutrient, this assumption has been recently questioned. Cumulative evidence has demonstrated that the players associated with B uptake and translocation by plant roots include a sophisticated set of proteins used to cope with B levels in the soil solution. Here, we summarize compelling evidence supporting the essential role of B in mediating plant developmental programs. Overall, most plant species studied to date have exhibited specific B transporters with tight genetic coordination in response to B levels in the soil. These transporters can uptake B from the soil, which is a highly uncommon occurrence for toxic elements. Moreover, the current tools available to determine B levels cannot precisely determine B translocation dynamics. We posit that B plays a key role in plant metabolic activities. Its importance in the regulation of development of the root and shoot meristem is associated with plant developmental phase transitions, which are crucial processes in the completion of their life cycle. We provide further evidence that plants need to acquire sufficient amounts of B while protecting themselves from its toxic effects. Thus, the development of in vitro and in vivo approaches is required to accurately determine B levels, and subsequently, to define unambiguously the function of B in terrestrial plants.

Advances in Plant Boron

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Assessment of a 18F-Phenylboronic Acid Radiotracer for Imaging Boron in Maize

Boron (B) is an essential plant micronutrient. Deficiencies of B have drastic consequences on plant development leading to crop yield losses and reductions in root and shoot growth. Understanding the molecular and cellular consequences of B deficiency is challenging, partly because of the limited availability of B imaging techniques. In this report we demonstrate the efficacy of using 4-fluorophenylboronic acid (FPBA) as a B imaging agent, which is a derivative of the B deficiency mimic phenylboronic acid (PBA). We show that radioactively labelled [¹⁸F]FPBA (t_½=110 m) accumulates at the root tip, the root elongation zone and at lateral root initiation sites in maize roots, and also translocates to the shoot where it accumulates along the leaf edges. Treatment of maize seedlings using FPBA and PBA causes a shortened primary root phenotype with absence of lateral roots in a dose-dependent manner. The primary root defects can be partially rescued by the addition of boric acid indicating that PBA can be used to induce B deficiency in maize and that radioactively labelled FPBA can be used to image sites of B demand on a tissue level.