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Aim: The rate of nitrate (NO3−) uptake and changes in rhizosphere properties were studied growing seedlings of two maize inbred lines differing in nitrogen use efficiency (NUE) in rhizoboxes.Results: Changes in NO3− uptake rates occurred in response to anion addition (induction) in seedlings grown both in hydroponic culture and in soil in rhizoboxes. The characterization of root exudate composition showed a line-specific metabolite profile, which was also affected by NO3− availability. The induction affected respiration, nitrification, ammonification and enzyme activities of the rhizosphere. Furthermore, the composition of rhizosphere bacterial communities of the two maize lines differed suggesting the selective capacity of plants.Conclusions: Overall, results showed a strong and fast modification of rhizospheric soil properties in response to physiological changes in plants caused by fluctuating NO3− availability. [ABSTRACT FROM AUTHOR]

A fully mechanistic dynamical model for plant nitrate uptake is presented. Based on physiological and regulatory pathways and based on physical laws, we form a dynamic system mathematically described by seven differential equations. The model evidences the presence of a short‐term positive feedback on the high‐affinity nitrate uptake, triggered by the presence of nitrate around the roots, which induces its intaking. In the long run, this positive feedback is overridden by two long‐term negative feedback loops which drastically reduces the nitrate uptake capacity. These two negative feedbacks are due to the generation of ammonium and amino acids, respectively, and inhibit the synthesis and the activity of high‐affinity nitrate transporters. This model faithfully predicts the typical spiking behavior of the nitrate uptake, in which an initial strong increase of nitrate absorption capacity is followed by a drop, which regulates the absorption down to the initial value. The model outcome was compared with experimental data and they fit quite nicely. The model predicts that after the initial exposure of the roots with nitrate, the absorption of the anion strongly increases and that, on the contrary, the intensity of the absorption is limited in presence of ammonium around the roots. [ABSTRACT FROM AUTHOR]

A fully mechanistic dynamical model for plant nitrate uptake is presented. Based on physiological and regulatory pathways and based on physical laws, we form a dynamic system mathematically described by seven differential equations. The model evidences the presence of a short‐term positive feedback on the high‐affinity nitrate uptake, triggered by the presence of nitrate around the roots, which induces its intaking. In the long run, this positive feedback is overridden by two long‐term negative feedback loops which drastically reduces the nitrate uptake capacity. These two negative feedbacks are due to the generation of ammonium and amino acids, respectively, and inhibit the synthesis and the activity of high‐affinity nitrate transporters. This model faithfully predicts the typical spiking behavior of the nitrate uptake, in which an initial strong increase of nitrate absorption capacity is followed by a drop, which regulates the absorption down to the initial value. The model outcome was compared with experimental data and they fit quite nicely. The model predicts that after the initial exposure of the roots with nitrate, the absorption of the anion strongly increases and that, on the contrary, the intensity of the absorption is limited in presence of ammonium around the roots. [ABSTRACT FROM AUTHOR]

A search of the term biostimulants on the most renowned scientific online databases such as Web of Science results in more than one thousand documents. Although some reviews have been previously published, there is no unified and comprehensive bibliometric review of the scientific literature related to biostimulants. This study examines the scientific literature on biostimulants from 2000 to February 2022 by conducting a bibliometric analysis of the literature published on the Web of Science database to deepen its evolution, trends, and macroareas to represent a quick reference guide for interdisciplinary researchers. We identify the most productive countries and journals, detect the major research streams and perspectives, and trace overall research development over the years. Furthermore, the results highlight aspects that have had little consideration in the current scientific literature, such as economic assessments of the use of biostimulants and more comprehensive explanations of the molecular mechanisms responsible for their positive effects. [ABSTRACT FROM AUTHOR]

The low bioavailability of nutrients, especially nitrogen (N) and phosphorus (P), is one of the most limiting factors for crop production. In this study, under N- and P-free nutrient solution (-N-P), nodulating white lupin plants developed some nodules and analogous cluster root structures characterized by different morphological, physiological, and molecular responses than those observed upon single nutrient deficiency (strong acidification of external media, a better nutritional status than -N+P and +N-P plants). The multi-elemental analysis highlighted that the concentrations of nutrients in white lupin plants were mainly affected by P availability. Gene-expression analyses provided evidence of interconnections between N and P nutritional pathways that are active to promote N and P balance in plants. The root exudome was mainly characterized by N availability in nutrient solution, and, in particular, the absence of N and P in the nutrient solution triggered a high release of phenolic compounds, nucleosides monophosphate and saponines by roots. These morphological, physiological, and molecular responses result from a close interplay between N and P nutritional pathways. They contribute to the good development of nodulating white lupin plants when grown on N- and P-free media. This study provides evidence that limited N and P availability in the nutrient solution can promote white lupin-Bradyrhizobium symbiosis, which is favourable for the sustainability of legume production. [ABSTRACT FROM AUTHOR]

Abstract: Aim of the present work was to investigate the involvement of plasma membrane (PM) H+-ATPase (E.C. 3.6.3.6) isoforms of cucumber (Cucumis sativus L.) in the response to Fe deficiency. Two PM H+-ATPase cDNAs (CsHA1 and CsHA2) were isolated from cucumber and their expression analysed as a function of Fe nutritional status. Semi-quantitative reverse transcriptase (RT)-PCR and quantitative real-time RT-PCR revealed in Fe-deficient roots an enhanced accumulation of CsHA1 gene transcripts, which were hardly detectable in leaves. Supply of iron to deficient plants caused a decrease in the transcript level of CsHA1. In contrast, CsHA2 transcripts, detected both in roots and leaves, appeared to be unaffected by Fe. This work shows for the first time that a transcriptional regulation of PM H+-ATPase involving a specific isoform occurs in the response to Fe deficiency. [Copyright &y& Elsevier]

Uptake of 14C-sugars and activities of sucrose metabolizing enzymes were determined in order to study the mechanism(s) of sucrose accumulation in developing peach fruit. Mesocarp of young peach fruit contained glucose and fructose but little sucrose. Starting 88 days after anthesis (DAA) the sucrose concentration increased greatly. The mechanism of sucrose accumulation was studied by measuring 14C-sucrose and 14C-glucose uptake rates at three different stages of fruit development, and by assaying weekly the activity of enzymes involved in the hydrolysis and/or synthesis of the soluble sugars. Uptake of 0.5–100 mM 14C-sucrose and 14C-glucose by mesocarp tissue slices showed a complex pattern at the first stage of fruit development (62 DAA). During the subsequent growth stages the pattern of sugar uptake changed and was approximately monophasic at the third stage of fruit development. At 10 mM, glucose was taken up more rapidly than sucrose at the first and second stage of fruit development. Uptake was partially inhibited by the uncoupler carbonylcyanide m-chlorophenylhydrazone (CCCP) at 25 µM. These results, together with the presence of a putative extracellular invertase, suggest an apoplastic route for sucrose uptake which is dependent, at least in part, on energy supply. Activities of sucrose hydrolyzing enzymes (insoluble acid invertase, soluble acid invertase, neutral invertase, sucrose synthase) were high in young fruits and declined sharply with fruit development concomitantly with accumulation of sucrose. The storage of the sugar was not accompanied by a rise in synthetic activities (sucrose synthase, sucrose phosphate synthase), suggesting that sucrose could, at least in part enter the carbohydrate pool directly. [ABSTRACT FROM AUTHOR]

Humic substances are known to positively influence plant growth and nutrition. In particular, the water-extractable fraction of humic substances (WEHS) has been shown to enhance nitrate acquisition, increasing the activity of high affinity nitrate uptake system. However, molecular bases of this physiological response are not clarified so far. Thus, in the present work, the physiological effect of WEHS on nitrate acquisition in maize roots was correlated with changes in the root transcriptomic profile. Results confirmed that WEHS caused a faster induction of a higher capacity to take up nitrate in maize roots. Comparing the root transcriptomic profile of Nitrate - and Nitrate   +   WEHS -treated plants with Control (-N) ones, more than 2000 transcripts appeared to be modulated only in the presence of WEHS. Among these, genes involved in nitrate transport and assimilation ( NRT1s, NRT2s, NAR2.1, NR, GS, GOGAT, CNX, UPM ) were strongly modulated by WEHS. Furthermore, also some genes known to be linked to the nitrogen limitation responses were affected by WEHS, as transcripts coding for transcription factors (as LBD37, NIN-like protein, NFY-A, GRF5 ) and enzymes of hormones’ metabolism. The modulation of these transcripts might play a crucial role in coordinating the induction to nitrate, favouring its uptake and assimilation in WEHS-treated plants. The overexpression of nitrogen assimilatory genes by WEHS might led to an early feedback regulation of the high affinity nitrate transport system, as being operated by N-metabolites. Results of the present work shed further light on the contribution of the organic soil component to the nitrogen use efficiency in crops. [ABSTRACT FROM AUTHOR]

A number of connections and insights are emerging regarding the molecular and physiological basis of Fe and S interplay response of combined Fe and S starvation of durum wheat roots are here presented. Microarray analysis revealed that 128 transcripts were commonly modulated by both single and combined deficiencies, thus representing the “core” set of transcripts involved in the responses both to S and Fe shortage, whereas a total of 509 transcripts were modulated only by the simultaneous deficiency of S and Fe. Interestingly, among these latter, most of the genes of nitrate uptake and assimilation were down-regulated, while those involved into ammonium uptake were up-regulated as confirmed by the decrease in nitrate reductase enzyme activity. Transcripts playing a role into phosphate uptake were down-regulated in agreement with the observed lower P accumulation in roots. Combined deficiency mainly up-regulated transcripts involved with oxidative stress response although the related enzyme activities did not appear to differ significantly. Results allowed the identification of transcripts that are specific as well as those that are shared among single and combined deficiency responses, thus providing a starting point for detailed studies on candidate genes to improve the understanding of the molecular basis of nutrient acquisition. [ABSTRACT FROM AUTHOR]

Background: Under limited iron (Fe) availability maize, a Strategy II plant, improves Fe acquisition through the release of phytosiderophores (PS) into the rhizosphere and the subsequent uptake of Fe-PS complexes into root cells. Occurrence of Strategy-I-like components and interactions with phosphorous (P) nutrition has been hypothesized based on molecular and physiological studies in grasses. Results: In this report transcriptomic analysis (NimbleGen microarray) of Fe deficiency response revealed that maize roots modulated the expression levels of 724 genes (508 up- and 216 down-regulated, respectively). As expected, roots of Fe-deficient maize plants overexpressed genes involved in the synthesis and release of 2'-deoxymugineic acid (the main PS released by maize roots). A strong modulation of genes involved in regulatory aspects, Fe translocation, root morphological modification, primary metabolic pathways and hormonal metabolism was induced by the nutritional stress. Genes encoding transporters for Fe2+ (ZmNRAMP1) and P (ZmPHT1;7 and ZmPHO1) were also up-regulated under Fe deficiency. Fe-deficient maize plants accumulated higher amounts of P than the Fe-sufficient ones, both in roots and shoots. The supply of 1 µM 59Fe, as soluble (Fe-Citrate and Fe-PS) or sparingly soluble (Ferrihydrite) sources to deficient plants, caused a rapid down-regulation of genes coding for PS and Fe(III)-PS transport, as well as of ZmNRAMP1 and ZmPHT1;7. Levels of 32P absorption essentially followed the rates of 59Fe uptake in Fe-deficient plants during Fe resupply, suggesting that P accumulation might be regulated by Fe uptake in maize plants. Conclusions: The transcriptional response to Fe-deficiency in maize roots confirmed the modulation of known genes involved in the Strategy II and revealed the presence of Strategy I components usually described in dicots. Moreover, data here presented provide evidence of a close relationship between two essential nutrients for plants, Fe and P, and highlight a key role played by Fe and P transporters to preserve the homeostasis of these two nutrients in maize plants. [ABSTRACT FROM AUTHOR]

The aim of this work was to assess the impact of a novel P nanofertilizer (P-NF) on P solubility, microbial toxicity, soil respiration rate, soil enzyme activity and soil microbial community composition of two soils with contrasting properties in a laboratory incubation study. From the comparison with a commercial triple superphosphate (TSP), the P-NF induced lower release of soluble P, did not cause microbial toxicity, nor reduced soil respiration. Among the measured enzyme activities involved in C, N, P and S mineralization, only the protease activity was significantly inhibited by the P-NF in both the studied soils. Analysis of soil microbial communities showed no significant impacts on bacteria, fungi and archaea, after 1 and 7 d of incubation. We concluded that the tested novel P-NF could be safely used in agriculture. • A P nanofertilizer (P-NF) was tested for P release and impact on soil microorganisms. • The NF showed lower P solubility, no ecotoxicity, and no reduction of soil respiration of two soils. • Among enzymes involved in C, N, P and S mineralization, only protease activity was inhibited. • No significant short-term effects on the bacteria, fungi and archaea were observed. • The novel P-NF could be considered effective and ecologically safe to be used. [ABSTRACT FROM AUTHOR]

Background: It is well known that in the rhizosphere soluble Fe sources available for plants are mainly represented by a mixture of complexes between the micronutrient and organic ligands such as carboxylates and phytosiderophores (PS) released by roots, as well as fractions of humified organic matter. The use by roots of these three natural Fe sources (Fe-citrate, Fe-PS and Fe complexed to water-extractable humic substances, Fe-WEHS) have been already studied at physiological level but the knowledge about the transcriptomic aspects is still lacking. Results: The 59Fe concentration recorded after 24 h in tissues of tomato Fe-deficient plants supplied with 59Fe complexed to WEHS reached values about 2 times higher than those measured in response to the supply with Fe-citrate and Fe-PS. However, after 1 h no differences among the three Fe-chelates were observed considering the 59Fe concentration and the root Fe(III) reduction activity. A large-scale transcriptional analysis of root tissue after 1 h of Fe supply showed that Fe-WEHS modulated only two transcripts leaving the transcriptome substantially identical to Fe-deficient plants. On the other hand, Fe-citrate and Fe-PS affected 728 and 408 transcripts, respectively, having 289 a similar transcriptional behaviour in response to both Fe sources. Conclusions: The root transcriptional response to the Fe supply depends on the nature of chelating agents (WEHS, citrate and PS). The supply of Fe-citrate and Fe-PS showed not only a fast back regulation of molecular mechanisms modulated by Fe deficiency but also specific responses due to the uptake of the chelating molecule. Plants fed with Fe-WEHS did not show relevant changes in the root transcriptome with respect to the Fe-deficient plants, indicating that roots did not sense the restored cellular Fe accumulation. [ABSTRACT FROM AUTHOR]

Even though urea and nitrate are the two major nitrogen (N) forms applied as fertilizers in agriculture and occur concomitantly in soils, the reciprocal influence of these two N sources on the mechanisms of their acquisition are poorly understood. Therefore, molecular and physiological aspects of urea and nitrate uptake were investigated in maize (Zea mays), a crop plant consuming high amounts of N. In roots, urea uptake was stimulated by the presence of urea in the external solution, indicating the presence of an inducible transport system. On the other hand, the presence of nitrate depressed the induction of urea uptake and, at the same time, the induction of nitrate uptake was depressed by the presence of urea. The expression of about 60,000 transcripts of maize in roots was monitored by microarray analyses and the transcriptional patterns of those genes involved in nitrogen acquisition were analyzed by real-time reverse transcription-PCR (RT-PCR). In comparison with the treatment without added N, the exposure of maize roots to urea modulated the expression of only very few genes, such as asparagine synthase. On the other hand, the concomitant presence of urea and nitrate enhanced the overexpression of genes involved in nitrate transport (NRT2) and assimilation (nitrate and nitrite reductase, glutamine synthetase 2), and a specific response of 41 transcripts was determined, including glutamine synthetase 1-5, glutamine oxoglutarate aminotransferase, shikimate kinase and arogenate dehydrogenase. Also based on the real-time RT-PCR analysis, the transcriptional modulation induced by both sources might determine an increase in N metabolism promoting a more efficient assimilation of the N that is taken up. [ABSTRACT FROM AUTHOR]

Aims: Study of the changes in soil microbial biomass, enzyme activity and the microbial community structure in the rhizosphere of two contrasting maize lines differing in the nitrogen use efficiency (NUE). Methods: The Lo5 and T250 inbred maize characterized by high and low NUE, respectively, were grown in rhizoboxes allowing precise sampling of rhizosphere and bulk soil and solution. We also determined microbial biomass, enzyme activities involved in the C, N, P and S cycles, and the microbial community structure using a phylogenetic group specific PCR-DGGE approach in the rhizosphere and bulk soil of both Lo5 and T250 maize lines. Results: High NUE Lo5 maize induced faster inorganic N depletion in the rhizosphere and larger changes in microbial biomass and enzyme activities than the low NUE T250 maize line. The two maize lines induced differences in the studied microbial groups in the rhizosphere, with the larger modifications induced by the high NUE Lo5 maize line. Conclusions: The Lo5 maize line with higher NUE induced larger changes in soil chemical properties and in the enzyme activity, soil microbial biomass and community structure than the low NUE T250 maize line, probably due to differences in the root exudates of the two maize lines. [ABSTRACT FROM AUTHOR]

In higher plants, NO3− can induce its own uptake and the magnitude of this induction is positively related to the external anion concentration. This phenomenon has been characterized in both herbaceous and woody plants. Here, different adaptation strategies of roots from two maize ( Zea mays L., ZmAGOs) inbred lines differing in nitrogen use efficiency (NUE) and exhibiting different timing of induction were discussed by investigating NO3−-induced changes in their transcriptome. Lo5 line (high NUE) showing the maximum rate of NO3− uptake 4 h after the provision of 200 μmol/L NO3− treatment modulated a higher number of transcripts relative to T250 (low NUE) that peaked after 12 h. The two inbred lines share only 368 transcripts that are modulated by the treatment with NO3− and behaved differently when transcripts involved in anion uptake and assimilation were analyzed. T250 line responded to the NO3− induction modulating this group of genes as reported for several plant species. On the contrary, the Lo5 line did not exhibit during the induction changes in this set of genes. Obtained data suggest the importance of exploring the physiological and molecular variations among different maize genotypes in response to environmental clues like NO3− provision, in order to understand mechanisms underlying NUE. [ABSTRACT FROM AUTHOR]

Plants mainly rely on a mixture of Fe complexes with different organic ligands, like carboxylates and soluble fractions of water-extractable humic substances (WEHSs), to sustain the supply of this micronutrient. It has been demonstrated that the Fe-WEHS complex is more efficiently acquired by plant roots as it enhances functionality of the mechanisms involved in Fe acquisition at the root and leaf levels, allowing a faster recovery of the Fe-deficiency symptoms. The aim of this work is to verify whether this recovery involves also the allocation and accumulation of nutrients other than Fe to and within the leaf tissues. Iron-deficient plants treated with Fe-WEHS recovered more quickly the functionality both to uptake nitrate at the root level and to fixate CO in the leaves than those supplied with Fe-citrate. Concomitantly, Fe-WEHS-treated plants also accumulated other cationic nutrients faster and at a higher extent. Synchrotron 2D-scanning μ-X-ray fluorescence analyses of the leaves revealed that the recovery promotes a change in the allocation of these nutrients from the vascular system (K, Cu, and Zn) or trichomes (Ca and Mn) to the entire leaf blade. Fe-WEHS treatment efficiently promotes the recovery from Fe-deficiency-induced chlorosis with an enhanced allocation of other nutrients into the leaves and promoting their distribution into the entire leaf blade. [ABSTRACT FROM AUTHOR]

The phenomenon of NO[sub 3] [sup -] induction in plant roots has been characterised both in herbaceous and woody plants. Grapevine (Vitis vinifera L.) plants, hydroponically grown, showed an increase in NO[sub 3] [sup -] uptake rate in response to anion treatment for different periods in the nutrient solution after 1 week of NO[sub 3] [sup -] deprivation. The expression profile of the two high-affinity NO[sub 3] [sup -] transporters VvNRT2.4A and VvNRT2.4B, and the gene encoding the accessory protein VvNAR2.2 exhibits a similar trend to that of the anion uptake. The induction, also involving the increase in activity and protein levels of plasma membrane H[sup +]-ATPase, is correlated with the expression profile of two (VvHA2 and VvHA4) out of eight putative plasma membrane H [sup +]-ATPase genes identified in grapevine genome. Understanding the biochemical and molecular determinants of nitrogen nutrition in grapevine is important for the quality of production and environmental protection. The nitrate uptake mechanism was studied in this crop for the first time, focusing on the high-affinity component and the need for energy coupling, highlighting nitrate induction in grapevine. The involvement of the NRT2, NRT3 and plasma membrane H[sup +]-ATPase gene families in nitrate uptake by roots was evaluated. [ABSTRACT FROM AUTHOR]

The aim of this work is to evaluate the capability of tomato plants to use different Fe sources, such as Fe citrate, Fe phytosiderophores, and Fe complexed by a water-extractable humic substances (Fe-WEHS) also in relation to physiological and molecular adaptations induced by these complexes at the root level. Tomato plants acquired higher amounts of Fe from Fe-WEHS than from the other two sources and this phenomenon occurred only when the treatment lasted 24 h. The higher acquisition of Fe from Fe-WEHS than other sources depended on a reductive mechanism and on rhizosphere acidification and appeared to be due neither to a higher apoplastic loading nor to a higher resistance of WEHS to microbial degradation. Supply of the different Fe complexes to deficient plants induced a transient upregulation of Fe(III)-chelate reductase ( LeFRO1) and Fe transporter genes, LeIRT1 and LeIRT2. In Fe-WEHS-fed plants, where a quicker and higher upregulation of these genes was evident, a coordination in the expression of LeFRO1, LeIRT1, and LeIRT2 genes occurred already after 1 h treatment when the amount of Fe acquired by the plants from the three sources was similar. Iron from Fe-WEHS could be efficiently acquired in a mixture of natural Fe complexes possibly occurring in the rhizosphere. This phenomenon is due to an altered expression of Fe uptake-related genes and to the root capacity to create favorable conditions for the micronutrient uptake into the rhizosphere. [ABSTRACT FROM AUTHOR]

It is well known that in the rhizosphere soluble Fe sources available for plants are mainly a mixture of complexes between the micronutrient and organic ligands such as organic acids and phytosiderophores (PS) released by roots, microbial siderophores as well as fractions of humified organic matter. In the present work, mechanisms of Fe acquisition operating at the leaf level of plants fed with different Fe-complexes were investigated at the micro-analytical, physiological and molecular levels. Fe-deficient tomato plants ( Solanum Lycopersicum L., cv. ‘Marmande’) were fed for 24 h with a solution (pH 7.5) containing 1 µM Fe as Fe-PS, Fe-citrate or Fe-WEHS. Thereafter, leaf tissue was used for the visualization of Fe distribution, measurements of Fe content, reduction and uptake, and evaluation of expression of Fe-chelate reductase ( LeFRO1), Fe-transporter ( LeIRT1) and Ferritin ( Ferritin2) genes. Leaf discs isolated from Fe-deficient plants treated for 24 h with Fe-WEHS developed higher rates of translocation, Fe-chelate reduction and 59Fe uptake as compared to plants supplied with Fe-citrate or Fe-PS. Leaves of plants treated with Fe-WEHS also showed higher transcript levels of LeFRO1, LeIRT1 and Ferritin2 genes with respect to plants fed with the other Fe-sources. Data obtained support the idea that the efficient use of Fe complexed to WEHS-like humic fractions involves, at least in part, also the activation of Fe-acquisition mechanisms operating at the leaf level. [ABSTRACT FROM AUTHOR]

White lupin ( Lupinus albus L.) is able to grow on soils with sparingly available phosphate (P) by producing specialized structures called cluster roots. To mobilize sparingly soluble P forms in soils, cluster roots release substantial amounts of carboxylates and concomitantly acidify the rhizosphere. The relationship between acidification and carboxylate exudation is still largely unknown. In the present work, we studied the linkage between organic acids (malate and citrate) and proton exudations in cluster roots of P-deficient white lupin. After the illumination started, citrate exudation increased transiently and reached a maximum after 5 h. This effect was accompanied by a strong acidification of the external medium and alkalinization of the cytosol, as evidenced by in vivo nuclear magnetic resonance (NMR) analysis. Fusicoccin, an activator of the plasma membrane (PM) H+-ATPase, stimulated citrate exudation, whereas vanadate, an inhibitor of the H+-ATPase, reduced citrate exudation. The burst of citrate exudation was associated with an increase in expression of the LHA1 PM H+-ATPase gene, an increased amount of H+-ATPase protein, a shift in pH optimum of the enzyme and post-translational modification of an H+-ATPase protein involving binding of activating 14-3-3 protein. Taken together, our results indicate a close link in cluster roots of P-deficient white lupin between the burst of citrate exudation and PM H+-ATPase-catalysed proton efflux. [ABSTRACT FROM AUTHOR]

Abstract: The impact of flavonoids released by phosphorus-deficient white lupin roots on inorganic P and soil microorganisms is largely unknown. We report that flavonoids isolated from white lupin roots mobilized inorganic phosphorus and decreased soil microbial respiration, citrate mineralization, and soil phosphohydrolase activities, but did not reduce the soil ATP content. The results suggest that white lupin''s release of flavonoids into the rhizosphere plays a significant role in its efficient P-acquisition strategy by solubilizing Fe-bound P and by limiting the microbial mineralization of citrate. [Copyright &y& Elsevier]

The effect of a low-molecular weight, water-extractable fraction of humic substances (WEHS) derived from sphagnum peat on post-embryonic plant development has been studied using Arabidopsis roots. Application of humic substances caused an array of changes in root morphology, such as an increase in root hair length and density, formation of ectopic root hairs, and an increase in cell proliferation in the root ground tissue. Application of WEHS affected genes involved in epidermal cell fate specification, suggesting that humic substances can alter developmental programs at an early stage of root cell differentiation. The WEREWOLF and GLABRA2 genes, encoding negative regulators of the root hair cell fate, were significantly down-regulated in the presence of WEHS. Thus, the presence of humic substances caused an ordered remodeling of the root morphology, leading to an increased absorptive surface of the root. Growth in the presence of WEHS did not rescue the phenotype of the root hair defective rhd6 mutant. Analyzing BA3:uidA and DR5:uidA transgenic plants, carrying auxin response elements, and monitoring the expression of the auxin-responsive GH3 gene by real-time RT-PCR did not provide evidence for a WEHS-induced expression of auxin-related genes. It is concluded that WEHS do not exert their effects in an auxin-like manner. [ABSTRACT FROM AUTHOR]

Chlorosis-susceptible fruit trees growing on calcareous soils have been observed to recover in the presence of grass cover species. However, the physiological mechanisms behind this phenomenon are only scarcely understood. An investigation was carried out to verify whether citrus plants can use 59Fe solubilized from a sparingly soluble source by the phytosiderophores (PS) released from graminaceous species. Experiments were performed in hydroponics, using two citrus rootstocks differing in their sensitivity to Fe-deficiency in the field ( Poncirus trifoliata × Citrus paradisi, citrumelo “Swingle”, highly susceptible, and Citrus aurantium L., moderately tolerant). Barley ( Hordeum vulgare L., cv Europa) was used as a model species for PS-releasing graminaceous plants. Fe-deficient citrus plants increased 59Fe-uptake from 59Fe-hydroxide supplied inside a dialysis tube, when Fe-deficient barley plants or PS-containing barley root exudates were present in the uptake solution, this effect being particularly evident for the susceptible rootstock. 59Fe-uptake from 59Fe-hydroxide was also enhanced in Fe-deficient citrumelo “Swingle” in the presence of Fe-deficient Poa pratensis L. and Festuca rubra L., two perennial grasses normally grown in association with fruit trees; no effect was found when Fe-sufficient grasses were employed. The uptake of 59Fe by the susceptible citrus rootstock increased in proportion to the amount of 2′-deoxymugineic acid (DMA), the major PS released by Fe-deficient F. rubra, present in the uptake solution. The beneficial effect of F. rubra or P. pratensis was evident from the leaf re-greening observed when Fe-deficient citrumelo “Swingle” plants were grown in association with the grasses in pots filled with a calcareous soil. Leaf re-greening was not observed when citrumelo “Swingle” plants and yellow stripe 3 ( ys3) maize ( Zea mays L.) mutant plants, unable to release PS, were co-cultivated in pots filled with calcareous soil, unless exogenous PS were added to the soil. Results indicate that graminaceous cover species can improve the Fe-nutrition of fruit trees grown on calcareous soils by enhancing Fe-availability. [ABSTRACT FROM AUTHOR]

A research was carried out to evaluate the leaves' ability to utilize Fe supplied as a complex with water-extractable humic substances (WEHS) and the long-distance transport of 59Fe applied to sections of fully expanded leaves of intact sunflower (Helianthus annuus L.) plants. Plants were grown in a nutrient solution containing 10 µM Fe(III)-EDDHA (Fe-sufficient plants), with the addition of 10 mM NaHCO3 to induce iron chlorosis (Fe-deficient plants). Fe(III)-WEHS could be reduced by sunflower leaf discs at levels comparable to those observed using Fe(III)-EDTA, regardless of the Fe status. On the other hand, 59Fe uptake rate by leaf discs of green and chlorotic plants was significantly lower in Fe-WEHS-treated plants, possibly suggesting the effect of light on photochemical reduction of Fe-EDTA. In the experiments with intact plants, 59Fe-labeled Fe-WEHS or Fe-EDTA were applied onto a section of fully expanded leaves. Irrespective of Fe nutritional status, 59Fe uptake was significantly higher when the treatment was carried out with Fe-EDTA. A significant difference was found in the amount of 59Fe translocated from treated leaf area between green and chlorotic plants. However, irrespective of the Fe nutritional status, no significant difference was observed in the absolute amount of 59Fe translocated to other plant parts when the micronutrient was supplied either as Fe-EDTA or Fe-WEHS. Results show that the utilization of Fe complexed to WEHS by sunflower leaves involves an Fe(III) reduction step in the apoplast prior to its uptake by the symplast of leaf cells and that Fe taken up from the Fe-WEHS complexes can be translocated from fully expanded leaves towards the roots and other parts of the shoot. [ABSTRACT FROM AUTHOR]

An investigation was carried out to assess the effect of nitrate supply on the root plasma membrane (PM) H+‐ATPase of etiolated maize (Zea mays L.) seedlings grown in hydroponics. The treatment induced higher uptake rates of the anion and the expression of a putative high‐affinity nitrate transporter gene (ZmNRT2.1), the first to be identified in maize. Root PM H+‐ATPase activity displayed a similar time‐course pattern as that of net nitrate uptake and investigations were carried out to determine which of the two isoforms reported to date in maize, MHA1 and 2, responded to the treatment. MHA1 was not expressed under the conditions analysed. Genome analysis revealed that MHA2, described as the most abundant form in all maize tissues, was not present in the maize hybrid investigated, but a similar form was found instead and named MHA3. A second gene (named MHA4) was also identified and partially sequenced. Both genes, classified as members of the PM H+‐ATPase subfamily II, responded to nitrate supply, although to different degrees: MHA4, in particular, proved more sensitive than MHA3, with a greater up‐ and down‐regulation in response to the treatment. Increased expression of subfamily II genes resulted in higher steady‐state levels of the enzyme in the root tissues and enhanced ATP‐hydrolysing activity. The results support the idea that greater proton‐pumping activity is required when nitrate inflow increases and suggest that nitrate may be the signal triggering the expression of the two members of PM H+‐ATPase subfamily II. [ABSTRACT FROM PUBLISHER]

In several cultivation areas, grapevine can suffer from Fe chlorosis due to the calcareous and alkaline nature of soils. This plant species has been described to cope with Fe deficiency by activating Strategy I mechanisms, hence increasing root H+ extrusion and ferric-chelate reductase activity. The degree of tolerance exhibited by the rootstocks has been reported to depend on both reactions, but to date, little emphasis has been given to the role played by root exudate extrusion. We studied the behaviour of two hydroponically-grown, tolerant grapevine rootstocks (Ramsey and 140R) in response to Fe deficiency. Under these experimental conditions, the two varieties displayed differences in their ability to modulate morpho-physiological parameters, root acidification and ferric chelate reductase activity. The metabolic profiling of root exudates revealed common strategies for Fe acquisition, including ones targeted at reducing microbial competition for this micronutrient by limiting the exudation of amino acids and sugars and increasing instead that of Fe(III)-reducing compounds. Other modifications in exudate composition hint that the two rootstocks cope with Fe shortage via specific adjustments of their exudation patterns. Furthermore, the presence of 3-hydroxymugenic acid in these compounds suggests that the responses of grapevine to Fe availability are rather diverse and much more complex than those usually described for Strategy I plants. [ABSTRACT FROM AUTHOR]

Nitrogen use efficiency (NUE) of crops is estimated to be less than 50%, with a strong impact on environment and economy. Genotype-dependent ability to cope with N shortage has been only partially explored in maize and, in this context, the comparison of molecular responses of lines with different NUE is of particular interest in order to dissect the key elements underlying NUE. Changes in root transcriptome and NH4+/NO3− uptake rates during growth (after 1 and 4 days) without N were studied in high (Lo5) and low (T250) NUE maize inbred lines. Results suggests that only a small set of transcripts were commonly modulated in both lines in response to N starvation. However, in both lines, transcripts linked to anthocyanin biosynthesis and lateral root formation were positively affected. On the contrary, those involved in root elongation were downregulated. The main differences between the two lines reside in the ability to modulate the transcripts involved in the transport, distribution and assimilation of mineral nutrients. With regard to N mineral forms, only the Lo5 line responded to N starvation by increasing the NH4+ fluxes as supported by the upregulation of a transcript putatively involved in its transport. [ABSTRACT FROM AUTHOR]

Nanomaterials are widely used in medical and pharmaceutical fields, but their application in plant nutrition is at its infancy. Phosphorous (P) and iron (Fe) are essential mineral nutrients limiting in a wide range of conditions the yield of crops. Phosphate and Fe fertilizers to-date on the market display low efficiency (P fertilizers) and low persistence in soil (Fe fertilizers) and negatively affect the environment. In the tentative to overcome these problems, we developed a continuous industrially scalable method to produce FePO4 NPs based on the rapid mixing of salt solutions in a mixing chamber. The process, that included the addition of citrate as capping agent allowed to obtain a stable suspension of NPs over the time. The NPs were tested for their effectiveness as P and Fe sources on two hydroponically grown crop species (cucumber and maize) comparing their effects to those exerted by non-nanometric FePO4 (bulk FePO4). The results showed that FePO4 NPs improved the availability of P and Fe, if compared to the non-nano counterpart, as demonstrated by leaf SPAD indexes, fresh biomasses and P and Fe contents in tissues. The results open a new avenue in the application of nanosized material in the field of plant nutrition and fertilization. [ABSTRACT FROM AUTHOR]

Background: Magnesium (Mg) deficiency causes physiological and molecular responses, already dissected in several plant species. The study of these responses among genotypes showing a different tolerance to the Mg shortage can allow identifying the mechanisms underlying the resistance to this nutritional disorder. To this aim, we compared the physiological and molecular responses (e.g. changes in root metabolome and transcriptome) of two grapevine rootstocks exhibiting, in field, different behaviors with respect to Mg shortage (1103P, tolerant and SO4 susceptible). Results: The two grapevine rootstocks confirmed, in a controlled growing system, their behavior in relation to the tolerance to Mg deficiency. Differences in metabolite and transcriptional profiles between the roots of the two genotypes were mainly linked to antioxidative compounds and the cell wall constituents. In addition, differences in secondary metabolism, in term of both metabolites (e.g. alkaloids, terpenoids and phenylpropanoids) and transcripts, assessed between 1103P and SO4 suggest a different behavior in relation to stress responses particularly at early stages of Mg deficiency. Conclusions: Our results suggested that the higher ability of 1103P to tolerate Mg shortage is mainly linked to its capability of coping, faster and more efficiently, with the oxidative stress condition caused by the nutritional disorder. [ABSTRACT FROM AUTHOR]

Investigates the effects of plasma membrane enzyme activity on the development of iron-deficiency responses in cucumber roots. Marker enzyme activities; Immunoblotting and trypsin treatment of plasma membrane enzymes; Western blot analysis of plasma membrane vesicle proteins.