Proliferation Of Root Hairs Research Articles

Physiological effects of Acmella ciliata essential oil on root development of Nicotiana tabacum

In this study, the essential oil of Acmella ciliata, characterized by the presence of significant amounts of spilanthol, α-phellandrene epoxide, and carvotanacetone, was assessed for its influence on the growth of Nicotiana tabacum cv. Xanthi, with the focus primarily on root hair density and primary root length. Following its extraction through microwave-assisted hydrodistillation, the oil was stored at 4°C in amber vials, distinguishable by its unique yellowish-reddish hue, with a refractive index of 1.3478 and a density of 0.847 g cm-3. Among the various dilutions evaluated, the undiluted oil (T3) and the dilution 1.5:0.5 (Oil:EtOH) (T6) demonstrated the most prominent effects. The T3 and T6 treatments markedly enhanced root hair numbers, with T6 additionally promoving root length compared to other treatments. Considering the presence of bioactive alkamides such as spilanthol in the oil, these compounds may have contributed to the observed root growth modulation. When compared against the positive control, affinin, Acmella ciliata essential oil displayed a more pronounced effect on root hair proliferation, while affinin predominantly boosted primary root elongation. The findings highlight the differential effects of the essential oil on specific plant growth parameters.

TARGET OF RAPAMYCIN signaling plays a role in Arabidopsis growth promotion by Azospirillum brasilense Sp245

Azospirillum brasilense colonizes plant roots and improves productivity, but the molecular mechanisms behind its phytostimulation properties remain mostly unknown. Here, we uncover an important role of TARGET OF RAPAMYCIN (TOR) signaling on the response of Arabidopsis thaliana to A. brasilense Sp245. The effect of the bacterium on TOR expression was analyzed in the transgenic line TOR/tor-1, which carries a translational fusion with the GUS reporter protein, and the activity of TOR was assayed thought the phosphorylation of its downstream signaling target S6K protein. Besides, the role of TOR on plant growth in inoculated plants was assessed using the ATP-competitive inhibitor AZD-8055. A decrease in growth of the primary root correlates with an improved branching and absorptive capacity via lateral root and root hair proliferation 6 days after transplant to different concentrations of the bacterium (103 or 105 CFU/mL). Bacterization increased the expression of TOR in shoot and root apexes and promoted phosphorylation of S6K 3 days after transplant. The TOR inhibitor AZD-8055 (1 μM) inhibited plant growth and cell division in root meristems and in lateral root primordia, interfering with the phytostimulation by A. brasilense. In addition, the role of auxin produced by the bacterium to stimulate TOR expression was explored. Noteworthy, the A. brasilense mutant FAJ009, impaired in auxin production, was unable to elicit TOR signaling to the level observed for the wild-type strain, showing the importance of this phyhormone to stimulate TOR signaling. Together, our findings establish an important role of TOR signaling for the probiotic traits elicited by A. brasilense in A. thaliana.

Hydrothermal Extraction of Microalgae Fatty Acid Influences Hydrochar Phytotoxicity

Hydrothermal carbonization (HTC) of microalgae biomass for the production of triacylglycerides is a potentially valuable enabling technology for a waste water treatment-based integrated biorefinery. Here, HTC was used to treat Phaeodactylum tricornutum lipid-rich biomass producing a solid hydrochar from the surface of which adsorbed lipids were removed by hexane extraction following filtration of the solid hydrochar from the process liquid product. Approximately 7% of the input biomass was recovered and transesterified for qualitative and quantitative GCMS analysis for fatty acid methyl esters. Transesterifiable lipids accounted for 94% of the material recovered by solvent extraction. Of the transesterified fatty acids (FA) analysed, the majority was monounsaturated (40.4%) and saturated (37%) C-16 FA. Other FA detected included saturated and monounsaturated C-18 (7.7% and 1.9%) and saturated C-14 (5.3%) and C-25 (1.5%). Thermal analysis (TGA/DSC) of the hydrochar in air showed calorific values of 10.6 MJ kg-1 (delipidated hydrochar) and 3.1 MJ kg-1 (non-delipidated hydrochar) with the latter exhibiting the presence of volatalisable components. Germination trials were conducted to assess the potential phytotoxic effects of these hydrochars. Delipidated hydrochar showed a germination index of 73% suggesting the presence of some phytotoxicity. Non-delipidated hydrochar showed high germination index results of 102% (unground) and 126 % (ground). Taken together with the observation of reduced root hair proliferation in these two test conditions, this suggests the operation of a second phytotoxic effect that is removed by delipidation.

CuO and ZnO Nanoparticles Modify Interkingdom Cell Signaling Processes Relevant to Crop Production.

As the world population increases, strategies for sustainable agriculture are needed to fulfill the global need for plants for food and other commercial products. Nanoparticle formulations are likely to be part of the developing strategies. CuO and ZnO nanoparticles (NPs) offer potential as fertilizers, as they provide bioavailable essential metals, and as pesticides, because of dose-dependent toxicity. Effects of these metal oxide NPs on rhizosphere functions are the focus of this review. These NPs at doses of ≥10 mg metal/kg change the production of key metabolites involved in plant protection in a root-associated microbe, Pseudomonas chlororaphis O6. Altered synthesis occurs in the microbe for phenazines, which function in plant resistance to pathogens, the pyoverdine-like siderophore that enhances Fe bioavailability in the rhizosphere and indole-3-acetic acid affecting plant growth. In wheat seedlings, reprogramming of root morphology involves increases in root hair proliferation (CuO NPs) and lateral root formation (ZnO NPs). Systemic changes in wheat shoot gene expression point to altered regulation for metal stress resilience as well as the potential for enhanced survival under stress commonly encountered in the field. These responses to the NPs cross kingdoms involving the bacteria, fungi, and plants in the rhizosphere. Our challenge is to learn how to understand the value of these potential changes and successfully formulate the NPs for optimal activity in the rhizosphere of crop plants. These formulations may be integrated into developing practices to ensure the sustainability of crop production.

Comparative transcriptome analysis of root hairs proliferation induced by water deficiency in maize

Root hairs functions as water channels and nutritional components transporters in plants. It has been shown to enhance nutrient uptake including phosphate, nitrogen, potassium and calcium. In the experiment, the droughtinduced root hairs were collected. By transcriptome sequence and analysis, the molecular mechanisms and differentially expressed genes related to root hairs growth and development were studied. As a result, by using the HiSeq 2500 platform, 61,872,790 clean reads with 96.23% Q20 bases and 9.28 Gb clean bases with 58.88% GC ratio were obtained for normal root. In contrast with Control group, 67,650,572 clean reads with 96.43% Q20 bases and 10.15 Gb clean bases with 58.3% GC content were obtained for drought-induced root hairs. Totally, 323 differentially expressed genes (DEGs) were identified. Among these DEGs, 109 genes were upregulated and 214 genes were downregulated in drought-induced root hairs. Moreover, metabolic pathway enrichment analysises on the 323 DEGs revealed that totally 10 metabolic pathways were distinctly regulated. In details, alanine, aspartate and alutamate metabolism, galactose metabolism and nitrogen metabolism were significantly upregulated. 7 metabolic pathways such as phenylpropanoid biosynthesis, phenylalanine metabolism, biosynthesis of secondary metabolites and flavonoid biosynthesis were significantly downregulated. Furthermore, functional genes and transcription factors were both found to be involved in drought-induced root hair proliferation. These results will help us understand better the molecular mechanism of maize root hair growth and development.

Cu from dissolution of CuO nanoparticles signals changes in root morphology

Utilization of CuO nanoparticles (NPs) in agriculture, as fertilizers or pesticides, requires understanding of their impact on plant metabolism. Inhibition of root elongation by CuO NPs (>10 mg Cu/kg) occurred in wheat grown in sand. Morphological changes included root hair proliferation and shortening of the zones of division and elongation. The epidermal cells in the compressed root tip were abnormal in shape and file patterning but staining with SYTOX Blue did not reveal a general increase in epidermal cell death. Inhibition of root elongation and proliferation of root hair formation occurred also in response to exogenous indole acetic acid (IAA) supplied through tryptophan metabolism by the root-colonizing bacterium, Pseudomonas chlororaphis O6. Altered root morphology caused by the CuO NPs was likely due to release of Cu from dissolution at the root surface because similar changes occurred with Cu ions (≥6 mg/kg). Use of a fluorescent probe showed the accumulation of nitric oxide (NO), required for root hair formation, was not changed by the NPs. These findings suggested that dissolution of the NPs in the rhizosphere resulted levels of Cu that modified IAA distribution to causing root shortening but permitted NO cell signaling to promote root hair proliferation.

Effects induced by living mulch on rhizosphere interactions in organic artichoke: The cultivar's adaptive strategy

AbstractThe plant root apparatus and the surrounding micro-environment is strongly influenced by specific abiotic and biotic conditions which occur in the plant rhizosphere system. The hypothesis of the reported research was that, in an organically managed horticultural system, the use of living mulch (LM) promotes the arbuscular mycorrhizal fungi (AMF) colonization among neighboring roots, because of the coexistence of different plants roots in confined soil spaces. This effect determines nutrient uptake optimization, although roots belong to different plant species. In the reported 2-yr field experiment (2012–2013), two Italian artichoke cultivars [Cynara cardunculusL. var.scolymus(L.),Jesinocv. andMazzaferratacv.] were intercropped with a LM mixture of plant species and compared with a no LM control. Every year, the effect of LM on artichoke root morphology and AMF colonization was evaluated by scanning electron microscopy, in order to assess abiotic and biotic rhizosphere interactions, as affected by artichoke cultivars. Also the artichoke yield, the soil available phosphorus (P) and rhizosphere P were determined. Results showed that the LM did not reduce yield of both the artichoke cultivars, when compared with the no LM ones. Furthermore, LM has: (i) induced structural changes in artichoke roots by proliferation of root hairs resulting in an increase of effective absorbing surface; (ii) promoted the rhizosphere mycorrhizal infection which improved P uptake. The modified rhizosphere interactions were found to be cultivar-dependent, being recorded only inJesinoartichoke.

The TRANSPLANTA collection of Arabidopsis lines: a resource for functional analysis of transcription factors based on their conditional overexpression

Transcription factors (TFs) are key regulators of gene expression in all organisms. In eukaryotes, TFs are often represented by functionally redundant members of large gene families. Overexpression might prove a means to unveil the biological functions of redundant TFs; however, constitutive overexpression of TFs frequently causes severe developmental defects, preventing their functional characterization. Conditional overexpression strategies help to overcome this problem. Here, we report on the TRANSPLANTA collection of Arabidopsis lines, each expressing one of 949 TFs under the control of a β-estradiol-inducible promoter. Thus far, 1636 independent homozygous lines, representing an average of 2.6 lines for every TF, have been produced for the inducible expression of 634 TFs. Along with a GUS-GFP reporter, randomly selected TRANSPLANTA lines were tested and confirmed for conditional transgene expression upon β-estradiol treatment. As a proof of concept for the exploitation of this resource, β-estradiol-induced proliferation of root hairs, dark-induced senescence, anthocyanin accumulation and dwarfism were observed in lines conditionally expressing full-length cDNAs encoding RHD6, WRKY22, MYB123/TT2 and MYB26, respectively, in agreement with previously reported phenotypes conferred by these TFs. Further screening performed with other TRANSPLANTA lines allowed the identification of TFs involved in different plant biological processes, illustrating that the collection is a powerful resource for the functional characterization of TFs. For instance, ANAC058 and a TINY/AP2 TF were identified as modulators of ABA-mediated germination potential, and RAP2.10/DEAR4 was identified as a regulator of cell death in the hypocotyl-root transition zone. Seeds of TRANSPLANTA lines have been deposited at the Nottingham Arabidopsis Stock Centre for further distribution.

Effect of copper on seed germination, root elongation and shoot elongation of seedlings of commercially cultivated tea varieties

Tea (Camellia sinensis L. (0.) Kuntze) is an economically important plantation crop of India but is prone to attack by several fungal pathogens. Copper based fungicides are being used for decades to control fungal disease in tea which may lead to accumulation of copper in the soil. The aim of the present work was to investigate toxic effect of Cu+2 on seed germination, growth and morphological changes in tea seedlings. Different concentration of copper sulphate was applied on three different commercially cultivated tea varieties (TS-462, TS-520 and TS-463). The effect of different concentrations of copper (0.5 – 8 mM) on seed germination, root elongation and shoot elongation of the tea plant were evaluated. Percent germination was found to decrease progressively with increasing concentrations of Cu+2. Maximum reduction of seed germination was showed by TS-463. Several damaging effects such as reduced root hair proliferation, structural deformation and reduction in length of root and shoot were observed when the germinated seedlings were allowed to grow at higher concentrations of copper solutions. Decrease in the dry mass of both root and shoot were also recorded. The results showed that excess copper have negative effect on germination of tea seeds and subsequent growth of the seedlings.

The insect‐pathogenic fungus Metarhizium robertsii (Clavicipitaceae) is also an endophyte that stimulates plant root development

The soil-inhabiting insect-pathogenic fungus Metarhizium robertsii also colonizes plant roots endophytically, thus showing potential as a plant symbiont. Metarhizium robertsii is not randomly distributed in soils but preferentially associates with the plant rhizosphere when applied in agricultural settings. Root surface and endophytic colonization of switchgrass (Panicum virgatum) and haricot beans (Phaseolus vulgaris) by M. robertsii were examined after inoculation with fungal conidia. We used light and confocal microscopy to ascertain the plant endophytic association with GFP-expressing M. robertsii. Root lengths, root hair density, and lateral roots emerged were also observed. Initially, M. robertsii conidia adhered to, germinated on, and colonized roots. Furthermore, plant roots treated with Metarhizium grew faster and the density of plant root hairs increased when compared with control plants. The onset of plant root hair proliferation was initiated before germination of M. robertsii on the root (within 1-2 d). Plants inoculated with M. robertsii ΔMAD2 (plant adhesin gene) took significantly longer to show root hair proliferation than the wild type. Cell free extracts of M. robertsii did not stimulate root hair proliferation. Longer-term (60 d) associations showed that M. robertsii endophytically colonized cortical cells within bean roots. Metarhizium appeared as a mycelial aggregate within root cortical cells as well as between the intercellular spaces with no apparent damage to the plant. These results suggest that M. robertsii is not only rhizosphere competent but also displays a beneficial endophytic association with plant roots that results in the proliferation of root hairs.

Effect of low-phosphate supply on the root system architecture in Arabidopsis thaliana.

Using Johnson medium,under climatic chamber condition,we detected the change of root architecture under Pi starvation in Arabidopsis. Results showed that the P deficiency inhibited primary root growth,enhanced lateral root concentration and stimulated root hair elongation and root hair proliferation. Moreover,P-starvation decreases the distance from root tip to first lateral root primordium and to first root hair. These changes increased the root specific surface area and distributed the root system closer to soil surface,therefore enhanced the absorption ability of root. P starvation also induced the cell distortion,arrested columella cells development. The kinetic assays on cell length and primary root growth showed a reduction in the primary root elongation and in the cell length when compared with high P-grown plants. CycB1;1:GUS staining suggested that P-starvation destroyed cell division in root meristem. Therefore,the reduced primary root growth was due to the reduced cell elongation and cell division.

Granular Size Effect of Clinoptilolite on Maize Seedlings Growth

Clinoptilolite has been successfully used in growing media for containerized horticultural and floricultural production. However, limited data exist on the effects and interaction between particle size and organic nutrient enrichment of the clinoptilolite. One granular (1-3 mm) and micronized (< 30 µm) clinoptilolite was added to quartz sand, an inert growing substrate, at two doses (0.1% and 3% v/v), without or with addition of wine vinasse as nutrient source at four concentrations (0 mgF×Lsubst-1, 10 mgF×Lsubst-1, 100 mgF×Lsubst-1 and 1000 mgF×Lsubst-1) to evaluate their effect on root growth for five days or the appearance of the second true leaf. Root mucigel was produced in zones where clinoptilolite particles adhered to the root surface. Microscopic analysis of isolated roots showed the increase of secondary roots and the proliferation of root hairs in maize treated with both micronized and granular clinoptilolite, with the contemporary production of root mucigel in zones where zeolite particles adhered to the root surface. It is hypothesized that the enhanced production of mucigel by root cells can favour not only the penetration of roots into the inert substrate, but also the solubilization of organic matter and nutrient availability, in particular when micronized clinoptilolite was present in the growing medium. Therefore, micronized clinoptilolite behaved as a sort of a “physical stimulant” for roots during seedlings, promoting, as a consequence, maize shoot development. Effectively, the highest increase in shoot growth was observed at the highest dose (3% v/v) of micronized zeolite, with the optimal rate of organic fertilizer (100 mgF×Lsubst-1).

Nitric oxide alleviates Fe deficiency-induced stress in Solanum nigrum

The possible involvement of nitric oxide in response of Solanum nigrum seedlings to Fe deficiency was investigated. Iron deficiency resulted in decreased shoot height and chlorophyll content and increased proliferation of root hairs and H2O2, K+ and Ca2+ content. NO donor S-nitrosoglutathione (GSNO) was effective in preventing Fe deficiency-induced increase in content of H2O2 and the ion uptake. The protective effects of GSNO were reversed by cPTIO, an NO scavenger, and tungstate, a nitrate reductase (NR) inhibitor.

Phenotypic Analysis of Arabidopsis Mutants: Ethylene Hormone Response: Figure 1.

Ethylene is one of the five classic plant hormones, having profound effects at all stages of plant growth and development from seed germination to tissue senescence. Tremendous strides have been made in our understanding of the molecular components of the ethylene signal transduction pathway through the identification of mutants having altered responses to ethylene. These mutants were isolated by screening for seedlings with an altered triple-response phenotype, which is manifested upon exposure to high levels of ethylene in the dark. The triple response consists of the formation of a pronounced apical hook, along with a shortening and thickening of both the hypocotyl and root and a proliferation of root hairs. This is unlike an untreated seedling, which normally has a long etiolated hypocotyl, normal root, and no apical hook formation. To carry out an ethylene gas treatment, seedlings must be grown in an enclosed system to maintain the levels of ethylene desired. This protocol describes ethylene treatment of seedlings in wide-mouth Mason jars sealed with canning jar lids.

Nitric oxide accumulation is required for molecular and physiological responses to iron deficiency in tomato roots

Iron is an essential and commonly limited nutrient for plants. To increase the uptake of iron during times of low iron supply, plants, except the grasses, activate a set of physiological and morphological responses in their roots that include iron reduction, soil acidification, Fe(II) transport and proliferation of root hairs. It is not known how root cells sense and transduce the changes that occur after the onset of iron deficiency. This work presents evidence that nitric oxide (NO) is produced rapidly in the root epidermis of tomato plants (Solanum lycopersicum) that are grown in iron-deficient conditions. The scavenging of NO prevented iron-deficiency-induced upregulation of the basic helix-loop-helix transcription factor FER, the ferric-chelate reductase LeFRO1 and the Fe(II) transporter LeIRT1 genes. On the other hand, exogenous application of the NO donor S-nitrosoglutathione enhanced the accumulation of FER, LeFRO1 and LeIRT1 mRNA in roots of iron-deficient plants. The activity of the root ferric-chelate reductase and the proliferation of root hairs induced by iron deficiency were stimulated by NO supplementation and suppressed by NO scavenging. Nitric oxide was ineffective in inducing iron-deficiency responses in the tomato fer mutant, which indicates that the FER protein is necessary to mediate the action of NO. Furthermore, NO supplementation improved plant growth under low iron supply, which suggests that NO is a key component of the regulatory mechanisms that control iron uptake and homeostasis in plants. In summary, the results of this investigation indicate that an increase in NO production is an early response of roots to iron deprivation that contributes to the improvement of iron availability by (i) modulating the expression of iron uptake-related genes and (ii) regulating the physiological and morphological adaptive responses of roots to iron-deficient conditions.

The Effect of Copper Toxicity on the Growth and Root Morphology of Rhodes Grass (Chloris gayana Knuth.) in Resin Buffered Solution Culture

A solution culture experiment was conducted to examine the effect of Cu toxicity on Rhodes grass (Chloris gayana Knuth.), a pasture species used in mine-site rehabilitation. The experiment used dilute, solution culture to achieve external nutrient concentrations, which were representative of the soil solution, and an ion exchange resin to maintain stable concentrations of Cu in solution. Copper toxicity was damaging to plant roots, with symptoms ranging from disruption of the root cuticle and reduced root hair proliferation, to severe deformation of root structure. A reduction in root growth was observed at an external Cu concentration of < 1 μM, with damage evident from an external concentration of 0.2 μM. Critical to the success of this experiment, in quantitatively examining the relationship between external Cu concentration and plant response, was the use of ion exchange resin to buffer the concentration of Cu in solution. After some initial difficulty with pH control, stable concentrations of Cu in solution were maintained for the major period of plant growth. The development of this technique will facilitate future investigations of the effect of heavy metals on plants.

Molecular and biochemical characterization of VR-EILs encoding mung bean ETHYLENE INSENSITIVE3-LIKE proteins.

ETHYLENE INSENSITIVE3 (EIN3) is a transcription factor involved in the ethylene signal transduction pathway in Arabidopsis. Two full-length cDNA clones, pVR-EIL1 and pVR-EIL2, encoding EIN3-LIKE proteins were isolated by reverse transcriptase-polymerase chain reaction and by screening the cDNA library of mung bean (Vigna radiata) hypocotyls. VR-EIL1 and VR-EIL2 share 70% identity and display varying degrees of sequence conservation (39%-65%) with previously isolated EIN3 homologs from Arabidopsis, tobacco (Nicotiana tabacum) and tomato (Lycopersicon esculentum) plants. Gel retardation assay revealed that both VR-EILs were able to interact specifically with optimal binding sequence-1, the recently identified optimal binding sequence for tobacco TEIL, with the binding of VR-EIL2 being more efficient than that of VR-EIL1. Transient expression analysis using a VR-EIL::smGFP fusion gene in onion (Allium cepa) epidermal cells indicated that the VR-EIL proteins were effectively targeted to the nucleus. The fusion protein of VR-EIL2 with GAL4 DNA-binding domain strongly activated transcription of a reporter gene in yeast cells, and an essential domain for transcription-stimulating activity was localized to the amino-terminal acidic region that consists of 50 amino acid residues. In contrast with what has been previously found in EIN3- and TEIL-overexpressing Arabidopsis plants, transgenic tobacco seedlings expressing the VR-EIL genes under the control of cauliflower mosaic virus 35S promoter did not exhibit a constitutive triple response. Instead, they displayed a markedly enhanced proliferation of root hairs, one of the typical ethylene response phenotypes, and increased sensitivity to exogenous ethylene. In addition, the pathogenesis-related (PR) genes encoding beta-1,3-glucanase, osmotin, and PR1 were constitutively expressed in 35S::VR-EIL lines without added ethylene, and were hyperinduced in response to ethylene treatment. These results indicate that VR-EILs are functional in tobacco cells, thereby effectively transactivating the GCC-box-containing PR genes and enhancing sensitivity to ethylene. The possible physiological role of VR-EILs is discussed in the light of the suggestion that they are active components of the ethylene-signaling pathway and their heterologous expressions constitutively turn on a subset of ethylene responses in tobacco plants.

Field Verification of the Barber–Cushman Mechanistic Phosphorus Uptake Model for Maize

A two‐year field study in southeastern South Dakota examined how phosphorus (P) fertilizer applied to a silt loam soil affected the predictability of P uptake in maize (Zea mays L.) using the Barber–Cushman mechanistic P uptake model. Liquid ammonium polyphosphate was applied to provide 0, 10, 20, and 40 kg P ha−1 comparing a concentrated single or double band application, or comparing a concentrated single band to a fertilizer band diluted with water. Soil, plant tissue, and roots were sampled intensely. The model simulation used observed measurements as well as reasonable estimates and assumptions derived from the literature. Predicted P uptake was affected more by soil solution P (C li ) than applied fertilizer P rate. The agreement of observed with predicted P uptake was improved when their regressions were grouped according to C li ranges rather than applied P rates. In 1991, the model predicted 86–90% of observed P uptake at the high C li range (21–77 µmol L−1) but only predicted 23–44% of observed P uptake at the low C li range (1–16 µmol L−1) at the V6 (6th leaf) and V12 (12th leaf) growth stages. Predicted P uptake was much lower than observed at all C li ranges for the simulation period at the R2 (silking) growth stage. Parameters used in simulating maize P uptake were suitable at the high C li values up to the V12 growth stage. At low C li values at the V12 and R2 growth stages, additional soil factors that may affect maize P uptake (i.e., root hair proliferation, mycorrhizal infection, rhizosphere acidification, root architecture) should be included in a simulation model to improve P uptake predictability.

The tomato fer gene encoding a bHLH protein controls iron-uptake responses in roots.

Iron deficiency is among the most common nutritional disorders in plants. To cope with low iron supply, plants with the exception of the Gramineae increase the solubility and uptake of iron by inducing physiological and developmental alterations including iron reduction, soil acidification, Fe(II) transport and root-hair proliferation (strategy I). The chlorotic tomato fer mutant fails to activate the strategy I. It was shown previously that the fer gene is required in the root. Here, we show that fer plants exhibit root developmental phenotypes after low and sufficient iron nutrition indicating that FER acts irrespective of iron supply. Mutant fer roots displayed lower Leirt1 expression than wild-type roots. We isolated the fer gene by map-based cloning and demonstrate that it encodes a protein containing a basic helix-loop-helix domain. fer is expressed in a cell-specific pattern at the root tip independently from iron supply. Our results suggest that FER may control root physiology and development at a transcriptional level in response to iron supply and thus may be the first identified regulator for iron nutrition in plants.

Localization of the plasma membrane H+-ATPase in Fe-deficient cucumber roots by immunodetection

As in several Strategy I plants, iron-deficiency induces in cucumber (Cucumis sativus L.) roots a strong increase in the PM (plasma membrane) H + -ATPase activity with a consequent acidification of the rhizosphere. This increase is mainly due to enhanced synthesis of the enzyme even though other regulatory mechanisms have not yet been ruled out. As it was found in many other dicot species, in Fe-deficient cucumber roots we found a strong development of short lateral roots and swollen root tips; furthermore an enhanced H + extrusion was particularly confined to the subapical swollen zone. Analysis of the root tissue structure by optical and electron microscopy showed a strong proliferation of root hairs at the subapical level and some ultrastructural modifications in the external layers. The structural localization of the PM H + -ATPase studied by immunohistochemistry showed that the increase of the PM protein is not simply due to a greater number of root tips in Fe-deficient plants but also to an increased enzyme content in each tip; moreover, the enhanced H + extrusion seems to be functionally coupled to the root hairs formation. Northern analysis of PM H + -ATPase mRNA extracted from apical root segments using a cDNA probe specific for the PM H + -ATPase of cucumber roots suggests that the modulation of the enzyme synthesis occurs at the transcriptional level.