Sulphur deprivation limits Fe-deficiency responses in tomato plants

The aim of this work was to clarify the role of S supply in the development of the response to Fe depletion in Strategy I plants. In S-sufficient plants, Fe-deficiency caused an increase in the Fe(III)-chelate reductase activity, ⁵⁹Fe uptake rate and ethylene production at root level. This response was associated with increased expression of LeFRO1 [Fe(III)-chelate reductase] and LeIRT1 (Fe²⁺ transporter) genes. Instead, when S-deficient plants were transferred to a Fe-free solution, no induction of Fe(III)-chelate reductase activity and ethylene production was observed. The same held true for LeFRO1 gene expression, while the increase in ⁵⁹Fe²⁺ uptake rate and LeIRT1 gene over-expression were limited. Sulphur deficiency caused a decrease in total sulphur and thiol content; a concomitant increase in ³⁵SO₄ ²⁻ uptake rate was observed, this behaviour being particularly evident in Fe-deficient plants. Sulphur deficiency also virtually abolished expression of the nicotianamine synthase gene (LeNAS), independently of the Fe growth conditions. Sulphur deficiency alone also caused a decrease in Fe content in tomato leaves and an increase in root ethylene production; however, these events were not associated with either increased Fe(III)-chelate reductase activity, higher rates of ⁵⁹Fe uptake or over-expression of either LeFRO1 or LeIRT1 genes. Results show that S deficiency could limit the capacity of tomato plants to cope with Fe-shortage by preventing the induction of the Fe(III)-chelate reductase and limiting the activity and expression of the Fe²⁺ transporter. Furthermore, the results support the idea that ethylene alone cannot trigger specific Fe-deficiency physiological responses in a Strategy I plant, such as tomato.     

Wuxal amino (Bio stimulant) improved growth and physiological performance of tomato plants under salinity stress through adaptive mechanisms and antioxidant potential

In the present study, ameliorative capabilities of wuxal amino (bio stimulant) under salt stress has been investigated through adaptive mechanisms and antioxidant potential in tomato plants. In the experiment, two different concentrations (2 cm L^-1 and 3 cm L^-1) of wuxal amino through foliar application and soil irrigation were applied to the salt (150 mM) treated tomato plants and then morphological traits, photosynthetic pigments, osmolytes, secondary metabolites, oxidative stress and antioxidant enzymes activity were assessed at 60 days after planting. The results revealed that salt stress decreased the growth parameters, photosynthetic pigments, soluble sugars and soluble protein whereas, content of proline, ascorbic acid, total phenols, malondialdehyde, hydrogen peroxide and the activity of antioxidant enzymes activity increased under salt stress. Moreover, Wuxal amino application through foliar or soil to salt stressed plants improved morphological traits, photosynthetic pigments, osmolytes, total phenol and antioxidant enzymes activity. Interestingly, the deleterious impact of salinity on tomato plants were significantly reduced and it can be evident from reduced MDA and H₂O₂ levels. These responses varied with the mode (foliar or soil) of application of Wuxal amino under different concentrations (2 cm L^-1 and 3 cm L^-1). It was concluded that application of Wuxal amino (2 cm L^-1, foliar) and (3 cm L^-1; soil) proved best and could be commercially used as eco-friendly tool for the protection of tomato plants grown under salinity stress.     

Nitrate Reductase Activity in Calcifugous and Calcicolous Tomatoes as Affected by Iron Stress

Calcicolous plants are generally more Fe-efficient than calcifugous plants, because they respond to Fe stress by releasing H-ions and “reductants” from their roots that causes Fe to become available. The objective of our study was to determine if differential response to Fe stress in calcicolous and calcifugous varieties affects nitrate reductase activity. T3238FER (Fe-efficient) and T3238fer (Fe-inefficient) tomato (Lycopersicon esculentum Mill.) cultivars were grown in nutrient solutions supplied with N as NH₄⁺-N plus NO₃^?-N, and as NO₃^?-N only. The chemical reactions induced by Fe stress concomitantly increased nitrate reductase activity in roots and tops of calcicolous, but not in calcifugous tomato. This nitrate reductase activity decreased, however, when Fe was made available to the plants. When Fe stress was eliminated by adding Fe, nitrate reductase activity was comparable in the two cultivars.     

Is ethylene involved in regulation of root ferric reductase activity of dicotyledonous species under iron deficiency?

Most dicotyledonous species respond to Fe deficiency by developing some mechanisms known as Fe-deficiency responses. The role of ethylene in regulation of root ferric reductase activity of wild-type tomato (Lycopersicon esculentum L.) and its mutant Never ripe (Nr), bean (Phaseolus vulgaris L., cv. Bifeng 80-30), and cucumber (Cucumis sativus L., cv. Xintaimici) plants grown in nutrient solution without Fe supply was studied under controlled condition. The results show that: (i) the tomato mutant Nr, which is insensitive to ethylene, presented rapid increase in root ferric reductase activity after omitting Fe from the nutrient solution; (ii) the initial time for increase in root ferric reductase activity was earlier than that in ethylene production after onset of Fe deficiency in the three species; (iii) like cobalt (3 μM Co²⁺), an inhibitor for ethylene production, high concentration of zinc (50 μM Zn²⁺) and copper (5 μM Cu²⁺) also suppressed the increase in root ferric reductase activity of Fe-starved plants; (iv) under Fe-sufficient conditions, indol-3-butylric acid (IBA) stimulated root ferric reductase activity of cucumber and bean plants, and this stimulating effect could not be suppressed by aminoethoxyvinylglycine (AVG, an inhibitor for ethylene synthesis). These results suggested that ethylene might not be directly involved in the regulation of root ferric reductase activity of Fe-deficient dicotyledonous species.     

Plasma membrane-bound NADH: Fe3+-EDTA reductase and iron deficiency in tomato (Lycopersicon esculentum). Is there a Turbo reductase?

The properties of NADH-dependent Fe³⁺-EDTA reductase in plasma membranes (PM) from roots of iron-deficient and -sufficient tomato plants [Lycopersicon esculentum L. (Mill.) cv. Abunda] were examined. Iron deficiency resulted in a 3-fold increase of in vivo root iron-chelate reductase activity with a K_m (Fe³⁺-EDTA) of 230 μM. In purified root PM, average specific activities of ferric chelate reductase of 410 and 254 nmol Fe (mg protein)^?1 min^?1 were obtained for iron-deficient and -sufficient plants, respectively. In both cases, the PM-bound activity showed a pH optimum at pH 6.8. Activity depended on NADH and not on NADPH and on the presence of detergent. The activity was inhibited 40-50% by superoxide dismutase (EC 1.15.1.1) and ca 30% by oxygen. Kinetic analysis of the membrane-bound enzyme revealed a K_m (Fe³⁺-EDTA) of ca 200 μM for both iron-stressed and -sufficient plants. For NADH, K_m values around 230 μM were obtained. The ferric chelate reductase could be solubilised from salt-washed PM with Triton X-100 at a protein:detergent ratio of 1:2.8 (w/w). The Triton-soluble fraction revealed one enzyme-stained band in native polyacrylamide electrophoresis. Although the membranes showed no nitrate reductase (NR; EC 1.6.6.1) activity, anti-spinach NR immunoglobulin G (IgG) recognized a 54 kDa band both in the PM and the Triton-soluble fraction, but not in the enzymatically active material obtained from the native gel. No evidence could be found for the synthesis of a new, biochemically distinct PM-bound ferric chelate reductase under iron deficiency, which might be identified as the so-called Turbo reductase. It is concluded that iron deficiency in tomato induces increased expression of a ferric chelate reductase in root PM, which is already present in iron-sufficient plants and probably also in plants, which do not contain the Turbo reductase, like the grasses. The iron reductase is not identical with the recently reported PM-associated nitrate reductase.     

HmuS from Yersinia pseudotuberculosis is a non-canonical heme-degrading enzyme to acquire iron from heme

Some Gram-negative pathogens import host heme into the cytoplasm and utilize it as an iron source for their survival. We report here that HmuS, encoded by the heme utilizing system (hmu) locus, cleaves the protoporphyrin ring to release iron from heme. A liquid chromatography/mass spectrometry analysis revealed that the degradation products of this reaction are two biliverdin isomers that result from transformation of a verdoheme intermediate. This oxidative heme degradation by HmuS required molecular oxygen and electrons supplied by either ascorbate or NADPH. Electrons could not be directly transferred from NADPH to heme; instead, ferredoxin-NADP⁺ reductase (FNR) functioned as a mediator. Although HmuS does not share amino acid sequence homology with heme oxygenase (HO), a well-known heme-degrading enzyme, absorption and resonance Raman spectral analyses suggest that the heme iron is coordinated with an axial histidine residue and a water molecule in both enzymes. The substitution of axial His196 or distal Arg102 with an alanine residue in HmuS almost completely eliminated heme-degradation activity, suggesting that Fe-His coordination and interaction of a distal residue with water molecules in the heme pocket are important for this activity.     

Effects of nitric oxide and Fe supply on recovery of Fe deficiency induced chlorosis in peanut plants

The effects of nitric oxide (NO) and/or iron (Fe) supplied to Fe deficient plants have been investigated in peanut (Arachis hypogaea L.) grown in Hoagland nutrient solution with or without Fe. Two weeks after Fe deprivation, recovery was induced by addition of 250 μM sodium nitroprusside (SNP, a NO donor) and/or 50 μM Fe (Fe-EDTA) to the Fe deprived (-Fe) nutrient solution. Activities of antioxidant enzymes, leaf chlorophyll (Chl), and active Fe content decreased, whereas activities of H⁺-ATPase, ferric-chelate reductase (FCR), nitrate reductase, and nitric oxide synthase and NO production increased in Fe deficient plants, consequently an Fe chlorosis symptom appeared obviously. In contrast, these symptoms disappeared gradually after two weeks with NO and/or Fe supply, which caused an increases in leaf Chl and active Fe content, especially following by co-treatment with NO and Fe to values found in Fe sufficient plants. Increased activities of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) and decreased accumulation of reactive oxygen species (H₂O₂, O ₂ ^?? ) and malondialdehyde enhanced the ability of resistance to oxidative stress. Supplied NO alone had the obvious effect on increased NO production and on activity of H⁺-ATPase and FCR, whereas root length and root/shoot ratio were most effectively increased by Fe supplied alone. Co-treatment with NO and Fe did the best effects on recovery peanut chlorosis symptoms by significantly increased Chl and available Fe content and adjusted distribution of Fe and other mineral elements (Ca, Mg, and Zn) in both leaves and roots.     

Iron acquisition by plants: the reduction of ferrisiderophores by higher plant NADH: Nitrate reductase

Siderophores are avid Fe³⁺-chelators of microbial origin. Plant roots are colonized by fungi and bacteria which synthesize siderophores, and plants have been shown to metabolize these substances to obtain iron. We have previously shown that nitrate reductase from squash catalyzed the reduction of the ferrisiderophore ferrioxamine B with the subsequent loss of Fe²⁺. Using a spectrophotometric assay which traps Fe²⁺ in a ferrozine complex, we have noted that the substrate diversity of nitrate reductase as a ferrisiderophore reductase includes ferrichrome A, ferrichrome, ferrirhodotorulic acid, ferrischizokinen, and the novel siderophore ferri-‘AAHS’. These reductions were inhibited by polyclonal antibodies against nitrate reductase, but ferrisiderophore reductase activity, as evidenced with ferrirhodotorulic acid, was unaffected by low concentrations of azide. In addition, maximal activity occurred between pH 4 and 5, and appaarent K_m values were approx. 100 μmolar. Thus, we suggest that plant nitrate reductases might be involved in iron assimilation as well as nitrate reduction.     

In vitro and in vivo antimicrobial activity of Xenorhabdus bovienii YL002 against Phytophthora capsici and Botrytis cinerea

Aims: Developing new bio‐agents to control plant disease is desirable. Entomopathogenic bacteria Xenorhabdus spp. have potential antimicrobial activity in agriculture. This work was conducted to evaluate the antimicrobial activity of Xenorhabdus bovienii YL002 on plant pathogenic fungi and oomycete in vitro and the efficiency of this strain to reduce the in vivo incidence of grey mould rot on tomato plants caused by Botrytis cinerea and leaf scorch on pepper plants caused by Phytophthora capsici. Methods and Results: The antimicrobial activity of X. bovienii YL002 was firstly determined on in vitro plant pathogenic fungi and oomycete and then on tomato fruits and plants infected with B. cinerea and pepper plants infected with P. capsici. The cell‐free filtrate of X. bovienii YL002 exhibited highest inhibition effects (>98%) on mycelia growth of P. capsici and B. cinerea. The 50% inhibition concentration (EC₅₀) of the methanol‐extracted bioactive compounds (methanol extract) of the cell‐free filtrate against P. capsici and B. cinerea were 164·83 and 42·16 μg ml^?1. The methanol extract also had a strong effect on the spore germination of P. capsici and B. cinerea, with a EC₅₀ of 70·38 and 69·33 μg ml^?1, respectively. At 1000 μg ml^?1, the methanol extract showed a therapeutic effect of 70·82% and a protective effect of 77·4% against B. cinerea on tomato plants compared with the control. The methanol extract also showed potent effect against P. capsici, with a therapeutic effect of 68·14% and a protective effect of 65·46% on pepper plants compared with the control. Conclusions: Xenorhabdus bovienii YL002 produces antimicrobial compounds with strong activity on plant pathogenic fungi and oomycete and has the potential for controlling grey mould rot of tomato plants and leaf scorch of pepper and could be useful in integrated control against diverse plant pathogenic fungi and oomycete. Significance and Impact of the Study: This study showed the potential that X. bovienii YL002 can be used to control the grey mould rot caused by B. cinerea on tomato plants and leaf scorch caused by P. capsici on pepper plants with the objective to reduce treatments with chemical fungicides.     

小金海棠中三价铁螯合物还原酶基因的表达分析

以从铁高效基因型小金海棠中克隆得到的三价铁螯合物还原酶基因片段为探针,对小金海棠进行Southern杂交。结果显示,三价铁螯合物还原酶基因在小金海棠基因组中为单拷贝。Northern杂交结果表明:在根中,三价铁螯合物还原酶基因的转录受缺铁胁迫诱导,并随缺铁胁迫时间的延长而增强;在叶中,此种基因的转录水平很高,但不受低铁胁迫诱导。根中的三价铁螯合物还原酶活性随缺铁胁迫的时间进程而不断增强,动态变化与其转录水平的变化趋势一致。     

Iron Uptake by Symbiosomes from Soybean Root Nodules

To identify possible iron sources for bacteroids in planta, soybean (Glycine max L. Merr.) symbiosomes (consisting of the bacteroid-containing peribacteroid space enclosed by the peribacteroid membrane [PBM]) and bacteroids were assayed for the ability to transport iron supplied as various ferric [Fe(III)]-chelates. Iron presented as a number of Fe(III)-chelates was transported at much higher rates across the PBM than across the bacteroid membranes, suggesting the presence of an iron storage pool in the peribacteroid space. Pulse-chase experiments confirmed the presence of such an iron storage pool. Because the PBM is derived from the plant plasma membrane, we reasoned that it may possess a ferric-chelate reductase activity similar to that present in plant plasma membrane. We detected ferric-chelate reductase activity associated with the PBM and suggest that reduction of Fe(III) to ferrous [Fe(II)] plays a role in the movement of iron into soybean symbiosomes.     

Copper uptake and translocation in chicory (Cichorium intybus L. cv Grasslands Puna) and tomato (Lycopersicon esculentum Mill. cv Rondy) plants grown in NFT system. II. The role of nicotianamine and histidine in xylem sap copper transport

The effect of rooting media Cu concentration (0.05–20 mg Cu L^-1) on amino acid concentrations and copper speciation in the xylem sap of chicory and tomato plants was measured using 6 week old plants grown in a nutrient film technique system (NFT). Irrespective of the Cu concentration in the nutrient solutions, more than 99.68% and 99.74% of total Cu in tomato and chicory xylem sap was in a bound form. When exposed to high Cu concentrations in the rooting media, amino acid concentrations in the sap increased. Relative to other amino acids, the concentrations of glutamine (Gln), histidine (His), asparagine (Asn), valine (Val), nicotianamine (NA) and proline (Pro) in tomato xylem saps, and His, γ-aminobutyric acid (Gaba), glutamic acid (Glu), leucine (Leu), NA and phenylalanine (Phe) in chicory xylem saps showed the greatest increases. The data indicate that induced synthesis of some free amino acids as a specific and proportional response to Cu treatment. For a single complexation amino acid, the solution Cu²⁺concentration vs pH titration curve for NA at 0.06–0.07 mM was most similar, closely followed by His at 0.5–0.6 mM, to the solution Cu²⁺concentration behaviour in both tomato and chicory xylem sap. It is concluded that increased Cu concentrations in the rooting media induced selective synthesis of certain amino acid which include NA, His, Asn and Gln which have high stability constants with Cu. NA and His have the highest binding constants for Cu and the concentrations of NA and His in chicory and tomato xylem saps can account for all the bound Cu carried in the sap. This revised version was published online in June 2006 with corrections to the Cover Date.