Iron-dependent changes of heavy metals,nicotianamine, and citrate in different plant organs and in the xylem exudate of two tomato genotypes. Nicotianamine as possible copper translocator

The influence of Fe nutrition on the distribution of the heavy metals Fe, Mn, Zn, and Cu and of the heavy metal chelators nicotianamine (NA) and citrate in 6 different shoot and 3 different root parts and in xylem exudate of a NA-containing tomato wild type and its NA-less mutant was investigated. Under the same Fe supply the mutant showed higher Fe, Mn, and Zn concentrations in all organs investigated, with exception of the shoot apex. The Cu concentration in the mutant was only in root parts higher than in the wild type but much lower in leaves. Analyses of xylem exudate showed that Fe, Mn, and Zn were readily translocated by both genotypes from the roots to the shoot at all levels of Fe supply, whereas in the absence of NA, Cu was only poorly transported. Citrate as main Fe chelator in the xylem was present in high concentrations in xylem exudate of the wild type under low Fe supply but in the mutant also at 10 M FeEDTA. NA occurred in xylem exudate of the wild type in concentrations high enough to chelate heavy metal ions.Generally, high Fe supply induced a decrease of Mn, Cu, and Zn concentrations in all organs of the wild type whereas high concentrations were observed in most cases under Fe deficiency. A positive correlation between Fe supply and NA concentration existed only in the shoot apex and in the xylem exudate of wild type plants. From the correlation between Cu and NA translocation and from the high stability constant of the NA-Cu-complex (log K=18.6) it is concluded that NA is a chelator for Cu in the xylem, whereas the translocation of Fe, Mn, and Zn is independent of NA.     

Nicotianamine and histidine/proline are, respectively, the most important copper chelators in xylem sap of Brassica carinata under conditions of copper deficiency and excess

The effect of two different copper conditions (deficiency andexcess) on the amino acid composition in B. carinata xylem sapwas analysed. When the Cu in the nutrient solution was increasedfrom 0.12 to 2.5 or 5 µM, the concentrations of histidine,threonine, glutamine, proline, methionine, and glycine weremuch increased in the xylem sap. When Cu was made deficientin the nutrient solution by decreasing its concentration from0.12 µM to 0 µM, nicotianamine, glutamine, and threoninewere significantly increased in the xylem sap. Aqueous solutionscontaining different Cu–amino acid complexes (simulatedsaps) responded in a specific way to the changes in pH, providinga signature that was used to evaluate, by comparison with thereal xylem sap, the importance of each amino acid in the xylemtransport of Cu. For a single amino acid, the free solutionCu²⁺ concentration versus pH titration curves for histidineand proline were the most similar to that for xylem under Cuexcess. Under Cu deficiency, this Cu concentration versus pHtitration curve appeared to be very similar to that for nicotianamine.It is concluded that increased Cu concentrations induced theselective synthesis of certain amino acids in the sap, of whichhistidine and proline are the most important. Under Cu deficiency,the concentration of nicotianamine was induced the most. Thefact that nicotianamine is induced under Cu starvation and notunder Cu excess, is in contrast to similar studies indicatingspecies-specific reactions. However, the induction of nicotianamineunder Cu starvation is in line with recent molecular data ofthe role of nicotianamine in intracellular Cu delivery. Key words: Brassica carinata, copper, histidine, nicotianamine, proline, xylem sap Received 30 September 2008; Revised 16 October 2008 Accepted 20 October 2008     

Uptake of zinc from chelate-buffered nutrient solutions by wheat genotypes differing in zinc efficiency

Zinc-efficient Triticum aestivum (cv. Warigal) and Zn-inefficientTriticum turgidum conv. durum (cv. Durati) were grown in chelate-buffered,complete nutrient solutions providing either deficient or sufficientZn supply. When transferred to fresh chelatebuffered nutrientsolutions containing a wide range of Zn supplies (0–1.28µmol m^–3 Zn²⁺ activity) for 24–48 h, bothgenotypes increased net Zn uptake linearly with an increasein solution Zn²⁺ activities. Zincefficient Warigal accumulatedZn at a greater rate than Zn-inefficient Durati. The greaterrate of net Zn uptake was observed by plants of both genotypeswhen pretreated at deficient Zn supply. Net loss of Zn to thesolution was higher in plants pretreated with sufficient Znand was inversely related to Zn²⁺ activity in the external solution.When continuously supplied with 40 nmol m^–3 Zn²⁺, netZn uptake by Zn-efficient Warigal was significantly greaterthan that of Zn-inefficient Durati, but the difference diminishedwith plant age. Shoot concentrations of Fe, Mn and Cu were higherwhen plants were grown at deficient than at sufficient Zn supply.The Zn-efficient genotype transported less Zn and Fe to shootsand had higher Fe concentrations in roots than the Zn-inefficientgenotype, supporting the hypothesis that Zn efficiency may beconnected with inefficient transport of Fe from roots to shootsand thus initiation of the Fe-deficiency response resultingin increased release of Zn- and Fe-binding phytosiderophores.It is concluded that differential Zn efficiency of wheat genotypesis at least partly due to a greater ability of efficient genotypesto accumulate Zn. Key words: Chelate-buffering, genotypes, micronutrients, Triticum spp., uptake, zinc efficiency     

Phloem translocation of Fe,Cu, Mn,and Zn in Ricinus seedlings in relation to the concentrations of nicotianamine,an endogenous chelator of divalent metal ions,in different seedling parts

During the first 8 days of germination the Ricinus seedling is supplied with all nutrients by the endosperm via phloem transport. In 4- to 8-days-old seedlings the concentrations and contents of Fe, Cu, Mn and Zn, and nicotianamine (NA) in the endosperm, cotyledons, hypocotyl and roots were estimated. From the data obtained translocation rates and flow profiles for the metals were established. The main sink for Fe, Mn and Zn were the cotyledons whereas Cu was mainly imported into the hypocotyl. Maximum flow rates occurred between days 5 and 7, for Zn between days 6 and 8.The time kinetics of NA and divalent metal ion concentrations and contents are interpreted as co-transport. The role of NA as transport vehicle of micronutrients in the sieve tubes is discussed.     

Evidence of phloem boron transport in response to interrupted boron supply in white lupin (Lupinus albus L. cv. Kiev Mutant) at the reproductive stage

The present study investigates whether previously acquired boron(B) in mature leaves in white lupin can be retranslocated intothe rapidly growing young reproductive organs, in response toshort-term (3 d) interrupted B supply. In a preliminary experimentwith white lupin in soil culture, B concentrations in phloemexudates remained at 300–500 µM, which were substantiallyhigher than those in the xylem sap (10–30 µM). Thehigh ratios of B concentrations in phloem exudates to thosein the xylem sap were close to values published for potassiumin lupin plants. To differentiate ‘old’ B in theshoot from ‘new’ B in the root, an experiment wascarried out in which the plants were first supplied with 20µM ¹¹B (99.34% by weight) in nutrient solution for 48d after germination (DAG) until early flowering and then transferredinto either 0.2 µM or 20 µM ¹⁰B (99.47% by weight)for 3 d. Regardless of the ¹⁰B treatments, significant levelsof ¹¹B were found in the phloem exudates (200–300 µMin 20 µM ¹⁰B and 430 µM in 0.2 µM ¹⁰B treatment)and xylem sap over the three days even without ¹¹B supply tothe root. In response to the 0.2 µM ¹⁰B treatment, thetranslocation of previously acquired ¹¹B in the young (the uppermostthree leaves), matured, and old leaves was enhanced, coincidingwith the rise of ¹¹B in the xylem sap (to >15 µM) andphloem exudates (430 µM). The evidence supports the hypothesisthat previously acquired B in the shoot was recirculated tothe root via the phloem, transferred into the xylem in the root,and transported in the xylem to the shoot. In addition, somepreviously acquired ¹¹B in the leaves may have been translocatedinto the rapidly growing inflorescence. Phloem B transport resultedin the continued net increment of ¹¹B in the flowers over 3d without ¹¹B supply. However, it is still uncertain whetherthe amount of B available for recirculation is adequate to supportreproductive growth until seed maturation. Key words: ¹⁰B, ¹¹B, B recirculation, Lupinus albus L., phloem exudate, xylem sap Received 9 October 2007; Revised 28 November 2007 Accepted 30 November 2007     

Effects of Zinc on Meristem Size and Proximity of Root Hairs and Xylem Elements to the Root Tip in a Zinc-tolerant and a Non-tolerant Cultivar of Festuca rubra L.

A 4 d exposure to zinc (0.1 and 02 µg Zn cm^–3) reducedthe length of the root apical meristem in a Zn-sensitive cultivar(S59) of Festuca rubra L. to a much greater extent than in aZn-tolerant cultivar (Merlin). In S59, Zn treatment also inducedroot hair and xylem formation much closer to the root cap boundarythan in control roots, whereas Merlin was only marginally affectedby Zn treatment. The data are discussed in relation to previouslyestablished effects of Zn on the cell cycle and other cellularcharacters of the two cultivars. zinc, meristem size, root hair, xylem, Festuca rubra     

Characterization of Cd translocation and identification of the Cd form in xylem sap of the Cd-hyperaccumulator Arabidopsis halleri

Arabidopsis halleri is a Cd hyperaccumulator; however, the mechanismsinvolved in the root to shoot translocation of Cd are not wellunderstood. In this study, we characterized Cd transfer fromthe root medium to xylem in this species. Arabidopsis halleriaccumulated 1,500 mg kg^–1 Cd in the shoot without growthinhibition. A time-course experiment showed that the releaseof Cd into the xylem was very rapid; by 2 h exposure to Cd,Cd concentration in the xylem sap was 5-fold higher than thatin the external solution. The concentration of Cd in the xylemsap increased linearly with increasing Cd concentration in theexternal solution. Cd transfer to the xylem was completely inhibitedby the metabolic inhibitor carbonyl cyanide 3-chlorophenylhydrazone(CCCP). Cd concentration in the xylem sap was decreased by increasingthe concentration of external Zn, but enhanced by Fe deficiencytreatment. Analysis with ¹¹³Cd-nuclear magnetic resonance (NMR)showed that the chemical shift of ¹¹³Cd in the xylem sap wasthe same as that of Cd(NO₃)₂. Metal speciation with Geochem-PCalso showed that Cd occurred mainly in the free ionic form inthe xylem sap. These results suggest that Cd transfer from theroot medium to the xylem in A. halleri is an energy-dependentprocess that is partly shared with Zn and/or Fe transport. Furthermore,Cd is translocated from roots to shoots in inorganic forms.     

Regulation of Mineral Redistribution in Pod-Bearing Soybean Explants

On the way from the roots to the seeds during reproductive developmentin soybean (Glycine max), a large proportion of the mineralspass through the leaves rather than travelling directly viathe xylem. This direct and indirect movement of mineral nutrientshas important implications for mineral redistribution, seeddevelopment and leaf senescence. Therefore, we have studiedthe role of cytokinin and mineral flux from the roots in regulatingmineral redistribution from the leaves to the seeds using explants,i.e. a leaf, a pod and a subtending stem segment, with theirbases immersed in treatment solutions. Thus, defined solutionscontaining cytokinin and/or minerals can be substituted forthe roots. When explants (excised at early-mid podfill) aresupplied H₂O only, leaf N, P, K, Mo, Mg, Zn, Fe, B, Cu, Ca,and Mn decline, ranging from 93% for Mo to 38% for Fe. In explantson H₂O, N, P, K, Mo, Mg, Zn, and Fe appear to be redistributedfrom the leaves to the seeds, while the B, Cu, Ca, and Mn lostfrom the leaves do not seem to move to the seeds. Although amixture of minerals resembling xylem sap can delay net lossof these elements from the leaves, it does not prevent the decreases.The cytokinin zeatin (4.6 µM) inhibits the loss of N,IC, Mo, Mg, Zn, Fe, B, Cu, Ca, and Mn from the leaves, but notthat of P. When combined with minerals, zeatin not only preventsthe loss of the minerals from the leaves but may even greatlyincrease them with the possible exception of Zn, Fe, and Cu.Supplying the mineral nutrient mixture increases the quantitiesof N, P, K, Mg, Cu, and B in the seeds but not Zn, Fe, Mn, Ca,and Mo. For those minerals, especially N, where zeatin inhibitsefflux from the leaves, it may reduce the amounts in the seeds,but it does not change P, K, Mg, and Ca. The accumulation andredistribution patterns of the different mineral nutrients showmany dissimilarities thereby suggesting differences in the controlof their distribution. Key words: Cytokinin, mineral transport, seed development, senescence     

The plant-endogenous Fe(II)-chelator nicotianamine restricts the ferrochelatase activity of tomato chloroplasts

Stripped chloroplasts were prepared from young leaves of a tomatowild type (Lycopersicon esculentum Mill.) and its mutant chloronerva.Several morphological and biochemical abnormalities of thismutant are caused by the total lack of the plant-endogenousFe²⁺ chelator nicotianamine (NA). The ferrochelatase activitywas estimated by determination of ⁵⁹Fe incorporated into haem.A mercaptoethanol concentration of 250 mM was necessary to maintainfull enzyme activity. The reducing agent supported the reducedstate of the active site of the enzyme more than that of theiron as revealed by use of ferrous and ferric ionproviding compoundsas substrates. Chloroplasts of both genotypes exhibited a similar enzyme activity.NA inhibited this activity by nearly 100% depending on the concentrationapplied. On the basis of the formation constant of the Fe(ll)–NAcomplex and the concentrations of iron and NA in the enzymeassay as well as in the tomato shoot apex region it is proposedthat ferrochelatase acts in vivo with an iron level at the attomolarrange which is provided by NA. Key words: Ferrochelatase activity, ferrous ion concentration, nicotianamine, tomato chloroplasts, substrate limitation     

Xylem fluxes of fixed N through nodules of the legume Acacia littorea and haustoria of an associated N-dependent root hemiparasite Olax phyllanthi

Nodulated 1-1.5-year-old plants of Acacia littorea grown inminus nitrogen culture were each partnered with a single seedlingof the root hemiparasite Olax phyllanthi. Partitioning of fixedN between plant organs of the host and parasite was studiedfor the period 4–8 months after introducing the parasite.N fluxes through nodules of Acacia and xylem-tapping haustoriaof Olax were compared using measured xylem flows of fixed Nand anatomical information for the two organs. N₂ fixation duringthe study interval (635 µg N g FW nodules^–1 d^–1)corresponded to a xylem loading flux of 0.20 µg N mm^–2d^–1 across the secretory membranes of the pencycle parenchymaof the nodule vascular strands. A much higher flux of N (4891µg mm^–2 d^–1) exited through xylem at the junctionof nodule and root. The corresponding flux of N from host xylemacross absorptive membranes of the endophyte parenchyma of Olaxhaustorium was 1.15 µg N mm^–1 d^–1, six timesthe loading flux in nodules. The exit flux from haustorium toparasite rootlet was 20.0 pg N mm^–1 d^–1, 200-foldless than that passing through xylem elements of the nodule.Fluxes of individual amino compounds in xylem of nodule andhaustorium were assessed on a molar and N basis. N flux valuesare related to data for transpiration and partitioning of Cand N of the association recorded in a companion paper. Key words: Olax phyllanthi, host-parasite relationships, N flux, Acacia, N₂ fixation     

Long Distance Transport of Abscisic Acid in NaCI-Treated Intact Plants of Lupinus albus

Plants of Lupinus albus were grown for 51 d under control (1.1mol m^–3 NaCl) and saline (40 mol m^–3 NaCl) conditions.Plants were harvested and changes of carbon, nitrogen and abscisicacid (ABA) contents of individual organs were determined 41d and 51 d after germination. In the period between the twoharvests xylem and phloem saps were collected and respirationand photosynthesis of individual organs were measured. Usingflows of carbon, C/ABA ratios and increments of ABA flows ofABA in phloem and xylem and rates of biosynthesis and degradationof ABA were calculated. Both under control and saline conditionsnet biosynthesis occurred in the root, the basal strata of leavesand in the inflorescence. Metabolic degradation of ABA tookplace in the stem internodes and apical leaf strata. Salt stress increased xylem transport of ABA up to 10-fold andphloem transport to the root up to 5-fold relative to that ofthe controls. A considerable amount of ABA in the xylem saporiginated from biosynthesis in the roots, i.e. 55% in salt-treatedand smaller than 28% in control plants. The remaining part ofABA in the xylem sap originated from the shoot: it was translocatedin the phloem from fully differentiated leaves towards the rootand from there it was recirculated back to the aerial partsof the plant. The data suggest that ABA may serve as a hormonalstress signal from the root system. Key words: Lupinus albus, salt stress, abscisic acid, long distance transport     

Interactions of NH4+ and L-glutamate with NO3- transport processes of non-mycorrhizal Fagus sylvatica roots

The processes of NO₃^– uptake and transport and the effectsof NH₄⁺ or L-glutamate on these processes were investigatedwith excised non-mycorrhizal beech (Fagus sylvatica L.) roots.NO₃^– net uptake followed uniphasic Michaelis-Menten kineticsin a concentration range of 10µM to 1 mM with an apparentK_m of 9.2 µM and a V_max of 366 nmol g^–1 FW h^–1.NH₄⁺, when present in excess to NO₃^–, or 10 mM L-glutamateinhibited the net uptake of NO₃^– Apparently, part of NO₃^–taken up was loaded into the xylem. Relative xylem loading ofNO₃^– ranged from 3.21.6 to 6.45.1% of NO₃^– netuptake. It was not affected by treatment with NH₄⁺ or L-glutamate.¹⁶N/¹³N double labelling experiments showed that NO₃^–efflux from roots increased with increasing influx of NO₃^–and, therefore, declined if influx was reduced by NH₄⁺ or L-glutamateexposure. From these results it is concluded that NO₃^–net uptake by non-mycorrhizal beech roots is reduced by NH₄⁺or L-glutamate at the level of influx and not at the level ofefflux. Key words: Nitrate transport, net uptake, influx, efflux, ammonium, Fagus, Fagaceae     

Photoinhibition and light-induced cyclic electron transport in ndhB(-) and psaE(-) mutants of Synechocystis sp. PCC 6803

The ndhB^– and psaE^– mutants of the cyanobacteriumSynechocystis sp. PCC 6803 are partly deficient in PSI-drivencyclic electron transport. We compared photoinhibition in thesemutants to the wild type to test the hypothesis that PSI cyclicelectron transport protects against photoinhibition. Photoinhibitorytreatment greatly accelerated PSI cyclic electron transportin the wild type and also in both the mutants. The psaE^–mutant showed rates of PSI cyclic electron transport similarto the wild type under all conditions tested. The ndhB^–mutant showed much lower rates of PSI cyclic electron transportthan the wild type following brief dark adaptation but exceededwild type rates after exposure to photoinhibitory light. Thewild type and both mutants showed similar rates of photoinhibitiondamage and photoinhibition repair at PSII. Photoinhibition atPSI was much slower than at PSII and was also similar betweenthe wild type and both mutants, despite the known instabilityof PSI in the psaE^– mutant. We conclude that photoinhibitorylight induces sufficient PSI-driven cyclic electron transportin both the ndhB^– and psaE^– mutants to fulfill anyrole that cyclic electron transport plays in protection againstphotoinhibition. ⁴ Corresponding author: E-mail, sherbert@uwyo.edu; Fax, +1-307-766-2851;Phone, +1-307-766-4353.     

Absorption and Distribution of Copper in Plants with Sufficient or Deficient Supplies

Wheat, red clover and ryegrass were grown in flowing solutionculture with sufficient (+ Cu) and deficient (–Cu) suppliesof copper. The rates of Cu absorption (µg g^–1 dryroot day^–1) did not differ greatly between species ineither treatment. Wheat plants, when transferred from the –Cu to the +Cu treatment, absorbed Cu at a much slower rate thanthose which had remained throughout in the + Cu treatment. Inall plants considerable proportions of the absorbed Cu wereretained in the roots, even when the plants were Cu-deficient,and the concentration in roots usually exceeded that in anypart of the shoots in both treatments. Transferring wheat plantsfrom the +Cu to the –Cu treatment decreased the concentrationin all plant parts except old leaves; similarly, transferringfrom the –Cu to +Cu treatment increased the concentrationin all parts of the shoots, execept old leaves, and in the roots. Lolium perenne, Trifolium pratense, Triticum aestivum, ryegrass, red clover, wheat, absorption, copper, flowing solution culture     

Mobilization of Minerals to Developing Seeds of Legumes

The mineral nutrition of fruiting plants of Pisum sativum L.,Lupinus albus L. and Lupinus angustifolius L. is examined insand cultures supplying adequate and balanced amounts of essentialnutrients. Changes in content of specific minerals in leaves,pods, seed coat, and embryo are described. P, N and Zn tendto increase precociously in an organ relative to dry matteraccumulation, other elements more or less parallel with (K,Mn, Cu, Mg and Fe) or significantly behind (Ca and Na) dry weightincrease. Some 60–90 per cent of the N, P and K is lostfrom the leaf, pod and seed coat during senescence, versus 20–60per cent of the Mg, Zn, Mn, Fe and Cu and less than 20 per centof the Na and Ca. Mobilization returns from pods are estimatedto provide 4–39 per cent of the seeds' accumulations ofspecific minerals, compared with 4–27 per cent for testatransfer to the embryo. Endosperm minerals are of only minorsignificance in embryo nutrition. Comparisons of the mineral balance of plant parts of Lupinusspp. with that of stem xylem sap and fruit tip phloem sap supportthe view that leaves and pod are principal recipients of xylem-borneminerals and that export from these organs via phloem is themajor source of minerals to the seeds. Endosperm and embryodiffer substantially in mineral compostition from phloem sap,suggesting that selective uptake occurs from the translocationstream during seed development. Considerable differences are observed between species in mineralcomposition of plant organs and in the effectiveness of transferof specific minerals to the seeds Differences between speciesrelate principally to Ca, Na and certain trace elements.     

Phloem and Xylem Transport in the Supply of Minerals to a Developing Legume (Lupinus albus L.) Fruit

The economy of carbon, nitrogen, water and mineral elementsin fruits of Lupinus albus L. was studied by measuring accumulationof these quantities in the developing fruit and estimating itstranspirational losses and CO₂ exchanges. Combining this informationwith data on levels of mineral elements in the xylem sap andphloem sap supplying the fruit, it was possible to test whethertransport based on mass inflow through xylem and phloem wouldaccount for the observed intake of elements. A model of transportbased on water and carbon intake suggested that vascular intakeduring the fruit's life matched the recorded increment for mineralsto within ± 15 per cent for N, Na, Zn, Fe and Cu, andto within ± 23 per cent for P, K and S. However, estimatedvascular intake of Ca, Mg and Mn accounted for less than one–thirdof the recorded intake by the fruit, inadequacy of vascularintake being especially great early in growth. Transport inphloem accounted for more than 80 per cent of the fruit's vascularintake of C, N and S, and 70–80 per cent of its P, K,Mg and Zn. Xylem contributed 68 per cent of the vascular inputof Ca, 59 per cent of the Na, and 34–38 per cent of theFe, Mn and Cu. Enclosure and darkening of fruits reduced levelsof Ca and Fe but increased levels of N, P, K and Zn in fruitdry matter relative to unenclosed, illuminated fruits. Resultswere related to previous observations on fruit functioning. Lupinus albus, legume fruit, mineral supply, phloem, xylem     

Sodium Exclusion from the Shoots by Roots of Zea mays (cv. LG 11) and its Breakdown with Oxygen Deficiency

The effects of sodium chloride salinity and root oxygen deficiency(anoxia) were studied in 11-12d old maize plants (Zea mays L.cv. LG 11) in nutrient solution culture. Transport of ²²Na bythe roots to the shoot in 24 h was markedly increased by anoxiawhen the external concentration of NaCl was in the range 0·1-10·9mol m^–3. Anoxia severely inhibited uptake of ⁴²K by rootsand its transport to the shoot, so that the ratio of Na⁺/K⁺moving into the shoot was increased by a factor of approximately10. When the external concentration of NaCl was increased to2.4 mol m^–3, the roots showed much less ability to excludeNa⁺ under aerobic conditions, and anoxia caused no further increasein the movement of Na⁺ to the shoot. It is concluded that atthe higher concentration the ability of the roots to excludeNa⁺, presumably through an active mechanism in the xylem parenchymacells or in the root cortex and transporting Na⁺ to the outersolution, is saturated by excessive inward diffusion of Na⁺.The ratio of Na⁺/K⁺ transported to the shoot increased by afactor of 600 when the concentration of NaCl was increased from2·4 mol m^–3 to 40 mol m^–3 and roots weremade anoxic. Such imbalances in the supply of cations to theshoot, particularly when roots are oxygen-deficient, may contributeto salinity damage. Key words: Anaerobic, Anoxic, Oxygen deficiency, Roots, Salinity, Salt stress, Sodium chloride, Zea mays     

Influence of Glutathione (GSH) on Sulphate Influx, Xylem Loading and Exudation in Excised Tobacco Roots

In short-term experiments sulphate influx of excised tobaccoroots {Nicotiana tabacum L. var. 'Samsun') followed monophasicMichaelis-Menten kinetics with an approximate K_m of 12 ±4 µM and v_max of 657 ± 211 nmol g^–1 FW h^–1.An inhibition of sulphate influx, xylem loading and exudationof more than 70% was achieved with 01 mM GSH within 1 h. Cysteinewas two orders of magnitude more effective as an inhibitor thanGSH. An inhibition of more than 75% was already obtained with1.0µM cysteine. It may, therefore, be assumed that GSHis decomposed to yield cysteine concentrations that may inhibitsulphate influx, xylem loading and exudation. When BSO, a specificinhibitor of the initial step of GSH synthesis, was added, cysteine-mediatedinhibition on sulphate influx, xylem loading and exudation wasstrongly diminished. Apparently, GSH synthesis is required toobtain inhibition of these processes by cysteine. The physiologicalmechanisms that may cause the inhibition of sulphate influx,xylem loading and exudation by glutathione are discussed. Key words: Sulphate transport, Nicotiana, Solanaceae, glutathione, cysteine, buthionine sulphoximine     

Nicotianamine functions in the Phloem-based transport of iron to sink organs, in pollen development and pollen tube growth in Arabidopsis

The metal chelator nicotianamine promotes the bioavailability of Fe and reduces cellular Fe toxicity. For breeding Fe-efficient crops, we need to explore the fundamental impact of nicotianamine on plant development and physiology. The quadruple nas4x-2 mutant of Arabidopsis thaliana cannot synthesize any nicotianamine, shows strong leaf chlorosis, and is sterile. To date, these phenotypes have not been fully explained. Here, we show that sink organs of this mutant were Fe deficient, while aged leaves were Fe sufficient. Upper organs were also Zn deficient. We demonstrate that transport of Fe to aged leaves relied on citrate, which partially complemented the loss of nicotianamine. In the absence of nicotianamine, Fe accumulated in the phloem. Our results show that rather than enabling the long-distance movement of Fe in the phloem (as is the case for Zn), nicotianamine facilitates the transport of Fe from the phloem to sink organs. We delimit nicotianamine function in plant reproductive biology and demonstrate that nicotianamine acts in pollen development in anthers and pollen tube passage in the carpels. Since Fe and Zn both enhance pollen germination, a lack of either metal may contribute to the reproductive defect. Our study sheds light on the physiological functions of nicotianamine.     

Copper Nutrition of Sugarbeet

Sugarbeet (Beta vulgaris L.) plants were grown in refined sandat graded levels of copper ranging from acute deficiency (0.000325µg Cu cm^–3) to excess (65 µg Cu cm^–3).Visible effects of copper deficiency appeared up to 0-00065µg Cu cm^–3and depression in growth up to 00065µCucm^–3. Copper deficiency decreased the concentrations ofDNA and RNA and the activities of polyphenol oxidase, cytochrome-coxidase, catalase and aldolase; and it increased the activitiesof peroxidase, ribonuclease and acid phosphatase in leaves.The maximum sucrose concentration in roots was obtained at 0-65µCucm^–3 Twenty four h after infiltration of a solution of 65µCucm^–3into copper deficient leaves, the activities of cytochrome-coxidase and peroxidase had increased even in the presence ofcycloheximide but that of polyphenol oxidase increased onlyin the absence of this inhibitor. Key words: Beta vulgaris, Cu deficiency: Enzymes