High-resolution structures of complexes of plant S-adenosyl-L-homocysteine hydrolase (Lupinus luteus)

S-Adenosyl-L-homocysteine hydrolase (SAHase) catalyzes the reversible breakdown of S-adenosyl-L-homocysteine (SAH) to adenosine and homocysteine. SAH is formed in methylation reactions that utilize S-adenosyl-L-methionine (SAM) as a methyl donor. By removing the SAH byproduct, SAHase serves as a major regulator of SAM-dependent biological methylation reactions. Here, the first crystal structure of SAHase of plant origin, that from the legume yellow lupin (LlSAHase), is presented. Structures have been determined at high resolution for three complexes of the enzyme: those with a reaction byproduct/substrate (adenosine), with its nonoxidizable analog (cordycepin) and with a product of inhibitor cleavage (adenine). In all three cases the enzyme has a closed conformation. A sodium cation is found near the active site, coordinated by residues from a conserved loop that hinges domain movement upon reactant binding. An insertion segment that is present in all plant SAHases is located near a substrate-pocket access channel and participates in its formation. In contrast to mammalian and bacterial SAHases, the channel is open when adenosine or cordycepin is bound and is closed in the adenine complex. In contrast to SAHases from other organisms, which are active as tetramers, the plant enzyme functions as a homodimer in solution.

Lysine decarboxylase catalyzes the first step of quinolizidine alkaloid biosynthesis and coevolved with alkaloid production in leguminosae

Lysine decarboxylase (LDC) catalyzes the first-step in the biosynthetic pathway of quinolizidine alkaloids (QAs), which form a distinct, large family of plant alkaloids. A cDNA of lysine/ornithine decarboxylase (L/ODC) was isolated by differential transcript screening in QA-producing and nonproducing cultivars of Lupinus angustifolius. We also obtained L/ODC cDNAs from four other QA-producing plants, Sophora flavescens, Echinosophora koreensis, Thermopsis chinensis, and Baptisia australis. These L/ODCs form a phylogenetically distinct subclade in the family of plant ornithine decarboxylases. Recombinant L/ODCs from QA-producing plants preferentially or equally catalyzed the decarboxylation of L-lysine and L-ornithine. L. angustifolius L/ODC (La-L/ODC) was found to be localized in chloroplasts, as suggested by the transient expression of a fusion protein of La-L/ODC fused to the N terminus of green fluorescent protein in Arabidopsis thaliana. Transgenic tobacco (Nicotiana tabacum) suspension cells and hairy roots produced enhanced levels of cadaverine-derived alkaloids, and transgenic Arabidopsis plants expressing (La-L/ODC) produced enhanced levels of cadaverine, indicating the involvement of this enzyme in lysine decarboxylation to form cadaverine. Site-directed mutagenesis and protein modeling studies revealed a structural basis for preferential LDC activity, suggesting an evolutionary implication of L/ODC in the QA-producing plants.

Rhizostabilization of metals in soils using Lupinus luteus inoculated with the metal resistant rhizobacterium Serratia sp. MSMC541

The aim of this work was to test Lupinus luteus plants, inoculated with metal resistant rhizobacteria, in order to phytostabilise metals in contaminated soils. The resistance to heavy metals of strains isolated from nodules of Lupinus plants was evaluated. The strain MSMC541 showed multi-resistance to several metals (up to 13.3 mM As, 2.2 mM Cd, 2.3 mM Cu, 9 mM Pb and 30 mM Zn), and it was selected for further characterization. Furthermore, this strain was able to biosorb great amounts of metals in cell biomass. 16S rDNA sequencing positioned this strain within the genus Serratia. The presence of arsenic resistance genes was confirmed by southern blot and PCR amplification. A rhizoremediation pot experiment was conducted using Lupinus luteus grown on sand supplemented with heavy metals and inoculated with MSMC541. Plant growth parameters and metal accumulation were determined in inoculated vs. non-inoculated Lupinus luteus plants. The results showed that inoculation with MSMC541 improved the plant tolerance to metals. At the same time, metal translocation to the shoot was significantly reduced upon inoculation. These results suggest that Lupinus luteus plants, inoculated with the metal resistant strain Serratia sp. MSMC541, have a great potential for phytostabilization of metal contaminated soils.

Consequences of transforming narrow leafed lupin (Lupinus angustifolius [L.]) with an ipt gene under control of a flower-specific promoter

Phenotypes of five transgenic lines of narrow-leafed lupin (Lupinus angustifolius [L] cv Merrit) stably transformed with the isopentenyl pyrophosphate transferase (ipt) gene from Agrobacterium tumefaciens coupled to a flower-specific promoter (TP12) from Nicotiana tabacum [L.] are described. Expression of the transgene was detected in floral tissues and in shoot apical meristems on all orders of inflorescence. In each transgenic line there was significant axillary bud outgrowth at all nodes on the main stem with pronounced branch development from the more basal nodes in three of the lines. The lowest basal branches developed in a manner similar to the upper stem axillary branches on cv Merrit and bore fruits, which, in two lines, contained a significant yield of filled seeds at maturity. Senescence of the cotyledons was delayed in all lines with green cotyledons persisting beyond anthesis in one case. IPT expression increased cytokinin (CK) levels in flowers, meristem tissues and phloem exudates in a form specific manner, which was suggestive of localized flower and meristem production with significant long-distance re-distribution in phloem. The total number of fruits formed (pod set) on some transgenic lines was increased compared to cv Merrit. Grain size compared to cv Merrit was not significantly altered in transgenic lines.

Time and substrate dependent exudation of carboxylates by Lupinus albus L. and Brassica napus L

Root exudates influence significantly physical, chemical and biological characteristics of rhizosphere soil. Their qualitative and quantitative composition is affected by environmental factors such as pH, soil type, oxygen status, light intensity, soil temperature, plant growth, nutrient availability and microorganisms. The aim of the present study was to assess the influence of growth substrate and plant age on the release of carboxylates from Lupinus albus L. and Brassica napus L. Both plant species were studied in continuously percolated microcosms filled with either sand, soil or sand + soil (1:1) mixture. Soil solution was collected every week at 7, 14, 21, 28 and 35 days after planting (DAP). Carboxylate concentrations were determined by reversed-phase liquid chromatography - electrospray ionization - time of flight mass spectrometry (LC-ESI-TOFMS). Oxalate, citrate, succinate, malate and maleate were detected in soil solutions of both plant species. Their concentrations were correlated with the physiological status of the plant and the growth substrate. Oxalate was the predominant carboxylate detected within the soil solution of B. napus plants while oxalate and citrate were the predominant ones found in the soil solutions of L. albus plants. The sampling determination of carboxylates released by plant roots with continuous percolation systems seems to be promising as it is a non-destructive method and allows sampling and determination of soluble low molecular weight organic compounds derived from root exudation as well as the concentration of soluble nutrients, which both might reflect the nutritional status of plants.

Sucrose controls storage lipid breakdown on gene expression level in germinating yellow lupine (Lupinus luteus L.) seeds

This study revealed that cytosolic aconitase (ACO, EC 4.2.1.3) and isocitrate lyase (ICL, EC 4.1.3.1, marker of the glyoxylate cycle) are active in germinating protein seeds of yellow lupine. The glyoxylate cycle seems to function not only in the storage tissues of food-storage organs, but also in embryonic tissue of growing embryo axes. Sucrose (60mM) added to the medium of in vitro culture of embryo axes and cotyledons decreased activity of lipase (LIP, EC 3.1.1.3) and activity of glutamate dehydrogenase (NADH-GDH, EC 1.4.1.2). The opposite effect was caused by sucrose on activity of cytosolic ACO, ICL as well as NADP(+)-dependent (EC 1.1.1.42) and NAD(+)-dependent (EC 1.1.1.41) isocitrate dehydrogenase (NADP-IDH and NAD-IDH, respectively); activity of these enzymes was clearly stimulated by sucrose. Changes in the activity of LIP, ACO, NADP-IDH, and NAD-IDH caused by sucrose were based on modifications in gene expression because corresponding changes in the enzyme activities and in the mRNA levels were observed. The significance of cytosolic ACO and NADP-IDH in carbon flow from storage lipid to amino acids, as well as the peculiar features of storage lipid breakdown during germination of lupine seeds are discussed.

Dehulled-micronised lupin (Lupinus albus L. cv. Multitalia) as the main protein source for broilers: influence on growth performance, carcass traits and meat fatty acid composition

BACKGROUND

A study was carried out to compare the effect of diets containing micronised-dehulled lupin (Lupinus albus L. cv. Multitalia) on growth performance, carcass yields and meat fatty acid profile of broiler chickens.

RESULTS

Hubbard strain chicks receiving from 14 d to slaughtering age (49 d) a wheat middlings-based diet containing either deffatted soybean meal (195 g kg(-1), control) or dehulled micromicronised lupins (240 g kg(-1)) as the main protein source were used. The inclusion of treated lupin meal in the diet did not result in lower growth rates of chicks. Lupin diet had no effect on dressing percentage, or breast and drumstick muscles relative weights, but a reduction of abdominal fat content was reported (P < 0.05). White and dark meats of birds fed lupin diet had significant (P < 0.05) lower L* (lightness) values and fat content (P < 0.05). Total collagen and water-holding capacity values were higher in lupin treatment. Feeding the lupin diet resulted in lower saturated fatty acid content in breast and drumstick meat, as well as the n-6/n-3 polyunsaturated fatty acid (PUFA) ratio and saturation, atherogenic and thrombogenic indexes, while total PUFA and monounsaturated fatty acids levels increased (P < 0.05).

CONCLUSION

These results suggest that replacing soybean meal with dehulled-micronised lupin meal in diet for broiler chickens can produce meat with favourable lipid profile and quality, with no adverse effects on productive parameters.

Metabolic analysis revealed altered amino acid profiles in Lupinus albus organs as a result of boron deficiency

We analysed the changes in the metabolites of Lupinus albus organs (leaf-blades, petioles, apexes, hypocotyls and roots) as a consequence of B deficiency. The deficiency did not affect malate concentration and induced only minor changes in the sugar content, suggesting that the carbohydrate metabolism is little affected by the deficiency. Contrarily, marked changes in the content of free amino acids were observed, with some specific variations associated with the different organs. These changes indicate that various aspects of metabolism implicated in the amino acid accumulation were affected by B deficiency. Most of the detected changes appear to have implications with some stress responses or signalling processes. Asparagine and proline that increase in many stresses also accumulated in petioles, apexes and hypocotyls. Accumulation of γ-aminobutyric acid shunt amino acids, indicative of production of reactive oxygen species, occurs in the same three organs and also the roots. The increase in the branched-chain amino acids, observed in all organs, suggests the involvement of B with the cytoskeleton, whereas glycine decrease in leaf-blades and active growing organs (apexes and roots) could be associated with the proposed role of this amino acids in plant signalling in processes that might be associated with the decreased growth rates observed in B deficiency. Despite the admitted importance of free amino acids in plant metabolism, the available information on this matter is scarce. So our results bring new information concerning the effects of B deficiency in the metabolism of the several L. albus organs.

Activation of phenylpropanoid pathway in legume plants exposed to heavy metals. Part II. Profiling of isoflavonoids and their glycoconjugates induced in roots of lupine (Lupinus luteus) seedlings treated with cadmium and lead

We examined changes in profiles of isoflavonoids in roots of lupine (Lupinus luteus L. cv. Juno) seedlings in response to treatment with two heavy metals: cadmium (at 10 mg/l) and lead (at 150 mg/l). Overall, 21 flavonoid conjugates were identified in root extracts, some of them with up to six positional isomers. The total amount of all isoflavonoids increased by about 15 % in cadmium-treated plants and by 46 % in lead-treated ones. Heavy metals markedly increased the content of two compounds: 2'-hydroxygenistein glucoside and 2'-hydroxygenistein 7-O-glucoside malonylated. Possible functions of the identified isoflavonoids in yellow lupine exposed to heavy metal stress are discussed.

Identification and characterisation of seed storage protein transcripts from Lupinus angustifolius

BACKGROUND

In legumes, seed storage proteins are important for the developing seedling and are an important source of protein for humans and animals. Lupinus angustifolius (L.), also known as narrow-leaf lupin (NLL) is a grain legume crop that is gaining recognition as a potential human health food as the grain is high in protein and dietary fibre, gluten-free and low in fat and starch.

RESULTS

Genes encoding the seed storage proteins of NLL were characterised by sequencing cDNA clones derived from developing seeds. Four families of seed storage proteins were identified and comprised three unique α, seven β, two γ and four δ conglutins. This study added eleven new expressed storage protein genes for the species. A comparison of the deduced amino acid sequences of NLL conglutins with those available for the storage proteins of Lupinus albus (L.), Pisum sativum (L.), Medicago truncatula (L.), Arachis hypogaea (L.) and Glycine max (L.) permitted the analysis of a phylogenetic relationships between proteins and demonstrated, in general, that the strongest conservation occurred within species. In the case of 7S globulin (β conglutins) and 2S sulphur-rich albumin (δ conglutins), the analysis suggests that gene duplication occurred after legume speciation. This contrasted with 11S globulin (α conglutin) and basic 7S (γ conglutin) sequences where some of these sequences appear to have diverged prior to speciation. The most abundant NLL conglutin family was β (56%), followed by α (24%), δ (15%) and γ (6%) and the transcript levels of these genes increased 103 to 106 fold during seed development. We used the 16 NLL conglutin sequences identified here to determine that for individuals specifically allergic to lupin, all seven members of the β conglutin family were potential allergens.

CONCLUSION

This study has characterised 16 seed storage protein genes in NLL including 11 newly-identified members. It has helped lay the foundation for efforts to use molecular breeding approaches to improve lupins, for example by reducing allergens or increasing the expression of specific seed storage protein(s) with desirable nutritional properties.

Cross-talk interactions of sucrose and Fusarium oxysporum in the phenylpropanoid pathway and the accumulation and localization of flavonoids in embryo axes of yellow lupine

This study investigated the effects of cross-talk interactions of sucrose and infection caused by a pathogenic fungus Fusarium oxysporum f.sp. lupini on the regulation of the phenylpropanoid pathway, i.e. the level of expression of genes encoding enzymes participating in flavonoid biosynthesis, as well as cell location and accumulation of these compounds in embryo axes of Lupinus luteus L. cv. Polo. Embryo axes, both non-inoculated and inoculated, were cultured for 96h on Heller medium with 60mM sucrose (+Sn and +Si) or without it (-Sn and -Si). Real-time RT-PCR to assess expression levels of the flavonoid biosynthetic genes, phenylalanine ammonialyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI) and isoflavone synthase (IFS) were used. Sucrose alone strongly stimulated the expression of these genes. There was a very high expression level of these genes in +Si embryo axes in the early phase of infection. Signal amplification by sucrose and the infection was most intense in the 48-h +Si axes, resulting in the highest level of expression of flavonoid biosynthetic genes. In -Si tissues, the expression level of these genes increased at 48 and 72h after inoculation relative to 24h; however, the relative level of expression was much lower than in +Si axes, except at 72h for PAL and CHS.Moreover, at 48h of culture, considerably higher activity of CHI (EC 5.5.1.6) was observed in axes with a high level of sucrose than in those with a sucrose deficit. CHI activity in +Si axes at 48 and 96h post-inoculation was over 1.5 and 2 times higher than that in +Sn axes, as well as higher than in -Si axes.Observations of yellow lupine embryo axes under a confocal microscope showed an increased post-infection accumulation of flavonoids, particularly in cells of embryo axes infected with F. oxysporum and cultured on a medium containing sucrose (+Si). Up to 48h post-infection in +Si axes, a very intensive emission of green fluorescence was observed, indicating high accumulation of these compounds in whole cells. Moreover, a nuclear location of flavonoids was recorded in cells. Strong staining of flavonoid end products in +Si embryo axes was consistent with the expression of PAL, CHS, CHI and IFS.These results indicate that, in the early phase of infection, the flavonoid biosynthesis pathway is considerably enhanced in yellow lupine embryo axes as a strong signal amplification effect of sucrose and the pathogenic fungus F. oxysporum.

Endophytes and their potential to deal with co-contamination of organic contaminants (toluene) and toxic metals (nickel) during phytoremediation

The aim was to investigate if engineered endophytes that are capable of degrading organic contaminants, and deal with or ideally improve uptake and translocation of toxic metals, can improve phytoremediation of mixed organic-metal pollution. As a model system, yellow lupine was inoculated with the endophyte Burkholderia cepacia VM1468 possessing (a) the pTOM-Bu61 plasmid, coding for constitutive toluene/TCE degradation, and (b) the chromosomally inserted ncc-nre Ni resistance/sequestration system. As controls, plants were inoculated with B. vietnamiensis BU61 (pTOM-Bu61) and B. cepacia BU72 (containing the ncc-nre Ni resistance/sequestration system). Plants were exposed to mixes of toluene and Ni. Only inoculation with B. cepacia VM1468 resulted in decreased Ni and toluene phytotoxicity, as measured by a protective effect on plant growth and decreased activities of enzymes involved in antioxidative defence (catalase, guaiacol peroxidase, superoxide dismutase) in the roots. Besides, plants inoculated with B. cepacia VM1468 and B. vietnamiensis BU61 released less toluene through the leaves than non-inoculated plants and those inoculated with B. cepacia BU72. Ni-uptake in roots was slightly increased for B. cepacia BU72 inoculated plants. These results indicate that engineered endophytes have the potential to assist their host plant to deal with co-contamination of toxic metals and organic contaminants during phytoremediation.

Interaction and accumulation of manganese and cadmium in the manganese accumulator Lupinus albus

The effects of the interaction between Mn and Cd on the growth of the white lupin (Lupinus albus), uptake of these metals, their accumulation, and effects on heavy metal stress indicators were studied under glasshouse conditions. Plants were grown with and without Mn and/or Cd for 4 weeks. The absence of Mn and Cd led to lipid peroxidation-induced loss of flavonoids and anthocyanins in the roots, reduced the size of the plant canopy, and led to the appearance of proteoid roots. Sensitivity to Cd in white lupin was enhanced by a low Mn supply, despite lower Cd uptake and accumulation (leaf Mn:Cd concentration ratio <3), as evidenced by increased lipid peroxidation in the leaves and strong inhibition of growth. However, when the Mn supply was adequate, the plants showed few symptoms of Cd toxicity, even though Cd uptake and accumulation increased. A Mn:Cd ratio of up to 20 was enough to minimize Cd stress in the leaf, reflecting the plants' relative tolerance to Cd under such conditions. Irrespective of the Mn supply, the increase in antioxidant compounds observed in the roots of Cd-treated plants might act as a protective mechanism by minimizing the oxidative stress caused by Cd exposure. In summary, high leaf Mn concentrations seem to render white lupins more tolerant to Cd stress.

Nitric oxide is involved in phosphorus deficiency-induced cluster-root development and citrate exudation in white lupin

*White lupin (Lupinus albus) forms specialized cluster roots characterized by exudation of organic anions under phosphorus (P) deficiency. Here, the role of nitric oxide (NO) in P deficiency-induced cluster-root formation and citrate exudation was evaluated. *White lupin plants were treated with the NO donor sodium nitroprusside (SNP) and scavenger or inhibitor of NO synthase under conditions of P deficiency (0 muM) or P sufficiency (50 muM). *Phosphorus deficiency enhanced NO production in primary and lateral root tips, with a greater increase in cluster roots than in noncluster roots. NO concentrations decreased with cluster root development from the pre-emergent stage, through the juvenile stage, to the mature stage. The P deficiency-induced increase in NO production was inhibited by antagonists of NO synthase and xanthine oxidoreductase, suggesting the involvement of these enzymes in NO production. SNP markedly increased the number of cluster roots. Citrate exudation from different root segments in P-deficient roots was positively correlated with endogenous root NO concentrations. *These findings demonstrate differential patterns of NO production in white lupin, depending on root zone, developmental stage and P nutritional status. NO appears to play a regulatory role in the formation of cluster roots and citrate exudation in white lupin under conditions of P deficiency.

Diverse accumulation of several dehydrin-like proteins in cauliflower (Brassica oleracea var. botrytis), Arabidopsis thaliana and yellow lupin (Lupinus luteus) mitochondria under cold and heat stress

BACKGROUND

Dehydrins represent hydrophilic proteins acting mainly during cell dehydration and stress response. Dehydrins are generally thermostable; however, the so-called dehydrin-like (dehydrin-related) proteins show variable thermolability. Both groups immunoreact with antibodies directed against the K-segment of dehydrins. Plant mitochondrial dehydrin-like proteins are poorly characterized. The purpose of this study was to extend previous reports on plant dehydrins by comparing the level of immunoprecipitated dehydrin-like proteins in cauliflower (Brassica oleracea var. botrytis), Arabidopsis thaliana and yellow lupin (Lupinus luteus) mitochondria under cold and heat stress.

RESULTS

All the analyzed plant species showed constitutive accumulation of thermostable mitochondrial putative dehydrins ranging from 50 to 70 kDa. The mitochondrial dehydrin-like proteins observed in cauliflower and Arabidopsis ranged from 10 to 100 kDa and in lupin imbibed seeds and hypocotyls--from 20 to 90 kDa. Cold treatment increased mainly the accumulation of 10-100 kDa cauliflower and Arabidopsis dehydrin-like proteins, in the patterns different in cauliflower leaf and inflorescence mitochondria. However, in lupin mitochondria, cold affected mainly 25-50 kDa proteins and seemed to induce the appearance of some novel dehydrin-like proteins. The influence of frost stress on cauliflower leaf mitochondrial dehydrin- like proteins was less significant. The impact of heat stress was less significant in lupin and Arabidopsis than in cauliflower inflorescence mitochondria. Cauliflower mitochondrial dehydrin-like proteins are localized mostly in the mitochondrial matrix; it seems that some of them may interact with mitochondrial membranes.

CONCLUSIONS

All the results reveal an unexpectedly broad spectrum of dehydrin-like proteins accumulated during some abiotic stress in the mitochondria of the plant species analyzed. They display only limited similarity in size to those reported previously in maize, wheat and rye mitochondria. Some small thermolabile dehydrin-like proteins were induced under stress conditions applied and therefore they are likely to be involved in stress response.

Effect of jasmonic acid-methyl ester on the composition of carbohydrates and germination of yellow lupine (Lupinus luteus L.) seeds

Mature seeds of yellow lupine contained sucrose, raffinose family oligosaccharides (RFOs), and galactosyl cyclitols as major soluble carbohydrates. The study showed that RFOs dominated in lupine seeds (16% DW). The disappearance of both types of alpha-d-galactosides in germinating lupine seeds was strongly inhibited by the presence of jasmonic acid-methyl ester (JA-Me) at a concentration of 10(-3)M in the incubation medium. JA-Me inhibited the activity of alpha-D-galactosidase (fraction I) during seed germination. Anatomical studies of lupine roots have shown certain cell structure differences between control and JA-Me-treated seedlings. The cross-sections of plant roots treated with JA-Me showed a characteristic folding of the cell walls in all root tissues, starting from the rhyzodermis, cortex and vascular cylinder. In water-treated (control) plants, the cell walls were rounded with no folding.

Storage lipids as a source of carbon skeletons for asparagine synthesis in germinating seeds of yellow lupine (Lupinus luteus L.)

The (14)C-acetate metabolism and regulatory functions of sucrose and sodium fluoride (NaF) were examined in embryo axes and cotyledons isolated from yellow lupine seeds and grown in vitro. After 15 min of incubating organs in solutions of labeled acetate, more radioactivity was found in amino acids (particularly in glutamate, asparagine and glutamine) than in sugars. After 120 min of incubation, (14)C was still localized mainly in amino acids (particularly in asparagine and glutamate). The (14)C atoms from position C-1 of acetate were mostly localized in the liberated (14)CO(2), whereas those from position C-2 were incorporated chiefly into amino acids, sugars and the insoluble fraction of the studied organs. The addition of NaF caused a decrease in the amount of (14)C incorporated into amino acids and in the insoluble fraction. The influence of NaF on incorporation of (14)C into sugars differed between organs. In embryo axes, NaF inhibited this process, but in cotyledons it stimulated (14)C incorporation into glucose. The release of (14)CO(2) with the C-1 and C-2 carbon atoms from acetate was more intensive in embryo axes and cotyledons grown on a medium without sucrose. This process was markedly limited by NaF, which inhibits glycolysis and gluconeogenesis. Alternative pathways of carbon flow from fatty acids to asparagine are discussed.

Study of soil-plant transfer of 226Ra under greenhouse conditions

A soil-plant transfer study was performed using soil from a former uranium ore processing factory in South Bohemia. We present the results from greenhouse experiments which include estimates of the time required for phytoremediation. The accumulation of (226)Ra by different plant species from a mixture of garden soil and contaminated substrate was extremely variable, ranging from 0.03 to 2.20 Bq (226)Ra/g DW. We found differences in accumulation of (226)Ra between plants from the same genus and between cultivars of the same plant species. The results of (226)Ra accumulation showed a linear relation between concentration of (226)Ra in plants and concentration of (226)Ra in soil mixtures. On the basis of these results we estimated the time required for phytoremediation, but this appears to be too long for practical purposes.

"In situ" phytostabilisation of heavy metal polluted soils using Lupinus luteus inoculated with metal resistant plant-growth promoting rhizobacteria

The aim of this work is the evaluation of metal phytostabilisation potential of Lupinus luteus inoculated with Bradyrhizobium sp. 750 and heavy metal resistant PGPRs (plant-growth promoting rhizobacteria), for in situ reclamation of multi-metal contaminated soil after a mine spill. Yellow lupines accumulated heavy metals mainly in roots (Cu, Cd and especially Pb were poorly translocated to shoots). This indicates a potential use of this plant in metal phytostabilisation. Furthermore, As accumulation was undetectable. On the other hand, zinc accumulation was 10-100 times higher than all other metals, both in roots and in shoots. Inoculation with Bradyrhizobium sp. 750 increased both biomass and nitrogen content, indicating that nitrogen fixation was effective in soils with moderate levels of contamination. Co-inoculation of lupines with a consortium of metal resistant PGPR (including Bradyrhizobium sp., Pseudomonas sp. and Ochrobactrum cytisi) produced an additional improvement of plant biomass. At the same time, a decrease in metal accumulation was observed, both in shoots and roots, which could be due to a protective effect exerted on plant rhizosphere. Our results indicate the usefulness of L. luteus inoculated with a bacterial consortium of metal resistant PGPRs as a method for in situ reclamation of metal polluted soils.

Chemical and biological properties in the rhizosphere of Lupinus albus alter soil heavy metal fractionation

To understand better the suitability of white lupin (Lupinus albus L.) for phytoremediation of heavy metal-contaminated soils, the effect of its roots on chemical and biological properties of the rhizosphere affecting soil metal fractionation was studied. Plants were cultivated in two similar soils, with high levels of Zn, Cd, Cu and Pb but differing pH values (4.2 and 6.8). In the rhizosphere of both soils, its roots induced increases in water-soluble carbon, which influenced the fractionation of heavy metals and ultimately their uptake by plant roots. In the rhizosphere of the acid soil, the concentrations of 0.1M CaCl(2)-extractable Mn, Zn and Cu were lower than in the bulk soil, possibly due to their increased retention on Fe (III) hydroxides/oxyhydroxides, while in the neutral soil only the Zn concentration was lower. Higher concentrations of heavy metals were found in plants growing on the acid soil, reflecting their greater availability in this soil. The restricted transfer of heavy metals to the shoot confirms the potential role of this species in the initial phytoimmobilisation of heavy metals, particularly in neutral-alkaline soils.

Localized application of soil organic matter shifts distribution of cluster roots of white lupin in the soil profile due to localized release of phosphorus

BACKGROUND AND AIMS

Phosphorus (P) is a major factor controlling cluster-root formation. Cluster-root proliferation tends to concentrate in organic matter (OM)-rich surface-soil layers, but the nature of this response of cluster-root formation to OM is not clear. Cluster-root proliferation in response to localized application of OM was characterized in Lupinus albus (white lupin) grown in stratified soil columns to test if the stimulating effect of OM on cluster-root formation was due to (a) P release from breakdown of OM; (b) a decrease in soil density; or (c) effects of micro-organisms other than releasing P from OM.

METHODS

Lupin plants were grown in three-layer stratified soil columns where P was applied at 0 or 330 mg P kg(-1) to create a P-deficient or P-sufficient background, and OM, phytate mixed with OM, or perlite was applied to the top or middle layers with or without sterilization.

KEY RESULTS

Non-sterile OM stimulated cluster-root proliferation and root length, and this effect became greater when phytate was supplied in the presence of OM. Both sterile OM and perlite significantly decreased cluster-root formation in the localized layers. The OM position did not change the proportion of total cluster roots to total roots in dry biomass among no-P treatments, but more cluster roots were concentrated in the OM layers with a decreased proportion in other places.

CONCLUSIONS

Localized application of non-sterile OM or phytate plus OM stimulated cluster-root proliferation of L. albus in the localized layers. This effect is predominantly accounted for by P release from breakdown of OM or phytate, but not due to a change in soil density associated with OM. No evidence was found for effects of micro-organisms in OM other than those responsible for P release.

Effects of phosphorus supply on growth, phosphate concentration and cluster-root formation in three Lupinus species

BACKGROUND AND AIMS

In some lupin species, phosphate deficiency induces cluster-root formation, which enhances P uptake by increasing root surface area and, more importantly, the release of root exudates which enhances P availability.

METHODS

Three species of Lupinus, L. albus, L. atlanticus and L. micranthus, with inherently different relative growth rates were cultivated under hydroponics in a greenhouse at four phosphate concentrations (1, 10, 50 and 150 microm) to compare the role of internal P in regulating cluster-root formation.

KEY RESULTS

The highest growth rate was observed in L. atlanticus, followed by L. albus and L. micranthus. At 1 microm P, cluster-root formation was markedly induced in all three species. The highest P uptake and accumulation was observed in L. micranthus, followed by L. atlanticus and then L. albus. Inhibition of cluster-root formation was severe at 10 microm P in L. atlanticus, but occurred stepwise with increasing P concentration in the root medium in L. albus.

CONCLUSIONS

In L. atlanticus and L. albus cluster-root formation was suppressed by P treatments above 10 microm, indicating a P-inducible regulating system for cluster-root formation, as expected. By contrast, production of cluster roots in L. micranthus, in spite of a high internal P concentration, indicated a lower sensitivity to P status, which allowed P-toxicity symptoms to develop.

Molecular analysis of SCARECROW genes expressed in white lupin cluster roots

The Scarecrow (SCR) transcription factor plays a crucial role in root cell radial patterning and is required for maintenance of the quiescent centre and differentiation of the endodermis. In response to phosphorus (P) deficiency, white lupin (Lupinus albus L.) root surface area increases some 50-fold to 70-fold due to the development of cluster (proteoid) roots. Previously it was reported that SCR-like expressed sequence tags (ESTs) were expressed during early cluster root development. Here the cloning of two white lupin SCR genes, LaSCR1 and LaSCR2, is reported. The predicted amino acid sequences of both LaSCR gene products are highly similar to AtSCR and contain C-terminal conserved GRAS family domains. LaSCR1 and LaSCR2 transcript accumulation localized to the endodermis of both normal and cluster roots as shown by in situ hybridization and gene promoter::reporter staining. Transcript analysis as evaluated by quantitative real-time-PCR (qRT-PCR) and RNA gel hybridization indicated that the two LaSCR genes are expressed predominantly in roots. Expression of LaSCR genes was not directly responsive to the P status of the plant but was a function of cluster root development. Suppression of LaSCR1 in transformed roots of lupin and Medicago via RNAi (RNA interference) delivered through Agrobacterium rhizogenes resulted in decreased root numbers, reflecting the potential role of LaSCR1 in maintaining root growth in these species. The results suggest that the functional orthologues of AtSCR have been characterized.

gamma-Conglutin, the Lupinus albus XEGIP-like protein, whose expression is elicited by chitosan, lacks of the typical inhibitory activity against GH12 endo-glucanases

gamma-Conglutin, a glycoprotein from Lupinus albus seed, has been characterized at molecular level but its physiological function is still unknown. gamma-Conglutin shares a high structural similarity with xyloglucan-specific endo-beta-1,4-glucanase inhibitor proteins (XEGIPs) and Triticum aestivum xylanase inhibitor (TAXI-I), which act specifically against fungal glycosyl hydrolase belonging to families 12 and 11, respectively. To assess the possible involvement of gamma-conglutin in plant defense, germinating lupin seeds were incubated with chitosan. The relative quantification of gamma-conglutin mRNA extracted from cotyledons was then carried out by RT-qPCR and indicated that chitosan strongly elicited the expression of gamma-conglutin. Moreover, biochemical trials aimed to test the inhibitory capacity of the protein have been also carried out. gamma-Conglutin failed to inhibit representative fungal endo-glucanases and other cell wall-degrading enzymes. To explain the lack of inhibitory capacity we investigated the possible structural differences between gamma-conglutin and XEGIPs and TAXI-I, including the construction of a predictive 3D model of the protein. Bioinformatic analysis suggests that the lack of inhibitory activity of gamma-conglutin can be attributed to sequence differences in the inhibitor interaction domains, and in particular to a sequence deletion in one of the functional loops.