Cytokinin activity in Lupinus albus

The distribution and metabolism of {8-¹⁴C}zeatin incorporated into the transpiration stream of fruiting white lupin plants ( Lupinus albus L.) has been studied. The distribution pattern of ¹⁴C in the different aerial organs suggests that the amount of cytokinin being incorporated into any one organ may have been a function of its transpiration rate. Once in these organs, particularly the leaves, zeatin was rapidly metabolised and or utilised. This resulted in the formation of a number of labelled compounds that did not give a response with the soybean callus bioassay. Substances co-eluting with zeatin glucoside and ribosylzeatin appeared to be the principal biologically active metabolites. From the present evidence it can be concluded that the leaf and side shoots received a major proportion of the applied labelled cytokinin. However, the presence of a small amount of radioactivity co-eluting with zeatin and ribosylzeatin in the fruits indicates that the high levels of cytokinins normally associated with these organs need not necessarily all have been synthesised in situ.     

Cytokinin Activity in Lupinus albus

The cytokinin content of the root exudate and leaves of fruiting white lupin plants (Lupinus albus L.) was investigated at 2 weekly intervals after anthesis of the lowest flower on the primary inflorescence. Up to 8 weeks after anthesis the level of cytokinins in the root exudate increased. However, at 10 weeks after anthesis insufficient sap was produced for analysis. Cytokinins co-eluting with zeatin and zeatin riboside were detected in the root exudate after fractionation on Sephadex LH-20. The cytokinin levels in the mature leaves steadily increased up to 8 weeks after anthesis and thereafter remained relatively constant. Three peaks of activity, co-eluting with zeatin, zeatin riboside and the glucoside cytokinins were recorded in the leaf extracts. The level of glucoside cytokinins in the leaves was high at 8 and 10 weeks after anthesis. Paper chromatography of extracts of fruits collected at 2 weeks after anthesis indicated that as fruit development proceeded there was a build up of cytokinin in this region of the plant. It is suggested that, in the white lupin, the cytokinins translocated to the shoot are accumulated in the leaves and in the fruits and that it is only later when there is a considerable decrease in sap (10 weeks after anthesis) production that a decreasing supply of cytokinins leads to shoot senescence.     

Cytokinin Activity in Lupinus albus L: IV. Distribution in Seeds

Endogenous levels of cytokinin activity were examined in Lupinus albus L. seed at intervals of 2 weeks after anthesis using the soybean callus bioassay. High levels of cytokinin activity per gram seed material were present in the seeds at 2, 4, and 6 weeks after anthesis. The cytokinin activity per gram seed material was low at 8 and 10 weeks after anthesis. Cytokinin activity associated with each seed was greatest at 6 weeks after anthesis. The majority of the activity in the seeds at 4, 6, and 8 weeks after anthesis was in the endosperm. Cytokinin activity was also detected in the testas and embryos at 4, 6, 8, and 10 weeks, and the suspensors at 4 weeks. Column chromatography of extracts of the different seed fractions on Sephadex LH-20 indicated that the cytokinins present coeluted with zeatin, zeatin riboside, and the glucoside cytokinins. It is suggested that cytokinins are accumulated in the seeds and are stored in the endosperm mainly in the form of ribosides and glucosides of zeatin. The reduction in cytokinin activity in the seed coincides with the reduction in endosperm volume and embryo growth and suggests that these compounds are utilized during the course of seed maturation.     

Carbon Dioxide Fixation in the Carbon Economy of Developing Seeds of Lupinus albus (L.)

The effects of CO₂ concentration and illumination on net gas exchange and the pathway of ¹⁴CO₂ fixation in detached seeds from developing fruits of Lupinus albus (L.) have been studied.

Increasing the CO₂ concentration in the surrounding atmosphere (from 0.03 to 3.0% [v/v] in air) decreased CO₂ efflux by detached seeds either exposed to the light flux equivalent to that transmitted by the pod wall (500 to 600 micro-Einsteins per square meter per second) in full sunlight or held in darkness. Above 1% CO₂ detached seeds made a net gain of CO₂ in the light (up to 0.4 milligrams of CO₂ fixed per gram fresh weight per hour) but ¹⁴CO₂ injected into the gas space of intact fruits (containing around 1.5% CO₂ naturally) was fixed mainly by the pod and little by the seeds.

Throughout development seeds contained ribulose-1,5-bisphosphate carboxylase activity (EC 4.1.1.39), especially in the embryo (up to 99 micromoles of CO₂ fixed per gram fresh weight per hour) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) in both testa (up to 280 micromoles of CO₂ fixed per gram fresh weight per hour) and embryo (up to 355 micromoles of CO₂ fixed per gram fresh weight per hour).

In kinetic experiments the most significant early formed product of ¹⁴CO₂ fixation in both light and dark was malate but in the light phosphoglyceric acid and sugar phosphates were also rapidly labeled. ¹⁴CO₂ fixation in the light was linked to the synthesis of sugars and amino acids but in the dark labeled sugars were not formed.

     

A Lupinus albus root glycoprotein homologous to the polygalacturonase inhibitor proteins

A glycoprotein with an apparent molecular mass of 42 kDa (GP42), detected in the roots of Lupinus albus L. (cv. Rio Maior), was found to increase along the root axis with increasing distance from the apex and to be induced in roots cultured in vitro upon exogenous supply of high IAA (10^-3 M ). GP42 is ionically bound to the cell wall, it has a pl>8.3, and it is N -glycosylated. The purification of GP42 was accomplished by affinity chromatography (ConA-Sepharose) followed by cation-exchange chromatography (Mono S). The amino acid sequence of the amino terminal part of the protein shows 70% identity to that of polygalacturonase inhibitor proteins (PGIPs) from other species. GP42 inhibits the polygalacturonase activity from Aspergilltus niger in vitro suggesting that it is a PGIP. The possible relationship between the L. albus PGIP and root development is discussed.     

Organogenesis from hypocotyl thin cell layers of Lupinus mutabilis and Lupinus albus

When thin cell layers (TCLn), isolated from the nodalregion of the hypocotyl of 5 day old seedlings, werecultured in medium M1 with IAA and BA, entire plantswere obtained from L. mutabilis explants andprolific shoots from L. albus explants.Histological studies carried out on L. mutabilisTCLn showed that meristematic cells, present in theexplants at the time of inoculation, gave rise to theformation of a primary meristem resulting inorganogenesis. In TCLn where apical or axillarymeristematic cells were absent, we observed theformation of a nodular structure with a cambium-likelayer at its periphery which divided to form a primarymeristem leading to organogenesis. Plant regenerationfrom TCLn may be useful in genetic transformationassays.     

Characterization of an isoflavonoid-specific prenyltransferase from Lupinus albus

Prenylated flavonoids and isoflavonoids possess antimicrobial activity against fungal pathogens of plants. However, only a few plant flavonoid and isoflavonoid prenyltransferase genes have been identified to date. In this study, an isoflavonoid prenyltransferase gene, designated as LaPT1, was identified from white lupin (Lupinus albus). The deduced protein sequence of LaPT1 shared high homologies with known flavonoid and isoflavonoid prenyltransferases. The LaPT1 gene was mainly expressed in roots, a major site for constitutive accumulation of prenylated isoflavones in white lupin. LaPT1 is predicted to be a membrane-bound protein with nine transmembrane regions and conserved functional domains similar to other flavonoid and isoflavonoid prenyltransferases; it has a predicted chloroplast transit peptide and is plastid localized. A microsomal fraction containing recombinant LaPT1 prenylated the isoflavone genistein at the B-ring 3' position to produce isowighteone. The enzyme is also active with 2'-hydroxygenistein but has no activity with other flavonoid substrates. The apparent K(m) of recombinant LaPT1 for the dimethylallyl diphosphate prenyl donor is in a similar range to that of other flavonoid prenyltransferases, but the apparent catalytic efficiency with genistein is considerably higher. Removal of the transit peptide increased the apparent overall activity but also increased the K(m). Medicago truncatula hairy roots expressing LaPT1 accumulated isowighteone, a compound that is not naturally produced in this species, indicating a strategy for metabolic engineering of novel antimicrobial compounds in legumes.     

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     

Characterization of isoperoxidase-B2 inactivation in etiolated Lupinus albus hypocotyls

One basic peroxidase isoenzyme, with a pI of 8.8, is present in the intercellular washing fluid in the aerial part of 6-day-old Lupinus albus hypocotyl seedlings. This isoenzyme, called LuP-B2, is the principal soluble component secreted into the apoplastic space and it is a constitutive enzyme along the whole length of etiolated hypocotyl. The enzymatic inactivation process which this apoplastic peroxidase undergoes is described for the first time. The kinetic constants which describe its inactivation by H(2)O(2) in the absence of reductant substrates are determined. LuP-B2 is inactivated in situ and in vitro in a time- and concentration-dependent manner. H(2)O(2) acts as a suicide substrate according to a model previously proposed by us. The constant values calculated are similar to those calculated for the basic isoenzyme of horseradish roots, HRP-C. LuP-B2 presents a k(inact) value of 7.5 x 10(-3) s(-1) and a k(cat) of 6.7 s(-1). This isoenzyme makes 889 catalytic cycles for each inactivation event. The similarity in behavior and the constant values, together with other situations (both are excreted, soluble and constitutive isoenzymes) suggest that the inactivation process could play an important role in plant development and stress situations.     

Changes in lipoxygenase activity during seedling development of Lupinus albus

A lipoxygenase preparation was obtained from Lupinus albus seeds and was shown to differ from previously characterized lipoxygenase. This study describes changes in lipoxygenase activity during seedling development of Lupinus albus. The enzyme activity shows a decrease from 0–6 h postgermination (about 15%), is roughly constant or even rises slightly from 6–30 h and then shows a large increase between 30 and 48 h (about 50%). Enzymatically active proteins from 48 h-old seedlings were isolated and the increase of enzyme activity was mainly due to the presence of two components with maximum activity at pH 6 and pH 8.5, respectively. When arachidonic acid was used as substrate, the two enzymatic activities produce 15 HPETE. The increase in lipoxygenase activity during seedling development was inhibited by cycloheximide. Cordycepin appears to have no direct effect on lipoxygenase synthesis in vivo at the studied doses.     

Protein and Respiration in the Apical Region of the Shoot of Lupinus albus

This investigation is a study of differentiation in the apicalregion of the shoot in terms of the protein content and respirationof the dome and of each of the first seven primordia and internodes.The results obtained have been compared with others reportedearlier showing the volumes and number of cells of each morphologicalcomponent of the same system. It has been shown that internodalcells tend to have a higher content but a lower concentrationof protein than primordium cells. As the series is traversedfrom the upper younger to the lower older units respirationper unit protein tends to increase in the primordia. In theinternodes it is highest in the first three, decreases abruptlyfrom the third to the fourth, and then increases again. Frequentlythe values for the dome are intermediate between those for thefirst internode and those for the first primordium. The significanceof these differences is discussed.     

Distribution of Growth in the Apical Region of the Shoot of Lupinus albus

The purpose of the investigation is the determination of thevolumes and numbers of cells of the meristematic dome and ofeach of the first 7 primordia and internodes at the apex ofthe shoot of Lupinui albus. This system occupies a zone whichis about 0·4 mm. in length. Techniques are describedfor dissecting the region in which the observations are made,for determining the numbers of cells and the volumes of theseveral fragments. From the number of cells and the volume ofeach fragment an average cell volume it calculated. It is shown that in the midphase of the plastochron the domecontains 3,500 cells and has a volume of 1·6 x10^–3mm.³,the first primordium contains 1,630 cells and has a volume of0·38 x10^–3 mm.³, and the first intemode containsabout 700 cells and has a volume of about 1·4 x10^–3mm³The number of cells and the volume of the primordium increaseexponentially with increasing plastochron age, and the seventhprimordium contains 26,000 cells and has a volume of 20·9x 10^–3mm³ The seventh intemode contains about 5,000 cellsand has a volume of 8·6x10^–3mm³ The average cell volume in the dome is 4·7 x 10^–7mm.³in the first primorndium it is 2·3 x 10^–7mm.³ andin the first internode it is 20·9x 10^–7mm.³ Inthe seventh primordium the average cell volume increases to7·9 x 10^–7mm.³ In the internodes there is little,if. any, change in cell volume from the first to the seventhof the series. The significance of these changes is discussed.     

Leghemoglobin in Lupin Plants (Lupinus albus cv Multolupa)

Leghemoglobin was localized by immunogold techniques in nodules of Lupinus albus cv Multolupa inoculated with Bradyrhizobium sp. (Lupinus) strain ISLU 16. The protein localization was performed in nodules embedded in Spurr's and Araldite epoxy resins and Lowycryl K4M. A very good preservation of both the ultrastructure and antigenicity was obtained with the tissues embedded in Araldite following glutaraldehyde fixation and unpostfixed in osmium tetroxide. Lupin leghemoglobin is a stable and abundant protein which allows a conventional method to be safely used for localization of leghemoglobin. Labeling of leghemoglobin was specifically confined to the cytosol matrix and nuclei. Gold particles were never observed in the peribacteroidal spaces nor in the cytoplasmic organelles of the infected cells. Decrease of leghemoglobin was observed when the plants were grown with 10.7 micromolar and 21.4 micromolar of nitrate.     

Phosphorus Stress-Induced Proteoid Roots Show Altered Metabolism in Lupinus albus

Proteoid roots develop in Lupinus albus L. in response to nutrient stress, especially P. Proteoid roots excrete citrate and thus increase the availability of P, Fe, and Mn in the rhizosphere. In an effort to understand citrate synthesis and organic acid metabolism in proteoid roots of lupin, we have evaluated in vitro enzyme activities of citrate synthase (CS), malate dehydrogenase (MDH), and phosphoenolpyruvate carboxylase (PEPC) in proteoid and normal roots of plants grown with or without P. Organic acid concentrations, respiration rates, and dark 14CO2-labeling patterns were also determined. The in vitro specific activities of CS, MDH, and PEPC and in vivo dark 14CO2 fixation were higher in proteoid roots compared to normal roots, particularly under P stress. Western blot analysis showed that PEPC enzyme protein was more highly expressed in -P proteoid roots compared to other tissues. The majority of the fixed 14C was found in organic acids, predominantly malate and citrate. A larger fraction of citrate was labeled in P- stressed proteoid roots compared to other root tissue. Respiration rates of proteoid roots were 31% less than those of normal roots. The data provide evidence for increased synthesis of citrate in proteoid roots compared to normal roots, particularly under P stress. A portion of the carbon for citrate synthesis is derived from nonautotrophic CO2 fixation via PEPC in proteoid roots.     

Sucrose Metabolism in Lupinus albus L. Under Salt Stress

Salt stress (50 and 150 mM NaCl) effects on sucrose metabolism was determined in Lupinus albus L. Sucrose synthase (SS) activity increased under salt stress and sucrose phosphate synthase activity decreased. Acid invertase activity was higher at 50 mM NaCl and decreased to control levels at 150 mM NaCl. Alkaline invertase activity increased with the salt stress. Glucose content decreased with salt stress, sucrose content was almost three times higher in plants treated with 150 mM NaCl and fructose content did not change significantly. The most significant response of lupin plants to NaCl excess is the increase of sucrose content in leaves, which is partially due to SS activity increase under salinity. This revised version was published online in July 2006 with corrections to the Cover Date.     

An examination of the peroxidases from Lupinus albus L. hypocotyls

Peroxidases (EC 1.11.1.7) from hypocotyls of Lupinus albus L. cv. Rio Maior have been characterised using one- and two-dimensional, native electrophoretic techniques. Data are presented showing the complexity in charge and molecular size or shape of these peroxidases. We report the finding of a new acidic peroxidase and several new basic peroxidases in these hypocotyls, and of their stability to treatments considered to break ligand-induced variants and conformational variants derived from differences in polypeptide folding. Densitometric data demonstrate that these new peroxidases contribute up to 60 of the total peroxidase activity in hypocotyls. Studies of intercellular fluid, cell-wall and soluble fractions, with assays of purity were conducted in an attempt to define the subcellular locations of these additional peroxidases. The acidic form (pI 4.1) is greatly enriched in soluble fractions, three of the basic peroxidases (pIs 9.5, 9.7 and >9.7) are strongly associated to the cell wall, ad a minor, basic component (pI 9.7) is enriched in the intercellular fluid. Individual peroxidase activities with the substrates coniferyl alcohol, ferulic acid or indole acetic acid were compared by densitometric analysis of zymograms with those for guaiacol, and notable differences between these peroxidases in their capacity to oxidise indole acetic acid in vitro were identified. The possible functions of these peroxidases in vivo and their implications to current understanding of peroxidases in L. albus are discussed.Abbreviations APAGE anionic polyacrylamide gel electrophoresis - CA coniferyl alcohol - CPAGE cationic polyacrylamide gel electrophoresis - IEF isoelectric focusin - NEIEF non-equilibrated isoelectric focusing - 2D two dimensional - pI isoelectric point - RCPAGE reversed current polyacrylamide gel electrophoresis     

Effect of drought and rewatering on the metabolism of Lupinus albus organs

Alterations in the metabolism of Lupinus albus organs that result from and subsequently follow a period of severe water deficit (WD) are described. By means of 13C-nuclear magnetic resonance (NMR), changes in the major metabolites were monitored in several plant organs (leaflets and petiole, roots, stem stele and cortex). During the stress, most of the leaves were lost and the stem functioned as a storage repository of sugars (glucose and sucrose) and amino acids (asparagine and proline). Upon rewatering, lupin plants rapidly re-established the relative water content (RWC) and produced new leaves. However, at the metabolic level, the events seem to be more complex, since proline (a stress related metabolite) disappeared rapidly while sugars and asparagine reached the initial pattern more slowly, particularly in the stem.