pH above 6.0 reduces nodulation in Lupinus species

Lupinus angustifolius and Lupinus pilosus differ substantially in root growth in response to high solution pH with L. angustifolius showing much greater sensitivity to pH above 6. This study examined the effect of pH above 6 on nodulation of these two species in buffered solution. Shoot weight and root weight and length in L. pilosus was not significantly affected by pH, whereas the growth of shoots and roots of L. angustifolius was markedly impaired by increasing pH. Total root length, the number of lateral roots, and the length of individual lateral roots were greatly decreased, resulting in decreased uptake of iron and phosphorus. In addition, L. angustifolius had a higher internal requirement for iron than L. pilosus. A solution pH above 6 decreased the number of nodule initials and nodules similarly in both species but decreased nodule mass much more in L. angustifolius. The effect of high pH on nodule formation occurred prior to that on host shoot growth. High pH also decreased nitrogen concentration and content in both species but to a greater extent for L. angustifolius. The results suggested that pH above 6 has a specific effect in the impairment of nodulation in lupins.     

High pH Causes Disintegration of the Root Surface in Lupinus angustifolius L.

The effect of high pH on the morphology and anatomy of the rootsof lupin (Lupinus angustifolius L. cv. Yandee) and pea (Pisumsativum L. cv. Dundale) was examined in buffered solution. Themorphology and anatomy of lupin roots were markedly altered,and root growth was reduced by increasing solution pH from 5·2to 7·5, whereas pea roots were unaffected. In lupin roots,pH 7·5 caused disintegration of the root surface andimpaired root hair formation. Lupin roots grown at pH 7·5also had decreased cell lengths but increased cell diameterin both the epidermis and the cortex in comparison to rootsgrown at pH 5·2. High pH reduced cell volume greatlyin the epidermis, to a lesser extent in the outer cortex andnot at all in the inner cortex. It appears that in lupins, theprimary detrimental effects of growth at pH 7·5 is reducedlongitudinal growth of cells near the root surface with a consequentreduction in elongation of the cells in inner cortex.Copyright1993, 1999 Academic Press Lupinus angustifolius L., Pisum sativum L., high pH, root morphology, root anatomy     

Lupinus species differ in their requirements for iron

The effect of iron supply on the growth and nodulation ofLupinus angustifolius L. (Gungurru),Lupinus luteus L. (R-1171) andLupinus pilosus Murr. (P20957) was studied in acid solutions. Plants of the three species were grown together in the same solution and inoculated withBradyrhizobium (Lupinus) WU 425. Plants were then grown with or without applied NH₄NO₃. The lupin species differed greatly in their sensitivity to low iron concentrations in solution withL. pilosus being most tolerant andL. luteus most sensitive.L. pilosus had the highest iron concentration in tissues and had a higher ratio of iron concentration in the youngest fully expanded leaf blades (YEB) to that in roots than the other two species.L. luteus had higher iron concentrations in roots but lower iron concentration in YEB and shoots than didL. angustifolius. The requirements of internal iron for the maximal chlorophyll synthesis in YEB were 65 μg g^-1 forL. angustifolius andL. luteus, and 52 μg g^-1 forL. pilosus. In contrast to effects on growth, the three species had similar external iron requirements for nodule formation in roots and for maximal nitrogen concentrations in shoots. The results indicate that iron tolerant lupin species require lower internal and external iron supply and have a greater ability than sensitive species to translocate iron from roots to shoots.     

High pH in the nutrient solution impairs water uptake in Lupinus angustifolius L.

Root growth in Lupinus angustifolius is greatly decreased when the nutrient solution has a pH above 6.0. This study examined the water relations in this species (cv. Yandee) in response to high pH in solution culture in a glasshouse.The dry weight of roots, the length of taproots and lateral roots and the number of lateral roots were significantly reduced at day 12 after transfer to solution with a pH of 7.5 compared to pH 5.2. This resulted in a marked reduction of total root surface area. However, shoot growth and total leaf area were not affected. In comparison with pH 5.2, plants grown at pH 7.5 in the nutrient solution had a 14–38% more-negative leaf water potential, and their stomatal resistance had increased by 67%.The observations indicate that the impairment of the water relations by high pH is mainly caused by decreased root growth.     

Cluster-root production and organic anion exudation in a group of old-world lupins and a new-world lupin

We examined the capacity of several Old-World lupin species (Lupinus luteus L., L. hispanicus Boiss. et Reuter and L. angustifolius L.) and one species of a New-World lupin (L. mutabilis Sweet) to form cluster roots under a range of conditions in solution culture. The effect of the synthetic auxin, IBA (indole-3-butyric acid), on cluster-root development in L. luteus and L. albus L. provided with an adequate phosphorus (P) supply was also investigated. In addition, the effect of a high nitrate-N (NO₃-N) supply on the efflux of citrate and malate from roots of L. angustifolius was examined to determine if specific regions of the root system exuded these organic anions. When P-deficient, L. hispanicus, L. luteus and L. mutabilis formed cluster roots that secreted organic anions. Citrate was generally the dominant organic anion exuded, although succinate was also exuded in large quantities from L. luteus. Citrate efflux by L. hispanicus and L. luteus was at least comparable to that reported for P-deficient L. albus[up to 1.092 nmol g^–1 fresh weight (FW) s^–1], but was over an order of magnitude lower in L. mutabilis (0.036 nmol g^–1 FW s^–1). Citrate and malate were not detected in significant amounts from either the lateral roots or the root tips of any species grown under P-sufficient or -deficient conditions. Citrate efflux from cluster roots of L. luteus showed a diurnal pattern, similar to that reported for L. albus, with maximum efflux during the day, and declining to a minimum before dawn. IBA added to the nutrient solution induced cluster-root formation on both L. albus and L. luteus at concentrations of P that would normally suppress the production of these roots. However, the IBA-induced cluster roots did not exude significant amounts of citrate. Although L. angustifolius did not produce cluster roots when P-deficient, it produced cluster-like root structures that exuded citrate (0.053 nmol g^–1 FW s^–1) when grown at a high nitrate-N (NO₃-N) supply. L. angustifolius did not exude significant citrate or malate from lateral roots or root tips when grown at either high or low NO₃-N supply. Our findings for L. hispanicus and L. luteus are the first reports of cluster-root formation in response to P deficiency for these Old-World species, and for L. mutabilis, it is the first report of cluster roots for a New-World lupin species. These reports indicate that evolutionary and biogeographical aspects of cluster-root formation in the genus Lupinus need to be revised. Furthermore, investigation is warranted to determine the capacity of species of the large group of New-World lupins to form cluster roots in soils of their native habitats.     

Effects of pH and bicarbonate on the nutrient status and growth of three Lupinus species

Aims

High pH, and high bicarbonate (HCO₃⁻) and calcium (Ca) availability characterise calcareous soils. High [Ca] only partially explains why some Lupinus species are calcifuge, so we explored high [HCO₃⁻] and high pH.

Methods

We grew six Lupinus genotypes in hydroponics with pH 5, 6.5 and 8^a (adjusted by KOH), and 8^b (adjusted by KHCO₃). Leaf symptoms and areas, root appearance and biomass were recorded; whole leaf and root nutrient concentrations, and leaf cellular phosphorus (P), Ca and potassium (K) concentrations were determined using elemental X-ray microanalysis.

Results

Chlorosis was observed in young leaves at high pH for L. angustifolius and L. cosentinii, and P deficiency at high pH for all genotypes. High pH decreased iron (Fe) and zinc (Zn) uptake in all genotypes. It also decreased lateral root growth, the uptake of P, K, Ca, and manganese (Mn) by all sensitive species; and translocation of P, Fe, Zn, Mn, and Ca to leaves in most sensitive species. However, leaf [Ca], leaf [K], [K] within each measured cell type, and translocation of K and Ca to leaves of L. pilosus and L. cosentinii at pH 8 were greater than at pH 5 and 6.5. Compared with pH 8^a, all L. angustifolius genotypes translocated more P, Fe, Zn, Mn and K from roots to leaves at pH 8^b. High pH did not affect the leaf cell types that accumulated P and Ca, but decreased the leaf cellular [P].

Conclusions

Lupinus angustifolius and L. cosentinii were sensitive to high [HCO₃⁻] and/or high pH; L. pilosus was relatively tolerant. High pH decreased lateral root growth and nutrient uptake, inhibiting growth of sensitive species. High [HCO₃⁻] diminished the negative effect of pH 8 on nutrient translocation to leaves in most L. angustifolius genotypes. This knowledge provides critical insights into the habits of Lupinus species to guide breeding of calcicole plants.

     

Penetration of very strong soils by seedling roots of different plant species

The abilities of seedling roots of twenty-two plant species to penetrate a strong growth medium were compared under controlled conditions. Seedlings were grown for 10 days in compression chambers filled with siliceous sandy soil at 0.2 kg kg^–1 water content and mean penetrometer resistance of 4.2 MPa. Root elongation and thickening were measured after growth. The results show that soil strength reduced the elongation of roots of all plant species by over 90% and caused the diameters of the roots to increase compared with control plants grown in vermiculite (0 MPa resistance).Differences in both root elongation and root diameter were observed among plant species. Generally, the roots of dicotyledons (with large diameters) penetrated the strong medium more than graminaceous monocotyledons (with smaller diameters). There was a significant positive correlation (r=0.78, p<0.05) between root diameter and elongation over all the species in the stressed plants. The species were ranked according to the relative root elongation and relative root thickening. Based on this ranking, lupin (Lupinus angustifolius), medic (Medicago scutelata) and faba bean (Vicia faba) were the species with the greatest thickening and elongation while wheat (Triticum aestivum), rhodesgrass (Chloris gayana) and barley (Hordeum vulgare) had the least. The weight of the seeds did not seem to influence either the thickening or elongation of the roots.     

Spatio-temporal mapping of local soil pH changes induced by roots of lupin and soft-rush

Aims

The rhizosphere is a dynamic system strongly influenced by root activity. Roots modify the pH of their surrounding soil causing the soil pH to vary as a function of distance from root surface, location along root axes, and root maturity. Non-invasive imaging techniques provide the possibility to capture pH patterns around the roots as they develop.

Methods

We developed a novel fluorescence imaging set up and applied to the root system of two lupin (Lupinus albus L., Lupinus angustifolius L.) and one soft-rush (Juncus effusus L.) species. We grew plants in glass containers filled with soil and equipped with fluorescence sensor foils on the container side walls. We gained highly-resolved data on the spatial distribution of H⁺ around the roots by taking time-lapse images of the samples over the course of several days.

Results

We showed how the soil pH in the vicinity of roots developed over time to different values from that of the original bulk soil. The soil pH in the immediate vicinity of the root surface varied greatly along the root length, with the most acidic point being at 0.56–3.36 mm behind the root tip. Indications were also found for temporal soil pH changes due to root maturity.

Conclusion

In conclusion, this study shows that this novel optical fluorescence imaging set up is a powerful tool for studying pH developments around roots in situ.     

Changing proton concentrations at the surfaces of gravistimulated Phleum roots

The pH patterns at the surfaces of both vertically growing roots of Phleum pratense L. and roots tilted by 45° were recorded using H ⁺-sensitive microelectrodes. During vertical growth the root cap exhibited lower pH values than the meristematic zone. The highest pH values were found at the border between meristematic and elongation zones. In the apical part of the elongation zone the values strongly decreased basipetally. They reached a minimum value of pH 5.4–5.5 (medium pH of about 6.0) at a distance of 700 m from the root tip. This region of strongest acidification usually coincided with that of the highest relative rates of elongation. The region of the first visible curvature following gravistimulation was positioned at 100–200 m more apically. The pH values increased in the basal elongation zone towards the mature zone. The H⁺-flux pattern around a vertically growing Phleum root was characterized by high influxes in the meristematic zone and smaller effluxes in the elongation zone. Tilting the root by 45° induced changes in the pH values of the upper and lower sides of a Phleum root. At a distance of 300–500 m from the root tip, the upper side was strongly acidified while the pH of the lower side slightly increased compared with the values during vertical orientation. pH differences of up to 0.9 pH units between the two sides of a root were detected. These differences decreased basipetally and could not be measured more distant than 700–800 m from the tip. Compared with a vertically growing root, the H⁺-flux pattern of a Phleum root tilted by 45° exhibited effluxes on the entire upper organ flank while the pattern was scarcely altered on the lower side. The curvature-initiating zone in Phleum roots is positioned within that section of the root in which pH changes occur after tilting. The region of highest pH differences, however, is nearer to the apex of the root than the curvature-initiating zone. The pH changes began 8.2 min after a root had been tilted. The bending process started after 17.2 min, i.e. after double the time needed for differential acidification. After reorienting a root, which had just begun to bend, to its previous vertical position the inversion of the pH gradient could be measured within the same mean time of about 8 min. This is again significantly earlier than the beginning of the rebending process. The results indicate that, during the graviresponse, ionic movements occur much earlier than the changes in hormonal activities reported in the literature.Abbreviation CIZ curvature-initiating zone A preliminary report was presented at the 29th Plenary Meeting of the Committee on Space Research (COSPAR) in Washington D.C., USA, 28 Aug – 5 Sept 1992 (Zieschang and Sievers 1993)This work was supported by the Deutsche Forschungsgemeinschaft. We thank Professor H. Felle (Botanisches Institut, Universität Gießen, Gießen, FRG) for practical instructions concerning the method of H⁺-sensitive microelectrodes and Professor W. Simonis (Botanisches Institut, Universität Würzburg, Würzburg, FRG) for allowing to use the microelectrode amplifier.     

Wheat growth responses of cultivars to H+ concentration

Shoot length (cm), shoot fresh weight (g/pot), root length (cm), and root fresh weight (g/pot) were measured on six cultivars of wheat (Triticum aestivum L. cv Saluda, C9733, Gore, Stacy, FL301, and FL302) grown at pH 6.0, 5.5, 5.0, 4.5, or 4.0 for 14 days in white quartz flintshot sand. Plants were watered on alternate days with pH-adjusted buffer solutions. All measured plant parameters decreased as H⁺ concentration increased from pH 6.0 to 4.0. Decreased lengths of shoots and roots were similar among the cultivars as the pH decreased. This indicated a uniform response of wheat cultivars to excess H⁺ concentration in the soil solution; however, the decrease in shoot and root length was only about 50% as large as was previously reported for sorghum [Sorghum bicolor (L.) Moench.].     

Release of phenols from Lupinus albus L. roots exposed to Cu and their possible role in Cu detoxification

The mechanisms enabling plants to tolerate high concentrations of available Cu in their rhizosphere are still poorly understood. To better understand the mechanisms involved, Lupinus albus L. (white lupin) was grown over 40 days in a hydroponic system compelling roots to develop under sterile conditions in the presence of a nutrient solution containing 0.5, 20 or 62 M Cu. The following parameters were investigated in detail: low molecular weight phenols in nutrient solution (colorimetric assay), high molecular weight phenols in roots and in solution (HPLC-MS, HPLC-UV), pH, redox potential in solution (electrochemistry) and Cu distribution in the plant (AAS) as well as in apical root sections (EDX microanalysis). Finally, in vitro adsorption studies using voltammetry were conducted to evaluate the Cu adsorption behaviour of different phenolic compounds. When exposed to 62 M Cu, biomass production of white lupin was strongly reduced. Plants grown in the presence of 20 M Cu had a similar dry matter production compared to the control plants grown in a 0.5 M Cu solution. However, an increased release of soluble and high molecular weight phenols into the solution was observed. The concentration of polyphenolic compounds in the roots (particularly isoflavonoids like genistein and genistein-(malonyl)-glucoside) was significantly higher for lupins grown in a 20 M Cu solution compared to the control plants. As shown by an in vitro adsorption study, these phenolic compounds can bind Cu ions. In addition, plants exposed to 20 and 62 M Cu cumulated high Cu amounts in root cell walls whereas only low amounts reached the symplasm. Therefore, it is proposed that the complexation of Cu²⁺ ions in the rhizosphere and in the roots apoplasm by phenolic compounds could alleviate Cu-mediated toxicity.     

Effects of solution pH and bicarbonate on the growth and nodulation of a range of grain legume species

Defining plant adaptation to soil conditions is critical for the successful introduction of grain legume species into farming systems. This nutrient solution study examined the effects of pH (4, 5, 6, 7 and 8) and bicarbonate (5 mM KHCO₃) on the growth and nodulation of 14 grain legume species supplied with N or reliant on N₂-fixation. Species includedPisum sativum L.,Cicer arietinum L.,Lens culinaris Med., and a range ofLupinus, Vicia andLathyrus species. Species differed greatly in response to solution pH. For both N-fertilized and N₂-fixing plants, shoot growth ofL. culinaris was very sensitive to low pH (pH < 7), whereas shoot growth ofLupinus angustifolius L. andLupinus albus L. was sensitive to higher pH (pH ≥ 6). Other species had a broader optimal pH range for growth when supplied with N, but were generally sensitive to low pH (pH < 7 forC. arietinum andVicia sativa L., pH < 6 forP. sativum, Vicia faba L.,Lathyrus sativus L. andLathyrus cicera L., and pH < 5 forVicia benghalensis L. andVicia narbonensis L.) when reliant on N₂-fixation. For these other species, symbiotic N₂-fixation appeared to be more sensitive than host plant growth to low pH. This finding was supported by lower nodule numbers and mass, and lower N concentrations in shoots of sensitive species at low pH relative to higher pH. ForL. culinaris, nodule numbers and mass were relatively unaffected by pH 5–8, N concentrations in shoots were high at low pH and plants developed symptoms relating to H⁺ toxicity at pH as high as 7. These results indicate that host plant growth ofL. culinaris is more sensitive to low pH than theRhizobium symbiosis. ForL. albus andL. angustifolius, both host plant growth and symbiotic N₂-fixation appeared to be equally sensitive to pH ≥ 6.Lupinus pilosus Murr. was more tolerant of high pH than the otherLupinus species. At pH 4, two genotypes ofC. arietinum had better early nodulation than other species.Vicia ervilia L. nodulated poorly at all levels of solution pH, indicating that the commercial Group E inoculum (Rhizobium leguminosurum bv.viceae SU303) may not be effective for this species in solution culture. Addition of bicarbonate decreased shoot growth, nodulation and N concentrations in shoots of most species. Early nodulation (nodule number) ofLathyrus ochrus (L.) DC was not affected by the bicarbonate treatment.     

Evaluation of Lupinus Species to Accumulate Heavy Metals From W aste Waters

Several Lupinus species, for example, Lupinus albus, Lupinus luteus, Lupinus angustifolius, and Lupinus hispanicus were used to accumulate Mn(II), Cd(II), Pb(II), Cr(III), Cr(VI), Hg²⁺, and CH₃Hg⁺ from waste waters. The influence of different species concentrations (50 and 100 mg L^-1) and pH on growing behavior as well as the resulting distribution of metals in the plants were investigated. The results obtained showed that lupins were able to germinate and to grow in the presence of the metals mentioned above, even when they were present at levels as high as 50 mg L^-1. Accumulation of Pb(II), Cr(III), and Cd(II) was higher in roots than in shoots. As far as mercury is concerned, the highest CH₃Hg and Hg²⁺ accumulation was detected in roots, but fast transport toward the leaves was noticed. In contrast to mercury, the uptake of chromium seems to be influenced by the chemical form of the analyte, remaining Cr(VI) in solution. No differences in growing behavior and accumulation were observed for the four Lupinus species studied. Even though plants were exposed only a relatively short time to the metal solutions, metal concentrations of approximately 2 g/kg of dry matter were detected in the young lupins plants. The feasibility of utilizing Lupinus plants for the removal of heavy metals from wastewater was also investigated. Lupins were able to grow under extreme conditions (wastewater, pH lower than 2) and to remove 98% of the initial amount of toxic metals present in the sample.     

In-situ soil solution chemistry in an acid forest soil as influenced by growing roots of Norway spruce (Picea abies [L.] Karst.)

A new approach for non-destructive monitoring of soil solution chemistry in high spatial and temporal resolution for rhizosphere studies is presented. In a 5×10 mm grid, 30 micro suction cups (1mm) were installed in a rhizotron with Norway spruce (Picea abies [L.] Karst.) growing in low pH B-horizon soil. Roots grew through the grid, closely passing the suction cups. Soil solution composition before, during and after root passage was determined. For K⁺ and Mg²⁺ a significant decrease of soil solution concentration near root tips and elongation zones was observed, indicating a marked uptake of these elements. Mg²⁺ concentration was also significantly lowered when the root system aged, suggesting that this ion might also be taken up in older parts of the root system. No influence of growing roots was found on Na⁺-concentrations.     

Evidence for the acid-growth theory of fusicoccin action

Three predictions of the acid-growth theory of fusicoccin (FC) action in inducing cell elongation were reinvestigated using abraded segments of maize (Zea mays L.) coleoptiles. i) Quantitative comparison of segment elongation and medium-acidification kinetics measured in the same sample of tissue shows that these FC-induced processes are strictly correlated in time and respond coordinately to cations present in the medium. ii) Fusicoccin (1 mol l^-1) induces a rapid acidification of the cell-wall solution, reaching a final level of pH 3.8–4.0. Exogenous protons are able to substitute quantitatively for FC in causing segment elongation at pH 3.8–4.0. At pH 4, FC has no additional effect on cell elongation. iii) Neutral buffers (pH 7) completely abolish the FC-mediated growth response. iv) Cycloheximide (10 mg l^-1) inhibits both FC-induced and acid-buffer(pH 4)-induced elongation after a lag of 40–45 min, and FC-induced H⁺ excretion after a lag of 2 h. Under the same conditions, indole-3-acetic acid-induced elongation and H⁺ excretion are inhibited without detectable lag. It is concluded that these results are fully compatible with the acid-growth theory of FC action.Abbreviations IAA indole-3-acetic acid - CHI cycloheximide - FC fusicoccin     

Effect of root environment on proton efflux in wheat roots

Proton net efflux of wheat (Triticum aestivum L.) roots growing in sand culture or hydroponics was determined by measuring the pH values of the solution surrounding the roots by pH microelectrodes, by base titration and by color changes of a pH indicator in solid nutrient media. The proton net efflux was dependent on light, aeration, and source of nitrogen (NH ₄ ⁺ , NO ₃ ^? ). Ammonium ions caused the highest proton efflux, whereas nitrate ions decreased the proton efflux. Iron deficiency had no significant effect on proton efflux. Replacement of ammonium by nitrate inhibited proton efflux, whereas the reverse enhanced proton extrusion. A lag period between changes in plant environment and proton efflux was observed. The proton net efflux occurred at the basal portion of the roots but not in the root tips or at the elongation zone. Under optimal conditions, proton efflux capacity reached a maximum value of 5.7 μmole H⁺ g^?1 fresh weight h^?1 with an average (between different measurements) of 3.4 μmole H⁺ g^?1 fresh wth^?1 whereas the pH value decreased to 3.2–3.7 and reached a minimal value of 2.9. Inhibition of ATPase activity by orthovanadate inhibited proton efflux. The results indicate that proton efflux in wheat roots is ammonium ion and light dependent and probably governed by ATPase activity.     

Promotion of root elongation by phosphorus deficiency

Decrease of culture solution pH and increase in cation/anion ratio in the plant were observed when horsegram (Macrotyloma uniflorum (Lam.) Verdc.) was grown in solution culture deficient in phosphorus. The effux of H⁺ from the roots of –P plants was observed in bromocresol purple agar. The length of root cells was considerably increased by –P treatment. Thus a close correlation between H⁺ excretion, length of the root cells and root elongation in response to P deficiency was established.     

Glutamate activates cation currents in the plasma membrane of<Emphasis Type="Italic"> Arabidopsis</Emphasis> root cells

The effect of glutamate on plant plasma membrane cation transport was studied in roots of Arabidopsis thaliana (L.) Heynh. Patch-clamp experiments using root protoplasts, ²²Na⁺ unidirectional fluxes into intact roots and measurements of cytosolic Ca²⁺ activity using plants expressing cytosolically-targeted aequorin in specific cell types were carried out. It was demonstrated that low-millimolar concentrations of glutamate activate within seconds both Na⁺ and Ca²⁺ currents in patch-clamped protoplasts derived from roots. The probability of observing glutamate-activated currents increased with increasing glutamate concentration (up to 29% at 3 mM); half-maximal activation was seen at 0.2–0.5 mM glutamate. Glutamate-activated currents were voltage-insensitive, instantaneous (completely activated within 2–3 ms of a change in voltage) and non-selective for monovalent cations (Na⁺, Cs⁺ and K⁺). They also allowed the permeation of Ca²⁺. Half-maximal Na⁺ currents occurred at 20–30 mM Na⁺. Glutamate-activated currents were sensitive to non-specific blockers of cation channels (quinine, La³⁺, Gd³⁺). Although low-millimolar concentrations of glutamate did not usually stimulate unidirectional influx of ²²Na⁺ into intact roots, they reliably caused an increase in cytosolic Ca²⁺ activity in protoplasts isolated from the roots of aequorin-transformed Arabidopsis plants. The response of cytosolic Ca²⁺ activity revealed a two-phase development, with a rapid large transient increase (lasting minutes) and a prolonged subsequent stage (lasting hours). Use of plants expressing aequorin in specific cell types within the root suggested that the cell types most sensitive to glutamate were in the mature epidermis and cortex. The functional significance of these glutamate-activated currents for both cation uptake into plants and cell signaling remains the subject of speculation, requiring more knowledge about the dynamics of apoplastic glutamate in plants.Abbreviations GLR Gene in plants encoding glutamate receptor-like protein - iGluRs Ionotropic glutamate receptors     

Regulators of cell division in plant tissues

[³H]zeatin was supplied through the transpiration stream to de-rooted lupin (Lupinus angustifolius L.) seedlings. The following previously known metabolites were identified chromatographically: 5-phosphates of zeatin riboside and dihydrozeatin riboside, adenosine-5-phosphate, zeatin riboside, zeatin-7-glucopyranoside, zeatin-9-glucopyranoside, adenine, adenosine and dihydrozeatin. Five new metabolites were purified; four of these contain an intact zeatin moiety. Two were identified unequivocally, one as l--[6-(4-hydroxy-3-methylbut-trans-2-enylamino)-purin-9-yl]alanine, a metabolite now termed lupinic acid, and the second as O--d-glucopyranosylzeatin. These two compounds were the major metabolites formed when zeatin solution (100 M) was supplied to the de-rooted seedlings. The radioactivity in the xylem sap of intact seedlings, supplied with [³H]zeatin via the roots, was largely due to zeatin, dihydrozeatin and zeatin riboside. When [³H]zeatin (5 M) was supplied via the transpiration stream to de-rooted Lupinus luteus L. seedlings, the principal metabolite in the lamina was adenosine, while in the stem nucleotides of zeatin and adenine were the dominant metabolites. O-Glucosylzeatin and lupinic acid were also detected as metabolites. The level of the latter varied greatly in the tissues of the shoot, and was greatest in the lower region of the stem and in the expanding lamina. Minor metabolites also detected chromatographically were: (a) dihydrolupinic acid, (b) a partially characterized metabolite which appears to be a 9-substituted adenine (also formed in L. angustifolius), (c) glucosides of zeatin riboside and/or dihydrozeatin riboside, and (d) O-glucosyldihydrozeatin. While lupinic acid supplied exogenously to L. luteus leaves underwent little metabolism, chromatographic studies indicated that O-glucosylzeatin was converted to its riboside, the principal metabolite formed, and also to adenosine, zeatin and dihydrozeatin. A thinlayer chromatography procedure for separating zeatin, dihydrozeatin, zeatin riboside and dihydrozeatin riboside is described.Abbreviations Me₃Si trimethylsilyl - TLC thin-layer chromatography - UV ultraviolet XXIV=Gordon et al., 1975     

Monitoring uptake and contents of Mg,Ca and K in Norway spruce as influenced by pH and Al,using microprobe analysis and stable isotope labelling

In a model system using intact spruce trees (Picea abies [L.] Karst.) we followed the path of magnesium, calcium and potassium during uptake into the root and during long-range transport into the shoot, by multiple stable isotope labelling. The roots of two- and three-year-old spruce trees originating from soil culture were removed from the soil and, in part or in toto, exposed to labelling solutions containing the stable isotopes ²⁵Mg or ²⁶Mg, ⁴¹K and ⁴²Ca or ⁴⁴Ca. Optical-emission-spectroscopy (ICP-OES) of plant fractions and labelling solutions was combined with the quantitative analysis of stable isotope ratios in sections of shock frozen, cryosubstituted material using the laser-microprobe-mass-analyser (LAMMA). This combination allowed us to distinguish, both in bulk samples and on the cellular level between (i) the fraction of elements originally present in the plant before the start of the labelling, (ii) the material taken up from the labelling solution into the plant and (iii) any material released by the plant into the labelling solution.In single-root labelling experiments, roots of three-year-old spruce trees, grown in nursery soil, were exposed to various pH conditions. The exchange of Mg and Ca with the labelling solution was nearly 100% in the cell walls of the mycorrhized finest roots. This exchange was only slightly affected by a step down to pH 3.5. The absolute Mg and Ca content in the cell walls was moderately reduced by incubation at pH 3.5 and strongly reduced in the presence of Al at this pH. After a pH 3.5 and 2 mM Al treatment we found Al in the xylem cell walls and the cortex cell lumina at elevated concentrations. To analyse the combined effect of high Al and high proton concentrations on the long-range transport, we used a split-root system. The root mass of an intact two-year-old spruce tree, grown in mineral soil, was divided into even parts and both halves incubated in solutions with two sets of different stable isotopes of Mg and Ca (side A: no Al, ²⁵Mg and ⁴²Ca; side B: +Al, ²⁶Mg and ⁴⁴Ca) and ⁴¹K on both sides. We observed a large uptake of Mg, Ca and K into the plant and a pronounced release. The net uptake of all three elements was lower from the Al-doted solution. In cross-sections of the apical shoot we found after seven-day labelling period about 60–70% of the Mg and Ca and 30% of the K content in the xylem cell walls originating from both labelling solutions. The clear majority of the Mg and Ca label originated from the Al-doted side.