bluuebunny/crossref_metadata_2025 huggingface dataset:
Distinct sequence elements in a napin promoter interact in vitro with DNA‐binding proteins from Brassica napus
Authors: Gustavsson Hans‐Olof , Ellerström Mals , Stålberg Kjell , Ezcurra Inés , Koman Ahmet , Höglund Anna‐Stina , Rask Lars , Josefsson Lars‐Göran
Published: May 2006

Nuclear extracts obtained from developing seeds of oilseed rape, Brassica napus cv. Svalöv Karat K 20516, were shown to contain several distinct DNA‐binding proteins as evidenced by gel retardation experiments. Four of the proteins were capable of interacting in vitro with oligonucleotide probes containing sequences related to motives in a napin gene promoter and its upstream region. Another protein interacted with an A/T‐rich repeated sequence present at the 3’end of the gene. The proteins appear to be present also in leaf nuclei and do not show any detectable variations that correlate with napin expression during seed development. Thus, analogous with many transcription factors, the DNA‐binding proteins that we have identified are present in both expressing and non‐expressing cells.
Water status of callus from Hevea brasiliensis during induction of somatic embryogenesis
Authors: Etienne H. , Berger A. , Carron M. P.
Published: May 2006

To improve somatic embryogenesis in Hevea brasiliensis, the water and plant growth regulator status of the culture medium was studied. Induction of embryogenic tissue from the internal integument of immature seeds was clearly favored by stabilizing the water potential of the culture medium at –0.7 MPa, by using low and decreasing concentrations of 3,4‐dichlorophenoxyacetic acid and benzyladenine or by incorporating 10‐7M abscisic acid in the medium. Each of these changes in the medium favored a specific water status in the callus, namely a high relative water content (93 to 95%) and an elevated water potential (–0.9 MPa). These characteristics were apparently important for initiating somatic embryogenesis, and their decrease corresponded to the loss of embryogenic potential in the callus. Thus, the relative water content and water potential of callus appear to be good markers of its embryogenic state.
Changes in ascorbate, glutathione, and related enzyme activities during thidiazuron‐induced bud break of apple
Authors: Wang Shiow Y. , Jiao Hong J. , Faust Miklos
Published: May 2006

The changes of ascorbic acid, dehydroascorbic acid, and glutathione content and related enzyme activities were studied in apple buds during dormancy and thidiazuron‐induced bud break. An increase in ascorbic acid, reduced form of glutathione (GSH), total glutathione, total non‐protein thiol (NPSH) and non‐glutathione thiol (RSH) occurred as a result of induction by thidiazuron during bud break, whereas dehydroascorbic acid and oxidized glutathione (GSSG) decreased during the same period. Thidiazuron also enhanced the ratio of GSH/GSSG, and activities of ascorbate free radical reductase (AFR; EC 1.6.5.4), ascorbate peroxidase (EC 1.11.1.11). dehydroascorbate reductase (DHAR; EC 1.8.5.1) and glutathione reductase (GR; EC 1.6.4.2). The ascorbic acid content and the activities of AFR, ascorbate peroxidase, and DHAR peaked when buds were in the side green or green tip stage just prior to the start of rapid expansion, and declined thereafter. The GSH, NPSH, RSH, ratio of GSH/GSSG, and activities of GR increased steadily during bud development.
Function of the polygalacturonase convertor in ripening tomato fruit
Authors: Knegt Erik , Vermeer Evert , Pak Caroline , Bruinsma Johan
Published: May 2006

In extracts from pericarp tissue of ripening tomato (Lycopersicon esculentum Mill. cv, Sonato) fruits, two isoenzymes of polygalacturonase (E.C. 3.2.1.15), PG1 and PG2, are usually found. Also in such extracts, or as part of PG1, a convertor (CV) occurs. Incubation of PG2 with this CV gives rise to PG1 or a different isoenzyme, PGx, that is also stable at 65°C but differs in pH optimum and size from PG1. It appears that CV has two affinity sites that can bind with PG2 or with a polydextran. PG1 is an extraction artifact, consisting of one molecule of CV and two molecules of PG2. PGx is made up of one molecule of CV and one molecule of PG2. It is the CV part of PGx that binds to polydextrans such as Blue Dextran 2000, Sephadex G‐100, and cell wall preparations. In this last form PGx is the physiologically active form of the enzyme, solubilizing demethylated pectin.

On Sephacryl S‐300, CV appears to have a molecular weight of 81 kDa, but because of its heat stability and partial leakage through a 10 kDa cut‐off membrane, it might be a much smaller, rod‐like molecule. The polygalacturonase convertor might be a lectin without intrinsic enzyme activity, with a function to immobilize, stabilize and activate enzymic proteins in the cell wall.
Contribution of aleurone layer and scutellum to α‐amylase synthesis and secretion in wheat and rice grains
Authors: Thévenot Cluadine , Simond‐Côte Elizabeth , Daussant Jean
Published: May 2006

Intact aleurone layers from wheat (Triticum aestivum L. cv Camp Rémy) and rice (Oryza sativa L. cv Cigalon) grains both contained and secreted more α‐amylase (EC 3.2.1.1.) than did the corresponding scutellar tissues. This discrimination was already evident at the earliest stages of germination at which the tissues could be isolated, and became more pronounced upon subsequent germination and growth. Isoenzyme patterns obtained upon isoelectric focusing showed a considerable polymorphism of the α‐amylases of each cereal. The enzyme polymorphism pattern was the same in the aleurone layer and in the scutellum, but some secondary constituents appeared to be more specific for the one or the other of the tissues. Moreover, the isozymes found in the tissues were the same as those found to be secreted. A third α‐amylase antigen which differs from the well established α1 and α11 forms was identified in the germinating wheat grains. The presence of Ca2+ in the secretion medium favoured maximum secretion of α‐amylases from the wheat scutellum and aleurone layers, whereas it inhibited the secretion of the enzymes from the rice aleurone layer.
Further studies on autoclaved‐induced toxicity in tissue culture media: gauging sugar breakdown by spectrophotometry
Authors: Hsiao Ke‐Cheng , Bornman Chris H.
Published: May 2006

Fructose and sucrose were used to investigate cyanide‐induced absorption changes after high temperature treatment. By comparing the time‐resolved absorbance difference spectra obtained under aerobic conditions with those under aerobic conditions, absorbance changes that are associated with the process of oxygen consumption were identified. The rates of absorbance changes of autoclaved sucrose solution or of autoclaved MS medium (Murashige and Skoog 1962. Physiol. Plant. 15: 473–497) were correlated with those of oxygen consumption measured by polarography and used for determining the toxicity of culture media (Hsiao and Bornman 1991. Physiol. Plant. 81: 55–58). When autoclaved together with sucrose, FeNa‐EDTA promotes its degradation. Absorbance change, therefore, is a convenient parameter for measuring not only the extent of carbohydrate breakdown at high temperature but also the relative toxicity of culture media autoclaved under different conditions.
The effect of aluminium on uptake and distribution of magnesium and calcium in roots of mycorrhizal Norway spruce seedlings
Authors: Jentschke Georg , Schlegel Hedda , Godbold Douglas L.
Published: May 2006

Spruce seedlings (Picea abies (L.) Karst.) colonized with Lactarius rufus (Scop.) Fr. or Lactarius theiogalus Fr. were grown in an axenic silica sand culture system with frequently renewed nutrient solution. After successful mycorrhizal colonization the seedlings were exposed to 800 μM Al(NO3)3 (pH 3.9) for 13 or 17 weeks. Concentrations of Al, Mg, and Ca in the tissues of the mycorrhizal root tips were determined by X‐ray microanalysis. After 13 or 17 weeks of exposure to Al, high Al concentrations were found in cell walls of all mycorrhizal tissues except the stele tissues. Compared to the controls Mg levels in most of the mycorrhizal structures were reduced by Al treatment. Calcium levels in cortex cell walls of root tips colonized with L. rufus were reduced by exposure to Al. However, in cell walls of the stele Ca levels were significantly increased. No differences in Al or Mg levels were detected in structures of mycorrhizal and non‐mycorrhizal root tips from the same individual seedlings. These results suggest that (1) the endodermis is the primary barrier to radial Al transport and (2) the presence of a hyphal sheath did not prevent Al from reaching the root cortex and from displacing Mg and Ca.
Effect of linolenic acid on release of the 43 kDa polypeptide and manganese from photosystem II membranes depleted of the 33 kDa extrinsic polypeptide
Authors: Garstka Maciej , Kaniuga Zbigniew
Published: May 2006

The effect of linolenic acid (18:3) on release of the 43 kDa polypeptide and manganese from photosystem II (PS II) membranes depleted of extrinsic polypeptides was studied. In both control and NaCl‐washed particles which were depleted of the extrinsic 23 and 16 kDa polypeptides, the 18:3 treatment caused a 20% release of the 33 and 43 kDa polypeptides. In CaCl2, (or urea + NaCl)‐washed particles, which were depleted of the 33 kDa polypeptide in addition to the 23 and 16 kDa polypeptides, the release of the 43 kDa polypeptide increased to 70%, whereas only 25% of the 47 kDa polypeptide was removed. These findings suggest (i) that the 33 and the 43 kDa polypeptides are neighbows in the photosynthetic membrane and (ii) that the 33 kDa polypeptide shields the 43 kDa polypeptide against the action of 18:3. Incubation of CaCl2, or (urea + NaCI)‐treated PSII particles in the presence or absence of 18:3 resulted in the loss of only 2 of the 4 Mn atoms present per reaction center. this indicates that the 2 Mn atoms more firmly associated with PSII are not affected by the removal of the extrinsic 16, 23 and 33 kDa polypeptides, and the intrinsic 43 kDa polypeptide. nor by the treatment with linolenic acid.
Effect of source‐sink relations and nitrogen nutrition on senescence and N remobilization in the flag leaf of wheat
Authors: Guitman Maria R. , Arnozis Patricia A. , Barneix Atilio J.
Published: May 2006

The relation between the source‐sink ratio and nitrogen nutrition on grain yield of wheat (Triticum aestivum L. cv. Klein Chamaco) was studied in a greenhouse experiment. Plants were grown until anthesis in pots with soil fertilized with 0.16 mmol N per plant twice a week. At anthesis, all leaves but the flag leaf were excised in a group of plants. In another group the treatment consisted in a similar defoliation plus the longitudinal excision of half the ear, while a third group was left untouched as a control. At the same time, the N supply to half of the plants in each group was interrupted, while the other half continued receiving 16 mM N. The defoliated plants showed a longer functional life of the flag leaf than the control, retaining the chlorophyll, soluble proteins and total reduced nitrogen for a longer time. The ear‐excised plants showed an intermediate behavior. The plants with the interrupted N supply showed a faster leaf senescence than the N supplied ones, and this coincided with an increase in the proteolytic activity and nitrogen transport to the ear. However there were no differences in ear weight between the two nitrogen treatments. It is concluded that leaves and ear compete for the nitrogen, and that a low level of carbohydrates in the flag leaf, due to a low source‐sink ratio, delays leaf senescence.
Reversal by light of deleterious effects of chilling on oxygen evolution, manganese and free fatty acid content in tomato thylakoids is not accompanied by restoration of the original membrane conformation
Authors: Garstka Maciej , Kaniuga Zbigniew
Published: May 2006

Free fatty acids (FFA) generated in thylakoids upon chilling of tomato leaves at 0°C for a few days result in release of functionally active Mn and inactivation of O2 evolution. Chilling does not lead to a decrease in the extrinsic 16, 23 and 33 kDa polypeptides. Upon illumination of chilled leaves both Mn content and O2 evolution in thylakoids are restored and FFA content is reduced to the level of the control. Photoactivation of O2 evolution in chilled leaves does not change the ratio of unsaturated/saturated FFA. Constant Arrhenius activation energy (Ea) for O2 evolution by thylakoids isolated from control leaves was found, whereas it increased at temperatures below 8.0 and 10.5°C in thylakoids from cold‐treated and photoactivated leaves, respectively. This indicates that restoration of O2 evolution as well as of FFA and Mn contents is not accompanied by a complete reversal of membrance conformation.
Changes in membrane lipid components and antioxidant levels during natural ageing of seeds of Acer platanoides
Authors: Pukacka Stanislawa
Published: May 2006

Changes in membrane lipid components and cellular antioxidant systems were investigated through 7 years in seeds of Acer platanoides L. after storage in natural conditions, i.e. ‐ 3°C and 10% water content. The loss of germination capacity in aged seeds was associated with increased solute leakage during imbibition, reduced content of phospholipids, especially phosphatidylcholine, and increased free fatty acid content. A marked decrease of unsaturated fatty acids in the phospholipid fraction was observed after one year of storage. Antioxidant potential in the lipid fraction and level of ‐SH groups decreased during storage. The results are consistent with the hypothesis that ageing in seeds is mediated by a free radical mechanism.
Carotenoids and abscisic acid (ABA) biosynthesis in higher plants
Authors: Parry Andrew D. , Horgan Roger
Published: May 2006

Recent research has revealed that abscisic acid (ABA), synthesised in response to water stress, is an apo‐carotenoid. Two potential carotenoid precursors, 9′‐cis‐neoxanthin and 9‐cis‐violaxanthin, have been identified in light‐grown and etiolated leaves, and in roots of a variety of species. Experiments utilizing etiolated Phaseolus vulgaris leaves and deuterium oxide strongly suggest that 9′‐cis‐neoxanthin, synthesised from all‐trans‐violaxanthin, is the immediate pre‐cleavage precursor of ABA. The cleavage of 9′‐cis‐neoxanthin, performed by an inducible and specific dioxygenase, is likely to be the rate‐limiting step in ABA biosynthesis. Any apocarotenoids formed as by‐products of cleavage are probably rapidly degraded by lipoxygenase or related enzymes. After cleavage xanthoxin is converted via ABA‐aldehyde to ABA by constitutive enzymes in the cytosol.
Regulation of type I phytochrome mRNA abundance
Authors: Colbert James T.
Published: May 2006

The plant photoreceptor phytochrome regulates many aspects of plant development. Not surprisingly, phytochrome gene expression is also carefully regulated. In most of the plant species that have been studied, type I phytochrome mRNA levels in etiolated seedlings are decreased after exposure of the seedlings to light. The dramatic decrease in type I phytochrome mRNA abundance in oat seedlings appears to be due to a combination of a phytochrome‐mediated decrease in transcription of the type I phytochrome gens coupled with the inherent instability of the type I phytochrome mRNA.
Contrasting photo‐ and thermoperiod‐induced changes in abscisic acid and lipid contents in leaves of mungbean seedlings
Authors: Aghofack‐Nguemezi Jean , Christmann Alexander , Frosch Silvia , Trémoliéres Antoine , Wagner Edgar
Published: May 2006

Seedlings of Phaseolus aureus ROXB were grown under 12/12 h light/dark cycles with the light period at 32.5°C and darkness at 10°C (normal conditions N) or with light at 10°C and darkness at 32.5°C (inverse conditions, I). I‐conditions affected the level of chlorophyll and carotenoids (very low), monogalactosyldiacylgycerol (low) and phosphatidylinositol (high) in the leaves. Leaves of I‐seedlings showed a sharp and durable decline of relative water content during the low temperature phase. For the N‐seedlings, loss of water was restricted to the end of this period. The loss of water was accompanied by visible symptoms of wilting at specific times of day. Although the pigment content remained nearly unchanged, ABA content of leaves of both N‐and I‐seedlings increased during water stress. Upon return to the warm period, ABA level continued to increase after the leaves had regained turgor, this ‘after stress’increase being more pronounced in the leaves of I‐seedlings. Exogenous application of ABA induced a slight increase in the content of phospholipids in N‐ and I‐leaves and a decrease in free fatty acids, whereas monogalactosyldiacylglycerol content was significantly reduced in N‐leaves after application of ABA. Upon transfer of I‐plants to 20°C for 12 h during the light period, pigment and chloroplastic lipid content increased rapidly whereas upon a further exposure to 10°C in light, pigments and especially monogalactosyldiacylglycerol were lost. The control of pigment and lipid metabolism and the role of ABA during chilling stress are discussed.
NAD(P)H dehydrogenases on the inner surface of the inner mitochondrial membrane studied using inside‐out submitochondrial particles
Authors: Rasmusson Allan G. , Møller Ian M.
Published: May 2006

Submitochondrial particles (SMP) were isolated from potato (Solanum tuberosum L. cv. Bintje) tubers. The SMP were 91% inside‐out and they were able to form a membrane potential, as monitored by oxonol VI, with succinate, NADH and NADPH. The pH dependence and kinetics of NADH and NADPH oxidation by these SMP was studied using three different electron acceptors – O2, duroquinone and ferricyanide. In addition, the SMP were solubilized, fractionated by non‐denaturing polyacrylamide gel electrophoresis, and the gels were stained for NAD(P)H dehydrogenase activity and specificity at different pH using Nitro Blue Tetrazolium. From the results we conclude that there are at least two distinct NAD(P)H dehydrogenases on the inner surface of the inner membrane: (1) Complex 1 which oxidizes NADH and deamino‐NADH in a rotenone‐sensitive manner, (O2 as acceptor) with optimum activity at pH 8 and a very low Km(NADH) of 3 μM. It also oxidizes NADPH and deamino‐NADPH in a rotenone‐sensitive manner, but with a pH optimum at pH 5.8 and a very high Km(NADPH) of more than 1 mM. This complex is found as a broad, diffuse band at the top of the gels. (2) A second dehydrogenase which oxidizes NADH in a rotenone‐insensitive manner with optimum activity at pH 6.2 and a higher Km(NADH) of 14 μM. It also oxidizes NADPH in a rotenone‐insensitive manner with an activity optimum at pH 6.8 and low Km(NADPH) of 25 μM. This dehydrogenase does not oxidize deamino‐NAD(P)H. One of the sharp bands around the middle of the native gels may be caused by this dehydrogenase indicating that it has a relatively low molecular mass compared to Complex I. Several other NAD(P)H dehydrogenase bands were observed on the gels which we cannot yet assign.
Influence of an inhibitor of gibberellin biosynthesis, paclobutrazol, on apple seed gibberellin content
Authors: Steffens G. L. , Stafford A. E. , Lin J. T.
Published: May 2006

Tissue‐culture‐propagated own‐rooted cv. Spartan apple trees (Malus domestica Borkh.) planted in 1979 were treated in 1983 and 1985 via a soil‐line trunk drench with the plant growth retardant paclobutrazol [(2RS, 3RS)‐1‐(4‐chlorophenyl)‐4.4‐dimethyl‐2‐(1,2, 4‐triazol‐1‐yl) pentan‐3‐ol]. Seeds of immature fruits from untreated and treated trees were sampled in 1989 ca 75 days after full bloom. After seeds were freeze‐dried, gibberellins (GAs) were extracted, purified and fractionated via C18 reversed‐phase high‐performance liquid chromatography (HPLC). Gibberellins A1, A3, A4, A7, A8, A9, A15, A17, A19, A20, A24, A34, A35, A44, A51, A53, A54, A61, A62, A63 and A68 were identified by using C18 HPLC, gas chromatography‐selected ion monitoring and Kovats retention indices. Eight of the GAs identified were also quantified by using deuterated internal standards. The paclobutrazol applications caused a 55% reduction of vegetative shoot elongation in 1989, but both treated and untreated trees had developed a biennial bearing pattern by that time (heavy bloom or “on year’in 1989). Levels of early 13‐hydroxylation pathway GAs, viz. GA53, GA19, GA20, GA1 and also GA3, were not altered by treatment. However, GA4, GA7 and GA9 were increased 13.4, 6.5 and 3.8 times, respectively, in seeds of fruit from treated compared to untreated trees.
Photoinhibition of photosynthesis in intact willow leaves in response to moderate changes in light and temperature
Authors: Rosenqvist Eva , Wingsle Gunnar , Ögren Erling
Published: May 2006

When willow leaves were transferred from 270 to 650 μmol m‐2 s‐1 photosynthetic photon flux density (PPFD), partial photoinhibition developed over the next hours. This was manifested as roughly parallel inhibitions of the ratio of variable over maximal chlorophyll fluorescence (Fv/FM), and of the maximal quantum yield and the capacity of photosynthesis. This occurred even though photosynthesis was operating well below its capacity and only about one fourth of the reaction centres of photosystem (PS) II were in the closed state. When the air temperature was lowered from 25 to 15°C (18°C leaf temperature) photoinhibition was markedly accelerated. This temperature effect is suggested to be mediated largely by a decrease in the rate of energy dissipation through photosynthesis and indicated by a 50% increase in the number of closed PSII reaction centres. The pool size of the carotcnoid zeaxanthin and the extent of inhibition of the Fv/FM ratio were positively correlated during the treatment. However, the relaxation following imposition of darkness was much faster for zeaxanthin than for the Fv/FM ratio, ruling out the possibility of a direct causal relationship. The energy distribution between PSII and PSI was unaltered upon photoinhibition. However, the functioning of the PSII reaction centres was altered, as indicated by a rise in the minimal fluorescence, Fa.
Correlation between cell wall extensibility and the content of diferulic and ferulic acids in cell walls of Oryza sativa coleoptiles grown under water and in air
Authors: Tan Kah‐Siew , Hoson Takayuki , Masuda Yoshio , Kamisaka Seiichiro
Published: May 2006

Rice (Oryza sativa L. cv. Sasanishiki) coleoptiles grown under water achieved greater length than those grown either in air or under water with constant air bubbling. The extensibility of cell walls in coleoptiles grown under water was larger than that in the other treatments. Per unit length of the coleoptile, the content of ferulic and diferulic acids ester‐linked to hemicelluloses was higher in air and bubbling type coleoptiles than in water type ones. The extensibility of the coleoptile cell walls correlated with the content of diferulic acids per unit length and per hemicellulose, suggesting that the enhancement of the formation of diferulic acid bridges in hemicelluloses in air or under water with air bubbling makes the cell walls mechanically rigid; thereby inhibiting cell elongation in rice coleoptiles. In addition, the ratio of diferulic acid to ferulic acid was almost constant irrespective of coleoptile age, zone and growth conditions, suggesting that the feruloylation of hemicelluloses is rate‐limiting in the formation of diferulic acid bridges in the cell walls of rice coleoptiles.
Proton and sucrose transport in isolated tonoplast vesicles from sugarcane stalk tissue
Authors: Getz Hans Peter , Thom Margaret , Maretzki Andrew
Published: May 2006

Tonoplast vesicles prepared from immature sugarcane (Saccharum spp., hybrid cv. H65–7052) tissue and purified on a discontinuous dextran gradient take up sucrose. Uptake was stimulated by MgATP. Evidence that the mechanism is linked to proton transport is derived from “pH jump’data and from inhibition of ATP‐stimulated sucrose transport by the protonophore carbonyl cyanide m‐chlorophenylhydrazone (CCCP) and by the proton‐channel blocker of proton‐linked ATPases. N. N'‐dicyclo‐hexylcarbodiimide (DCCD). A saturable phase of sucrose uptake was found at low substrate concentrations, and a linear phase characterized uptake at higher concentrations. Uptake was specific for sucrose, as demonstrated by competition experiments with various sugars. Sucrose uptake by the vesicle fraction was inhibited by KNO3, protonophores and protein modifying reagents, whereas sodium orthovanadate had no effect. Overall, the evidence suggests an ATP‐hydrolysis‐dependent tonoplasl antiport for sucrose transport, although a more direct influence of ATP on conformational changes in relevant tonoplast proteins cannot be ruled out.
Development of fertilized ovules and their role in the growth of the pea pod
Authors: García‐Martínez José L. , Martí Manuel , Sabater Teresa , Maldonado Amparo , Vercher Yolanda
Published: May 2006

The histological development of fertilized ovules during fruit‐set and development in pea (Pisum sativum L. cv. Alaska) has been investigated. Killing the ovules on day 0 (anthesis) or day 1 prevented fruit‐set and resulted in ovary degeneration. When the ovules were destroyed at later stages the ovaries developed, though the rate of growth of the pod was reduced significantly. Pollination in pea occurs normally the day before anthesis, and fertilization of the egg cell 32 to 48 h later. The first divisions of the zygote and endosperm nuclei started simultaneously (ca 48 h after pollination) but the endosperm developed more rapidly than the embryo; the embryo sac cavity was lined with free endosperm nuclei at the time of beginning suspensor elongation. Extracts of endosperm and ovule coats from ovules at day 7 after anthesis showed fruit‐set activity in pea, the latter material having about 3 times more activity than the former per ovule basis. These results indicate that fertilization of the ovule is necessary for fruit‐set in pea, and that compounds which induce fruit‐set are probably synthesized in the ovules following fertilization.
Hydrogen cyanide and embryonal dormancy in apple seeds
Authors: Bogatek Renata , Dziewanowska Katarzyna , Lewak Stanislaw
Published: May 2006

Embryos of apple (Malus domestica Borh. cv. Antonówka) were treated with 1 mM gaseous HCN for 6 h and cultured under a 12 h photoperiod. HCN pretreatment stimulated germination, increased the length of hypocotyls, shortened the main root and decreased the percentages of seedlings with asymmetrically grown as well as with asymmetrically greened cotyledons. High activity of β‐cyanoalanine synthase (EC 4.4.1.9) and a sharp increase in cyanogen content during embryo culture suggested very low levels of endogenous HCN. despite the activity of HCN releasing enzymes. The obtained data allow us to postulate an important role for cyanide in the regulatory complex controlling dormancy in apple seeds. Experiments with respiratory inhibitors indicated, however, that HCN pretreatment affected neither the alternative electron transport pathway nor residual respiration.
Cyanide controls enzymes involved in lipid and sugar catabolism in dormant apple embryos during culture
Authors: Bogatek Renata , Lewak Stanislaw
Published: May 2006

The activities of alkaline lipase (EC 3.1.1.3, AlkL), isocitrate lyase (EC 4.1.3.1. ICL), pyruvate kinase (EC 2.7.1.40. PK) and glucose–6–phosphate dehydrogenase (EC 1.1.1.49, G6PDH) were determined in cultured, dormant embryos of apple (Malus domestica Borb. cv. Antonówka), pretreated with gaseous HCN. The C6/C1, ratio was estimated in the same material. The activities of AlkL and ICL were not stimulated by HCN pretreatment until the period of maximum stimulation of germination. The activity of G6PDH was inhibited by cyanide only late during the culture of embryos. Therefore, the changes in these activities are considered to be the result and not the cause of enhanced germination. On the other hand, also PK, active very early during the culture of embryos, was modified as a result of the treatment. The cyanide‐induced changes in activity of this enzyme in cotyledons (inhibition followed by stimulation) were similar to those in the whole embryo, whereas its changes in the embryonal axis (stimulation followed by inhibition) resembled CN‐induced changes in PK in axes of apple seeds submitted to cold stratification (Bogatek and Lewak 1988). The estimation of C6/C1 ratios partly confirmed these observations. A role of HCN‐induced modifications of PK activity in embryonal dormancy is proposed.
Kinetics of NH4+ and K+ uptake by ectomycorrhizal fungi. Effect of NH4+ on K+ uptake
Authors: Jongbloed R. H. , Clement J. M. A. M. , Borst‐Pauwels G. W. F. H.
Published: May 2006

NH4+ and K+ uptake experiments have been conducted with 3 ectomycorrhizal fungi, originating from Douglas fir (Pseudotsuga menziesii (Mirb.] Franco) stands. At concentrations up to 250 μM, uptake of both NH4+ and K+ follow Michaelis‐Menten kinetics. Laccaria bicolor (Maire) P. D. Orton, Lactarius rufus (Scop.) Fr. and Lactarius hepaticus Plowr. ap. Boud. exhibit Km values for NH4+ uptake of 6, 35, and 55 μM, respectively, and Km values for K+ uptake of 24, 18, and 96 μM, respectively. Addition of 100 μM NH4+ raises the Km of K+ uptake by L. bicolor to 35 μM, while the Vmax remains unchanged. It is argued that the increase of Km is possibly caused by depolarization of the plasma membrane. It is not due to a competitive inhibition of K+ by NH4+ since the apparent inhibitor constant is much higher than the Km, for NH4+ uptake. The possibility that NH4+ and K+ are taken up by the same carrier can be excluded. The Km, values for K+ uptake in the two other fungi are not significantly affected by 100 μM NH4+. Except for a direct effect of NH4+ on influx of K+ into the cells, there may also be an indirect effect after prolonged incubation of the cells in the presence of 100 μM NH4+.
Voltammetric studies of the cell membrane of the alga Nitellopsis obtusa as modified by positively charged amphiphilic derivatives of glycine esters
Authors: Przestalski Stanislaw , Janas Tadeusz , Trela Zenon , Witek Stanislaw , Gwoździński. Krzysztof
Published: May 2006

Voltammetric studies in the presence of amphiphilic derivatives of glycine esters were performed on cells of the alga Nitellopsis obtusa (Desv. in Lois) J. Gr. using intracellular microelectrodes. The effect of these ammonium salts on the algal cell membrane was observed on multi‐impulse voltammograms, cyclic voltammograms and electrically‐induced action potential curves. An equivalent circuit of the investigated system with a theoretical description is presented. The results suggest that an amphiphilic ammonium salt blocks K+ channels in the plasmalemma and enhances the passive efflux of Cl− ions (as opposed to the action of tetraethylammonium chloride, TEA+ Cl−, and the non‐polar amphiphilic compound dimethyldodecyloamine, DDA). A comparative analysis is presented of the postulated molecular action of the investigated ammonium salts with the effects of TEA+ and DDA.
Aluminium effects on growth, nutrient net uptake and transport in 3 rice (Oryza sativa) cultivars with different sensitivity to aluminium
Authors: Jan Farid
Published: May 2006

Varietal differences in net nutrient uptake rate and transport efficiency in the presence of aluminium have seldom been investigated in rice. Therefore, effects of Al on growth, uptake and transport of macronutrients (K, P, Ca, and Mg) and micronutrients (Fe, Zn, Cu, and Mn) were evaluated in 3 rice cultivars (BG35, DA14 and IR45) with different Al sensitivity. The plants were grown in nutrient solution at pH 4.1. An initial growth was completed in the time interval 1 to 5 days immediately before the addition of Al. The final growth period with Al (0, 140, 280 or 560 μM) was completed on day 26. With Al, a comparatively high P accumulation occurred in shoots and roots of the Al tolerant cultivar BG35. In contrast, the Al sensitive cultivar IR45 maintained a relatively high Ca accumulation during the Al treatment. A reduced total net uptake rate of P and Ca by IR45 in the time period 5 to 26 days was due to both a reduced root fresh weight and a reduced net uptake rate per g fresh weight of root. Moreover, net Ca transport to the shoots higher than net uptake rate in DA14 and IR45 at > 140 μM Al during the test period suggests restricted Ca uptake by the roots in combination with a continuous net loss of Ca from the roots to the shoots as time proceeds. In the case of Mg and Mn, there was a general reduction of net uptake rates, irrespective of Al sensitivity of cultivars. With Al treatment, comparatively high accumulation of Fe, Zn and Cu occurred in the roots of IR45, concomitant with a high net Zn and Cu uptake rate. It is concluded that differences in Al sensitivity among rice cultivars BG35, DA14 and IR45 are not primarily linked to the depressed internal Mg or Mn status of the plants but rather to changes in the uptake and distribution of Ca and P.
Relationship between growth irradiance and the xanthophyll cycle pool in the diatom Nitzschia palea
Authors: Willemoës Michael , Monas Elizabeth
Published: May 2006

The size and de‐epoxidation state of the xanthophyll cycle pool was measured in cultures of Nitzschia palea grown at six fluence rates in continuous light or with a 12 h photoperiod. In both series the size of the pool increased with increasing irradiance. The de‐epoxidized form, diatoxanthin, was only present at fluence rates saturating for growth. The portion of diadinoxanthin, which was not readily de‐epoxidized in saturating light, was constant and not related to the size of the pool. In the culture grown in a light‐dark cycle at 300 μmol photons m‐2 s‐1 (PAR) increasing de‐epoxidation took place in the latter half of the photoperiod, when the rate of photosynthesis was decreasing. A rapid, spectrophotometric method for measuring the extent of de‐epoxidation of the xanthophyll cycle pool in a culture of diatoms is described. Upon addition of a small volume of hydrochloric acid to an extract of pigments in 90% acetone, the absorbance at 480 nm is reduced. The size of the reduction is a measure of the state of the xanthophyll cycle pool, since the absorbance of diatoxanthin is reduced by 5%, but the absorbance of diadinoxanthin by 87% due to an epoxide‐furanoid rearrangement, which causes the absorption spectrum to be shifted by ca 20 nm towards shorter wavelengths.
Calcium dependence of the effects of abscisic acid on RNA synthesis during germination of Cicer arietinum seeds
Authors: Colorado Pilar , Nicolás Gregorio , Rodríguez Dolores
Published: May 2006

The effect of abscisic acid (ABA) and CaCl2 in the medium on RNA synthesis in embryonic axes of seeds of chick‐pea (Cicer arietinum L. cv. Castellana) during the first hours of germination has been studied. ABA decreases the incorporation of 3H‐uridine in the embryonic axes and modifies the mRNA populations by preventing the disappearance of three polypeptides of 25, 22 and 21.6 kDa and inducing the appearance of two polypeptides of 35 and 27 kDa absent in the control. Calcium increases the effect of ABA on the synthesis of these mRNAs and seems to be involved in the synthesis of at least the polypeptide of 25 kDa, as this polypeptide disappears in the treatments with EGTA and Verapamil. Moreover, cytosolic calcium seems to be necessary for the accumulation of these messengers since treatment with TMB‐8 (chelating agent for endogenous calcium) decreases the intensity of the bands corresponding to these 5 polypeptides. The possible synergistic action of ABA and calcium in this process is discussed.
Effect of aluminium on lipid peroxidation, superoxide dismutase, catalase, and peroxidase activities in root tips of soybean (Glycine max)
Authors: Cakmak Ismail , Horst Walter J.
Published: May 2006

Inhibition of root elongation and modification of membrane properties are sensitive responses of plants to aluminium. The present paper reports on the effect of AI on lipid peroxidation and activities of enzymes related to production of activated oxygen species. Soybean seedlings (Glycine max L. cv. Sito) were precultured in solution culture for 3–5 days and then treated for 1–72 h with Al (AICI3) concentrations ranging from 10 to 75 μM at a constant pH of 4.1. In response to Al supply, lipid peroxidation in the root tips (< 2 cm) was enhanced only after longer durations of treatment. Aluminium‐dependent increase in lipid peroxidation was intensified by Fe2+ (FeSO4). A close relationship existed between lipid peroxidation and inhibition of root‐elongation rate induced by Al and/or Fe toxicity and/or Ca deficiency. Besides enhancement of lipid peroxidation in the crude extracts of root tips due to Al, the activities of superoxide dismutase (EC 1.15.1.1) and peroxidase (EC 1.11.1.7) increased, whereas catalase (EC 1.11.1.6) activity decreased. This indicates a greater generation of oxygen free radicals and related tissue damage. The results suggest that lipid peroxidation is part of the overall expression of Al toxicity in roots and that enhanced lipid peroxidation by oxygen free radicals is a consequence of primary effects of Al on membrane structure.
Respiratory energy requirements of roots vary with the potential growth rate of a plant species
Authors: Poorter Hendrik , Van der Werf Adrie , Atkin Owen K. , Lambers Hans
Published: May 2006

The rates of growth, net rate of nitrate uptake and root respiration of 24 wild species were compared under conditions of optimum nutrient supply. The relative growth rate (RGR)of the roots of these species varied between 110 and 370 mg g‐1 day‐1 and the net rate of nitrate uptake between 1 and 7 mmol (g root dry weight)‐1 day‐1. The rate of root respiration was positively correlated with the RGR of the roots. Root respiration was also calculated from the measured rate of growth and nitrate uptake, using previously determined values for the costs of maintenance, growth and ion uptake of two slow‐growing species. The calculated rate of respiration was slightly lower than the measured one for slow‐growing species, but twice as high as measured rates for rapid‐growing species. This discrepancy was not due to a relatively smaller electron flow through the alternative pathway and, consequently, a more efficient ATP production in the fast‐growing species. Neither could variation in specific costs for root growth or maintenance explain these differences. Therefore, we conclude that fast‐growing species have lower specific respiratory costs for ion uptake than slow‐growing ones. Due partly to these lower specific costs of nutrient uptake, the fraction of respiration that rapid‐growing species spend on anion uptake is lower than that of slow‐growing species, in spite of the much higher rate of ion uptake of the fast‐growing ones.
Translocation of nitrogen and expression of nodule‐specific uricase (nodulin‐35) in Robinia pseudoacacia
Authors: Atkins Craig A. , Storer Paul J. , Young Erica B.
Published: May 2006

Uricase (urate oxidase, EC 1.7.3.3) activity and nodule‐specific uricase II (nodulin‐35) were detected in the nodules from a number of legume: Rhizobium symbioses (Vigna unguiculata (L.) Walp., Phaseolus vulgaris L., and Kennedia coccinea Vent.) in the Phaseoleae, as well as in those of Robinia pseudoacacia L. which belongs to the tribe Robineae. Neither uricase activity nor nodulin‐35 was detected in nodules from Lupinus angustifolius L., an amide‐forming symbiosis of the tribe Genisteae. Nodules of R. pseudoacacia also showed high levels of allantoinase (EC 3.5.2.5) activity but activity of enzymes earlier in the pathway of ureide synthesis (xanthine dehydrogenase, EC 1.2.1.37; inosine monophosphate dehydrogenase, EC 1.2.1.14; and xanthosine nucleosidase, EC 3.2.2.1) could not be detected. Analysis of transport fluids (xylem, phloem and nodule exudates) from R. pseudoacacia found that asparagine, and, to a lesser extent, glutamine were the major translocated nitrogenous solutes. Ureides accounted for, at most, 2.6% of the N in transport fluids (tracheal xylem sap) and in nodule exudate, 0.1%. In common with nodules of the ureide‐forming symbioses, those of R. pseudoacacia contained a high proportion of uninfected interstitial cells (53.7 ± 2.3%) in the central N2‐fixing tissue whereas in L. angustifolius only 2.5 ± 0.4% of cells in this tissue were uninfected. These data have been interpreted to indicate that expression of nodule‐specific uricase is related to the differentiation of uninfected interstitial cells in nodules and not to the synthesis of ureides.
Circadian rhythm of volatile emission from flowers of Nicotiana sylvestris and N. suaveolens
Authors: Loughrin John H. , Hamilton‐Kemp Thomas R. , Andersen Roger A. , Hildebrand David F.
Published: May 2006

The volatile profiles from flowers of Nicotiana sylvestris and N. suaveolens were investigated by means of dynamic headspace sampling and capillary gas chromatography. Under conditions of light/dark entrainment both species emitted phenylpropanoid‐derived volatiles (e.g. benzyl alcohol, methyl benzoate) with maximum emission occurring during the dark period. Emission of these compounds was demonstrated to be circadian by continuance of rhythmicity under conditions of constant light and subsequent re‐entrainment to a new light/dark cycle. In contrast, emission of the sesquiterpene hydrocarbon, caryophyllene, from N. sylvestris followed no apparent pattern. The emission of monoterpene hydrocarbons from flowers of N. suaveolens showed diurnal differences only under conditions of light/dark entrainment.
Gas exchange parameters, water relations and carbohydrate partitioning in leaves of field‐grown Prunus domestica following fruit removal
Authors: Gucci Riccardo , Xiloyannis Cristos , Flore James A.
Published: May 2006

The effect of fruit removal on gas exchange, water relations, chlorophyll and non‐structural carbohydrate content of leaves from mature, field‐grown plum trees (Prunus domestica L. cv. Stanley) was determined over 2 consecutive growing seasons. Removal of fruits during stage II of fruit development decreased CO2 assimilation rate within 24 h from 12.6 to 8.5 μmol m‐2 s‐1 in 1986, and from 12.1 to 10.2 μmol m‐2 s‐1 in 1987. Depression of net photosynthesis persisted for at least 5 days and was greatest in the early afternoon. Recovery of the CO2 assimilation rate to pretreatment levels coincided in defruited trees with vegetative growth that was more than 5‐fold that of fruiting trees in the first 6 weeks after fruit removal in 1986. Estimated photorespiration was similar in both fruiting and defruited trees. The stomatal contribution to the decrease of CO2 assimilation rate, calculated from assimilation/intercellular CO2 curves, ranged from 31 to 46%. Defruiting did not affect leaf water potential, but decreased leaf osmotic potential. Leaf levels of chlorophyll, fructose, glucose, sorbitol and sucrose were not affected by defruiting, whereas starch content increased up to 51% in leaves of defruited trees within 24 h after fruit removal. However, because of the small starch pool present in plum leaves (<1.9% dry weight) it is unlikely that starch accumulation was responsible for the observed decline in CO2 assimilation rate after fruit removal. The decrease of CO2 assimilation rate is discussed in relation to the hypothesis of assimilate demand regulating photosynthesis through a feedback mechanism.
The glands of Tamarix aphylla: a system for salt recretion or for carbon concentration?
Authors: Waisel Yoav
Published: May 2006

During periods of high atmospheric humidity, twigs of Tamarix aphylla (L.) Karst. become covered by an alkaline solution. The pH of that solution fluctuates between 8.0 – 8.5 in the dark and 10.5 during the light hours. Such a solution, produced by the glands, constitutes an efficient trap for atmospheric CO2. Upon the periodic drop in pH, much of the preabsorbed carbon may gradually be released from the solution. This enriches the immediate surroundings of the twigs with CO2 for prolonged periods of time. The expected concentrations of CO2, at the boundary layer between the atmosphere and the surfaces of the twigs, are over 1 000 ppm. As net photosynthesis of T. aphylla reaches maximal rates only at CO2 concentrations of above 500 ppm, the plants may benefit from this extra source of carbon and may exploit it for maximal assimilation during the early morning hours. Thus, the “salt glands’of Tamarix, which are liable for the production of the alkaline recretum, may serve a triple purpose: (a) removal of excess salts out of the twigs, (b) provision of a cover of hygroscopic solutes that moistens the twigs and shortens the duration of transpiration, and (c) providing the plants with an environment enriched in CO2.
Compartmental analysis of efflux of K+(86Rb+) and Rb+(86Rb+) from roots of intact plants of barley (Hordeum vulgare) of high and low K+ status, and after excision of the shoot
Authors: Kasimir‐Klemedtsson Åsa , Pettersson Sune
Published: May 2006

The classic compartment analysis of ion efflux from roots is often applied with the assumption that there is a system of 3 compartments in series. However, complex ion transport across the root tissues, as well as influences from the shoot, may complicate the picture. The present experiments were performed to study the immediate effects that excision of the shoot before the experiment exerts on the efflux of Rb+(86Rb+) and of K+(86Rb+) from 9‐day‐old roots of plants of barley (Hordeum vulgare L. cv. Salve). The efflux from high K+ and low K+ roots of intact and detopped plants were compared. After excision of the shoot of high K+ plants, a marked increase in efflux was observed after 2.5 h with a maximum at about 7 h. The increase in efflux was seen as a peak in plots of efflux versus time. Excision of the shoot from low K+ roots did not give rise to a consistent increase in efflux. Regular K+ ion efflux curves were observed from roots of intact plants of high or low K+ status. Furthermore, after a pulse treatment of 9‐day‐old roots of intact plants of high or low K+ status with a solution containing Rb+(86Rb+), the Rb+(86Rb+) transport to the shoots was not reduced during the following 3 h in unlabelled solution. It is suggested that both the peak appearing in the efflux plots and the maintained tracer transport to the shoots after transfer of the roots to an unlabelled solution indicate the existence of a K+/Rb+ transport system in the symplasm of the roots that has only a slow exchange with the bulk cytoplasm and vacuoles.
Responsiveness to abscisic acid of embryos of dormant oat (Avena sativa) seeds. Involvement of ABA‐inducible proteins
Authors: Corbineau F. , Poljakoff‐Mayber A. , Côme D.
Published: May 2006

Abscisic acid (ABA) inhibited the germination of embryos isolated from oat (Avena sativa L.) dormant seeds. The inhibition increased with ABA concentration. The embryos were 1 000 times more responsive to ABA at 30°C than at 10°C (30°C being the temperature at which dormancy is expressed). Exposure of embryos to 0.5 μM ABA for less than 8 h did not affect subsequent germination in water, and did not induce synthesis of new proteins. Exposure for at least 14 h was necessary to induce subsequent inhibition of germination. Such long exposure to ABA also affected protein synthesis. The molecular weights of the main ABA‐inducible proteins were in the range between 44 and 24 kDa. Synthesis of small polypeptides, around 10 and 6 kDa was also induced. Synthesis of most of these ABA‐inducible proteins disappeared when embryos were transferred to water. The general results suggest that the presence of ABA was necessary to maintain the synthesis of ABA‐inducible proteins; on removal of ABA their synthesis ceased. No apparent correlation between these proteins and germination was revealed. However, a 26 kDa band was observed in the extract of control embryos imbibed for 24 h in water: this band was not present after 8 or 16 h imbibition and was also absent in extracts of ABA treated embryos.