bluuebunny/crossref_metadata_2025 huggingface dataset:
Ammonium toxicity: description of the syndrome in Sinapis alba and the search for its causation
Authors: Mehrer Ingrid , Mohr Hans
Published: May 2006

In many plant species, prolonged application of ammonium (NH4+) as a source of nitrogen results in physiological and morphological disorders (‘ammonium toxicity’). In the mustard (Sinapis alba L.) seedling we have previously observed particularly severe symptoms of ammonium toxicity in the absence of external nitrate (NO3‐) or with increasing NH4+/NO3‐ ratios. In the present investigation we have studied the symptoms of this ‘toxicity’in more depth, i.e. at the morphological, plastidic, enzyme and mRNA levels, in an effort to elucidate the causation of the syndrome.

It could be confirmed that the syndrome is specific for ammonium and is not caused by a surplus of nitrogen. The syndrome is caused neither by pH changes in the medium nor by non‐specific osmotic effects. Furthermore, the syndrome is not causally related to the fact that nitrate reductase (NR; EC 1.6.6.1.) is induced by ammonium. Development of the syndrome requires neither photosynthesis nor intact plastids. Nevertheless, the plastids are severely affected by ammonium application as is anthocyanin synthesis.

Enzymes are differently affected. Among the plastidic enzymes, levels of ribulose‐1,5‐bisphosphate carboxylase (RuBPCase; EC 4.1.1.39) and NADP‐dependent glyceraldehyde‐3‐phosphate dehydrogenase (NADP‐GPD; EC 1.2.1.13) are strongly reduced and abundance of translatable mRNA of the small subunit of RuBPCase is decreased, whereas nitrite reductase (NIR; EC 1.7.7.1) is not affected. Among extraplastidic enzymes, the level of chalcone synthase (CHS; EC 2.3.1.74) is strongly reduced, the NAD‐dependent glyceraldehyde‐3‐phosphate dehydrogenase (NADGPD; EC 1.2.1.12) level is unaffected, whereas the isocitrate lyase (ICL; EC 4.1.3.1) level is strongly promoted.

The fat → carbohydrate transformation seems to be impaired by ammonium: fat degradation is reduced, starch accumulation is strongly inhibited and the levels of glucose and fructose are decreased.

It appears from the present data and from results obtained in a companion study (U. Hecht and H. Mohr, in preparation) that the ammonium toxicity syndrome is detectable as soon as ammonium accumulation occurs in the plant. However, the actual mechanism through which the excess ammonium affects metabolism remains unclear at present.
Effects of Russian wheat aphid infestation on barley plant response to drought stress
Authors: Riedell Walter E.
Published: May 2006

The influence of Russian wheat aphid (Diuraphis noxia Mordvilko) infestation on the response of barley (Hordeum vulgare L. ev Hazen) plants to drought stress was investigated. Fourteen‐day‐old plants were infested with eight apterous adult aphids, which were removed 7 days later with systemic insecticide. Leaves previously infested with aphids had lower relative water content, reduced stomatal conductance, more negative water potential, lower levels of chlorophyll and higher levels of amino‐N, proline and glycinebetaine than corresponding leaves from uninfested plants. When water was withheld for a period of 7 days after aphids were removed, the relative water content of previously infested plants dropped steadily from 0.89 to 0.60, while the relative water content of uninfested plants remained at about 0.94 for the first 4 days of the drought stress period followed by a steady drop to about 0.77 by the end of the drought stress period. Leaf water potentials dropped steadily during the drought stress period in both previously infested (‐1.14 to ‐1.91 MPa) and unin‐fested (‐0.54 to ‐1.52 MPa) plants. Analysis of glycinebetaine and proline levels at the end of the drought stress period indicated that leaves of previously infested plants accumulated lower levels of these solutes than leaves from uninfested plants. Upon alleviation of drought stress, plants previously infested with aphids showed little increase in dry weight while younger leaves and tillers from uninfested plants showed large increases. It is concluded that Russian wheat aphids cause drought‐stress symptoms in leaves of infested plants even in the presence of ample root moisture. The observations of low levels of glycinebetaine and proline present in leaves after water was withheld from roots and lack of leaf growth upon alleviation of drought stress in previously‐infested plants, suggest that aphid infestation limits the capacity of barley plants to adjust successfully to drought stress.
Feruloyl‐ and caffeoylputrescine in stem explants from photoperiodically determined Nicotiana species
Authors: Wyss‐Benz Markus , Streit Luc , Ebert Edith
Published: May 2006

The distribution and formation of hydroxycinnamoyl amides (HCA) in in vitro grown stem explants from day‐neutral Nicotiana tabacum L. var. Xanthi no were investigated using [14C]‐labelled precursors. Feruloylputrescine (FP) (labelled from [14C]‐putrescine) was continually formed with a decreasing formation rate during a culture period of 35 days. The specific radioactivity, however, remained constant. In contrast, caffeoylputrescine (CP) was labelled in the second part of culture only. [UC]‐Label from putrescine, spermidine, spermine, and cinnamic acid was incorporated into FP and p‐coumaroylspermidine. CP was labelled from [14C]‐putreseine and [14C]‐spermidine only, while diferuloylputrescine (diFP) failed to be labelled by any of the precursors used. Tissue investigations showed that FP is dominant in cortex during formation of cortical callus, while CP showed a sequential gradient from pith to cortical callus to floral buds. Experiments with photoperiodical Nicotiana species were used to investigate the pattern of HCAs in induced and non‐induced plants. The origin of explants had no influence on the pattern of FP and CP but resulted in different growth responses. FP is a marker of cortical callus formation in all explants. CP does not trigger the growth processes observed in the expants since CP also increased in photoperiodically non‐induced explants of tobacco, which stopped growing after the formation of cortical callus.
Two‐dimensional protein profiles of palisade parenchyma and of spongy parenchyma of Vicia faba leaf
Authors: Shen Liming , Outlaw William H.
Published: May 2006

Specific probes such as targeted‐enzyme assays have failed to reveal qualitative differences between the metabolism of spongy parenchyma and that of palisade parenchyma cells. To determine whether the results from these definite assays support a general conclusion concerning the overall biochemical similarity of these cells, two‐dimensional protein profiles have been constructed for these two types of cells. Protein extracts were prepared from freeze‐dried homogeneous tissue samples or from isolated protoplasts of Vicia faba L. cv. Longpod leaves. Proteins separated by micro two‐dimensional gel electrophoresis were stained with silver. The relative apparent abundance (based on visual judgment of the area and intensity of staining) was estimated for each spot. Pairwise comparison of nominally 125 stained proteins of each of approximately 75 gel pairs did not reveal a consistent qualitative difference between the profiles. Recognizing that polypeptides escaped detection in our investigation through loss, failure to stain sufficiently, or incomplete resolution, we qualify our conclusion that spongy parenchyma and palisade are similar in their overall protein complement.
Porphyrin metabolism in chill‐stressed seedlings of Scots pine (Pinus sylvestris)
Authors: Hodgins R. R. W. , Öquist G.
Published: May 2006

Scots pine (Pinus sylvestrisL.) is generally resistant to chilling temperatures. Porphyrin metabolism under low temperature stress was studied in etiolated seedlings of Scots pine. Low temperatures affect porphyrin accumulation in at least 3 different temperature sensitive sites: 1) the light activated accumulation of 5‐aminolevulinic acid, a porphyrin precursor, 2) the metabolism of 5‐aminolevulinic acid to form porphyrins and 3) a preferential accumulation of chlorophyllaover chlorophyllb. The temperature sensitivity of pine is compared to maize (Zea maysL.), a chilling sensitive plant.
Isoperoxidases as markers of somatic embryogenesis in carrot cell suspension cultures
Authors: Joersbo Morten , Andersen Jytte M. , Okkeis Finn T. , Rajagopal Ranganatha
Published: May 2006

Growth, peroxidase activity and isoperoxidase pattern were studied during the growth cycle of 3 cell suspension lines of carrot (Daucus carota L.), an embryogenic, a non‐embryogenic and a habituated cell line. Isoelectric focusing of extracted proteins on agarose gels revealed the isoperoxidase pattern of the embryogenic line to include, among other differences, an isoperoxidase with a pl of pH 7.0 when grown under conditions stimulating embryogenesis. This isoperoxidase (P7.0: EC 1.11.1.7) was present between days 2 and 6 after subculturing, and this period correlates well with the early stages of somatic embryogenesis. This isoenzyme showed very low activity in the non‐embryogenic and habituated cell suspension lines as well as in the embryogenic cell line in the presence of Daucus carota, 2,4–dichlorophenoxyacetic acid. P7.0 could probably be used as a biochemical marker of somatic embryogenesis.
Effect of butyric acid on the germination of the seeds ofPhacelia tanacetifolia
Authors: Cocucci Sergio M. , Morgutti Silvia , Ranieri Anna Maria
Published: May 2006

The effect of a weak acid (butyric acid) on the germination of seeds ofPhacelia tanacetifoliaBenth. (cv. Bleu Clair) has been studied. Butyric acid inhibited the early phase of germination, and the inhibition was correlated to the amount of the per‐meant undissociated form present in the incubation medium. The inhibition by butyric acid in the dark was also correlated to a decrease of dark fixation of CO2and to a more pronounced decrease in malic acid levels during the early phase of germination; suggesting that the uptake of the uncharged form of this weak acid was followed by a release of H+ into the cytoplasm, leading to a decrease in its pH. The inhibitory effect of butyric acid in the dark on many metabolic events (rise in respiratory activity, levels of reducing sugars, glucose‐6–phosphate and malic acid, dark CO2fixation, transport activities and macromolecular synthesis) appeared similar to the one of light. Fusicoccin (FC), which directly stimulates the H+pump at the plasmalemma level, ameliorated the effect of butyric acid, as well as that of light, on germination. The bulk of these data is interpreted as suggesting that the mechanism of light inhibition of germination ofPhacelia tanacetifoliaseeds might be the consequence of a general block of metabolic reactivation due to the presence of an unfavourable (acidic) cytoplasmic pH; which might be explained with the lack of the phytochrome‐dependent activation of the H+pump at the plasmalemma level.
Purification and characterization of glutathione reductase from Scots pine needles
Authors: Wingsle G.
Published: May 2006

Glutathione reductase (EC 1.6.4.2) was purified from Scots pine (Pinus sylvestris L.) needles. The enzyme had a specific activity of 3.65 μkat (mg protein)−1, and the apparent molecular weight of the polypeptide was 59 kDa. Sulfhydryl‐modifying reagents such as N‐ethylmaleimide and iodoacetate inactivated the enzyme in the presence of NADPH. Oxidized glutathione protected the enzyme against this inactivation. NADPH inactivated the enzyme by ca 35% within 5 min. High concentrations of hydrogen peroxide (32 μM) had no effect on enzyme activity. High concentrations of sulfite (5 μM) inhibited the enzyme but low concentrations (60 μM) did not affect the activity. The Km for oxidized glutathione and NADPH was 28 and 1 μM, respectively. The pi was 4.7 and the amino‐acid composition was similar, with minor exceptions, to that of glutathione reductase obtained from rice embryos, human erythrocytes and E. coli.
Changes in the level of tubulin subunits during development of cotton (Gossypium hirsutum) fiber
Authors: Kloth Reiner H.
Published: May 2006

The levels of tubulin protein in developing cotton (Gossypium hirsutum L. cv. Stoneville 825) fibers were measured from 8 to 28 days post‐anthesis using commercially available monoclonal antibodies against alpha‐ and beta‐tubulin. As the monoclonal antibodies against alpha‐ and beta‐tubulin were prepared from yeast tubulin and chick brain tubulin, respectively, indirect immunofluorescence microscopy was used to establish that the two monoclonal antibodies recognized microtubule structures in cotton fibers. Western blots of electrophoretically separated proteins in crude extracts of cotton roots and fibers showed that single polypeptides with the expected apparent molecular weight for tubulin subunits were recognized by the antisera. An enzyme‐linked immunosorbent assay was used to quantify tubulin levels. From 10 to 20 days post‐anthesis the level of tubulin protein increases approximately three‐fold. After 20 days post‐anthesis, the amount of tubulin relative to total fiber protein reaches a plateau or decreases slightly. The rapid rise in tubulin is correlated with the elongation of the fiber and an increase in cellulose synthesis.
Promotive effect of capillarol and related compounds on root growth
Authors: Ueda Junichi
Published: May 2006

The promotion of root growth by capillarol [methyl 3‐(3‐methylbut‐2‐enoyl)‐4‐hydroxycinnamate] and related phenolic compounds were studied in relation to structure‐activity relationships. Concentrations above 5 × 10−5M capillarol stimulated the root growth of rice (Oryza sativa L. cv. Tanginbozu and cv. Nihonbare) seedlings to about 180% of the control value at 5 × 10−4M. Capillarol had no promotive and hardly any inhibitory effect on the growth of the second leaf sheath. Capillarol promoted the root growth also in seedlings of lettuce (Lactuca sativa L. cv. Grand Rapids) to ca 150% of the control value at 5 × 10−4M. The free acid form of capillarol (capillaric acid) was about as effective as capillarol. Para‐hydroxy‐ but not m‐methoxy‐ substituted cinnamic acid, phenylpyruvic acid, phenylacetic acid and amino‐hydrocinnamic acid could stimulate root growth, but p‐hydroxybenzoic acid was inactive. It is concluded that the important structural requirements for high root growth‐promoting activity of phenolic compounds are the hydroxyl group substitution at the C‐4 position of the benzene ring, and the propanoic or propenoic acid side chain at the C‐1 position. A possible mode of the action of capillarol on root growth‐promoting activity is also discussed.
Influence of nicotianamine and iron supply on formation and elongation of adventitious roots in hypocotyl cuttings of the tomato mutant ‘chloronerva’ (Lycopersicon esculentum)
Authors: Becker Roswitha , Pich Axel , Scholz Günter , Seifert Karlheinz
Published: May 2006

The influence of nicotianamine (NA) on formation and elongation of adventitious roots in hypocotyls of de‐rooted NA‐less mutant seedlings of Lycopersicon esculentum Mill, was examined in relation to the iron supply [ferric N‐N'‐ethylenediaminedi‐(2‐hydroxyphenylacetate) (FEDDHA), ferric ethylenediaminetetracetate (FeEDTA), ferric N‐(2‐hydroxyethyl)‐ethylenediaminetriacetate (FeHEDTA, Fe‐citrate and FeCl3] in the nutrient solution. The initiation of root primordia in hypocotyl cuttings was independent of NA and occurred with about the same frequency in both, mutant and wild‐type. In the mutant the development of primordia to adventitious roots was blocked at all iron sources used, except FeEDTA. Addition of NA (5x 10−6 to 2 × 10−5M) to the rooting medium resulted in a fast growth of adventitious roots in mutant cuttings with all iron sources tested. Rooting of wild‐type cuttings was independent from NA application and iron sources. We suppose that NA is involved in the intracellular transport of iron. Its function is possibly linked with chelation of ferrous iron in the cell.
Photoinhibition of white clover seed germination at low water potential
Authors: Niedźwiedź‐Siegień Irena , Lewak Stanislaw
Published: May 2006

Photosensitivity of germination of white clover (Trifolium repens L. cv. Podkowa) seeds was studied under water deficit (low water potential) conditions at 25°C. The seeds showed negative photoblastism, which was most pronounced at ‐0.03 MPa polyethylene glycol solution. Inhibition was observed at two different wavelength bands with maxima at 660 nm (R) and around 730 nm (FR). Red light acted identically to white light (maximum inhibition ca 50%). The effect of far‐red illumination was less inhibitory (20–30%). The photoresponse required long illuminations (3 h exposures); saturation level was at 0.1 W m−2, independently of the light quality. White clover seed germination showed no reversibility of the effects of R and FR light. Prolonged illumination with R and FR increased the inhibition, and intermittent illumination had a higher effect than a continuous one. It was concluded that the photoinhibition of germination of seeds of Trifolium repens involves a reaction dependent on the rate of phytochrome interconversion, a property that is characteristic for the high irradiance reaction.
Nucleotide sequence of the 5.6 kbp psbB operon of pea chloroplast DNA
Authors: Lehmbeck J. , Stummann B. M. , Henningsen K. W.
Published: May 2006

The nucleotide sequence of a 5.7 kbp region of pea (Pisum sativum L.) chloroplast DNA containing the psbB operon and a putative promotor and termination site has been determined and compared to the corresponding sequences from spinach, maize, tobacco and the liverwort Marchantia polymorpha. The organization of the operon is the same as for the other species, i.e. psbB/psbH/petB/petD. These genes code for a 56 kDa chlorophyll‐binding photosystem 2 (PS2) polypeptide, an 8 kDa PS2 polypeptide, cytochrome b6 (24 kDa) and subunit 4 (18 kDa) of the cytochrome b6/f complex. Two short and oppositely directed putative polypeptide genes are located between psbB and psbH. The petB and petD genes contain introns of 818 and 715 bp, respectively. The psbB, petB and petD proteins encoded in the pea operon are 89–98% homologous to those from the other species, while the pea psbH protein has a homology of 65–96% to that of the other species. The nucleotide sequences of introns and intergenic regions from the higher plants are 60–70% homologous. From comparisons with spinach sequences we conclude that the primary pea transcript probably has a length of 5603 bases.
Enzymes of starch and sugar phosphate metabolism in achlorophyllous ribosome‐deficient plastids from high‐temperature‐grown rye leaves
Authors: Otto Sabine , Feierabend J.
Published: May 2006

Several enzymes of non–photosynthetic sugar phosphate and starch metabolism were measured in gradient–purified chloroplasts from normal rye leaves (Secale cereale L. cv. Halo) grown at 22°C and in the non‐photosynthetic plastids isolated from 70S ribosome‐deficient rye leaves grown at a non–permissive elevated temperature of 32°C. Activities of the enzymes phosphoglycerate kinase (EC 2.7.2.3), hexokinase (EC 2.7.1.1), phosphoglucose isomerase (EC 5.3.1.9), phosphoglucomutase (EC 2.7.5.1), glucose‐6‐phosphate dehydrogenase (EC 1.1.1.49), 6‐phosphogluconate de‐hydrogenase (EC 1.1.1.46), ADPglucose pyrophosphorylase (EC 2.7.7.27), starch synthase (EC 2.4.1.21), and phosphorylase (EC 2.4.1.1) were present in ribosome‐deficient plastids from 32°C‐grown leaves indicating a cytoplasmic origin of the plastid‐specific forms of these enzymes. While the photosynthetic marker enzyme NADP+‐dependent glyceraldehyde‐3‐phosphate dehydrogenase (EC 1.2.1.13) was considerably diminished, both the specific activities and the total activities per leaf of the plastid‐specific forms of hexokinase, phosphoglucose isomerase and phosphoglucomutase were markedly increased in the ribosome–deficient plastids, relative to normal chloroplasts. The results demonstrate that after elimination of functional protein synthesis in the chloroplasts the supply of chloroplast–specific enzymes by the cytoplasm is not generally suppressed as observed for many enzymes and proteins involved in photosynthesis, but may even be increased in accord with changed metabolic demands.
A relationship between irradiation, carbohydrates and rooting in cuttings of Pisum sativum
Authors: Bertram Lise , Veierskov Bjarke
Published: May 2006

Rooting ability was studied for cuttings derived from pea plants (Pisum sativum, L. cv. Alaska) grown in controlled environment rooms. When the cuttings were rooted at 70 μmol m−2 s−, 1 (photosynthetic photon flux density) or more, a stock plant irradiance at 100 μmol m−2 s−1 decreased rooting ability in cuttings compared to 5 μmol m−2, s−1, However, cuttings rooted at 160 μmol m−2 s−1 formed more roots compared to 5 (μmol m−2 s−1. Although a high irradiance increased the number of roots formed, it could not overcome a decreased potential for root formation in stock plants grown at high irradiance. Light compensation point and dark respiration of cuttings decreased by 70% during the rooting period, and the final levels were strongly influenced by the irradiance to the cuttings. Respiratory O2 uptake decreased in the apex and the base of the cutting from day 2 onwards, whereas a constant level was found in the leaves. Only the content of extractable fructose, glucose, sucrose and starch varied during the early part of the rooting period. We conclude that the observed changes in the cuttings are initiated by excision of the root system, and are not involved in the initiation of adventitious roots.
Free radical and freezing injury to cell membranes of winter wheat
Authors: Kendall Edward J. , McKersie Bryan D.
Published: May 2006

The symptoms of injury in microsomal membranes isolated from crowns of seedlings of Triticum aestivum, L. cultivar Fredrick after a lethal freeze‐thaw stress included an increased lipid phase transition temperature, loss of lipid phosphate (lipid‐P), and increased free fatty acid levels. However, minimal changes in fatty acid saturation were observed, suggesting minimal amounts of lipid peroxidation. All of these injury symptoms, including the lack of lipid peroxidation, were simulated in vitro by treatment of isolated membranes with oxygen free radicals, generated from either xanthine oxidase (EC 1.1.3.22) or paraquat (l,r‐dimethyl‐4,4′‐bipyridinium dichloride). Further evidence indicating a relationship between free radicals and freezing injury comes from the observation that both protoplasts and microsomal membranes isolated from wheat seedlings, that had been acclimated to induce freezing tolerance, also had increased tolerance of oxygen free radicals, and contained higher lipid‐soluble antioxidant levels, than those from non‐acclimated seedlings. Lipid‐soluble antioxidants accumulated in the crown tissue of the wheat seedling during the acclimation period. Freezing stress accelerated the formation of oxygen free radicals. Membranes isolated from crowns after a freeze–thaw stress tended to produce higher levels of superoxide as shown by the reduction of Tiron (1,2‐dihydroxy‐l,3‐benzenedisulfonic acid). In protoplasts, increased superoxide production coincided with lethal freezing injury. These results are discussed in terms of the possible involvement of oxygen free radicals in mediating aspects of freezing injury to cell membranes.
Chemical nature of P efflux from P‐adequate Spirodela and Lemna plants
Authors: McPharlin I. R. , Bieleski R. L.
Published: May 2006

The chemical nature of P released (efflux) from healthy (P‐adequate) Spirodela oligorrhiza (Kurz) Hegelm, and Lemna major L. plants growing in sterile solution culture was investigated using thin‐layer chromatography and autoradiography. Ester patterns of P efflux material from [32 Pi] labelled plants was compared with P ester patterns in the tissue of the same plants.

Nearly all of the released P was Pi (99.8% in Spirodela, 99.6% in Lemna) there being little consistent evidence for the release of significant amounts of organic P (0.2% and 0.4% of released P –Spirodela and Lemna respectively). Efflux of P predominantly as organic P (hexose or nucleotide P) would have resulted in an important loss of energy for the plant. The corresponding proportion of organic P in the tissue of the labelled plants from which the P efflux material arose was 15% (Spirodela) and 8% (Lemna). Consequently there was no evidence for the preferential release of phosphorylcholine, a compound implicated in P efflux because of its high membrane permeability. Autoradiographic resolution of the chromatogram was improved by labelling plants at high 32P specific activity [185 GBq (mol Pi)−1] compared with levels considered safe [37 GBq (mol Pi)‐1] without any detrimental effects.

Spirodela and Lemna plants appear to exert a close control over both the quantity (rates of P efflux) and quality (proportion of Pi to organic P) of their P efflux. The possible role of externally located phosphatases in minimising the release of organic P is also discussed.
Abscisic acid, indole‐3‐acetic acid and cytokinin changes in buds of Pseudotsuga menziesii during bud quiescence release
Authors: Pilate G. , Sotta B. , Maldiney R. , Jacques M. , Sossountzov L. , Miginiac E.
Published: May 2006

Bud quiescence release, considered as the ultimate dormancy breaking phase, was achieved in Pseudotsuga menziesii (Mirb.) Franco by a 9‐week cold (5°C) treatment, under short daylength (9 h) followed by a transfer to mild temperature (22°C) under long daylength (16 h). Indole‐3‐acetic acid (IAA), abscisic acid (ABA), zeatin‐type (Z) and isopentenyladenine‐type (iPA) cytokinin (CK) levels were measured by means of an ELISA technique performed on HPLC‐fractionated extracts of terminal and axillary buds. During the cold period, all hormones except IP‐type CK levels decreased, whereas the opposite observation was made after transfer to mild temperature and long daylength, when buds started to grow. Some other immunoreactive compounds were also detected and quantified. The ABA‐glucosyl ester (ABA‐GE) level pattern was similar to that of ABA, but no accumulation occurred at mild temperatures. A putative IAA conjugate, more polar than IAA, was also detected. Its level increased transiently like IAA in terminal buds and, to a lesser extent, in axillary buds during the 10th week of the experiment. In terminal buds, isopentenyladenosine ([9R]‐iP) was released by alkaline hydrolysis of a polar immunoreactive compound detected with anti‐[9R]iP antibodies. This compound accumulated during the cold period and quickly dropped at 22°C. Relationships between environmental conditions and endogenous hormones are discussed.
The response of stomata to CO2 relates to its effect on respiration and ATP level
Authors: Shaish Aviv , Roth‐Bejerano Nurit , Itai Chanan
Published: May 2006

External ATP enhanced stomatal opening of Commelina communis L. differently from EDTA. ATP was more effective in opening stomata than EDTA, when both were applied in amounts yielding equivalent free Ca2+ concentration. The stimulation by ATP depended upon its de‐phosphorylation and was not due to the P1 released. Hence an energetical contribution of external ATP appears possible. Increase in CO2 concentration increased the stimulation of stomatal opening by ATP and diminished the internal ATP level, ATP/(ADP+AMP) ratio and respiration rate.
Regulation of cytosol acidity in plants under conditions of drought
Authors: Venekamp J. H.
Published: May 2006

In plants under water stress, the activity of photosynthesis declines most. Stimulation of the oxidative respiration and fermentation results in an increase in the amount of related organic acids: citrate, malate and lactate. In spite of some decline in photo‐respiratory activity, dehydration may enhance the concentration of related organic acids, glycerate and glycolate. The resulting amount of H+ should stimulate NAD(P)H reduction of organic acids by dehydrogenases. Accumulation of proline could be the consequence of such reactions. In the oxidation of glycine, regeneration of NAD(P)H does not liberate H+ but NH4+.

Assimilation of NH4+ by cytosolic glutamine synthetase (EC 6.3.1.2) results in positively charged glutamine. It is also conceivable that the charge is essential in the final asparagine synthesis by cytosolic asparagine synthetase (EC 6.3.1.1).

At low pH the activity of the oxidative respiration declines. In water‐stressed plants, maintenance of oxidative respiration will depend on the availability of sufficient amounts of carbohydrates and on adequate removal of excess H+ by accumulation of proline and asparagine.
Signal transduction and phosphatidylinositol turnover in plants
Authors: Morse M. J. , Satter R. L. , Crain R. C. , Coté G. G.
Published: May 2006

Transduction of light and hormone signals in plants may utilize a mechanism similar to one widely used in animal systems, that of accelerated phosphatidylinositol (PI) turnover. The elements of this central mechanism and consequences of the acceleration as well as recent evidence for its operation in plants are described.
Ethylene‐associated phase change from juvenile to mature phenotype of daylily (Hemerocallis) in vitro
Authors: Smith David L. , Kelly Kevin , Krikorian A. D.
Published: May 2006

Hemerocallis plantlets maintained in vitro for extended periods of time in tightly closed culture vessels frequently show a phenotype, albeit on a miniaturized scale, typical of more mature, field‐grown plants. The positive relationship of elevated ethylene in the headspace of such vessels to the phase shift from juvenile to mature form is established. Rigorous restriction in air exchange with the external environment by means of silicone grease seals hastens the phase change and improves uniformity of response. Although some plantlets may take longer to accumulate enough ethylene in sealed jars to undergo change, added ethylene and ethylene‐releasing agents promote it. Ethylene adsorbants (e.g. mercuric perchlorate) block the shift of juvenile to mature form. Critical ambient ethylene level for the shift is ca 1 μl l−1. Levels up to 1000 μl l−1 do not hasten the response but are not toxic. The phase change is fully reversible when air exchange permits ethylene to drop below 1 μl l−1. At least 1 μl l−1 ethylene is required to sustain the mature phenotype. The ethylene synthesis inhibitor aminoethoxyvinylglycine (AVG) prevents the phase change, while the ethylene biosynthesis intermediate 1‐aminocyclopropanecarboxylic acid (ACC) improves it. KOH, as a CO2 absorbant, does not prevent the phase change. Histology sections demonstrate subtle changes in the form of shoot tips of plantlets undergoing phase change.
Biosynthesis of chlorophyll b in pigment mutant C‐2A′ of Scenedesmus obliquus
Authors: Kotzabasis Kiriakos , Senger Horst
Published: May 2006

It is demonstrated that chlorophyll b does not only derive from chlorophyll a, but is also formed separately from an in vivo‐occurring chlorophyllide b. The branching point for the latter synthesis is at the level of chlorophyllide, since no protochlorophyllide b was detectable. We have indications that the enzyme oxidizing chlorophyll a to chlorophyll b accepts also non‐phytylated 17,18 dihydroporphyrins and is not restricted to chlorophylls. Preparations of chlorophyllide a and chlorophyll a could both be transferred with the same enzyme fraction to chlorophyllide b and chlorophyll b, respectively. Preliminary experiments show this enzyme to be membrane bound and light independent. An updated scheme for chlorophyll b biosynthesis is presented.
Correlation of reduced chilling injury with Increased spermine and spermidine levels in zucchini squash
Authors: Kramer George F. , Wang Chien Y.
Published: May 2006

The development of chilling injury symptoms in zucchini squash (Cucurbita pepo L. cv. Ambassador) was reduced by preconditioning the fruit for 2 days at 10°C. In the control group, held continuously at 2.5°C, increasing chilling injury correlated with an increase in putrescine and decreases in spermidine and spermine. Preconditioning led to a significant increase in spermidine arid spermine levels, beginning after the initiation of storage at 2.5°C and lasting for 5 days, after which the levels decreased but remained elevated relative to the control. The elevation of polyamine levels by direct treatment of the fruit with spermine prior to storage resulted in reduced chilling injury, indicating that polyamines may be involved in the protective mechanism of preconditioning. We have also examined the extent of lipid peroxidation by determining the levels of chloroform‐soluble fluorescent products in the skin of the fruit subjected to chilling. The chilling injury in the control group resulted in an increase in the fluorescent products. The levels of fluorescent products were significantly reduced by the preconditioning treatment. These results may indicate that polyamines can act to prevent chilling injury in squash by a mechanism which involves protecting membrane lipids from peroxidation.
Epidermal focussing and the light microenvironment within leaves of Medicago sativa
Authors: Martin Greg , Josserand Sedley A. , Bornman Janet F. , Vogelmann Thomas C.
Published: May 2006

The light microenvironment within leaves of Medicago sativa L. cv. Armor was related to the anatomy of the epidermis. Leaf epidermal cells had a convex shape and appeared to act as lenses that focussed light within the upper region of the palisade. In leaves irradiated with collimated light, epidermal focussing was demonstrated by ray tracing, photomicrography and fiber optic probe measurements, where lens signatures were observed. No relationship was observed between the location of focal spots within the palisade and chloroplast positioning. Epidermal focussing could be largely eliminated by irradiating leaves with diffuse light or by coating their surface with a thin layer of mineral oil that closely matched the refractive index of the cell walls. Measurement of variable chlorophyll fluorescence after elimination of epidermal focussing on the adaxial leaf surface caused a 19 and 11% decrease in the initial fluorescence level (F0) and maximum fluorescence (Fmax), respectively, whereas similar measurements from the abaxial surface were twice as large. These results suggest that some of the chloroplasts within the leaf may be adapted to local high‐light conditions created by the epidermis.
Quantitation of gibberellins and indoleacetic acid in Begonia leaves: Relationship with environment, regeneration and flowering
Authors: Odén Per Christer , Heide Ola M.
Published: May 2006

Indole‐3‐acetic acid (IAA) was purified by high performance liquid chromatography (HPLC) and identified by gas chromatography ‐ mass spectrometry (GC‐MS) in leaf extracts of Begonia × cheimantha Everett cv. Nova. The content of IAA and of gibberellins A4, A9, A19 and A20 (GAs) previously identified in this material, were quantified by GC‐MS in leaves of Begonia plants grown under different temperature and daylength conditions, using deuterated compounds as internal standards. GA1, which was also identified, was present in too low quantities for reliable quantitation. Rapid and significant decreases (within 2–4 days) occurred in the content of both IAA and GAs when the plants were transferred from conditions which are non‐inductive for adventitious bud formation and flowering (24°C/long day) to inductive conditions (24°C/short day, 15°C/long day or 15°C/short day). GA4 and GA9 were affected by photoperiod only, whereas IAA, GA19 and GA20 were affected by both photoperiod and temperature. The data suggest that biosynthesis of GA9 and GA4 are blocked in short days at a step located before GA9. Conversion of GA19 to GA20 seemed to be blocked by both short days and low temperature, while an additional block located before GA19 seemed to be imposed in 15°C/short day. The results confirm earlier results and support the hypothesis that photoperiod and temperature effects in Begonia are mediated by endogenous hormones.
Carbohydrate and organic acid composition of effective and ineffective root nodules of Phaseolus vulgaris
Authors: Lafontaine Pierre J. , Lafrenière Carole , Chalifour Francois‐P. , Dion Patrice , Antoun Hani
Published: May 2006

Dicarboxylic acid transport mutants of Rhizobium species are usually deficient in their ability to fix atmospheric dinitrogen. We report here a study comparing the physiology of root nodules on Phaseolus vulgaris L. cv. Goldie induced by an effective strain of Rhizobium leguminosarum biovar phaseoli and a C4‐dicarboxylic acid utilization mutant. The mutant, while able to form nodules, was ineffective in N2 fixation. Carbohydrates and organic acids of roots and nodules formed by the 2 strains were monitored at 3‐day intervals from 13 to 34 days after inoculation. Both carbohydrates and organic acids accumulated in ineffective nodules in comparison with the effective nodules. The concentration of malic acid was tenfold higher in ineffective nodules than in effective nodules. Other organic acids, i.e., lactate, malonate, ascorbate and gluconate, were also detected. Lactate and ascorbate were the only other organic acids accumulating in ineffective nodules. The most prevalent carbohydrates found in both types of nodules were sucrose, glucose and fructose. Myo‐inositol was the only cyclitol detected in both types of nodules. Carbohydrates and organic acids were present in lower concentration in roots than in nodules, except for lactate. These compounds were not consistently detected in higher concentration in roots from plants inoculated with the mutant strain, as was the case in nodules.
Extracellular exo‐polygalacturonase secreted from carrot cell cultures. Its purification and involvement in pectic polymer degradation
Authors: Konno Haruyoshi , Yamasaki Yoshiki , Katoh Kenji
Published: May 2006

Exo‐polygalacturonase (exo‐PGase, EC 3.2.1.67) activity has been detected in a culture filtrate of cell suspension cultures of carrot (Daucus carota L. cv. Kintoki). The extracellular exo‐PGase was purified to electrophoretic homogeneity using DEAE‐Sephadex A‐50 ion‐exchange chromatography, Sephadex G‐150 gel filtration, and preparative polyacrylamide gel electrophoresis (PAGE). The molecular mass of the purified enzyme was calculated to be 48 kDa from Sephadex G‐200 gel filtration, and 50 kDa from sodium dodecyl sulfate (SDS)‐PAGE after treatment with SDS and 2‐mercaptoethanol. The isoelectric point was at pH 6.2. The Km and Vmax values for polygalacturonate (degree of polymerization: 52) were 14.4 μM and 25.6 μmol (mg protein)−1 h−1, respectively. The optimal activity in McIlvaine's buffer occurred at pH 4.6. The enzyme activity was inhibited by Ba2+, Cu2+, Mn2+ and Hg2+. The enzyme was involved in ca 15% hydrolysis of the acidic polymer purified from carrot pectic polysaccharides, and connected with the release of galacturonic acid. Even after an exhaustive reaction the enzyme had, however, little or no effect on cell walls from carrot cell cultures.
Putrescine metabolism in excised cotyledons of Pinus radiata cultured in vitro
Authors: Kumar Prakash P. , Thorpe Trevor A.
Published: May 2006

The metabolism of 14C‐putrescine and the changes in the endogenous concentrations of putrescine, spermidine and spermine were studied when cotyledons of Pinus radiata D. Don were cultured under shoot‐forming (SF, + N6‐benzyladenine) and non‐shoot‐forming (NSF, ‐ N6‐benzyladenine) conditions. Differences in the total uptake of 14C‐putrescine during a 2 h pulse feeding were not significant between the SF and NSF cotyledons except on day 3. The maximum uptake of label was on day 3 in the SF cotyledons, which released the highest amount of 14CO2 as well. 14C from the labeled putrescine was incorporated mainly into γ‐aminobutyric acid, aspartate and glutamate. High performance liquid chromatography of the endogenous polyamines indicated that spermidine was the most predominant polyamine in the cultured cotyledons of radiata pine. Spermine increased by about 60% in the SF and 25% in the NSF cotyledons between days 0 and 3 of culture.
Effects of aluminium on ATP pools and utilization in the cyanobacterium Anabaena cylindrica: a model for the in vivo toxicity
Authors: Pettersson Annette , Bergman Birgitta
Published: May 2006

ATP pools extracted from the cyanobacterium Anabaena cylindrica, grown in the absence or presence of AlCl3, were measured using the luciferin‐luciferase assay. Addition of low concentrations of AlCl3 (3.6–36 μM) increased the ATP pool 20–40% within 24 h, the effect being more marked with time. When using the Tris‐EDTA boiling technique for extraction of cellular ATP, the ATP from aluminium‐exposed cells appeared more stable during the extraction than the ATP from untreated cells. The higher ATP pools in aluminium‐exposed cells were also evident after dark treatment and addition of the phosphorylating inhibitors carbonylcyanide m‐chloro‐phenylhydrazone (CCCP) and N,N‐dicyclohexylcarbodiimide (DCCD). The formation of elevated ATP pools in cells exposed to aluminium was curtailed by high concentrations of cellular phosphate and postincubation at high pH (>8). These results favour the hypothesis that intracellular aluminium binds to ATP by competing with Mg2+ and, as a consequence, the stable Al3+‐ATP complex formed is no longer available for cellular metabolism. The cyanobacterium is assumed to compensate by increasing the total pool of ATP. At high AlCl3‐concentrations, and in particular at low phosphate: aluminium molar ratios (<1), aluminium apparently also interferes with the membranes in A. cylindrica as indicated by inhibited O2 production, reduced ATP production and cell lysis.
Characterization of reconstituted plasma membrane H+‐ATPase from maize roots
Authors: Hsu An‐Fei C. , Brauer David , Tu Shu‐I
Published: May 2006

Corn (Zea mays L.) plasma membranes from KI‐washed microsomal fractions were further purified by isopycnic sucrose density centrifugation. An examination of separated fractions indicated that vesicles with nitrate‐insensitive proton transport copurified with fractions containing vanadate‐sensitive ATPase activity. The ATPase in purified plasma membrane was reconstituted into liposomes by a detergent dilution technique using deoxycholate. The reconstituted ATPase exhibited characteristics similar to those of the native enzyme. However, reconstituted preparations showed an enhanced sensitivity to vanadate, a diminished phosphatase activity and a high specific rate of ATP‐dependent H+‐transport. Apparent Ki values of reconstituted and native enzymes with respect to vanadate were 20 and 50 μM, respectively; the KJ value of the H+‐pumping of reconstituted ATPase was 30 μM. The proton pumping of reconstituted vesicles could be discharged rapidly by p‐trifluoromethoxyphenyl hydrazone (FCCP), hexokinase and vanadate. The hydrolysis of Mg‐ATP by both native and reconstituted ATPases obeyed simple Michaelis‐Menten plots with a Km between 0.5 and 0.6 mM. The reconstituted ATPase retained a pH profile similar to that of native enzyme with a maximum of pH 6.5.
The embryonic axis controls lipid catabolism in cotyledons of apple seeds during germination
Authors: Bogatek Renata , Zarska‐Maciejewska Boźena , Sińska Irena , Lewak Stanislaw
Published: May 2006

Activities of alkaline lipase (AlkL, EC 3.1.1.3), isocitrate lyase (ICL, EC 4.1.3.1), glucose 6‐phosphate dehydrogenase (G6PDH, EC 1.1.1.49) and pyruvate kinase (PK, EC 2.7.1.40) were determined in embryos of apple (Malus domestica Borb. cv. Antonówka) during culture in darkness or at 12 h photoperiod; in both cases either in the presence of gibberellin A3 (GA3) or AMO 1618 (inhibitor of GA synthesis). AlkL and ICL were stimulated by light and GA3; light stimulation was reversed by AMO. G6PDH and PK were not affected by culture conditions. Almost all the activity of all enzymes was found in the cotyledons; only PK was distributed between axis and cotyledons. GA‐like activity was found almost exclusively in the embryo axis. Cultured isolated cotyledons lost their sensitivity to light and AMO, but AlkL and ICL were still stimulated by GA3. Translocation of GA from axis to cotyledons during the culture of embryos is postulated.
The relationships between ethylene production and cell elongation during the initial growth period of chick‐pea seeds (Cicer arietinum)
Authors: Sánchez‐Calle I. M. , Delgado M. M. , Bueno M. , Diaz‐Miguel M. , Matilla A.
Published: May 2006

Ethylene production by isolated chick‐pea embryonic axes during the initial stages of germination has been studied. Maximum production of ethylene occurs when growth is entirely due to cell elongation and before mitotic activity begins. This peak increases three‐fold in the presence of calcium, but it is diminished by osmotic inhibitors, polyamines and abscisic acid (ABA), with a parallel fall in growth rate. Fusicoccin stimulates ethylene production and counteracts the effects of polyethylene glycol; thiourea, which breaks thermodormancy in chick‐pea seeds, reduces ethylene production but does not counteract the effects of osmotic inhibitors. Of the polyamines studied, spermine (in low concentrations, 0.1 to 1.0 mM) is the only one to stimulate ethylene production and cell elongation. It is concluded that there is a close relationship between ethylene production and cell elongation.
Translocation of 14C, carbohydrate content and activity of the enzymes of sucrose metabolism in rose petals temperatures
Authors: Khayat Eli , Zieslin Naftaly
Published: May 2006

Both export of 14C from the source leaves of roses (Rosa×hybrida cv. Golden Times) and import of 14C to the petals were reduced by plant exposure to low night temperature. However, the import was affected to a greater extent than the export. During all stages of flower bud development the concentration of reducing sugars in petals of roses grown at reduced night temperature was lower than in petals of plants grown at higher night temperature. There was no significant difference in starch content in response to the night temperature, and the content of starch decreased toward complete flower bud opening. The concentration of sucrose in flowers at the low night temperature remained low during all stages of flower bud development, while at the high night temperature the concentration of sucrose increased during flower bud development, reaching a peak at the stage when petals start to unfold. At both temperatures the concentration of sucrose declined at complete flower opening. The activity of sucrose synthase (EC 2.4.1.14) was inhibited by low temperature in young rose shoots more than in the petals, while the activity of acid invertase (EC 3.2.1.26) was affected similarly in both tissues by the temperature treatments.
Natural 15N enrichment of amide‐exporting legume nodules
Authors: Shearer Georgia , Kohl Daniel H.
Published: May 2006

The natural 15N abundance of amide‐exporting nodules was compared to that of shoots in 12 plant species. Nodules were statistically less abundant in 15N than shoots in one of three cultivars of Pisum sativum L., in Vicia faba L. and in Medicago sativa L., but the 15N depletion of nodules was very samall. Nodules were statistically more abundant in 15N than shoots in Trifolium pratense L., depending on time during the growing season, Cyamopsis tetragonaloba L. Taub. and 7 Lupinus species, but the enrichment was small except for C. tetragonalova and 6 Lupinus species. Nodules of 3 Lupinus species infected with Rhizobium lupini isolated from Lupinus subcarnosa Hook, were only slightly enriched in 15N, but nodules of two of these species were substantially enriched in 15N when infected with a mix of other Rhizobium lupini strains. The third species, L. texensis Hook., was not infected by this mix of strains. Differences in 15N abundance between nodules and other tissues of amide‐exporting and ureide‐exporting nodules from several studies are tabulated. All ureide‐exporting nodules in this tabulation are enriched in 15N. Amide‐exporting nodules are considerably more variable in this regard. These results confirm that events associated with ureide synthesis or transport cannot be the sole cause of the substantial 15N enrichment seen in nodules.