bluuebunny/crossref_metadata_2025 huggingface dataset:
The accumulation and metabolism of plant growth regulators during organogenesis in cultures of thin cell layers of Nicotiana tabacum
Authors: Heylen Christine , Vendrig Jan C. , van Onckelen Henri
Published: May 2006

The accumulation and metabolism of exogenously applied and endogenously produced auxins and cytokinins were studied in relation to organogenesis in thin cell layers of Nicotiana tabacum L. It was shown that, in order to obtain maximal flower bud formation, both exogenous auxin and cytokinin needed to be present during the first 4 days of culture (to the formation of a subepidermal meristematic zone) whereas cytokinins needed to be present for at least 4 days more (until formation of organogenic centres). Explants taken from floral branches have higher endogenous indole‐3‐acetic acid (IAA) levels compared with explants from the basal part of the stem which form only vegetative buds. This might be related to a different IAA metabolism in these two types of explants as was shown by the different accumulation of exogenously applied IAA. Both ‘floral’ and ‘vegetative’ cells layers contained comparable amounts of zeatin riboside (ZR) as their major cytokinin. Free bases, zeatin (Z) and dihydrozeatin [(diH)Z], given exogenously, were largely metabolised to their respective ribosides. The observation that Z was less effective than (diH)Z in the induction of flower buds could be related to (diH)ZR apparently not being a substrate for cytokinin oxidase.
Photoinhibition of holly (Ilex aquifolium) in the field during the winter
Authors: Groom Quentin J. , Baker Neil R. , Long Steve P.
Published: May 2006

The distribution of holly (Ilex aquifolium) and its habitat preferences indicate a sensitivity to low temperature, particularly when exposed to high light. Experiments were conducted to determine whether photoinhibition of photosynthesis occurs in holly leaves in the field in United Kingdom during the winter. Photosynthetic efficiency was assessed in holly leaves that were exposed to or shaded from direct sunlight using measurements of photosynthetic oxygen evolution and chlorophyll fluorescence. Field measurements were conducted over 3 weeks during January and February. Correlation of the measurements of photosynthetic efficiency with weather conditions indicated that holly was suffering photoinhibition, particularly in leaves exposed to direct sunlight. Controlled environment studies demonstrated that exposure of leaves to low temperature and high light resulted in reductions in photosynthetic efficiency; however, leaves recovered rapidly when exposed to a higher temperature and reduced light level.
Effects of hydroxy‐benzaldehydes on rooting and indole‐3‐acetic acid‐oxidase activity in bean cuttings
Authors: Vàzquez Adelina , Mato Maria C.
Published: May 2006

Changes in the rooting capativity and indole‐3‐acetic acid (IAA)‐oxidase activity of bean (Phaseolus vulgaris L. cv. Contender) cuttings treated with 2‐, 3‐, or 4‐hydroxy‐benzaldehyde (2‐, 3‐ and 4‐OH‐Bal) were monitored in parallel with the chemical changes undergone by these aldehydes in the cuttings. All three compounds enhanced rooting. 2‐OH‐Bal was the most effective and acted synergistically with 10μM IAA at 0.4 mM. 3‐ and 4‐OH‐Bal also stimulated rooting and acted additively with IAA. The position of the hydroxyl group, thus, clearly influences the rooting activity of hydroxy‐benzaldehydes. The action of 2‐OH‐Bal appeared to be due to its inhibition of the IAA‐oxidase activity. All the aldehydes were metabolized chiefly by reduction: after 4 h of treatment, HPLC showed almost all to have been converted to the corresponding alcohol or acid, with an alcohol/acid ratio of 10 for 3‐ and 4‐OH‐Bal and 20 for 2‐OH‐Bal. It is possible that the oxidative effect of the aldehydes may benefit the early stages of root formation.
Characteristics of action potentials in Helianthus annuus
Authors: Zawadzki Tadeusz , Davies Eric , Dziubinska Halina , Trebacz Kazimierz
Published: May 2006

The action potentials induced by nondamaging electrical stimuli in 16‐ to 22‐day‐old plants of Helianthus annuus were examined. Typical recordings are presented. Mean values of their amplitudes and conduction velocities in the stem, the strength‐duration relation, the ‘all‐or‐none’ law and the refractory periods have been determined. The amplitude and velocity of propagation were essentially identical in the upward and downward direction, but greater in the upper than in the lower half. In ‘electrically active’ plants, the rheobase value is 2 V, the minimum period for stimulation is 1.8 s. and the chronaxie 2.3 s. It is noted that the excitability level between similar plants on the same day and in the same plant on different days is highly variable and undergoes periodic changes.
Phosphatidylcholine biosynthesis in celery cell suspension cultures with altered sterol compositions
Authors: Rolph Carole E. , Goad L. John
Published: May 2006

Cell suspension cultures of celery were treated with the plant growth regulator, paclobutrazol. Lipid analysis revealed that use of this xenobiotic had little effect on the quantity or acyl quality of the major phospholipid classes or on the actual amounts of free sterol present in the cell. It did however, cause dramatic changes in the free sterol profile exhibited by treated cultures. In this respect, an increase in 14α‐methylsterols was observed.

The synthesis of phosphatidylcholine in celery cell suspension cultures with altered free sterol compositions was studied using two radiolabelled biosynthetic precursors, [3H‐methyl]choline and [3H‐methyl]methionine. The studies showed that the rate of phosphatidylcholine biosynthesis via the CDP‐base pathway proceeded at a slower rate in paclobutrazol treated cultures. Accumulation of label phosphocholine was observed arising from reduced CTP:cholinephosphatecytidylyltransferase activity. In contrast, phosphatidylcholine biosynthesis via the sequential methylation of ethanolamine derivatives appeared to be enhanced in cells that had an unusually high 14α‐methylsterol content. From these investigations it may be postulated that the biosynthesis of phosphatidylcholine in Apium graveolens suspension cultures may be regulated by membrane sterol composition.
Ethylene in relation to protein, peroxidase and polyphenol oxidase activities during rooting in hazelnut cotyledons
Authors: González Aida , Tamés Ricardo Sánchez , Rodríguez Roberto
Published: May 2006

During formation of adventitious roots, the effects of 2‐chlorethylphosphonic acid (CEPA), 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and aminoethoxyvinylglycine (AVG) added to a Cheng basal medium, supplemented with indole‐3‐butyricacid (IBA) and kinetin were determined on peroxidase (PO; EC 1.11.1.7) and poiyphenol oxidase (PPO; EC 1.10.3.1) activities in cotyledon explants of hazelnut (Corylus avellana L. cv. Casina). CEPA stimulated PO and PPO activities while AVG inhibited. SDS‐polyacrylamide gel electrophoresis of preparations from hazelnut cotyledons showed a correlation between proteins and rooting. Ethylene seems to modify total protein content and the activities of PO and PPO. As compared to the control extracts, AVG inhibited the anodic (53, 30.7 and 27 kDa) and cathodic (66.2 and 53.4 kDa) isoperoxidases and anodic (27.5 and 21 kDa) and cathodic (67.5 kDa) isopolyphenol oxidases, whereas CEPA promoted the anodic (30.7, 28.8 and 27 kDa) and cathodic (53.4 and 27.2 kDa) isozymes with PO activity. The increased PO activity during rooting in hazelnut cotyledons could enhance isozymes with lignin biosynthetic activity.
Changes in carbohydrate and enzyme levels during development of leaves of Prunus persica, a sorbitol synthesizing species
Authors: Merlo Lucia , Passera Calvino
Published: May 2006

Carbohydrate levels and activities of enzymes associated with starch, sucrose and sorbitol metabolism were assayed in leaves of peach [Prunus persica (L.) Batsch cv. Redhaven] of different ages, in order to examine developmental changes in leaf carbohydrate metabolism. Dry matter, soluble protein, chlorophyll and the activities of key enzymes of the reductive pentose phosphate pathway increased during leaf development. The levels of leaf carbohydrates, especially sorbitol and starch, also increased. Changes of starch levels were related to increases in the activities of enzymes associated to starch metabolism, such as ADPglucose‐pyrophosphorylase (E.C. 2.7.7.27) and amylase (E.C. 3.2.1.1. plus E.C. 3.2.1.2). The activities of enzymes involved in sucrose and sorbitol degradation decreased during leaf development, whereas the activities of aldose‐6‐phosphate reductase (E.C. 1.1.1.200) and cytosolic fructase‐1,6‐bisphosphatase (E.C. 3.1.3.11) increased. In contrast, the activity of sucrose‐phosphate synthase (E.C. 2.4.1.14) did not vary in a significant manner. The results suggest that the ability to synthesize and utilize both sucrose and sorbitol changes as peach leaves mature, and also that there are differences in metabolism of these two transport sugars during leaf development.
Phosphorus translocation in salt‐stressed cotton
Authors: Martinez Vicente , Lächli André
Published: May 2006

The effect of salinity on plants has usually been studied at high inorganic P concentration ([Pi]) in the nutrient solution, and salinity × Pi interactions have been examined at much higher [Pi] than found in soil solutions. Short‐term 32Pi experiments were carried out to study the effect of salinity (150 mM NaCl) on phosphorus translocation in cotton plants (Gossypium hirsutum L. cv. Acala SJ‐2) grown in nutrient solutions containing 10 μM [Pi]. The effect of additional Ca to a concentration of 10 μM was also tested. Salinity inhibited 32P translocation from root to shoot. This inhibition was more evident at higher [Pi] in the root medium. Increasing [Pi] 33‐fold in the solution resulted in a 4.3‐fold increase in [32P] in the root under saline conditions, but only in a 1,8‐fold increase in the shoot. In older shoot tissues total [P] was elevated in the salinized plants. In the young tissues, however, total P concentration was higher in control plants. Inhibition of 32P translocation by salinity was greater from root to young leaves than to mature shoot tissues. Salinity also decreased 32P recirculation from the cotyledons to the young leaf. Inhibition by salinity of both 32P translocation and recirculation to young leaves was fully reversed by increasing Ca supply from 1 to 10
Changes in gene expression patterns during the sexual life cycle of Chlamydomonas reinhardtii
Authors: Treier Ulrike , Beck Christoph F.
Published: May 2006

In the sexual life cycle of Chlamydomonas reinhardtii, three types of cells can be distinguished: vegetative cells, gametes, and zygotes. Using is vivo pulse labelling of proteins with 35S‐sulfate, followed by two‐dimensional separation of the polypeptides on polyacrylamide gels, we analyzed the patterns of protein synthesis typical for each cell type. Approximately 20% of the proteins detected were synthesized at very different rates when the pattern from vegetative cells was compared to that of gametes or zygotes. Gamete formation from vegetative cells is a two‐step process controlled by two extrinsic signals: first, nitrogen‐starvation induces the differentiation of vegetative cells to pregaroetes, which are then competent for a light–induced differentiation to mature gametes. The majority of the changes in rate of synthesis of different proteins during the switch from vegetative cells to gametes was observed already in pregametes. Between the stages of pregametes and gametes, changes in the rates of synthesis of four proteins were detected. Induction of zygote germination resulted in complex changes in the patterns of gene expression. Evidence is presented for three groups of proteins whose synthesis is turned on or turned off during zygote germination.
Cell wall structure regulates the autolytic process throughout growth of Cicer arietinum epicotyls
Authors: Dopico Berta , Muñoz Francisco José , Nicolás Gregorio , Labrador Emilia
Published: May 2006

The autolytic process in epicotyl cell walls of Cicer arietinum L. cv. Castellana, and also the hydrolysis of heat‐inactivated cell walls as mediated by a cell wall β‐galactosidase (EC 3.2.1.23) (named βIII and previously characterized as responsible for the autolysis), are maximal on the fourth day of germination and coincide with the maximal growth capacity. They decrease during the following days, in which the growth rate diminishes. In both cases, no differences were observed in the percentages of the different sugars released, galactose being the principal one. The βIII fraction from aged epicotyl cell walls hydrolyzed young walls in proportion to its specific activity, and more efficient than when cell walls from aged material were used as the substrate. The βIII fraction from 4 day‐old epicotyls (the time for maximal autolysis) was incapable of hydrolyzing aged epicotyl cell walls to the same extent as young ones. These results, together with the levels and activity of the enzyme throughout growth, allow the assumption that the variations in the autolysis and hydrolysis caused by βIII during growth processes are due to structural modifications in the cells walls, modifications that would limit access of the enzyme to its substrate, thus impeding the release of galactose, even though the enzyme is present.
Cytochrome and alternative pathway respiration in white spruce (Picea glauca) roots. Effects of growth and measurement temperature
Authors: Weger Harold G. , Guy Robert D.
Published: May 2006

Interactions between growth temperature and measurement temperature were examined for their effects on white spruce [Picea glauca (Moench) Voss] root respiration. Total dark respiration rates increased with measurement temperature and were unaffected by growth temperature. Partitioning of respiratory electron flow between the cytochrome and alternative pathways was also unaffected by growth temperature. The proportion of respiration mediated by the alternative pathway was constant at measurement temperatures between 4°C and 18°C, but was increased at higher temperatures. Changes in alternative pathway activity were paralleled by changes in capacity, and the alternative pathway was almost fully engaged at all temperatures. Roots grown at low temperature displayed higher carbohydrate levels than roots grown at higher temperatures, but respiration rate was unaffected. Spruce root respiration did not appear to acclimate to growth temperature, and the alternative pathway was not preferentially engaged at low temperature.
When plant teratomas turn into cancers in the absence of pathogens
Authors: Gaspar Thomas , Hagège Daniel , Kevers Claire , Penel Claude , Crèvecoeur Michèle , Engelmann Isabelle , Greppin Hubert , Foidart Jean‐Michel
Published: May 2006

Habituated calli have long been classified as neoplasms together with tumors from different origins. The general opinion is that habituation is a reversible process with an epigenetic basis. This is probably true in most cases examined. However, we show here that there might be several degrees of habituation, which can be considered as steps of a neoplastic progression leading to cancerisation in the absence of an introduced oncogenic pathogen. Cell rejuvenation, loss of the capacity to organize meristematic centers, and loss of totipotency are proposed to define plant cancer through this neoplastic progression of a callus.

Habituated tissues share many morphological and biochemical similarities with so‐called vitreous shoots from micropropagation. Vitrification and hyperhydric malformations of shoots raised in vitro may be considered as steps of another neoplastic progression, which leads to cancerisation also in the absence of introduced oncogenic pathogens. In this case death of the whole organism occurs either through direct apex necrosis or indirectly, from the loss of the capacity for the primary meristems to function normally, which gives rise to completely anarchic structures. As in the animal kingdom, carcinogenesis in plants is the final result of a multistep process involving the irreversible conversion of a stem cell to a terminal‐differentiation‐resistant cell.
The photoprotective role of carotenoids in higher plants
Authors: Young Andrew John
Published: May 2006

Carotenoids have two important roles in photosynthetic organisms. First, they act as accessory light‐harvesting pigments, effectively extending the range of light absorbed by the photosynthetic apparatus. Secondly, they perform an essential photoprotective role by quenching triplet state chlorophyll molecules and scavenging singlet oxygen and other toxic oxygen species formed within the chloroplast. Only recently an additional, novel, protective role has been proposed for the carotenoid zeaxanthin, involving the dissipation of harmful excess excitation energy under stress conditions. Zeaxanthin may be formed through de novo synthesis in response to long‐term environmental stress, and through the rapid enzymic de‐epoxidation of the carotenoid violaxanthin (the xanthophyll cycle) in response to short‐term alterations in the plant's light environment. Interspecific differences occur in the ability of plants and algae to produce zeaxanthin under stress conditions, and hence the ability to photoprotect the photosynthetic apparatus through this means varies from species to species. The ability of a plant to respond to light‐mediated environmental stress by producing zeaxanthin may therefore affect, at least in part, the ability of that plant to inhabit or colonise certain habitats (e.g. sun or shade conditions).
Purification of endoplasmic reticulum from wheat roots and shoots (Triticum aestivum). Comparison of their blue light‐sensitive redox components with those of highly purified plasma membrane
Authors: Widell Susanne , Sommarin Marianne
Published: May 2006

Plasma mebranes (PM) and endoplasmic reticulum (ER) were prepared from 4.5‐day‐old, light‐grown wheat (Triticum aestivum L. cv. Drabant) shoots and roots, using phase partitioning for the PM, which yields very pure PM preparations, and sucrose gradient centrifugation for the ER. Also the ER fractions were highly purified, being totally free from mitochondria (cytochrome c oxidase, EC 1.9.3.1), PM (glucan synthase II, EC 2.4.1.34) and thylakoid membranes (chlorophyll), and with a low content of tonoplast (nitrate‐sensitive ATPase) and Golgi (latent IDPase). Sodium dodecyl sulphate polyacrylmide gel electrophoresis of root ER resulted in a similar polypeptide pattern as for shoot ER, but very different from the crude fraction from which the ER fractions were purified, also indicative of a high purity. The PM and ER preparations were compared with respect to their blue light‐sensitive flavoprotein‐cytochrome b. About half of the dithionite‐reducible cytochrome b of shoots (PM as well as ER) and root PM was light‐sensitive, compared to only 10–20% of that of root ER. Shoot PM needed 2–3 times less light compared to the other membranes, for half saturation of the reaction. NADH‐cytochrome c reductase activity was found with all four membrane fractions, with ER having activities 5–10 times higher than PM. The relevance of photoreducible components in the PM and the ER is discussed in connection with blue light photobiology.
Effect of auxins on spermidine uptake into carrot protoplasts
Authors: Kanchanapoom Malee , Antognoni Fabiana , Pistocchi Rossella , Bagni Nello
Published: May 2006

The effect of an auxin, indole‐3‐acetic‐acid (IAA), on spermidine uptake into protoplasts of carrot (Daucus carota L. cv. Ingrid) was studied. In the presence of 1 mM Ca2+, IAA (10−7 to 10−4M) enchances [14C]‐spermidine uptake into carrot protoplasts, while no stimulation occurs in the absence of Ca2+. The time course of the uptake with and without IAA is very rapid and reaches saturation within 1 to 2 min. Preincubation of protoplasts with IAA inhibits the spermidine uptake. La3+, known not to penetrate the plasmalemma, exerts the same effect as Ca2+, but gives lower uptake values than Ca2+. The application of vanadate, an ATPase inhibitor, strongly inhibits IAA‐stimulated spermidine uptake, suggesting that an energy‐dependent mechanism may be involved in this transport. Neither spermidine nor Ca2+ alone stimulate IAA uptake. The synthetic auxin 2,4‐dichlorophenoxyacetic acid, yields the same results as IAA with regard to time course of spermidine uptake with and without preincubation while, unlike IAA, no significant effect was observed on the Ca2+ ‐induced increase of spermidine uptake.
Inhibition of auxin‐induced elongation and xyloglucan breakdown in azuki bean epicotyl segments by fucose‐binding lectins
Authors: Hoson Takayuki , Masuda Yoshio
Published: May 2006

Auxin‐induced elongation of epicotyl segments of azuki bean (Vigna angularis Ohwi and Ohashi cv. Takara) was suppressed by fucose‐binding lectins from Tetragonolobus purpureus Moench and Ulex europaeus L. These lectins also inhibited auxin‐induced cell wall loosening (decrease in the minimum stress‐relaxation time of the cell walls) of segments. Auxin caused a decrease in molecular mass of xyloglucans extracted with 24% KOH from the cell walls. The lectins inhibited auxin‐induced changes in molecular mass of the xyloglucans. The autolytic release of xylose‐containing products from the pectinase‐treated cell walls was also suppressed by the lectins. Fucose‐binding lectins pretreated with fucose exhibited little or no inhibitory effect on auxin‐induced elongation, cell wall loosning, or breakdown of xyloglucans. These results support the view that the breakdown of xyloglucans is involved in the cell wall loosening responsible for auxin‐induced elongation in dicotyledons.
Effects of temperature on the mode of pollen development in anther culture of Brassica campestris
Authors: Hamaoka Yoh , Fujita Yukio , Iwai Sumio
Published: May 2006

In anther culture of Brassica campestris L., the yield of pollen‐derived embryoids is greatly stimulated by a high‐temperature (35°C) tratment for the first 1 to 3 days of the culture. We have inestigated the effects of the high‐temperature treatment on the mode of pollen division in cultured anthers.

Anthers containing late uninucleate pollen were cultured on modified B5 medium. High‐temperature treatment for the first 24 h inhibited the normal development of the pollen and induced abnormal symmetrical division. Which is the first step in androgenesis. This symmetrical division was rarely observed in pollen developed in vivo. In anthers cultured without high‐temperature treatment, the mode of pollen development was similar to that in vivo. This suggests that the normal differentiation of the pollen is blocked by high temperatures, and sporophtic growth is induced. Sucrose (0.29 M) was essential for the induction of this symmetrical division, though neither plant growth regulator nor any other nurient was necessary. Pollen division could not be induced effectively if sucrose was replaced by either mannitol or sorbitol plus a lower concentration of sucrose. Therefore, it seems that sucrose actively influences the embryogenic division of pollen, and does not have only an osmotic effect.
Leaf respiration in Piper species native to a Mexican rainforest
Authors: Fredeen Arthur L. , Field Christopher B.
Published: May 2006

We measured leaf respiration with a Clark‐type oxygen‐electrode in 6 species of the genus Piper (Piperaceae) growing naturally in wet evergreen rainforest, in microsites characterized by a broad range of light availabilities. Species normally found in large gaps and clearings (Piper auritum and P. umbellatum) had approximately twice the dark respiration per unit of leaf area or dry mass as species found predominantly in shaded understory sites (P. aequale, P. lapathifolium and P. amalago). within a species, dark respiration was lower in the individuals growing in low‐light sites than in the individuals growing in high‐light sites. Over all species, leaf respiration was positively correlated with the average daily photosynthetically active photon flux density (PFD) at each site, and negatively correlated with mean leaf longevity. Respiration was insensitive to leaf age in a shade species. (P. lapathifolium) and in a generalist (P. hispidum) but decreased with increasing leaf age in a gap specialist (P. aurtium).

In experiments on greenhouse‐grown plants, we titrated respiration with potassium cyanide (KCN) and/or salicylhydroxamic acid (SHAM) to determine the cytochrome and alternative pathway components to respiration in 4 Piper species. All 4 species, representing gap, generalist and shade species, exhibited alternative pathway respiration. Engagement of the cytochrome pathway (ϱcyt) varied from 0.69 in P. auritum to 1.04 in P. lapathifolium and engagement of the alternative pathway (ϱalt varied from 0.41 to 1.02. Although the shade species had lower respiration rates than the gap species, the capacities for cytochrome and alternative pathway respiration made up similar or greater fractions of total respiration in shade species.
Proteinase nature of an enzyme capable of activating the galactosyltransferase involved in volume regulation of Poterioochromonas malhamensis
Authors: Rausch Ulrike , Ahmad Hassan , Maier Gernot , Kauss Heinrich
Published: May 2006

A simplified procedure for the assay and purification of an enzyme which activates a galactosyltransferase (EC 2.4.1.96) involved in volume regulation of the unicellular alga Poterioochromonas malhamensis (Peterfi) is described. The enzyme was extracted with water from membranes, followed by chromatography on DEAE‐Sephacel, phenyl‐Sepharose and fetuin‐agarose. Its proteinase activity was demonstrated by cleavage of oxidized insulin A‐ and B‐Chains. The predominant cleavage site of the oxidized A‐chain is the peptide bond between 13Leu and 14Tyr whereas 16Leu‐17Glu is also hydrolyzed with minor activity. Besides this chymotrypsin‐like endopeptidase activity some carboxypeptidase activity was also observed.
Regeneration of shoots from pea (Pisum sativum) hypocotyl explants
Authors: Nielsen S. V. S. , Poulsen G. B. , Larsen M. E.
Published: May 2006

A sequential indole‐3‐acetic acid (IAA)‐zeatin treatment was applied to Pisum sativum hypocotyl explants, resulting in shoot formation from 50% of the explants. Shoots were easily rooted and transplantable plants could be obtained in 3 months. The method has been applicable to the 5 cultivars tested. Histological examination of explants suggests the shoots to be of de novo origin, which would make the system suitable for transformation experiments.
Ethanol metabolism in suspension cultured carrot cells
Authors: Perata P. , Alpi A.
Published: May 2006

Ethanol production in plant tissues deprived of oxygen is a well known process. Nevertheless, little information is available on the toxic effects of ethanol on plant cells and tissues, or on the possible role of acetaldehyde, the first oxidative product of ethanol, in inducing toxic effects in plants. Data on the metabolism of ethanol in suspension cultured cells of carrot (Daucus carola L. cv. S. Valery, cell line T22), a system highly sensitive to the presence of ethanol in the culture medium, indicate that carrot cells oxidize only small amounts of ethanol to CO2. Instead, they convert ethanol mainly to acetaldehyde, which accumulates in the culture medium. This suggests a possible role of acetaldehyde in causing ethanol‐induced injury to carrot cells.
Isolation and characterization of colchicine‐resistant cell lines of carrot
Authors: Borkird Chumpol , Sung Z. Renee
Published: May 2006

Colchicine changes plant cell shape by disrupting cortical microtubules. This change in cell shape involves the loss of cell rigidity and, subsequently, an increase in cell volume. Dimethylsulfoxide prevents the colchicine‐stimulated cell enlargement but cannot maintain the cell shape. We have isolated colchicine‐resistant cell lines, col‐4 and col‐3, which can maintain their cell shape in colchicine at 10−4 and 10−3M, respectively. Both col‐4 and col‐3 accumulate a low level of tubulins when grown in colchicine while the wild‐type cells do not. Hence the ability to accumulate tubulins correlates with the ability to maintain cell shape. The mechanism of colchicine‐resistance of col‐4 is not clear but may be associated with the expression of 5 proteins with molecular masses of 64, 45, 29, 28, and 26 kDa. Col‐3 cells were isolated from col‐4 and presumably shared this mechanism of resistance since they also express these 5 proteins. However, col‐3 cells have an additional defect resulting in reduced colchicine uptake.
Physiological indicators of nitrogen response in a short rotation sycamore plantation. I. CO2 assimilation, photosynthetic pigments and soluble carbohydrates
Authors: Tschaplinski Timothy J. , Norby Richard J.
Published: May 2006

American sycamore (Platanus occidentalis L.) seedlings were grown in the field under different urea‐nitrogen fertilization regimes to identify physiological variables that characterize the growth response. Treatments included fertilization at the beginning of the growing season with 50, 150, 450 kg N ha−1, fertilization 3 times each at 37.5 kg N ha−1 and unfertilized control. The greatest aboveground biomass accumulation (3× that of control) occurred in plots fertilized with 450 kg N ha−1, but nearly as much growth occurred when 37.5 kg N ha−1 was added periodically. Photosynthesis, chlorophyll concentrations and growth increased rapidly after the midseason application of 37.5 kg N ha−1 but not after the late‐season application. Although nitrogen fertilization increased leaf area per plant, leaf nitrogen concentration did not differ between treatments. There was no evidence to indicate that fertilization extended the physiologically active season or increased susceptibility to drought or cold. Sycamore leaves accumulated sucrose and mannose in response to water stress in all treatments. Photosynthetic pigment concentrations and net photosynthetic rate were the most sensitive indicators of growth response to nitrogen fertilization in the first growing season. Careful timing (based on physiological indicators) of low level applications of nitrogen fertilizer can optimize growth.
The germination characteristics of phytochrome‐deficient aurea mutant tomato seeds
Authors: Georghiou Kyriacos , Kendrick Richard E.
Published: May 2006

The germination of tomato (Lycopersicon esculentum Mill.) cv. Moneymaker seeds of a phytochrome‐deficient aurea (au) mutant and its isogenic wild types were investigated. In contrast to the wild type whose seeds germinate in darkness, those of the au mutant have a low dark germination level. Continuous far‐red light (FR) inhibits the germination of the wild type, whereas in au‐mutant seed batches exhibiting some dark germination, no inhibition of these dark‐germinating seeds was observed. Germination of the au mutant was promoted by continuous red light (R). Intermittent pulses of R were also effective and phytochrome was implicated as the photoreceptor, since cyclic treatments of 2 min R/2 min FR/26 min darkness led to a significantly lower germination than the control receiving 2 min R/28 min darkness. Germination of the au mutant in darkness increased with the period of post‐harvest storage in paper packers at laboratory temperature. Germination could also be induced in darkness at 25°C by treatment of the imbibed seeds for a period of time at a lower or higher temperature. Germination was also promoted by the presence of nitrate ions in the imbibition medium. In this case simultaneous irradiation with FR failed to inhibit germination of the au mutant, whilst germination of the wild‐type controls was strongly inhibited. In the case of a highly dormant au seed batch where continuous R, low temperature treatment and nitrate ions were partially effective (promotive), full germination could be induced by the combination of continuous R with one of the other factors. The stable pool of phytochrome is predicted to be the pool involved in the promotion of seed germination in darkness as a result of residual Pfr being present in it during dehydration. The au‐mutant seeds are more dormant than wild type seeds and therefore require more of the active FR‐absorbing form of phytochrome (Pfr) to achieve germination. Since the au mutant exhibits a phytochrome‐controlled promotion of germination, it must contain phytochrome and it is speculated that this is stable pool of phytochrome which has been demonstrated to be present in the light‐grown au mutant plants.
Flower formation in vitro in a quantitative short‐day tobacco: interrelation between photoperiod and infructescence development
Authors: Altamura Maria Maddalena , Pasqua Gabriella , Monacelli Barbara , Tomassi Marisa , Archilletti Tiziana , Falasca Giuseppina
Published: May 2006

The flowering response of thin layers excised from branch internodes of Nicotiana tabacum cv. Maryland Catterton (quantitative short‐day plant for induction) was studied under three photoperiodic treatments. The explants were excised from inflorescences bearing flowers only, flowers and green fruits, or from infructescences with green fruits only. The aim of the study was to investigate the post‐inductive photoperiodic effects on in vitro flower bud formation in a quantitative short‐day tobacco and the relation with infructescence development. Short days quantitatively enhanced the flower bud regeneration capacities of explants in all stages of development, both as number of explants induced to produce flowers and as mean number of flowers per explant. There was no significant difference in flower bud formation on explants of the first two stages, which produced much more flowers than those of the third stage. Observations in planta showed that, during the 20 days separating the second stage from the first stage, there was no significant difference in the number of floral buds and flowers present on the inflorescence; however, the branch internodes lengthened, as did the floral buds and flowers. During the 10 days leading to the third stage, the number of capsules did not change significantly, but a high rate of floral abscission occurred. The present results show that in Nicotiana tabacum cv. Maryland Catterton short day quantitatively controls not only the inductive step of the flowering process, but also affects the capacity to regenerate flower buds during the late post‐inductive phases. The responsiveness to the photoperiodic signal decreases only when the plant exhibits only fruits.
Glycine oxidation in mitochondria isolated from light grown and etiolated plant tissue
Authors: Lernmark Ulrika , Henricson Dag , Wigge Bosse , Gardeström Per
Published: May 2006

Mitochondria were isolated from light grown and dark grown monocotyledonous (wheat‐Triticum aestivum and barley‐Hordeum vulgare) and dicotyledonous (pea‐Pisum sativum) plants and their capacity to oxidize glycine was measured. In all of the studied plant species the rate of mitochondrial glycine oxidation was high in light grown leaves. Glycine oxidation in mitochondria from etiolated leaves was also very substantial; the rate of glycine oxidation relative to the oxidation of other substrates was about half as compared to green tissue. In etiolated non‐photosynthetic tissues the relative glycine oxidation was only ca 20% of that measured in green leaves. The effect of light on the development of glycine oxidation capacity was studied using etiolated barley which was transferred to light for 6 to 24 h. During this time the rate of glycine oxidation as compared to the oxidation of NADH and malate increased, approaching the ratio observed in light grown leaves. It is concluded that the synthesis of proteins involved in glycine oxidation is regulated both in a light dependent and in a tissue specific manner. Monocotyledonous plants should be very useful for further studies of this aspect due to the relatively small developmental difference between etiolated and light grown leaf tissue.
Proteolysis and nitrogen fixation in faba‐bean (Vicia faba) nodules under water stress
Authors: Guérin Vincent , Pladys Dominique , Trinchant Jean‐Charles , Rigaud Jean
Published: May 2006

Nodulated faba‐beans (Vicia faba L. var. minor) exhibiting high rates of N2 fixation (133 μmol C2H4 g−1 dry weight h−1), were subjected to water restriction. A loss of C2H2 reduction due to water stress was always associated with a decline of the leghemoglobin content for each of the 4 decreasing values of Ψmod. Electron micrographs showed ultrastructural alterations of the fixing tissue, which affected both partners and increased with the severity of water stress. In the nodule cytosol, the alkaline proteolysis approximately doubled when Ψmod decreased from −0.55 MPa to −1.55 MPa. Concomitantly, an increase of the nodule intracellular pH from 6.3 to 7.0 was observed. Proteolysis was due to serine proteases, exhibiting a pH‐optimum of 8 and which actively degraded purified leghemoglobin in vitro (Km=100 μM). The degradation of leghemoglobin during water stress may contribute to the loss of C2H2 reduction and may affect the pattern of recovery upon rewatering.
Purification and properties of β‐xylosidase isozymes from cucumber seeds
Authors: Mujer Cesar V. , Miller A. Raymond
Published: May 2006

Two soluble thermostable isozymes of β‐xylosidase, 1,4 β‐D‐xylan xylohydrolase (EC 3.2.1.37) were isolated and characterized from immature seeds of cucumber (Cucumis sativus L. cv. Heinz 3534) to determine their role in xylan hydrolysis. The major isozyme (A) was purified 592‐fold to near homogeneity using ammonium sulfate fractionation, chromatography on SP‐Sephadex, heat treatment (75°C, 30 min) and chromatography on con A‐Sepharose 4B, Bio‐Gel HTP hydroxylapatite and Sephadex G‐100. The minor isozyme (B) was purified partially (18‐fold) using ammonium sulfate fractionation and chromatography on SP‐Sephadex and con A‐Sepharose 4B. Both isozymes were glycoproteins. Their native molecular weight was 68 kDa as determined by gel filtration. The purified isozyme A migrated as a single major polypeptide in SDS‐PAGE, with a molecular weight of 68 kDa. Isozyme A had a net negative charge at pH 5, exhibited optimal activity at pH 4.5 and 68°C and had a Km of of 1.5 mM for p‐nitrophenyl β‐D‐xylopyranoside. In contrast, isozyme B was positively charged at pH 5, exhibited optimal activity at pH 4.5 and 50°C and had a Km of 5.4 mM. The hydrolysis of p‐nitrophenyl β‐D‐xylopyranoside by isozyme A was inhibited competitively by D‐xylose, AgNO3 and HgCl2 with Ki values of 1.6.0.08 and 0.15 mM, respectively. In the absence of D‐xylose, isozyme A was inactivated after incubation at 75°C for 30 min. However, 50% of the enzyme activity remained after 1 h at 75°C in the presence of 200 mM D‐xylose. Of 14 potential substrates tested, purified isozyme A exhibited activity only toward p‐nitrophenyl β‐D‐xylopyranoside and oligosaccharide fragments [degree of polymerization (DP) >10] obtained from beechwood xylan. Incubation of the latter substrate with the enzyme yielded free xylose. The ability of the enzyme to utilize xylan fragments generated by a previously characterized endo‐xylanase suggests that β‐xylosidase and endo‐xylanase may be involved in the metabolism of xylan from cucumber cell walls.
Active uptake of sucrose by plant plasma membrane vesicles: determination of some important physical and energetical parameters
Authors: Lemoine Rémi , Bourquin Sophie , Delrot Serge
Published: May 2006

The present paper investigates some characteristics of plant plasma membrane vesicles in relation to sucrose uptake. The plasma membrane vesicles purified by aqueous two‐phase partitioning from sugar beet (Beta vulgaris L.) leaf microsomes had an average diameter of 291 ± 13 nm and their internal volume was 2.2 μl (mg protein)−1. Although the vesicles were subjected to one freeze‐thaw cycle for the purpose of storage, they retained mainly (78 %) their original right‐side‐out orientation as estimated either by labelling with peroxidase‐labelled Concanavalin A or by measurements of ATPase latency. The use of higher concentrations of protecting agents [5 mM ethylenediaminetetraacetic acid (EDTA) and 2 mM dithiothreitol (DTT)] in the grinding buffer led to an increase of sucrose uptake by the vesicles. Measurements of the two components (pH and electrical gradients) of the proton motive force (PMF) showed that a high PMF (‐200 mV) was created under the experimental conditions used. The accumulation of sucrose which theoretically could be obtained by this PMF is much larger than the accumulation actually measured. Although the data support the conclusion that an active uptake of sucrose is driven by the PMF in plasma membrane vesicles from sugar beet leaves, they also stress some limits of this experimental system.
In vitro evidence for the involvement of activated oxygen in light‐induced aggregation of thylakoid proteins
Authors: Roberts D. R. , Kristie D. N. , Thompson J. E. , Dumbroff E. B. , Gepstein S.
Published: May 2006

Protein aggregation in thylakoids incurred in situ during light‐induced heat shock damage can be simulated in vitro by illuminating isolated thylakoids at normal temperatures. Aggregation is detectable in the in vitro model system by fluorography of [35‐S]‐methionine‐labelled thylakoids fractionated by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS‐PAGE) and also by Coomassie staining after SDS‐PAGE of unlabelled thylakoids. As in the case of light‐induced heat shock damage, protein aggregation in the in vitro system is completely light dependent, and the D‐1 protein of PS][is present in the protein aggregate. The model system has also provided evidence for the involvement of activated oxygen in aggregation of thylakoid proteins. Histidine, which scavenges singlet oxygen, and n‐propylgallate; a non‐specific scavenger of activated oxygen, both provided complete protection against light induced protein aggregation in isolated thylakoids. These compounds also strongly reduced the levels of activated oxygen by illuminated thylakoids as measured by electron spin resonance. The involvement of activated oxygen is further supported by the finding that protein aggregation in the model system proved to be oxygen dependent. The herbicide dichlorophenyldimethyl urea, which binds to the QB site of the D‐1 protein of PSII and provides protection against photoinhibition and light dependent degradation of the D‐1 protein, also provided partial protection against protein aggregation in the in vitro system. Protein continues to aggregate after PSII activity has reached undetectable levels suggesting that aggregation is a consequence rather than a cause of photoinhibition. The observations collectively indicate that aggregation of thylakoid proteins is attributable to activated oxygen.
A comparison between ethylene production, ACC and mACC contents, and hydroperoxide level in normal and habituated sugar beet calli
Authors: Hagège Daniel , Kevers Claire , Gaspar Thomas
Published: May 2006

In contrast to normal hormone, requiring sugar beet callus, habituated auxin‐ and cytokinin‐independent callus of the same plant produces very little ethylene, contains less 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and malonyl‐ACC (mACC), has a low capacity to convert ACC into ethylene and has lower levels of hydroperoxides. The low ethylene production is apparently controlled by the rate of ACC synthesis and conversion to mACC, as well as by the activity of the ethylene forming enzyme. The interactions between ethylene and polyamine metabolism are discussed, as well as the possible causal relation between the low level of ethylene and the low degree of differentiation of the habituated cells.
Alanine aminotransferase in Leptosphaeria michotii. Isolation, properties and cyclic variations of its activity in relation to polypeptide level
Authors: Abou‐Zeid A. M. , Jerebzoff S. , Jerebzoff‐Quintin S.
Published: May 2006

Alanine aminotransferase (EC 2.6.1.2) was obtained from the fungus Leptosphaeria michotii (West) Sacc, and enriched 714‐fold by a 5‐step purification procedure as a dimer of Mr 110000, associated with a polypeptide of Mr 25000. Its isoelectric point was 5.25. The enzyme was active from pH 3.5 to 9.5 with a maximum at pH 7.5. Its specific activity was 6000 nkat (mg protein)−1; the Km was 6.85 mM for L‐alanine and 0.2 mM for 2‐oxoglutarate. The enzyme did not show any detectable activity in the presence of L‐aspartate, cysteine sulfinate, α‐aminobutyrate or cyclic amino acids as substrates. It did not express alanine:glyoxylate aminotransferase activity. Alanine aminotransferase in L. michotii has previously been shown to have an activity rhythm in constant temperature and darkness. The enzyme level was quantified along the activity rhythm by enzyme‐linked immunosorbent assay (ELISA), using a monospecific polyclonal antibody against the purified enzyme. The cyclic variations of alanine aminotransferase activity were correlated with cyclic variations in the enzyme level.
Ethylene responsiveness changes in Pelargonium×domesticum florets
Authors: Evensen Kathleen B.
Published: May 2006

Florets of Pelargonium x domesticum L. H. Bailey respond to ethylene with rapid petal abscission. Florets become increasingly responsive to ethylene with age, with the greatest change in responsiveness occurring between the day of anthesis and 2 days later. The ethylene responsiveness coefficient (the ratio of the concentrations of ethylene giving 90% and 10% abscission) declined from 21 in 1‐day‐old florets to slightly greater than 1 in older florets; therefore abscission was ultraresponsive (responsiveness coefficient <81) even in 1‐day old florets. Younger florets required a higher concentration of ethylene and longer duration of ethylene exposure to induce the abscission response. Even florets aged 2–3 days after anthesis required at least 40 min of exposure to ethylene for the abscission response to occur, irrespective of the concentration.
Ethidium bromide preferentially releases high mobility group chromosomal proteins HMGc and HMGd from wheat embryo nuclei
Authors: Arwood Laura J. , Hill Elizabeth , Spiker Steven
Published: May 2006

The High Mobility Group (HMG) chromosomal proteins have been implicated as structural proteins of transcriptionally poised chromatin in animal systems. Despite the suspected functions of these proteins, no bioassay for them exists and they are defined operationally (by the procedures used to isolate and purify them). Plant systems have chromosomal proteins that can be operationally defined as HMG proteins. However, because of the lack of suitable bioassays and because the plant HMG proteins are structurally distinct from their putative animal counterparts, no clear relationship between plant and animal HMG proteins has been established. One diagnostic characteristic of vertebrate animal HMG proteins is that a subset of them is released from chromatin by intercalating agents that affect the topology of DNA. We show here that wheat (Triticum aestivum) embryo HMGc and HMGd (but not HMGa and HMGb) are preferentially released from nuclei treated with 7.5 mM ethidium bromide. Because vertebrate animal HMG14/17 (but not HMG1/2) displays this characteristic, the observation suggests that these wheat chromosomal proteins may be the plant analogs of vertebrate HMG14/17.