bluuebunny/crossref_metadata_2025 huggingface dataset:
Uniconazole‐induced thermotolerance in soybean seedling root tissue
Authors: Upadhyaya Abha , Davis Tim D. , Larsen M. H. , Walser R. H. , Sankhla N.
Published: May 2006

Soybean [Glycine max(L.) Merr. cv. A2] seeds were germinated in 0 or 1 mg 11 (3.4 uM) uniconazole, after which seedling roots were excised and exposed to 22 or 48°C for 90 min. Prior to the temperature treatments there were few ultrastructural differences between uniconazole‐treated seedling roots and the controls. Following exposure to 48°C, electron micrographs revealed near complete loss of normal ultrastructure in control epidermal root cells, whereas cellular integrity was maintained in treated roots, indicating that uniconazole conferred tolerance to high temperature. Total electrolyte, sugar and K+ leakage were all greater from control roots than treated roots during exposure to 48°C. Proline content in the roots was unaffected by uniconazole at 22°C but was 25–30% greater in treated tissue than in controls following exposure to 48°C. Malondialdehyde content was unaffected by uniconazole at 22°C but was nearly 20% less in treated tissue than in controls following high temperature exposure. This indicates that uniconazole decreased high‐temperature‐induced lipid peroxidation. Uniconazole elevated several antiox‐idant systems in the roots, including water‐soluble sulfhydryl concentration and catalase, peroxidase and superoxide dismutase activities. These findings are consistent with the hypothesis that uniconazole‐induced stress tolerance is due, at least in part, to enhanced antioxidant activity which reduces stress‐related oxidative damage to cell membranes.
Alterations in nitrogen assimilation and partitioning in nitrogen stressed plants
Authors: Rufty Thomas W. , MacKown Charles T. , Volk Richard J.
Published: May 2006

Although nutrient stress is known to alter partitioning between shoots and roots, the physiological basis for the phenomenon is unresolved. Experiments were conducted to examine assimilation of 15NO3 by N‐stressed plants and to determine whether apparent changes in assimilation in the root contributed to alterations in whole‐plant partitioning of reduced‐N. Tobacco plants (Nicotiana tabacum L. cv. NC 2326) were exposed to a low concentration of NO3− in solution (80 μM) for 9 days to effect a N‐stress response. Exposure of plants to 1000 μM15NO3− for 12 h on selected days revealed that roots of N‐stressed plants developed an increased capacity to absorb NO3−, and accumulation of reduced‐15N in the root increased to an even greater extent. When plants were exposed to 80 or 1000 μM15NO3− in steady‐state, 15NO3− uptake over a 12 h period was noticeably restricted at the lower concentration, but a larger proportion of the absorbed 15N still accumulated as reduced‐15N in the root. The alteration in reduced‐15N partitioning was maintained in N‐stressed plants during the subsequent 3‐day “chase” period when formation of insoluble reduced‐15N in the root was quantitatively related to the disappearance of 15NO3− and soluble reduced‐15N. The results indicate that increased assimilation of absorbed NO3−, in the root may contribute significantly to the altered reduced‐N partitioning which occurs in N‐stressed plants.
Endocytosis in plants
Authors: Robinson David G. , Milliner Stefan
Published: May 2006

Endocytosis in animal cells has been heavily documented. Both fluid‐phase and receptor‐mediated modes of uptake have been frequently studied, and the endocytic pathway is well defined. This contrasts markedly with the situation in plants where our knowledge of this process is still rudimentary. Partly responsible for this situation has been the view, widely held among plant physiologists, that because of turgor, endocytosis cannot occur in plant cells. As discussed below, the case against endocytosis is no longer water‐tight.

Endocytosis is a fact in protoplasts. It can be demonstrated with electron‐dense tracers as well as with membrane impermeant dye Lucifer Yellow CH. The latter has also been used with success on both suspension‐cultured and tissue cells of higher plants, suggesting that fluid‐phase endocytosis is also a feature of cells with walls. Through the application of fluorescently labelled elicitor molecules, which specifically bind to the cell surface of suspension‐cultured cells, it has also been possible to provide convincing evidence for the operation of receptor‐mediated endocytosis in plants. A number of studies on protoplasts and cells clearly indicate that endocytosis in plants can be mediated by coated pits in the plasma membrane. At least one of the organelles that lie on the endocytic pathway in plants has a structurally similar counterpart in animal cells: the multivesicular body. The first recipient of internalized molecules is the partially coated reticulum, although its relationship to the Golgi apparatus and Golgi function remain to be clarified. The final target for endocytosis in plants appears to be the vacuole.
The utility of transposable elements as tools for the isolation of plant genes
Authors: Chandlee Joel M.
Published: May 2006

Transposable elements are segments of DNA which have the unique capability of being able to excise from one site in the genome and reintegrate into new, different sites elsewhere in the genome. When transposition takes place and integration occurs within a gene locus, mutations are frequently generated producing variegated or recessive phenotypes. This ability of transposable elements to act as mutagenic agents through their association with particular gene sequences has lead to the development of the procedure of transposon tagging or gene tagging in higher plants. Through this technique, transposable elements can be used to clone and isolate genes of interest for which little or nothing is known about the final product (i.e., polypeptide). This offers tremendous potential for the isolation of a variety of agronomically important genes, which are virtually impossible to recover by other currently available gene cloning methodologies. To date, the technique has been used successfully to isolate genes from corn and snapdragon. Using gene transfer technologies, the potential now exists to extend this approach to clone genes from other plant species. Advantages and limitations of transposon tagging for isolating plant genes will be discussed.
Governing equations for plant cell growth
Authors: Ortega Joseph K. E.
Published: May 2006

Governing equations are important in the evolution of a science from a qualitative or descriptive state to a quantitative state. This review discusses recent progress made toward the goal of establishing governing equations for plant cell growth. Recent extensions of the previously established growth equations are reviewed, and recent pressure probe methods which have been used to determine the magnitude and behavior of biomechanical and biophysical parameters are emphasized. Two recently developed pressure probe methods (in vivo creep and in vivo stress relaxation), which have been used to determine the wall extensibility and the yield threshold of plant cells, are discussed and compared. Also reviewed are pressure probe methods which have been used to measure the volumetric elastic modulus, and transpiration rate from a single plant cell.
Agrobacterium‐mediated gene delivery and the biology of hostrange limitations
Authors: Binns Andrew N.
Published: May 2006

Insertion of foreign DNA into Ti plasmid‐derived vectors in Agrobacterium tumefaciens is currently the most frequently used strategy for generating transgenic plants in a wide variety of species. Limitations of the host range of Agrobacterium restrict its usefulness in many cases, particularly when dealing with monocotyledonous plants. The objective of this presentation is to briefly discuss the efficiency of the transformation process utilized by Agrobacterium tumefaciens, potential barriers to efficient transformation by Agrobacterium that result in limitation of its useful host range, and how an understanding of the successful Agrobacterium/plant cell interaction might lead to advances in a variety of DNA delivery methodologies.
Agroinfection
Authors: Grimsley Nigel H.
Published: May 2006

Agroinfection, the delivery of viral or viroidal sequences to plants by Agrobacterium, can be used to approach important basic questions in plant molecular biology. The combined use of three biological entities allows the analysis of plant‐Agrobacterium interactions using the virus as a marker for T‐DNA transfer, or the investigation of viral biology using Agrobacterium as a delivery vehicle for the virus. Plants transgenic for viral constructs offer possibilities for studying recombination, plant protection, and development of high copy number plant vectors. Relevant examples of these approaches are discussed.
Cauliflower mosaic virus as a gene expression vector for plants
Authors: Fütterer J. , Bonneville J. M. , Hohn T.
Published: May 2006

It is possible to replace the CaMV (cauliflower mosaic virus) ORF (open reading frame) II with foreign sequences without interfering with virus viability. Such recom‐binants can induce the synthesis of substantial amounts of a foreign protein in infected plants and confer new properties to these plants. However, so far only three genes have been successfully cloned and expressed in this way. The expression mechanism of CaMV demands precise replacement of ORF II and probably certain structural features of the viral 35S RNA, which should not be disturbed by inserted sequences. Since these features are largely unknown, it cannot at present be pre‐dicted whether an insert will be tolerated. It is more likely that larger inserts will disturb the viral gene expression mechanism than smaller ones.
Electroporation of cells
Authors: Lindsey K. , Jones M. G. K.
Published: May 2006

By measuring uptake of the membrane impermeable dye. phenosafranine, it can be shown that the plasma membrane of intact cells within cell aggregates can be reversibly permeabilized by electroporation. However, the plant cell wall is a barrier to DNA uptake by intact cells, although under certain circumstances expression of DNA, electroporated into intact cells, can be demonstrated. The level of expression is about 20–50 times lower than that obtained by electroporation of protoplasts, and depends on cell wall properties and pretreatments of cell aggregates. In contrast, efficient transformation of whole cells of bacteria and yeasts can be achieved by electroporation. Factors which influence DNA transfer into whole plant cells and the possibility of stable transformation are discussed.
Liposome‐mediated transfer of nucleic acids in plant protoplasts
Authors: Caboche M.
Published: May 2006

Liposomes spontaneously interact with the plasma membrane of protoplasts. The delivery of their content to the protoplast, however, has to be induced by physical or chemical treatments. Three major approaches have been used to study and optimize the delivery of RNA or DNA molecules: viral infection, transient gene expression and stable transformation. Conclusive evidence for the delivery of nuclei acids to the treated protoplasts has been obtained. Stable transformants expressing kanamycin resistance have been further characterized by hybridization techniques and progeney analysis. The potential and limitations of this approach for the transformation of higher plants is discussed.
Introduction of foreign DNA into walled plant cells via liposomes injected into the vacuole: a preliminary study
Authors: Lucas W. J. , Lansing A. , de Wet J. R. , Walbot V.
Published: May 2006

Plasmids containing the firefly luciferase reporter gene were introduced into tobacco and maize by electroporation. They were used to calibrate the performance characteristics of an Hamamatsu C1966 AVEC/VIM photonic camera‐Leitz photomicroscope image processing system. Luciferin‐dependent light emission was readily detected, on an individual cell basis, using the analytical photon counting mode of the Hamamatsu system. An efficient liposome‐DNA encapsulation protocol was developed and used to introduce the firefly luciferase plasmid into walled cells of tobacco, maize, carrot and rice. This was achieved by pressure‐injecting the liposomes (DNA encapsulated inside the vesicle) into the vacuole where they subsequently fused with the tonoplast, releasing the DNA into the cytoplasm. Analytical photon counting studies were conducted on injected cells to determine whether the DNA introduced in this way was expressed. To date all experiments have proved negative. Reasons for this lack of expression are discussed.
Genetic changes induced in higher plant cells by a laser microbeam
Authors: Weber Gerd , Monajembashi Shamci , Wolfrum Jürgen , Greulich Karl‐Otto
Published: May 2006

Introducing foreign genes into higher plants has proved to be complicated, with the exception of transformation of protoplasts of some plants (Negrutiu et al. 1987). In particular, culture of protoplasts and regeneration to plants are difficult in many monocotyledonous crops. Therefore, it would be desirable to avoid extensive tissue culture by introducing cloned genes directly into cells. A laser microbeam can perforate plant cell walls, thus facilitating uptake of genes into cells.
Potential of in vitro pollen maturation for gene transfer
Authors: Alwen Anna , Eller Norbert , Kastler Monika , Moreno Rosa Maria Benito , Heberle‐Bors Erwin
Published: May 2006

Microspores and young pollen grains can be isolated from the anther and matured in vitro. Pollination with in vitro matured pollen leads to seed set. This technique has potential applications in plant breeding. During in vitro maturation, the pollen can be used as a target for gene transfer.
Hybrid genes in the analysis of transformation conditions: II. Transient expression vs stable transformation—analysis of parameters influencing gene expression levels and transformation efficiency
Authors: Negrutiu I. , Dewulf J. , Pietrzak M. , Botterman J. , Rietveld E. , Wurzer‐Figurelli E. M. , Ye De , Jacobs M.
Published: May 2006

Reports on direct gene transfer have dealt with either the obtention of stable transformants and transgenic plants, or described the use of reporter genes to analyse different aspects of gene expression in plant protoplasts and conditions for their use in transient gene expression assays.

In this paper we present comparisons between several transformation techniques, show species‐specific differences in efficiencies of stable transformants and in the levels of transient gene expression, and report on the identification of major parameters responsible for DNA uptake as judged from transient chloramphenicol acetyl transferase (CAT) expression levels and from efficiencies of transformation based on kanamycin‐resistance. The described procedures have been simplified, optimized and standardized and should allow routine use with a great variety of plant species.
New roads towards chloroplast transformation in higher plants
Authors: Haring M. A. , De Block M.
Published: May 2006

The attempts to manipulate organelle DNA of higher plants have not yet been succesfull. Although some Agrobacterium mediated and direct gene transfer experi‐ments suggested that chloroplasts of Nicotiana tabacum could be transformed, these experiments could not be reproduced. New transformation techniques have emerged: laser‐injection, microinjection and high velocity microprojectiles. The biolistic ex‐periments with Chlamydomonas made it clear that organelle DNA can support introduced DNA fragments by homologous recombination. In view of these devel‐opments, we describe the parameters and new possibilities for chloroplast trans‐formation of higher plants.
Conversion of D‐tryptophan to indole‐3‐acetic acid in coleoptiles of a normal and a semi‐dwarf barley (Hordeum vulgare) strain
Authors: Tsurusaki Ken‐ichi , Watanabe Sachiko , Sakurai Naoki , Kuraishi Susumu
Published: May 2006

Exogenously applied D‐tryptophan (D‐Trp) was more effective than L‐Trp in inducing elongation of coleoptile segments of a normal barley (Hordeum vulgare L. cv. Akashinriki) strain and a semi‐dwarf strain with lower endogenous indole‐3‐acetic acid (IAA) level. D‐cycloserine, an inhibitor of D‐aminotransferase, completely inhibited both the D‐ and L‐Trp‐induced elongation of both strains. Addition of D‐Trp increased IAA levels in both strains 4‐fold over endogenous levels. The increase in IAA level was completely inhibited by D‐cycloserine. The endogenous L‐Trp level of semi‐dwarf coleoptiles was similar to that of normal ones. These results suggested that IAA is synthesized by the conversion of L‐Trp to indole‐3‐pyruvic acid via D‐Trp in both strains, and that the lower IAA level of the semi‐dwarf strain probably is a result of the impeded IAA biosynthesis involved in D‐Trp.
Biotin‐streptavidin immunofluorescent detection of DNA replication in root meristems through BrdUrd incorporation: cytological and microfluorimetric applications
Authors: Levi Marisa , Sparvoli Elio , Sgorbati Sergio , Chiatante Donato
Published: May 2006

The method for the immunofluorescent detection of S‐cells in Pisum sativum L. after bromodeoxyuridine‐labeling, reported previously (Levi et al. 1987), has been modified with the use of the biotin‐streptavidin system and Texas Red as fluorescent tag. This improvement led to a marked increase in the potential of the method, permitting the determination of the labeling index also after short pulses (15 min), bivariate bromodeoxyuridine/DNA cytofluorimetry and a high resolution of the distribution of labeling over the nucleus.
The roles of calcium and manganese ions in the in vitro conversion of 1‐aminocyclopropane‐1‐carboxylic acid to ethylene by lentil root membranes
Authors: Penel Claude , Gaspar Thomas , Crèvecoeur Michèle , Kevers Claire , Greppin Hubert
Published: May 2006

Ca2+ and Mn2+ activate the conversion of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) by root microsomes of Vicia lens as they do in other similar systems. The preparation of microsomes in the presence of Mn2+ greatly increases their ability to convert ACC into ethylene, without addition of Mn2+ in the reaction mixture. Ca2+ does not have this property. The effect could not be attributed to Mn2+ entrapping into membrane vesicles (sonication followed by repelleting had no effect) but, possibly, in part to Mn2+‐mediated binding to microsomes of a soluble factor favouring the conversion of ACC to C2H4. Although no direct correlation could be established in vitro between ethylene‐forming‐enzyme (EFE) and peroxidase activities, some soluble peroxidases might be this soluble factor. Mn2+ favoured attachment to membranes of some peroxidase activity from the soluble fraction and from commercial HRP and lipoxygenase. This binding effect of Mn2+ cannot be readily distinguished from its role in the generation of a chain of free radicals and in redox mechanisms.
Control of barley root respiration
Authors: Williams John H. H. , Farrar John F.
Published: May 2006

Evidence from barley [Hordeum distichum (L.) Lam. cv. Maris Mink], and from many other species, suggests that respiration is controlled by either supply of carbohydrate or demand for ATP. The relationship between root respiration rate (measured as O2 consumption or CO2 production) and ethanol‐soluble carbohydrate content altered with time following selective pruning, and the change could not be accounted for by buffering of the cytoplasmic carbohydrate concentration by sugars in the vacuole. Exogenous sucrose supplied to the roots prevented any decline of the respiration rate in shoot‐pruned plants, and if supplied for 24 h stimulated the respiration rate after any treatment. Root extension responded to sucrose in a similar manner. We suggest that respiration is under fine control by adenylates, but the capacity of the respiratory system is fixed by the supply of sucrose, possibly via coarse control of the respiratory machinery, or of the processes requiring metabolic energy.
Changes in the starch content during organogenesis in in vitro cultured Begonia rex stem explants
Authors: Mangat B. S. , Pelekis M. K. , Cassells A. C.
Published: May 2006

Stem explants, excised from greenhouse‐grown Begonia rex plants, were cultured on basal medium (T. Murashige and F. Skoog, Physiol. Plant. 15: 473–497, 1962) contained in sterile Petri dishes. The medium was supplemented with benzyladenine (0.1 mg 1−1) naphthaleneacetic acid (0.01 mg 1−1) and, according to experimental requirements, with either sucrose (3%) or mannitol (3%). Histochemical and biochemical examination of the starch content of the explant was carried out over several days. There was no starch deposition or organogenesis in tissue cultured on mannitol and carbohydrate‐free growth medium. The most dramatic finding was the heavy accumulation of starch in tissue cultured on sucrose medium. This copious accumulation preceded any organ formation and was mainly in regions which ultimately gave rise to shoot primordia. The heavy build‐up of starch preceding organogenesis was also observed when explants previously cultured on mannitol medium were transferred to medium containing sucrose. During shoot primordia development there was a decrease in the starch content of the cultured tissue indicating the utilization of the polyglucan in the organogenic process.
Apparent phytotoxicity of mononuclear hydroxy‐aluminum to four dicotyledonous species
Authors: Kinraide Thomas B. , Parker David R.
Published: May 2006

It has long been assumed that Al3+ is an important rhizotoxic ion in acid soils around the world, but the toxicity of Al3+ relative to mononuclear hydroxy‐Al [AlOH2+ and Al(OH)+2] has been examined in detail only for an Al‐sensitive wheat variety (Triticum aestivum L. cv. Tyler). That plant appears to be sensitive to Al3+ but not to AlOH2+ and Al(OH)+2. New experiments, and reanalyses of previously published experiments, provide evidence that dicotyledonous species may be sensitive to mononuclear hydroxy‐Al and that Al3+ may be nontoxic, or less toxic, to those plants. Despite these consistently measured differences between wheat and the dicotyledons, the determination of relative toxicities (Al3+ vs mononuclear hydroxy‐Al) may be an intractable problem. Because of hydrolysis equilibria, (AlOH2+) and (Al(OH)+2) are equivalent to (Al3+)k1(H+)−1 and (l3+)k2(H+)−2, respectively, in which k1 and k2 are the first and second hydrolysis constants (braces denote activities). Thus, any expression of root elongation as a function of mononuclear hydroxy‐Al can be alternatively expressed as a function of (Al3+) and (H+). Toxicity attributed to mononuclear hydroxy‐Al may actually be Al3+ toxicity that increases as pH rises (i.e. Al3+ toxicity ameliorated by H+).
Polysome formation and incorporation of new ribosomes into polysomes during germination of the embryonic axis of maize
Authors: Dommes Jacques , Van de Walle Claude
Published: May 2006

Isolated axes of Zea mays L. cvs CiV2 and CUZCO were imbibed for different periods of time, and free polysomes were extracted and analysed by centrifugation in a sucrose gradient. The amount of rRNA per axis was determined at different moments of germination. Polysome reassembly was practically completed by 8 h and 54% of the preformed ribosomes were found in the polysome fraction. An increase in the proportion of large polysomes was also observed during this period of germination. During the following period, the polysome content and the distribution of the various classes of polysomes remained unchanged.

The time of appearance of newly synthesized ribosomes into the polysomes was investigated using axes germinated in the presence of [3H]‐uridine. Centrifugal analysis of EDTA‐dissociated polysomes and gel electrophoretic analysis of polysomal RNA showed that new ribosomes appeared into polysomes a few hours after completion of the initial polysome assembly. When released into the cytoplasm, the new ribosomes were preferentially incorporated into polysomes rather than stored as free ribosomes.
Calcium ion transport in higher plant mitochondria (Helianthus tuberosus)
Authors: Rugolo Michela , Pistocchi Rossella , Zannoni Davide
Published: May 2006

A study on Ca2+ transport by mitochondria isolated from Jerusalem artichoke (Helianthus tuberosus L. cv. OB1) tubers is presented. By following the distribution of Ca2+ under respiratory conditions, we have been able to show that Ca2+ accumulation into the matrix space depends on membrane potential (ΔΨ) since the uptake is not affected by the protonophore nigericin but fully blocked by valinomycin and carbonyl cyanide‐p‐trifluoromethoxy phenylhydrazone (FCCP). Ca2+ uptake requires phosphate (Pi) and is inhibited by mersalyl and by ruthenium red (RR). In addition to a Ca2+ influx route, mitochondria from H. tuberosus possess an RR‐insensitive Ca2+ efflux pathway which is not stimulated by external Na+, Ca2+ is rapidly released from Ca2+‐loaded mitochondria in the presence of ionophores such as A23187 and valinomycin and of the uncoupler FCCP. The Pi‐transport inhibitor mersalyl also induces a massive Ca2+ release through reversal of the uptake route, the latter process being blocked by RR. Thus Jerusalem artichoke mitochondria possess a Ca2+ cycling mechanism which is different from that of animal mitochondria and certain other plant species.
Conversion of indole‐3‐acetaldoxime to indole‐3‐acetonitrile by plasma membranes from Chinese cabbage
Authors: Ludwig‐Müller Jutta , Hilgenberg Willy
Published: May 2006

The in vitro conversion of [14C]‐indole‐3‐acetaldoxime (IAOX) to [14C]‐indole‐3‐acetonitrile (IAN) by plasma membranes enriched by aqueous two‐phase partitioning of Chinese cabbage (Brassica campestris L. ssp. pekinensis cv. Granat) has been studied. The reaction product was identified by thin‐layer chromatography (TLC) and high performance liquid chromatography (HPLC). A reducing agent, e.g. ascorbic acid, was needed as cofactor for the formation of IAN from IAOX. Reduction equivalents and metal ions were not involved in the conversion of IAOX to IAN. The pH optimum for the reaction was at 6.0 and the apparent Km for IAOX was 6.3 μM. The enzyme was not inhibited by thiol reagents. The pI of the enzyme was determined to be 7.1 by isoelectric focusing (IEF). Gel permeation chromatography showed one major activity peak of 40 kDa. The reaction is considered as part of a channeling process leading from tryptophan to IAN with IAOX as an intermediate. This process is probably regulated by the indole derivatives IAOX and IAN.
Detection of mRNAs correlated with proliferation of cells in suspension cultures of Catharanthus roseus
Authors: Kodama Hiroaki , Ando Satoshi , Komamine Atsushi
Published: May 2006

Gene expression correlated with proliferation was investigated in Catharanthus roseus (L.) G. Don. cells. Polyadenylated RNAs were isolated from cells in proliferative states or in nonproliferative states and the variations in the population and levels of mRNA were analyzed by in vitro translation followed by separation of the corresponding polypeptides by two‐dimensional gel electrophoresis. Levels of two mRNAs increased in the actively cycling cells, while they were hardly detected in cells in stationary phase or in cells arrested by starvation of phosphate, sucrose or nitrogen. The molecular masses of the translated products of these two mRNAs were 53 and 60 kDa. No mRNAs were specifically synthesized in common among the various cultures of cells whose growth was arrested by nutrient starvation.
Indole‐3‐acetic acid oxidase and syringaldazine oxidase activities of peroxidase isozymes in soybean root nodules
Authors: De Forchetti Silvia Milrad , Tigier Horacio A.
Published: May 2006

Many isoperoxidases with indole‐3‐acetic acid oxidase (IAA) and syringaldazine oxidase activities were detected by polyacrylamide gel electrophoresis in soybean root nodules [Glycine max (L.) Merrill, cv. Asgrow], detached at the onset of flowering. The kinetics of the two activities were studied with some of the isoperoxidases partially purified by ion exchange chromatography. IAA oxidase activity of the cationic isoforms showed a sigmoidal kinetic behaviour and a higher substrate affinity than the anionic ones, whereas typical saturation kinetics were found with an anionic fraction that contained leghemoglobins. So, nodule IAA oxidase activity may mainly be displayed by the cationic isoforms. These cationic isoperoxidases had high affinity towards syringaldazine and they also may be associated with cell wall rigidification.
Leaf development in Lolium temulentum: Gradients of RNA complement and plastid and non‐plastid transcripts
Authors: Ougham Helen J. , Davies T. G. E.
Published: May 2006

Gradients of gene expression in the developing fourth leaf of the grass Lolium temulentum L. strain Ba 3081 were investigated using cell‐free translation and Northern analysis of RNA extracted from succesive leaf segments. The transition from growth at the leaf base to photosynthesis in the blade was reflected in relative levels of transcripts from the plastid genome (psb A, pet A and rbc L, encoding plastid polypeptides) and nuclear genome (cab and PCR, encoding plastid polypeptides, and histone H3 and PAL encoding extra‐plastidic polypeptides). These data combined with information on polypeptide synthesis in vivo indicate that post‐transcriptional regulation plays an important part in controlling gene expression in this tissue.
Plasma membrane‐bound NADH: Fe3+‐EDTA reductase and iron deficiency in tomato (Lycopersicon esculentum). Is there a Turbo reductase?
Authors: Brüggemann Wolfgang , Moog Petra R. , Nakagawa Hikoki , Janiesch Peter , Kuiper Pieter J. C.
Published: May 2006

The properties of NADH‐dependent Fe3+‐EDTA reductase in plasma membranes (PM) from roots of iron‐deficient and ‐sufficient tomato plants [Lycopersicon esculentum L. (Mill.) cv. Abunda] were examined. Iron deficiency resulted in a 3‐fold increase of in vivo root iron‐chelate reductase activity with a Km (Fe3+‐EDTA) of 230 μM. In purified root PM, average specific activities of ferric chelate reductase of 410 and 254 nmol Fe (mg protein)−1 min−1 were obtained for iron‐deficient and ‐sufficient plants, respectively. In both cases, the PM‐bound activity showed a pH optimum at pH 6.8. Activity depended on NADH and not on NADPH and on the presence of detergent. The activity was inhibited 40‐50% by superoxide dismutase (EC 1.15.1.1) and ca 30% by oxygen. Kinetic analysis of the membrane‐bound enzyme revealed a Km (Fe3+‐EDTA) of ca 200 μM for both iron‐stressed and ‐sufficient plants. For NADH, Km values around 230 μM were obtained. The ferric chelate reductase could be solubilised from salt‐washed PM with Triton X‐100 at a protein:detergent ratio of 1:2.8 (w/w). The Triton‐soluble fraction revealed one enzyme‐stained band in native polyacrylamide electrophoresis. Although the membranes showed no nitrate reductase (NR; EC 1.6.6.1) activity, anti‐spinach NR immunoglobulin G (IgG) recognized a 54 kDa band both in the PM and the Triton‐soluble fraction, but not in the enzymatically active material obtained from the native gel. No evidence could be found for the synthesis of a new, biochemically distinct PM‐bound ferric chelate reductase under iron deficiency, which might be identified as the so‐called Turbo reductase. It is concluded that iron deficiency in tomato induces increased expression of a ferric chelate reductase in root PM, which is already present in iron‐sufficient plants and probably also in plants, which do not contain the Turbo reductase, like the grasses. The iron reductase is not identical with the recently reported PM‐associated nitrate reductase.
Cell wall synthesis in carrot cells: Comparison of suspension‐cultured cells and regenerating protoplasts
Authors: Mock Hans‐Peter , Emmerling Michael , Seitz Hanns Ulrich
Published: May 2006

The synthesis of cell walls and extracellular material during the regeneration of carrot (Daucus carota L. ssp. sativus) protoplasts was examined. Cell walls and extracellular material were analysed for their carbohydrate content. In cell walls, the amount of carbohydrate increased 4‐ to 5‐fold with only minor changes in neutral sugar composition. Glucose was abundant, during cultivation, making up to 70% (w/w) followed by mannose, which accounted for 17%. This indicates the formation of a glucomannan. The neutral sugar composition of extracellular polysaccharides showed greater variety with a signifiant increase of arabinose and galactose during cultivation. This feature is probably connected to the occurrence of arabinogalactan proteins in the culture medium. Hydroxyproline, an indicator for extensin and arabinogalactan proteins, showed an increase parallel to the formation of cell walls and extracellular polysaccharides. Results are compared with corresponding data from suspension‐cultured cells used for protoplast isolation.
Diffusible IAA and dominance phenomena in fruits of apple and tomato
Authors: Gruber J. , Bangerth F.
Published: May 2006

The relationships between indole‐3‐acetic acid (IAA) diffusing out of the fruit and competition among fruits, and between fruits and shoot tips were investigated using apple (Malus domestica Borkh. cv. Jonagold) and tomato (Lycopersicon esculentum Mill.) plants. Dominant fruits always had more diffusible IAA than subordinated, inhibited fruits. Alterations in dominance – by fruit‐ or shoot tip removal – led to significant changes in diffusible IAA by the remaining fruits. This change could be detected one day after dominance modification.

It is suggested that diffusible IAA is involved in the correlative signal regulating dominance relationship between fruits, and between fruits and shoots in apple and tomato.
Induction of ammonium assimilation: leguminous roots compared with nodules using a split root system
Authors: Reynolds Paul H. S. , Boland Michael J. , McNaughton Graeme S. , More Raymond D. , Jones William T.
Published: May 2006

A split root system for nitrogen uptake, in which one part of the root system was exposed to nitrogen‐free nutrient and the other to circulated buffered ammonium, was used to investigate the effects of ammonium per se on the enzyme pathway for its assimilation in nodules and roots of leguminous plants. Plants of Trifolium repens L. cv. Grasslands Huia grown in the system showed similar growth and similar free amino acid content in the NH+4‐fed roots and in nodulated plants. Studies of ammonium assimilation using [13N]‐NH+4, applied to Glycine max [L.] Merr. cv. Amsoy plants, showed the label to be assimilated into amino acids in the NH+4‐fed roots and to be transported to the tops before subsequently appearing in the minus‐N side of the split root system. Analysis of the xylem sap showed [13N]‐asparagine to be the principal labelled amino acid component. In these plants, levels of both allantoate and the nodule‐specific isoenzyme aspartate aminotransferase‐P2 were at least 10 times higher in the NH+4‐fed roots than in the minus‐N side of the split root system. These studies strongly suggest that a nodule‐type of ammonium assimilation was occurring in the NH+4‐fed side of the split root, and that this part of the root was transporting assimilatory products to the tops of the plants in a fashion analogous to that of a nitrogen‐fixing nodule. These data implicate the involvement of NH+4 in the induction of its own assimilatory pathway.
Synergistic effect of 1‐aminocyclopropane‐1‐carboxylic acid and ethylene during senescence of isolated carnation petals
Authors: Overbeek J. H. M. , Woltering E. J.
Published: May 2006

The effects of ethylene (C2H4), (2‐chloroethyl)phosphonic acid (ethefon) and 1‐aminocyclopropane‐1‐carboxylic acid (ACC) on senescence of isolated intact petals and of upper petal parts of carnation flowers (Dianthus caryophyllus L. cv. White Sim) were investigated.

Isolated upper petal parts did not respond to treatment with ethefon or ACC. These tissues did, however, show severe wilting in intact petals that were treated with ethefon or ACC. When isolated upper petal parts were simultaneously treated with ACC and ethefon or ACC and ethylene, a marked synergistic effect on senescence was found. Treatment of isolated petals with radiolabeled ACC led to the accumulation of radiolabeled ACC and N‐malonyl‐ACC (MACC) in the upper parts. The formation of ethylene and the malonylation of ACC were inhibited by pretreatment of the flower with the inhibitor of ethylene action, silver thiosulphate (STS), which indicates that both were induced by endogenously produced ethylene. Treatment of isolated upper parts with ACC slightly increased their ethylene production. However, when these petal parts were simultaneously treated with ethylene and ACC, the conversion of ACC to ethylene was markedly stimulated.

The results indicate that, in intact petals, ethylene may be translocated from the basal to the upper part where it stimulates the activity of the ethylene‐forming enzyme (EFE), thereby making the tissue receptive to ACC.

In addition, it was found that upon incubation of petal portions in radiolabeled ACC, both the petal tissue and the incubation solutions produced radiolabeled carbon dioxide. This was shown to be due to microorganisms that were able to metabolize the carbon atoms in the 2 and 3 position of ACC into carbon dioxide.
Effects of artificially enhanced levels of ascorbate and glutathione on the enzymes monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase in spinach (Spinacia oleracea)
Authors: Hausladen Alfred , Kunert Karl Josef
Published: May 2006

Effect of high intracellular concentrations of the antioxidants ascorbate and glutathione on the extractable activity of the reducting enzymes dehydroascorbate reductase, monodehydroascorbate reductase, and glutathione reductase were investigated with spinach cells (Spinacia oleracea). An elevated ascorbate concentration was obtained by treatment with the ascorbate biosynthesis precursor L‐galactono‐1,4‐lactone (GAL). To increase the intracellular level of glutathione, cells were treated with the 5‐oxo‐L‐proline analog L‐2‐oxothiazolidin‐4‐carboxylate (OTC), or with the peroxidative herbicide acifluorfen (sodium 5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2‐nitrobenzoic acid). Extractable monodehydroascorbate reductase activity increased in the presence of a high level of ascorbate or glutathione, and enzyme activity was at maximum when cells were treated with acifluorfen + OTC, or acifluorfen + GAL. Extractable dehydroascorbate reductase activity decreased when the intracellular concentration of glutathione was high and non‐enzymatic reduction of dehydroascorbate by glutathione was the dominant reaction. Maximal decrease of enzyme activity was found in cells treated with acifluorfen + OTC. Extractable activity of glutathione reductase (GR) increased after treatment of cells with acifluorfen alone, or acifluorfen + OTC, but enzyme activity was unaffected by a high intracellular concentration of glutathione obtained by treatment of cells with OTC alone, or by treatment with acifluorfen + GAL. The degree of GR activation seemed to be controlled by several factors including inhibition by a high concentration of glutathione and possibly oxidative damage to the enzyme. Overall, the enzymes tested in this study, which provide the reduced forms of ascorbate and glutathione, were differently affected by high antioxidant levels.
Study on nutrient stress tolerance of nine Taraxacum microspecies with a contrasting mineral ecology by cultivation in a low nutrient flowing solution
Authors: Hommels C. H. , Kuiper P. J. C. , Telkamp G. P.
Published: May 2006

Growth and mineral status of 9 Taraxacum microspecies were studied under mineral stress conditions, using a flowing solution of low nutrient concentration. Relative growth rate of (whole) plant dry weight, leaf area, and (whole) plant tissue water were used to describe growth. For 4 microspecies, specific uptake rates of NO−3, H2PO−4, K+, Mg2+ and Ca2+ were investigated.

The applied nutrient condition clearly discriminated between the studied Taraxacum microspecies. With respect to relative growth rate, 3 groups of microspecies could be distinguished: T. nordstedtii > T. lancidens, T. adamii, T. hollandicum, T. taeniatum > T. sellandii, T. eudontum, T. ekmanii, T. ancistrolobum. These categories coincided well with the mineral ecology of the microspecies, going from infertile to fertile sites.

T. nordstedtii, a microspecies of infertile sites, was most efficient in absorbing NO−3, H2PO−4 and K+. T. sellandii and T. eudontum, both occurring in fertile grasslands, showed poor uptake performances for all studied ions. In all Taraxacum microspecies studied, except T. eudontum, internal N concentration appeared to limit growth. Efficiencies in N use, at sub‐optimal internal N concentrations, varied with the mineral habitat of the microspecies studied. T. nordstedtii, from infertile sites, and T. sellandii, from fertile sites, were established as high and low extremes, respectively.
Hormonal changes associated with fruit set and development in mandarins differing in their parthenocarpic ability
Authors: Talon Manuel , Zacarias Lorenzo , Primo‐Millo Eduardo
Published: May 2006

Satsuma [Citrus unshiu (Mak) Marc.] and Clementine [Citrus reticulata (Hort.) Ex. Tanaka, cv. Oroval] are two related species of seedless mandarins which differ in their tendency to set parthenocarpic fruits. Satsuma fruits naturally set parthenocarpically whereas Clementine mandarins show very low ability to set fruit in the absence of cross‐pollination. The endogenous levels of gibberellins (GAs) and free and conjugated indole‐acetic acid (IAA) and abscisic acid (ABA) throughout early stages of fruit development were investigated in seedless cultivars of both species. Analyses performed by full‐scan combined gas chromatography‐mass spectrometry (GC‐MS) of extracts from ovaries at anthesis demonstrated the presence of GA19, GA20, GA29, GA1, GA8, GA3 and iso‐GA3 in Satsuma mandarin, whereas only GA29, GA3 and trace levels of GA8 were detected in Clementine. At this developmental stage GA‐like substances, as estimated by bioassay, reached their highest levels in Satsuma, while Clementine mandarins contained relatively lower levels. In both species the highest levels of free IAA were found at petal‐fall stage at which time free ABA levels also peaked. Developing fruits of Clementine had higher amounts of both free IAA and ABA. In Satsuma, levels of conjugated IAA remained low throughout reproductive development whereas in Clementine they increased as the free form declined. In contrast, conjugated ABA was at low levels in Clementine but reached higher concentrations in Satsuma. These results suggest that in these mandarins the potential for setting parthenocarpic fruits is mainly influenced by the hormonal status of the fruit during the later stages of cell division and early stages of cell enlargement. Thus, the condition of low ability to set parthenocarpic fruits appears to be associated with lower levels of active GAs, lower capability to catabolize ABA to conjugated ABA and higher ability to conjugate IAA during this period.
Diferulic and ferulic acid in the cell wall of Avena coleoptiles—Their relationships to mechanical properties of the cell wall
Authors: Kamisaka Seiichiro , Takeda Satomi , Takahashi Keiko , Shibata Kozo
Published: May 2006

Alkaline hydrolysis liberated ferulic and diferulic acid from polysaccharides of the Avena coleoptile (Avena sativa L. cv. Victory I) cell walls. The amount of the two phenolic acids bound to cell walls increased substantially at day 4–5 after sowing, when the growth rate of the coleoptile started to decrease. The level of these acids was almost constant from the tip to base in 3‐day‐old coleoptiles, but increased toward the basal zone in 4‐ and 5‐day‐old ones. The ratio of diferulic acid to ferulic acid was almost constant irrespective of coleoptile age and zone. An increase in the amount of ferulic and diferulic acids bound to cell wall polysaccharides correlated with a decrease in extensibility and with an increase in minimum stress‐relaxation time and relaxation rate of the cell wall. The level of lignin in the cellulose fraction increased as coleoptiles aged, but this increase did not correlate with changes in mechanical properties of the cell walls. These results suggest that ferulic acid, ester‐linked to cell wall polysaccharides, is oxidized to give diferulic acid, which makes the cell wall mechanically rigid by cross‐linking matrix polysaccharides and results in limited cell extension growth. In addition, it is probable that the step of feruloylation of cell wall polysaccharides is rate‐limiting in the formation of in‐termolecular bridges by diferulic acid in Avena coleoptile cell walls.
Inhibition of electron transport activities in mitochondria from avocado and pepper fruit by naturally occurring polyamines
Authors: Phelps Donna C. , McDonald Roy E.
Published: May 2006

The effects of the naturally occurring polyamines, spermine, putrescine, and spermidine were explored on mitochondrial state 3. state 4, and uncoupled respiration activities, ADP/O ratio, respiratory control ratio of pepper (Capsicum annuum L. cv. Early Cal Wonder) and avocado (Persea americana Mill. cv. Booth‐8 or Simmonds) mitochondria oxidizing either succinate, external NADH, malate, α‐ketoglutarate or tetramethyl‐p‐phenylenediamine. Abnormally high concentrations of spermine and spermidine such as might occur during chilling stress of these chilling‐sensitive fruits were detrimental to several oxidase activities, especially to external NADH oxidase. State 3 respiration for NADH oxidase was inhibited more than 70% by 10 mM spermine. The spermine inhibition of uncoupled NADH oxidase was not reversed by the presence of divalent cations including Ca2+, Mg2+, Mn2+, and Sr2+ at concentrations up to 10 mM or by 100 mM KCl. The inhibition primarily affected the Vmax. Other possible sites of polyamine interactions are discussed.
How can the electrical polarity of axial organs regulate plant growth and IAA transport?
Authors: Medvedev Sergei S. , Markova Irene V.
Published: May 2006

Alteration of the electrical polarity in sections of maize (Zeamays L. cv. Odesskaya‐80) coleoptiles and pea (Pisum sativum L. cv. Cubanecz) internodes by passing a weak electric current longitudinally (6 μA, anode placed at the apical end of the section) increased their elongation rate 2–3 fold with a lag period of 2.5 min. Inhibitors of polar auxin transport, e.g. N‐1‐naphthylphtalamic and 2,3,5‐triiodobenzoic acids and also ethylene glycol‐bis(β‐aminoethylether)‐N,N,N'N'‐tetraacetic acid (EGTA), a chelator of divalent cations, decreased the growth rate of the sections and inhibited the growth‐stimulating effect of the electric current. The observed acceleration of growth of axial plant organs under the action of a weak electric current is suggested to be connected with changes in the mode of action of the basipetal auxin transport system.
Influence of air and soil temperature on water relations and freezing tolerance of spinach (Spinacia oleracea)
Authors: Fennell Anne , Li Paul H. , Markhart Albert H.
Published: May 2006

Root and shoot temperatures were varied independently to determine the importance of root temperature during cold acclimation. Spinach (Spinacia oleracea L. cvs Harbin and Bloomsdale) plants were subjected to 20/20°C. 20/5°C, 5/20°C, and 5/5°C (shoot/root) temperature treatments. Leaf freezing tolerance, water potential, stomatal resistance, osmotic potential, and water content were measured at 0.25. 1.25, 3.25, and 7.25 days of treatment. There was no change in freezing tolerance or the water relations of the 20/20°C treated plants during the course of the experiment. Freezing tolerance was increased by the 5°C shoot temperature treatments, but was not enhanced by water stress induced by the low root temperature. Leaf water potential and water content decreased and stomatal resistance increased within 6 h in the 20/5°C plants. By day 3, osmotic potential began decreasing in the 20/5°C plants. Leaf water content, osmotic potential, and water potential decreased more gradually in plants grown with 5°C shoot temperature, irrespective of root temperature. Decreased water content and osmotic potential were not correlated with increased freezing tolerance as reported for other herbaceous crop plants.