bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of nitrogen application on growth and photosynthetic nitrogen use efficiency in two ecotypes of wild strawberry, Fragaria chiloensis
Authors: Moon J. W. , Bailey D. A. , Fallahi E. , Jensen R. G. , Zhu G.
Published: May 2006

The relationships between increasing nitrogen fertilization and growth, maximum CO2 assimilation and the initial slope of the CO2 response curve were studied in 2 ecotypes of wild strawberry, Fragaria chiloensis (L.) Duchn. Nitrogen accumulation of CA11, an ecotype from a low‐nutrient dune site, was greater at all nitrogen concentrations than that of RCP37, an ecotype from a higher‐nutrient strand site. Maximum CO2 assimilation, total Rubisco activity, dry weight, and initiation of leaves and crowns were higher in CAI1 than RCP37 as nitrogen treatment was increased from 0 to 200 mg l‐1, whereas these parameters were lower in CAl1 when fertilized at 300 mg T1, but not in RCP37. The mean leaf area of CA11 was greater than RCP37 when grown with no supplemental nitrogen, but mean leaf area of the 2 lines was similar under nitrogen fertilization. Maximum CO2 assimilation and carboxylation efficiency increased with increasing leaf nitrogen in both clones. At equivalent concentrations of leaf nitrogen, RCP37 had higher CO2 assimilation and carboxylation efficiency than CA11 and the difference between the 2 clones increased as ieaf nitrogen increased. Thus, RCP37 had a higher photosynthetic nitrogen use efficiency than CA11. However, at a given applied nitrogen level, CA11 allocated more nitrogen to a unit of leaf area so that photosynthetic rates were higher than RCP37, except at the highest application of 300 mg l‐1. The high nitrogen accumulation capacity and resource allocation to fruiting structures (crowns) in CA11 leads us to suggest that this clone may possess genes that could increase fruit yield in cultivated strawberry.
Influence of leaf age and light environment on the gas exchange of lupins and wheat
Authors: Henson Ian E. , Jensen Christian R. , Turner Neil C.
Published: May 2006

Rates of net photosynthesis (A), transpiration (E) and leaf conductance to water vapour transfer (gH2O) were measured on leaves ofLupinus angustifoliusL. cv. Ritson's andL. cosentiniiGuss. cv. Eregulla throughout development and on flag leaves of wheat (Triticum aestivumL. cvs Gutha, Gamenya and Warigal) after full expansion. Plants were grown in large containers of soil, in a naturally‐lit, temperature controlled glasshouse. Throughout most of their life, lupin leaves had higher photosynthetic rates and leaf conductances than found for wheat. During leaf ageing in lupins, photosynthesis and conductance changed proportionately such that leaf intercellular CO2concentration was maintained relatively constant at about 200 ppm. Under continuously cloudy conditions, leaf conductance at midday of lupins and wheat was higher than at similar photon flux densities at other times of day on cloudless days. On cloudy days the relationship between gH2O and photon flux density in lupins was very different from that derived from diurnal measurements on clear days. The potentially low water use efficiency under cloud, evident as decreases in the A/gH2O ratio, was rarely realised in practise due to a reduction in leaf‐to‐air water vapour concentration difference on cloudy days. The possible reasons for the high conductance on cloudy days are discussed.
Salinity effects on CO2 assimilation and diffusive conductance of cowpea leaves
Authors: Plaut Z. , Grieve C. M. , Maas E. V.
Published: May 2006

The effect of NaCl salinity at concentrations of 43–173 mM in nutrient solution on net gas exchange of attached cowpea [Vigna unguiculata (L.) Walp cv. California Black‐eye No. 5 (CB5)] leaves was investigated under both greenhouse and growth chamber conditions.

There was a marked decrease in leaf conductance to water vapor after exposure to low salinity levels and a slighter decrease when salinity levels were higher. The decrease in net assimilation was much more gradual throughout the entire salinity range. The altered responses of net assimilation and leaf conductance to salinity were more evident at a high light intensity. A decrease in intercellular partial CO2 pressure [p(CO2)] was found at the low and intermediate salinity levels but not at the high level. These findings suggest that CO, assimilation was mainly controlled by stomatal conductance and the fixation of CO, might have been increased due to stimulated biochemical activity or to higher chlorophyll concentration per unit leaf area. A decrease in assimilation was already found one day after salinization and pro‐ceeded up to 4 days when it was inhibited by 50% at 43 mM NaCl and up to 85% at 173 mM. The decrease in transpiration was larger than the decrease in net assimila‐tion, and both were attributed to osmotic stress. Partial recovery was found thereaf‐ter and new steady‐state rates, in the range of 55 to 100% of the control, were then obtained for salinity levels between 43 and 130 mM. Inhibition of net CO, assimila‐tion at this stage was attributed partly to a specific sodium effect and partly to plant water status. A linear relationship between leaf sodium content and net photosynthe‐sis was also evident at this stage. Net CO, assimilation recovered more completely than transpiration when salt stress was removed, but at 173 mM NaCl recovery was neglible.
Genetic transformation using Agrobacterium rhizogenes
Authors: Tepfer D.
Published: May 2006

Agrobacterium rhizogenes transfers genes encoding phenotypic alterations that serve as morphological markers for the presence of foreign DNA. These alterations facilitate root culture and thus studies of roots and their interactions with their biological and physical environments. They also provide insights into how plants develop.
Expression of engineered wheat dwarf virus in seed‐derived embryos
Authors: Töpfer R. , Gronenborn B. , Schaefer S. , Schell J. , Steinbiß H.‐H.
Published: May 2006

Delivery of DNA into dry and viable embryos of wheat by imbibition in DNA solution was detected by monitoring the transient expression of chimeric genes. The gene expression vectors used comprise of a neomycin phosphotransferase II (NPT II) reporter gene, under the control of various promoters or as part of a cloned plant virus genome. The genome of wheat dwarf virus (WDV), a monopartite Gemini virus of gramineae, has been used to amplify the NPT II gene in embryos of wheat, thereby leading to high levels of transient expression. Constructions were designed which permitted NPT II expression only if inter‐ or intramolecular recombination had occurred.
Gene amplification and expression by RNA viruses and potential for further application to plant gene transfer
Authors: Ahlquist Paul , Pacha Radiya F.
Published: May 2006

The great majority of plant viruses encapsidate messenger‐sense ssRNA and have no natural DNA phase in their life cycle. Despite their RNA nature, essentially any desired change can be introduced into such genomes by using recombinant DNA techniques with suitably constructed, expressible viral cDNA clones. For some viruses such as brome mosaic virus, these methods have been used to define the sequences controlling RNA‐directed genomic RNA replication and the expression of internal genes via subgenomic mRNAs. The results suggest a surprising degree of genetic flexibility, which appears to be reflected in the varied gene complements and genetic organizations of presumably related plant and animal RNA viruses sharing conserved replication genes. Foreign genes inserted in such RNA virus genomes can be amplified and expressed to a high level in transfected plant cells. In addition to the potential use of such viruses as episomal expression vectors, it should be possible to couple the viral pathways of RNA‐dependent RNA synthesis to amplify and to further regulate the expression of genes transformed into plant chromosomes.
Biolistic plant transformation
Authors: Sanford John C.
Published: May 2006

The biolistic process represents a completely new approach to the problem of how to deliver DNA into intact cells and tissues. High velocity microprojectiles are used to carry DNA or other substances past cell walls and membranes. Because DNA is being ‘shot’ into cells, it represents a type of biological ballistics, hence the term “biolistics”.

There are several fundamental advantages to the biolistic process over other plant transformation techniques. The biolistic process appears to be effective regardless of species or tissue type, it is a rapid and very simple procedure, and it should facilitate the direct transformation of totipotent tissues such as pollen, embryos, meristems and morphogenic cell cultures. In addition, the biolistic process appears to be uniquely suitable for organelle transformation.

The disadvantages of the biolistic process are that it requires special instrumentation, and is still in the early stages of its development. Consequently, delivery efficiencies are still not as high as can be achieved in highly optimized transformation systems such as electroporation or agrobacterial‐infection of tobacco. Furthermore, potential users should be prepared to spend some time adapting existing protocols to their specific species or tissue of interest.
Soybean transformation by electric discharge particle acceleration
Authors: Christou Paul
Published: May 2006

By the use of a direct DNA‐delivery system based on electric discharge particle acceleration we have been able to obtain transgenic soybean plants expressing the neomycin phosphotransferase II and the β‐glucuronidase genes. Techniques for efficient introduction of foreign genes into agronomically important crop plants have been limited by the inability to regenerate fertile plants from single cells or by the limited hostrange of Agrobacterium vectors. In the case of soybean (Glycine max) the problem has been compounded due to the lack of a regeneration method compatible with existing transformation technology. In a commercial genetic engineering program the following points need to be considered: (a) not all crops/cultivars can be regenerated from transformed tissues, (b) long time frames are required for the regeneration of transgenic plants from callus, (c) Agrobacterium has a rather limited host specificity and (d) problems associated with somaclonal variation.
Plant transformation by microinjection techniques
Authors: Neuhaus Gunther , Spangenberg German
Published: May 2006

Several techniques have been developed for introducing cloned genes into plant cells. Vectorless delivery systems such as PEG‐mediated direct DNA uptake (e.g. Pasz‐kowski et al. 1984), electroporation (e.g. Shillito et al. 1985), and fusion of protoplasts with liposomes (Deshayes et al. 1985) are routinely used in many experiments (see several chapters of this issue). A wide range of plant species, dicotyledonous as well as monocotyledonous, has been transformed by these vectorless DNA transfer systems. However, the availability of an efficient protoplast regeneration system is a prerequisite for the application of these techniques.

For cells with intact cell walls and tissue explants the biological delivery system of virulent Agrobacterium species has been routinely used (for review see Fraley et al. 1986). However, the host range of Agrobacterium restricts the plant species, which can be transformed using this vector system. In addition, all these methods depend on selection systems for recovery of transformants. Therefore a selection system has to be established first for plant species to be transformed.

The microinjection technique is a direct physical approach, and therefore host‐range independent, for introducing substances under microscopical control into defined cells without damaging them. These two facts differentiate this technique from other physical approaches, such as biolistic transformation and macroinjection (see chapters in this issue). In these other techniques, damaging of cells and random manipulation of cells without optical control cannot be avoided so far.

In recent years microinjection technology found its application in plant sciences, whereas this technique has earlier been well established for transformation of animal tissue culture cells (Capecchi 1980) and the production of transgenic animals (Brin‐ster et al. 1981, Rusconi and Schaffner 1981). Furthermore, different parameters affecting the DNA transfer via microinjection, such as the nature of microinjected DNA, and cell cycle stage, etc, have been investigated extensively in animal cells (Folger et al. 1982, Wong and Capecchi 1985), while analogous experiments on plant cells are still lacking.
Light stimulation and darkness requirement for the symbiotic germination of Dactylorhiza majalis (Orchidaceae) in vitro
Authors: Rasmussen H. , Andersen T. F. , Johansen B.
Published: May 2006

Germination percentage of Dactylorhiza majalis (Rchb.f.) Hunt & Summerh. (Orchidaceae) was increased by illuminating surface‐sterilized, rinsed and incubated seeds with white light in 16 h photoperiods. Optimal exposures (10–14 days) raised germination from 40 to 75%. Longer light treatments resulted in reduced germination percentage and smaller seedlings. Only about 2% of the seeds could actually germinate in photoperiods; the germination of the rest was delayed by initial light and required about 14 days in constant darkness. Interruption of this darkness period with two consecutive photoperiods increased the germination percentage when the interruption occurred before day 8, but not when occurring later than that.
Increases in cytokinin levels in Scots pine in relation to chilling and bud burst
Authors: Qamaruddin Mohammed , Dormling Ingegerd , Eliasson Lennart
Published: May 2006

Levels of isopentenyladenosine and zeatin riboside were monitored in buds and needles of Scots pine (Pinus sylvestris L.) seedlings grown under controlled climatic conditions and in field‐grown trees. Extracts were purified by immunoaffinity chromatography and high‐performance liquid chromatography. Cytokinin levels were quantified with an enzyme‐linked immunosorbent assay. The cytokinin content was low in buds and needles of dormant seedlings but increased during dormancy release, reaching peak values in buds just before resumption of shoot growth. Samples collected in the field also showed a marked increase in the levels of cytokinins just prior to bud burst. Further, the biological activity of applied cytokinins in activating the dormant buds of Scots pine is shown. The results indicate a probable role of cytokinins in seedlings during dormancy release.
Metabolism of tritiated and deuterated gibberellin A9 in Norway spruce (Picea abies) shoots during the period of cone‐bud differentiation
Authors: Moritz Thomas , Odén Per Christer
Published: May 2006

A mixture of tritiated and deuterated gibberellin A9 (GA9) was injected into elongating shoots of Norway spruce [Picea abies (L.) Karst.] grafts grown under environmental conditions that were either inductive (heat and drought, HD) or noninductive (cool and wet, CW) for flowering. The shoots were divided into needles and shoot stems. The metabolites were purified by high performance liquid chromatography (HPLC), detected by liquid scintillation counting of aliquots of collected fractions and identified by gas chromatography‐mass spectrometry (GC‐MS). Deuterated GA9 was converted to deuterated GA4 in both treatments. The major metabolite in the CW‐treated material was GA51. The HD‐treated material did not convert GA9 to GA51, but a cellulase‐hydrolysable GA9‐conjugate was formed. The same metabolites were found in the shoot stems, though in smaller amounts. The amounts of detected metabolites were higher in the HD material, caused by a higher rate of metabolism and/or smaller losses of the metabolites during sample purification. The estimated amounts of endogenous GAs show that the HD‐treated material contained higher amounts of GA9 but no differences in the amounts of GA4 were found.
Factors increasing ethylene production enhance the sensitivity of root growth to auxins
Authors: Bertell Gertrud , Bolander Eva , Eliasson Lennart
Published: May 2006

Light inhibits root elongation, increases ethylene production and enhances the inhibitory action of auxins on root elongation of pea (Pisum sativum L. cv. Weibulls Marma) seedlings. To investigate the role of ethylene in the interaction between light and auxin, the level of ethylene production in darkness was increased to the level produced in light by supplying 1‐aminocyclopropane‐1‐carboxylic acid (ACC) or benzylaminopurine (BAP). Ethylene production was measured in excised root tips after treatment of intact seedlings for 24 h, while root growth was measured after 48 h. Auxin, at a concentration causing a partial inhibition of root elongation, did not increase ethylene production significantly. A 4‐fold increase in ethylene production, caused either by light, 0.1 μM ACC or 0.1 μM BAP, inhibited root elongation by 40–50%. The auxins 2,4‐dichlorophenoxyacetic acid and indolebutyric acid applied at 0.1 μM inhibited root elongation by 15–25% in darkness but by 50–60% in light. Supply of ACC or BAP in darkness enhanced the inhibitory effects of auxins to about the same extent as in light. The inhibition caused by the auxins as well as by the BAP was associated with swelling of the root tips. ACC and BAP treatment synergistically increased the swelling caused by auxins. We conclude that auxin and ethylene, when applied or produced in partially inhibitory concentrations, act synergistically to inhibit root elongation and increase root diameter. The effect of light on the response of the roots to auxins is mediated by a light‐induced increase in ethylene production.
Influence of the alternative respiratory pathway on the adenylate pools in heterotrophic Euglena gracilis
Authors: Benichou Pierre , Bomsel Jean‐Loup , Vinel Dominique , Claisse Maurice L. , Calvayrac Régis
Published: May 2006

Etiolated Euglena gracilis Pringsheim, strain Z, were cultured in a lactate medium either in the presence of 2 μM antimycin A for cells adapted to this inhibitor, or in the absence of antimycin A for controls. The adenylates (ATP, ADP and AMP) and the energy charge (EC) were followed during the growth of both types of cells. The effects of KCN, salicylhydroxamic acid (SHAM) and rotenone on the respiration and the adenylate pool, were investigated during the exponental and stationary phases. EC values of controls and antimycin‐adapted cells were not significantly different during culture. In the logarithmic phase, EC of controls was unaffected by 3 mM SHAM, an inhibitor of the alternative pathway, but markedly decreased by 0.3 mM KCN, which inhibits the cytochrome pathway. In contrast, in antimycin‐adapted Euglena, in which the cytochrome pathway was blocked, ATP content and EC were markedly lowered in the presence of SHAM but slightly increased by 0.3 mM KCN. The combination of the preceeding treatments, as well as 15 mM KCN alone, were deleterious for both types of cells, in the logarithmic and the late stationary phases. The data indicate that the energy level in Euglena was dependent on the alternative pathway when the cytochrome pathway was blocked. Such dependence could be explained by the engagement of the first rotenone‐sensitive site of phosphorylation. Indeed, 50 μM rotenone caused a similar relative decrease of oxygen consumption and ATP content in controls and in antimycin‐adapted Euglena. In the absence of cytochrome respiration, the alternative pathway allowed electrons to flow through this first segment of the respiratory chain, and ATP production by the first site of phosphorylation.
Electron spin resonance evidence for the formation of free radicals in plants exposed to ozone
Authors: Mehlhorn Horst , Tabner Brian J. , Wellburn Alan R.
Published: May 2006

Electron spin resonance (ESR) spectroscopy was used to demonstrate that free radicals are formed in O3‐fumigated plant leaves prior to the formation of visible leaf injury. ESR signals with a g‐value of 2.0037 to 2.0043, were observed in pea (Pisum sativum L. cv. Feltham first) and bean (Phaseolus vulgaris L. cv. Pinto) plants that had been fumigated for 4 h with 70–300 nl l−1 of ozone after they had been treated with the spin‐trap N‐t‐butyl‐α‐phenylnitrone (PBN). The size of the ESR signals increased with the concentration of ozone used but the nature of the trapped radicals could not be identified. However, further experiments using an inhibitor of ethylene biosynthesis, arninoethoxyvinyl glycine (AVG), showed that the reaction between ozone and ethylene is the cause for ozone toxicity.
The roots of nodulins
Authors: Nap Jan‐Peter , Bisseling Ton
Published: May 2006

Nodulin gene expression is an integral and highly specific part of the formation of nitrogen‐fixing nodules on the roots of leguminous plants. Dependent on the time of expression during root nodule development, nodulin genes can be divided into early and late nodulin genes. A brief overview of the functions assigned to early and late nodulins is presented. We hypothesize that nodulin genes originate from regular plant genes that evolved to fit the regulatory and/or physiological constraints of symbiotic nitrogen fixation. Data on nodulins and nodulin genes, nodulation taxonomy and nodule development are evaluated in the light of this hypothesis.
The structure and function of the photosystem I reaction centre
Authors: Evans M. C. W. , Bredenkamp G.
Published: May 2006

Current models of the photosystem I reaction centre are reviewed. The polypeptide composition of the reaction centre is described and the genetic origin of the peptides is documented. The properties of the redox components bound to the complex are reviewed. The chemical identity of the components, their location in the complex and the kinetics of electron transfer are discussed. It is concluded that a linear electron transport chain remains the best description of the function of the complex, but that the function and identity of the component A1 remains uncertain.

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Physiology and firmness determination of ripening tomato fruit
Authors: Ahrens M. Joseph , Huber Donald J.
Published: May 2006

Tomato (Lycopersicon esculentum Mill.) genotypes varying in intrinsic firmness were examined to determine the quantitative relationships between polygalacturonase (EC 3.2.1.15) activity, firmness and other ripening parameters including rate (days from mature‐green to full red) and intensity (rate of ethylene production at climacteric peak) of ripening. Texture, respiration and ethylene production were monitored in the immature‐green through the red (ripe) stages of development. Polygalacturonase activity was measured by direct assay of salt‐extractable wall protein or by monitoring the release of pectins from isolated, enzymically active wall. In all fruit, polygalacturonase activity was highly correlated with pericarp softening, but only moderately correlated with softening of whole fruit (r = 0.920 and 0.757, respectively). Polygalacturonase activity was positively correlated with cell‐wall autolytic activity in pink (r = 0.969) and red (r = 0.900) fruit. Firmer genotypes exhibited lower rates of respiration and ethylene production during ripening. Polygalacturonase activity in isolates prepared from fruit at the climacteric peak was positively correlated with ethylene production and respiration, and negatively correlated with days to ripening (r = 0.929, 0.805, and ‐0.791, respectively). The data demonstrate the importance of selecting the appropriate method of firmness determination and are consistent with the hypothesis that pectin fragments released by polygalacturonase contribute to the production of autocatalytic (system II) ethylene.
Filtration stress‐induced variations of peroxidase activity in cell suspension cultures of sycamore (Acer pseudoplatanus) cells
Authors: Li Z. S. , Attias J. , Thellier M.
Published: May 2006

Filtration stress, consisting in the rapid filtration of Acer pseudoplatanus L. cell suspension cultures, resulted in significant differences between the peroxidases (EC 1.11.1.7) released during cell growth and those released after filtered cells were resuspended in fresh medium (recovery medium). These differences concerned mainly modifications of (i) the pH optimum of peroxidase activity (guaiacol as electron donor), (ii) the number and the pI values of the peroxidase isoenzymes as shown by isoelectric focusing, and (iii) the molecular weights of the different peroxidase fractions determined by gel filtration chromatography. The presence of 1 mM Li+ in the recovery medium inhibited the release of peroxidase and this effect was partially reversed by K+. The release of peroxidase by stressed cells was also strongly inhibited by Na2CO3 in the recovery medium. The results presented are consistent with the proposal that the characteristic isoperoxidase patterns induced by filtration stress might be used as a model to study the response of plant cells to stress.
Influence of ammonium and extracellular pH on the amino and organic acid contents of suspension culture cells of Acer pseudoplatanus
Authors: Goodchild Jonathan A. , Givan Curtis V.
Published: May 2006

The effects of supplied ammonium and nitrate on the amino and organic acid contents and enzyme activities of cell suspension cultures of Acer pseudoplatanus L. were examined. Regardless of nitrogen source the pH of the culture medium strongly affected the malate and citrate contents of the cells; these organic acid pools declined at pH 5, but increased at pH 7 and 8. Over a period of two days, ammonium had little effect on the responses of the organic acid pool sizes to the pH of the medium. In contrast, ammonium had a strong influence on amino acid pool sizes, and this effect was dependent on the pH of the medium. At pH 5 there was no increase in cell ammonium or amino acid contents, but at higher pH values cellular ammonium content rose, accompanied by accumulation of glutamine, glutamate and asparagine. Over several days, supplied ammonium led to an increase in activity of glutamate dehydrogenase irrespective of any changes in internal ammonium and amino acid contents. If the pH of the medium was allowed to fall below pH 4 in the presence of ammonium, phosphoenolpyruvate (PEP) carboxylase activity declined to a very low value over several days; at higher pH, the activity of this enzyme, and that of NAD malic enzyme and NAD malate dehydrogenase, remained substantial irrespective of whether the nitrogen source was NH+4 or NO‐3.
Sorption of the cytokinin N6‐benzyladenine by leaf cuticles: prediction from n‐octanol:water partition coefficients
Authors: Shafer Warren E.
Published: May 2006

Partition and sorption characteristics of the cytokinin N‐(phenylmethyl)‐lH‐purine‐6‐amine (N6‐benzyladenine, BA) in two model systems were studied at 25°C. Apparent partition coefficients (KpH) for BA in an n‐octanol:water (buffer) system were independent of BA concentration but decreased with increasing buffer concentration (ionic strength). A plot of KpH values versus pH (2 to 12) was a bell‐shaped curve. At pH 2 or 12, KpH values were low (less than 2). As pH approached neutrality, KpH values increased approximately 20‐fold. Estimates of pK1(3.3) and pK2 (10.7) values for BA were obtained from these data. The accuracy of this approach to determining pK values was verified with 2‐(1‐naphthyl)acetic acid (NAA). Correction of KpH values for dissociation effects on BA yielded partition coefficients (K) whose overall mean was 37. Sorption of BA by cuticles enzymatically isolated from abaxial and adaxial surfaces of mature rubber plant (Ficus elastica Roxb. cv. decora) leaves was initially rapid, however equilibrium was not reached by 432 h. At pH 2, sorption was low (approximately 5 μmol kg−1), whereas at pH 6 sorption increased approximately 11‐fold. Sorption by abaxial cuticular membranes (CM) and dewaxed CM (DCM) was slightly higher than corresponding adaxial CM and DCM. Using natural logarithm values, KpH data were linearly‐correlated with CM (r = 0.98) and DCM (r = 0.99) sorption data.
Effects of quaternary ammonium salts on membrane potential and electric conductance in internodal cells of Nitettopsis obtusa
Authors: Trela Zenon , Janas Tadeusz , Witek Stanistaw , Przestalski Stanislaw
Published: May 2006

Effects of amphiphilic derivatives of glycine esters of the general formula (CH3)3N+CH2COOCnH2n+1Cl‐ (n = 10, 12, 14, 16) on membrane potential and conductance in internodal cells of the alga Nitellopsis obtusa were studied. The compounds decreased the potential difference between vacuole and external medium and increased the electric conductance. The effects depended on the length of the alkyl chain (n) and the concentration of these quaternary ammonium salts. Light‐induced hyperpolarization was suppressed by the salts. We suggest that the ammonium salts inhibit the electrogenic proton pump in the plasmalemma and enhance the passive efflux of Cl‐ from the algal cell.
L‐α‐Aminooxy‐β‐phenylpropionic acid inhibits lignification but not the differentiation to tracheary elements of isolated mesophyll cells of Zinnia elegans
Authors: Ingold Edgar , Sugiyama Munetaka , Komamine Atsushi
Published: May 2006

The influence of L‐α‐aminooxy‐β‐phenylpropionic acid (AOPP), an inhibitor of L‐phenylalanine ammonia‐lyase (PAL; EC 4.3.1.5), and thus of lignin formation, on the differentiation of tracheary elements from isolated mesophyll cells of Zinnia elegans L. cv. Canary Bird was investigated. At low concentrations of AOPP (5–25 μ,M) lignification of differentiating cells was almost completely prevented whereas number of differentiating cells, viability of the cells, fresh and dry weights, and the packed cell volume were higher than corresponding parameters in control cultures. At higher concentrations of AOPP (50–75 μM) the formation of tracheary elements was inhibited but division, elongation and expansion of cells were still observed. Cells cultured for 96 h in the presence of 100 μM AOPP were morphologically similar to cells at 12 h of culture, the time at which AOPP was added. At concentrations of AOPP that did not inhibit differentiation, AOPP caused an increase in the amounts of uronic acid and total carbohydrate (per unit volume of cell suspension) in the extracellular polysaccharide fraction and in the total cell wall fraction, although these parameters were not significantly different from control values when expressed on a dry weight basis. AOPP caused the release of polysaccharides which contained xylose into the medium when added before the onset of visible differentiation and the release of polysaccharides which contained glucose when added at the time when the formation of the secondary cell wall thickenings took place. The results indicate that AOPP at low concentrations specifically inhibits the formation of lignin without adversely affecting the synthesis of cell wall polysaccharides, although the proper integration of these compounds into the wall may be disturbed. O‐Benzylhydroxyla‐mine, on the other hand, did not prove to be a useful agent to affect lignin synthesis in differentiating Zinnia cells.
Freezing pattern in apple seeds as affected by the temperature of fruit storage
Authors: Nguyen Xuan Vinh , Kacperska Alina
Published: May 2006

Storage of apple fruits (Pyrus malus L. cv. Golden Delicious) at different temperatures (0, 12 and 35°C) markedly altered the pattern of water freezing in the seeds. Higher temperatures of storage brought about a shift from the sequential to the discontinuous type of freezing in seeds, the low temperature exotherm (LTE) being much more pronounced than the high temperature one (HTE). The occurrence of LTE was highly correlated with embryo death. Fruit storage at higher temperatures also caused a decrease in the threshold super cooling temperature of seeds and of naked embryos, removed from the seed coat and endosperm. The decrease was less pronounced in naked embryos than in intact seeds. The results presented show that the frost resistance of apple seeds relies mainly on the supercooling ability of the embryos and is increased by the presence of seed coat and endosperm. The broad peak of the LTE indicates that, in contrast with other seeds and many super cooling organs, massive ice nucleation in apple seeds occurs within the embryo tissues and that extra organ freezing seems to be of less importance. Therefore, the increased super cooling ability of apple seeds, isolated from fruits stored at higher temperatures, seems to rely on those seed properties that protect embryo cells against heterogeneous ice nucleation.
Stomatal and photosynthetic responses to variable sunlight
Authors: Knapp Alan K. , Smith William K.
Published: May 2006

Most plants experience many fluctuations in sunlight from full sun to shade throughout the day. Under these conditions, stomatal and photosynthetic responses vary dramatically among species depending on water status and growth form. Many herbaceous, fast‐growing species rapidly reduce stomatal opening during short‐term shade periods. Rapid stomatal closure during shade conserves water, but may also reduce CO2 uptake. Because periods of alternating sun and shade can reduce accumulative water stress that would otherwise severely curtail carbon gain, some herbs are restricted to habitats with intermittent periods of shade. In contrast to herbaceous growth forms, woody species maintain relatively constant stomatal opening during both sun and shade periods. This results in greater CO2 uptake, but with greater water loss. These two generalized response patterns for woody and herbaceous species to natural variations in sunlight conflict with conventional ideas of water use and carbon gain based on measurements made under constant light.
The effect of water stress on the vacuole‐extravacuole compartmentation of proline in potato cell suspension cultures
Authors: Fricke W. , Pahlich E.
Published: May 2006

Solute compartmentation in cells is an important component of metabolic regulation. There is only little information on how stress treatment of cells effects this component. Therefore, the effect of water stress [10% (w/v) PEG 6000] on the vacuolar‐extravacuolar proline compartmentation was studied in a cell suspension culture of Svlanum tuberosum L, cv, HH258, In non‐stressed cells 34% of the total cellular proline was located in the vacuole. After 20 h of water stress the proline pool of the cells was increased 4‐6 fold and only t6% of it was found in the vacuole. A negative correlation between the total cellular proline content and its percentage in the vacuole was observed, irrespective of the culture method (stress or non‐stress culture). The stress‐induced changes in proline compartmentation are discussed.
Factors controlling nitrate and ammonium accumulation in mustard (Sinapis alba) seedlings
Authors: Hecht Ursula , Mohr Hans
Published: May 2006

Prolonged application of ammonium as a source of nitrogen leads to serious physiological and morphological disorders in many plants, including mustard (Sinapis alba L,) seedlings (ammonium toxicity syndrome). Ammonium tolerance was previously observed in mustard seedlings in the presence of considerable amounts of nitrate in the medium. In the present study, the question was addressed as to what extent accumulation of nitrate and ammonium occurs in the mustard seedling and how this relates to ammonium toxicity and tolerance. Emphasis was on light control of accumulation in the attached cotyledons. Both NQ3 and NH4 became strongly accumulated in the mustard cotyledons once the concentration in the medium exceeded 1 mM, In the cotyledons, we measured concentrations > 30 mM in the case of nitrate and > 50 mM in the case of ammonium 4 days after sowing. Accumulation of inorganic nitrogen in the mustard cotyledons did not depend on photosynthesis nor on intact chloroplasts. However, the rate of nitrate accumulation was strongly stimulated by light, operating through phytochrome, while ammonium accumulation was not affected by light in short‐term experiments, i,e, within 24 h and only weakly (and probably indirectly) in long‐term light.

We conclude that strong interaction between NQ3 and NHJ is characteristic for accumulation of inorganic nitrogen. In the presence of NQ3, accumulation of NH3 is diminished and, to a lesser extent, vice versa. Using [15N]‐labelling it was found that incorporation of inorganic nitrogen into organic compounds was stimulated strongly whenever nitrate and ammonium were provided simultaneously. It appears from the data that accumulation of nitrate is strictly controlled by the mustard cotyledons while the accumulation of ammonium is not. The data indicate that the level of ammonium is governed primarily by the rate of ammonium assimilation. Stimulation of ammonium assimilation by simultaneously applied nitrate appears to explain nitrate‐mediated ammonium tolerance in the mustard plant.
Maximal biomass production can occur in corn (Zea mays) in the absence of NO3 accumulation in either leaves or roots
Authors: Khamis Saadi , Lamaze Thierry
Published: May 2006

In order to investigate effects of limited NO3 availability in corn (Zea mays L. cv. Brulouis) 17‐day‐old plants were grown for a further 25 days on sand in a growth chamber. The plants received frequent irrigation with a complete nutrient solution containing 0.2, 0.6, 1.5 or 3.0 mM NO3. With 0.2 mM NO; nitrate levels in both roots and leaves diminished rapidly and were almost zero after 10 days treatment. Concurrently, as signs of nitrogen deficiency appeared, shoot growth was restricted, whereas root growth was enhanced. In addition, the concentration of reduced nitrogen and malate in the leaves declined, and in vitro nitrate reductase activity (NRA. EC 1.6.6.1), soluble protein and chlorophyll levels of leaf tissue were depressed and starch concentration was enhanced. With 0.6 mM NO3 in the nutrient solution, the decrease in NO3 levels in the tissues and the increase in root development were similar to those observed with 0.2 mM NO3. However, shoot growth, reduced nitrogen concentration in leaves, and the above‐mentioned biochemical characteristics were almost identical to those obtained at 1.5 and 3.0 mM NO3. This indicates that when supplied with 0.6 mM NO3, corn plants were able to absorb sufficient NO3 to support maximal biomass production without appreciable NO3 accumulation in roots or shoot. It is, thus, suggested that the plants responded to low NO3, availability in medium by enhancing root growth and by maximizing NO3 reduction relative to NO3 accumulation.
Mobilisation of storage reserves during germination and early seedling growth of sugar beet
Authors: Lawrence D. M. , Halmer P. , Bowles D. J.
Published: May 2006

The principal storage reserve of sugar beet seeds is starch, which is localised in the perisperm. Additional storage reserves include the seed proteins, albumins, globulins and glutclins, which are exclusively located in the embryo. Soluble sugars are also detectable in all the organs of the mature seed. The time‐course of reserve mobilisation in the different organs of the sugar beet (Beta vulgaris L. cv. Regina) seed during germination and early seedling growth is documented, with particular reference to changes in (a) activities of hydrolases: a‐amylase, β‐amylase, and α‐glucosidases; (b) levels of carbohydrates and (c) proteins. Amylase activities increase substantially in both cotyledons, as well as the perisperm, whereas the increase in α‐glucosidase activities is largely confined to the perisperm.
Nitrate reductase and nitrate accumulation in relation to nitrate toxicity in Boronia megastigma
Authors: Reddy K. S. , Menary R. C.
Published: May 2006

Moderate levels of N were toxic to the native Australian plant boronia (Boronia megastigma Nees). As NO‐3 is the major N form available for plants under cultivated conditions, NO‐3 reduction and accumulation patterns in boronia were examined following the supply of various levels of NO‐3 to understand the physiological basis of this toxicity. At a low level of supplied NO‐3 [15 mmol (plant)‐1], NO‐3 was reduced without any detectable accumulation and without nitrate reductase activity (NRA) reaching its maximum capacity. When higher NO‐3 levels [≥25 mmol (plant)‐1] were supplied, both NRA and NO‐3 accumulation increased further. However, NRA increased to a maximum of ca 500 nmol NO‐3 (g fresh weight)‐1 h‐1, both in the roots and leaves, irrespective of a 4‐fold difference in the levels of supplied NO‐3, whereas NO‐3 continued to accumulate in proportion to the level of supplied NO‐3. Chlorotic toxicity symptoms appeared on the leaves at an accumulation of ca 32 μmol NO‐3 (g fresh weight)‐1. High endogenous NO‐3 concentrations inhibited NRA. The low level of NRA in boronia was not limited by NO‐3 or electron donor availability. It is concluded that the low NR enzyme activity is a genetic adaptation to the low NO‐3 availability in the native soils of boronia. Thus, when NO‐3 supply is high, the plat cannot reduce it at high rates, leading to large and toxic accumulations of the ion in the leaf tissues.
Light‐quality and irradiance‐level control of light‐harvesting complex of photosystem 2 in maize mesophyll cells. Evidence for a low fluence‐rate threshold in blue‐light reduction of mRNA and protein
Authors: Eskins Kenneth , Beremand Phillip D.
Published: May 2006

Levels of pigment‐proteins and mRNA coding for proteins associated with the light‐harvesting complex of photosystem 2 (LHCP2) were reduced in maize (Zea mays L. cv. OP Golden Bantum) plants grown for 14 days in 8.0 nmol m‐2s‐1 of blue light compared to those in plants grown under an equal irradiance of red light. At the same time, there was a small increase in steady state levels of mRNA for the Dl protein of PS2 (psbA) in blue‐grown plants. The reduction of LHCP2 mRNA and the increase in psbA mRNA were observed in both 5‐ and 10‐day‐old blue‐light‐grown leaves, but the degree of reduction or increase was much greater in 10‐day‐old leaves. Maize grown under 6 different mixtures of blue and red light, each with a total irradiance level of 8.0 μmol m‐2 s‐1, showed the same degree of LHCP2 mRNA reduction relative to red light. This is different from the behavior of psbA which increased in a linear manner with increasing amounts of blue light. The amounts of Chi a and Chi b in these mixed‐light samples were not significantly different froi those found in pure red light. This indicates that a low fluence level of blue light, even when combined with red light, is sufficient to reduce equilibrium levels of proteins and mRNA of LHCP2, and this reduction is independent of pigment formation. It also suggests that the mechanisms of blue‐light regulation of mRNA may operate differently at the nuclear and chloroplast levels.
Apical dominance in mulberry (Morus alba): Effects of position of lateral and accessory buds and leaves
Authors: Suzuki Takeo
Published: May 2006

Suzuki, T. 1990. Apical dominance in mulberry (Morus alba): Effects of position of lateral and accessory buds and leaves. – Physiol. Plant. 78: 468‐474.

Removing apical portions of current growth coppice shoots from field‐grown, low‐pruned stumps of mulberry (Morus alba L. cv. Shin‐ichinose) caused sprouting of one or more upper main buds, almost concurrently with that of accessory buds. However, removal of the new sprouts, including those from accessory buds, slightly enhanced the sprouting of buds immediately below them, and did not affect buds lower down. In contrast, mature leaves inhibited the buds in their axils. Budless, leafy nodes on the upper part of pruned shoots tended to swell after treatment, perhaps due to the accumulation of substances translocated from the roots and possibly from the remaining leaves. Lateral buds at different positions along the shoot differed in their sprouting ability with buds lower on the shoot being more inhibited. This inhibition gradient dissappeared when all coppice shoots on one stump were pruned to the same bud position, suggesting inhibition from neighboring, actively growing shoots. These results demonstrate that acropetal influences are important in bud dominance relationships.
Photosystem I polypeptides
Authors: Scheller Henrik Vibe , Møller Birger Lindberg
Published: May 2006

Photosystem I mediates light‐induced electron transport from reduced plastocyanin in the thylakoid lumen to oxidized ferredoxin in the stroma. Photosystem I is located in the stroma lamellae of the thylakoid system and consists of a peripheral light‐harvesting pigment‐protein complex and a core complex carrying the electron transfer components and additional antenna pigments. The core complex consists of 11 different polypeptide subunits, five of which are chloroplast encoded and six of which are encoded by nuclear genes. The structure and function of the different subunits of the photosystem 1 core complex is discussed.
Histochemical technique: A low‐volume, enzyme‐amplified immunoassay with sub‐fmol sensitivity. Application to measurement of abscisic acid in stomatal guard cells
Authors: Harris Michael J. , Outlaw William H.
Published: May 2006

Immunological protocols are useful for quantitative histochemistry because of the high specificity and affinity of antibody‐antigen binding. This interaction, followed by amplification steps, is the basis of an assay that has a sensitivity of 10‐10 mol abscisic acid. This assay, combined with extant single‐cell methodologies, makes it possible to determine the cellular localization of abscisic acid within a leaf. This general approach possibly has wide application in plant physiological research; therefore, we give a brief general description of our implementation here.
Calcium‐calmodulin in germination of Phacelia tanacetifolia seeds: effects of light, temperature, fusicoccin and calcium‐calmodulin antagonists
Authors: Cocucci Maurizio , Negrini Noemi
Published: May 2006

Germination in the dark and at 16°C of photoblastic and thermosensitive seeds of Phacelia tanacetifolia was inhibited when incubated with EGTA and the Ca2+‐ionophore A 23187; A 23187 in the presence of Ca2+ still inhibited germination, but to a lesser extent. Treatments with EGTA or Ca2+ at different concentrations in the presence or in the absence of A 23187 did not remove light inhibition. The calmodulin (CaM) inhibitor, calmidazolium, strongly inhibited germination. The specificity of these inhibitors and their effects on seed germination are discussed.

CaM from Phacelia tanacetifolia seeds has been purified and its characteristics (molecular weight, heat and acid stability, kinetics of phosphodiesterase [EC 3.1.4.17] activation) were very similar to those of other plant sources. More than 90% of total CaM was present in the soluble fraction (ca 41 μg g‐1 fresh weight in ungerminated seeds). The CaM level greatly increased in the early phases of seed germination; this increase did not take place when germination was inhibited by light or high temperature. When fusicoccin, a toxin which promotes germination by activating membrane functions, relieved light or high temperature inhibition, CaM increased up to the control value in the dark at 16°C. The parallel increase in CaM and seed germination suggest that CaM plays an important role in the process. Fusicoccin in the dark at 16°C stimulated CaM and fresh weight increase, but not the metabolic reactivation measured as increase in DNA and total RNA levels; at 30°C fusicoccin stimulated the increase in fresh weight and in CaM level, but the increases in DNA and total RNA were very low. These results suggest that the activation of membrane functions with cell enlargement induced by fusicoccin is related to CaM increase.