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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 28 (2005), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Nitric oxide (NO) is a free radical that had been known for many years simply as a toxic air pollutant. The discovery of enzymatic NO production in many living organisms has established a new paradigm: NO being an essential molecule endogenously produced in the cells. In plant science it has been suggested that NO acts as a plant hormone equivalent to ethylene; that is, as a gaseous signal transmitter. Even after experiencing such a scientific breakthrough, however, researchers may still feel difficulty in exploring plant NO signalling systems with conventional approaches. A major difference between plants and animals is that the growth and development of plants is closely linked to the surrounding environment where NO levels vary according to biotic and abiotic activities. This fundamental difference may make the NO-signalling network system of plants larger and more complicated than that of vertebrates. This review intends to show prospects for the future of NO signalling research in plants by introducing a holistic concept to aid in the exploration of complicated systems such as the plant-environment system. Furthermore, the novel ONS hypothesis is proposed to encompass the complexity and simplicity of NO in chemistry, biochemistry and physiology.
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  • 2
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A QTL analysis for three different adaptive traits was performed in an F1 progeny of Castanea sativa Mill. The female and male parents originated from two Turkish chestnut populations adapted to a drought and humid environment, respectively. QTLs for bud flush, growth and carbon isotope discrimination were detected over a 3-year period. Bud set was also recorded in the last year of measurement. Thirty-five individual QTLs were detected for phenology, 28 for growth and 17 for carbon isotope discrimination, most of them explaining a low to moderate proportion of the total phenotypic variance. QTLs were distributed throughout the whole genome. Temporally stable QTLs were identified for all the traits analysed, with phenology showing the higher proportion of stable QTLs. Interesting phenotypic correlations and co-localizations among QTLs for different adaptive traits were observed, allowing the formulation of an hypothesis about the genetic adaptation of the female parent to drought.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 27 (2004), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The activity of alcohol dehydrogenase (ADH) was measured in corms and roots of the submerged freshwater macrophyte Isoetes alpinus Kirk. growing in situ, and related to its capacity for internal oxygen transport and to carbohydrate translocation. ADH activity was present in roots but not corms at uniform activity (0.15–0.35 × 10−6 mol  g−1 fresh weight s−1) over the entire plant depth range (3–7 m depth), and was intermediate to that developed in excised roots after 1-week exposure to either dissolved oxygen at air-saturation or to anoxia. Responses of photosynthesis and root oxygen release to light intensity confirmed that shoot-to-root oxygen transport saturated at similar light intensities to photosynthetic oxygen evolution, but was positive in the dark and at irradiances below the compensation point for photosynthesis, due to contributions to transport by oxygen diffusion from the external medium. Transport of 14C-labelled photo-assimilates to roots nevertheless ceased when intact plants were exposed to a combination of leaf darkness and root external anoxia, even when high 14C concentrations were present in shoots, but remained high when the roots were provided with external oxygen. The lack of any control over permeability of the root surface to gases in this species suggested that ADH activity and reduced translocation is most likely caused by development of hypoxic tissues in the apical tissue. These results suggest that reductions in ambient light intensity may have indirect effects on I. alpinus viability by increasing the degree of root hypoxia and impairing carbon partitioning.
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  • 4
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Seasonal evaluation of total soluble protein fractions extracted from cortical parenchyma cells of mulberry (Morus bombycis Koidz.) tree identified a predominant 18 kDa protein that was directly correlated to periods of cold acclimation. The 18 kDa protein, designated as WAP18 (winter accumulating 18 kDa proteins) increased from September to December and then gradually decreased until June. The maximum levels of WAP18 were detected in mid-winter, which corresponds to the maximum freeze tolerance in cortical parenchyma cells of mulberry tree. Two-dimensional gel electrophoresis confirmed that WAP18 consists of at least three proteins that range between an isoelectric point of 5.0 and 6.0. All three proteins reacted with anti-WAP18 antibodies, thereby suggesting that they represent individual isoforms. Furthermore, N-terminal amino acid sequence analysis demonstrated that all three proteins contain high sequence similarity to each other and high homology to pathogenesis-related (PR) −10/Bet v 1 protein families. The purified WAP18 exhibited in vitro cryoprotective activity for the freeze labile l-lactate dehydrogenase (LDH) enzyme. These results suggest that WAP18 may function in the freezing tolerance mechanism of cortical parenchyma cells of mulberry tree during winter.
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  • 5
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 2,4-dichlorophenoxyacetic acid (2,4-D) is an analogue compound to the plant hormone indole-3-acetic acid (IAA), which is used either as a growth-promoting substance or as a herbicide, depending on its concentration. In this work, the effect of 2,4-D on the growth and ROS metabolism of pea (Pisum sativum L.) leaves is reported. The herbicide considerably reduced the plant growth and negatively influenced several physiological parameters in a dose-dependent manner. At structural level, damage of the mesophyll cells and the enlargement and dilation of thylakoids were observed in 2,4-D-treated plants. 2,4-D notably affected xanthine oxidase and superoxide dismutase activities, as well as the activity and transcript levels of the ascorbate–glutathione cycle enzymes, ascorbate peroxidase, monodehydroascorbate reductase, and glutathione reductase. Furthermore, in herbicide-treated plants, an increase in the H2O2 production, levels of lipid peroxidation, endopeptidase activity and oxidatively modified proteins took place. Results obtained showed that an overproduction of superoxide radicals (O2−) and hydrogen peroxide (H2O2) could take place in plants treated with 2,4-D, thus contributing to the generation of oxidative stress, with the concomitant degradation of proteins. A model of the role of ROS-mediated enzymatic systems in the oxidative mode of action of 2,4-D and other auxinic herbicides is proposed.
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  • 6
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The impact of a heterogeneous within-crown light environment on carbon allocation was investigated on young walnut trees trained on two branches: one left in full sunlight, the other shaded until leaf fall resulting in 67% reduction in photosynthetically active radiation. In September, the two branches were separately labelled with 14CO2 and 13CO2, respectively, so that the photosynthates from each branch could be traced independently at the same time. Although some carbon movements could be detected within 5 d in both directions (including from the shaded branch to the sun branch), between-branch carbon movements were very limited: approximately 1% of the diurnal net assimilation of a branch. At this time of the year branch autonomy was nearly total, leading to increased relative respiratory losses and a moderate growth deficit in the shaded branch. The ratio of growth to reserve storage rate was only slightly affected, indicating that reserves acted not as a mere buffer for excess C but as an active sink for assimilates. In winter, branch autonomy was more questionable, as significant amounts of carbon were imported into both branches, possibly representing up to 10% of total branch reserves. Further within-plant carbon transfers occurred in spring, which totally abolished plant autonomy, as new shoots sprouted on each branch received significantly more C mobilized from tree-wide reserves than from local, mother-branch located reserves. This allowed great flexibility of tree response to environment changes at the yearly time scale. As phloem is considered not functional in winter, it is suggested that xylem is involved as the pathway for carbohydrate movements at this time of the year. This is in agreement with other results regarding sugar exchanges between the xylem vessels and the neighbouring reserve parenchyma tissues.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 27 (2004), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Hydroxyl radicals (*OH) as produced in the Fenton reaction (Fe2+ + H2O2 = Fe3+ + OH– + *OH) have been used to reversibly inhibit aquaporins in the plasma membrane of internodes of Chara corallina. Compared to conventional agents such as HgCl2, *OH proved to be more effective in blocking water channels and was less toxic to the cell. When internodes were treated for 30 min, cell hydraulic conductivity (Lp) decreased by 90% or even more. This effect was reversed within a few minutes after removing the radicals from the medium. In contrast to HgCl2, radical treatment reduced membrane permeability of small lipophilic organic solutes (ethanol, acetone, 1-propanol, and 2-propanol) by only 24 to 52%, indicating some continued limited movement of these solutes across aquaporins. The biggest effect of *OH treatment on solute permeability was found for isotopic water (HDO), which largely used water channels to cross the membrane. Inhibition of aquaporins reduced the diffusional water permeability (Pd) by about 70%. For the organic test solutes, which mainly use the bilayer to cross the membrane, channel closure caused anomalous (negative) osmosis; that is, cells had negative reflection coefficients (σs) and were transiently swelling in a hypertonic medium. From the ratio of bulk (Lp or osmotic permeability coefficient, Pf) to diffusional (Pd) permeability of water, the number (N) of water molecules that align in water channels was estimated to be N = Pf/Pd = 46 (on average). Radical treatment decreased N from 46 to 11, a value still larger than unity, which would be expected for a membrane lacking pores. The gating of aquaporins by *OH radicals is discussed in terms of a direct action of the radicals when passing the pores or by an indirect action via the bilayer. The rapid recovery of inhibited channels may indicate an easy access of cytoplasmic antioxidants to closed water channels. As hydrogen peroxide is a major signalling substance during different biotic and abiotic stresses, the reversible closure of water channels by *OH (as produced from H2O2 in the apoplast in the presence of transition metals such as Fe2+ or Cu+) may be downstream of the H2O2 signalling. This may provide appropriate adjustments in water relations (hydraulic conductivity), and a common response to different kinds of stresses.
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  • 8
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The patch clamp technique was applied to protoplasts isolated from the epidermis and pericycle of Arabidopsis roots and their plasma membrane currents investigated. In the whole cell configuration, all protoplasts from the epidermis exhibited depolarization-activated time-dependent outwardly rectifying (OR) currents whereas OR currents were present in only 50% of cells from the pericycle. The properties of the OR currents in the epidermis and pericycle were compared with respect to their selectivity, pharmacology and gating. The time-dependent activation kinetics, selectivity and sensitivity to extracellular tetraethyl ammonium of the OR current in each cell type were not significantly different. The reversal potential (Erev) of the OR currents indicated that they were primarily due to the movement of K+. However, the gating properties of the OR currents from the epidermis differed markedly from those exhibited in the pericycle. Although both cell types displayed OR currents with voltage-dependent gating modulated in a potassium-dependent fashion [i.e. the activation threshold (V0.5) was displaced to more positive voltages as extracellular K+ increased], the OR currents in the epidermis also displayed voltage-independent gating by extracellular K+ which dramatically regulated current density. In the present study, reducing extracellular K+ activity from 40 to 0.87 mm reduced the OR current density in epidermal cells by approximately 80%. The chord conductance of the OR current saturated as a function of extracellular K+ and could be fitted with a Michaelis–Menten function to yield a binding constant (Km) of 10.5 mm. The ability of other monovalent cations to substitute for K+-gating of the OR currents was also investigated and shown to exhibit a relative sequence of K+ ≥ Rb+ 〉 Cs+ 〉 Na+ ≥ Li+ (Eisenmann sequence IV) with respect to efficacy of gating. Furthermore, single channel recordings demonstrated that channel activity rather than the single channel conductance was modulated by extracellular K+. In contrast, OR current density in the pericycle was largely independent of extracellular K+. It is suggested that the contrasting gating properties of the K+ channels in the epidermis and pericycle reflect their different physiological roles, particularly with respect to their role in K+ (nutrient) transport from the soil solution to the shoot.
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  • 9
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The natural variation in quantity and quality of light modifies plant morphology, growth rate and concentration of biochemicals. The aim of two growth-room experiments was to study the combined effects of red (R) and far-red (FR) light and ultraviolet-B (UV-B) radiation on the concentrations of leaf phenolics and growth and morphology of silver birch (Betula pendula Roth) seedlings. Analysis by high-performance liquid chromatography showed that the leaves exposed to supplemental FR relative to R contained higher concentrations of total chlorogenic acids and a cinnamic acid derivative than the leaves treated with supplemental R relative to FR. In contrast, concentration of a flavonoid, quercetin 3-galactoside, was higher in the R + UV-B leaves than in the FR + UV-B leaves. The UV-B induced production of kaempferols, chlorogenic acids and most quercetins were not modified by the R : FR ratio. Growth measurements showed that the leaf petioles and stems of FR seedlings were clearly longer than those of R seedlings, but leaf area was reduced by UV-B radiation. Results of these experiments show that exposure of silver birch seedlings to supplemental FR compared to R leads to fast elongation growth and accumulation of phenolic acids in the leaves.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 27 (2004), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Inflorescences of the arum lily Symplocarpus foetidus are thermogenic and thermoregulatory. The spadix increases respiratory heat production rate as ambient temperature decreases. This study examined the relationships between spadix temperature (Ts), respiration rate (〈inlineGraphic alt="inline image" href="urn:x-wiley:01407791:PCE1206:PCE_1206_mu1" location="equation/PCE_1206_mu1.gif"/〉) and ambient temperature (Ta) at equilibrium and during transient responses to step changes in Ta. Intact inflorescences inside a miniature constant temperature cabinet in the field showed the most precise temperature regulation yet recorded; over a 37.4 °C range in Ta (−10.3 to 27.1 °C), Ts changed only 3.5 °C (22.7 to 26.2 °C). Regulated temperatures were not related to spadix size (1.9–7.3 g) or circadian cycle. Dynamic responses to step changes in Ta involved a phasic change in Ts, first in the same direction as Ta, then reversing at 38.3 min, and finally approaching equilibrium at 87.6 min, on average. Meanwhile 〈inlineGraphic alt="inline image" href="urn:x-wiley:01407791:PCE1206:PCE_1206_mu1" location="equation/PCE_1206_mu1.gif"/〉 changed in a monotonic curve toward equilibrium. Models revealed that the dynamics of temperature change were inconsistent with simply a physical lag in the system, but involved some form of biochemical regulation, possibly by changes in activity of a rate-limiting functional protein.
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