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  • 1
    Electronic Resource
    Electronic Resource
    Early degradation of photosynthetic membranes in carob and sunflower cotyledons (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 96 (1996), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The assimilatory activity of cotyledons can play an essential role in the survival of seedlings with a slow and delayed development of primary leaves. Changes in the photosynthetic activity of the cotyledon, from the onset of greening through senescence, were studied in two such plants, carob and sunflower, in order to determine its efficiency and duration, also in connection with the achievement of assimilatory autonomy by the plantlet. Chlorophyll analyses showed that the cotyledon's chloroplasts reached maximal greening in plantlets with a pair of expanded leaves. In contrast, the cotyledon's photosynthetic activity, measured as the rate of oxygen release, started to decrease early, before expansion of primary leaves. The decrease was due to the inactivation of a number of photosystem II (PSII) units, as revealed by immunodetection of breackdown products of the reaction centre's D1 and D2 thylakoid proteins. No signals of PSII alteration were noticed in the primary leaf chloroplasts that differentiated under the same environmental conditions. The damage to the cotyledon PSII, occurring in a non-photoinhibitory situation, might be due to a slower rate of turnover of D1 polypeptide than in the leaf thylakoids. The differential turnover of this protein in cotyledons and in leaves might represent an organ-specific regulation of the photosynthetic activity. The peculiarity of the cotyledon thylakoids make these organs useful objects for studying the metabolic cycle of both D1 and D2 proteins in vivo, under non-photoinhibiting conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1996.tb00466.x
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  • 2
    Electronic Resource
    Electronic Resource
    Expression of chloroplastic and cytosolic glutamine synthetase in barley leaves after cold-sensitive blocking of β-carotene synthesis by amitrole or mutation (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 94 (1995), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 3-Amino- 1,2,4-triazole (amitrole) provided to germinating barley at 20°C in the light led to bleached seedling leaves and photodynamic destruction of chloroplast structure, whereas normal greening and chloroplast ultrastructure was obtained when the seedlings developed in the presence of amitrole in the light at 30°C. Mass spectrometric analysis of the extractable herbicide demonstrated the same content of amitrole in leaves developed at 20 and 30°C. A very similar temperature-sensitive syndrome is characteristic for the nuclear gene mutant ligrina-o34 in barley. Amitrole and the mutation were shown to inhibit the cyclization of lycopene, leading to severe deficiencies in β-carotene and its xanthophyll derivative lutein. Besides accumulation of lycopene, also its precursors phytoene, phytofluene and ξ-carotene accumulated. Inhibition of carotenoid biosynthesis by amitrole and the mutation at 20°C in the light led to a strong reduction of both transcript and protein levels for chloroplastic glutamine synthetase (GS2) while transcript amount and protein of the cytosolic isoenzyme (GS1) were unaffected. At 30°C increased levels of mRNA for the chloroplastic isoform GS2 were observed in wild type, mutant and amitrole-treated seedlings, but protein levels remained unchanged. Turnover rates of the GS2 protein were the same at 20 and 30°C. This extensive translational control of chloroplastic GS2 synthesis was also observed in a heat shock experiment, which revealed transiently increased mRNA levels for chloroplastic GS2 but unchanged protein levels.Permissive synthesis of β-carotene and chloroplastic glutamine synthetase (GS2) at 30°C in the presence of amitrole or the tigrina-o34 mutation might be due to two alternative pathways of ionone ring formation using either lycopene or neurosporene as substrates for cyclization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1995.tb00965.x
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  • 3
    Electronic Resource
    Electronic Resource
    Changes in onion root development induced by the inhibition of peptidyl-prolyl hydroxylase and influence of the ascorbate system on cell division and elongation (1999)
    Springer
    Planta 209 (1999), S. 424-434 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Allium (root development) ; Ascorbate ; Cell division ; Cell expansion ; Hydroxyproline-containing protein ; Root development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Post-translational hydroxylation of peptide-bound proline residues, catalyzed by peptidyl-prolyl-4 hydroxylase (EC 1.14.11.2) using ascorbate as co-substrate, is a key event in the maturation of a number of cell wall-associated hydroxyproline-rich glycoproteins (HRGPs), including extensins and arabinogalactan-proteins, which are involved in the processes of wall stiffening, signalling and cell proliferation. Allium cepa L. roots treated with 3,4-DL-dehydroproline (DP), a specific inhibitor of peptidyl-prolyl hydroxylase, showed a 56% decrease in the hydroxyproline content of HRGP. Administration of DP strongly affected the organization of specialized zones of root development, with a marked reduction of the post-mitotic isodiametric growth zone, early extension of cells leaving the meristematic zone and a huge increase in cell size. Electron-microscopy analysis showed dramatic alterations both to the organization of newly formed cell walls and to the adhesion of the plasma membranes to the cell walls. Moreover, DP administration inhibited cell cycle progression. Root tips grown in the presence of DP also showed an increase both in ascorbate content (+53%) and ascorbate-specific peroxidase activity in the cytosol (+72%), and a decrease in extracellular “secretory” peroxidase activity (−73%). The possible interaction between HRGPs and the ascorbate system in the regulation of both cell division and extension is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050745
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  • 4
    Electronic Resource
    Electronic Resource
    Morphological and ultrastructural aspects of dehydration and rehydration in leaves of Sporobolus stapfianus (1998)
    Springer
    Plant growth regulation 24 (1998), S. 219-228 
    Details
    ISSN: 1573-5087
    Keywords: Sporobolus stapfianus ; resurrection plant ; desiccation-tolerance ; leaf morphology ; leaf ultrastructure ; leaf dehydration/rehydration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The resurrection species Sporobolus stapfianus Gandoger has been studied by LM, TEM and SEM in order to define the leaf morphology and fine structure and to analyse the cellular changes occurring during the processes of dehydration and rehydration of the plant. Some characteristics of the fully hydrated leaf and some ultrastructural and physiological events which take place during leaf wilting are discussed in relation to their possible role in plant desiccation-tolerance. The leaves of S. stapfianus show several characteristics common among xerophytic species. In the resurrection leaf they could play a role in slowing down the drying rate, thus leaving time to activate the mechanisms protecting the cell structures against drought damage. Actually, the S. stapfianus leaves do not undergo important cellular alterations during dehydration. The chloroplasts, in particular, retain part of their photosynthetic pigments and thylakoid membranes. Upon rewatering leaf recovery is rather fast and the tissue structure and cell organization of the fully hydrated state are already regained after two days.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005853527769
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of seed chilling or GA3 supply on dormancy breaking and plantlet growth in Cercis siliquastrum L. (1998)
    Springer
    Plant growth regulation 25 (1998), S. 53-61 
    Details
    ISSN: 1573-5087
    Keywords: Cercis siliquastrum ; germination ; gibberellic acid ; seed chilling ; seed dormancy ; morphogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Germination and post-germination events have been compared in seeds of Cercis siliquastrum whose dormancy was removed by fulfilling the natural chilling requirement or by exogenous GA3 application. Compared to the chilled ones, the GA3 treated seeds showed precocious embryo growth and an earlier reserve mobilization, which started before radicle emergence. Although the hormonal application was interrupted at seed germination, the plantlets of Cercis siliquastrum that originated from GA3-supplied seeds were taller than those from chilled ones. Moreover, they produced a greater number of leaves but a reduced root mass and had some difficulty in maintaining a good water balance. Thus, the treatment of Cercis siliquastrum seeds with exogenous GA3 broke dormancy and induced germination, but also caused long-lasting consequences on morphogenesis of the growing plantlet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005960708857
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  • 6
    Electronic Resource
    Electronic Resource
    Differential ethylene-inducible expression of cellulase in pepper plants (1995)
    Springer
    Plant molecular biology 29 (1995), S. 735-747 
    Details
    ISSN: 1573-5028
    Keywords: Capsicum annuum ; endo-β-(1,4)-glucanase ; ethylene ; leaf abscission ; nucleotide sequence ; ripening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Ethylene promotes the abscission of leaves and the ripening of fruits in pepper plants, and in both events an increase in cellulase activity is observed. However, two enzyme isoforms (pI 7.2 and 8.5, respectively) are differentially involved in the two physiological phenomena. The pI 8.5 form has been purified from ripe fruits. It is a glycoprotein with an apparent molecular mass of 54 kDa. Two short peptides were sequenced and a very high homology to a tomato cellulase was observed. Polyclonal antibodies, raised against the purified enzyme, have allowed us to demonstrate that the observed ethylene-induced increase in cellulase activity is paralleled by de novo synthesis of protein. Three cDNAs (CX1, CX2 and CX3), encoding different cellulases, were obtained and characterized and their expression investigated. Accumulation of all three mRNAs is induced by ethylene treatment, though to different levels. CX1 is mainly expressed in ripe fruits while CX2 is especially found in abscission zones. CX3 accumulates at very low levels in activated abscission zones. Comparisons with other known cellulases demonstrate clear heterogeneity within the higher plant cellulases. Differences in ethylene inducibility and molecular structure suggest different physiological roles for cellulase in pepper plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00041164
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