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  • 11
    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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  • 12
    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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  • 13
    Electronic Resource
    Electronic Resource
    Cab gene expression in bleached leaves of carotenoid-deficient maize (2000)
    Springer
    Photosynthesis research 64 (2000), S. 119-126 
    Details
    ISSN: 1573-5079
    Keywords: amitrole ; bleaching herbicides ; Cab gene expression ; carotenoid-deficient mutants ; chloroplast photodamage ; norflurazon ; ultrastructure ; Zea mays L
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The chloroplast photo-oxidation and the expression of the Cab gene Lhcb1, encoding the Lhcb1 light-harvesting chlorophyll a/b-protein of PS II, have been studied in leaf cells of maize treated with the two bleaching herbicides norflurazon and amitrole and of the two carotenoid-free mutants vp9 and vp2 grown under high photodamaging light. Both herbicides and mutations caused severe photo-oxidation of organelles. However, the plastids of norflurazon-treated and vp2 leaves were totally devoid of thylakoids and did not contain any chlorophyll, while the organelles of amitrole-treated and vp9 leaves still had a few altered and photosynthetically unfunctional membranes and very small quantities of chlorophylls. Despite the dramatic photodamage undergone by the plastids over several days, the cells of amitrole-treated and vp9 leaves maintained a certain expression of the Lhcb1 gene which, on the contrary, was completely blocked in the cells of norflurazon-treated and vp2 leaves. The experimental results, obtained by integrating biochemical and molecular analyses with ultrastructural observations, show that the maintainance of Cab gene expression does not strictly depend on intact and functional chloroplasts. The transcription of these genes, still maintained in cells with greatly photo-oxidized organelles, seems to be inversely related to the degree of thylakoid demolition, which can affect the last steps of chlorophyll biosynthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006477215572
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  • 14
    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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  • 15
    Electronic Resource
    Electronic Resource
    An ultrastructural study of maize leaf etioplasts throughout their entire life-cycle (1986)
    Springer
    Protoplasma 130 (1986), S. 98-107 
    Details
    ISSN: 1615-6102
    Keywords: Zea mays L. ; Etioplasts ; Etioplast differentiation ; Etioplast senescence ; Optical diffraction ; Prolamellar body arrangement ; Prothylakoids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The entire life-cycle of maize leaf etioplasts has been followed. Prolamellar bodies with different types of tubular membrane arrangement can be found in the juvenile stages of the organelles, while in mature etioplasts nearly all the prolamellar bodies exhibit an “hexagonal ring” arrangement, which, by optical diffraction, appears to be the most regular and compact possible. The prothylakoid membranes also undergo changes during organelle differentiation, and their different organization and arrangement produce a clear dimorphism between the etioplasts of mesophyll and bundle sheath cells. In senescent etioplasts the prothylakoids are more affected, while the prolamellar bodies appear rather stable, also in situations where protochlorophyll(ide) content is very low. The formation of clusters of osmiophilic globules is coupled with the breakdown of the etioplast membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01276591
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  • 16
    Electronic Resource
    Electronic Resource
    Ultrastructural study of different types of callus from leaf expiants ofAesculus hippocastanum L. (1987)
    Springer
    Protoplasma 138 (1987), S. 89-97 
    Details
    ISSN: 1615-6102
    Keywords: Aesculus hippocastanum ; Callus cultures ; Callus ultrastructure ; Embryogenic callus ; Non-embryogenic callus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cell ultrastructure in three types of callus obtained from leaf explants ofAesculus hippocastanum L. has been studied. Remarkable differences have been shown between the cells of the forerunner E1 callus and those of the callus arising from it, according to the culture conditions. The peculiar characteristics of E1 are the scarcity of intercellular spaces and the occurrence of autophagic vacuoles in the cells. An embryogenic friable callus (E2) is formed in time when E1 is maintained on solid culture medium. The E2 cells show cytological features typical of a higher metabolic level and contain starch. Diffused middle lamella digestion leads to the detachment of small embryogenic cell aggregates consisting of vacuolated parenchymatous-like cells and small meristematic cells which may be regarded as embryoids initials. Shaking E1 in the same liquid medium and subsequent culture on solid medium lead to the differentiation of a non-embryogenic callus (NE), whose cells are very large and highly vacuolated, devoid of starch and with organelle-rich cytoplasm. The NE callus shows a high degree of growth, but does not attain embryogenic competence in time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01281017
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  • 17
    Electronic Resource
    Electronic Resource
    Intrathylakoidal crystal appearance during the vital cycle of spinach chloroplasts (1985)
    Springer
    Protoplasma 126 (1985), S. 153-157 
    Details
    ISSN: 1615-6102
    Keywords: Spinacia oleracea L. ; Chloroplast ontogenesis ; Chloroplast senescence ; Spinach chloroplasts ; Intrathylakoidal crystals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The entire vital cycle of chloroplasts was followed in spinach leaves, in order to determine the plastidial situations leading to the build-up of intrathylakoidal crystals. This kind of inclusion was noticed in the juvenile ontogenetic stages as well as in the senescent chloroplast stage, while intrathylakoidal crystals were not present in the mature organelles. The appearance of such crystals, which are known to consist of ribulose 1,5-diphosphate carboxylase, is interpreted as a consequence of an imbalance between enzyme level and membrane function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01287682
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  • 18
    Electronic Resource
    Electronic Resource
    The ultrastructural development of plastids in leaves of maize plants exposed to continuous illumination (1980)
    Springer
    Protoplasma 102 (1980), S. 131-139 
    Details
    ISSN: 1615-6102
    Keywords: Chloroplast ontogenesis ; Prolamellar body ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Chloroplast differentiation in relation to increasing leaf age has been investigated in maize plants exposed to continuous illumination. In the young leaves the proplastids differentiate into chloroplasts containing well organized grana as well as prolamellar bodies. In the older leaves, while plastids differentiate, the prolamellar bodies are no longer detectable. Chloroplast ability to build up prolamellar bodies does not seems so much a light dependent process as it is affected by cell differentiation rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01276953
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  • 19
    Electronic Resource
    Electronic Resource
    Etioplast-chloroplast transformation in maize leaves: Effects of tissue age and light intensity (1984)
    Springer
    Protoplasma 119 (1984), S. 110-120 
    Details
    ISSN: 1615-6102
    Keywords: Plastid greening ; Zea mays ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The effects of light intensity and cell age on the greening of etioplasts were studied in seedlings of maize. We could see that in the youngest tissues examined by us the etioplast greening is very fast and occurs according to a particular pattern which is characterized by the contemporary presence of grana and large non crystalline prolamellar bodies. On the contrary, in the oldest examined tissues the etioplast greening is slow and the formation of grana appears to be delayed and subsequent to the using up of the prolamellar bodies. In the young tissues the intensity of the light mainly affects the duration of the lag-phase preceding the chlorophyll accumulation, while in the old tissues it also affects the total amount of chlorophyllous pigments, the restraining effect of the light appearing amplified by a concomitant restraining effect of cell age.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01287823
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  • 20
    Electronic Resource
    Electronic Resource
    Chloroplast ontogenesis inHelianthus annuus L. (1978)
    Springer
    Protoplasma 97 (1978), S. 165-172 
    Details
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Research carried out into successively older sunflower leaves has allowed us to follow the different ontogenetic stages leading to the building up of a well-differentiated chloroplast. In all the intrathylakoid compartments of the young plastids there is very electron-dense material whose accumulation causes the dilatation of some thylakoid profiles and, consequently, the forming of roundish bodies. The thylakoid membranes appear as “Lithtly Stained Membranes” which, according to the most recent interpretation, are considered as incompletely organized ones. At a subsequent stage there is an increase of the thylakoid membrane staining along with a decrease of the electron-density of the intrathylakoid compartments that, at the end of the ontogenetic process, appear electrontransparent and flattened. Therefore, the intrathylakoid material appears to have been used up in the forming of well-organized membranes. This particular situation, present in the early ontogenetic stages of the plastids, may be attributed to an initial disequilibrium between the synthesis speed of membranal material and the capability to build up well-organized membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01276691
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