1,720,983 research outputs found
Découpage e sinossi nell’analisi delle pratiche educative
No full textNell’ampio panorama delle metodologie per l’analisi delle videoriprese una prospettiva assai significativa viene suggerita dalla ricerca francese sulle pratiche educative. Questo contributo nasce dall’intento di descrivere specificatamente due dispositivi metodologici che, fra tanti, si distinguono per innovazione, analiticità e pluralità di sguardi: la découpage e la sinossi
LOCATION OF HEITZ ZERSTAUBUNGSSTADIUM (DISPERSION PHASE) IN THE MITOTIC-CYCLE OF PHASEOLUS-COCCINEUS AND THE CONCEPT OF ANGIOSPERM ENDOMITOSIS
No full textDNA microdensitometry and autoradiography after treatment with 3H-thymidine were used to study the phase of dispersion of chromocenters (Z phase) in parallel with chromocentric nuclei in Phaseolus coccineus. In all materials studied, two types of chromocentric nuclei were present. In radicle apices of dry seeds, two classes of nuclear DNA contents were measured, 2 C (G 1) and 4 C (G 2). The 2 C DNA class comprised all chromocentric type I nuclei, the 4 C class included Z phases and chromocentric type II nuclei. The 4 C (G 2) condition of Z phases implies that Z phases maintain their nuclear structure for some time after the end of DNA replication. Shoot apices also contain 2 C (G 1) and 4 C (G 2) nuclei but 4 C nuclei (Z phases and chromocentric type II nuclei) are rare. In seedling root apices, Z phases are from 1.02 to 4.08 times as frequent as prophases. This excludes that Z phase is a very early prophase. DNA microdensitometry shows that the chromocentric type I includes 2 C (G 1) nuclei and nuclei in the first part of the S phase, Z phases include 4 C (G 2) nuclei and nuclei in the last stage of the S phase and chromocentric type II includes mainly 4 C (G 2) nuclei and nuclei in the second part of S. After 90 minutes of treatment with 3H-thymidine all Z phase nuclei are labeled. This result and the microdensitometric data unequivocally demonstrate that Z phase is located at the end of S. The present results and those of previous authors on Z phase are discussed in relation to Geitler's concept of Angiosperm endomitosis. It is concluded that the term "Angiosperm endomitosis" must be abandoned and substituted by the term "chromosome endoreduplication"
EFFECT OF LIGHT AND GIBBERELLIC-ACID ON COLEOPTILE AND 1ST FOLIAGE-LEAF GROWTH IN DURUM-WHEAT (TRITICUM-DURUM DESF)
No full textA comparison has been made of the relative effectiveness of light quality and quantity and gibberellic acid (GA3) treatment on the elongation growth of the coleoptile and the first foliage leaf in durum wheat (Triticum durum Desf. cvs. Cappelli and Creso). The cultivar Creso is a shortstrawed variety carrying the Gai 1 gene on chromosome 4A, which influences both plant height and insensitivity to applied gibberellins. The main conclusions are as follows: 1) coleoptile elongation growth appears to be modulated via the fluencerate-dependent action of a blue-light receptor and via a low energy response of phytochrome; 2) the inhibition of first-foliage-leaf growth depends on the operation of a single blue-light-responsive photoreceptor; 3) high energy blue light produces the same inhibitory effect on the two wheat cultivars, whereas at relatively low fluences of white and blue light, the cultivar Creso is more sensitive; 4) the insensitivity to applied GA3 exerted by the gene Gai 1 in Creso is independent of light; 5) in Cappelli, the action of light on coleoptiles appears to be independent of the applied GA3, whereas the hormone is able to change the pattern of growth inhibition of the first-foliage-leaf
EFFECT OF LIGHT AND GIBBERELLIC-ACID ON CELL-DIVISION IN THE 1ST FOLIAGE LEAF OF DURUM-WHEAT (TRITICUM-DURUM DESF)
No full textThe present paper is part of a research program which aims at a quantitative analysis of the effects of light and gibberellic acid (GA3) on growth of the first foliage leaf in durum wheat (Triticum durum Desf.). Since leaf growth is the combined result of the increase in cell number (cell division) and cell enlargement, the influence of light and GA3 treatment on cell division in the basal meristem of the first leaf in two cultivars, Cappelli and Creso, was investigated. Creso is a short-strawed cultivar carrying the Gai 1 gene which influences both plant height and insensitivity to applied GA3. Cell division, as measured by mitotic index, was similar in darkness, continuous red light and dichromatic irradiation (far-red plus red), while lower mitotic rates were observed under continuous far-red light: this indicates that the response of cell division is modulated by a high-irradiance reaction of phytochrome in both cultivars. The two cultivars showed different responses to blue light. In Cappelli, blue light and dichromatic irradiation (blue plus red) gave lower mitotic indices than the dark control, indicating the action of a specific blue-light-absorbing photoreceptor, whereas in Creso the response kinetics to all light regimes which included blue light were more complex. On the basis also of the results obtained with GA3 application in Cappelli, it appears that (i) the hormonal treatment is able to change the pattern of mitotic index only in the presence of the action of a blue-light receptor and (ii) the different responses of the two cultivars could be the result of different endogenous hormonal levels. The importance of the observations in relation to the data for first-leaf longitudinal growth reported in a previous paper (Baroncelli et al. 1984, Planta 160, 298-304) is discussed
DIPLOIDY AND CHROMOSOME ENDO-REDUPLICATION IN THE DEVELOPMENT OF EPIDERMAL-CELL LINES IN THE 1ST FOLIAGE LEAF OF DURUM-WHEAT (TRITICUM-DURUM DESF)
No full textThe development of epidermal cell lines in the first foliage leaf of Triticum durum was studied with a combined cytological and DNA cytophotometric analysis. It was shown that: (1) At emergence, the distal portion of the leaf is made of the cells pre-existing in the embryonic leaf and the mitotic activity is localized at the base of the leaf lamina (basal meristem). (2) The proliferating protoderm (outermost cell layer of the basal meristem) contains a meristematic cell population and a differentiating cell population. The cells produced by the protoderm differentiate with 2C, 4C, 8C, and 16 C nuclear DNA contents. (3) The endoreduplicated cells (EC) together with 4C cells form prominent cell rows in the leaf epidermis. The interstomatal cells (ISC) are all 2 C and the inter-hairs cells (IHC) are mostly 2 C (rare 4 C cells lie adjacent to the EC). (4) In the fully developed leaf, the frequency distribution of EC (8 C and 16 C) and 4C cells in a given epidermal segment (Fig. 1) corresponds to the frequency established in the epidermis differentiation zone (zone b, segment 1) at the time of development of that segment:e.g., segment 6 developed at 1-2 days after seed germination, segment 5 at 3 days after germination and so on. (5) Epidermal cell elongation starts in segment 1 and reachs its maximum in the older leaf segments, 5 and 6. The rate of cell elongation is independent of nuclear DNA content; chromosome endoreduplication precedes elongation. (6) The possibility of using epidermal cell parameters in studies on first leaf growth in T. durum is discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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