Ricerche di Citofisiologia della Segregazione
- 1 January 1953
- journal article
- research article
- Published by Taylor & Francis in Giornale botanico italiano
- Vol. 60 (3) , 463-517
- https://doi.org/10.1080/11263505309432118
Abstract
Researches on the cytophysiology of secretion, excretion and recretion. I. Sectal nettaria. Flower buds, flowers and young fruits of Canna indica, Hemerocallis citrica, Kniphophia Krooki and Funkia ovata were fixed at different stages of development. The structural changes in the sectal nectaria of these species were observed, and the following four main phase distinguished: I. Differentiation, from the first appearance of the epidermal primordia in the sectal nectarium (ENS) to its complete differentiation; II. Accumulation, characterized by the passage of a noticeable amount of material from the carpellar parenchym to the cells of the ENS; III. Expulsion, wich is the true phase of secretion of the material previously accumulated; IV. Restoration, wich includes the period of life of the cells of the ENS, after the end of the' secretion phase (this last phase may be observed only on those nectaria wich do not degenerate soon after the third phase). Nucleic acid (NA) was estimated by means of the Feulgen's reaction, for desoxyribonucleic acid (DNA), and of Brachet's technique, modified by Gerola and Vannini, for ribonucleic acid (RNA). This last method, by staining in buffered media, allows an estimation of the concentration of RNA in the cell structures, as these appear stained in a green-bleu color at pH values so much lower, as content in RNA is lower. The cytochemical study was integrated, for Canna, by statistical determinations of nuclear and nucleolar volumes of the ENS cells, in the various phases of secretion. Table X shows the distribution of the nuclear diameter of the ENS cells of Canna, for five successive periods of fixation. Fig. 1 shows the diagram of the distribution of frequencies of nuclear diameters. Average diameters, standard errors and variability coefficients are reportes in Table. XI. Table XII, fig. 2 and Table XIII show the corresponding figures for the nucleolus. Table XIV, fig. 3 and Table XV show the analogous values for the ratio nucleus to nucleolus (N/n), calculated on the basis of the diameters of these two structures. Tables XVI, XVII and XVIII show the values of the Student's «t», between the average values of nuclear diameters and, respectively, of the nucleoli and of the N/n ratio. The diagram of fig. 4 illustrates the virage to a violet color of the cytoplasm of the ENS cells of Kniphophia (methyl-pironine staining in buffered solutions). On the abscissa are the pH values of the staining solution, on the ordinate the stages of bud fixation. The arrows separate the successive secretion phases. In fig.5 the analogous diagram of the virage to the green color of chromatin, and in fig. 6 the virage of the nucleoli to a dark red color are reported. The analogous diagrams for Hemerocallis are shown in figg. 7, 8 and 9, the same for Canna in figg. 10, 11, 12. Fig. 10 shows also two curves: the dotted line indicates the values of the N/n ratio, calculated by making = 10 the initial ratio; the solid line indicates the nuclear diameters in the different phases, calculated by making = 10 the inital nuclear diameter. Fig. 11 shows the curve of the nucleolar diameters, constructed attributing a value of 10 to the nucleoli of the earliest phase of the nectarium. The fig. 13 illustrates the behavior, somewhat schematized, of the ENS cells during the successive phases of secretion. As a whole, it may be observed that some of the nectaria degenerate very quickly, showing a variably rapid lysis of chromatin and nucleolus. Some times, at earliest stages of degeneration, the comparison of vacuolized or anulated nuclei may be observed. On the other hand in those of the sectal nectaria wich do not degenerate rapidly, the general cycle of secretion may be resumed as follows a). Differentiation phase. The cells enlarge and vacuolize. In the cytoplasm the RNA decreases. Nuclei show only a moderate tendency to enlarge. Chromatin has never a very compact aspect (at least uniformly in the whole nucleus) and it appears rather diffuse. Nucleoli do not show noticeable variations in volume, and they mantain unchanged their content in RNA. b). Accumulation phase. The cells reach their maximal dimension and on their surface large papillae ar often recognizable. In the cell a very remarkable and rather rapid accumulation of nectariferous granula is observed: the granula give a positive reaction for RNA, though this acid appears present at low concentrations. Nuclei are very-large, larger than in the earliest stages. Their form may be little changed, or they may present-very accentuated protuberances: these are to be put in relation with the enlargement coefficent of the nuclei, as they are so nuch more accentuated as greater is the nuclear enlargement. Chromatin appears to be in a very diffuse state, particularly in the largest nuclei, and its DNA partially.depolimerised. The volume and the content in RNA of the nucleoli are steadly decresasing from the beginning to the end of this phase. c). Expulsion phase. At the beginnig of the expulsion large vacuols appear, often situated in the direction of the cavity of the nectarium (Hemerocallis). As nectar secretion proceeds, the cells lose their nectariferous granula and also their RNA, wich seems to be expelled together with the granula, transformed into liquid nectar. Typical of this phase are nuclei showing their chromatin condesed in chromocentres, or in thikc clods, simulating a prophase (Kniphophia), or in a single compact mass (picnotic nuclei of Hemerocallis and Kniphophia). Nucleoli are very small, with a tendency to desappear. When present, they are very poor in RNA. d). Restoration phase. The cells show again moderate dimension and in the scanty cytoplasm little, if any, RNA is observed. In the nucleus, the chromatin, non longer condensed into compact masses, is now very diffuse or it appears in chromocentres standing by the nuclear membrane. Nucleoli are always present, with an amount of RNA lower than that they show at stages earliest than secretion phase. These chemical-morphological variations of the nuclei could be put in relation 1). For the accumulation phase, with the intense metabolic synthesis through wich nectariferous granula ere accumulated in the cell. It is know that nuclear structures similar to those described above are usually found in cells endowed with an intense synthetic activity. It is to be noted, howerer, that in the ENS nuclei an enlargement of the nucleoli due to chromatine dispersion was not observed, probably as consequence of the strong request of RNA from the cytoplasm, and of the particular type of synthesis (essentially carbohydrates) in the nectariferous granula. 2). In the expulsion phase, the transfer of RNA from the nucleus (from chromatin as from nucleoli) to the cytoplasm, and the complete breakdown of this acid in the course of the secretion process. The typical aspect of the nucleus could be a result of the loss of RNA, and of the concomitant loss of proteins. 3). In the restoration phase, what is most notewothy is the reappearence of the nucleoli. These should originate, directly or indirectly, from the DNA, wich (as I have observed in foregoing works) should have weight in this regard, beyond the mitosis too. Moreover, plasmatic synthesis appears to be precedeed by the reppearence of the nucleolus, and this by the recharge of chromatin with RNA. From what we have related above, the following points seem the most worthy pf consideration a). The possibility to represent in a single scheme the complex of phenomena of nectariferous secretion in their evolution, as far as the chemical and structural modification of the cells are concerned. b). The description and the intepretation of those changes, wich occour in the ENS cells during the various phases of the secretion. c). The demostration of a continuous loss of RNA from the cytoplasm, the chromatin, and the nucleoli, during the phases of accumulation and expulsion. d). The recharge in RNA in the restoration phase, at first in the chromatin, then in the nucleolus and at last in the cytoplasm. e). The confirmation of the clear relation between nuclear structures and cell function, as well as between chromatin and nucleolus.Keywords
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