Descriptive and Quantitative Study of Ultrastructural Changes in the Apical Meristem of Mustard in Transition to Flowering

1974 ◽  
Vol 16 (2) ◽  
pp. 421-432
Author(s):  
A. HAVELANGE ◽  
G. BERNIER ◽  
A. JACQMARD
Keyword(s):  
Apical Meristem ◽  
Quantitative Methods ◽  
Succinic Dehydrogenase ◽  
Ultrastructural Changes ◽  
Cytoplasmic Matrix ◽  
Membrane Area ◽  
Early Effect ◽  
Long Day ◽  
Transition To Flowering ◽  
In Cells

Transition to flowering was induced in the shoot apical meristem of Sinapis alba (mustard), a long-day species, by subjecting vegetative plants to a single 22-h long day. The ultrastructural changes occurring in the meristematic cells during the complete morphogenetic switch were investigated by quantitative methods. The earliest detectable changes are seen 18 h after the start of the inductive long day. One of these changes is the replacement of the large vacuoles of the cells of vegetative meristems by an increased number of smaller vacuoles in the cells of meristems of plants induced to flower (evoked meristems). The other earliest change is an increase in size of the chondriome. Remarkably enough both changes have in common that they lead to an increase in membrane area and are thus concerned with increased membrane synthesis. In this respect this very early effect of the leaf-generated floral stimulus is very similar to that produced by various animal and plant hormones in their respective target tissues. The large rise in chondriome size is paralleled by an increase in succinic dehydrogenase activity. Both changes certainly reflect a rise in cellular respiratory activity which produces the necessary energy supply for the morphogenetic switch. As the size of the plastidome does not change during the transition to flowering, the plastidome:chondriome ratio decreases markedly. The size of the cytoplasmic matrix is greater in cells of evoked meristems than in cells of vegetative meristems. A first size maximum is reached at 26 h after the start of the long day and a second at 54 h. These 2 maxima occur just prior to 2 mitotic waves culminating respectively at 26-30 and 62 h. The increases in amount of endoplasmic reticulum (ER) and dictyosome number that are found in evoked meristems collected just prior to or at the time of the second mitotic wave are also probably related to the mitotic activation of the tissue. As the size of the vacuolar apparatus considered as a whole does not change at all and the size of the cytoplasmic matrix increases, the vacuoles:cytoplasm ratio decreases in evoked meristems collected following 26 h after the start of the long day. Also, there is an unexpected decrease in the nucleus:cytoplasm ratio in the cells of evoked meristems after 46 h.

Descriptive and Quantitative Study of Ultrastructural Changes in the Apical Meristem of Mustard in Transition to Flowering

1974 ◽  
Vol 15 (3) ◽  
pp. 633-644
Author(s):  
A. HAVELANGE ◽  
G. BERNIER
Keyword(s):  
Apical Meristem ◽  
Sinapis Alba ◽  
Condensed Chromatin ◽  
Ultrastructural Changes ◽  
Point Counting ◽  
Meristematic Cells ◽  
Long Day ◽  
Genetic Activity ◽  
Loss Of Compactness ◽  
Transition To Flowering

Transition to flowering was induced in the shoot apical meristem of Sinapis alba (mustard), a long-day species, by subjecting vegetative plants to a single 22-h long day. The ultrastructural changes occurring in the meristematic cells during the complete morphogenetic switch were quantitatively investigated using both the planimetric and the point-counting stereological methods. The 2 methods yield very similar results and are thus equally appropriate for the study. The cell, nucleus, and dispersed chromatin sizes are greater in meristems of plants induced to flower (evoked meristems) than in meristems of control vegetative plants. A first size maximum is reached at 26 h after the start of the inductive long day and a second at 54 h. These 2 maxima occur just prior to 2 mitotic waves culminating respectively at 26-30 and 62 h. Neither the condensed chromatin size nor the number of chromocentre profiles per nucleus section change. Consequently the dispersed chromatin: condensed chromatin ratio increases in evoked meristems. This change is discussed in relation to current views on the differential genetic activity of the 2 kinds of chromatin. There is a late but large increase in size of the nucleolus. Dramatic changes in texture are associated with the enlargement of this organelle. These changes are the disappearance of the segregation of fibrillar and granular components and a loss of compactness due to marked vacuolation. All these changes in size and structure are interpreted as indicating a late increase in nucleolar synthesis of ribosomes in the evoked meristems.

Ultrastructure and Senescence in an Achloroplastic Mutant of Hordeum vulgare L. cv. Dyan

1992 ◽  
Vol 50 (1) ◽  
pp. 844-845
Author(s):  
R.H.M. Cross ◽  
C.E.J. Botha ◽  
A.K. Cowan ◽  
B.J. Hartley
Keyword(s):  
Cell Wall ◽  
Hordeum Vulgare ◽  
Leaf Tissue ◽  
Ultrastructural Changes ◽  
Hordeum Vulgare L ◽  
Mesophyll Cells ◽  
Lethal Mutant ◽  
Cytoplasmic Matrix ◽  
Close Proximity ◽  
Pinocytotic Vesicles

Senescence is an ordered degenerative process leading to death of individual cells, organs and organisms. The detection of a conditional lethal mutant (achloroplastic) of Hordeum vulgare has enabled us to investigate ultrastructural changes occurring in leaf tissue during foliar senescence.Examination of the tonoplast structure in six and 14 day-old mutant tissue revealed a progressive degeneration and disappearance of the membrane, apparently starting by day six in the vicinity of the mitochondria associated with the degenerating proplastid (Fig. 1.) where neither of the plastid membrane leaflets is evident (arrows, Fig. 1.). At this stage there was evidence that the mitochondrial membranes were undergoing retrogressive changes, coupled with disorganization of cristae (Fig. 2.). Proplastids (P) lack definitive prolamellar bodies. The cytoplasmic matrix is largely agranular, with few endoplasmic reticulum (ER) cisternae or polyribosomal aggregates. Interestingly, large numbers of actively-budding dictysomes, associated with pinocytotic vesicles, were observed in close proximity to the plasmalemma of mesophyll cells (Fig. 3.). By day 14 however, mesophyll cells showed almost complete breakdown of subcellular organelle structure (Fig. 4.), and further evidence for the breakdown of the tonoplast. The final stage of senescence is characterized by the solubilization of the cell wall due to expression and activity of polygalacturonase and/or cellulose. The presence of dictyosomes with associated pinocytotic vesicles formed from the mature face, in close proximity to both the plasmalemma and the cell wall, would appear to support the model proposed by Christopherson for the secretion of cellulase. This pathway of synthesis is typical for secretory glycoproteins.

Ultrastructural Changes in the Root Meristem Cells of Rubus Chamaemorus L. (Cloudberry)

1975 ◽  
Vol 33 ◽  
pp. 562-563
Author(s):  
Arya K. Bal
Keyword(s):  
Root Meristem ◽  
Uranyl Acetate ◽  
Particulate Material ◽  
Ultrastructural Changes ◽  
Cell Organelles ◽  
Cytoplasmic Matrix ◽  
Golgi Membranes ◽  
Rubus Chamaemorus ◽  
Dense Substance ◽  
Ultrathin Sections

In the course of studies in the root meristem tissue of Rubus chamaemorus L. some important changes in the ultrastructural morphology were observed during the initiation of senescence at the end of the growing season.Root meristems were collected from naturally growing healthy populations of Cloudberry plants, and fixed in Karnovsky's mixture or in 2.5% glutaraldehyde in phosphate buffer. The samples were osmicated, dehydrated following usual methods and embedded in Epon. Ultrathin sections were stained in uranyl acetate and lead citrate.Figure 1 shows part of a dense cell in the meristem. The electron density of these cells is due to large amounts of a particulate material in the cytoplasmic matrix. The smallest particle seen in electron micrographs is about 40 A, although larger aggregates are also found, which remain randomly distributed in association with various cell organelles. Dense substance has been found associated with golgi membranes, proplastids, vacuoles and microtubules (Fig. 2).

Ethylene formation in the leaves of short- and long-day tobacco during transition to flowering

1988 ◽  
Vol 30 (6) ◽  
pp. 422-426 ◽  
Author(s):  
Veronika N. Lozhnikova ◽  
V. I. Rakitin ◽  
J. Krekule ◽  
Ivana Macháčková ◽  
M. KChailakhyan
Keyword(s):  
Ethylene Formation ◽  
Long Day ◽  
Transition To Flowering

scholarly journals Agronomic Performance and Flowering Behavior in Response to Photoperiod and Vernalization in Barley (Hordeum vulgare L.) Genotypes with Contrasting Drought Tolerance Behavior

2021 ◽  
Author(s):  
Jamal Abu-Elenein ◽  
Rabea Al-Sayaydeh ◽  
Zahera Akkeh ◽  
Zakaria Al-Ajlouni ◽  
AbdRaheem A. Al-Bawalize ◽  
...  
Keyword(s):  
Drought Tolerance ◽  
Shoot Apical Meristem ◽  
Apical Meristem ◽  
Agronomic Performance ◽  
Short Day ◽  
Drought Tolerant ◽  
Long Day ◽  
Meristem Development ◽  
Rainfed Conditions ◽  
Barley Genotypes

Abstract Background In barley, flowering behavior is a highly regulated and complex process where the appropriate matching of reproductive development with seasonal variation in water availability confer barley adaptation to different environments. In this study, the role of variation in flowering time and drought tolerance in four selected barley genotypes was studied under field and controlled conditions. For this purpose, field trials were conducted for two consecutive seasons at three diverse environments where the studied genotypes were subjected to either rainfed conditions or rainfed plus supplementary irrigation under two different sowing dates. Furthermore, reproductive meristem development in two selected barley genotypes, Rum (drought tolerant) and Steptoe (drought-sensitive) was also assessed in response to both vernalization and water stress under two different photoperiod conditions.Results Variation in the number of days to heading was more pronounced under rainfed conditions than under well water conditions. For agronomic performance, Rum was superior under all tested environments, which assure its general adaptability to multiple environments, while Steptoe was the poorest. The transition to reproductive meristem was faster under vernalized long-day conditions as compared to vernalized short-day conditions. The progress of shoot apical meristem development and heading under long-day conditions was significantly faster in Rum than that of Steptoe. A clear effect of drought stress was observed on shoot apical meristem development in Steptoe. Under short-day conditions, vernalized Rum plants subjected to water deficit showed an advanced meristem development stage a significant earlier HD when compared with non-stressed plants. This early flowering behavior in stressed Rum plants under short-day conditions was accompanied by higher gene expression of the Vrn-H1 gene. Conclusion In conclusion, the integration of vernalization and photoperiod signals in drought-tolerant barley genotypes is associated with early flowering behavior and higher productivity in dry environments.

Ultrastructural Changes in Euglena After Ultraviolet Irradiation

1973 ◽  
Vol 13 (3) ◽  
pp. 799-809
Author(s):  
A. MICHAELS ◽  
A. GIBOR
Keyword(s):  
Ultraviolet Light ◽  
Ultraviolet Irradiation ◽  
Euglena Gracilis ◽  
Structural Changes ◽  
Ultrastructural Changes ◽  
Electron Microscopic ◽  
Bleaching Process ◽  
In Cells

The structural changes associated with the ultraviolet-induced bleaching of light-grown cells of Euglena gracilis were investigated. Our light- and electron-microscopic observations of the bleaching process indicate that there is a continuity of plastid structure in cells 5 generations after receiving a bleaching dose of ultraviolet light. There seems to be a continuous dilution of the plastid thylakoids and a decrease in plastid size in the bleaching cells. There also seems to be a change in the position of the plastids in relation to the mitochondria in the bleaching cells. The plastids and possibly the mitochondria are the only organelles which are affected by the ultraviolet irradiation. The continuity of plastids in bleaching cells of Euglena is discussed in relation to the proposed effect of the ultraviolet light.

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