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Autoradiographic studies of 3H-uridine incorporation (20-min incubation) and dynamics of radioactive particle translocation from nucleolus into cytoplasm (following 80-min postincubation in non-radioactive medium) in root meristematic cells of soybean have been carried out. The experiment was performed with plants subjected to 4-day acclimation in chilling or subjected to 2-hour cold stress and control plants. Three cultivars of soybean: Mazowia, Polan and Progres (cultivated in Poland) were used in the experiment. It has been shown that in control conditions the greatest number of RNA precursor is incorporated into nucleoli after 20-min incubation. Following 80-min postincubation cytoplasm is the most radioactive area of the cell - this mainly testifies to dynamic translocation of radioactive ribosome subunits from nucleolus into cytoplasm. In chilling conditions the reduction of 3H-uridine incorporation into cells occurs, as compared to control conditions. Plants subjected to a 4-day acclimation incorporate the radioactive precursor more intensively than plants subjected to cold stress. Following 80-min postincubation - in the case of acclimated plants - the nucleolus is the most radioactive area of the cell, which testifies to accumulation of pre-rRNA in it. After the cold stress cytoplasm is more radioactive than the nucleolus. In all three cultivars the processes of synthesis and transport of pre-rRNA particles are similar, only their intensity is different. Morphometric measurements of nucleoli in all cultivars subjected to 4-day chilling have shown that root cell nucleoli are larger than those in control. This phenomenon can be connected with stronger inhibition of rRNA transport than its synthesis.
Root meristem nucleoli from soybean (Glycine max. cv. Aldana) seedlings germinated for 3 days at 25°C and then for 4 days at 10°C or still at 25°C (control) were examined. Chill was observed to reduce root meristematic zone growth 15-fold. Nucleoli doubled their volume at 10°C. Autoradiographic studies showed that after 20 min 3H-uridine incubation at 10°C, incorporation of this precursor (postincubation time 0) into nucleoli of chilled seedlings was 4.7 times weaker than in the control. After 80 min postincubation in nonradioactive medium, the cytoplasm became the most intensely labelled cell area in the control material, while in chilled roots the nucleoli were still most intensely labelled and the cytoplasm was 11 times less labelled than in the control. The increase in nucleoli volume at 10°C is suggested to result from greater cold-induced inhibition of the dynamics of maturation and transport of ribosome subunits than of rRNA synthesis dynamics. Ultrastructural studies of chilled seedling nucleoli showed a significant decrease in the fibrillar component and an increase in the granular component, forming characteristic clusters. They are supposed to correspond to shortened and condensed pre-rRNA transcription complexes (compacted "Christmas trees").
"Elaioplasts" observed in Vanilla planifolia, Funkia Sieboldiana and Althaea rosea exhibit all the features characteristic of lipotubuloids earlier described in Ornithogalum umbellatum. They are cytoplasmic domains containing aggregates of lipid bodies connected with microtubules. The immunogold technique confirmed the presence of tubulin in this domain. These structures do not have their own membranes but they are surrounded by a tonoplast at the side of a vacuole since they invaginate into it. In cytoplasm of this domain among lipid bodies there are numerous ribosomes, ER cisternae and vesicles as well as few mitochondria, Golgi structures and microbodies while at older developmental stages there are also autolytic vacuoles. The fact that they are so similar to O. umbellatum lipotubuloids suggest that "elaioplasts" of V. planifolia, F. Sieboldiana and A. rosea can also be named lipotubuloids.
Lipotubuloids in ovary epidermis of Ornithogalum umbellatum which are a domain of cytoplasm containing a lot of lipid bodies, microtubules and actin filaments, ribosomes, endoplasmic reticulum as well as scarce mitochondria, microbodies, dictyosomes, autolytic vacuoles, exhibit progressive-rotary motion. The immunogold method demonstrated that microtubules and actin filaments of lipotubuloids might be connected with one another by myosin and kinesin. It was supposed that collaboration of motor proteins with actin filaments and microtubules makes autonomic high peripheral speed rotary motion of lipotubuloids in epidermis cells possible. Moreover, myosin was also detected in Golgi bodies in lipotubuloid. In lipotubuloids, the immunogold method demonstrated immunosignals after the use of an antibody to dynein light chains but spectroscopy mass analysis showed that in O. umbellatum epidermis lacked dynein heavy chains.
In the cells of Haemanthus albiflos leaf epidermis there are structures containing lipids analogous to ‘‘elaioplasts’’ (Wakker in Jahrb F Wiss Bot 19:423–496, 1888). Ultrastructural analysis has shown that they are cytoplasmic domains—lipotubuloids, since they exhibit all the features of Ornithogalum umbellatum lipotubuloids. They are composed of numerous lipid bodies surrounded by microtubules, ER cisternae and vesicles, some mitochondria, Golgi structures, and microbodies. In the center of some lipotubuloids there are also autolytic vacuoles. Microtubules adjacent to H. albiflos lipid bodies were revealed only when taxol preincubation was used before fixing the epidermis in the mixture of glutaraldehyde and OsO₄. The presence of tubulin in H. albiflos and O. umbellatum lipotubuloids was confirmed with use of the immunogold method involving antibodies against tubulin α. It is possible that the association of microtubules with lipid bodies may be more common than originally thought, but it is difficult to reveal due to the methodological problems.
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