Comparative organization of tubulin microtubules in root cells of Zea mays (Poaceae) and Beta vulgaris (Chenopodiaceae s. str. / Amaranthaceae s. l.) under the influence of clinorotation

In order to identify the mechanism of functioning of the tubulin cytoskeleton, we have investigated the impact of clinorotation on cortical microtubules organization in the process of cell differentiation in growth zones of plant roots of Zea mays and Beta vulgaris. The similar organization of cortical and endoplasmic microtubules’ network in both species is noted. Clinorotation did not significantly change the organization of microtubules in meristem cells and the central elongation root zone. However, in the distal elongation zone of roots, both Z. mays and B. vulgaris expressed deviations of individual microtubules from the ordered transverse organization (at an angle greater than 45º). This deviation of the microtubules is likely caused by clinorotation and results in discoordination of root growth under these conditions. In addition, it has been found that the scope of destruction of the MT network by taxol in the root cells of both species is not dependent on clinorotation.

Ultrastructure of ER-bodies in statocytes and cells of the distal elongation zone of Arabidopsis thaliana (L.) heynh. root apices under X-radiation

Among plants used in spaceflight experiments, species of family Brassicaceaeare considered as the most resistant to radiation exposure. It is supposed that ER-bodies, which are derivative of granular endoplasmic reticulum and selectively accumulate an enzyme β-glucosidase, may be responsible for this resistance. The aim of the study was to investigate the ultrastructure and topography of ER-bodies in statocytes and cells of the distal elongation zone in root apices of A. thaliana seedlings in the control and under X-radiation. Methods. Seedlings grown on agar nutrient medium were treated with X-rays of doses 0.5 Gy, 1 Gy, 2 Gy, 4 Gy, 6 Gy, 8 Gy, 10 Gy, and 12 Gy on the unit RUM-17 (dose rate 0.43 cGr/s). The root apices were fixed with a mixture of epoxide resins. Ultra-thin longitudinal sections were investigated with a transmission electron microscope JEM-1230 EX. Results. It was shown the similarity in the root apex cell ultrastructure in control and under X-radiation. At the same time there were some differences in the ultrustructure of statocytes and cells of the distal elongation zone under X-radiation. An increase in the number of profiles of granular endoplasmic reticulum and the total area of ER-bodies per cell in two hours and ten days after X-radiation more than twice in comparison to control was established. It was revealed the variability of ER-bodies in shape and size depending on the dose of X-rays. The nature of such alterations in the cell may indicate certain changes in metabolism, carried out within the range of cell physiological responses. Conclusions. For the first time, the influence of X-radiation on dynamics of the formation of ER-bodies, which are derivative of granular endoplasmic reticulum, in statocytes and cells of the distal elongation zone in root apices of A. thaliana seedlings has been studied. The increased area of ER-bodies, which contain β-glucosidase (PYK 10), is considered as an adaptive cell response to ionizing radiation.

Actin microfilament and microtubule distribution patterns in the expanding root of Arabidopsis thaliana

Determination of the precise role(s) of actin microfilaments in the control of cell shape and elongation in the root tips of the model genetic system Arabidopsis thaliana (L.) Heynh is frustrated by inadequate microscopy imaging techniques. In this paper, we documented both microfilaments and microtubules in the root tips of Arabidopsis by double immunofluorescence labelling and computer-generated reconstruction of confocal image series. Our procedure, which complements the use of recently developed fluorescent reporter proteins, revealed hitherto undescribed aspects of the Arabidopsis microfilament cytoskeleton that may provide important clues about mechanisms behind cell elongation. We found that preservation of extensive arrays of transverse cortical microfilaments depends on unperturbed microtubule organization. Compared with ordinary epidermal cells, cells situated in the trichoblast or hair-forming cell files were comparatively devoid of endoplasmic microfilaments when in the distal elongation zone, well before hair formation begins. Computer-aided reconstructions also revealed that the nonexpanding end walls of cells in the distal elongation zone have radially oriented microtubules and randomly arranged microfilaments. In dividing cells, microfilaments became more prominent in the cell cortex, and subtle differences between microtubule and microfilament organization were seen within the phragmoplast. These observations will form the basis of understanding the roles of the cytoskeleton in controlling elongation in root tissues. In light of the many Arabidopsis mutants with altered root morphology, our methods offer a reliable approach to assess the function of cytoskeletal proteins and signalling systems in root morphogenesis.Key words: actin microfilaments, Arabidopsis thaliana, distal elongation zone, microtubules, phragmoplast, roots.