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In response to abiotic and biotic stress factors the production of reactive oxygen species (ROS) in plant cells is increased and series of cascade reactions for their neutralization are being triggered. Targets of ROS in cells can be various biochemical and physiological processes, as well as cellular organelles including the cytoskeleton. Many abiotic stress factors, by provoking increase of the level of ROS in plant cells, elicit reorganization of the microtubules leading to disruption of mitosis. The reorganization of interphase and mitotic microtubule system was proposed to be an integral part of the response of cells to external stimuli. The state of microtubule system (tubulin cytoskeleton) under various abiotic stresses, including salinity, low temperatures, Al toxicity and fl ooding, was analysed in cells of representatives of family Solanaceae (S. lycopersicum L., S. tuberosum L. and N. tabacum L.) and cereals (T. aestivum L. and H. vulgare L.) by using transmission electron microscopy. Various tubular structures that were structurally different from microtubules were observed in plant cells subjected to abiotic stress. Fibrillar bundles with different densities of their constituent components, macrotubules, orderly packed paracrystalline aggregates and strands having hexagonal packing in cross sections, were observed in potato leaf mesophyll cells under low positive temperature stress, wheat root cells subjected to fl ooding stress, barley root cells under Al toxicity stress, as well as in root cells of tomato and tobacco under salinity stress imposed by NaCl or Na2SO4. The structure of these cytoskeletal elements is identical to stable atypical tubulin polymers induced by different chemical treatments. The presented data suggests that the formation of abnormal tubulin structures in plant cells is a common and non-specific response to various abiotic stress factors. [ABSTRACT FROM AUTHOR]

Utilization of storage starch in the cells of cotyledon mesophyll and root meristem in the course of alfalfa ( Medicago sativa L.) seed germination on the solutions of NaCl, Na2SO4, and mannitol at different concentrations and identical osmotic pressure was investigated using the method of transmission electron microscopy. Ultrastructural analysis showed changes in the number of starch grains and deceleration of chloroplast development depending on the osmotic component of salt influence. At low concentrations corresponding to osmotic pressure of 202.6 kPa, Na2SO4 did not affect the formation of the photosynthetic machinery and utilization of starch inclusions; mannitol contributed to the preservation of considerable reserve of starch without disturbing the development of chloroplasts; NaCl did not inhibit the development of the photosynthetic machinery and induced an increase in the number of starch grains presumably at the expense of newly produced starch. When the concentration of the investigated substances increased up to the values corresponding to the osmotic pressure of 607.8 kPa, NaCl did not suppress transformation of amyloplasts into chloroplasts and utilization of starch; Na2SO4 inhibited the development of chloroplasts and starch utilization; mannitol decelerated transformation of amyloplasts and inhibited mobilization of starch grains. The obtained results make it possible to propose a method of preliminary estimation of tolerance of dicotyledons to abiotic stresses based on the cytological analysis of utilization of starch grains and formation of photosynthetic compartments of chloroplasts in the mesophyll of cotyledons. [ABSTRACT FROM AUTHOR]

The effects of NaCl, Na2SO4, and mannitol on mobilization of storage lipids in the cotyledon mesophyll and root meristem cells during the germination of purple alfalfa ( Medicago sativa L.) seeds were studied using the transmission electron microscopy technique. The ultrastructural analysis showed that the number and shape of specific organelles, oleosomes, depended on the osmotic effects of a salt used. In control seedlings grown on distilled water, lipid mobilization in roots terminated by the 4th day, and in cotyledons, only by the 8th day. The disruptions in the storage lipid mobilization in the treated seedlings were specific and depended on the stress agent used, the osmotic pressure induced by this agent, as well as on the tissue type. The presence of a great number of oleosomes in the cytoplasm of cells subjected to osmotic stress, in contrast to the control ones, demonstrated the inhibition of mobilization processes. All concentrations of Na2SO4 and mannitol suppressed lipid mobilization in the cotyledons and roots. At the same time, NaCl markedly suppressed this process in the root cells only at a higher osmotic pressure of the solution. The results obtained suggest that the cytological analysis of cotyledon storage-lipid mobilization can tentatively assess the resistance of dicotyledonous plants to abiotic stresses. [ABSTRACT FROM AUTHOR]