[Efficiency of the Induction of Cytomixis in the Microsporogenesis of Dicotyledonous (N. tabacum L.) and Monocotyledonous (H. distichum L.) Plants by Thermal Stress].

The efficiencies of the induction of cytomixis in microsporogenesis by thermal stress are compared in tobacco (N. tabacum L.) and barley (H. distichum L.) It has been shown that different thermal treatment schedules (budding tobacco plants at 50°C and air-dried barley grains at 48°C) produce similar results in the species: the frequency of cytomixis increases, and its maximum shifts to later stages of meiosis. However, the species show differences in response. The cytomixis frequency increase in tobacco is more pronounced, and its maximum shifts from the zygotene­pachytene stages of meiotic prophase I to prometaphase­metaphase I. Later in the meiosis, aberrations in chromosome structure and meiotic apparatus formation typical of cytomixis are noted, as well as cytomixis activation in tapetum cells. Thermal stress disturbs the integration of callose- bearing vesicles into the callose wall. Cold treatment at 7°C does not affect cytomixis frequency in tobacco microsporogenesis. Incubation of barley seeds at 48°C activates cytomixis in comparison to the control, shifts its maximum from the premeiotic interphase to zygotene, and changes the habit of cytomictic interactions from pairwise contacts to the formation of multicellular clusters. Thermal treatment induces cytomictic interactions within the tapetum and between microsporocytes and the tapetum. However, later meiotic phases show no adverse consequences of active cytomixis in barley. It is conjectured that heat stress affects callose metabolism and integration into the forming callose wall, thereby causing incomplete closure of cytomictic channels and favoring intercellular chromosome migration at advanced meiotic stages.

Intra- and intertissular cytomictic interactions in mic-rosporogenesis of mono- and dicotyledonous plants.

A comparative cytological analysis of intra- and intertissular cytomictic interactions in early micro-sporogenesis of mono- and dicotyledonous plants was performed by the example of the two cellular systems - microsporocytes and tapetum. It is found that cytomixis is the component of intratissular interactions mainly. In the tapetum cells cytomixis is notable for structural and temporary taxon specific features. The nuclear migration in microsporocytes is confined mainly to zygotene-pachytene meiotic stages and characterized by a certain synchronism with cytomixis at the tapetum. Intertissular cytomictic interactions (tapetum - microsporocytes) were found in the monocot anthers only. Intertissular interactions are likely to reflect the intensification of competitive relations between the tapetum and microsporocytes for area in the process of anther tissue differentiation. Polyploid tapetum nucleus and syncytia being powerful acceptors are able to compete with microsporocytes and direct the chromatin translocation to their favor. The absence of intertissular interactions in dicots probably reflects a better balance between the processes of differentiation at somatic and generative tissues into microsporangium compared to monocots.

[Cytomixis and its role in the regulation of plant fertility].

UV and gamma irradiation of barley seedlings induces an increase in the number of various pathologies in the male reproductive system of plants. The majority of cytological abnormalities are rather nonspecific. The main type of the observed pathologies of microsporogenesis is cytomixis, whose activation correlates with a callose hypersecretion in microsporocyte walls. A negative correlation between cytomixis and the sterility of microspores (in the case of gamma irradiation) or the sterility of mature pollen grains (in the case of UV-B irradiation) is revealed. It is supposed that cytomixis represents a kind of a premeiotic cell selection in plants characterized by an intraorganismic genetic heterogeneity (mosaics). The novelty of the idea is that the cytopathology that accompanies cytomixis is considered as a mechanism of the induced death of genetically imbalanced or nonrepairable cells, which is intended to keep the fertility of a male reproductive system. The activation of this mechanism has a threshold character.

[Cytomixis, its nature, significance and the cytological consequences].

Cytomixis is the widespread natural process of intercellular interaction which is characteristic for vegetative and generative tissues in both normal and pathological conditions. The origin significance and genetic control cytomixis still remain not completely clear. The popularity of view of the pathological nature of cytomixis based on its peculiar plants with genetic instability and impaired homeostasis. In the genetic control of cytomixis seem to be involved meiotic genes which are responsible for segregation and organization of chromosomes. Their activity is modified by environmental factors through signal transduction. It is assumed via cytomixis, from one side, the informational contact can be reached and meiosis and gametogenesis are synchronized, with another, increase of the genetic variety and level of the heterozygosis of microsporocytes. The activity of cytomixis varies over wide limits. The greatest influence on its activity have mutagenesis hybridization and polyploidy. In this context cytomixis can fulfill the function of cell selection which is activated by exceeding of the threshold level of the microsporocyte damages (or genetical disbalance).

[Structural architectonics of apical root meristems in coherence with the quantitative assessment of its damage by radiation].

The dose dependencies of the aberrant anaphases frequency in the root meristem in 48 hours after irradiation in the range of doses of 4-10 Gy is characterized by threshold and plateau at 33% aberrant anaphase. The plateau indicates the activation of the recovery processes. Topology of cell rows in the primary meristem of the dose to 8 Gy are conserved and recovered damages. New cell rows are formed by local cell pools in the distal meristem, pericycle cells and subepidermy. It grows by intrusive character displacing the rows of damaged cells. Apparently the competition between clones of normal and aberrant cells plays the primary role in the mechanisms of recovery. Resulting to competition the promotion of aberrant cells to the extension zone is slowed down or blocked. So critical level of damage of the root apical meristem was defined about 50% of aberrant anaphase. Exceeding of this level leads to lethal consequence for meristem and it is accompanied by the inclusion of more radical process of restoration through regeneration. Regeneration leads to complete replacement of the apex tissues including the extension zone.

[Critical level of radiation damage of root apical meristem and mechanisms for its recovery in Pisum sativum L].

The dose dependencies of growth and cytogenetical values have been built to determine the critical level of root apical meristem damage induced by cute irradiation in the range from 2 to 20 Gr. We have analyzed the frequencies of aberrant anaphases and the aberration distribution per cell, on the one hand, and the growth of biomass, the survival and regeneration of the root meristem, on the other hand. The critical level of damage to the stem apical meristem and root of seedlings was defined as 44-48% of aberrant anaphase. Exceeding of this level leads to the launch of suicidal program through induction of multiaberrant damages and interphase cell death. It appears that competition of clones of non-aberrant cells, the cells bearing 1 and 2 damages and multiaberrant cells plays the primary role in the mechanisms of recovery. The regeneration provides full or partial restoration of the main root apical meristem. However these local processes are insufficient to restore morphogenesis and survival of seedlings in excess of the critical level damage.

[Cellular and tissue mechanisms of restoration processes in Hordeum distichum L. after irradiation].

The ionizing and UV-B irradiation of barley seedlings results in an increase of a number of chromosome aberrations in vegetative and generative meristems as well as pathology in the microsporo- and microgametogenesis. Dynamics of chromosome aberration formatting in root meristem has the invert correlation to the dose of irradiation. Induced damages in the range of not significant doses of irradiation were discovered during the whole ontogenesis of the plants. The increase of irradiation dose has activated the cytolysis processes during pre-meiotic interphase and early meiosis that caused the decrease of pollen grain pathology count. Fertility of pollen grains restored under the maximum exposition of ultraviolet and moderate doses of gamma irradiation. This may be result of cell competition. Cell competition under irradiation limits mutagenesis, regulates the condition and quantity of cell population, causes reparation of fertility and maintains homeostasis.

[Polyspermism and antipodal fertilization in Lilium (Tourn.) L. species].

It has been shown that several pollen tubes can penetrate into the embryo sac on the source side of the antipodal apparatus. One of the pair of sperms of additional pollen tube copulates with the upper antipodal, the second sperm copulates with the lower antipodal or rarely penetrates in the central cell. The process of fertilization was accomplished by the phase of nuclei morphological similarity characteristic ofsyngamy (by postmitotic type of fertilization according to Gerasimova-Navashina). A directional growth of additional pollen tubes involves a specifically differentiation of antipodal cells that imitates the egg cell.

[The influence of UV-B radiation on reproductive function of Hordeum vulgare L. plants].

It has been shown that ultraviolet-B radiation induced acceleration of flowering and differentiation of sexual spike elements in barley. Increasing of pollen asynchronous development and variability of pollen grains with growing of pollen grain sterility were observed as well. The productivity of plants irradiated with UV-B radiation did not change. Considerable doses of irradiation resulted in decreasing of pollen sterility by intensification of haplontic cell selection. The influence of UV-B radiation on the plants can be considered as a genotoxical effects via formation of initial cell DNA damages and photoinduction.

[Analysis of reproductive development of mutant Nicotiana sylvestris plants resistant to isopropyl-N-phenylcarbamate].

An analysis of Nicotiana sylvestris mutant plants resistant to isopropyl-N-phenylcarbamate (IPC), one of the representative from phenylcarbamate herbicides, was carried out. The plants were characterized by pollen semi-sterility caused by disruptions during microsporogenesis and cytoplasm synthesis in microspores. Low seed productivity of mutant plans was caused by the high pollen sterility and partially by the low vital activity of seed-buds. Obtained data testify that mutations inducing IPC-resistance lead to cytogenetical and morphological abnormalities in male generative system development, that results in decreasing of seed productivity in N. sylvestris mutants. Character of discovered cytological disruptions testifies about possible defects in organization and functioning of microtubules in mutant plants that can correlate with mutation(s) in one or several microtubule protein genes.