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.

[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.