Abstract
The phenomenon of male sterility has often been observed in investigations on the role of histone H1 in regulation of morphogenetic and cytological processes in transgenic tobacco plants. These changes were accumulated by disturbances in flower development, consisting in lengthening of the pistil style in relation to stamen heads. This prevented pollination and production of seeds. As similar abnormalities occurred also in the present investigations (depending on combination, the sterility% was 84.4 to 19.9, at only 8.1 in the control), the main problem of our investigations was an attempt to explain their reasons. It is commonly known that one of the conditions for formation of fertile pollen is the properly functioning tapetum. Here, we carried out observations of ultrastructure of anther tapetum control cells in respect of abnormalities which occurred during microsporogenesis of transgenic plants with inactivated expression of two major (A, B) and two minor (C, D) histone H1 variants. The investigations were carried out on the following groups of plants: (1) control group with a full set of histone variants (K), (2) with inactivated A and B variants (-AB); (3) with inactivated A, B, C and D variants (-ABCD), (4) with inactivated C and D variants (-CD). It was found that tapetal development was normal in all the investigated groups of plants, and the sequence of changes was similar as in the control. However, certain ultrastructural differences appeared when tapetum functioned as secretory tissue, and in the degeneration phase. In tapetal cell cytoplasm, with participation of rER, lipid bodies were formed, which, having penetrated to the cell surface and to locules, took part in formation of pollen grain sporoderm. Both in the control and in the remaining combination, excluding -ABCD, these bodies looked similar: they were grey, homogenous and surrounded by black jagged deposits. In -ABCD plants, these bodies were more translucent, slightly rarefied, and not surrounded by the deposits. Moreover, in -CD plants, large lipid deposits were frequently observed between remainders of degraded tapetal cells. They did not occur in the control and the remaining combinations.
Highlights
The histone H1 is one of the main structural proteins of chromatin, occurring in nucleus of almost all eukaryotic organisms (Kasinsky et al 2001; Jerzmanowski 2002)
Disorders of microsporogenesis process and the percentage of sterile pollen grains were different in particular combinations (Przew3oka et al 2002; lusarczyk et al 2003)
Inner tapetum cells are derived from connective tissues, while outer tapetum cells are differentiated from anther wall layers (Periasamy and Swamy 1966)
Summary
The histone H1 is one of the main structural proteins of chromatin, occurring in nucleus of almost all eukaryotic organisms (fungi, plants and animals) (Kasinsky et al 2001; Jerzmanowski 2002). Experimental reduction of the level of the main H1 variants in tobacco combined with elevated levels of its small variants, has caused various phenotypic changes (Prymakowska-Bosak et al 1999; lusarczyk et al 2001b). Similar changes occurred in our investigations on plants with modified proportion of histon H1 variants (Przew3oka et al 2002). Disorders of microsporogenesis process and the percentage of sterile pollen grains were different in particular combinations (e.g. the percentage of sterility oscillated between 19.9 to 84.4 at the level 8.1 in control plants) (Przew3oka et al 2002; lusarczyk et al 2003)
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