Dynamic Features of the Pollen Chromatin
Mature pollen grain of the typical angiosperm plant species contains two types of cells. The vegetative cell enables nutrition and transport of the generative cell, which is enclosed within the vegetative cell. The vegetative cell forms an extremely long protrusion called pollen tube at the stigma of the seed parent. During the pollen tube growth through the pistil, the generative cell gives rise to two gametes ? the sperm cells. As a result of an adaptation to different functions, the vegetative cell nuclei differ from the generative and sperm nuclei. The most pronounced difference is apparent in the level of chromatin condensation - the vegetative cell nucleus is highly decondensed in contrast with the compact generative nucleus. It has been shown that the control of chromatin structure is accompanied by changes in histone H4 acetylation and DNA methylation: the condensed chromatin structure is often connected with the DNA hypermethylation and histone H4 underacetylation. Our results in Lilium longiflorumusing the immunocytochemical approach show that the chromatin of vegetative nucleus is (in spite of its decondensed structure) rather histone H4 hypoacetylated and DNA hypermethylated. During the pollen tube growth, the vegetative nucleus becomes extensively histone H4 acetylated and DNA demethylated so that even reaches a higher intensity of histone acetylation and a lower level of DNA methylation in comparison with the generative nucleus. The silent status of the vegetative nucleus probably serves to prevent a premature germination and enables a long term survival of pollen grain in the absence of nutrients. The decondensed status of the vegetative nucleus can be interpreted as a result of the absence of histone H1. Different DNA methylation and histone acetylation patterns were observed in the mature pollen and pollen tubes of Gagea lutea (Liliaceae) which belongs to ephemeral spring species and its pollen is adapted for immediate germination and dynamic pollen tube development. Our study of the global level of methylation using the immunocytochemical approach is ensembled by the study of DNA methylation level of a gene expressed in mature pollen grains of Silene latifolia (Caryophyllaceae), MROS1 (Male Reproductive Organ Specific) using sodium bisulfite based genomic sequencing and restriction analysis of cloned PCR products. - This research was supported by the Grant Agency of the Czech Republic (521/98/POG1).
B. Janousek1, S. Matsunaga 2 and B. Vyskot1
1Institute of Biophysics, Academy of Sciences of the Czech Republic,