The developmental fate of angiosperm pollen is associated with a preferential decrease in the level of histone H1 in the vegetative nucleus |
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Authors: | Ichiro Tanaka Kaori Ono Takuya Fukuda |
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Institution: | (1) Department of Biology, Yokohama City University, Seto 22-2, Kanazawa-ku, Yokohama 236-0027, Japan, JP |
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Abstract: | In angiosperm pollen, the vegetative cell is assumed to function as a gametophytic cell in pollen germination and growth
of the pollen tube. The chromatin in the nucleus of the vegetative cell gradually disperses after microspore mitosis, whereas
the chromatin in the nucleus of the other generative cell remains highly condensed during the formation of two sperm nuclei.
In order to explain the difference in chromatin condensation between the vegetative and generative nuclei, we analyzed the
histone composition of each nucleus in Lilium longiflorum Thunb. and Tulipa gesneriana immunocytochemically, using specific antisera raised against histones H1 and H2B of Lilium. We found that the level of histone H1 decreased gradually only in the vegetative nucleus during the development of pollen
within anthers and that the vegetative nucleus in mature pollen after anther dehiscence contained little histone H1. By contrast,
the vegetative nucleus contained the same amount or more of histone H2B than the generative nucleus. The preferential decrease
in the level of histone H1 occurred in anomalous pollen with one nucleus (uninucleate pollen) or with two similar nuclei (equally
divided pollen), which had been induced by treatment with colchicine. The nuclei in the anomalous pollen resembled vegetative
nuclei in terms of structure and staining properties. The anomalous pollen was able to germinate and extend a pollen tube.
From these results, it is suggested that the preferential decrease in level of histone H1 in pollen nuclei is essential for
development of the male gametophytic cell through large-scale expression of genes that include pollen-specific genes, which
results in pollen germination and growth of the pollen tube.
Received: 9 May 1998 / Accepted: 4 June 1998 |
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Keywords: | Key words: Chromatin Histone H1 Immuno-fluorescence Lilium Pollen Vegetative nucleus |
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