The appearance of male gamete-specific histones gH2B and gH3 during pollen development in Lilium longiflorum.

The male gametic (generative) nucleus within the nearly mature pollen of Lilium longiflorum contains specific variants of histone H2B and H3, which have been designated gH2B and gH3, respectively. Using specific antibodies raised against gH2B and gH3, we examined in detail the temporal and spatial aspects of the appearance of these histone variants during male gametogenesis. Neither gH2B nor gH3 was detected in microsporocytes during meiotic division or in microspores before microspore mitosis. However, both gH2B and gH3 were abundantly present in mid bicellular pollen and these histones continued to be detectable in germinated pollen tubes after pollination. Furthermore, immunocytochemistry revealed that these proteins were present not only in generative nuclei during the maturation process, but also in the two sperm nuclei formed by division of the generative nucleus. By contrast, these proteins were not found in the vegetative nuclei. It appears, therefore, that both gH2B and gH3 are specific to male gametic (generative and sperm) nuclei in L. longiflorum. The results also suggest that these male gamete-specific histones might be newly synthesized in the progenitor of sperm cells for the differentiation of male gametes, as occurs in spermatogenesis in animals.