Brassica napus pollen development during generative cell and sperm cell formation

Abstract

Brassica napus pollen development during the formation of the generative cell and sperm cells is analysed with light and electron microscopy. The generative cell is formed as a small lenticular cell attached to the intine, as a result of the unequal first mitosis. After detaching itself from the intine, the generative cell becomes spherical, and its wall morphology changes. Simultaneously, the vegetative nucleus enlarges, becomes euchromatic and forms a large nucleolus. In addition, the cytoplasm of the vegetative cell develops a complex ultrastructure that is characterized by an extensive RER organized in stacks, numerous dictyosomes and Golgi vesicles and a large quantity of lipid bodies. Microbodies, which are present at the mature stage, are not yet formed. The generative cell undergoes an equal division which results in two spindle-shaped sperm cells. This cell division occurs through the concerted action of cell constriction and cell plate formation. The two sperm cells remain enveloped within one continuous vegetative plasma membrane. One sperm cell becomes anchored onto the vegetative nucleus by a long extension enclosed within a deep invagination of the vegetative nucleus. Plastid inheritance appears to be strictly maternal since the sperm cells do not contain plastids; plastids are excluded from the generative cell even in the first mitosis.

Ultrastructural changes ofArabidopsis thalianapollen during final maturation and rehydration

“…The cytoplasmic channels in the in tine layer which are present at the closed anther stage may be involved in the translocation of nutritive solutes from the tapetum/locular fluid to the developing pollen grain (Mascarenhas, 1975;Pacini et al, 1985;Murgia et al, 1991). The disappearance of these cytoplasmic channels during the terminal stage of pollen maturation may mark the blocking of gametophytic-sporophytic exchange and indicate the isolation of the pollen grain from its environment.…”

Rearrangement of the actin filament and microtubule cytoskeleton during induction of microspore embryogenesis inBrassica napus L. cv. Topas

“…21, Agriculture and Agri-Food Canada, Ottawa, Ontario K1A 0C6, Canada. microspore, while the plastids and very small vacuoles accumulate at the opposite pole (Fan et al 1988, Kott et al 1988, Murgia et al 1991, Telmer et al 1993. Changes have also been observed in the actin microfilament (MF) and microtubule (MT) cytoskeleton (Simmonds et al 1991(Simmonds et al , 1998Hause et al 1992;Gervais et al 1994;Simmonds 1994;Simmonds and Keller 1999).…”

“…We have found that MFs in the phragmoplast are amongst the most stable of actin structures in microspore and pollen development as they are preserved by a variety of preparative techniques (Gervais et al 1994). After the first pollen mitosis, the bicellular pollen grain consists of a small generative cell, which is devoid of plastids, and a large vegetative cell (Fan et al 1988, Kott et al 1988, Murgia et al 1991, Telmer et al 1992.…”

Biogenesis and function of the lipidic structures of pollen grains

“…In addition to the elaioplast, another type of lipid body has been described in the tapetal cytoplasm of a wide range of plant families including the Liliaceae (Reznickova and Willemse 1980), Apocynaceae (Cousin 1979), Tiliaceae (Hesse 1993), Lamiaceae (Ubera Jimenez et al 1996, Geraniaceae (Weber 1996) and it is particularly well described in the Brassicaceae (Dickinson and Lewis 1973;Polowick and Sawhney 1990;Murgia et al 1991;Ferreira et al 1997;Wang et al 1997;Wu et al 1997;Murphy and Ross 1998). Similarly to cytoplasmic storage oil bodies from seeds (Hills et al 1993;Sarmiento et al 1997), the tapetal cytoplasmic lipid bodies are probably derived from the ER (Hesse 1993;Hesse and Hess 1993;Weber 1996;Murphy and Ross 1998).…”