Disposition of Pollenin situand its Relevance to Anther/Pollen Culture

Abstract

Disposition of pollen in immature anthers of Hordeum vulgare is illustrated by scanning and transmission electron microscopy. Freeze-fracture confirms that the pollen is confined to a uniseriate column aligned against the tapetum. There is no free pollen in the lumen of the anther loculi. In contrast, in Nicotiana tabacum and Paeonia lactlflora the pollen is disposed at random and occupies the whole of each loculus. Freezing preserves the fluid content of the loculi, appearing in fracture profiles as an amorphous matrix in which the pollen is embedded. The matrix, which generally obscures the tapetum, is present throughout the microspore phase but diminishes as the spores enlarge. It is still present in N. tabacum and H. vulgare at the first pollen division, fragmentary at this stage in P. lactiflora, but is no longer discernible in any of the species at the onset of pollen-grain maturation. Pretreatment of excised Hordeum spikes at 4 °C during the microspore phase, a prerequisite for anther/pollen culture, disrupts the normal developmental sequence but does not alter the uniseriate disposition. Before the spores start to divide, however, the tapetum degenerates and the fluid phase is dispersed. The observations are discussed in relation to isolated pollen culture, float culture of anthers and the switch in programme from gametophytic to sporophytic development.