On some anomalies during megasporogenesis in Gasteria verrucosa (Liliaceae)

Meiotic division of the megaspore mother cell in Gasteria gives rise to unequal dyad cells. The next division is non-synchronous producing an intermediate triad stage. In tetrads the cell wall between the micropylar cells has an irregular shape, random orientation, and is sometimes incomplete. Normally the micropylar cell degenerates first. Rarely the second cell from below may either show characteristics of the functioning megaspore or may degenerate earlier. Degeneration is related to deficient nutrient supply and loss of turgidity of the megaspore and physical pressure of the functioning megaspore. Lower osmolarity, electron dense cytoplasm, incomplete wall synthesis are the early symptoms of degeneration. Genetical constitution, the callose deposition, the cell organell polarity, the position of plasmodesmata, contribute to the selection of one functional megaspore, but also the favourable location for the low nutrient flow to the surrounding nucellar tissue.