Megasporogenesis in normal and a synaptic-mutant (sy-2) of Solanum commersonii Dun

Nomarski differential interference contrast microscopy was used to study megasporogenesis in intact ovules of Solanum commersonii Dun., following staining with Mayer's hemalum and clearing with methyl salicylate or cedarwood oil. Previous studies in Solanum have observed the Polygonum type of megasporogenesis, in which a linear tetrad of megaspores is formed. The three micropylar megaspores then degenerate, leaving the chalazal megaspore to divide mitotically to form the egg sac. Contrary to expectation, only 30% of the observed sporads within the same ovary were tetrads. Triads, including some with one deteriorating cell at the micropylar end, were the predominant form. Many dyads, which are an intermediate stage in megasporogenesis, were found with one cell prematurely deteriorating. These observations can be explained if the micropylar daughter cell of the dyad stage, which formed after telophase I, began deteriorating before the second meiotic division, such that it never underwent the second division. The chalazal daughter cell would still undergo the second meiotic division, followed by death of the new micropylar megaspore.Key words: Solanum, potato, megasporogenesis, S. commersonii, ovule, clearing.