Pollen development in Liriodendron tulipifera: some unusual features

Pollen development in Liriodendron tulipifera has some unusual features. Two arrangements in tetrads could be detected: isobilateral and decussate types. The occurrence of one or the other pattern seems to be random. The sulcus position is marked early by an exine fold forming at the beginning of wall deposition at the distal pole of tetrad cells. During increasing microspore volume, the exine outgrowth is unfolded, then stretched and finally broken up, thus exposing the intine below. Plastids are usually excluded from the generative cell, indicating that their inheritance is predominantly maternal. Nevertheless our cytological results give evidence of a trace paternal transmission of plastids. Some evolutionary considerations are made. Key words: microsporogenesis, Liriodendron tulipifera, postmeiotic cytokinesis, sulcus determination, ultrastructure.