Three-dimensional aspects of EXINE INITIATION AND DEVELOPMENT IN LILIUM LONGIFLORUM (Liliaceae)

Pollen development in Lilium longiflorum was reinvestigated with high resolution scanning electron microscopy, with special attention to three-dimensional conformation in the exine pattern formation. At the early tetrad stage, the invaginated plasma membrane takes the form of a reticulate pattern that corresponds to the mature exine tectum. Protectum is the first exine layer to be deposited on the reticulate-patterned plasma membrane. The initial protectum consists of aggregated fibrous threads and granules. Subsequently, probacules are formed under the protectum on the plasma membrane. At the free microspore stage the developing exine becomes further enlarged and the protectum develops into mature verrucate muri. The present three-dimensional investigation conflicts with the previous studies on exine development in Lilium.