Angiosperm microsporogenesis diagramatically presented
Five phases may be recognized
Coordinate development of tapetum
As is shown here, microsporogenesis may be subdivided into five phases:
(1) differentiation of compact sporogenous tissue with thin cellulosic walls and numerous plasmodesmatal connections between microspore mother cells;
(2) isolation of each microspore mother cell by a callosic wall in which the plasmodesmata become severed and the conversion from tissue structure to individual cells that undergo meiosis I and II;
(3) tetrads, when each of four young haploid microspores becomes encapsulated in the callosic wall and the onset of exine synthesis in the pollen wall;
(4) dissolution of callose and the release of microspores from tetrads; and
(5) vacuolation and enlargement of microspores with the completion of exine deposition and pollen wall development.
Microsporogenesis is coordinated with both pollen wall development and tapetum development in the sense that they simultaneously differentiate (phase 1) and begins to degenerate at the end of microsporogenesis, when the exine is complete. This coordination reflects the important role the tapetum plays in microspore development.