Microspore Embryogenesis and In Vitro Pollen Maturation in Tobacco

Microspores have two developmental options when they are isolated from anthers and cultured in vitro. In a rich medium, they can develop into mature pollen grains that are fertile on pollination in vivo (1 ,2 ). Their development closely resembles pollen formed in vivo, whereas the in vitro culture conditions simulate the changing environment a microspore/pollen grain experiences inside the anther. The microspore divides by an asymmetrical division, and the daughter cells differentiate into mature pollen grains, with their characteristic cell-cycle arrest (vegetative cell in Gl, generative cells in G2). This simple pathway makes in vitro pollen maturation an excellent system to study developmental processes, such as cell fate determination and cellular differentiation (3 ). In addition, in vitro pollen maturation has also been used for pollen selection (4 ) and plant transformation (5 ). Another potential application is the rescue of sterile or self-incompatible pollen for “self”-pollinations.