Pollen cultures as a tool to study plant development.

In in vitro cultures, isolated microspores and pollen grains can undergo two fundamentally different types of development. In conditions that simulate the tapetum they continue normal gametophytic development to produce functional pollen. Under stress conditions, they are induced to form haploid embryos and plants (sporophytes). In vitro matured pollen is a "minimal" pollen that lacks substances to enhance its reproductive success. In vitro pollen maturation is presented as an experimental system to study pollen development and its interaction with the tapetum. For young binucleate pollen grains, a starvation treatment is sufficient to induce sporophytic development, for microspores a heat shock treatment is required. During the stress treatments, transcription of specific mRNAs is activated. An important aspect of embryogenic induction of binucleate pollen is the derepression of the cell cycle in the G1-arrested vegetative cell.