The switch of the gametophytic developmental program of the microspore towards embryogenesis to form a haploid plant represents an important tool in plant breeding for obtaining isogenic lines and new varieties through double-haploid plants. This process can be induced in microspore in vitro cultures by stress treatments, like starvation or heat-shock. Microspore embryogenesis also constitutes an interesting in vitro system for basic studies on cellular and molecular mechanisms controlling plant development, cell fate, stress response and signalling pathways. This process has been induced in many plant species but little is known about the mechanisms and factors involved in this change of developmental program. In this work, various ultrastructural in situ approaches have been performed to characterize changes in the subcellular organization and the localization of stress proteins, specifically the HSP70, during the induction and early microspore embryogenesis