Tapetum uncommon behavior, orbicule development, and pollenkitt: mini-review, with new data on orbicule simulations

This special mini-review was planned as a synthesis of current understanding of the role of tapetum and orbicules, of the knowledge on pollenkitt, with addition of our own data on experimental orbicule simulation. The aim was to show the development of knowledge and ideas through time. Tapetum types are so changeable that the idea of norm becomes ghostly. The review is based on our own and other authors' results. Cyclic-invasive tapeta, surprising exine-like tapetal surface, direct connections of tapetum with microspores via filaments are probably not rare phenomena. Our in vitro experiments on microspore exine simulations, which have led also to appearance of orbicule-like structures, support the view of their by-product nature, based on self-assembly. Different types of orbicules and their development are examined. Tapetum and orbicule functions and especially pollenkitt production are reviewed, together with the data on sporopollenin. Some concise data on molecular and genetic studies are added.