Understanding Seed and Protocorm Development in Orchids

Abstract

In this overview, the development of orchid seed and protocorm is summarized. Although the structural organization of seed and protocorm appears simple, information is presented indicating that they have developmental programs similar to and as complex as other flowering plants. The varied suspensor morphologies, the presence of cuticular material covering the surface of the embryo, and the delicate seed coat structure ensure embryo survival, albeit unusual. The embryo is programmed to form a protocorm. The protocorm cells are destined to form a shoot apical meristem at the apical (chalazal) end and to house the symbiont at the basal (micropylar) end of a protocorm. Changes in protocorms during asymbiotic and symbiotic seed germination are discussed.