Asymbiotic Protocorm Morphogenesis

Morphogenetic changes of asymbiotic germinated protocorms are documented in this chapter, and questions related to key development events are discussed. The early morphological events of seed germination and protocorm development are similar among the orchids studied. The embryo swells when germinating on a suitable germination medium, and mitotic activities follow. Suitable carbohydrates such as sucrose are needed for asymbiotic seed germination and protocorm development. The basal protocorm cells are large and tend to become polyploid. Rhizoids appear soon after seed germination and are more abundant on the surface at the basal end of the protocorm. The shoot apical meristem (SAM) and associated protocorm leaf differentiate from the protocorm apical meristematic cell layers. Once formed, the SAM becomes the growth center of the protocorm. The first seedling roots develop after the formation of the SAM. Orchid roots are adventitious in origin. The protocorm tissue usually degenerates with seedling formation. Although descriptive accounts of protocorm morphogenesis are available in the literature, more detailed studies are needed.