Diversity of plastid morphology and structure along the micropyle-chalaza axis of different Crassulaceae

The suspensor is a unique embryonic region that connects the embryo to the seed coat. In many angiosperms, the suspensor attains remarkably diverse morphological forms ranging from vesicular single-celled (Orchidaceae) to differentiated multicellular structures (Fabaceae). These variations may be specific to the genera and species of different families, and even members of a single family show a fair amount of diversity in suspensor morphology. Clear differences in the structure of plastids were observed due to type and phylogenetic relationship of angiosperm suspensors. In present study, diversity within suspensor plastids was evident in representatives of four Crassulaceae genera. In more closely related genera this difference was smaller, while in genera less related to each other, it was larger. In this family a decreasing gradation in the size and complexity of plastids from the basal cell to the chalazal suspensor cells and the embryo proper was found. In angiosperms, also a gradient in the size of nuclei and the degree of ploidy along the micropyle-chalaza axis embryo exists. Such a gradient can also be correlated with the gradient of plastids and the variation in plasmodesmata diameter along the micropyle-chalaza axis in the Crassulaceae embryo.