Root Cell Ultrastructure in Developing Aerenchyma Tissue of Three Wetland Species

Abstract

Patterns of root cortex cell development and ultrastructure were analysed in Sagittaria lancifolia L., Thalia geniculata L. and Pontederia cordata L. using scanning and transmission electron microscopy (SEM, TEM). In all three species, cortex cells were arranged in radial columns extending from the endodermis to the hypodermis/epidermis. During gas space formation, the cortex cells elongated parallel to the root radius and shrank in the plane perpendicular to the radius leaving long and thin rows of cortex cells extending from the endodermis to the epidermis. Although the cortex cells appeared collapsed in tissue with well-developed gas spaces, TEM revealed that the cortical cells as well as the epidermal cells maintained intact membranes and many normal organelles. Formation of root cortex tissue with well-developed gas spaces does not require cell death in these species. Living cortex cells in root tissue with mature gas spaces could provide a symplastic pathway for transport between the root stele and the living epidermal cells.