Abstract
Plants grow indeterminately by the activities of shoot and root apical meristems at the opposite ends of poles of the embryo, establishing a vertical body plan. By contrast, aquatic eudicot family Podostemaceae develop a horizontal plant body that allows them to adapt to their peculiar habitats, i.e., submerged rock-surfaces in fast-flowing rivers. Seedlings of Terniopsis species, belonging to subfamily Tristichoideae, retain a vertical growth by shoot and root meristems, while members of subfamily Podostemoideae cease vertical growth by rudimentary embryonic shoot and root meristems. Instead, an adventitious root arises from the lateral side of the hypocotyl and form adventitious shoots on the dorsal or lateral side. Here I review our recent study focusing on the loss/reduction of the embryonic shoot and root meristems. Comparative embryonic anatomical studies revealed that the developmental changes in the cellular embryogenesis of Podostemoideae caused the loss of embryonic shoot and root meristems.
