Substomatal ion-adsorbent bodies are reported on here for
the first time. A brief survey of the plant kingdom suggests that
the structures are mainly restricted to the Commelinaceae and Filicales
although analogous structures way occur in other plant groups.
Microscopical studies indicate that the bodies have a solid external
aspect, a hollow lumen, and are situated extracellularly. In
Polypodium, the bodies are narrowly attached to the lower periclinal
walls in the polar regions of the guard cell complex, whilst in
Tradescantia they are located in the intercellular space between the
poles of the complex and the adjacent subsidiary cells. In both
genera, the body is covered by the endocuticle which can be distended
into a substomatal sac by the body pressing against it. The
endocuticle, in the immediate vicinity of the bodies, is modified
into a series of hollow trabeculae which are considered to be
important apoplastic pathways. The bodies are formed at an early
stage of stomatal ontogeny from the migration of outer elements of the
lower periclinal wall of the guard-cell mother-cell to both poles of
the eventual guard cell complex. The walls of the body are believed
to be highly pectinaceous and capable of adsorbing a wide variety of
ions non-selectively. Preliminary X-ray microanalyses suggest that
the bodies may be involved in potassium fluxes associated with
stomatal movements.
Ultrastructural studies of immature Polypodium guard cells
resulted in the erection of a hypothetical model for stoma formation.
Ontogenetic studies revealed a major anomaly in existing stomatal
classifications which is rectified in a proposed new classification of
stomatal types which is explicit a.t both ontogenetic and morphological
levels. Previously unrecorded ontogenetic and morphological stomatal
types are reported from Polypodium