A STRUCTURAL AND FUNCTIONAL STUDY OF STOMATA
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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.
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