Diversity In guard cell plastids of the Orchidaceae: a structural and functional study

Author:

D'Amelio Elisa D'Antoni,Zeiger Eduardo

Abstract

Guard cells of species representing 27 genera from the Orchidaceae were surveyed under fluorescence microscopy. With the exception of the genus Paphiopedilum, chlorophyll a fluorescence was observed in all species, indicating that, as in other families, chloroplasts are strongly conserved in the stomata of the Orchidaceae. The achlorophyllous stomata of Paphiopedilum therefore constitute a unique variation in that pattern, with its expression at the generic level pointing to an early, stable evolutionary event. Five of the orchid species, Vanilla aromaticum, Phragmipedium longifolium, Haemaria discolor, Paphiopedilum harrisianum, and Paphiopedilum insigne, were also studied ultrastructurally. There was a close correlation between plastid fluorescence intensity in guard cells and the presence of grana thylakoids in the organelles, with Vanilla showing an intense fluorescence and extensive grana stacking, while the Paphiopedilum stomata were completely devoid of both features. Phragmipedium stomata had an intermediate level of fluorescence and a reduced number of thylakoids, whereas Haemaria guard cells, which had no chlorophyll fluorescence in intact tissue but a weak fluorescence in cryostat sections, showed an unusual array of pleomorphic plastids with only a few exhibiting some thylakoids. Other ultrastructural features of orchid guard cells were also documented. These observations and a marked variation in fluorescence intensity and plastid number and size seen in the guard cells of the surveyed genera point to a broad structural diversity in the guard cell plastids of the Orchidaceae. This diversity could underlie specialized functional properties associated with stomatal adaptations to different growing habitats.

Publisher

Canadian Science Publishing

Subject

Plant Science

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