A light and electron microscopy study of the epidermis of Paphiopedilum spp. with emphasis on stomatal ultrastructure

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Abstract
Light and fluorescence microscopy studies indicated that chlorophyll was absent from the guard cells of the lady slipper orchids, Paphiopedilum insigne (Wall.) Pfitz, P. insigne (hybrid), P. venustum (Wall.) Pfitz and P. harrisseanum Hort. In the guard cells of P. aureum hyeanum Hort., however, very slight red fluorescence suggested that chlorophyll and hence chloroplasts were present.Ultrastructural studies of the lower epidermis of P. insigne (hybrid) confirmed the absence of chloroplasts in guard and epidermal cells although plastids of an unusual structure were found in these cells. In fully developed epidermal cells the plastids contained large amounts of a fibrous, possibly proteinaceous substance, spherical, lightly staining vesicles and an electron‐dense material located in reticulate and non‐reticulate regions. Additionally, latticed crystalline inclusions and plasto‐globuli were occasionally observed in the epidermal cell plastids. In plastids of fully developed guard cells the fibrous material, starch and plastoglobuli were present.From the earliest stages of development of the epidermal tissue starch was present in both epidermal cell and guard cell plastids. At maturity, however, starch had accumulated to greater levels in the guard cell plastids and had entirely disappeared in the epidermal cell plastids. In differentiating epidermal tissue, plasmodesmata were found between neighbouring epidermal cells and between guard and epidermal cells. At maturity, plasmodesmata between guard and epidermal cells were not observed. Mitochondria were particularly abundant in guard cells. Large oil drops developed in guard and epidermal cells, being especially abundant in the former at maturity.Our results confirm the observations of Nelson & Mayo (1975) that certain lady slipper orchids possess functional stomata the guard cells of which do not contain chloroplasts.