Developmental and Structural Section
Horner, Harry T. , Swanson, Katherine , Healy, Rosaria .
Comparison of leaf crystals and their macropatterns in +20 species of Peperomia (Piperaceae).
LEAVES of over 20 greenhouse-grown succulent Peperomia species vary considerably in their shape, thicknesss, lamina size, and coloration. Most leaves are relatively thick and, in section, display between their adaxial and abaxial epidermises an upper multi-layered, large-celled hypodermis of water-containing cells, immediately below which is a thin, green, typically single-layered palisade parenchyma. This layer is sandwiched between the hypodermis and spongy mesophyll associated with the vasculature. Leaf clearings and vibratome sections show a multitude of calcium oxalate crystal idioblasts that individually contain druses, and sometimes prisms or bundles of raphides. The druses, specifically and consistently occur singly in the palisade parenchyma cells, and form layered uniform or reticulate macropatterns that are species specific. In contrast, prisms or bundles of raphides, when present, generally occur in the spongy mesophyll and also are species specific. These variations in the occurrence of these three types of crystals may be a very useful internal taxonomic indicator when applied to a broader array of species within the genus. The druses, aggregates of spherical crystals, also vary from one species to another in terms of their average diameters, and the number and the shape of individual crystal facets, as shown by light microscopy in conjunction with crossed polarizers, and by scanning electron microscopy. These prevalent and specifically located druses in the photosynthetic palisade parenchyma may have a special function in light gathering and reflection under subdued light. The data will be discussed in terms of their comparative crystal macropatterns and their taxonomic associations within the genus.
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1 - Iowa State University, Department of Genetics, Development & Cell Biology, Bessey Microscopy Facility, 3A Bessey Hall, Ames, Iowa, 50011-1020, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 312/Bell Memorial Union
Date: Monday, July 31st, 2006
Time: 4:30 PM