Developmental and Structural Section
Horner, Harry T. .
Unusual pit fields are associated with wall interfaces between large hypodermal cells and small crystal-containing photosynthetic parenchyma in Peperomia leaves.
Peperomia leaves contain a large multilayered hypodermis subtended by a very small single- layered photosynthetic palisade parenchyma. Depending on species, this latter cell layer contains druses (spherical aggregates of crystals) which are configured in different ways forming distinct crystal macropatterns. Each palisade parenchyma cell containing a druse shows it in a central vacuole surrounded by large chloroplasts. In Peperomia obtusifolia, for example, each most basal large hypodermal cell is in contact with many palisade cells. Freeze fractured or torn segments of FAA-fixed leaves expose internal leaf anatomy of this cell-cell wall interface. Cell walls surrounding hypodermal cells are all relatively thin, except for the thick periclinal walls associated with the thin upper periclinal walls of the subtending palisade parenchyma cells. These thick hypodermal walls show the ‘quilted’ impressions (mounds) of the many smaller appressed palisade parenchyma cells. The cell walls of these palisade cells are much thinner. What becomes obvious in the fractures and tears is the presence of conspicuous circular depressions in the thick periclinal hypodermal walls associated with each palisade parenchyma cell mound. Each mound displays depressions that contain what appear to be many plasmodesmata that connect these two types of cells to each other. These depressions can be considered special pit fields and represent thin regions (‘windows’ or ‘skylights’) in the thick hypodermal cell walls. Similar pit field regions occur in the adjacent thin palisade parenchyma periclinal walls. The druses in the palisade parenchyma cell vacuoles are often near these pit field regions suggesting an interesting physical relationship that could provide a pathway for light waves being filtered through the multiple hypodermis to pass into the palisade parenchyma cells and be collected and dispersed by the druses to surrounding chloroplasts. This hypothesis implies an intriguing possible photosynthetic adaptation for plants growing in a low-light environment.
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1 - Iowa State University, Genetics, Development and Cell Biology & Microscopy and NanoImaging Facility, Ames, IA, 50011-1020, USA
unusal pit fields
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 28th, 2008
Time: 8:15 AM