The Functional Significance of Leaf Shape Variation - Towards a Consensus from Gene to Community
Dengler, Nancy G. .
Development of leaf shape diversity in the monocotyledons.
Simple elongate leaves characterize a majority of monocotyledons, particularly the species-rich Poaceae and Cyeraceae, In these groups, the site of leaf initiation extends around the flanks of the shoot apical meristem, and morphogenesis of leaf shape occurs through highly polarized, but diffuse, growth which results in a linear blade and intercalated sheath. While many aspects of the development and function of graminoid leaf shape are understood, much less is known about monocotyledons with more complex shapes. Pinnately and palmately compound leaves are found in at least three orders, the Pandanales, Dioscoreales and Arecales, and phylogenetic analyses indicate that these represent independent evolutionary origins. The developmental mechanisms resulting in complex leaf morphogenesis differ among lineages as well. Dissected leaves in certain members of the Araceae and Dioscoreaceae arise through blastozone fractionation, similar to many dicotyledons. In contrast, the corrugated, dissected leaves of palms (Arecaceae) develop through a two-step process: first, plications are formed through localized intercalary growth in a submarginal position, and, second, adjacent leaflets are separated through schizogeny and/or mechanical rupture. A third mechanism, perforation formation, is employed in Monstera and five related genera of the Araceae. Here, discrete patches of cells undergo programmed cell death during blade development, resulting in the formation of open perforations. In some species, mechanical disruption of the thin bridges of marginal tissue results in a deeply pinnatisect blade. These mechanisms reflect developmental convergence on complex leaf shapes thought to enhance heat transfer and mechanical support.
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1 - University of Toronto, Department of Ecology and Evolutionary Biology, 25 Willcocks St., Toronto, Ontario, M5S 3B2, Canada
Presentation Type: Symposium or Colloquium Presentation
Location: Williford B/Hilton
Date: Monday, July 9th, 2007
Time: 9:15 AM