Developmental and Structural Section
McKown, Athena D. , Moncalvo, Jean-Marc , Dengler, Nancy G. .
Evolution of Kranz anatomy in the genus Flaveria (Asteraceae).
C4 photosynthesis and associated Kranz anatomy represent a complex adaptation that has been the focus of much research on plant physiology, ecology and evolution. The genus Flaveria provides one of the best examples for studying evolution of C4 photosynthesis as it possesses C3 and C4 species, in addition to species classified as intermediates based on biochemical properties (C3-C4 or as C4-like). While headway has been made in exploring the molecular aspects of C4 biochemistry in this genus, much less is known about the evolution of Kranz anatomy and C4 vein pattern, both of which are required for C4 biochemical function. A comparative examination of quantitative leaf anatomy in ten Flaveria species (C3, C4 and intermediate (C3-C4, C4-like)) identifies specific anatomical and vein pattern differences among photosynthetic types and assesses potential steps in the evolution of Kranz anatomy. Flaveria demonstrates variation in leaf anatomy, from typical C3-like anatomy to fully expressed C4 Kranz anatomy, including a reduced mesophyll (M) to bundle sheath (BS) tissue volume ratio and increased vein density. Reduced vein spacing, decreased M volume and increased BS chloroplast density are observed in the most basal C3-C4 intermediate species, based on an ITS phylogeny of the genus, and may be considered initial steps towards the evolution of Kranz anatomy. Further reductions to vein spacing and M tissue (through reduced cell size and number of cell layers) precede the appearance of other C4 physiological characteristics; however, fully expressed Kranz anatomy, including vein pattern, is required before complete compartmentation of enzymes occurs. Results herein are mapped onto the ITS phylogeny and provide evidence for a step-wise acquisition of anatomical traits. Furthermore, derived C4 anatomical traits are shared between C4-like intermediate and C4 species of different clades, demonstrating parallel evolution of Kranz anatomy within Flaveria.
1 - Royal Ontario Museum, Centre for Biodiversity and Conservation Biology, Royal Ontario Museum 100 Queen's Park, Toronto, Ontario, M5S 2C6, Canada
2 - University of Toronto, Department of Botany, 25 Willcocks St., Toronto, Ontario, M5S 3B2, Canada
Presentation Type: Paper
Location: Alpine A (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 4:45 PM