Recent Topics Posters
McKown, Athena D. , Dengler, Nancy G. .
Key innovations in evolution of Kranz anatomy in Flaveria.
THE evolution of Kranz anatomy and C4 vein pattern is required for C4 biochemical function in nearly all known C4 plants. Two important aspects of Kranz anatomy which ensure rapid cycling of C4 metabolites include the ratio of mesophyll tissue to bundle sheath tissue, and low vein spacing. Analysis of sixteen Flaveria species (C3, C4 and two biochemically intermediate types [C3-C4, C4-like]) highlights specific differences in mesophyll, bundle sheath and vein spacing among photosynthetic groups, and identifies novel anatomical variables in intermediate species. Data are assessed using a well-resolved phylogenetic history of Flaveria. Observed differences from the C3 condition in intermediate and C4 Flaveria species of different clades outline a step-wise acquisition of anatomical and vein pattern traits. Vein pattern alteration is an early adaptation increasing vein density contributing to lower mesophyll: bundle sheath tissue ratios. This adaptation precedes further modifications, including changes to bundle sheath tissue. Mesophyll tissue volume is also altered during leaf development through the number of ground tissue layers and mesophyll cell expansion. This developmental shift results in the loss of two or three ground tissue layers and has occurred four times within the genus. Differences between C3 and C4 mesophyll: bundle sheath ratios in Flaveria are a result of these modifications to mesophyll tissue volume. The gain of similar derived features in different clades of the Flaveria phylogeny suggests common anatomical requirements for the evolution of intermediate and C4 photosynthesis.
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1 - University of Toronto, Department of Botany, 25 Willcocks Street, Toronto, Ontario, M5S 3B2, Canada
Presentation Type: Recent Topics Poster
Date: Thursday, January 1st, 1970