AOBPreview published online on April 18, 2005
Annals of Botany, doi:10.1093/aob/mci148
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1 Department of Chemical and Biological Sciences, Faculty of Science, Japan Women's University, 8-1, Mejirodai 2-chome, Tokyo 112-8681, Japan
* To whom correspondence should be addressed.
Background and Aims The Podostemaceae are a family of unusual aquatic angiosperms that live in rapids and waterfalls. To adapt to such extreme habitats, the family shows unusual morphologies. This study investigated the developmental anatomy of the shoot of Zeylanidium subulatum borne on the prostrate root attached to submerged rock surfaces. Methods Shoots of Z. subulatum were observed under the microscope using resin-sections. Key Results The shoot has no shoot apical meristem (SAM) and, without it, forms leaves distichously dorsiventrally facing the immediately older leaf. A new leaf forms on the adaxial side of a pre-existing leaf and also on the abaxial side of a leaf on flowering shoots. In both cases, the young leaf is endogenous below the older leaf and maintains histological continuity with it. Shortly after internal initiation, the leaf primordia become separate from each other due to cleavage between adjacent leaves of opposite ranks. The cleavage is caused by intercellular separation as well as by degeneration of vacuolated cells. Loss of the SAM is probably linked with the speculated shift of the site of leaf formation to the root. Conclusions The shoot of Z. subulatum is characterized by the absence of a SAM, endogenous leaf formation in the absence of a SAM, cleavage between leaf primordia, and adventitious leaf formations. These innovations occur in some Podostemaceae that have become increasingly adapted to extreme aquatic habitats.
Received November 24, 2004
Revised January 12, 2005
Accepted March 2, 2005
Article
Leaf Development in the Absence of a Shoot Apical Meristem in Zeylanidium subulatum (Podostemaceae)
2 Department of Biological Sciences, Graduate School of Science, University of Tokyo, 3-1, Hongo 7-chome, Tokyo 113-0033, Japan
RYOKO IMAICHI, E-mail: ryoko{at}fc.jwu.ac.jp
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