Cellular basis of developmental plasticity observed in heterophyllous leaf formation of Ludwigia arcuata (Onagraceae)
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When heterophyllous plants of Ludwigia arcuata Walt. (Onagraceae) were transferred from aerial condition to submergence, young developing leaves were matured into leaves with intermediate shape between aerial-type and submerged-type, showing spatulate shape (spoon-shaped). This change was also induced by the exposure of plants to ethylene. On the other hand, when the plants were transferred from submergence to aerial conditions, young developing leaves were matured into intermediate-type leaves with elliptic shape (spearhead shape). Anatomical analysis revealed that the formation of spatulate leaf was caused by the reduction of the number of epidermal cells aligned in the leaf transverse direction in the basal region of the leaf while the tip regions remained as before and did not respond to this treatment. During development, the ethylene-induced spatulate leaves showed that three types of alterations in epidermal cell division were involved in this process. Changes in the distribution of cell divisions in leaf lamina were detected by the first day of ethylene exposure, and changes in the orientation of cell division planes were detected by the second day. However, changes in the number of cells aligned in the leaf transverse direction were not detected by this time. Three days after ethylene exposure, frequency of cell divisions changed, and by the time changes of cell numbers aligned in the leaf transverse direction were observed. Thus, the formation of intermediate-type leaves in L. arcuata was ascribed to the alterations of cell division patterns which was induced by ethylene.
KeywordsCell division Developmental plasticity Ethylene Heterophylly Leaf shape Ludwigia
- L/W ratio
Ratio of leaf length to width
We thank Dr. Michel Möller (Royal Botanic Garden Edinburgh, UK) for his critical reading of this manuscript and helpful comments. Thanks are also due to Dr. Mary Inaba (University of Tokyo, Japan) and Mr. Yasuhiro Yoshida for their helpful discussions and support. Also, we thank to Dr. Toshihiro Yamada (The National Science Museum, Japan) for his constructive discussions.
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