Developmental and Structural Section
Cury, Graziela , Rossi, Magdalena , Elbl, Paula Maria , De Menezes, Nanuza Luiza .
The expression of the scarecrow gene reveals the origin of primary thickening of the Xyris asperula Mart. (Xyridaceae) rhizome.
New lines of thought, which are based mainly on anatomical evidence, suggest that primary thickening of monocot stems occurs through the joint action of the pericycle and endodermis. Based on these results, the pericycle, originating from the procambium, gives rise to vascular bundles centripetally, while the endodermis, which originates from the ground meristem, gives rise to the cortex. The aim of this study was to demonstrate the meristematic activity of the endodermis in the rhizome of Xyris asperula through a combination of gene expression and anatomical analyses in order to emphasize the role of these tissues as responsible for primary thickening in this organ. The scarecrow(scr) gene encodes a transcription factor expressed in endodermal initials and participates in the regulation of periclinal cell divisions, which produce parenchyma cells that form the cortex. In the region responsible for primary thickening, anatomical analyses showed the pericycle giving rise to the vascular system in a centripetal manner and the endodermis producing cortical cells centrifugally. It is interesting to note that the boundary between the two tissues presents no correspondence between the cells, which reinforces the idea that both meristems have different origins. Moreover, the cortex of the rhizome consists solely of radially arranged cells, which suggests that each row originates from a single cell, the endodermal initial. Regarding the analysis of gene expression, it was found that the scr gene is expressed in endodermal initial cells and in their immediate resulting cells. In the cells around the leaf traces, near the pericycle, the presence of scr transcripts was also identified. Finally, the expression of scr made it possible to clearly determine the boundary between the two meristematic tissues, since while endodermal cells revealed the presence of mRNA from the marker gene, the adjacent pericyclic cells did not express it.
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1 - Universidade de São Paulo, Department of Botany, Rua do Matão, 277, São Paulo, São Paulo, 05508090, Brazil
Presentation Type: Poster:Posters for Sections
Location: Battelle South/Convention Center
Date: Monday, July 9th, 2012
Time: 5:30 PM