Plant and Cell Physiology Advance Access originally published online on November 29, 2006
Plant and Cell Physiology 2007 48(1):97-109; doi:10.1093/pcp/pcl045
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Protophloem Differentiation in Early Arabidopsis thaliana Development
1INRA, Centre de Versailles, Institut Jean-Pierre Bourgin, Laboratoire de Biologie Cellulaire, Route de St-Cyr, 78026 Versailles cedex, France
2INRA, Centre de Versailles, Institut Jean-Pierre Bourgin, Plateforme commune de cytologie, Route de St-Cyr, 78026 Versailles cedex, France
*Corresponding author: E-mail, palauqui{at}versailles.inra.fr; Fax, +33-130-833099
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Abstract |
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During Arabidopsis embryogenesis, procambial cells undergo coordinated, asymmetric cell divisions, giving rise to vascular precursor cells (protophloem and protoxylem precursors). After germination, these cells terminally differentiate into specialized conducting cells, referred to as protophloem and protoxylem cells. Few readily identifiable markers of the onset of specification and differentiation are available, hampering the molecular genetic analysis of protophloem development. Confocal microscopy was used to investigate the patterning and differentiation of phloem cells during early plant development. Longitudinal divisions of phloem initials allowed the identification of protophloem precursor cells and adjacent metaphloem initials along the length of the plant. During germination, protophloem differentiation was observed at two independent locations, in the cotyledons and the hypocotyl. In both locations, differentiation was concomitant with cell elongation. We identified five gene-trap lines (PD1–PD5) with marker gene expression in immature protophloem elements. The spatio-temporal marker expression pattern of the lines divides them into two groups. The early specification markers PD4 and PD5 were expressed in developing organs before procambium formation and then became restricted to phloem initial cells. The protophloem precursor markers PD1–PD3 were expressed in differentiating protophloem cells at different stages of their development. All markers were expressed transiently and iteratively during the differentiation of protophloem in newly formed organs. Flanking genes were identified for four out of five gene-trap insertion lines. The possible function of these genes with respect to phloem differentiation is discussed.
Keywords: Phloem - Differentiation - Development - Vascular tissue - Arabidopsis.
Abbreviations: AB, aniline blue; DAG, days after germination; GFP, green fluorescent protein; GPI, glycosylphosphatidylinositol; GUS, ß-glucuronidase; HAG, hours after germination; PD, phloem differentiation; PIP-4, 5-kinase, phosphatidylinositol phosphate-4,5-kinase; PP, protophloem precursor
(Received October 4, 2006; Accepted November 18, 2006)
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