About the Cover
On the Cover: A longitudinal section of zinnia stem, stained for 
-expansin mRNA (ZeExp2) by in situ hybridization and viewed in differential interference microscopy. -Expansins comprise a large family of wall-loosening proteins implicated in cell growth, fruit softening, and other developmental processes. During xylem cell differentiation, cells elongate by expansion of cell wall materials at either their apical or basal ends, depending on the cell and position in the organ. As described by Im et al. (pp. 463-470), three newly identified expansin genes are expressed in specific cells of xylem and the expansin mRNAs are localized to the ends of these cells. This represents the first subcellular localization of mRNA in plant cells and suggests that localization of expansin message may be important for localized cell wall changes. Messages for expansin genes, ZeExp1 and ZeExp3, are found at the apical end of these cells, whereas that of the ZeExp2 is found at the base (arrows).
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Copyright © 2008 by the American Society of Plant Biologists
