AOBPreview originally published online on February 17, 2006
Annals of Botany 2006 97(5):917-923; doi:10.1093/aob/mcj602
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The Production and Release of Living Root Cap Border Cells is a Function of Root Apical Meristem Type in Dicotyledonous Angiosperm Plants
1 Section of Plant Biology, College of Biological Sciences, University of California, Davis, CA 95616, USA and 2 Department of Plant Sciences, The University Arizona, Tucson, AZ 85712, USA
* For correspondence. E-mail tlrost{at}ucdavis.edu
Received: 13 August 2005 Returned for revision: 13 September 2005 Accepted: 30 September 2005 Published electronically: 17 February 2006
• Background and Aims The root apical meristems (RAM) of flowering plant roots are organized into recognizable pattern types. At present, there are no known ecological or physiological benefits to having one RAM organization type over another. Although there are phylogenetic distribution patterns in plant groups, the possible evolutionary advantages of different RAM organization patterns are not understood. Root caps of many flowering plant roots are known to release living border cells into the rhizosphere, where the cells are believed to have the capacity to alter conditions in the soil and to interact with soil micro-organisms. Consequently, high rates of border cell production may have the potential to benefit plant growth and development greatly, and to provide a selective advantage in certain soil environments. This study reports the use of several approaches to elucidate the anatomical and developmental relationships between RAM organization and border cell production.
• Methods RAM types from many species were compared with numbers of border cells released in those species. In addition, other species were grown, fixed and sectioned to verify their organization type and capacity to produce border cells. Root tips were examined microscopically to characterize their pattern and some were stained to determine the viability of root cap cells.
• Key Results The first report of a correlation between RAM organization type and the production and release of border cells is provided: species exhibiting open RAM organization produce significantly more border cells than species exhibiting closed apical organization. Roots with closed apical organization release peripheral root cap cells in sheets or large groups of dead cells, whereas root caps with open organization release individual living border cells.
• Conclusions This study, the first to document a relationship between RAM organization, root cap behaviour and a possible ecological benefit to the plant, may yield a framework to examine the evolutionary causes for the diversification of RAM organization types across taxa.
Key words: Border cells, root caps, root apical organization, root meristem
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