Submitted to: Canadian Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2003
Publication Date: 12/1/2003
Citation: Kladnik, A., Vilhar, B., Chourey, P.S., Dermastia, M. 2003. Sucrose synthase isozyme SUS1 is preferentially localized in the endopolyploid outer cells of the maize root tip.. Canadian Journal of Botany. 82(1):96-103. Interpretive Summary: Root cap is a thimble-like structure that provides protection to the growing root tip (a site for cell division and elongation) from physical damage and pathogen attack, and aids in the passage of roots through soil by secreting and covering the cap region with sugary slime that lubricates the soil. Very little is known however,about how the slimy coat on root caps is formed. Here in this report a team of international scientists from the Crop Genetics & Environmental Research Unit, Gainesville, FL and the University of Ljubljana, Ljubljana, Slovenia, report results that show: (1) a huge increase in the total DNA content in certain specific root cap cells, and (2) the same cells also produce greatly increased quantities of sucrose synthase protein which catalyses the synthesis of precursors for the production of the slimy coat on root cap cells. Overall, these data provide a new role for this enzyme in plant roots during early stages of seed germination at which plants are most vulnerable to both biotic and abiotic growth environments.
Technical Abstract: Spatial distribution of sucrose synthase isozyme SUS1 was studied in cells of maize (Zea mays L.) root cap in relation to the process of nuclear endoreduplication. Median longitudinal root cap sections were analysed using immunolocalization, quantitative DNA staining and image cytometry. Meristematic cells had nuclear ploidy level 2C to 4C, while the ploidy of the cells in the outer part of the root cap reached up to 16C. High immunolocalization signal for sucrose synthase was detected in the outermost cells of the root cap with the nuclear DNA content mostly 8C or higher. These cells had also the largest volumes in the root cap. The high amount of SUS1 protein in outer, endopolyploid cells implies the correlation of endoreduplication process with the abundance of this enzyme. SUS1 distribution was overlapping with the location of a fucose synthesizing enzyme GDP-d-mannose-4,6-dehydratase, involved in mucilage biosynthesis. In this regard, the possible role of sucrose synthase in supplying sugar monomers for mucilage production is discussed.