Sucrose synthase isozyme SUS1 in the maize root cap is preferentially localized in the endopolyploid outer cells

The structure of the maize (Zea mays L.) root cap was studied to quantitatively evaluate the relationship among the size of the cells, their endopolyploidy level, and the abundance of the sucrose synthase isozyme SUS1. Median longitudinal root cap sections were analysed using immunolocalization, quantitative DNA staining, and image cytometry. Both the immunolocalization signal for the SUS1 protein and the endopolyploidy level increased from calyptrogen towards the root cap periphery and were thus the highest in the outer cells. These cells had a nuclear DNA content of mostly 8C or higher and the largest volumes of all root cap cells. The high amount of SUS1 protein in the outer, endopolyploid cells suggests an association between endoreduplication and the abundance of this enzyme. The outer cells are involved in mucilage production; hence, there is a possibility that sucrose synthase provides monosaccharide precursors for mucilage synthesis.