Protein-level expression and localization of sucrose synthase in the sugarcane culm.

Abstract

No comprehensive studies on the localization of sucrose synthase (SuSy, EC 2.4.1.13) in sugarcane internodes have been reported. The expression and localization of SuSy in young (internode 3) to mature (internode 9) internodes of sugarcane (Saccharum spp. hybrids) var. N19 was investigated. Enzyme activity in the top and bottom, as well as the peripheral and core parts of the internodes suggested that SuSy is present ubiquitously but that levels can differ significantly in different parts of the internodes and with maturity. This was also confirmed by immunohistochemistry, which showed that both vascular and storage parenchyma tissues contain SuSy in young and mature internodes. The ratio of sucrose breakdown to synthesis activity increased approximately 12-fold from an average of 0.12 in internode three to 1.4 in internode nine. This indicates that different forms of SuSy are present in young and mature internodes, or that the ratios of different isoforms differ between young and mature internodes. Immunoblotting showed that at least one form of SuSy present in young tissue was absent, or present below detection limits, in mature culm tissue.