Spatial distribution and dynamics of sucrose metabolising enzymes in radiation induced mutants of sugarcane

• Dynamics of sucrose accumulation is balanced by activities of sucrose synthesising and hydrolysing enzymes in the sink.
• Significantly higher soluble acid invertase and neutral invertase activities in leaves of radiation induced mutants of sugarcane.
• Lower activities of invertases in the culm favoured higher sucrose accumulation in the culms of the mutant AKTS-02.
• Soluble acid invertase proven to play a crucial in regulation of sucrose accumulation in the internodes.

Sucrose metabolism in various source and sink organs of developing sugarcane (Saccharum officinarum L.) plant is accompanied with continuous synthesis and cleavage. In this regard, the involvement of four major enzymes viz. sucrose synthase (SS), sucrose phosphate synthase (SPS), soluble acid (SAI) and neutral invertases (NI) is considered crucial. In this study, we have analysed in vivo enzymatic activity of 12th month old field grown radiation-induced sugarcane mutants identified for sucrose accumulation. The mutants showed significant differences in the spatial enzymatic regulation in leaves, immature and mature internodes; SPS and SS activities were found highest in high sucrose accumulating mutants (AKTS-02 and AKTS-20) along with lower levels of SAI activity. Overall positive correlation of SPS, SS and negative correlation of SAI, NI activities with sucrose content of the respective tissue types was observed. The SPS activity was found strongly associated with sucrose content in leaves (r2 = 0.558) and internodes (r2 = 0.514), whereas, the SAI activity was found significant in leaves (r2 = 0.379) and weakly associated in internodal tissues (r2 = 0.248). However, the associations were found to be non-significant for SS and NI activities in both leaves and internodes. Despite this, the differences in the SPS and SAI activities (SPS-SAI) in leaves (r2 = 0.828) and internodal tissues (r2 = 0.619) had shown greater influence on net sucrose synthesis and accumulation. To summarize, our results suggest differential sugar metabolism in the induced mutants and that such contrasting mutant germplasm with a relatively uniform genetic makeup can be useful in molecular studies on sucrose accumulation.