Sugarcane internodal invertases and tissue maturity

The relationship between extractable invertase activities and sucrose accumulation in the sugarcane (Saccharum officinarum) stalk, and in vivo invertase mediated sucrose hydrolysis was investigated to determine the significance of invertases in sucrose utilisation and turnover. In vitro activities were determined by assaying the soluble acid, cell wall bound acid and neutral invertases from internodes three to ten in mature sugarcane plants of cultivar NCo376. Extractable activities were verified by immunoblotting. In vivo invertase mediated sucrose hydrolysis was investigated in tissue discs prepared from mature stalk tissue of the same cultivar. Sugarcane neutral invertase had a higher specific activity than soluble acid invertase (apoplastic and vacuolar) in the sucrose accumulating region of the sugarcane stem. Cell wall bound acid invertase was also present in significant quantities in both immature and mature tissue. Recombination experiments indicated the absence of activators and inhibitors, and immunodetection of neutral and soluble acid invertase followed comparable trends to that of activity expressed on a fresh mass or protein basis. When radiolabelled fructose was fed to both young and mature internodal tissue, label appeared in glucose which demonstrates that invertase mediated hydrolysis of sucrose occurs. In vitro invertase activities were used to calculate the theoretical turnover-times for the endogenous sucrose pool.