Curing Influences Sugar Metabolizing Enzyme Activity in Sweetpotato

Abstract

Sweetpotato roots (`Beauregard', `Hernandez', and LSU breeding line 9496) were cured (30 °C and 90% RH) for 10 days immediately after harvest to determine the effect of curing on several sugar-metabolizing enzymes. Free sugars and activities of invertase, sucrose synthase (SS), and sucrose phosphate synthetase (SPS) were assayed. Total sugars for the three genotypes ranged from 132.5 to 177.9 mg sugar/g DW at harvest, and from 162.3 to 204.3 mg sugar/g DW after curing. Enzyme activity at harvest averaged over the three genotypes ranged from: 154 to 251 mol sucrose DW/h for invertase; 18.6 to 23.1 mol sucrose DW/h for SS, and 7.4 to 15.7 mol sucrose DW/hr for SPS. Enzyme activity after curing averaged over the three genotypes ranged from: 251 to 288 mol sucrose DW/h for invertase; 20.3 to 25.8 mol sucrose DW/h for SS, and 11.3 to 17.3 mol sucrose DW/h for SPS. The increase in invertase activity during curing was highest in `Hernandez' and lowest in the breeding line 9496. The increase in invertase activity correlated to the increase in reducing sugar content for `Hernandez' and `Beauregard'. Curing also shifted the pH optima of invertase in `Hernandez' from pH 5.2 to 7.6.