Metabolism of sucrose during storage in intact sorghum stalk

Grasses of the Andropogoneae, such as sorghum (Sorghum bicolor [L.] Moench) and sugarcane (Saccharum spp.), accumulate large amounts of harvestable sucrose in the stalk. Sucrose is translocated from the leaves, yet the metabolic fate of sucrose up to and during storage in the stalk is uncertain. This study determined whether sucrose is necessarily routed through inversion and hexose-phosphate isomerization for storage in cells of the intact stalk. Sorghum stalks were dual-infused with [U-¹⁴C]sucrose and [fructose-1-³H(N)]sucrose during stages of sucrose accumulation. Unperturbed tissue was used for subsequent sugar analyses. Solutes in cell extracts were separated sequentially through enzymatic conversion and ion-exchange removal of the reaction products. The hexose moieties of sucrose were analyzed separately. A mean of 95% of recovered ¹⁴C was in sucrose. In sucrose, 46% of ¹⁴C and 77% of ³H were recovered in the fructose moiety. The significant retention of asymmetry in tritium labeling of sucrose indicates that a cycle of cleavage and resynthesis did not dominate sucrose accumulation in cells of the sorghum stalk. (author)