The location of acid invertase activity and sucrose in the vacuoles of storage roots of beetroot (Beta vulgaris)

Abstract

Vacuoles were isolated from freshly cut slices of the storage roots of beetroot (B. vulgaris), and from slices that were washed in aerated water for 1-3 days. The unique vacuolar location of betanin permitted the use of a correlative method to determine whether sucrose and acid invertase were located in the vacuoles. The specific content (the activity of the enzyme or amount of substrate per milligram of protein) and the percentage recoveries for betanin, sucrose and acid invertase were determined for the different fractions obtained during the isolation of the vacuoles. For each fraction the specific content of betanin was plotted against those of sucrose and acid invertase. Similar correlative plots were drawn for the percentage recoveries. For both specific contents and percentage recoveries the correlation coefficients for sucrose and for acid invertase vs. betanin were close to unity, and the lines passed near the origins. Apparently, in beetroot, most of the sucrose and much of the acid invertase are in the vacuoles. Measurements of vacuolar sucrose and acid invertase in beetroot slices washed for 1-3 days demonstrated an inverse relationship between sucrose content and acid invertase activity.