Sucrose suppression of chlorophyll synthesis in carrot tissue cultures: The role of invertase

Abstract

Free space invertase activities were determined in carrot callus strains CRT1 and CRT2 grown under conditions in which sucrose suppression of chlorophyll synthesis occurred in CRT1 but not CRT2. CRT2 possessed a high free space acid invertase activity (pH optimum 5.0 K_m for sucrose 3.1×10^-3M) while CRT1 lacked this enzyme. [U-¹⁴C] sucrose introduced into the free space of calluses was rapidly inverted by CRT2, but not by CRT1. Despite their different invertase levels, CRT1 and CRT2 showed similar sucrose uptake rates and took up [U-¹⁴C-glucosyl] sucrose and [5-T-glucosyl] sucrose from external bathing media essentially without prior inversion. It is concluded that acid invertase in callus tissue relieves the suppression of chlorophyll synthesis caused by sucrose in the free space. The invertase may in some circumstances hydrolyse sucrose before uptake, but is not an essential part of the sucrose uptake mechanism in carrot tissue cultures.