Effect of nitrate concentration during growth on carbon partitioning and sink strength in chicory

Abstract

Abstract Chicory plants (Cichorium intybus), which produce a tuberized root containing high concentrations of fructans, were grown with nitrate at either optimal (4 mol m−3) or suboptimal (0.6 mol m−3) concentration. At 120 DAS (days after sowing), shoot/root dry mass ratio in the plants grown at low N was less than one-third of that of plants grown at the higher concentration. This reflected differences in shoot dry mass, as root dry mass was similar in the two treatments. Pulse-chase experiments with 14CO2 showed increased allocation of carbon to the root and decreased partitioning to the growing shoot in the plants grown at low N. Root activities of three enzymes involved in sucrose and fructan metabolism were measured, in an attempt to identify the factors which determine sink strength. Whereas invertase activity showed little difference between the treatments, sucrose synthase and particularly sucrose-sucrose fructosyl transferase were higher in the roots of plants grown at low N. Activity of SST was also much greater in roots of young plants synthesizing large amounts of fructan than in mature roots no longer producing fructan. It is, therefore, suggested that SST plays a role in determining the sink strength. Possible interactions between N status and SST activity/sink strength are discussed.