INFLUENCE OF ABSCISIC-ACID ON NITROGEN PARTITIONING, SUCROSE METABOLISM AND NITRATE REDUCTASE-ACTIVITY OF CHICORY SUSPENSION CELLS

Batch suspension cultures of chicory cells (Cichorium intybus L, var, Witloof) possess a NADH-specific nitrate reductase activity that peaks on day 3 of a 10 d growth cycle, When both nitrate and ammonium are u sed as nitrogen sources, chicory cells absorb nitrate first. Ammonium uptake becomes predominant at day 3, even though NO3- was still presen t in the medium, Although abscisic acid impairs growth as well as (NO3 -)-N-15 uptake and reduction, it promotes nitrate reductase activity a s measured both in vivo and in vitro, Specific activity is 50% higher in ABA-treated cells than in controls, These conflicting data may be e xplained either in terms of nitrate reductase levels or by the availab ility of reducing power and energy. Since NRA is generally controlled by the availability of the reducing power, the energy status of the ce ll, the adenylate nucleotide pools, were measured simultaneously with the carbohydrate levels within the cell and the growth medium, The ene rgy charge was not modified during the growth cycle, regardless of the growth conditions. Yet ABA modified the intracellular carbohydrate me tabolism and inhibited the acidic invertase, the sucrose synthase and the sucrose phosphate synthase activities, Modified assimilation rates of nitrate in chicory cells grown in the presence of ABA, were probab ly correlated to modified carbohydrate metabolism pathways leading to increased availability of reducing power, energy and C-skeletons.