THE INFLUENCE OF NITROGEN (15NO3) SUPPLY TO CHICORY (CICHORIUM-INTYBUS L) PLANTS DURING FORCING ON THE UPTAKE AND REMOBILIZATION OF N RESERVES FOR CHICON GROWTH

Tuberized tap roots of Witloof chicory (Cichorium intybus L.) were forced by placing in a dark chamber in a hydroponic system under high RH to produce an etiolated bud, the chicon. Plants were fed nutrient solutions with two NO3 concentrations of 1.5 or 18 mol m-3 NO3, or demineralized water. The nutrient solutions were labelled with 2% atom excess N-15. Although the chicon biomass increased with increasing NO3 concentration in the nutrient solution, the chicon dry weight remained unchanged. The increased chicon biomass was, therefore, due to more water in the chicon. The N in the chicon originated from either an endogenous source, the root, and/or an exogenous source, the nutrient solution. Organic N reserves remobilization and transfer to the chicon were not been affected by NO3 supply. At the end of the forcing period 75% of the root N had been remobilized. Differences in the amount of N in the chicons of the three treatments were due to the uptake of exogenous N. The flux of exogenous nitrogen to the chicon in high NO3-plants was 2- to 6-fold higher than in the low NO3-plants and, at the end of the forcing period, exogenous nitrogen contributed 30% of total chicon N in high NO3-plants and 10% in low NO3-plants. Net uptake of NO3 by chicory plants during the forcing process was a function of N influx and N efflux. The increase in N influx was accompanied by an increase in exogenous N flux to the chicon and probably a shift in root and/or chicon osmotic potential which increased water flux to the chicon. Since NO3 did not accumulate in either the chicon or the root, it is proposed that osmotic solutes, such as organic acids and amino acids may be involved in osmotic potential changes in chicory during the forcing process.