CALCIUM (CA-45) ACCUMULATION AND TRANSPORT IN CHICORY (CICHORIUM-INTYBUS L) ROOT DURING BUD DEVELOPMENT (FORCING)

The lower part (4 cm) of the witloof chicory tap-root (15 cm) was immersed in a complete nutrient solution for 21 days, in the darkness at 18-degrees-C and at high RH. This process of forcing which leads to the emergence of an etiolated bud (chicon) was associated with a decrease in root dry weight. Although the amount of calcium in the root and the root cationic exchange capacity remained constant during forcing, the net uptake of calcium, negligible at the onset of forcing, progressively increased to a rate after ten days of 45-mu-mol day-1. Absorption of Ca-45 remained at a constant high rate, while the initially low upward migration of Ca-45 within the root and the chicon accelerated markedly. This upward migration was associated with a progressive decline in the release of newly absorbed Ca-45. The data support the hypothesis that calcium acquisition by witloof chicory root is predominantly determined by calcium efflux. As the forcing progressed, the influx remained almost constant while a large decrease in the efflux led to a net uptake of calcium. Upward translocation was probably linked to the formation of new negative exchange sites within the growing chicon. The hypothesis that calcium movement occurred along a preferential pathway (xylem vessels) or involved a mass movement through the root is discussed.