Effect of nitrogen concentration on fructan and fructan metabolizing enzymes in young chicory plants (Cichorium intybus)

Witloof chicory seeds (Cichorium intybus L. var. foliosum cv. Flash) were s o,vn in acid-washed vermiculite in a controlled environment growth chamber, Plants received a nitrogen poor ("N-poor": 0.2 mM NH4NO3) but otherwise co mplete medium, or a nitrogen rich ("N-rich": 2 mM NH4NO3) medium, After 1 m onth of growth the fructan concentration in the "N-poor" plants was about f ive times higher and also the activity of sucrose:sucrose 1-fructosyl trans ferase (1-SST; EC 2.4.1.99) was twice as high as in "N-rich" plants, The ac tivities of the catabolic enzymes fructan 1-exohydrolase (1-FEH; EC 3.2.1.8 0) and acrid invertase (EC 3.2.1.26),were higher in the "N-rich" plants whe re significant energy was invested in root and leaf growth, After one month of growth, part of the "N-poor" plants were switched to the "N-rich" mediu m. One day after this switch, a sharp decrease in sucrose and glucose conce ntration was observed in the roots, During the following days, both the act ivities of 1-SST and fructan:fructan 1-fructosyl transferase (1-FFT; EC 2.4 .1.100) decreased and the I-FEM and invertase activities increased. These c hanges were correlated with a decrease in fructan concentration. Ten days a fter the switch, glucose and sucrose concentrations increased again and fru ctan synthesis resumed, During this period 1-SST activity increased and 1-F EH activity decreased, Apparently 1-SST, 1-FFT and 1-FEH simultaneously con trol fructan in young chicory roots, The rather unexpected finding that 1-F EH activity, which was believed to occur only in older material, can be ind uced in very young roots indicates that this enzyme can be induced at any p hysiological stage.