Effect of defoliation on fructan pattern and fructan metabolizing enzymes in young chicory plants (Cichorium intybus)

Witloof chicory ( Cichorium intybus L. var. foliosum cv. Flash) was sown in acid-washed vermiculite in a controlled growth chamber. After 1 month of growth, one half of the chicory plants were defoliated whereas the intact chicory plants remained as a control. Twenty-four hours after defoliation, a very sharp decrease in hexose, sucrose, and total fructan concentration was observed in the roots. This coincided with a strong decrease in sucrose:sucrose 1-fructosyl transferase (1-SST; EC 2.4.1.99) activity and a strong increase in fructan 1-exohydrolase (1-FEH; EC 3.2.1.80) activity. After day 5, 1-SST activity increased and 1-FEH activity decreased. However, from day 5 to 15, both the activities of 1-SST and acid invertase (EC 3.2.1.26) remained significantly lower than in the control plants. From 10 days after defoliation, fructan synthesis resumed and hexose and sucrose concentrations increased. Up to now, 1-FEH activity was believed to occur only in mature tissues (end of the growing season, storage, forcing, or sprouting). Therefore, the rather unexpected finding that 1-FEH can also be induced in very young chicory roots after defoliation suggests that 1-FEH can be considered a 'survival' enzyme that can be induced at any physiological stage when energy demands increase.