Effect of osmolytes on the fructan pattern in feeder roots produced during forcing of chicory (Cichorium intybus L.)

During forcing of chicory tap roots (Cichorium intybus L. var, foliosum cv. Final) for witloof production in hydroponics a large number of thin feeder roots is formed. An inulin pattern of fructans (up to DP20) accumulated in these roots. The roots were also subjected to osmotic stress by addition of 0.2 mol/L NaCl or a PEG 6000 solution with the same water potential. Both addition of NaCl or PEG resulted in an increase of internal browning in the heads of witloof chicory, the most important disorder considerably reducing the market value of the chicon. The 0.2 mol/L NaCl treatment resulted in an important reduction in lateral root and chicon growth; a slightly increased fructan concentration in these feeder roots was also observed. PEG treatment was equally inhibitory on chicon growth, but feeder root growth was nearly not affected. Much lower fructan concentrations were found in these roots but the fructose, glucose and sucrose concentrations were much higher, apparently increasing the osmotic contribution of the stored carbohydrates in the feeder roots. It was demonstrated that this PEG-mediated drought stress effect has nothing to do with hypoxia. The dynamics of carbohydrates during forcing are discussed based both on the determination of enzymatic activities (invertase, I-SST, 1-FFT and 1-FEH) and the composition of the feeder root phloem exudate.