Plant Research International, Wageningen UR, Droevendaalsesteeg 1, 6708 PD Wageningen, The Netherlands.
J Plant Physiol. 2012 Oct 15;169(15):1520-9. doi: 10.1016/j.jplph.2012.06.005. Epub 2012 Jul 15.
Inulin is a fructose-based polymer that is isolated from chicory (Cichorium intybus L.) taproots. The degree of polymerization (DP) determines its application and hence the value of the crop. The DP is highly dependent on the field conditions and harvest time. Therefore, the present study was carried out with the objective to understand the regulation of inulin metabolism and the process that determines the chain length and inulin yield throughout the whole growing season. Metabolic aspects of inulin production and degradation in chicory were monitored in the field and under controlled conditions. The following characteristics were determined in taproots: concentrations of glucose, fructose and sucrose, the inulin mean polymer length (mDP), yield, gene expression and activity of enzymes involved in inulin metabolism. Inulin synthesis, catalyzed by sucrose:sucrose 1-fructosyltransferase (EC 2.4.1.99) (1-SST) and fructan:fructan 1-fructosyltransferase (EC 2.4.1.100) (1-FFT), started at the onset of taproot development. Inulin yield as a function of time followed a sigmoid curve reaching a maximum in November. Inulin reached a maximum mDP of about 15 in September, than gradually decreased. Based on the changes observed in the pattern of inulin accumulation, we defined three different phases in the growing season and analyzed product formation, enzyme activity and gene expression in these defined periods. The results were validated by performing experiments under controlled conditions in climate rooms. Our results show that the decrease in 1-SST that starts in June is not regulated by day length and temperature. From mid-September onwards, the mean degree of polymerization (mDP) decreased gradually although inulin yield still increased. The decrease in mDP combined with increased yield results from fructan exohydrolase activity, induced by low temperature, and the back transfer activity of 1-FFT. Overall, this study provides background information on how to improve inulin yield and quality in chicory.
菊粉是一种从菊苣（Cichorium intybus L.）块根中分离出来的果糖基聚合物。聚合度（DP）决定了其应用，因此也决定了作物的价值。DP 高度依赖于田间条件和收获时间。因此，本研究旨在了解菊苣中菊粉代谢的调控以及决定整个生长季节菊粉链长和产量的过程。在田间和控制条件下监测了菊苣中菊粉生产和降解的代谢方面。在块根中测定了以下特征：葡萄糖、果糖和蔗糖浓度、菊粉平均聚合度（mDP）、产量、参与菊粉代谢的酶的基因表达和活性。菊粉合成由蔗糖：蔗糖 1-果糖基转移酶（EC 2.4.1.99）（1-SST）和果聚糖：果聚糖 1-果糖基转移酶（EC 2.4.1.100）（1-FFT）催化，在块根发育开始时进行。菊粉产量随时间的变化呈 S 形曲线，在 11 月达到最大值。菊粉 mDP 在 9 月达到最大值约 15，然后逐渐下降。基于菊粉积累模式的变化，我们在生长季节定义了三个不同阶段，并在这些定义的阶段分析了产物形成、酶活性和基因表达。通过在气候室中进行控制条件下的实验验证了结果。我们的结果表明，6 月开始的 1-SST 减少不受日照时间和温度的调节。从 9 月中旬开始，尽管菊粉产量仍在增加，但平均聚合度（mDP）逐渐下降。mDP 的降低加上产量的增加是由于低温诱导的果聚糖外切水解酶活性和 1-FFT 的反向转移活性。总的来说，这项研究为如何提高菊苣中菊粉的产量和质量提供了背景信息。
