Influence of Shading on Flowering Induction and Inulin Metabolism in Roots of Cynara cardunculus L.

AbstractInulin-type fructan is a fructose polymer that has mostly or exclusively the ?(2->1) fructosyl-fructose linkage. In higher plants this carbon source plays animportant role in osmoregulation and crioprotection. The storage of fructans (inulinand water soluble sugars) in underground organs of Cynara cardunculus grown inMediterranean environment represents an adaptive strategy to overcome theMediterranean unfavorable conditions. Moreover, the variation in dry matteraccumulation is strictly correlated with inulin synthesis and breakdown in roots andinulin metabolizing enzyme activities. Since it has been shown that the maximumaccumulation in roots happens just before flower formation, the aim of this workwas to evaluate differences in inulin content and inulin metabolizing enzymes inroots of C. cardunculus var. sylvestris Lam. grown under two different treatments toobtain plants with flower induction (F) or not (WF). The experiments were carriedout at Catania (south Italy, 37°27'N; 15°4'E, 10 m a.s.l.) during 2005-2006. One wildcardoon Sicilian population S3, was sown in pots (35 cm diameter), containing soil assubstrate, for a total of 200 pots. The sowing was performed in October 2005. Half ofthe plants were grown in open air (F), the other half was placed under shade clothes(WF). Plants were harvested every fifteen days from March to June 2006 for a totalof 7 samplings. For each harvest total biomass, including roots, was immediatelyweighed to determine the fresh weight (FW). Corresponding to each sampling, theroot sugar characterization (glucose, fructose, sucrose and inulin), and the enzymeactivities of sucrose:sucrose 1-fructosyl transferase (1-SST; EC 2.4.1.99),fructan:fructan 1-fructosyltransferase (1-FFT, EC 2.4.1.100) and fructan 1-exohydrolase (1-FEH; EC 3.2.1.80) were analyzed. Results showed that the WFplants accumulated higher inulin content in roots than F plants and this result iscorrelated with the 1-FFT activity, the enzyme responsible of elongation of fructosechain of inulin-type fructans.