Inulin and inulin metabolizing enzyme activities during the growth cycle of wild cardoon

Inulin-type fructan is a fructose polymer that has mostly or exclusively the ? (2 -> 1) fructosyl-fructose linkage, essentially linear molecules, but a low degree of branching can occur through ? (2 -> 6) linkages. A study focusing on the sugar accumulation (inulin and water soluble sugars) in roots of the different taxon of Cynara cardunculus grown in Mediterranean environment for two years, showed the storage of fructans in underground organs of these species is as an adaptive strategy to overcome the Mediterranean unfavorable conditions. In this view the three taxa showed different biomass accumulation and partitioning, reflecting in inulin accumulation and/or breakdown in roots. The aim of this study was to analyze the activities of the enzymes involved in sugars metabolism in the roots of wild cardoon plants during their complete growth cycle under Mediterranean conditions. The experiments were carried out in Sicily (South Italy) at Catania (37°27' N, 15°4' E, 10 m a.s.l.) during 2005/06 on one wild cardoon Sicilian population "S3". During the whole plant growth, the DM plant accumulation, the root sugar characterization (glucose, fructose, sucrose and inulin), and the enzyme activities of sucrose:sucrose 1-fructosyl transferase (1-SST; EC 2.4.1.99), fructan 1-exohydrolase (1-FEH; EC 3.2.1.80), fructan 1-exohydrolase (1-FEH; EC 3.2.1.80) and acid invertase (EC 3.2.1.26) were analyzed. Results showed the variation in DM accumulation is strictly correlated with inulin synthesis and breakdown in roots and inulin metabolizing enzyme activities. In particular the maximum synthesis activity was recorded just before passing from the vegetative to reproductive phase, while with the beginning of the reproductive phase occurred the breakdown of inulin supplying stalks and flower formation. © ISHS.