Sucrose assimilation during early developmental stages of chicory (Cichorium intybus L.) plants

The activities of enzymes of both sucrose and fructan metabolism were measu red in chicory (Cichorium intybus L. cv. Turbo) plants during early vegetat ive growth. From 21 to 42 d after sowing (phase I), carbohydrates were used for structural growth and sucrose was predominantly cleaved by acid invert ase whereas neutral invertase (EC 3.2.1.26) and sucrose synthase (EC 2.4.1. 13) activities were low. From 49 to 63 d after sowing (phase II) a cambium formed producing secondary tissues, concomitant with induced sucrose:sucros e 1-fructosyl transferase (1-SST; EC 2.4.1.99) and fructan:fructan-1-fructo syl transferase (EC 2.4.1.100) activities, and fructan synthesis in the roo ts. Accumulation of 1-SST mRNA occurred at the onset of thickening, indicat ing that 1-SST is controlled at a transcriptional level. Acid invertase act ivity gradually increased during phase I and remained high during early pha se II. It subsequently decreased. The pattern of invertase mRNA accumulatio n correlated with the enzyme activities, indicating that acid invertase Is controlled at the transcriptional level. Both acid invertase and 1-SST prob ably contributed to the sink strength in the root at the beginning of phase II.