Fate of fructose supplied to leaf sheaths after defoliation of Lolium perenne L.:: assessment by 13C-fructose labelling

The role of fructans from leaf sheaths for the refoliation of Lolium perenne after severe defoliation was assessed by following the fate of C-13-fructose supplied to leaf sheaths at the time of defoliation. At the end of the 4 h labelling period on defoliated plants, 77% of the C-13 incorporated was still located in leaf sheaths. Only 4% and 0.9% were, respectively, allocated to stem and roots, while 18% was imported by the growing leaves where C-13 was allocated first to the proximal part of the leaf growth zone (0-10 mm). In all tissues, the most highly C-13-labelled carbohydrates was not fructose but sucrose. In leaf sheaths, C-13-loliose was produced. In the leaf growth zone (0-20 mm), fructans were simultanously synthesized from C-13 entering the leaves and degraded. The export of C-13 from leaf sheaths continued during the first day of regrowth but stopped afterwards. There was no net loss of C from C-13-fructose over the first 2 d of regrowth. The role of fructans and lollose is discussed as well as the physiological mechanisms contributing to defoliation tolerance in L. perenne.