Fructans and fructan-metabolizing enzymes in leaves of Lolium perenne

Longitudinal variability is reported in internal carbon partitioning as is the activity of enzymes involved in fructan synthesis during leaf development of Lolium perenne cv. Bravo. Sink activity was reduced in L. perenne plants by cooling the roots while continuous illumination enhanced source activity, resulting in preferential accumulation of fructans at the leaf base. Fructan contents and enzymatic activity of two trisaccharides (SST (sucrose:sucrose fructosyltransferase) and 6G-FT (fructan:fructan 6C-fructosyltransferase)) were measured in segments of elongating leaves, both mature leaf blades and sheaths. The complement of fructans accumulated was similar in both elongating leaves and mature leaf sheaths. 6G-FT activity was found in L. perenne and characterized in a crude extract; this activity was greatest in the basal segment of elongating leaves and mature leaf sheaths. Throughout the leaf blade, however, SST and 6G-FT activities remained low and constant, and did not increase under conditions of sucrose accumulation. Differences are shown in fructan accumulation between leaf tissues; the significance of these findings and the putative pathway of fructan synthesis in L perenne are discussed.