CARBOHYDRATE CONTENT, FRUCTAN AND SUCROSE ENZYME-ACTIVITIES IN ROOTS, STUBBLE AND LEAVES OF RYEGRASS (LOLIUM-PERENNE L) AS AFFECTED BY SOURCE SINK MODIFICATION AFTER CUTTING

Glucose, fructose, sucrose and fructans were the main. non-structural carbohydrates of perennial ryegrass. Fructans accumulated predominantly in stubble, i.e. in the basal part of the leaves. Regrowth after defoliation involved two different phases. The first one (0 - 6 days) was characterized by the mobilization of carbohydrates in both roots and stubble to sustain foliage development in the absence of current photosynthate. During the second phase (6 - 29 days) carbohydrate content rose to the values observed prior to cutting. Concomitant with a decrease in soluble protein and in non-structural carbohydrate contents, sucrose-sucrose-fructosyltransferase (SST) activity decreased during the first 6 days in roots and stubble whereas fructan exohydrolase (FEH) activity increased and invertase activity was high. Prior to the subsequent increase in carbohydrate content, sucrose synthase activity increased sharply while sucrose phosphate synthase showed only slight variation. During the second period of regrowth FEH declined and SST increased. In regrowing leaves, however, fructan accumulation was not paralleled by an increase in SST activity. Results are interpreted and discussed in terms of source-sink relationships and carbohydrate partitioning.