Fructan accumulation induced by nitrogen deficiency in barley leaves correlates with the level of sucrose : fructan 6-fructosyltransferase mRNA

Hydroponically cultivated barley plants were exposed to nitrogen (N)-defici ency followed by N-resupply. Metabolic and genetic regulation of fructan ac cumulation in the leaves were investigated, Fructan accumulated in bailey l eaves under N-deficiency was mobilized during N-resupply. The enhanced tota l activity of fructan-synthesizing enzymes, sucrose:sucrose 1-fructosyltran sferase (EC 2.4.1.99) and sucrose:fructan 6-fructosyltransferase (G-S FT; E C 2.4.1.10) caused by N-deficiency decreased with the mobilization of fruct an during N-resupply. The activity of the barley fructan-degrading enzyme, fructan exohydrolyase (EC 3.2.1.80) was less affected by the N status. The low level of foliar soluble acid invertase activity under N-deficiency cond itions was maintained during the commencement of N-resupply but increased s ubsequently. Further analyses by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, western blot and northern blot demonstrated that the fruct an accumulation and the total activity of fructan-synthesizing enzymes corr elated with the 6-SFT mRNA level. We suggest that the changes in fructan le vels under N stress are intimately connected with the regulation of fructan synthetic rate which is mostly controlled by 6-SFT.