Effects of leaf cytokinin induced by root nitrate absorption on the continuous regrowth of defoliated ryegrass

The effect of root nitrate (NO3-) absorption on the continuous regrowth of ryegrass under frequent defoliation was studied in this experiment. Results showed that frequent defoliation caused a significant decline in root bleeding sap quantity, NO3- and cytokinin content in leaves, as well as biomass of newly grown leaves when no external nitrate source was available. The absorption of NO3- by roots easily increased root bleeding sap quantity, NO3- content in roots, accumulated NO3- quantity in bleeding sap, NO3- and cytokinin content in leaves, as well as biomass of newly grown leaves whenever the external nitrate source was supplied after the first or third clipping. The stimulation effect of leaf cytokinin on the continuous regrowth of defoliated ryegrass is not depending on the cytokinin transported from root to leaf, but on the synthesis of leaf cytokinin induced by the NO3- transported from roots to newly grown leaves.