Changes in protein tyrosine phosphorylation during mannose and senescence induced cell death in rice

In mammals protein tyrosine phosphorylation plays an important role in the activation of apoptosis. However, tyrosine phosphorylation associated with cell death has not been examined in plants. We monitored changes in tyrosine phosphorylation during cell death in rice (Oryza sativa L.) suspension cultures. Cell death was induced in the cell cultures by mannose treatment or by allowing the cultures to senescence. We have demonstrated that both mannose and senescence induced DNA fragmentation in rice suspension cells. In the presence of mannose, the tyrosine phosphorylation patterns of mannose treated and non-treated cell proteins are basically the same, except the tyrosine phosphorylation intensity is considerably different. In aged suspension-cultured cells, the occurrence of DNA fragmentation was detected. In addition, the tyrosine phosphorylation pattern was changed. These results suggest that protein tyrosine phosphorylation may have a role in distinct signal transduction pathways responding to mannose and senescence. The expression of a gene that encodes mitogen-activated protein kinase (MAPK), OsMAPK2, is up-regulated during mannose treatment, suggesting the possible involvement of rice MAPK in pathways associated with rice cell death induced by >d-mannose.