Rapid induction of defense/stress-related proteins in leaves of rice (Oryza sativa) seedlings exposed to ozone is preceded by newly phosphorylated proteins and changes in a 66-kDa ERK-type MAPK

Ozone, a notorious environmental pollutant, potently induced defense/stress-related proteins in the leaves of two-week-old rice seedling, as evidenced by high-resolution two-dimensional electrophoresis. These inductions by ozone were preceded by very early (within minutes) and specific changes in the phosphorylation status of proteins, including the appearance of new phosphoproteins, over the unchanged filtered pollution free air control. Furthermore, a protein of approximately 66-kDa in leaf extracts showed strong and specific cross-reaction with an anti-MAPKinase (ERK1) antibody, and whose levels increased within 5 min of ozone exposure, over its decrease in control, which may suggest possible involvement of ERK-type MAPKs in the ozone-elicited self-defense response pathway(s) in rice. Furthermore, global signaling molecules, potent protein phosphatase inhibitors, and cut also significantly enhanced the level of this MAPK in leaf segments, providing additional support for its involvement in the cut/wound- and the defense/stress-response(s). Moreover, in-gel kinase assay revealed rapid activation of a 48-kDa. myelin basic protein-phosphorylating activity by ozone in seedling leaves over control. Present results provide first data on the activation of the kinase-signaling cascade(s) downstream of ozone perception in rice seedling leaves that might be involved in the ozone-elicited rice self-defense response(s).