NO-mediated hypersensitive responses of rice suspension cultures induced by incompatible elicitor

Magnaporthe grisea special races 98-186-1G1 and 97-23-2D1 induce incompatible and compatible reactions respectively with rice "Xiushui". The elicitor from the cell wall of M. grisea race 98-186-1G1, termed 1E, strongly induced the HR response in suspension cultures of rice "Xiushui", including increased PAL activity, transcription of pal, pr1, chi, cell death and the generation of NO. The elicitor prepared from the cell wall of M. grisea race 97-23-2D1, named CE, was much less efficient at inducing such effects. The NOS enzyme inhibitors L-NAA and PBITU suppressed the production of NO induced by 1E in "Xiushui" rice. The increased PAL activity and transcription of pr1, pal, chi genes induced by. 1E were blocked by L-NAA, PBITU or CPTIO pretreatment. Direct treatment of rice cultures with the NO donor (SNP) also induced the transcription of pr1, pal and chi genes. These data implicated that NO acted as a signal mediating the HR induced by 1E in rice and showed that NO, in combination with H2O2, is necessary for induction of cell death by IE in rice suspension cells.