Biochemical and morphological features of rice cell death induced by Pseudomonas avenae

Pseudomonas avenae is a Gram-negative phytopathogenic bacterium that causes the symptom of a brown stripe in infected susceptible plants. The host range of P, avenae is wide among the monocotyledonous plants, however, individual strains can infect only one or a few host species. A rice-incompatible strain, N1141, caused rapid cell death in sheath sections and in cultured rice cells. A rice-compatible strain, H8301, also induced cell death, however, this cell death in a compatible interaction was delayed compared to the cell death induced by the N1141 incompatible strain. Inoculation of N1141 strain induced expression of EL2 gene which is thought to be one of the defense-related gene. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) of cultured rice cells showed that DNA cleavage occurred only in N1141-inoculated rice cells. N1141 strain caused cytoplasmic condensation, shrinkage, and plasma membrane blebbing, all of which are important morphological characteristics of programmed cell death (PCD). In contrast, H8301 strain inoculated rice cells appeared to show weakening of the cell wall instead of cytoplasm condensation, shrinkage and membrane blebbing. These results suggest that the rapid cell death of rice induced by the incompatible strain is characterized as PCD.