Nitric Oxide Generation And Its Mediation To Hypersensitive Response During Incompatible Interaction Of Rice

Nitric oxide (NO) is highly diffusible and with very low solubility aqueous solutions, which could function as an intracellular and intercellular signaling molecule. The widespread biological significance of nitric oxide was first observed in the cardiovascular, central nervous and immune systems.The founctions of NO in animals were fairly well known. Research on NO in plant had reviewed in recent years that the biosynthesis of NO in plant was similar with its in animal. NO played an essential role in plant development, especially in disease resistance. However, the role and the mechanism of NO and NO signaling pathway during the molecular interaction of rice with bacterial phytopathogen were unclear.The publication of genome sequence of Oryzae sativa cv. Nipponbare and Xanthomonas oryzae pv. oryzae (Xoo) made the interaction of rice and Xoo become one of the plant-pathogen interaction research models. In this research, the interactions of incompatible bacterial phytopathogen Xanthomonas.campestris pv. vesicatoria (Xcv) and compatible bacterial phytopathogen Xoo with Nipponbare were used to investigate the production of NO, the activities of iNOS and the role of NO in hypersensitive response (HR).The results showed that first during the interaction of rice with Xcv, the production of a massive of NO occurred after inoculation, and the concentration was higher than 522μM . While NO was not found during the interaction of rice with Xoo; second, iNOS and NR were responsible for the production NO in incompatible interaction.We found that the iNOS activity varied directly as the time after inoculation, and the specific activity was 2.13pmol/min/mg. NOS competitive inhibitor L-NNA (50mM) could surpress iNOS activity obviously; In compatible reaction, iNOS activity was lifted at the beginning, and then suppressed to zero. At last, during the incompatible interaction, chromatin condensation and marginalization in the nucleus happened, but DNA cleavage of nucleosomal and"DNA Ladder"didn't occurre. Defense response genes encoding glutathione S-transferase (gst), peroxidase (pox) and phenylalanine ammonia lyase gene (pal) were induced and NO scavenger PTIO could eliminate the induction of such genes; In compatible interaction, morphological features of cell were similar with necrosis, and defense response genes expression were also inhibited .