Phytoglobins can interfere with nitric oxide functions during plant growth and pathogenic responses:: a transgenic approach

To investigate the possible role of the non-symbiotic plant hemoglobins (phytoglobins) in relation to nitric oxide (NO) functions and their presumable involvement in NO- or pathogenesis-induced necrosis, we have produced transgenic tobacco plants (HOT lines) overexpressing an alfalfa hemoglobin cDNA (Mhb1) under the control of CaMV35S promoter. Upon treatment with active sodium nitroprusside (SNP), a widely used NO donor, the germination of seeds and development of seedlings were significantly less retarded in transgenic lines compared with the retardation of non-transformed seedlings. SNP-injection necrotized mature plant leaves of Mhb1-transformants to a lower extent than control leaves. Furthermore, infection of tobacco leaves either with Pseudomonas syringae pv. phaseolicola or Tobacco Necrosis Virus (TNV) resulted in reduced necrosis of mature transgenic plants. In response to bacterial infection, reactive oxygen species (ROS) and salicylic acid (SA) were produced at a higher level in transgenic HOT plants than in control ones. The presented experimental data support a conclusion that plant non-symbiotic hemoglobins are active functional partners in NO-dependent physiological responses such as alteration of plant growth and development as well as cell death and symptom generation after pathogen infection. The described experiments provide new insights to the role of phytoglobins in ROS-, NO- and SA-mediated cellular events during the induction of necrotic cell death. (C) 2003 Elsevier Ireland Ltd. All rights reserved.