Suppression of the maize phytoglobin ZmPgb1.1 promotes plant tolerance against Clavibacter nebraskensis.

MAIN CONCLUSION: Suppression of the maize phytoglobin ZmPgb1.1 enhances tolerance against Clavibacter nebraskensis by promoting hypersensitive response mechanisms mediated by ethylene and reactive oxygen species. Suppression of the maize phytoglobin, ZmPgb1.1, reduced lesion size and disease severity in leaves following inoculation with Clavibacter nebraskensis, the causal agent of Goss's bacterial wilt disease of corn. These effects were associated with an increase of the transcriptional levels of ethylene biosynthetic and responsive genes, which resulted in the accumulation of reactive oxygen species (ROS) and TUNEL-positive nuclei in the proximity of the inoculation site. An in vitro system, in which maize cells were treated with induced xylem sap, was employed to define the cause-effect relationship of these events. Phytoglobins (Pgbs) are hemoglobins able to scavenge nitric oxide (NO). Suppression of ZmPgb1.1 elevated the level of NO in cells exposed to the induced xylem sap causing a rise in the transcript levels of ethylene biosynthesis and response genes, as well as ethylene. Accumulation of ethylene in the same cells was sufficient to elevate the amount of reactive oxygen species (ROS), through the activation of the respiratory burst oxidase homologs (Rboh) genes, and trigger programmed cell death (PCD). The sequence of these events was demonstrated by manipulating the content of NO and ethylene in culture through pharmacological treatments. Collectively, our results illustrated that suppression of ZmPgb1.1 evokes tolerance against C. nebraskensis culminating in the execution of PCD, a key step of the hypersensitive response.

Inhibitory effect of some transition metal ions on growth and pigment formation of Serratia marcescens.

The inhibitory effect of several first transition metal ions on growth and pigment formation on three strains of Serratia marcescens was studied by the method of minimal inhibitory concentration. From this study it can be concluded that several of the first transition metal ions, namely Cr (II), Mn (II), Fe (II), Co (II) and Cu (II), with the inclusion of Zn (II), have a definite inhibitory effect on both growth (strains 08, WF, 933) and pigment formation (strain 08) of Serratia marcescens. Based on their electron configuration and their effectiveness, these first transition metal ions can be divided into two groups: Cr (II), Mn (II), Fe (II) and Co (II), Ni (II), Cu (II) and Zn (II). Several suggestions were made to explain their inhibitory actions.