In order to better understand the role of antioxidant enzymes in plant stress protection mechanisms, transgenic tobacco ( Nicotiana tabacum cv. Xanthi) plants were developed that overexpress both superoxide dismutase (SOD) and ascorbate peroxidase (APX) in chloroplasts. These plants were evaluated for protection against methyl viologen (MV, paraquat)-mediated oxidative damage both in leaf discs and whole plants. Transgenic plants that express either chloroplast-targeted CuZnSOD (C) or MnSOD (M) and APX (A) were developed (referred to as CA plants and AM plants, respectively). These plant lines were crossed to produce plants that express all three transgenes (CMA plants and AMC plants). These plants had higher total APX and SOD activities than non-transgenic (NT) plants and exhibit novel APX and SOD isoenzymes not detected in NT plants. As expected, transgenic plants that expressed single SODs showed levels of protection from MV that were only slightly improved compared to NT plants. The expression of either SOD isoform along with APX led to increased protection while expression of both SODs and APX provided the highest levels of protection against membrane damage in leaf discs and visual symptoms in whole plants.

Aims: To screen bioherbicidal isolates and evaluate herbicidal activity of methoxyhygromycin (MHM) produced by Streptomyces sp. 8E-12. Methods and Results: Streptomyces sp. 8E-12 with herbicidal activity was selected through seed germination bioassay. An active metabolite, MHM was isolated from culture broth by carbon absorption, butanol extraction, silica gel, Sephadex LH-20 and G-10 chromatography, and preparative HPLC. The metabolite was identified by electrospray ionization mass spectra (ESI-MS) and 1 H-and 13 C-NMR spectral data analyses. In vivo herbicidal activity was examined against weeds and crops grown on pots. Conclusions: Streptomyces sp. 8E-12 produced a selective herbicidal metabolite which was identified as MHM. The metabolite showed stronger in vivo activity against monocotyledonous plants than dicotyledonous plants, and caused a bleaching (albino symptom) on some weeds including Digitaria sanguinalis and Echinochloa crus-galli. Significance and Impact of the Study: These results showed that Streptomyces sp. 8E-12 produced a bioherbicidal metabolite, MHM and can be developed as a biocontrol agent (BCA) for weed control.