Oxidative stress is a major damaging factor for plants exposed to environmental stresses. In order to develop transgenic potato plants with enhanced tolerance to environmental stress, the genes of both Cu/Zn superoxide dismutase and ascorbate peroxidase were expressed in chloroplasts under the control of an oxidative stress-inducible SWPA2 promoter (referred to as SSA plants). SSA plants showed enhanced tolerance to 250 microM methyl viologen, and visible damage in SSA plants was one-fourth that of non-transgenic (NT) plants that were almost destroyed. In addition, when SSA plants were treated with a high temperature of 42 degrees C for 20 h, the photosynthetic activity of SSA plants decreased by only 6%, whereas that of NT plants decreased by 29%. These results suggest that the manipulation of the antioxidative mechanism of the chloroplasts may be applied in the development of industrial transgenic crop plants with increased tolerance to multiple environmental stresses.
Seed priming is to expose seeds to specific compounds to enhance seed germination. Few studies of plant immune activation through seed priming have been conducted. Here, we introduce an emerging technology that combines seed priming with elicitation of plant immunity using biologically active compounds. This technology is named ‘seed defense biopriming’ (SDB). We prepared heat-stable metabolites from 1,825 root-associated Bacillus spp. isolated from the rhizosphere in South Korea. These preparations were tested for their ability to induce SDB in cucumber and pepper seeds and trigger plant immunity. SDB with heat-stable metabolites of the selected Bacillus gaemokensis strain PB69 significantly reduced subsequent bacterial diseases under in vitro and field conditions and increased fruit yield. Transcriptional analysis of induced resistance marker genes confirmed the upregulation of salicylic acid, ethylene, and jasmonic acid signaling. Mortality of the insect pest Spodoptera litura increased when larvae fed on SDB-treated cucumber tissues. Analysis of the causative bacterial metabolites identified a leucine-proline cyclodipeptide and a commercially obtained leucine-proline cyclodipeptide induced similar results as treatment with the bacterial preparation. Our results indicate that SDB treatment with the heat-stable bacterial metabolite effectively elicited immunity and controlled disease in seedlings to whole plants, thereby increasing yield even under field conditions.
Bioactive herbicidal compounds produced by soil microorganisms might be used to creating a bioherbicide for biological weed control. A total of 1,300 bacterial strains were isolated and screened for herbicidal activity against grass and broadleaf weeds. Among primarily selected 102 strains, the herbicidal activity of bacterial fermentation broths from the following three isolates strain-101, strain-128, and strain-329 reduced the growth of D. sanguinalis by 66.7%, 78.3%, and 100%, respectively as compared with control. Phylogenetic analysis of 16S rRNA gene sequencing determined that the strain-329 has 99% similarity to Streptomyces anulatus (HBUM 174206). The potential bioherbicidal efficacy of Streptomyces strain-329 was tested on grass and broadleaf weeds for phytotoxic activity through pre- and post-emergence applications. At pre-emergence application, the phytotoxic efficacy to D. sanguinalis and S. bicolor on seed germination were 90.4% and 81.3%, respectively at the 2x concentration, whereas in the case of Solanum nigrum, 85.2% phytotoxic efficacy was observed at the 4x concentration. The efficacy of Streptomyces strain-329 was substantially higher at post-emergence application, presenting 100% control of grass and broadleaf weeds at the 1x concentration. Two herbicidal compounds coded as 329-C1 and 329-C3 were extracted and purified by column chromatography and high-performance liquid chromatography methods. The active compound 329-C3 slightly increased leaf electrolytic leakage and MDA production as concentration-dependent manner. These results suggest that new Streptomyces sp. strain-329 produced bioherbicidal metabolites and may provide a new lead molecule for production an efficient bioherbicide to regulate grass and broadleaf weeds.
The synthesis of 2,6-dinitro-4-pentafluorosulfanyl-N,N-dipropylaniline, 2, was achieved in a straightforward manner from commercially available 1-nitro-4-pentafluorosulfanylbenzene. In postemergence screening 2 was found to be approximately twice as potent as trifluralin with the same general spectrum of activity. In contrast, in pre-emergence tests, 2 was nearly 5 fold more potent against quackgrass and crabgrass. Given the existing structureactivity-relationship for adverse properties of the dinitroaniline herbicides, 2 is proposed to have properties quite comparable to the commercial agent trifluralin.
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