|ARMSTRONG, DONALD - Oregon State University|
|MILLS, DALLICE - Oregon State University|
|BAILEY, BONNIE - Oregon State University|
|RUSSELL, BRIAN - Oregon State University|
|GROENIG, ALETA - Oregon State University|
|MCPHAIL, KERRY - Oregon State University|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2009
Publication Date: 6/30/2009
Citation: Armstrong, D., Azevedo, M.D., Mills, D., Bailey, B., Russell, B., Groenig, A., Halgren, A.B., Banowetz, G.M., Mcphail, K. 2009. Germination-Arrest Factor (GAF): 3. Determination that the herbicidal activity of GAF is associated with a ninhydrin-reactive compound and counteracted by selected amino acids. Biological Control. 51:181-190.
Interpretive Summary: A bioherbicide (GAF) that is produced by a soil bacteria and arrests the germination of several grassy weeds was characterized in preparation for subsequent efforts to produce sufficient quantities of the compound for commercialization. We found that the compound reacts with ninhydrin and that the GAF-ninhydrin complex shows up as a blue band on thin layer chromatography analysis. This discovery provides a way to screen other bacterial isolates for their production of GAF. We also showed that GAF appears to arrest germination of weed seeds by interfering with amino acid metabolism. Understanding the process by which GAF inhibits germination will help in the development of synthetic analogs that may have commercial use in agriculture.
Technical Abstract: A novel, naturally-occurring herbicide (Germination-Arrest Factor, GAF), produced by Pseudomonas fluorescens WH6 and several related isolates of rhizosphere bacteria, irreversibly arrests germination of the seeds of a wide range of graminaceous species, including a number of important grassy weed species. GAF activity has been shown previously to be associated with a hydrophilic, low molecular weight compound that contains an acid group. In the present study, thin-layer chromatography (TLC) of extracts of WH6 culture filtrate demonstrated that GAF-activity migrates on TLC plates with a particular ninhydrin-reactive compound. This compound was found to be present in GAF-producing P. fluorescens isolates and absent in P. fluorescens strains that lack the ability to produce GAF. Treatments, including mutagenesis, which resulted in the loss of GAF activity in culture filtrates from P. fluorescens WH6 were shown to result in the disappearance of this ninhydrin-reactive compound from extracts of WH6 culture filtrates or in alteration of its appearance on TLC chromatograms. These results suggest that GAF may be a small peptide or amino acid analog. Biological investigations motivated by this conclusion demonstrated that the effects of GAF in inhibiting the germination of seeds of annual bluegrass (Poa annua L.) could be reversed by treatment with alanine or glutamine and, to lesser extent, by several other amino acids, indicating that this compound may act by interfering with some aspect of amino acid metabolism.