Submitted to: Plant Cell Tissue and Organ Culture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/1997
Publication Date: N/A
Interpretive Summary: Leafy spurge is a serious weed problem in the pastures, rangelands and forests of the U.S. Great Plains that reduces the quality of feed for livestock and reduces land values. Chemical herbicides used to control leafy spurge are often ineffective, expensive, and may harm native plants. This has led to interest in biological control methods to manage leafy spurge using insects and disease agents. We previously selected bacteria that inhibit seedling growth of leafy spurge. We examined the intimate relationship of the bacteria with artificially grown leafy spurge cells (tissue culture) to gain more information on how the bacteria actually harm the plant. We found that our selected bacteria could cement or paste themselves directly to plant cells. In some cases, bacteria could nestle between cells and remain there, apparently feeding off nutrients leaked from the cells. The bacteria also produced toxic compounds that were absorbed by cells causing deformed cells and ultimately inhibiting growth of the tissue culture. Our results show that bacteria with potential for controlling leafy spurge can establish "factories" on plant cells that produce natural chemicals toxic to weed growth. Widespread use of these agents may aid in managing weed problems and in reducing our reliance on chemical herbicides.
Technical Abstract: The interaction of two rhizobacterial isolates, Pseudomonas fluorescens isolate LS102 and Flavobacterium balustinum isolate LS105, with leafy spurge cells at the cellular level was studied using scanning and electron microscopy. Leafy spurge callus tissue inoculated with either isolate showed considerable changes compared to non-inoculated tissue. The attachment of rhizobacteria to cell surfaces was associated with the elaboration of fibrillar material which may anchor bacteria to surfaces and contribute to mediation of the phytotoxic effect caused by rhizobacteria. At the ultracellular level, inoculated callus tissue showed numerous cell alterations including vesiculation and convolution of the plasmalemma, cell wall degradation, and disorganization of the cytoplasm, similar to those detected in the whole plant. It is concluded that callus tissue provides an excellent working model to investigate the mode and/or mechanism of action of potential biocontrol agents on their host plants.