An ultrastructural study, including cytochemistry and quantitative analyses, of the interactions between pseudomonads and leaves of Phaseolus vulgaris L. |
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| Authors: | I R Brown J W Mansfield |
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| Abstract: | Infection of Phaseolus vulgaris cultivars Red Mexican and Tendergreen with Pseudomonas fluorescens, P. syringae pv. coronafaciens, P.s. pv. phaseolicola races 1 and 3, and a mutant of race 3 (race 3 M1) with altered cultivar specific virulence was examined. In addition to qualitative observations of the development of colonies of bacteria and the responses in adjacent plant cells, quantitative analyses were made of the numbers of bacteria within sections of colonies, contact between bacteria and the plant cell wall, the accumulation of fibrillar acidic polysaccharides (which stained with ruthenium red) around bacteria, convolution of the plant cell membrane adjacent to bacteria, deposition of paramural papillae, rupture of the tonoplast and the occurrence of cytoplasmic disorganization. The presence at infection sites of material staining with the periodic acid, thiocarbohydrazide silver proteinate (PATAg) procedure to localize vicinal glycols was also quantified.Cells of P. fluorescens failed to multiply in the plant and seemed tightly bound at junctions between mesophyll cells. The pathovars of P. syringae all multiplied at similar rates during the first 12 h after inoculation and were not closely attached to the plant cell wall. Fibrillar, ruthenium red staining material, considered to be bacterial extracellular polysaccharides, accumulated around cells of the pathovars of P. syringae irrespective of the compatibility of their interaction with cultivars. Amorphous PATAg positive deposits formed around cells of the saprophyte and as condensed aggregates in colonies of P. syringae pathovars in tissue undergoing the hypersensitive reaction (HR) but not during compatible interactions. The PATAg positive material may be involved in the elicitation of responses by plants during the HR. The first response of plant cells to adjacent bacteria was the localized convolution of the plasma membrane; this response was neither race nor species specific. Deposition of paramural papillae was also found to be a non-specific response occurring during compatible and incompatible interactions. Some components of papillae were PATAg positive. Plasmolytic studies demonstrated that, during the HR, irreversible damage to the plasma membrane first occurred 5 and 8 h after initial convolution of the membrane following inoculation of cv. Tendergreen with P.s. pv. coronafaciens and P.s. pv. phaseolicola race 3 respectively. Tonoplast dysfunction appeared to follow irreversible damage to the plasma membrane and preceded loss of compartmentation and cytoplasmic collapse. The ultrastructural study showed that many plant responses were non-specific and therefore could be separated from irreversible damage to the plasma membrane which was the irrevocable event during the HR. |
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