Changes in Alfalfa Stem Conductance Induced by Corynebacterium insidiosum Toxin

Abstract

A toxin involved in bacterial wilt of alfalfa (Medicago sativa L.) has been isolated from cultures of the pathogen, Corynebacterium insidiosum, as well as from diseased plants (S. M. . Physiological Plant Pathology 2: 133-142). The influence of this toxin, a glycopeptide with a molecular weight of 5 X 106, on the water relations of alfalfa was examined. It was found that very small amounts of the toxin (2 Ag) significantly reduced stem conductance through 15-cm long stems. This decrease in stem conductance caused by the toxin best explains the rapid decrease in transpiration and stomatal conductance and the resultant wilting after alfalfa cuttings have been in 200 jug ml-' toxin for 2 hours. Membrane damage resulting in water leakage was ruled out as a factor in the wilting during the 2-hour period. It is postulated that the toxin acts by interfering with water movement through pit membranes.Bacterial wilt of alfalfa, Medicago sativa L. is caused by Corynebacterium insidiosumn (McCull.) Jensen. This bacterium produces a toxin in culture which reproduces the wilting symptoms of the disease when introduced into cuttings (4, 6). Ries and Strobel (4) purified this toxin and showed that it was a glycopeptide with a mol wt of 5 x 106. They also reported (5) that a similar glycopeptide could be isolated from diseased plants in amounts sufficient to cause wilting, indicating that the toxin is probably important in producing the disease symptoms in infected plants. Ries and Strobel (5) showed that the toxin was capable of inducing wilting symptoms in plants other than alfalfa. While indicating that the mode of action of the toxin was unknown, the same authors showed that it was more effective in causing wilting of tomatoes than amylopectin (mol wt = 70 X 106) or blue dextran (mol wt = 2 X 106), and thus they concluded that physical plugging of the transpiration stream was excluded as a possible mode of action and suggested that the toxin caused membrane damage in a similar manner to C. sepedonicum and C. michiganense (9). Our previous work (13) on the mode of action and suggested that the toxin caused membrane damage in a similar manner to C. sepedonicum and C. michiganense (9). Our previous work (13) and of 2 X 106 were also prepared at concentrations of 200 jug ml-' in H20 and filtered and degassed.The conductance of alfalfa (Medicago sativa L. var. Iroquois) stems, 0.2 to 0.3 cm in diameter and 15 cm long, to test solutions was determined using a pressure chamber (10) as previously described (13). The stem segment, without leaves, was sealed into the pressure chamber with one end dipping into a test tube containing the test solution. Petiole scars not submerged in the test solution were sealed with RTV-22 silicone rubber cement (General Electric). A short, small diameter tube was filled with H2O and attached to the end of the stem external to the pressure chamber. The tube was then attached to a horizontal 0.1-ml pipette. The time required for each 0.01 ml of solution to flow from the stem under pressure of...

The Plant Pathogenic Corynebacteria

“…Other workers have not detected any physiological (175) or ultrastructural (184) evidence of membrane damage in either alfalfa cuttings treated with low concentrations of C. m. ssp. insidiosum "toxin" (175) or in infected alfalfa plants (37) or infected tomato plants (184). In the Van Alfen & Turner (175) study, as little as 2 p.g of toxin forced into the stem resulted in a marked (19%) decrease in water conductance, and 200 p.g/ml was effective in visible wilting.…”

“…sepedonicum "toxin" per ml for 2 hr and for potato stems sampled 4 to 5 weeks after inoculation with the same organism (71). Other workers have not detected any physiological (175) or ultrastructural (184) evidence of membrane damage in either alfalfa cuttings treated with low concentrations of C. m. ssp. insidiosum "toxin" (175) or in infected alfalfa plants (37) or infected tomato plants (184).…”

Susceptibility of Plants to Vascular Disruption by Macromolecules

“…Van Alfen and Turner showed that two of these large phytotoxins, produced respectively by Corynebacterium insidiosum (8) and Ceratocystis ulmi (9), act by interfering with water conduction in the plant's vascular system and not by any direct toxicity to plant cells. The decrease in vascular conductance through stems of the wilted cuttings caused by these macromolecules was not large.…”

The effects of microbial exopolysaccharides (EPS) in vase water on the water relations and the vase life of Rosa cv. Sonia

“…In most of the work reported by other authors, purified bacterial polysaccharides (see Corey & Starr 1957) or artificially synthesized polymers were applied to elucidate the mechanisms of phytopathogenicity. The effects of polysaccharides on ornamental cut flowers, however, have rarely been studied (Hodgson et al 1949;Van Alfen & Turner 1975;Van Alfen & Allard-Turner 1979;Van Alfen et al 1983;de Stigter & Broekhuysen 1986;Neumann 1987). In the present work, molecular filtrates and retentates of supernatant fluids of pure cultures of several micro-organisms grown in an agitated sucrose-containing medium were used as a vase medium for cut roses cv.…”

“…Thus, in addition to diverting xylem flow, xylem-borne polymers might directly induce senescence of leaf cells (Neumann 1987). The apparent absence of visible xylem blockage by plant polysaccharides reported by Van Alphen &Turner (1975) andNeumann (1987) suggests that complex hormonal regulation may affect polysaccharide concentrations in specific sections of the xylem system. To reveal the occurrence of this phenomenon, further research is needed (Halverson & Stacey 1986).…”