Permeability Phenomena in Plant Disease

Abstract. Rates of uptake of 3-o-methylglucose (MeG) by squash (Cucurbita maxima) hypocotyl sections from above lesions caused by Hypomyces solani f. sp. cecurbitae, race 1, are 2-fold greater than uptake by comparable tissues from healthy plants. Kinetic analyses indicate (i) that a single (constitutive) carrier system, with a Michaelis constant (Km) of 25 to 30 mm, mediates the transport of MeG into healthy hypocotyl cells and (ii) that an additional (inducible) system with a much lower Km (ca. 2 mM) is present in diseased hypoootyls. In both systems MeG uptake is inhibited competitively by glucose. The inducible transport system(s) in diseased tissues has a higher temperature coefficient, greater sensitivity to metabolic inhibitors and larger accumulation capacity than the one in healthy plants. While the nature of the oonstitutive system is ambiguous, the inducible carrier mechanism is a typical active transport system. These results indicate that increased rates of uptake and accumulation of metabolites by diseased tissues can be caused by new transport systems.Changes in host membrane permeability during pathogenesis have been noted in many plant diseases (13). In a recent study of permeability changes in Hypomyces-infected squash hypocotyls, it was concluded that the permeability of host cells in tissues above lesions did not differ from that of comparable cells in healthy plants (6). In fact, the functioning of plasma membranes as barriers to the movement of water and low molecular weight nonelectrolytes was not altered in individual cells until the fungus grew within their vicinity ( 1-3 cell diameters). Then, the permeability change was sudden, and the plasmolyzability of host cells was destroyed.Thatcher l (11) In this study, transport kinetics of 3-o-methylglucose are compared in healthy squash hypocotyls and hypocotyl tissues above lesions caused by Hypomnyces (Fusarium) solani f. sp. cucurbitae, race 1. With the use of a glucose derivative, 3-o-methylglucose, uptake by glucose transport systems can be investigated while complications from metabolic processes are avoided (8). Materials and MethodsInoculation Procedures. Cultures of the pathogen (Hypomnyces solani f. sp. cucurbitae Snyd. and Hans., race 1) were maintained as described previously (5). Squash (Cucurbita inaxima Dcne "Pink Banana") were grown in the greenhouse in U. C. mix (1). Three-to 6-day-old seedlings were inoculated with 1 ml suspensions of macroconidia (6 X 105/ml) at the base of hypocotyls. Uninoculated seedlings of identical plantings were maintained as controls. Lesions developed at the base of hypocotyls 5 to 7 days after inoculation. As in a previous study (6), seedlings with lesions 1 to 2 cm in length were used as experimental materials.Uptake of 3-o-methylglucose. Methods for studying uptake are modified from those described by Reinhold and Eshbar (8). Batches of 20 hypocotyl cross sections (ca. 1.5 mm thick) were rinsed briefly (30 sec), blotted dry, and weighed (400-500 mg fresh wt). Sections were taken from uninocu...

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confidence: 99%

Uptake of 3-o-Methylglucose by Healthy and Hypomyces-infected Squash Hypocotyls

Hancock

1969

“…Permeability changes in oats (Avena sativa L.) infected with Helminthosporium victoriae are caused by a pathotoxic substance, vic-torin, secreted by the fungus. The disease is an excellent system for studies on pathological changes in physiology and ultrastructure of plants (13, 16,18). The pathotoxin causes loss of electrolytes and labeled compounds from tissues within minutes after treatment of susceptible oat varieties (11,15).…”

mentioning

confidence: 99%

Localization of Crystals in Diseased Oats Treated with Uranyl Acetate

Easton

Hanchey

1972

Uranyl acetate, a suppressor of victorin-induced electrolyte leakage in oat leaves when applied together with, or before, victorin, also suppressed victorin-induced changes in ultrastructure. Uranyl crystallized in cell walls and near the plasmalemma of vascular cells, but was excluded from the protoplasm. Fewer crystals occurred near the plasmalemma when leaves were allowed to take up uranyl and victorin simultaneously than when uranyl alone was absorbed, but deposition in cell wails was similar in the two treatments. No differences in crystal distribution were found in uranyl-treated leaves which subsequently took up either water or victorin. The most striking effect of prolonged exposure to uranyl was increased vesicular activity in the protoplasm, formation of complex concentric membranes, and tonoplast damage. Following victorin treatment, uranyl post-treatment was ineffective in suppressing electrolyte leakage or preserving normal cellular ultrastructure. More severe ultrastructural damage was found in victorintreated leaves after uranyl post-treatments than after posttreatment with water, a result of victorin-induced damage which facilitates uranyl entry into the protoplasm.Alterations in membrane permeability are characteristic of many diseased plant tissues, and these changes may result in secondary metabolic effects on respiration, photosynthesis, hormone activities, and phenolic levels (3,20). Permeability changes in oats (Avena sativa L.) infected with Helminthosporium victoriae are caused by a pathotoxic substance, victorin, secreted by the fungus. The disease is an excellent system for studies on pathological changes in physiology and ultrastructure of plants (13,16,18). The pathotoxin causes loss of electrolytes and labeled compounds from tissues within minutes after treatment of susceptible oat varieties (11,15). The earliest detected ultrastructural change in diseased oats is near the plasmalemma, suggesting that the primary effect of victorin is on plasmalemma permeability (7).Uranyl salts suppressed both blight symptoms and electrolyte leakage in victorin-treated leaves of susceptible oat varieties, but did not prevent victorin-induced inhibition of root growth (4). These compounds are effective whether supplied

“…Disruption of the integrity of the membranes would result in a more rapid loss of H20 than from -comparable stems with intact membranes (13,14). The fact that toxin-treated stems lost H20 at a slightly slower rate than H20-treated stems suggests that the path of H20 movement to evaporative surfaces was being blocked by the toxin.…”

Section: Discussionmentioning

confidence: 99%

Changes in Alfalfa Stem Conductance Induced by Corynebacterium insidiosum Toxin

Alfen

Turner²

1975

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...