Showing papers in "Physiologial Plant Pathology in 1971"

Formation and activity of phaseollin in the interaction between bean hypocotyls (Phaseolus vulgaris) and physiological races of Colletotrichum lindemuthianum

Abstract: Quantitative measurements, using thin layer chromatography plus ultraviolet spectophotometry and gas-liquid chromatography, have shown that phaseollin accumulation was limited to infected tissue which was visibly brown. Phaseollin accumulated much earlier following infection by an incompatible race, which caused hypersensitivity, than by a compatible race which eventually caused lesions to form. Basal phaseollin metabolism was not affected by the extensive intracellular growth of compatible races of Colletotrichum lindemuthianum which continued for several days before host cells collapsed and became brown. Concentrations of 71 to 147 μg phaseollin/g fresh weight excised hypersensitive tissue were detected. However, calculations suggest that phaseollin concentrations in hypersensitive cells might be many-fold higher than these values. Germination of all races was equally sensitive to low concentrations of phaseollin (less than 10 μg/ml). Although germ-tube growth was also inhibited by small amounts of phaseollin, mycelial growth was less sensitive and experiments indicated that phaseollin was metabolized by hyphae in liquid culture. The production, cellular distribution and concentration, and fungitoxicity of phaseollin are discussed in relation to the importance of phaseollin in restricting hyphal growth during hypersensitive reactions.

Pectic enzymes produced by Erwinia chrysanthemi and their effects on plant tissue

Abstract: Erwinia chrysanthemi produced extracellular enzymes which degrade pectic acid in a trans -eliminative manner. Isolate 307, from carnation, produced at least two, and isolate EC 23 , from Philodendron , produced at least four polygalacturonic acid trans -eliminases. The enzymes produced by each isolate were separated from each other and purified by ammonium sulfate fractionation, diethylaminoethylcellulose column chromatography, and electrofocusing. Molecular weights for the six enzymes ranged between 30,000 and 36,000 as determined by gel filtration in Sephadex G-75 and sucrose density gradient centrifugation. The isoelectric points of two enzyme fractions from isolate 307 were pH 9·1 and 7·9 and those for the four enzyme fractions from isolate EC 23 were pH 9·4, 8·4, 7·9 and 4·6. Random cleavage of pectic acid was greatest with the enzyme fractions having isoelectric points at pH 9·4 and 9·1, intermediate for the fraction with an isoelectric point at pH 4·6, and least with the fractions with isoelectric points at pH 8·4 and 7·9. All of the trans -eliminases exhibited a Ca 2+ requirement and had pH optima between pH 8·2 and 9·8. All but one of the purified polygalacturonic acid trans -eliminase fractions from both E. chrysanthemi isolates induced electrolyte loss, maceration and cell death of potato tissue. The enzyme fraction with an isoelectric point at pH 4·6 from isolate EC 23 did not macerate potato, carrot or cucumber tissue even though it readily degraded pectic acid prepared from onion, carrot and cucumber as well as commercial sources of sodium polypectate, polygalacturonic acid and pectin N.F.

A fungal growth stimulant in anthers which predisposes wheat to attack by Fusarium graminearum

Abstract: Massive growth of Fusarium graminearum occurred on the extruded anthers but not other parts of wheat plants within 48 h of inoculation. Infection experiments using either aerosols of conidia on emasculated or non-emasculated heads, or point inocula on anthers or glumes of non-emasculated heads showed that extruded anthers promoted the invasion of other head organs. Extracts of anthers were more stimulatory to the growth of the fungus in vitro than extracts of any other wheat organ. Hence the susceptibility of anthers appears to be due to a fungal growth stimulant.

Ultrastructure of an immune and a susceptible reaction of cowpea leaves to rust infection

Abstract: An ultrastructural comparison of the susceptible and immune reactions of Vigna sinensis leaves infected with Uromyces phaseoli var. vignae showed that signs of incompatibility were detectable in the immune variety during the early stages of haustorial formation when a deposit of callose-containing material was formed on the host cell wall around the point of entry of the haustorium. No such reaction was observed in the susceptible variety. Haustorial formation in the immune variety examined resulted in either the simultaneous necrosis of both host cell and haustorium or the enclosure of the living haustorium in a callose-containing sheath possibly derived from the activity of dilated rough endoplasmic reticulum. Before either of these reactions were detectable, however, the host plasmalemma around the haustorial body appeared much convoluted and was associated with aggregations of phospholipid-like material. It is suggested that, in the absence of the hypersensitive reaction, changes in the host plasmalemma, rather than sheath formation, are of primary importance in restricting further fungal growth.

Properties of syringomycin, a wide spectrum antibiotic and phytotoxin produced by Pseudomonas syringae, and its role in the bacterial canker disease of peach trees

Abstract: Methods were devised for the large-scale production of syringomycin using stainless steel trays which were poured with agar medium, and then covered with cellophane. The bacteria were grown on the surface of the cellophane. Syringomycin was then extracted from the cellophane and purified by ion exchange column chromatography and partition chromatography; it was a single, low molecular weight, ninhydrin-reactive compound. Nine ninhydrin-reactive spots were detected in the acid hydrolysate of syringomycin by two-dimensional chromatography. Eight of the spots corresponded in RF and color to amino acids tentatively identified as aspartic acid, d -glutamic acid, serine, glycine, α-alanine, valine, d -phenylalanine and d -lysine. Investigation of some of the properties of syringomycin showed that its antibiotic activity was labile in alkaline solutions, especially above pH 8. Syringomycin is soluble in water and the lower alcohols, and insoluble in ether and chloroform. Its isoelectric point is about pH 7. Syringomycin has a wide spectrum of antibiotic activity. A species of each of six genera of bacteria, four different fungal species, a unicellular algal species and a Daphnia species were all inhibited by low levels of syringomycin. The growth of Geotrichum candidum, the most sensitive of the organisms surveyed, was completely inhibited by 24 μg syringomycin per ml. Syringomycin produced phytotoxic symptoms in the leaves of peach shoots when the stems were immersed for 24 h in a water solution of syringomycin containing 600 μg syringomycin per ml. The stems of peach shoots became brown and necrotic after being immersed for one week in a solution containing 6 μg syringomycin per ml. Inoculations of peach shoots with Pseudomonas syringae showed that the symptoms produced by the bacterium were very similar to the phytotoxic symptoms produced by syringomycin. Inactivation of the antifungal activity of syringomycin by mild pH manipulation also decreased its phytotoxicity proportionately. An antibiotic which was indistinguishable from syringomycin was isolated from diseased host tissues. It was concluded that syringomycin is probably the major phytotoxin in the bacterial canker disease of peach trees.

Acquisition of virulence by non-pathogenic isolates of Agrobacterium radiobacter

Abstract: Tumours developed on tomato plants inoculated with Agrobacterium radiobacter var. tumefaciens biotype 2. When tumours were contaminated with the saprophyte, Agrobacterium radiobacter var. radiobacter biotype 1, the previously saprophytic bacterium became virulent. Acquisition of virulence was dependent on the efficiency of the recipients, on the duration of contact between saprophyte and tumour and on the stage of tumour development. A difference in the efficiency of the donors was not detected. There was no evidence for acquisition of virulence when the bacteria were mixed in liquid culture.

The role of cytokinins in clubroot formation

Abstract: The occurrence of cytokinins in healthy turnips (Brassica campestris L var rapa “Gelria”) and in turnips infected with Plasmodiophora brassicae has been studied Extracts of clubroots were about three times as active in cytokinin bioassays as extracts of healthy turnips Infected and healthy turnips contain compounds with the same RF values Extracts from clubroots have been partially purified and cochromatographed on paper and on thin layer silica gel with zeatin and zeatin riboside One of the active fractions upon silylation showed a gas chromatographic retention time which coincided with the retention time of silylated zeatin Total cytokinin activity was estimated to be 0·1 to 1·0 mg zeatin equivalent/100 kg fresh weight clubroots Healthy turnips contain 10 to 100 times lower amounts of cytokinins These findings are consistent with the fact that explants infected with P brassicae are independent of cytokinins and auxins for their growth, whereas callus of healthy turnip tissue requires these hormones for continued growth However, infected callus did not grow very well on media deficient in both growth hormones A considerable difference was found between the ratios of cytokinins and auxins which must be supplied to obtain maximum yield of infected and healthy callus tissue

A chemical method for estimating Fusarium oxysporum f. lycopersici in infected tomato plants

Abstract: The amount of Fusarium oxysporum f. lycopersici in stems of infected tomato was estimated by measuring N -acetylglucosamine derived from fungal mycelium by enzymic hydrolysis. Hydrolysis, with an enzyme system induced from a soil bacterium, was more convenient and subject to fewer interferences than acid hydrolysis. The variation in the glucosamine/dry weight of F. oxysporum f. lycopersici with morphology, age and cultural conditions was determined on fungus grown in vitro ; 80 μg glucosamine/mg dry weight of fungus was then adopted as a standard for in vivo determinations. The method compares favourably with plating techniques, and is capable of estimating, under optimum conditions, 5 μg fungus/g fresh weight tomato.

Role of cyclic hydroxamic acids in monogenic resistance of maize to Helminthosporium turcicum

Abstract: In maize, a single gene, Ht , conditions chlorotic lesion resistance to northern corn leaf blight caused by Helminthosporium turcicum Pass. The Bx gene mediates the production of cyclic hydroxamates and related compounds which have been implicated recently in the resistance mechanism of maize, wheat and rye to both insects and fungi. In this study, cyclic hydroxamates such as 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one were evaluated as to their role in the monogenic resistant reaction. Resistant deficient ( HtHtbxbx ) and susceptible deficient ( hthtbxbx ) genotypes were compared with resistant normal ( HtHtBxBx ) and susceptible normal ( hthtBxBx ) genotypes. The percentage of leaf area infected was significantly higher in the bxbx genotypes; this was due to an increase in the number and size of lesions. In hthtbxbx plants, the lesions enlarged and became flaccid. Non-infected tissue distal to the lesions became desiccated, suggesting plugging of xylem vessels. In HtHtbxbx plants, the chlorotic lesions became large and transparent before becoming flaccid, while non-infected tissue distal to the lesions remained turgid. The 2,4-dihydroxy-7-methoxy-1,4-benzoxazine-3-on isolated from maize inhibited germination of H. turcicum spores at concentrations of 1 to 10 parts/million. There was little or no germination above 6 parts/million, while spores that germinated had significantly shorter germ tubes at all concentrations.

Hydroxyphaseollin production by soybeans resistant and susceptible to Phytophthora megasperma var. sojae

Abstract: Soybean (Glycine max (L.) Merr.) varieties carrying either of two allelomorphic resistance genes (Rps and rps2) accumulated 6a-hydroxyphaseollin from 10 to 100 times faster when challenged with incompatible Phytophthora megasperma Drechs. var. sojae A. A. Hildb. races than lines inoculated with compatible races. In incompatible host-parasite combinations, the hydroxyphaseollin levels attained were 100 to 400 times the ED50 concentration for inhibition of mycelial growth of Phytophthora megasperma var. sojae; however, 6a-hydroxy-phaseollin accumulated to only 1 to 4 times the ED50 concentration in compatible host-parasite combinations. Hydroxyphaseollin was not detected in non-wounded, unchallenged soybean hypocotyls and did not begin to accumulate until 10 to 12 h after inoculation. Both resistant and susceptible soybean hypocotyls had the capacity to accumulate more 6a-hydroxy-phaseollin and were more resistant as a function of plant age. As reported previously by others, heat treatment broke resistance conferred by the Rps allele. This treatment con-comitantly decreased the rate of 6a-hydroxyphaseollin accumulation in inculated hypocotyls by 90%. The evidence indicated that 6a-hydroxyphaseollin may be the soybean phytoalexin described previously by other workers and that its rapid production is the mechanism of expression of genetically defined resistance to Phytophthora megasperma var. sojae.

The role of rishitin in localizing the invading hyphae of Phytophthora infestans in infection sites at the cut surfaces of potato tubers

Abstract: After inoculating the cut surfaces of tubers and leaf petioles of potatoes with an incompatible race of Phytophthora infestans, the time that elapsed before hypersensitive cell death and initiation of rishitin formation was measured. Rishitin was produced earlier in tuber tissue inoculated 24 h after cutting than in tissue inoculated just after cutting. However, the time that elapsed from hypersensitive death of 20% of the infected cells to initiation of rishitin formation was 8 to 9 h in both types of tissues. When leaf petioles were held in air for 15 h after cutting and then inoculated with the incompatible race, the time from 20% cell death to rishitin formation was about 5·5 h. In petiolar tissue, rishitin was first detected when the growth rate of the intracellular hyphae was about to decrease. In the case of the cut and air-exposed tuber tissue infected by the incompatible race, rishitin reached a concentration of 100 μg/g fresh weight at a time when development of the lesion was ceasing (calculated assuming rishitin accumulated locally in the upper third of the slices used for chemical analysis). This concentration was sufficient to inhibit hyphal growth in vitro. Rishitin seems therefore to play an important role in the inhibition of hyphal growth and lesion development.

Phenolic compounds in relation to phytoalexin biosynthesis in hypocotyls of Phaseolus vulgaris

Abstract: The major phenolic compounds in Phaseolus vulgaris hypocotyls are flavonol glycosides, leucoanthocyanins and hydroxycinnamic acid derivatives. These appear to account for all the reactivity of extracts towards Folin's reagent, when allowance has been made for interfering compounds. Treatment of the hypocotyls with drops of mercuric chloride solution or a culture filtrate of Penicillium expansum causes the production of the phytoalexin phaseollin but only small changes in the levels of endogenous phenols. Coumestrol, a compound related to phaseollin, is produced at the same time. It is suggested that phytoalexin formation in P. vulgaris may represent a specific stimulation of isoflavonoid metabolism which is separate from any general increase in phenol metabolism associated with cell necrosis.

Studies on the mode of action and biogenesis of the phytotoxin syringomycin

Abstract: Syringomycin, a polypeptide phytotoxin produced by Pseudomonas syringae , is involved in the disease development of bacterial canker of peach. Pathogenicity tests in several plant species indicated that disease development was not always related to the production of syringomycin on agar medium either by isolates of P. syringae , or other isolates such as P. mors-prunorum . At sublethal doses syringomycin inhibited uridylic acid incorporation in Geotrichum candidum but stimulated thymidylic acid incorporation. Syringomycin was found to inhibit tobacco mosaic virus local-lesion formation in tobacco and inhibit synthesis of the RNA phage MS2 in Escherichia coli . The nature of this inhibition was not completely determined, but for MS2 it appeared to involve an inhibition of phage attachment. Droplets of aqueous syringomycin solutions had a lower contact angle with polystyrene plastic than did water; this effect on surface tension indicated a possible membrane action for syringomycin. Further experiments revealed that syringomycin caused rapid hemolysis of rabbit red blood cells, and that leakage of 260 nm absorbing materials occurred from cells of G. candidum treated with syringomycin. Electron micrographs of syringomycin-treated G. candidum cells indicated that massive disruption of membrane integrity occurred with lethal doses, and that membrane abnormalities occurred at sublethal doses. Microautoradiography with 14 C-labeled syringomycin indicated that syringomycin was concentrated mainly over the plasmalemma and nuclear membranes. Inhibition of syringomycin activity by sterols and certain phospholipids in agar media indicated that the binding of syringomycin on the membranes could involve membrane lipids. Calcium and magnesium ions also inhibited syringomycin activity. Rabbit antisera for cell wall material from syringomycin-producing and non-producing isolates of P. syringae reacted strongly with syringomycin; this indicated that syringomycin was structurally related to cell wall materials. It appears that syringomycin is a haptenic group of a larger cell wall antigenic substance and that syringomycin may be a product of the cell wall metabolism of P. syringae . The primary action of syringomycin appears to be a rapid detergent-like lysis of cellular membranes. The action of syringomycin on nucleic acids is probably secondary to its action on membranes.

Nature of the phytoalexin produced by alfalfa in response to fungal infection

Abstract: A phytoalexin was isolated from alfalfa (Medicago sativa) leaves by the drop-diffusate technique using spore suspensions of Helminthosporium turcicum as inoculum. The phytoalexin was identified as (−)-3-hydroxy-9-methoxypterocarpan (demethylhomopterocarpin), a compound previously isolated from several tropical leguminous trees. The identification was made on the basis of the mass spectrum, proton magnetic resonance spectra of both the phytoalexin and its monoacetate, infrared and ultraviolet spectra and the physical constants.

Inhibition of Botrytis cinerea spores by bacteria on the surface of chrysanthemum leaves

Abstract: Spores of Botrytis cinerea exhibited poor germination and growth in water drops on the surface of chrysanthemum leaves. The presence of B. cinerea spores in water drops placed on chrysanthemum leaves, or on plastic Petri dishes previously exposed to the air under chrysanthemum plants, resulted in an increased in the number of bacteria together with an inhibition of germination of spores added to the drops after their removal from the leaf. After separating the bacteria from the drops there was a stimulation of germination and growth of test spores. Re-addition of the bacteria resulted in a return of the inhibition. Of five isolates of bacteria from spore drops one caused marked reduction in the length of germ tubes of test spores. The results indicate that bacteria sedimenting on to leaves from the air could have an effect on the resistance of chrysanthemum to B. cinerea . There was no evidence of antifungal substances produced by the leaves or that phytoalexins were formed in response to spores of B. cinerea .

Water relations of Fusarium wilt in tomato

Abstract: The possible causes of wilting in tomato plants infected with Fusarium oxysporum f.sp. lycopersici were examined. Determinations of leaf water potential and solute potential showed that the wilting was due to water stress. The diffusive resistance of leaves to water vapor loss in infected plants was as high as or higher than the resistance in healthy plants at a given leaf water potential, and it was concluded that an alteration in transpirational behavior did not cause water stress to occur in infected plants. Measurements of water flow through excised root systems indicated that infection did not increase the resistance of roots to water flow. When water was forced through stem segments the resistance of infected segments was found to be several times the resistance of healthy segments. However, accurate estimation of xylem resistance in infected plants was impossible by this technique because the resistance of infected segments decreased markedly as water flow occurred. Apparently, a major portion of the resistance in infected xylem can be attributed to material that was removed by abnormally high rates of water flow. In general, the results confirm the hypothesis that a high xylem resistance to water flow is the sole cause of the wilting which characterizes Fusarium wilt.

Wyerone increase in leaves of broad bean (Vicia faba L.) after infection by Botrytis fabae

Abstract: The level of wyerone, in leaves on broad bean plants following infection with Botrytis fabae was assessed using a sensitive gas-liquid chromatographic technique. The optimum levels of wyerone determined 4 days after infection (∼45 μg/g) were several hundred times greater than in the healthy leaves (

Ultrastructural changes in tobacco undergoing the hypersensitive reaction caused by plant pathogenic bacteria

Abstract: The hypersensitive reaction induced by either Erwinia amylovora or Pseudomonas pisi is indicative of widespread damage to membranes of subcellular organelles and particulate cellular components in tobacco leaf tissue. Plasmalemma, tonoplast, as well as the bounding and internal membranes of chloroplasts and mitochondria and the external membrane of microbodies, are profoundly deranged in 7 h. Cytoplasm, groundplasm of chloroplasts, mitochondria and microbodies and membrane-attached and free ribosomes are similarly affected. The damage coincides with and is probably the cause of the observed tissue collapse and rapid loss of electrolyte-laden water. The presence of few bacterial cells (not more than 4 × 106 cells/leaf disk 1 cm in diameter) cause the observed symptoms which appear, at the ultrastructural level, to be unique.

Phaseollin accumulation in bean (Phaseolus vulgaris) in response to infection by tobacco necrosis virus and the rust Uromyces appendiculatus

Abstract: Tobacco necrosis virus and Uromyces appendiculatus caused necrosis and cellular browning in tissues of selected cultivars of bean. Phaseollin accumulated in infected brown tissue but not in uninoculated tissue nor in tissue which, when infected with Uromyces appendiculatus , became chlorotic before producing uredia. The close association of necrosis and cellular browning with the accumulation of phaseollin is discussed.

Effect of bacterial inoculation of bean and pea leaves on the accumulation of phaseollin and pisatin

Abstract: Apparently similar hypersensitive responses of bean leaves were induced by infection of appropriate varieties with either an incompatible race of Pseudomonas phaseolicola or Ps. morsprunorum. Phaseollin formation accompanied hypersensitivity to the former but not the latter. Very little phaseollin was found in leaves which developed halo-blight symptoms after infection by a compatible race of Ps. phaseolicola. Phaseollin had no effect on bacterial growth in vitro. Two generalizations about phaseollin were shown to be untenable. First, fungal infection is not specifically necessary for phaseollin formation. Second, phaseollin accumulation is not linked inevitably to necrosis induced by pathogenesis in bean.

Peroxidase and ethylene production by barley leaves infected with Erysiphe graminis f. sp. hordei

Abstract: Inoculation of primary leaves of barley of differing compatibilities (types 0, 0–1, 2, 2H and 4) to race 3 of Erysiphe graminis f. sp. hordei resulted in increased peroxidase activity in all cases. An increase was usually evident within 24 h of inoculation and was accompanied by the appearance of one new major isoenzyme band after gel electrophoresis. This band was not seen in extracts of conidia of the pathogen, which contained little peroxidase. It was concluded that the increase in peroxidase was a host response to infection. Treatment of leaves with maleic hydrazide and 2-chloroethyltrimethylammonium chloride also increased peroxidase activity and stimulated the appearance of the same isoenzyme band seen after infection. Plants incubated in an ethylene-containing atmosphere, and plants sprayed with 2-chloroethane phosphonic acid showed neither quantitative nor qualitative changes in peroxidase. There was some indication that maleic hydrazide increased the resistance of susceptible plants to infection. Detached inoculated leaves containing the Ml-a and Ml-g genes for resistance (types 0 and 0–1) showed a marked peak in ethylene evolution within 24 h after inoculation, which however, was not always reproducible. Lines containing the ml-a and ml-g alleles for susceptibility did not show this peak. Later, ethylene evolution from the incompatible combinations declined to a low level while increasingly large amounts were produced by the compatible combinations. Extracts of infected leaves containing the Ml-g gene did not produce ethylene in vitro , and usually inhibited the production of ethylene from a methional/horse-radish peroxidase system. The inhibitor(s), of a low molecular weight, were heat stable but decreased in activity with time. Some evidence indicated that the inhibitor(s) may be phenols and that their changing levels might parallel the pattern of ethylene evolution from intact leaves.

Early effects of Helminthosporium victoriae toxin on plasma membranes and counteraction by chemical treatments

Abstract: Several lines of evidence show that the host-specific toxin of Helminthosporium victoriae has a drastic effect on plasma membranes of susceptible oats. Loss of electrolytes and of 14 C-labeled metabolites increased almost immediately after exposure of susceptible leaf tissues to toxin; loss from resistant tissues was not affected by toxin. Bisulfite, semicarbazide and hydroxylamine gave partial protection against toxin-induced leakage of ions, provided the protective compounds were present during the time of exposure to toxin. Semicarbazide also protected aleurone cells of susceptible oats against toxin-induced inhibition of α-amylase synthesis. There was no evidence that these substances had a direct effect on the toxin molecule. Semicarbazide, bisulfite and hydroxylamine are carbonyl-binding reagents, which could mean that there are carbonyl groups in the toxin-sensitive sites of the cell. Uranyl compounds, which bind to the plasma membrane, also counteracted effects of toxin. However, uranyl ions appeared to complex with the toxin molecule, as indicated by bioassay and spectrophotometric studies. The data are compatible with the hypothesis that toxin reacts with specific receptor sites on the cell membrane and that the resulting membrane damage is the primary lesion leading to all other effects of the toxin.

Benzoic acid: an antifungal compound formed in Bramley's Seedling Apple fruits following infection by Nectria galligena Bres.

Abstract: The resistance of immature apples of the variety Bramley's Seedling to rotting by Nectria galligena was found to be associated with the production of an antifungal compound after infection. The active compound was purified and identified as benzoic acid which was shown to be toxic only in acid conditions. Sufficient quantities were found in the diseased tissue to account for all the antifungal activity present at the pH of the tissue.

Inorganic polyphosphates in the wheat stem rust fungus and in rust-infected wheat leaves

Abstract: Results presented in this paper establish the presence of inorganic polyphosphates in saprophytic cultures of the wheat stem rust fungus (Puccinia graminis tritici), and in non-infected and rust- infected primary leaves of wheat. Evidence for the presence of these compounds was based on acid-lability, non-adsorption to charcoal, metachromatic reaction with toluidine blue, paper chromatographic mobility and histochemical staining. Ten days after inoculation, rust-infected primary leaves of wheat contained eight times more inorganic polyphosphate than control leaves of the same age. Much of this polyphosphate was located in the stem rust uredospores. Further analysis of the uredospores revealed that approximately 90% of the cold acid-soluble phosphorus which was not adsorbed to charcoal was in the form of inorganic polyphosphate. The corresponding figure for the saprophytic rust mycelium was 80%. Rust-infected wheat leaves and saprophytic mycelium contained both high and low molecular weight polyphosphates. The low molecular weight polyphosphates were heterogeneous with respect to electrophoretic mobility on polyacrylamide gels. In contrast, the polyphosphates of non-infected wheat leaves were of low molecular weight only and were relatively homogeneous.

Effects of fusicoccin and some related compounds on etiolated pea tissues

Abstract: At a concentration of 1 μg/ml fusicoccin and a number of closely related derivatives stimulate water uptake in cuttings of etiolated pea seedlings It has been observed that hydrogenation or removal of the t -pentenyl group, as well as partial or total deacetylation of fusicoccin, dihydrofusicoccin, and de- t -pentenylfusicoccin give compounds which show an activity comparable to that of the parent compound The glucose moiety appears to be necessary for high activity, but the deacetylaglycone is still capable of exerting an effect identical to that of fusicoccin when tested at 10 μg/ml Acetylation products of fusicoccin and other active derivatives do not stimulate water uptake Curvature of the apical segment of pea seedlings, repeatedly observed with fusicoccin, prompted a study on isolated internodes of pea seedlings The phytotoxin produced a pronounced increase of their wet weight and elongation, as well as a definite enhancement of tissue deformability

The influence of the carbohydrate source on pisatin breakdown by fungi pathogenic to pea (Pisum sativum)

Abstract: 14 C-Labelled pisatin, a phytoalexin of the isoflavanoid type, added to growing cultures of Fusarium oxysporum f. pisi and Fusarium solani f. pisi was broken down to 14 CO 2 and a product which was sparingly soluble in petroleum ether. The degradation of pisatin by these fungi, which are pathogenic to pea ( Pisum sativum ), appeared to be influenced by the nature and concentration of the carbohydrate source in the nutrient media. High initial glucose and sucrose concentrations completely prevented pisatin breakdown, suggesting that synthesis of pisatin-degrading enzymes is subject to catabolite repression. Glucose concentrations must have decreased below 2750 μg/ml before pisatin degradation occurred. With Ascochyta pisi degradation was less complete than with the other pea-pathogenic fungi, no 14 CO 2 being produced; here, the main breakdown product was a pisatin-like compound, showing spectral characteristics as pisatin, but being only sparingly soluble in petroleum ether. In this instance, the nature and concentration of carbohydrate had no effect on pisatin breakdown. Pisatin was also broken down in pea pods by Fusarium oxysporum f. pisi . However, no evidence was obtained for pisatin degradation in pea pods by Glomerella cingulata , a fungus non-pathogenic to peas.

Chemical and biological properties of a lipomucopolysaccharide from Pseudomonas lachrymans

Abstract: A lipomucopolysaccharide from cell-free culture fluids of Pseudomonas lachrymans induced water-soaking of cucumber leaves and was toxic to mice with an LD 50 of 7·5 μg/g body weight Purified preparations of the lipomucopolysaccharide were apparently homogeneous by electrophoretic, ultracentrifugal and chromatographic criteria The lipomucopolysaccharide solubilized casein and hemoglobin in trichloroacetic acid-based proteolytic enzyme assays, but did not liberate amino groups or produce lower molecular weight fragments from the proteins The lipomucopolysaccharide was a spherical particle with a molecular weight between 3 and 3·5 million It was composed of 12% protein, 27% carbohydrate, 15% lipid and 14% ash Evidence suggested that the lipomucopolysaccharide engaged in dissociable ionic complexes with proteins during incubation at neutral to alkaline pH and that the complexes were trichloroacetic acid-soluble if the lipomucopolysaccharide/protein ratio was sufficiently high

Production of an endo-polygalacturonate trans-eliminase by a potato dry-rot pathogen, Fusarium roseum ‘Avenaceum’, in culture and in diseased tissue

Abstract: Fusarium roseum (Lk.) Snyd. and Hans. ‘Avenaceum’, which causes a dry rot of Solanum tuberosum L., produces an extracellular endo-polygalacturonate trans -eliminase when cultured on a potato broth-pectic acid medium or on intact potato tubers. This enzyme is calcium dependent and exhibits maximum activity between pH 9·0 and 9·5. It has been purified 117-fold by ammonium sulfate fractionation and electrofocusing (pH range 7 to 10), and behaves as a single component with an isoelectric point of pH 8·2. It has a molecular weight of c . 30·5 × 10 3 as determined by sucrose density gradient centrifugation and gel filtration in Sephadex G-75. Both crude and purified preparations of the enzyme cause maceration and cell death of potato tuber tissue.

Further investigations of the toxicity of fusicoccins

Abstract: Fusicoccin is a non-specific phytotoxin. Variation in the response of the 75 plant species tested parallels their natural resistance to desiccation. Fusicoccin is effective when supplied via the sap stream but the wilt it produces is not caused by interruption of vascular flow. It penetrates undamaged plant surfaces very slowly. Fusicoccin, at high concentration, inhibits growth of seedlings in submerged culture but the effects disappear on transfer to fusicoccin-free media. The compound itself does not cause death of the cells and it does not destroy their semipermeability, as shown by the wilt's being reversible. Fusicoccin increases the susceptibility of a tissue to death by desiccation, and its precise site and mode of action remain obscure. Ophiobolins A and B destroy cell semi-permiability. Although they bear a close structural similarity to the fusicoccins the two groups have different modes of action. Progressive de-acetylation of fusicoccin reduces the degree of physiological activity as a wilting agent, but tomato shoots showed a novel response, involving an increase of fresh weight, after taking up small amounts of desacetyl-desisopentenyl fusicoccin. Some proposed mechanisms concerning the mode of action of fusicoccins are discussed.

The plasticizing of plant cell walls and tylose formation—a model

Abstract: The deposition, composition and structural organization of cell walls is reviewed, the basis for cell wall stability is discussed, and a two-step model system for plasticizing walls during tylose formation is presented. This model is based on a diurnal fluctuation in pH which conditions the cell walls, and the presence of common metabolic acids which remove calcium from the wall to permit wall extension. A metabolic basis for the plasticizing of cell walls is proposed.