Effect Of Validamycin Research Articles

Effects of validamycin in controlling Fusarium head blight caused by Fusarium graminearum: Inhibition of DON biosynthesis and induction of host resistance

Validamycin, known to interfere with fungal energy metabolism by inhibiting trehalase, has been extensively used to control plant diseases caused by Rhizoctonia spp. However, the effect of validamycin on controlling Fusarium graminearum has not been previously reported. In this study, when applied to F. graminearum in vitro, validamycin inhibited the synthesis of deoxynivalenol (DON), which is a mycotoxin and virulence factor, by decreasing trehalase activity and the production of glucose and pyruvate, which are precursors of DON biosynthesis. Because FgNTH encodes the main trehalase in F. graminearum, these effects were nullified in the FgNTH deletion mutant ΔFgNTH but restored in the complemented strain ΔFgNTHC. In addition, validamycin also increased the expression of pathogenesis-related genes (PRs) PR1, PR2, and PR5 in wheat, inducing resistance responses of wheat against F. graminearum. Therefore, validamycin exhibits dual efficacies on controlling Fusarium head blight (FHB) caused by F. graminearum: inhibition of DON biosynthesis and induction of host resistance. In addition, field trials further confirmed that validamycin increased FHB control and reduced DON contamination in grain. Control of FHB and DON contamination by validamycin increased when the antibiotic was applied with the triazole fungicide metconazole. Overall, this study is a successful case from foundational research to applied research, providing useful information for wheat protection programs against toxigenic fungi responsible for FHB and the consequent mycotoxin accumulation in grains.

The effect of validamycin A on tyrosinase: Inhibition kinetics and computational simulation

In this study, we investigated validamycin A as a tyrosinase inhibitor based on its structural properties. We found that the reversible inhibition of tyrosinase by validamycin A occurred in a mixed-type manner with Ki=5.893±0.038mM, as determined by integrating kinetics studies and computational simulations. Time-interval tyrosinase studies showed that the inhibition followed first-order kinetics with two phases. Fluorescence measurements of ANS binding showed that validamycin A induced changes in the tertiary protein structure of tyrosinase. To obtain further insight, computational docking and molecular dynamics were applied, and the results indicated that HIS85, HIS244, GLU256, HIS259, and ASN260 of tyrosinase interacted with validamycin A. This strategy of predicting tyrosinase inhibition based on hydroxyl group numbers might be useful in the design and screening of potential tyrosinase inhibitors.

Validamycin A improves the response of Medicago truncatula plants to salt stress by inducing trehalose accumulation in the root nodules

In this work, the role of trehalose as an osmoprotectant against salt stress conditions was examined in root nodules of Medicago truncatula. For this purpose, we used validamycin A, a potent trehalase inhibitor, in order to induce trehalose accumulation. Validamycin A induced an increase of trehalose concentration in root nodules of M. truncatula by inhibiting trehalase activity; no effect on trehalose concentration was observed in roots and leaves. Trehalose accumulation was accompanied by a decrease in sucrose and starch content, indicating interference with carbohydrate partitioning in the plants. Under salinity conditions, sucrose accumulation appears to be induced in M. truncatula to protect nodule functioning by the inhibition of sucrose catabolism by sucrose synthase and alkaline invertase activities. However, trehalose accumulation induced by val A in nodules improved the response to salinity by increasing plant dry weight (PDW), and no effects of validamycin A on nitrogenase activity and PDW were observed in nonsalinized plants.

Effects of validamycin on some enzymatic activities in soil

There have been few investigations of the possible effects of validamycin on the enzymatic activities in soil. The objective of this present work was to study the short-term influence of enzymatic activity in validamycin treated soils. The results showed that high dose of validamycin introduced into soil had an significant effect on soil enzymatic activities, the degree of inhibition or promotion of enzymatic activities was not only related to the concentration of validamycin, but also to the remain time. Compared with the control (non treatment with validamycin), 240 ml.mg(-1) validamycin treatment caused a significant decrease (14%) of soil catalase activity; validamycin also inhibited urease activity to 67.3%, but subsequently, validamycin stimulated its activity higher than that of the control. Only the highest dose stimulated acid phophatase activities by 29.7%, and other concentration treatments had no effects on these enzymatic activities. The above results indicated that validamycin had effects on soil enzyme, but the effective time was short. It is also interesting to speculate that validamycin can be easily used by the soil microorganism as carbon source and energy.

Control efficacy of validamycin A against Fusarium wilt correlated with the severity of phytotoxic necrosis formed on tomato tissues

Employing 20 race 2-susceptible tomato cultivars, the effect of validamycin A (VMA) treatment on the disease severity (DS) of Fusarium wilt (race 2), salicylic acid (SA) concentration, and plant injury index (PT) was examined. Statistical analysis of the obtained results suggested a negative correlation between the amount of SA and DS without VMA treatment, and between PT and DS with VMA treatment. PT with VMA treatment was positively correlated with the amount of SA with/without VMA treatment. Moreover, the possibility of the rapid screening of plant activators using phytotoxicity as a marker of plant-activator-sensitive cultivars was suggested. The intensity of enhanced systemic acquired resistance (SAR) may depend on the genetic background of each cultivar and its quantity of SAR gene expression.

Trehalose metabolism in root nodules of the model legume Lotus japonicus in response to salt stress

The effect of NaCl stress (50 mM) and validamycin A treatment (30 μM) on growth and nitrogen fixation of Lotus japonicus was investigated in plants cultured under symbiotic and hydroponics conditions for teen weeks (flowering stage). Validamycin A was used as a potent trehalase inhibitor, and was able to produce a five‐fold increase in the level of trehalose during salt treatment, concomitant with an enhance in biomass (20%) in salinized plants. Alterations of nodule metabolism related to some carbohydrates and some enzyme activities were also examined. The shoot and total plant dry weight were severely affected by saline conditions decreasing by 40% and only 15–20% in plant treated without or with validamycin A, respectively. Nitrogenase activity (E.C. 1.7.9.92) was inhibited almost 40% by salt stress and no effect of validamycin was observed. Based on these results, L. japonicus might be considered as a salt‐sensitive legume. In addition, the saline conditions also inhibited the enzyme activities of sucrose synthase (E.C. 2.4.1.13), alkaline invertase (E.C. 3.2.1.26) and trehalose‐phosphate synthetase (E.C. 2.4.1.15). The validamycin A treatment mainly decreased enzyme activities: sucrose synthase, trehalose‐phosphate phosphatase (E.C. 3.1.3.12) and trehalase (E.C. 3.2.1.28). On the other hand, a high concentration of the carbohydrates, starch, sucrose and glucose, seems not to be the mechanism induced in L. japonicus to protect nodules exposed to NaCl because all these sugars decreased in such conditions. Results of the present study support the possible role of trehalose as an osmoprotectant under salt stress.

Effects of validamycin A, a potent trehalase inhibitor, and phytohormones on trehalose metabolism in roots and root nodules of soybean and cowpea

Trehalose, a common microbial disaccharide, has been reported to be toxic to plants, and plant trehalase has therefore been hypothesized to function as a detoxifying enzyme. To test this, aseptically grown soybean (Glycine max L. Merr.) plantlets were supplied with trehalose. The plants accumulated trehalose only when validamycin A, a potent trehalase inhibitor, was added as well. Under these conditions, they accumulated trehalose to up to 8% of the dry weight in their primary leaves without any detectable impairment of growth or health. We have previously shown that in soybean nodules, trehalose is generated by the symbiotic bacteria, and trehalase is strongly induced. However, direct exposure of plants to trehalose did not affect their trehalase activity, whereas a treatment with auxin strongly increased it, indicating that the enzyme level is regulated by hormones rather than by its substrate. Addition of validamycin A to nodules caused an increase in the amount of trehalose and a decrease in the sucrose and starch pools, but nitrogen fixation was not affected. Similar results were obtained with cowpea (Vigna unguiculata L.) plantlets and nodules. These results indicate that plant trehalase is functional in metabolizing trehalose from exogenous and endogenous sources, even though the disaccharide has no obvious toxic effects.

Effects of Validamycin A on the Growth of and Trehalose Content in Mycelia of Rhizoctonia solani Incubated in a Medium Containing Several Sugars as the Sole Carbon Source.

Trehalose was the main sugar accumulated in the mycelia of Rhizoctonia solani and the trehalose content was 8% and more in dry weight mycelia irrespective of the sugar sources used for incubation. The addition of validamycin A (VM-A), an inhibitor of trehalases, increased the trehalose content even more. The inhibition of growth of the mycelia of R. solani by VM-A occurred when the fungus was incubated in a medium containing trehalose as the sole carbon source but not when incubated in a medium containing various sugars and carbohydrate polymers. The results indicated that trehalose was used as a storage molecule to supply glucose required for growth of R. solani and that the anti-fungal activity of VM-A resulted from the anti-trehalase activity of the chemical.

Antagonism by sugars of the effects of validamycin A on growth and morphology of Rhizoctonia cerealis

The effects of 0·2 m validamycin A in reducing internode length (the distance between adjacent branches on a hypha) and colony radial growth rate of Rhizoctonia cerealis were antagonized by some carbon sources (cellobiose, fructose, glucose, lactose, maltose, mannose and sucrose) but not by others (acetate, casamino acids, citrate, galactose, gluconate, glucuronate, glycerol, l -arabinose, mannitol, melibiose, ribose, sorbitol, and xylitol). Antagonism of the effects of the antibiotic by 5 m m sucrose and cellobiose (but not 5 m m fructose, glucose, lactose, maltose or mannose) from the onset of inoculation was correlated with the production by the fungus of extracellular invertase and cellobiase activities. The addition of 3- O -methyl- d -glucose to medium containing 5 m m glucose increased the sensitivity of R. cerealis to the antibiotic, suggesting that antagonism of validamycin A by glucose was dependent on the sugar being metabolized, rather than the sugar inhibiting uptake of the antibiotic. The onset of the response of the fungus to validamycin A appeared to be related to the length of time of exposure to the antibiotic, and mycelium grown on medium containing antibiotic continued to display the ‘inhibited’ phenotype even after growing for several hours on medium lacking antibiotic.

Effect of Validamycin A on the Production of Cellulase, Xylanase and Polygalacturonase by Rhizoctonia solani

Validamycin A decreased the biomass and extracellular protein produced by cultures of Rhizoctonia solani A79 grown on medium containing cellulose as the carbon source. In the presence of the antibiotic, the production of inducible enzymes active on filter paper (FPase), carboxymethylcellulose (CMCase) and (cellobiase) was decreased, but not the production of constitutive enzymes involved in hemicellulose (xylanase) and pectin (polygalacturonase) degradation. When incorporated in the assay mixtures, validamycin A did not affect the activity of the above enzymes, but the antibiotic did act as a substrate for cellobiase. Validamycin A did not affect the distribution of cellulase enzymes in stationary phase cultures of R. solani, and incorporation of inositol in the culture medium did not reverse the effect of the antibiotic on cellulase production. Addition of inositol to the medium decreased the activities of FPase and CMCase in the culture supernatant but had no effect on cellobiase activity. The results are discussed in relation to the way validamycin A controls rice sheath blight.

Effect of Validamycin A on the Inositol Content and Branching of Rhizoctonia cerealis and Other Fungi

The effects of the antibiotic validamycin A on the inositol content and hyphal branching of Rhizoctonia cerealis were investigated. Inositol was found associated with the cell wall and as a lipid extractable fraction composed of phospholipid, phosphosphingolipid and glycolipid. Validamycin A decreased the inositol content of the phospholipid fraction by 57% and the phosphosphingolipid fraction by 40%, but had no effect on the glycolipid fraction. The phosphatidylinositol (the only inositol-containing phospholipid detected) content of the biomass was reduced by 53 % in the presence of validamycin A and this decrease was compensated for by rises in the levels of phosphatidylserine and an unknown, minor phospholipid. Over the concentration range 1 to 5000 µm, validamycin A caused decreases in the colony radial growth rate, internode length (the distance between adjacent branches on a leading hypha) and inositol content of R. cerealis colonies, and a positive correlation was found between inositol content and internode length. Addition of inositol to the medium only slightly antagonized the effect of the antibiotic on mycelial morphology and did not restore phosphatidylinositol levels of the biomass to control values.

Effect of validamycin A on the activity of trehalase of Rhizoctonia solani and several sclerotial fungi.

Effect of validamycin A on the activity of trehalase of Rhizoctonia solani and several sclerotial fungi.

Effects of validamycin A on the morphology, growth and sporulation of Rhizoctonia cerealis, Fusarium culmorum and other fungi.

All Basidiomycotina screened were sensitive to validamycin A, whereas most Ascomycotina and all Mucorales and Oomycetes were insensitive. Studies with Rhizoctonia cerealis and Fusarium culmorum showed that, in semi-solid culture, the antibiotic caused a decrease in colony radial growth rate and that this was associated with a decrease in mean hyphal extension rate and an increase in hyphal branching. However, the antibiotic did not alter the morphology of R. cerealis grown in liquid culture (shaken or stationary). Validamycin A caused a reduction in the number and viability of conidia produced by F. culmorum.

Effects of validamycin on glucan synthesis by cell-free extracts from Rhizoctonia solani.

L'activation de la glucane synthetase provoquee par la validamycine est due a l'AMP et au Pi dont les teneurs s'accroissent lors de l'apport de l'antibiotique. L'enzyme est identifiee a la β-1,3-glucan synthetase.La quantite de glucose lie β-1,3 dans la fraction glucane s'accroit alors que celles de mannose lie β-1,3 ou d'arabinose decroissent sous l'influence de l'antibiotique

Effect of validamycin on .BETA.-D-glucan-degrading enzymes from Rhizoctonia solani.

Effect of validamycin on .BETA.-D-glucan-degrading enzymes from Rhizoctonia solani.

バリダマイシンAのイネ数種菌核病防除効果

バリダマイシンAのイネ数種菌核病防除効果

Effect of validamycin A on infection of Rhizoctonia solani in rice sheaths.

Pathological changes of rice sheath tissues caused by Rhizoctonia solani treated with validamycin A (VM-A) was anatomically observed. In sheaths inoculated with mycelial disks after dipping in solutions of 0.63, 1.25, and 2.5ppm VM-A, browning of sheaths and small elliptical spots arose, but no hyphae were observed in the inner space of the sheath. On the other hand, in the lessions formed by inoculation of untreated mycelial disks, abundant hyphae were present in the inner space of the sheaths and the parenchyma cells were severely damaged. Spraying of 10ppm VM-A at 8hr after inoculation of R. solani inhibited the penetration of hyphae into sheath tissues and the browning of sheaths on inoculated part or small elliptical spots were seen on the 4th day. When VM-A was sprayed 16hr after inoculation, hyphae became to be seen in the sheath tissues on the 4th day. Their growth, however, was strikingly inhibited accompanying with little damage of the tissues compared with the lesions formed by the untreated hyphae. The results demonstrate that VM-A is effective against R. solani by both preventing hyphal penetration and retarding its growth.

EFFECT OF VALIDAMYCIN ON THE GROWTH AND MORPHOLOGY OF PELLICULARIA SASAKII

The effect of validamycin on the growth of Pellicularia sasakii was studied biochemically and morphologically. Validamycin significantly inhibited the rate of colony extension on water-agar, and smaller and denser colony appeared. On the other hand, its growth was not inhibited significantly when determined by the increase in the amount of protein or ribonucleic acid. Although the increase in the total length of hyphae was suppressed to some extent, the increase in the total volume of hyphae as estimated from the length and width of hyphae was not suppressed significantly. Validamycin suppressed the elongation of the primary hypha and first secondary hyphae, while the elongation of the rest of secondary hyphae was even stimulated in the presence of validamycin. Although branching of hyphae at the periphery of colony was apparently much accelerated by validamycin, there was no difference in the total number of branching points between cultures with and without validamycin. There was no difference in the cell wall components of the fungus of both cultures. It was concluded that validamycin does not inhibit the fungal growth in mass but alters the morphology of the fungus. Among other fungi tested, all belonging to Basidiomycetes were affected by this antibiotic in the same manner, while its effect on fungi belonging to other classes was diverse.