药用植物及其产品中真菌及真菌毒素污染研究进展

药用植物从田间生长、采集后不及时干燥、贮存不当或在制备与加工过程中处理不善,均可能污染各种真菌并产生真菌毒素。为了保障人们用药安全,完善我国药用植物安全控制标准体系,对国内外药用植物及其产品中真菌及真菌毒素污染研究进展进行了综述,以期为同类研究提供参考。     

Toxic C17-Sphinganine Analogue Mycotoxin,Contaminating Tunisian Mussels,Causes Flaccid Paralysis in Rodents

Severe toxicity was detected in mussels from Bizerte Lagoon (Northern Tunisia) using routine mouse bioassays for detecting diarrheic and paralytic toxins not associated to classical phytoplankton blooming. The atypical toxicity was characterized by rapid mouse death. The aim of the present work was to understand the basis of such toxicity. Bioassay-guided chromatographic separation and mass spectrometry were used to detect and characterize the fraction responsible for mussels’ toxicity. Only a C17-sphinganine analog mycotoxin (C17-SAMT), with a molecular mass of 287.289 Da, was found in contaminated shellfish. The doses of C17-SAMT that were lethal to 50% of mice were 750 and 150 μg/kg following intraperitoneal and intracerebroventricular injections, respectively, and 900 μg/kg following oral administration. The macroscopic general aspect of cultures and the morphological characteristics of the strains isolated from mussels revealed that the toxicity episodes were associated to the presence of marine microfungi (Fusarium sp., Aspergillus sp. and Trichoderma sp.) in contaminated samples. The major in vivo effect of C17-SAMT on the mouse neuromuscular system was a dose- and time-dependent decrease of compound muscle action potential amplitude and an increased excitability threshold. In vitro, C17-SAMT caused a dose- and time-dependent block of directly- and indirectly-elicited isometric contraction of isolated mouse hemidiaphragms.     

Natural occurrence of citrinin in rice grains and its biocontrol byTrichoderma hamatum

Paddy rice was sampled from El-Sharkia, El-Gharbia, El-Dakahlia and Kafr El-Shekh governorates, Egypt. Of the 30 samples taken, ten were contaminated with the mycotoxin citrinin. An average of 6.79 × 10⁴ fungal spores per gram rice was found. The isolated fungi represented 47 species and 28 genera. The predominant genera wereAspergillus, Cladosporium andPenicillium. Aspergilli were represented by 22 species;Aspergillus niger andA. flavus had the highest occurrence.Penicillium viridicatum produced the highest amount of citrinin on glucose ammonium nitrate salts broth and rice grains, and hence this isolate was selected as a good producer of citrinin in this study. The presence ofTrichoderma hamatum reduced the amount of citrinin produced byP. viridicatum compared with its respective control. The excessive growth ofT. hamatum onP. viridicatum was increased with time. Viability ofP. viridicatum conidia decreased byT. hamatum with an increase in the incubation period. Chitinases and 1,3-β-glucanase enzyme activity ofT. hamatum increased with extending the incubation period onP. viridicatum mycelia up to maximum values at 72 and 84 h, respectively.T. hamatum led to a decrease in the production of citrinin byP. viridicatum on rice grains compared with the respective control values. http://www.phytoparasitica.org posting Dec. 19, 2004.     

Role of Deoxynivalenol in Aggressiveness of Fusarium graminearum and F. culmorum and in Resistance to Fusarium Head Blight

The data available indicate that aggressiveness of Fusarium graminearum and F. culmorum depends on their deoxynivalenol (DON) and nivalenol-producing capacity: toxin-producing ability correlated closely with the level of aggressiveness measured. This agrees well with other literature findings. However, the resistance of a cultivar influenced DON production significantly. In the most resistant genotypes, toxin contamination remained near zero, whereas the same isolates and inoculum produced very high toxin levels in susceptible cultivars. As toxin levels were correlated with the ratio of Fusarium-damaged kernels (FDK) and this ratio is very low in highly resistant cultivars, the conclusion is that the level of resistance level is more important in governing DON accumulation in a given cultivar than is the aggressiveness of an isolate. In susceptible cultivars, DON producing ability is decisive, but in highly resistant cultivars resistance is the major factor in suppressing disease development and DON accumulation. In different years, the same FDK values were associated with different DON concentrations and this depended very much on the precipitation towards the end of May, the time of inoculation.     

Saccharomyces Cerevisae and Arabidopsis Thaliana: Useful Model Systems for the Identification of Molecular Mechanisms Involved in Resistance of Plants to Toxins

Secondary metabolites produced by pathogens during the infection process are thought to play a role as pathogenicity or virulence determinants in many plant diseases. Baker's yeast and the plant Arabidopsis thaliana are attractive models for elucidating molecular mechanisms of resistance to toxic substances. For the Fusarium mycotoxin deoxynivalenol, the following resistance mechanisms were identified in yeast: (1) reduced toxin uptake due to the ABC transporter protein Pdr5p (molecular efflux pump), (2) detoxification by the acetyltransferase Ayt1p, and (3) modification of the ribosomal target by amino acid changes in the ribosomal protein L3 (Rpl3p). PDR5-like genes exist in plant genomes as large gene families and could play an important role as a first line of defence against a broad range of toxic metabolites. Amino acid alterations in the highly conserved RPL3 genes could likewise play a role in trichothecene resistance in plants. The knowledge obtained using model systems should be valuable in biotechnological approaches to disease control and marker-assisted resistance breeding.     

Effects of Fusarium mycotoxins with yeast cell wall absorbent on hematology,serum biochemistry,and oxidative stress in broiler chickens

The objectives of the present study were to investigate the toxicity of feed-borne Fusarium mycotoxins on hematology, serum biochemistry, and oxidative stress of broiler chickens, and to evaluate the efficacy of yeast cell wall adsorbent (YCW) in preventing mycotoxins-induced adverse effects. A total of 300 one-day-old Arbor Acres broiler chickens (mixed sex) were randomly divided into 3 groups and received different treatments (5 repetitions per treatment). Treatments were control, naturally contaminated diet (NCD; aflatoxin, 102.08 mg/kg; zearalenone, 281.92 mg/kg; fumonisin, 5,874.38 mg/kg; deoxynivalenol, 2,038.96 mg/kg), and NCD + 2 g/kg of YCW. Broilers fed NCD showed elevated serum alanine transaminase, aspartate transaminase, alkaline phosphatase, γ-glutamyl transferase (GGT), and malondialdehyde (MDA) at 21 d, and alanine transaminase, GGT, creatine kinase, and MDA at 42 d. Higher white blood cell, lymphocyte (LYM), platelet, red blood cell, hemoglobin, hematocrit, and mean corpuscular hemoglobin counts at 21 d, as well as LYM in whole blood and hepatic mRNA expression of heat shock protein 70 at 42 d were also observed in broilers fed with NCD compared with the control diet. However, lower mean corpuscular volume at 42 d and total superoxide dismutase (T-SOD) at both 21 and 42 d were observed in broilers with the NCD treatment when compared with those with the control treatment. Dietary addition of YCW at the level of 2 g/kg in addition to the NCD treatment showed a positive protective effect on GGT, T-SOD in serum, white blood cells, LYM, platelets, and hemoglobin in whole blood at 21 d, and T-SOD, MDA in serum, LYM, mean corpuscular volume in whole blood, and hepatic mRNA expression of heat-shock protein 70 at 42 d. It is suggested that feeding NCD for 42 d might result in a deleterious effect on broiler chickens, and addition of 2 g/kg of YCW can partly attenuate the detrimental effects of the NCD feeding.     

Production of fusaric acid byFusarium oxysporum

Summary The aim of the study was to determine whether isolates ofFusarium oxysporum Schlecht. produce fusaric acid in culture and whether mycelial growth can be used as a measurement of fusaric acid production. Three isolates produced significant levels of fusaric acid in culture filtrate, the maximum concentration being reached after 18 days, whereafter it remained constant. Mycelial growth could not be used to measure or estimate the production of fusaric acid. Growth curves from specific isolates could be used to determine the concentration of fusaric acid in culture filtrate after specific lengths of time.     

Correlation between Fusarium head blight severity and DON content in triticale as revealed by phenotypic and molecular data

Fusarium head blight (FHB) in triticale (× Triticosecale Wittmack) results in yield losses and mycotoxin contamination, for example, by deoxynivalenol (DON). This study aimed to analyse the correlation between FHB severity and DON content in a DH population of 146 entries across environments. Additionally, Fusarium damaged kernel (FDK) rating, heading stage and plant height were recorded. Highly significant (P < 0.001) genotypic variances were found throughout, but also significant (P < 0.001) genotype–environment interaction variances occurred. Correlation between FHB severity and heading stage or plant height was low (r = 0.144 and r = ?0.153, P < 0.10). A prediction of DON content from FHB severity or FDK rating is not possible caused by low correlations (r = 0.315 and 0.572, respectively, P < 0.001). A common quantitative trait locus (QTL) for all FHB‐related traits was found on wheat chromosome 2A being of minor importance for FHB severity, but of high importance for DON content and FDK rating. Another QTL on rye chromosome 5R was more important for FHB severity. In conclusion, DON content has to be measured in triticale after selection for FHB severity to gain for healthy and mycotoxin‐reduced feed.