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BACKGROUND Aflatoxin B-1 (AFB(1)) is the most dangerous of the mycotoxins that contaminate cereal seeds naturally. A stress lignin formation is linked with the accumulation of reactive oxygen species causing a change in the redox status and formation of stable organic radicals, constituting the first layer of defense. The relationship between AFB(1) and changes in lignin organic free radicals in seeds is not known, nor is the part of the seed that is more targeted. Using optical and electron paramagnetic resonance spectroscopy, we investigated AFB(1)-induced changes in lignin and organic free radicals in seeds, and whether the inner and outer seed fractions differ in response to increasing AFB(1). RESULTS Different changes in the content of lignin and free radicals with increasing AFB(1) concentrations were observed in the two seed fractions. There was a significant positive linear correlation (R = 0.9923, P = 0.00005) between lignin content and AFB(1) concentration in the outer fraction, and no correlation between the lignin content and the AFB(1) concentration in the inner fraction. We found a positive correlation between the area of the green spectral emission component (C4) and the AFB(1) concentration in the outer fraction. CONCLUSIONS To the best of our knowledge, the results showed, for the first time, that maize seed fractions respond differently to aflatoxin with regard to their lignin and organic free radical content. Lignin content and (C4) area may be reliable indicators for the screening of lignin changes against AFB(1) content in the seeds, and thus for seed protection capacity.

BACKGROUND Cereal seeds, such as maize seeds, are frequently contaminated with aflatoxin B1 (AFB1), one of the most dangerous naturally occurring carcinogens. In plants, phenolamides are involved in biotic stress response. The data on variations of phenolamides in AFB1-containing seeds are limited. RESULTS Five polyamine conjugates, including two spermidine and three putrescine conjugates, were tentatively identified in methanolic extracts, using HPLC-DAD-MS. The ratio of putrescine to spermidine conjugates changed with increasing AFB1 concentration in a logistic dose-response manner, with a ratio of below 1 up to a concentration of 51.51 mu g kg(-1), and approximately 2.54 and 3 at higher concentrations of 177.4 and 308.13 mu g kg(-1), respectively. The observed variations of the total antioxidant activity and the total phenolic content may support this biphasic behaviour of the seeds against AFB1 stress. CONCLUSIONS The obtained data are a contribution to the understanding of the roles of polyamine conjugates in seed defence to increasing AFB1 concentrations. According to our knowledge, this study reports for the first time the biphasic response of maize seeds to increasing AFB1 contamination level, comprising the induction of polyamine conjugate accumulation and variation in the ratio of conjugates. This dose-response relationship may provide useful information in the field of agricultural and food chemistry as an indicator of AFB1 contamination level and, hence, for selecting an appropriate seed quality.

Mathematical models which define the effects of molecular properties on the retention and lipophilicity and prediction lipophilicity of some Schiff base ligands, and complexes with copper(II) and nickel(II) were developed. Following molecular descriptors were calculated: molecular volume, surface area, energy of the highest occupied/lowest unoccupied molecular orbital, dipole moment, refractivity, polarizability, hydrophilic-lipophilic balance, and lipophilicity parameters, which are correlated with chromatographically determinated lipophilicity parameters. A multiple linear regression procedure was used to derive the models. High agreement between experimental and predicted values obtained in this validation procedure indicates the good quality of the derived models.