Lignin and organic free radicals in maize (Zea mays L.) seeds in response to aflatoxin B-1 contamination: an optical and EPR spectroscopic study

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.