Iron-deficiency responses in cereal seedlings

Acidity release as a characteristic of iron (Fe) deficiency stress responses was investigated during early seedling establishment of maize (Zea mays L.), barley (Hordeum vulgare L.), winter wheat (Triticum aestivum L.), and winter rye (Secale cereale L.). Ferric reduction as another characteristic of Fe deficiency stress responses was also investigated in maize. This has previously been considered a process only occurring in iron-stressed dicotyledonous plants. Measurements were made of the Fe efflux from maize endosperm under Fe-deficient and non-limiting conditions. The scutellum of Fe-stressed cereal seedlings (all species investigated) increased agar acidification by 30-40%, while manganese (Mn) or zinc (Zn) stressed seedlings did not demonstrate this reaction. Among the maize genotypes studied ('VIR-7569' and 'VIR7882'), the Fe-stressed acid release was more prolonged in relatively less Fe-efficient cv. 'VIR-7569.' In maize, the induced enhancement of acid release was accompanied by an increase in Fe efflux from endosperm. Conversely, maize scutellum Fe3+-reductase activity was not deficiency-dependent on Fe, indicating that enhanced acidity release is a biological phenomenon facilitating Fe supply at early development of graminaceous plants. In cereal seedlings, the coexistence of two marker responses to Fe-deficiency (Strategy I and Strategy II), which are usually typical of different taxonomic groups (dicotyledonous and graminaceous plants) can be regarded as evidence in favour of the hypothesis of common genesis in dicotyledonous and graminaceous plants.