Eisentoxizität bei Nassreis

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Iron toxicity in lowland rice is a condition caused by the microbial reduction of iron and involves an excessive uptake of Fe (II) by the rice roots and its acropetal translocation into the leaves. There, Fe(ll) can cause oxidative stress via an elevated production of oxygen radicals. The severity of the stress and its damaging effects on rive depend mainly on the amount of Fe (II) and the time of its occurrence and on type and extend of rice cultivar's tolerance mechanisms. We hypothesize that the environment-specific spatio-temporal variation in conditions of iron toxicity occurrence requires differential expression of adaptation mechanisms and their matching with prevailing iron stress situations. The type and the efficiency of adaptation mechanisms will be evaluated in representative hydroponically-grown lowland rice cultivars as follows: (1) Identification of tolerant cultivars: a) symptom expression and tissue Fe content at different growth stages; b) Dynamics of 59Fe-translocation. (2) Evaluation of adaptation strategies: a) Strategy I (Exclusion): Determination of the oxidation power of roots; b) Strategy II (translocation and partitioning): Quantification of Fe and stress signals in xylem and stem tissues; c) Strategy III (tissue tolerance): Avoidance of oxidative stress by the activity of radical-scavenging enzymes. (3) Classification of adaptation strategies regarding their effectiveness to control/tolerate different Fe stress types. The comparative evaluation is seen to allow the assessment and differentiation of adaptation mechanisms required for lowland rice to cope with the diverse conditions of iron toxicity occurrence.