Submitted to: Biometals
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/7/1991
Publication Date: N/A
Citation: Interpretive Summary: Iron deficiency is generally thought to be the most widespread human nutritional deficiency in the world. A less well-known fact is that iron deficiency is also an important problem in plants. Unfortunately, the mechanisms controlling iron uptake and translocation in food crops are poorly understood. More basic information on these mechanisms is needed in order to develop new food crops that accumulate more iron in their edible portions as well as crops that have the capability to grow normally on soils having low available iron stores. In a series of experiments with cucumbers, peas and tomatoes we have established that ethylene, a plant hormone, is directly involved in increasing the activity of an enzyme (an iron reductase) in root cell membranes that is essential for the uptake of iron from soils. Supplying ethylene precursors (compounds that can be converted to ethylene) to these plants results in increased iron accumulation by the crops. Supplying compounds that inhibit ethylene action resulted in less iron accumulation. Thus, ethylene plays a role in the regulation of iron accumulation by food crops. Possibly, the induction of root-cell membrane reductases is involved in stress resistance because root ethylene is known to be stimulated by various root stresses such as drought and nutrient deficiencies. This information will contribute to the development of plants that can grow on low iron soils and that will contain more iron in the edible portions.
Technical Abstract: Recently, ethylene was reported to be involved in the regulation of Fe(III)-chelate reducing capacity by cucumber (Cucumis sativus L.) roots (Romera and Alcantara, 1993, 1994). Here, we studied the effect of two ethylene inhibitors, AOA (aminooxyacetic acid) and cobalt (Co), on the Fe(III) reducing capacity in roots of mutant genotypes [E107 pea [Pisum sativum L.(brz, brz)] and chloronerva tomato (Lycopersicon esculentum L.] that exhibit high rates of Fe(III)-chelate reduction and excessive Fe accumulation. The ethylene inhibitors, AOA and Co, markedly inhibited Fe(III)-chelate reducing capacity in roots of both genotypes. Over- expression of root Fe(III) reductase activity by both mutants appears to be related to ethylene. Possibly, both mutants are genetically defective in their ability to regulate root-ethylene production. The large inhibitory effect of both ethylene inhibitors on Fe(III)-chelate reducing capacity in roots of the mutant tomato genotype, chloronerva, disputes the contention that the nicotianamine-Fe(II) complex is the repressor of the gene responsible for Fe(III)-chelate reductase activity, as previously suggested by others (Scholz et al., 1988). However, since nicotianamine shares the same biosynthetic precursor as ethylene, i.e., SAM (S- Adenosylmethionine), nicotianamine may affect Fe(III)-chelate reductase activity in dicot and non-grass monocot roots by influencing ethylene biosynthesis.