Iron-containing particles accumulate in organelles and vacuoles of leaf and root cells in the nicotianamine-free tomato mutantchloronerva

Summary

The mutantchloronerva ofLycopersicon esculentum Mill is the only known plant mutation that leads to a complete loss of the endogenous iron chelator nicotianamine. The mutant exhibits several morphological alterations and a permanent activation of the strategy I reactions of iron uptake as well as iron accumulation in roots and leaves. The electron microscopic energy loss technique of energy spectroscopic imaging (ESI) was used to localise the iron accumulated in the organs of wild-type and mutant plants. Iron-containing particles were detected in the chloroplast stroma and in vacuoles of mutant leaves, and in root cells in vacuoles and in mitochondria. In wild-type organs such particles were found at the same sites but they were smaller in size and occurred less frequently. The findings indicate that these compartments are preferential sites of iron storage or deposition in tomato tissues. It is discussed that the iron-containing particles detected are the result of iron release by oxidative stress. Application of nicotianamine to mutant plants, which reverts the mutant phenotype, led to a significant decrease of the iron-containing particles. This is seen as an indication that they may serve as intermediate iron stores and emphasises the crucial role of nicotianamine for the normal iron distribution in cells and organs.