Analysis of the mechanism of iron assimilation in chlamydomonas reinhardtii: A model system for strategy I plants

Abstract

The molecular mechanism of iron (Fe) assimilation in strategy I plants is only beginning to be understood. In an attempt to establish a model system for crop plants, the mechanism of Fe assimilation was investigated in Chlamydomonas reinhardtii. As in strategy I plants, Chlamydomonas responded to Fe deficiency through the induction of a cell surface Fe³⁺‐chelate reductase. Within 24 h following Fe removal, the Fe³⁺‐chelate reductase was increased by ≥ 15‐fold compared to Fe‐sufficent cells. The reductase activity was negatively correlated with the Fe concentration in the media, and resupply of Fe to Fe‐deficient cells resulted in a decrease in activity to control levels within 4–5 h. The Fe³⁺‐chelate reductase activity in Fe‐starved cells was saturable and was inhibited by uncouplers of the transmembrane proton gradient but not by SH‐specific reagents.

The analysis of uptake using radiolabelled Fe demonstrated that Fe uptake was only observed in cells grown in Fe‐deficient media. When Fe²⁺ was offered as the sole substrate, uptake increased slightly. However, Fe uptake rates were several orders of magnitude less than those for Fe³⁺‐chelate reduction, and it appeared that reduction was not the rate limiting step in Fe assimilation. Thus, both Fe³⁺ reduction and uptake in C. reinhardtii were regulated by the nutritional status; characteristics that were reminiscent of the mechanism of Fe uptake in strategy I higher plants.

Notes

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