The metal ion transporter IRT1 is necessary for iron homeostasis and ef®cient photosynthesis in Arabidopsis thaliana

The mutants irt1-1 and irt1-2 of Arabidopsis thaliana were identi®ed among a collection of T-DNA-tagged lines on the basis of a decrease in the effective quantum yield of photosystem II. The mutations responsible interfere with expression of IRT1, a nuclear gene that encodes the metal ion transporter IRT1. In irt1 mutants, photosensitivity and chlorophyll ¯uorescence parameters, as well as abundance and composition of the photosynthetic apparatus, are signi®cantly altered. Additional effects of the mutation under greenhouse conditions, including chlorosis and a drastic reduction in growth rate and fertility, are compatible with a de®ciency in iron transport. Propagation of irt1 plants on media supplemented with additional quantities of iron salts restores almost all aspects of wild-type behaviour. The irt2-1 mutant, which carries an En insertion in the highly homologous IRT2 gene of Arabidopsis thaliana, was identi®ed by reverse genetics and shows no symptoms of iron de®ciency. This, together with the ®nding that irt1-1 can be complemented by 35S::IRT1 but not by 35S::IRT2, demonstrates that, although the products of the two genes are closely related, only AtIRT1 is required for iron homeostasis under physiological conditions