Metallothionein deficiency impacts copper accumulation and redistribution in leaves and seeds of A rabidopsis

Most angiosperm genomes contain several genes encoding metallothionein ( MT ) proteins that can bind metals including copper ( C u) and zinc ( Z n). Metallothionein genes are highly expressed under various conditions but there is limited information about their function. We have studied A rabidopsis mutants that are deficient in multiple MT s to learn about the functions of MT s in plants. T‐ DNA insertions were identified in four of the five A rabidopsis MT genes expressed in vegetative tissues. These were crossed to produce plants deficient in four MT s ( mt1a / mt2a / mt2b / mt3 ). The concentration of C u was lower in seeds but higher in old leaves of the quad‐ MT mutant compared to wild‐type plants. Experiments with stable isotopes showed that C u in seeds came from two sources: directly from roots and via remobilization from other organs. Mobilization of C u out of senescing leaves was disrupted in MT ‐deficient plants. Tolerance to C u, Z n and paraquat was unaffected by MT deficiency but these plants were slightly more sensitive to cadmium ( C d). The quad‐ MT mutant showed no change in resistance to a number of microbial pathogens, or in the progression of leaf senescence. Although these MT s are not required to complete the plant's life cycle, MT s are important for C u homeostasis and distribution in A rabidopsis.