Metal physiology and accumulation in a Medicago truncatula mutant exhibiting an elevated requirement for zinc

A novel, metal accumulating mutant of Medicago truncatula was characterized for tissue metal concentrations, plant growth, percent leaf loss, and leaf-cell metal influx capacity relative to wild-type plants. Growth, mineral parameters, and functional analyses were determined using plants grown hydroponically in complete nutrient solutions with varying levels of Zn and Mn. Depending on the growth regime, the mutant exhibited leaf necrosis, and was found to have elevated concentrations of Zn, Mn, and Cu in most tissues, along with elevated Fe concentrations in roots. General growth was reduced, and percent leaf loss was elevated relative to nutritionally replete wild-type plants, but was similar to Zn-deficient wild-type plants. Growth of the mutant on moderately elevated Zn levels, in combination with lowered Mn, reduced leaf necrosis in new leaves. We have named the mutant and its recessive mutation raz , for r equires a dditional z inc, because leaf necrosis is reduced when plants contain elevated Zn levels. Due to its similarities to Zn-deficient wild-type plants, the raz mutant should serve as a useful model to study micronutrient metal homeostasis.