Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2003
Publication Date: 1/1/2003
Citation: Ellis, D.R., Lopez-Millan, A.F., Grusak, M.A. Metal physiology and accumulation in a Medicago truncatula mutant exhibiting an elevated requirement for zinc. New Phytologist. 2003. v. 158. p. 207-218. Interpretive Summary: Zinc is an essential metal for plants which must be taken up from the soil in adequate amounts in order to ensure proper growth and seed production. Humans and other animals also require zinc, and food plants can provide this dietary nutrient. The means by which zinc is taken up from and moved throughout the plant ultimately determines the zinc content of edible tissues; thus, we have been working to understand how plants control their uptake and internal distribution of zinc. In this study, we have identified a mutant of the plant Medicago truncatula, a relative of alfalfa, which has altered zinc characteristics. This mutant accumulates excess zinc, relative to normal plants, but it also shows various symptoms that are seen in non-mutant plants when they are deprived of zinc (such as lesions on leaves). When this mutant is provided slightly elevated levels of zinc, its leaves appear healthy, and thus we have named this plant the "raz" mutant, which is short for requires additional zinc. We also have shown that his mutant accumulates excess manganese in leaves and roots, and excess copper and iron in its roots, thereby demonstrating that the mutant has interesting alterations in its ability to control the uptake of other essential metals. We believe this mutant will serve as a useful tool to help us better understand various processes of metal nutrition in plants, and ultimately may help us improve the zinc content of our plant-based food supply.
Technical Abstract: 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 requires additional zinc, 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.