Metal Physiology and Nodule Development in a Medicago truncatula Mutant that Requires Additional Zinc (raz).

Success of the symbiotic plant-rhizobia relationship depends not only on adequate delivery of usable nitrogen from the rhizobia to the host plant, but also on the supply of requisite nutrients from the plant to the bacteria.  Among the nutrients necessary for proper nodule function are metals such as Mg, Fe, Mn, and Zn, which are essential cofactors in various bacterial enzymes.  Little is known about how these metals are delivered to the bacteria, the concentrations required for proper nodule function, or how their supply affects nodule development.  Therefore, this study examines the influence of zinc on root nodule formation and functions using a mutant of the model legume Medicago truncatula known as raz for “requires additional zinc”. Confocal microscopy together with nucleic acid and metal specific dyes was used to monitor the development and in-vivo Zn distribution in raz and wild type (WT) M. truncatula plants grown together through a 28 day developmental time course.  Synchrotron based x-ray tomography and x-ray absorption spectroscopy were also used to provide a first time look into the metal distribuiton and speciation in nodule tissues.  Initial results indicate that raz nodules accumulated more Zn, had delayed nodule development and function compared to the M. truncatula WT plants.