Mineral Allocation to Pod Walls Versus Seeds in Common Bean.

Common bean (Phaseolus vulgaris) is an important source of dietary nutrients, energy, and fiber.  Although its seeds store starch, protein, minerals and vitamins, we have yet to fully understand how the movement of minerals, amino acids, and sugars are regulated from the main plant to the seeds.  This movement of compounds from vegetative tissues and pod walls to the developing seeds determines not only the nutritional value of those seeds, but also impacts total harvest yield of the crop.  One aspect of this nutrient/yield phenomenon that has received only limited attention is the role of the pod wall in intercepting and re-routing nutrients and sugars from the main plant to the growing seeds.  We analyzed the final mineral partitioning between seeds and pod walls in 25 Andean bean lines grown in a greenhouse in Houston, TX (spring 2012), as well as 144 Andean bean lines grown in the field under drought or non-drought conditions in Prosser, WA (summer 2012).  Seed allocation of minerals varied significantly amongst different elements in the greenhouse study, ranging from >94% of total pod mineral for copper, iron, phosphorus, sulfur and zinc, to 42% of total pod mineral for calcium.  This compares with an average dry weight allocation of 76% to seeds, relative to the total pod dry mass.  Similar results were seen in the field study, with drought having no major effect on the allocation of minerals between pod walls and seeds.  Additional Andean lines were planted in the greenhouse to tag and harvest pods at different stages of pod development (i.e., post-flowering).  The seeds and pods were separated and analyzed to characterize and understand the temporal dynamics of mineral partitioning between pod walls and seeds.  The dynamics of mineral transport to developing pods, and the profiles we have identified with respect to the final allocation of minerals to seeds, will be used to discuss strategies for manipulating pod and seed nutrient allocation to enhance nutritional yield in bean.  This work was funded in part by the USDA Agricultural Research Service through Cooperative Agreement No. 58-6250-0-008 and by USAID as part of Feed the Future, the U.S. Government’s Global Hunger and Food Security Initiative.