Wednesday, November 15, 2006
257-8
Mechanistic Evaluation of Calcium Movement into Developing Chickpea Seeds.
Michael A. Grusak, USDA-ARS-SPA-CNRC, 1100 Bates St., Houston, TX 77030-2600 and Shahal Abbo, ISRAEL,Hebrew U.Jerusalem, Hebrew University of Jerusalem, Po Box 12 Faculty. Of Agriculture, Rehovot, 76100, ISRAEL.
Chickpea is an important staple food in many Asian and Middle Eastern countries and can provide dietary calcium to humans. Because calcium is often limiting in human diets, we have been interested in breeding new chickpea cultivars with enhanced concentrations of this mineral. To assist this effort, we are trying to understand the processes and pathways responsible for calcium movement to developing seeds, and have focused our studies on possible diffusional pathways within the pod. This focus was chosen because calcium delivery is not believed to occur via phloem transport, nor via xylem flow into developing seeds. We have taken advantage of the unique morphology of chickpea pods, which are inflated at an early stage and exhibit limited contact points between the pod wall and seed, to test whether calcium enters the ovule through contact between the seed coat and the inner surface of the pod walls. Plants were grown under controlled conditions, with developing seeds and pods harvested throughout the period of seed development. Seed dry weights, seed calcium content, and pod wall calcium concentrations were determined for tissues of cultivar Green and the wild accession Cr231. Our results indicated that for both lines, seed calcium import occurred prior to seed-to-pod wall contact, suggesting that calcium enters seeds via diffusional movement through the funiculus, at least during early stages of seed fill. Radiotracer studies verified that developing seeds are capable of absorbing calcium through their seed coat when applied exogenously, but experiments are still underway to establish the extent that this occurs in vivo. We will present these results, along with a general mechanistic model, to discuss the factors/processes thought to control calcium accretion in developing chickpea seeds. This work was supported in part by funds from USDA-ARS under Agreement No. 58-6250-6-001 to MAG.