Molybdenum (Mo) is a cofactor for nitrate reductase. When nitrate reductase activity is limited by Mo deficiency, crop yields are also potentially limited. Plant deficiencies in Mo often occur in acidic soil due to mineral fixation. The long-term goal is to identify genes that can be used to develop rice with enhanced Mo-accumulating capability. The objective of the present study is to identify plant physiological and morphological traits associated with rice seedling Mo uptake which will, in turn, be used to identify genes and biomolecular processes that enhance plant Mo uptake efficiency. In 2007 and 2008, 1640 rice accessions originating from 114 countries around the world were evaluated to identify rice germplasm with altered grain mineral composition. Four of the five accessions highest in grain Mo content originated from Malaysia, suggesting they share a heritable mechanism underlying their high Mo accumulation. Malaysian soils often have low available Mo, along with other minerals, due to acidic soil pH. The present study tested the hypothesis that the high-Mo grain of the Malaysian accessions resulted from enhanced ability to mine Mo from the soil, which would be reflected as well in increased seedling leaf concentrations. To establish correlations between seedling-leaf and grain mineral contents, the five rice accessions selected for their extreme grain Mo content were grown in an outdoor potted study alongside 35 diverse rice accessions previously found to produce seed of low to average Mo concentration. Sets of five seed per accession were planted in 7-10 day intervals to provide, on a single sampling date, a wide range of plant developmental stages. Leaf tips (5cm) for ionomic analysis were collected from the most recently fully emerged leaf per plant. Rice varieties from Malaysia (GSOR accessions 310354, 310355, 310356, 311643 and 311743) with high grain Mo also displayed high leaf Mo indicating that seedling leaf data can be used to identify high Mo accumulators. The high grain and leaf Mo in these Malaysian varieties is hypothesized to be due to a root-localized trait, possibly related to an acid-tolerance mechanism. Future study will quantify growth and physiology of roots and shoots of the high- versus low-Mo germplasm when grown under different pH regimes. Funded by NSF DBI 070111.