This report describes biomass production and compositional changes of developing castor seeds in response to change in the nitrogen resource (glutamine) of the medium. During the early developmental period (24-36 days after pollination), oil was found to initially accumulate in the developing seeds. Carbohydrates and oil were inversely related after glutamine provision (35 mM, in the culture medium). [U-14C] sucrose labeling was used to investigate the effect of metabolic fluxes among different storage materials. Addition of glutamine led to a 7% increase of labeling in lipids and an inverse decrease of labeling in carbohydrates. It was postulated that changes in the glutamine concentration in the medium are likely to influence the partitioning of resources between the various storage products, especially carbohydrates and oil. These observations will contribute to a better understanding of assimilate partitioning in developing castor seeds and the development of molecular strategies to improve castor bean seed quality and plant breeding studies.