2004 Annual Report 4.What were the most significant accomplishments this past year? D. Progress Report: This report serves to document research conducted under a specific cooperative agreement between ARS and the University of Illinois-Urbana. Additional details of research can be found in the report for the parent project 3611-21000-013-00D, "Identifying and manipulating determinants of photosynthate production and partitioning." In this new project which has just been established, studies will be initiated in several areas one of which is to identify protein complexes that may be involved in carbon and nitrogen metabolism. We have begun to explore the use of formaldehyde to crosslink proteins in vivo. In preliminary studies, we have found that incubation of plant tissues with formaldehyde could crosslink proteins in vitro and also in vivo. The cross links could be reversed by heating at 95 C. Thus, formaldehyde may be a useful tool to stabilize and identify protein complexes involving enzymes such as sucrose synthase. Understanding the complex mechanisms that control sucrose metabolism may produce new approaches to regulate crop growth. This work relates to the objectives of the in-house project, which includes defining the regulatory elements controlling photosynthate production and partitioning and determining sink strength.