Control of storage protein accumulation during legume seed development

The regulation of partitioning of carbohydrate skeletons into different sto rage products of developing seeds is still not understood. We explored two ways to gain more insight in the process. First we analyzed mechanisms that control storage protein accumulation in Vicia faba seeds of contrasting pr otein content. As expected, the seeds of the high protein genotypes (HP) co ntained more protein and total nitrogen as compared to the low protein geno types (LP) whereas starch and total amounts of carbon were not altered, The re was no major difference in the proportion of amino acids delivered from seed coats into the endospermal cavity of either HP or LP genotypes. Howeve r. HP genotype cotyledons contained two-fold higher levels of free amino ac ids at the later developmental stages when their higher protein content was expressed. After four hours of incubation, in vitro uptake rates of C-14 g lutamine by HP cotyledons were significantly higher for the protein rich co tyledons indicating a possible higher capacity to take up amino acids. in b oth genotypes C-14-glutamine was rapidly converted into glutamate and then partly decarboxylated to gamma -amino butyric acid. However, in the HP coty ledons the ratio of C-14-glutamine to C-14-glutamate was higher as compared to the LP cotyledons reflecting the observed higher glutamine uptake rate. In a second approach we studied Vicia narbonensis seeds which expressed AD P glucose pyrophosphorylase in antisense orientation. These seeds contained less starch and more sucrose and water but also more protein, in addition, blocking the starch synthesis pathway caused pleiotropic effects on water content and induced temporal changes in seed development. The resulting lon ger seed fill duration period could partially explain the observed elevated protein content in the AGP-antisense seeds.