Control of storage protein accumulation during legume seed development

The regulation of partitioning of carbohydrate skeletons into different storage 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 inVicia faba seeds of contrasting protein content. As expected, the seeds of the high protein genotypes (HP) contained more protein and total nitrogen as compared to the low protein genotypes (LP) whereas starch and total amounts of carbon were not altered. There was no major difference in the proportion of amino acids delivered from seed coats into the endospermal cavity of either HP or LP genotypes. However, HP genotype cotyledons contained two-fold higher levels of free amino acids at the later developmental stages when their higher protein content was expressed. After four hours of incubation,in vitro uptake rates of 14C glutamine by HP cotyledons were significantly higher for the protein rich cotyledons indicating a possible higher capacity to take up amino acids. In both genotypes 14C-glutamine was rapidly converted into glutamate and then partly decarboxylated to γ-amino butyric acid. However, in the HP cotyledons the ratio of 14C-glutamine to 14C-glutamate was higher as compared to the LP cotyledons reflecting the observed higher glutamine uptake rate. In a second approach we studiedVicia narbonensis seeds which expressed ADP 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 longer seed fill duration period could partially explain the observed elevated protein content in the AGP-antisense seeds.