Chatterjee Manash Dumez Sylvain Colonna Paul 398-412 16045475 Roldán Isaac Planchot Véronique D'Hulst Christophe Soluble starch synthase I: a major determinant for the synthesis of amylopectin in Arabidopsis thaliana leaves. Vyas Darshna 3 A minimum of four soluble starch synthase families have been documented in all starch-storing green plants. These activities are involved in amylopectin synthesis and are extremely well conserved throughout the plant kingdom. Mutants or transgenic plants defective for SSII and SSIII isoforms have been previously shown to have a large and specific impact on the synthesis of amylopectin while the function of the SSI type of enzymes has remained elusive. We report here that Arabidopsis mutants, lacking a plastidial starch synthase isoform belonging to the SSI family, display a major and novel type of structural alteration within their amylopectin. Comparative analysis of beta-limit dextrins for both wild type and mutant amylopectins suggests a specific and crucial function of SSI during the synthesis of transient starch in Arabidopsis leaves. Considering our own characterization of SSI activity and the previously described kinetic properties of maize SSI, our results suggest that the function of SSI is mainly involved in the synthesis of small outer chains during amylopectin cluster synthesis. Berbezy Pierre Wattebled Fabrice 43 Ball Steven Delvallé David Mérida Angel Delvallé David et al. 2005 Aug. Plant J. 43(3):398-412. 2005 Aug