Control of Starch Composition and Structure Through Substrate Supply in the Monocellular Alga Chlamydomonas reinhardtii

N. VAN DEN KOORNHUYSE, N. LIBESSART, B. DELRUE, C. ZABAWINSKI, A. DECQ, A.A. IGLESIAS, A. CARTON, J. PREISS Y S. BALL

JOURNAL OF BIOLOGICAL CHEMISTRY

American Society of Biochemistry and Molecular Biology

Año: 1996 vol. 271 p. 16281 - 16287

0021-9258

In Chlamydomonas, as in higher plants, synthesis ofADP glucose catalyzed by ADP-glucose pyrophosphorylaseis rate-limiting for the building of starch in thechloroplast. We have isolated disruptions of the STA1ADP-glucose pyrophosphorylase structural gene thatrendered the enzyme less responsive to the allostericactivator 3-phosphoglycerate. The structure and compositionof the residual starch synthesized by all mutantsof the STA1 locus is dramatically altered. The residualpolysaccharide is shown to be devoid of amylose despitethe presence of granule-bound starch synthase, the amylosebiosynthetic enzyme. In addition, the fine structureof the mutant amylopectin revealed the presence ofan altered chain-length distribution. This distributionmimicks that which is observed during growth and photosynthesisand differs markedly from that observedduring storage. We therefore propose that low nucleotidesugar concentrations are either directly or indirectlyresponsible for the major differences observed inthe composition or structure of starch during storageand photosynthesis.