Sucrose synthase, but not ADPglucose pyrophosphorylase, catalyzes the production of cytosolic ADPglucose linked to starch biosynthesis"

Abstract

Recent investigations have shown that most of ADPG linked to starch biosynthesis accumulates in the cytosol in source leaves, and is produced by sucrose synthase (SuSy). This finding is consistent with the occurrence of a gluconeogenic pathway wherein SuSy is involved in the de novo production of ADPG, whereas both plastidial phosphoglucomutase (pPGM) and ADPG pyrophosphorylase (AGP) play a prime role in the scavenging of starch breakdown products. To further test this hypothesis, we have compared the ADPG content in both Arabidopsis and potato WT leaves with those of the starch-deficient mutants with reduced pPGM and AGP. Importantly, ADPG levels in all the starch deficient lines were normal as compared with WT plants. Collectively, the accumulated data show that (a) SuSy exerts a strong control on the starch biosynthetic process and (b) SuSy, but not AGP, catalyzes the production of cytosolic ADPG linked to transitory starch biosynthesis in source leaves.