Decreased expression of plastidial adenylate kinase in potato tubers results in an enhanced rate of respiration and a stimulation of starch synthesis that is attributable to post-translational redox-activation of ADP-glucose pyrophosphorylase

Adenine nucleotides are of general importance for many aspectsof cell function, but their role in the regulation of biosyntheticprocesses is still unclear. It was previously reported thatdecreased expression of plastidial adenylate kinase, catalysingthe interconversion of ATP and AMP to ADP, leads to increasedadenylate pools and starch content in transgenic potato tubers.However, the underlying mechanisms were not elucidated. Here,it is shown that decreased expression of plastidial adenylatekinase in growing tubers leads to increased rates of respiratoryoxygen consumption and increased carbon fluxes into starch.Increased rates of starch synthesis were accompanied by post-translationalredox-activation of ADP-glucose pyrophosphorylase (AGPase),catalysing the key regulatory step of starch synthesis in theplastid, while there were no substantial changes in metabolicintermediates or sugar levels. A similar increase in post-translationalredox-activation of AGPase was found after supplying adenineto wild-type potato tuber discs to increase adenine nucleotidelevels. Results provide first evidence for a link between redox-activationof AGPase and adenine nucleotide levels in plants. Key words: Adenylate kinase, ADPglucose pyrophosphorylase, plastid, redox-regulation, potato, respiration, starch Received 18 September 2007; Revised 12 November 2007 Accepted 13 November 2007