PARENT SESSION

Symposium S4B Sugar signalling: Photosynthesis, hormones and development
Tuesday August 31st, 2004 2:40 PM-4:40 PM Room 210A
Chair: Dan Bush
Co-Chair: Mathew Paul

Sugar signalling and its interaction with thioredoxin-mediated light activation of ADP-glucose pyrophosphorylase in leaves. Anna Kolbe^*,1, Axel Tiessen¹, Henriette Schluepmann³, Peter Geigenberger¹, ¹ Max-Planck-Institute of Molecular Plant Physiologie, Potsdam, Germany³ Utrecht University, Utrecht, Netherlands

ABSTRACT- The reaction catalysed by ADP-glucose pyrophosphorylase is the first commited step in starch synthesis. This enzyme is subject to allosteric regulation by 3PGA/Pi ratio and to transcriptional regulation. It has recently been shown in potato tubers that this enzyme is also subject to redox-dependent post-translational regulation, leading to a stimulation of starch synthesis in response to sucrose supply. Redox-activation involves the reduction of an intermolecular disulfid-bridge between the two AGPB subunits of the heterotetrameric holoenzyme (Tiessen et al., 2002, Plant Cell 14: 2191-2213). Our data show that an analogous mechanism is also operating in photosynthesising leaves of potato, pea and Arabidopsis, where AGPase redox-activation is independently modulated by light and sugars (Hendriks et al., 2003, Plant Physiology 133, 838-849). Currently, the genetic resources of Arabidopsis are being used to investigating the components of the signalling pathways leading to AGPase redox-activation in response to these inputs. On the basis of these results it will be discussed how the sugar signal is transferred to the chloroplast and by which mechanism it interferes with the ferredoxin/thioredoxin system that is involved in the light-dependent redox-activation of the enzyme.

KEY WORDS: starch, thioredoxin, ADPglucose pyrophophorylase (AGPase), sugar signalling