Summary The thesis provides new insight into the influence of the plant cell redox state on the transient starch metabolism in Arabidopsis thaliana with a focus on starch biosynthetic enzymes. Two main hypotheses forms the basis of this thesis: 1) photosynthesis and starch metabolism are coordinated by the redox state of the cell via post-translational modification of the starch metabolic enzymes containing redox active cysteine residues and these cysteine residues became cross-linked upon oxidation providing a conformational change leading to activity loss; 2) cysteine residues of chloroplast enzymes can play a role not only in enzyme activity and redox sensitivity but also in protein folding and stability upon oxidation. Several redox sensitive enzymes identified in this study can serve as potential targets to control the carbon flux to and from starch during the day and night, respectively. The determined structural basis of the post-translational redox modification of AtSS1 could be extrapolated to other SS isoforms due to high conservation of the Cys545 equivalent among all the SS enzymes. The revealed multivalent importance of cysteine residues highlights the potential of these amino acids for targeted stress-tolerant enzyme bioengineering.