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Sensing and signaling allow organisms to adapt to changes in the environment. Here, in the PhD study, the pathway of sulfur assimilation in Arabidopsis is selected as subject for studying decision-making in response to changes in environment between continuous vegetative growth and adaptive reactions to stress-induced growth limitation. The sulfur assimilation pathway in plants uses sulfate taken up by sulfate transporters. It has first branching point between the metabolism of assimilatory and bioactive compounds after activation by ATP sulfurylase. The resulting adenosine-5'-phosposulfate (APS) can be used by redox-controlled APS kinase (APK) for secondary metabolism and can be directed by reduction to sulfide by redox-controlled APS reductase activity (APR) followed by sulfite reductase (SiR). On the other hand, the second branching point is redox-controlled by glutamate cysteine ligase (GCL) that catalyzes the first and committed step pf GSH synthesis.
Under non-stressed and thus predominately reducing cellular conditions, decision guides sulfur into secondary metabolism and protein synthesis for growth or maintenance. Under oxidative stress resulting from abiotic or biotic changes in the environment, APR and GCL need to coordinately activated to channel more sulfur into primary assimilation, allowing for increased synthesis of cysteine for the defense compound GSH. However, the mechanism of how these redox switches are regulated to influence the sulfur flux towards protein translation and secondary compound accumulation remains to be investigated.