Plants are stationary organisms that rely on the e cient uptake and remobilization of nutrientsfor growth and reproduction. One of the most abundant nutrients is nitrogen (N),of which the majority is located in proteins, however. N can also be found in nucleotidesas part of the purine and pyrimidine nucleobases and can furthermore be recycled bythe nucleotide catabolism pathway. During the degradation of ribo-nucleosides, derivedfrom RNA, the enzyme nucleoside hydrolase 1 (NSH1) hydrolyses the N-glycosidic bondbetween the nucleobase and the D-ribose residue. The N from the nucleobase is thenrecycled to ammonia in a multi-step process via uric acid and allantoin. The process ofD-ribose recycling is unknown up to now. Plant lines of mutant genes involved in thispurine nucleotide catabolism, like the guanosine deaminase (GSDA), show a necrotic phenotypeunder prolonged dark stress conditions, suggesting that carbon starvation, due tothe lack of recycled D-ribose, could lead to this drastic phenotype. The enzyme responsiblefor the recycling of D-ribose is ribokinase (RBSK). It phosphorylates D-ribose toD-ribose 5-phosphate, which can be used afterwards in the non-oxidative pentose phosphatepathway, the nucleotide de novo synthesis or the nucleotide salvage reactions.In this study, the RBSK from Arabidopsis thaliana is described (AtRBSK) as the rstplant RBSK. The homologous enzyme from Saccharomyces cerevisiae was included intothe analysis, because of contradicting results regarding the identi cation of yeast RBSKin a former study (Xu et al., 2013). The proteins were transiently produced in Nicotianabenthamiana with a C-terminal StrepII tag for protein puri cation and detection. For theevaluation of the kinetic constants, a HPLC kinase assay was developed and established.In the in vivo analysis, metabolites from double mutant lines of the purine and pyrimidinenucleotide metabolic pathways and the RBSK mutant line were extracted to clarify thecontribution of nucleotide metabolism to the D-ribose pool in plants. A comprehensivedark stress experiment coupled with metabolite analysis by mass spectrometry, showedan impact of prolonged dark stress on nucleotide metabolism and the D-ribose pool inplants. Furthermore, it could be excluded that the lack of D-ribose is causing the gsdadark stress phenotype.In the second part of this work, candidate genes for a plastidic D-ribose transporter werefound by comparative expression data analysis in legumes, linking cytosolic D-ribose,released by the nucleotide metabolism, with the plastidic D-ribose phosphorylation byRBSK. A promising candidate gene was found in pGLCT which is transcriptionally upregulatedin a situation of high D-ribose turnover, as found in nodules of ureide exportinglegumes. Furthermore, metabolite analysis in A. thaliana and transient overexpression inS. cerevisiae were used for the investigation of the role of pGLCT in D-ribose translocation.By investigating the plant RBSK from A. thaliana together with the homologous enzyme from S. cerevisiae and furthermore with pGLCT as the plastidic D-ribose transporter,the metabolic process of D-ribose recycling during purine nucleotide degradation was revealed.