In plants, putrescine is either aminopropylated to yield spermidine or methylated to afford Nmethylputrescine by the action of different enzymes, namely spermidine synthases or putrescine Nmethyltransferases, which use different cosubstrates. Based on functional and structural investigations, both transferases were analysed for their evolutionary relationships. Moreover, N-methylputrescine is the starter molecule for tropinone biosynthesis. Tropinone is reduced to either tropine or pseudotropine by the action of two different tropinone reductases. In A. thaliana, neither tropinone reductases nor tropane or nortropane alkaloids were found so far. Nevertheless, tropinone reductase-like enzymes were identified in A. thaliana with functions unknown until now. With the help of homology models and virtual screening, hints concerning their putative function were found. These theoretical analyses were supported by experimental work.