Abstract

Purine nucleoside phosphorylases (PNP) are thought to be involved in purine metabolism and rarely reported in plants. Bark storage protein (BSP) and wound inducible (Win4) are poplar proteins with the consensus motifs for PNP activity, which is unreported. Our group characterised a distinct homologue, StCKP1, in potato, an active PNP preferring cytokinins as substrate that prolongs dormancy in tubers and seed dormancy in arabidopsis. Arabidopsis has one homologue of StCKP1 and two of BSP /Win4; rice has two versions of StCKP1 and one of BSP /Win4. I have expressed the arabidopsis homologues of BSP /Win4 in E.coli using the pMal system, and purified the fusion proteins. PNP activity in both the phosphorolytic and synthetic directions was detected using an hplc-based assay. Both proteins showed activity with adenine/ adenosine, and one of the homologues is also capable of interconverting a subset of cytokinins. Bacterially expressed protein of one of the rice homologues of STCKP1 interconverted cytokinins. The coding sequence for this homologue has been constitutively over-expressed in wheat and T0 seed will shortly be available for dormancy determination. Current work includes determining kinetic constants for expressed proteins, and Southern analysis of T0 lines of wheat.