Polyamines are essential for all organisms and play crucial roles in various plant physiological processes. Although the biosynthetic pathway of polyamines has been studied extensively, the system that performs the cell-to-cell translocation or the long-distance transport of them remains poorly understood. Recently, PUT3 from Arabidopsis thaliana has been identified as a polyspecific transporter that transports polyamines, vitamin B1 and paraquat in the phloem. Interestingly, the AtPUT3 phloem polyamine transporter is polymorphic between the ecotypes Columbia and Landsberg erecta. Furthermore, their phloem saps differ in polyamine composition, while in the shoot and the root their polyamine profiles are the same. Here insertion mutants of both ecotypes (put3-1 and rmv1, respectively) were characterised and showed antagonistic changes in root growth rate, suggesting that the polymorphic genes act in different ways as their disruption results in opposing physiological changes. Both mutants showed resistance to paraquat, compared to the respective wild types, confirming loss of function in paraquat transport. In contrast to previous studies, it is demonstrated that rmv1 is likely to be a gain of function mutant and shows increased paraquat resistance compared to put3-1. Transgenic lines of rmv1 and put3-1 carrying either AtPUT3-Col or AtPUT3-Ler were created and will be characterised in future studies to validate hypotheses on the functionality of the respective PUT3 genes. The polyamine uptake deficient yeast strain agp2∆ was assessed as a model to validate polyamine specificity of the AtPUT3-Col and AtPUT3-Ler transporters but further work remains to be done. Finally, it has been proposed that polyamines stabilise negatively charged molecules like RNA. To investigate, whether the differential polyamine composition of the phloem saps result in different mRNA profiles in the phloem, a phloem sap collector device was constructed that enabled RNA to be extracted from phloem exudates. A set of mobile mRNA markers was assessed to validate phloem exudate purity, which can provide a basis of comparison in the future.