Ubiquitous in nature, polyamines are a group of aliphatic amines, cationic at neutral pH, that are essential for cell growth and viability. Because of their positive charge, polyamines are able to bind by electrostatic linkages to many cellular macromolecules, including DNA, RNA, and proteins (Kusano et al. 2008). Polyamines are involved in the regulation of a diverse range of vital cellular processes in both eukaryotic and prokaryotic cells, including cell proliferation, signal transduction and membrane stabilization (Wang et al. 2003; Kusano et al. 2008). They are also involved in the regulation of gene expression and translation (Igarashi & Kashiwagi, 2000; Kusano et al., 2008), and control programmed cell death in some organisms (Seiler & Raul, 2005). The diamine putrescine and the triamine spermidine are found in nearly all organisms and are the most abundant polyamines in prokaryotic cells, such as bacteria, while the tetraamine spermine is mainly found in eukaryotic cells. In plants the most common polyamines are putrescine, spermidine and spermine (Tiburcio et al., 1993; Grimes et al. 1986), which are present as free amines, conjugated to small molecules such as hydroxycinnamic acid, or bound to larger macromolecules such as proteins or nucleic acids. Less common polyamines found in plants are cadaverine, and the spermidineand spermine-related compounds, homospermidine, norspermidine, homospermine, norspermine and thermospermine (Martin-Tanguy, 2001). The structures of the common and less common polyamines found in plants are shown in Table 1. Polyamines are involved in many aspects of plant development (Martin-Tanguy, 2001; Li & Burritt, 2003; Hunter & Burritt, 2005; Baron & Stasolla, 2008) and are important molecules associated with both abiotic and biotic stress tolerance (Burritt, 2008). Because of their roles in a diverse array of fundamental processes, polyamines are found within all the compartments that make up the plant cell, including mitochondria, chloroplasts and the nucleus (MartinTanguy, 2001).