Polyamines: small polycations essential as cell pleiotropic modulators throughout plant life

Polyamines (PAs) are small polycations with an extraordinary capacity to influence almost all cellular functions; they are localised in all organs and organelles, as well as in the cytoskeleton and the cell wall. PAs are aliphatic charged molecules whose complex metabolism and translocation both intracellularly and along the plant have been described. PAs are present in both free and bound/conjugated forms. Examples of PA interactions with other molecules are described, including their conjugation with proteins catalysed by the widespread transglutaminases. In this review, many biological functions of PAs are described, such as the switch from the natural process of programmed cell death (PCD) to a new life programme in tuber explants of Helianthus tuberosus cultured in vitro. Circadian rhythm as well as stress conditions, are influenced by PAs. Reproduction, in particular pollen self-incompatibility as well as photosynthesis and senescence are regulated by PAs. PCD is described in pollen germination and in the flower corolla and in leaves.