Molecular genetic analyses of plant polyamines

Polyamines are small, positively charged aliphatic amines that play a variety of roles in plant physiology. Putrescine, spermidine, and spermine are usually what are collectively meant by the term polyamines, although plants also have a variety of other related compounds and secondary product conjugates to polyamines. Organisms synthesize putrescine, spermidine, and spermine by pathways leading from ornithine, arginine, and SAM, with three of the important enzymes being amino acid decarboxylases. There has been recent progress in understanding plant polyamines, both their function and the regulation of their synthesis, as a result of molecular genetic investigations. The cDNAs for many of the key enzymes have been cloned and sequenced, and studies on regulation of the enzymes have begun. Mutational and transgenic approaches are being used to perturb the pathway. Some of the phenotypes observed suggest interactions between polyamines and either ethylene or cytokinin, consistent with some of the correlations observed many years previously by polyamine physiologists. These studies, while still in their early stages, should improve our understanding of polyamine synthesis, but difficult problems remain to be solved before we can answer the question: What are the biological functions and associated mechanisms of action of polyamines?.