Polyamines and the integrity of the plant body.

Putrescine, spermidine and spermine are polyamines found in all eukaryotic cells. At cellular pH's they are cations, being attached to polyanions such as DNA, RNA and phospholipids. Some PAS are conjugated with phenolic acids. Massive polyamine biosynthesis precedes DNA biosynthesis, and cells deprived of polyamines are locked into the G1 stage of the cell cycle. In plants, polyamines can affect rates of growth, the nature of differentiation, and patterns of senescence. Polyamine titers are influenced by light, hormones and environmental stresses, which generally increase arginine decarboxylase (ADC) activity. Stress stimuli lead to massive putrescine accumulation. Some phytopathogenic fungi have only one pathway to putrescine formation, via ornithine decarboxylase (ODC) while higher plants have both ODC and ADC. Since specific inhibition of the ODC pathway can be accomplished chemically, some plant diseases can be prevented without adverse effects on the host plant.