Mechanisms of polyamine action during senescence responses induced by osmotic stress

The peeled Avena sativa L. leaf-system has been used as a simple and rapid model, which allows the study of the mechanisms of polyamine action during senescence responses induced by osmotic stress. The use of guazatine, an inhibitor of polyamine oxidase activity, has demonstrated the existence of a positive correlation between high levels of spermidine and spermine and delay of senescence in oat leaves and mesophyll protoplasts. The availability of antibodies specific for key polypeptides of thylakoid membranes in combination with ultrastructural studies have led to the discovery that spermine stabilizes the molecular composition and preserves the integrity of thylakoid membranes. The analyses of malondialdehyde and lipoxygenase levels has revealed that polyamines and guazatine treatments may prevent membrane destabilization, at least in part, by inhibiting lipid peroxidation. Finally, the availability of a cDNA coding for oat arginine decarboxylase (ADC) and the generation of ‘site-directed’ antibodies specific for ADC have led to the establishment of the basis for a model of regulation of ADC gene expression in oat leaves.