MECHANISMS OF POLYAMINE ACTION DURING SENESCENCE RESPONSES INDUCED BYOSMOTIC-STRESS

The peeled Avena sativa L. leaf-system has been used as a simple and r apid model, which allows the study of the mechanisms of polyamine acti on during senescence responses induced by osmotic stress. The use of g uazatine, an inhibitor of polyamine oxidase activity, has demonstrated the existence of a positive correlation between high levels of spermi dine and spermine and delay of senescence in oat leaves and mesophyll protoplasts. The availability of antibodies specific for key polypepti des of thylakoid membranes in combination with ultrastructural studies have led to the discovery that spermine stabilizes the molecular comp osition and preserves the integrity of thylakoid membranes. The analys es of malondialdehyde and lipoxygenase levels has revealed that polyam ines and guazatine treatments may prevent membrane destabilization, at least in part, by inhibiting lipid peroxidation. Finally, the availab ility of a cDNA coding for oat arginine decarboxylase (ADC) and the ge neration of 'site-directed' antibodies specific for ADC have led to th e establishment of the basis for a model of regulation of ADC gene exp ression in oat leaves,