Relationship between polyamines and paraquat toxicity in sunflower leaf discs

Polyamines have been reported as efficient antioxidant compounds in plants. Sunflower leaf discs, treated with 100 mu M paraquat (PQ), a well known ox idative stress inducer, showed decreased levels of putrescine (Put), spermi dine (Spd) and spermine (Spm) (between 33% and 80% with respect to the cont rols). Arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) activ ities decreased 42% and 33% respectively. Among the markers of oxidative st ress measured after PQ treatment, chlorophyll and glutathione content were reduced (30% and 49% respectively) and thiobarbituric acid reactive substan ces (TBARS) content increased (60%). Superoxide dismutase (SOD) activity de clined 60% with respect to the control and lipoxygenase (LOX) increased 25% when leaf-discs were treated with the herbicide. Pretreatment with exogeno us polyamines (1 mM) reversed paraquat toxicity to different degrees accord ing to the polyamine and/or the tested parameter. Spermidine was able to in hibit chlorophyll loss, while Spm reverted the effect of PQ on the level of TBARS almost completely and also restored SOD activity close to control va lues. Putrescine was the least effective as an oxidant protectant. These re sults provide support for the argument that polyamines are effective antiox idants through their ability to act as radical scavengers.