Involvement of lipoxygenase-dependent production of fatty acid hydroperoxides in the development of the hypersensitive cell death induced by cryptogein on tobacco leaves

Lipid peroxidation was investigated in relation with the hypersensitive rea ction in cryptogein-elicited tobacco leaves. A massive production of free p olyunsaturated fatty acid (PUFA) hydroperoxides dependent on a 9-lipoxygena se (LOX) activity was characterized during the development of leaf necrosis . The process occurred after a lag phase of 12 h, was accompanied by the co ncomitant increase of 9-LOX activity, and preceded by a transient accumulat ion of LOX transcripts. Free radical-mediated lipid peroxidation represente d 10% of the process. Inhibition and activation of the LOX pathway was show n to inhibit or to activate cell death, and evidence was provided that fatt y acid hydroperoxides are able to mimic leaf necrotic symptoms. Within 24 h , about 50% of leaf PUFAs were consumed, chloroplast lipids being the major source of PUFAs. The results minimize the direct participation of active o xygen species from the oxidative burst in membrane lipid peroxidation. They suggest, furthermore, the involvement of lipase activity to provide the fr ee PUFA substrates for LOX. The LOX-dependent peroxidative pathway, respons ible for tissue necrosis, appears as being one of the features of hypersens itive programmed cell death.