Ecotoxicology of ozone: bioactivation of extracellular ascorbate.

The ascorbate pools of the extracellular respiratory lining fluids and the plant apoplast are currently considered as part of the first line of defence against ambient ozone. Ozone is in fact rapidly decomposed by ascorbate, but the only product identified so far (singlet oxygen) is toxic. Peroxy-l-threonic and peroxy-oxalic acids are now derived as further decomposition products on the basis of Criegee-type ozone chemistry. These secondary toxicants may resemble known ozone induced transmitter molecules by participating in signalling events affecting plant and animal innate immunity.