Accumulation of lipid peroxide-derived, toxic alpha,beta-unsaturated aldehydes (E)-2-pentenal, acrolein and (E)-2-hexenal in leaves under photoinhibitory illumination

Lipid peroxide-derived alpha,beta-unsaturated aldehydes (2-alkenals) are potent toxins that inhibit enzymes in the Calvin cycle and in the mitochondrial photorespiratory pathway. Production of 2-alkenals in illuminated leaves and their participation in cellular damages have been suggested from the observation that the transgenic tobaccos overexpressing 2-alkenal reductase (AER), a 2-alkenal-detoxifying enzyme, showed tolerance to strong light. In order to identify the involved 2-alkenal species, we here analyzed the leaf aldehyde compositions in the AER-overproducing tobaccos and wild type (SR1), and compared their changes under photoinhibitory light. Aldehydes were extracted from the leaves at an early stage of photoinhibition, derivatized with 2,4-dinitrophenylhydrazine and analyzed on reversed-phase HPLC. In dark-adapted leaves of these tobacco lines, more than 40 carbonyl species were found, of which 17 were identified. In SR1 leaves, 2-alkenals such as (E)-2-pentenal, acrolein, and (E)-2-hexenal were increased by 70-290% after 30 min-illumination. In the leaves of AER-tobaccos, light-dependent increase of these 2-alkenals was apparently lower. Thus the production of highly reactive 2-alkenals in leaves was enhanced under photooxidative stress. The tolerance to strong light due to the overexpression of AER can be explained by the scavenging of these species.