Abstract
Alpha,beta-unsaturated aldehydes (reactive aldehydes; RAL) derived from lipid peroxides have strong cytotoxicity. Reported tolerance of the transgenic plants overproducing a RAL-detoxifying enzyme against various environmental stresses in plants suggests the involvement of RAL in the stresses. In this study, we identified the aldehyde species occurring in chloroplasts, and evaluated their toxicity to chloroplast components. Leaves of Arabidopsis thaliana Col-0 contained higher amounts of acrolein, (E)-2-pentenal and malondialdehyde than that of the mutant fad7fad8, which lacks trienoic fatty acids in chloroplasts, indicating these aldehydes were derived from linolenic acid in chloroplasts. Various aldehydes were added to spinach stromal fraction and thylakoid membranes. The most vulnerable targets were phosphoribulokinase, glutathione reductase and dehydroascorbate reductase. Among tested aldehydes, acrolein was the strongest, and other RAL followed. Malondialdehyde had only weak toxicity. Thylakoid electron transport chain, SOD and APX were insensitive to the aldehydes. Thus the RAL derived from linolenic acid attack specific targets in chloroplasts and cause cellular damage.
