Abstract
In chloroplasts, polyunsaturated fatty acids in the thylakoid membrane lipids are readily oxidized by reactive oxygen species, which are produced primarily within or on the membrane. Lipid peroxides are then degraded to toxic reactive aldehydes (RAL). We have provided evidence for the toxicity of RAL in plants by showing (i) the formation of RAL in illuminated leaves, (ii) light- and methylviologen-tolerance of the transgenic plants that have RAL-scavenging capacity and (iii) high sensitivity of stromal thiol enzymes to RAL. In this study, we compared the toxicity to photosynthesis of several RAL species. When stroma fraction was incubated with various RAL, phosphoribulokinase, glyceraldehydes-3-phosphate dehydrogenase and dehydroascorbate reductase were most sensitive. Among tested species, 4-oxo-(E)-2-hexenal (OHE) inactivated these target enzymes as strong as did acrolein, the most toxic RAL known. OHE was produced in thylakoids from (Z)-3-hexenal, a wounding-responsive aldehyde, and was scavenged by glutathione very efficiently. These results indicate potential toxicity of OHE to photosynthesis in wounded leaves.
