Abstract
Lipid peroxide-derived aldehydes produced in plants under various environmental stresses are potentially cytotoxic. Production of aldehydes inside chloroplasts can inhibit photosynthesis, in particular, at the Calvin cycle. Because the reactivity of aldehydes depends on their structure, it is important to determine the chemical species occurring in chloroplasts and their contents. In this study, we analyzed profile of aldehydes in spinach chloroplasts. LC/MS analysis showed that chloroplasts without stress treatments contained the following aldehydes at 10-600 μM; (i) C6-aldehydes (3Z)-hexenal, (2E)-hexenal and n-hexanal, (ii) α,β-unsaturated aldehydes such as crotonaldehyde and 4-hydroxy-2E-hexenal, (iii) short chain aldehydes formaldehyde, propionaldehyde and acetaldehyde and (iv) supposedly several oxo-fatty acids. Because these aldehydes were mainly distributed to thylakoids, their concentrations can reach mM levels in the membrane. In model experiments, it was found that formaldehyde, propionaldehyde, crotonaldehyde, butyraldehyde, (3Z)-hexenal, 4-hydroxy-2E-nonenal are produced from linolenic acid via its oxidation by singlet oxygen.
