Abstract
Lipid peroxides in cells are degraded to form cytotoxic α,β-unsaturated aldehydes (reactive aldehydes). We examined the effects of reactive aldehydes on photosynthesis. When spinach chloroplasts were incubated in either acrolein, 4-hydroxynonenal or crotonaldehyde at 2 mM for 8 min at 25 degree C in darkness, the CO2 photoreduction was inhibited by 100%, 75% or 50%, respectively. The electron transport activity (H2O -> NADP+) was inhibited by only 5%. Compared with the reactive aldehydes of the same carbon chain length, aldehydes without the α,β-unsaturated bond showed less than half extents of inhibition of the CO2 photoreduction. When the CO2 photoreduction was totally lost by acrolein, the Calvin cycle enzymes were inhibited to the following extents: ribulose-5-phosphate kinase, 90%; glyceraldehydes-3-phosphate dehydrogenase, 73%; aldolase, 47.3%; sedoheptulose-1,7-bisphosphatase, 32%; Rubisco, 23%; fructose-1,6-bisphosphatase, 22%. The total inhibition of the CO2 photoreduction can be explained by the accumulation of the partial inactivation of these enzymes.
