Identification of the photosynthetic CO2 fixation inhibitors in isolated pine chloroplasts as resin acids

Thus far all attempts to isolate CO, fixing chloroplasts from pine have failed. In this paper it is proposed that resin acids present in pine needles partition into membranes during chloroplast isolation and interfere with specific reactions of the Calvin cycle. CO, fixation by isolated spinach chloroplasts was strongly inhibited by the introduction of a suspension of chloroplasts isolated from Pinus sylvestris L. A partially purified organic extract obtained from chloroplasts of this pine species also strongly inhibited CO, fixation by the spinach chloroplasts. The major inhibitory compounds from the organic extract were identified as a mixture of resin acids by gas-liquid chromatography and mass spectrometry. Two resin acids, abietic acid and dehydroabietic acid, were tested for inhibitory activity. Both resin acids were potent inhibitors of photosynthetic CO₂fixation, with dehydroabietic acid being about three times more potent than abietic acid.