Polychlorinated biphenyls and their effects on photosynthesis and respiration

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Abstract
The effects of short-term exposures to polychlorinated biphenyls were investigated using Chlorella vulgaris and isolated spinach chloroplasts as experimental material. When Chlorella were immersed in a Warburg-Buck medium to which 10 mM glucose had been added. Aroclor 1221 was found to cause a significant inhibition of the respiration rate at concentrations above 10−7 M. When Chlorella were immersed in the same Warburg-Buck medium to which no glucose had been added, Aroclor 1221 caused a stimulation of the respiration rate at concentrations above 10−5 M. There appeared to be little effect on photosynthesis in Chlorella when Aroclor 1221 was present even at concentrations as high as 10−3 M. In contrast, oxygen evolution from isolated spinach chloroplasts using potassium ferricyanide as the electron acceptor was inhibited by Aroclor 1221. This inhibition was also apparent when the uncoupler ammonium chloride was present. Since there was no inhibition when photosystem I was examined on its own, it is suggested that Aroclor 1221 can inhibit photosynthesis in spinach chloroplasts at a site on the electron transport chain close to photosystem II.