Action of Some Organomercury Compounds on Photosynthesis in Spinach Chloroplasts

The effects of five organomercury compounds (methylmercuric chloride, phenylmercuric acetate, phenylmercuric borate, phenylmercuric citrate and diphenylmercury) on photosynthetic electron transport (PET) in spinach chloroplasts were investigated. The IC₅₀ values of organomercury compounds related to PET inhibition in spinach chloroplasts varied in the range from 468 mmol dm^-3 to 942 mmol dm^-3 and were approximately by one order higher than the corresponding value determined for HgCl₂ applied also in DMSO solution (IC₅₀ = 58 mmol dm^-3). Due to extremely low aqueous solubility of diphenylmercury, the corresponding IC₅₀ value could not be determined. Using EPR spectroscopy as probable sites of action of organomercury compounds in photosynthetic apparatus ferredoxin on the acceptor side of PS 1 and the quinone electron acceptors Q_A or Q_B on the reducing side of PS 2 were suggested.