CONCENTRATION-DEPENDENT INHIBITORY AND STIMULATING EFFECTS OF AMPHIPHILIC AMMONIUM-SALTS UPON PHOTOSYNTHETIC ACTIVITY OF SPINACH-CHLOROPLASTS

The effects of piperidinopropylesters of 2-, 3- and 4-alkoxy substitut ed phenylcarbamic acids (PPACs) on oxygen evolution rate (OER) in spin ach chloroplasts were investigated. PPACs show concentration-dependent effects, namely OER inhibition at higher effector concentrations and OER stimulation at lower concentrations, i.e. below the inhibitory con centration range. The inhibitory efficiency of PPACs showed dependence on the alkyl chain length of the alkoxy substituent as well as on the position of this substituent on the benzene ring. Using EPR spectrosc opy and fluorescence measurements it was confirmed that the site of PP AC inhibitory action is the donor side of photosystem 2, where D-1 and D-2 proteins are situated, namely the intermediates Z(+)/Y+, and the manganese cluster containing protein as well. The stimulating effects of PPACs on OER in spinach chloroplasts at relatively low effector con centrations are caused by photophosphorylation uncoupling due to proto nophore properties of the effectors.