Studies on the Effect of Diphenylcarbazide in Isolated Chloroplasts from Spinach

Abstract

The influence of diphenylcarbohydrazide (DPC) on electron transport parameters of chloroplasts was studied through the use of hypotonically disintegrated plastids in various states of membrane disarray. The observation that DPC acts as donator for PS II when the natural source becomes inefficient was confirmed. Contrary to prior contentions oxygen evolution is not diminished upon addition of DPC. A definite though transient influence of DPC on the pigment system was detected. At a certain state of structural disarray DPC increases the quantum yield and electron transport efficiency through PS II, while simultaneously decreasing the activity of PS I. The effect is not based on addition or removal of individual pigments to the pigment complexes. The analysis of light inten­sity curves and fluorescence kinetics suggest a better migration of trapped light to open reaction centers. The results are discussed for possible implications on the analysis of the oxygen evolving system as well as on spillover mechanisms.