An analysis of flash-induced electrical transients of a BLM containing chloroplast lamella extracts

Abstract

The electrical transients produced by chloroplast bilayer lipid membranes (Chl-BLM) from flash excitation are seen to result from three photocurrents and a discharge current. Each of the three photo-initiated charge transports in Chl-BLM (designated as Components A, B and C) exhibits an action spectrum similar to chlorophyll absorption spectra. The fast components (A and B), which are induced by electron acceptors such as Fe+3, have rise-times of ∼3 μsec and ∼20 msec, and occur in TLM (thin lipid membranes, i.e., colored membranes up to ∼1 μ thick) as well as in BLM. Component C is induced by a transmembrane pH difference or applied voltage, has a rise-time of ∼1 sec, and occurs only in BLM. Component C is associated with exciton dissociation and proton transport. The mobility of the Component A current carriers in TLM is estimated to be about 1×10−2 cm2/volt sec, and are, hence,electronic. The photovoltage waveforms are described by equations developed, which consider Component A as being caused by a direct charge separation proportional to the illumination intensity (within ≳0.5 μsec), and Components B and C being caused by two types of exciton processes which cause charge transport after the illumination period.