An improved method, using saturating light pulses, for the determination of photosystem I quantum yield via P700+-absorbance changes at 830 nm

Abstract

An improved method is introduced for the determination of the quantum yield of photosystem I. The new method employs saturating light pulses with steep rise characteristics to distinguish, in a given physiological state, centers with an open acceptor side from centers with a reduced acceptor side. The latter do not contribute to PSI quantum yield ((I)~). Oxidation of P700 is measured by a rapid modulation technique using the absorbance change around 830 nm. The quantum yield ~1 is calculated from the amplitude of the rapid phase of absorbance change (AA; 830 nm) upon application of a saturation pulse in a given state, divided by the maximal AA (830 nm) which is induced by a saturation pulse with far-red background illumination. Using this technique, q~t can be determined even under conditions of acceptor-side limitation, as for example in the course of a dark-light induction period or after elimination of CO 2 from the gas stream. Thus determined ~ values display a close-to-linear relationship with those for the quantum yield of PSII (q~H) calculated from chlorophyll fluorescence parameters. It is concluded that the proposed method may provide new information on the activity of the PSI acceptot side and thus help to separate the effects of acceptorside limitation from those of cyclic PSI, whenever a nonlinear relationship between q~ll and the P700-reduction level is observed.

Coregulation of electron transport through PS I by Cyt b 6 f, excitation capture by P700 and acceptor side reduction. Time kinetics and electron transport requirement

“…Recently, Klughammer and Schreiber (1994) developed a new method to assess the fraction of PS I centres that have closed acceptor side. The method is based on the complete oxidation of P700, by a saturating flash of white light, at those centres which have open acceptor side.…”

“…At the PSI centres with closed acceptor side charge separation is prevented and in those P700 does not become oxidised under the flash. In this work we have applied a similar technique as Klughanuner and Schreiber (1994), except that our flashes were weaker and longer. This allowed us to carry out 830 nm transmittance measurements with the standard PAM 101 equipment.…”

“…Photosynthetic control has a limited range of downregulation (Laisk and Oja 1994). Under severely rate-limiting CO2 concentrations P700 + and the acceptor side of PS I may become partially reduced Harbinson et al 1990b;Laisk et al 1992;Klughammer and Schreiber 1994). Under these conditions ETR through PS I is controlled in concert by donor side oxidation and acceptor side reduction.…”

In vivo temperature dependence of cyclic and pseudocyclic electron transport in barley

“…The PSI electron transport rate was calculated as the extent of P 700 oxidation in the light multiplied by k. In previous studies, PSI electron transport rate has been estimated as the product of reduced P 700 and irradiance (Harbinson and Woodward 1987;Klughammer and Schreiber 1994). This approach makes the assumption that the eciency of trapping by reduced PSI centres is constant under all conditions.…”

PSI Showed Higher Tolerance to Sb(V) than PSII Due to Stimulation of Cyclic Electron Flow Around PSI

“…Descriptive parameters of ETR(I) and ETR(II) during the light response reaction were derived from the RLCs. The following parameters were automatically calculated by the Dual-PAM-100 software according to the exponential function [13,23]: a, the initial slope of RLCs of ETR(I) or ETR(II), reflecting the photon-capturing efficiency [20]; ETR max , the maximal electron transport rates in PSI or PSII; and I k , the index of light adaptation of PSI or PSII, which was calculated as ETR max /a. The cyclic electron transport rate was calculated as ETR(I) -ETR(II) [10], which was used to investigate whether CEF was stimulated and its physiological role under Sb(V) and high light stress.…”