On the relationship between chlorophyll fluorescence quenching and the quantum yield of electron transport in isolated thylakoids

Abstract

The relationship between the empirical fluorescence index ΔF/Fm' and the quantum yield of linear electron flow, Φ(s), was investigated in isolated spinach thylakoids. Conditions were optimised for reliable determination of ΔF/Fm' and Φ(s) with methyl viologen or ferricyanide as electron acceptors under coupled and uncoupled conditions. Ascorbate in combination with methyl viologen was found to stimulate light-induced O2-uptake which is not reflected in ΔF/Fm' and interpreted to reflect superoxide reduction by ascorbate. In the absence of ascorbate, the plot of ΔF/Fm' vs. Φ(s) was mostly linear, except for the range of high quantum yields, i.e. at rather low photon flux densities. With ferricyanide as acceptor, use of relatively low concentrations (0.1-0.3 mM) was essential for correct Fm'-determinations, particularly under uncoupled conditions. Under coupled and uncoupled conditions the same basic relationship between ΔF/Fm' and Φ(s) was observed, irrespective of Φ(s) being decreased by increasing light intensity or by DCMU-addition. The plots obtained with methyl viologen and ferricyanide as acceptors were almost identical and similar to corresponding plots reported previously by other researchers for intact leaves. It is concluded that the index ΔF/Fm' can be used with isolated chloroplasts for characterisation of such types of electron flow which are difficult to assess otherwise, as e.g. O2 dependent flux. The origin of the 'non-linear' part of the relationship is discussed. An involvement of 'inactive' PS II centers with separate units and inefficient QA-QB electron transfer is considered likely.

Increased capacity for photosynthesis in wheat grown at elevated CO2: the relationship between electron transport and carbon metabolism

“…The relationship between the two efficiencies became non-linear at the higher quantum yields or at low measuring PFD (data not shown). This non-linearity could be due to several factors such as the different populations of cells seen by the fluorescence measurement and the gas exchange, inaccuracies in determining respiration in the light, the presence of cyclic electron transport around PSII (Genty 1989) or due to inactive PSII centres (Hormann et al 1994). The calculated rates of total non-cyclic electron flow J~, electron transport allocated to CO2 fixation, JA, and electron transport allocated to 02 reduction, JL, as a function of PFD are shown in Fig.…”

Light dependence of quantum yields for PSII charge separation and oxygen evolution in eucaryotic algae

“…Hormann et al (1994) and Schreiber et al (1995a) demonstrated a linear relationship between ap and (Dp, at high irradiances but a deviation from nonlinearity at high quantum efficiencies, i.e. at low irradiances.…”

“…high quantum yields) and are ascribed to the presence of PSI1 heterogeneity (e.g. Schreiber et al 1995a;Hormann et al 1994). However, microalgae have a more flexible photosynthetic machinery and can more easily adjust their optical properties.…”

Light inactivation of functional photosystem II in leaves of peas grown in moderate light depends on photon exposure

“…It is reminiscent of the 'Genty' plot of 1-Fs/Fm' against the quantum yield of oxygen evolution during short-term steady illumination (Genty et al 1989), where Fs is the steady-state fluorescence yield and Fm' the maximum fluorescence yield during illumination, and the parameter 1-Fs/Fm' represents the average quantum efficiency of PSII photochemistry during illumination. An empirical relationship, linear in high irradiances but asymptotic in the low irradiance (high quantum yield) region, has been reported in leaves (Seaton and Walker 1990; and thylakoids (Hormann et al 1994). In the low-irradiance region, the loss of quantum yield of oxygen evolution without appreciable decline of 1-Fs/Fm' has also been interpreted to mean the loss of a sub-population of PSII which contributes little to the flu-orescence parameter in thylakoids (Hormann et al 1994).…”