Chlorophyll thermofluorescence and thermoluminescence as complementary tools for the study of temperature stress in plants

Abstract

The photosynthetic apparatus, especially the electron transport chain imbedded in the thylakoid membrane, is one of the main targets of cold and heat stress in plants. Prompt and delayed fluorescence emission originating from photosystem II have been used, most often separately, to monitor the changes induced in the photosynthetic membranes during progressive warming or cooling of a leaf sample. Thermofluorescence of F (0) and F (M) informs on the effects of heat on the chlorophyll antennae and the photochemical centers, thermoluminescence on the stabilization and movements of charges and Delayed Light Emission on the permeability of the thylakoid membranes to protons and ions. Considered together and operated simultaneously, these techniques constitute a powerful tool to characterize the effect of thermal stress on intact photosynthetic systems and to understand the mechanisms of constitutive or induced tolerance to temperature stresses.

Responses of photosynthesis to high temperatures in oak saplings assessed by chlorophyll-a fluorescence: inter-specific diversity and temperature-induced plasticity

“…Such reversible effects may be quantified by the temperature inducing a 15% reduction of F v /F m , the dark-acclimated quantum yield of photochemistry (Epron, 1997b). Higher temperatures (above 40 • C) may involve direct damage to PSII photochemistry: PSII proteins may be denaturated and thylakoid membrane fluidity may increase to very high levels when temperature reaches critical values (Ducruet et al, 2007;Yordanov, 1992). This critical temperature for PSII functions may be assessed using chlorophyll a fluorescence records and by detecting the leaf temperature at the thermal breakpoint of ground level chlorophyll a fluorescence recorded under darkness (F 0 ), called critical temperature T c , (Bilger et al, 1984;Ducruet et al, 2007;Terzaghi et al, 1989).…”

“…Higher temperatures (above 40 • C) may involve direct damage to PSII photochemistry: PSII proteins may be denaturated and thylakoid membrane fluidity may increase to very high levels when temperature reaches critical values (Ducruet et al, 2007;Yordanov, 1992). This critical temperature for PSII functions may be assessed using chlorophyll a fluorescence records and by detecting the leaf temperature at the thermal breakpoint of ground level chlorophyll a fluorescence recorded under darkness (F 0 ), called critical temperature T c , (Bilger et al, 1984;Ducruet et al, 2007;Terzaghi et al, 1989). Increased F 0 denotes an inactivation of PS II reaction centres due to thylakoid instability and complex changes in PS II (Cajanek et al, 1998;Ducruet et al, 2007).…”

“…This critical temperature for PSII functions may be assessed using chlorophyll a fluorescence records and by detecting the leaf temperature at the thermal breakpoint of ground level chlorophyll a fluorescence recorded under darkness (F 0 ), called critical temperature T c , (Bilger et al, 1984;Ducruet et al, 2007;Terzaghi et al, 1989). Increased F 0 denotes an inactivation of PS II reaction centres due to thylakoid instability and complex changes in PS II (Cajanek et al, 1998;Ducruet et al, 2007). This technique has been used to assess the heat sensitivity of photosynthesis in a number of species (Knight and Ackerly, 2002).…”

“…Direct interspecific comparisons are made difficult by the fact that T c is a highly plastic trait (see Ducruet et al, 2007, for a synthesis). T c can be influenced by a series of environmental parameters like ambient temperature (Dreyer et al, 2001;Havaux, 1993;Robakowski et al, 2002), water availability (Epron, 1997a;Havaux, 1992;Ladjal et al, 2000) and plant growth regulators like ABA (Havaux, 1992;Ivanov et al, 1992).…”

Thermoluminescence as a complementary technique for the toxicological evaluation of chemicals in photosynthetic organisms

“…STL and HTL techniques have been applied in several in vitro toxicological studies, mainly using thylakoids and cell cultures (Ducruet et al, 2007). Using thylakoids isolated from leaves of greenhouse grown peas (Pisum sativum L.), Mohanty et al (1989) suggested that Cu (II) does not block electron flow between the primary and secondary quinonic electron acceptor but modifies the secondary quinonic acceptor site in such a way that it becomes unsuitable for further PSII photochemistry.…”