Changes in photosynthetic electron transfer and state transitions in an herbicide-resistant D1 mutant from soybean cell cultures

Abstract

Anomalies in photosynthetic activity of the soybean cell line STR7, carrying a single mutation (S268P) in the chloroplastic gene psbA that codes for the D1 protein of the photosystem II, have been examined using different spectroscopic techniques. Thermoluminescence emission experiments have shown important differences between STR7 mutant and wild type cells. The afterglow band induced by both white light flashes and far-red continuous illumination was downshifted by about 4 degrees C and the Q band was upshifted by 5 degrees C. High temperature thermoluminescence measurements suggested a higher level of lipid peroxidation in mutant thylakoid membranes. In addition, the reduction rate of P700(+) was significantly accelerated in STR7 suggesting that the mutation led to an activation of the photosystem I cyclic electron flow. Modulated fluorescence measurements performed at room temperature as well as fluorescence emission spectra at 77 K revealed that the STR7 mutant is defective in state transitions. Here, we discuss the hypothesis that activation of the cyclic electron flow in STR7 cells may be a mechanism to compensate the reduced activity of photosystem II caused by the mutation. We also propose that the impaired state transitions in the STR7 cells may be due to alterations in thylakoid membrane properties induced by a low content of unsaturated lipids.

Iron Deficiency Induces a Partial Inhibition of the Photosynthetic Electron Transport and a High Sensitivity to Light in the Diatom Phaeodactylum tricornutum

“…The mathematical analysis of the two components found by the simulation software showed t max values of 21 and 40°C with signal contributions of 43 and 57% for the B and AG bands, respectively ( Table 2 ). These results support that the 40°C band observed in P. tricornutum cell suspensions after excitation with white light flashes ( Figure 2 , 2F) corresponds to the same recombination reaction which gives rise to the FR-induced AG TL band previously described ( Roncel et al, 2007 ).…”

“…Analysis of TL yields in dark-adapted samples illuminated by a train of short saturating flashes allows the estimation of the ratio between S 0 :S 1 and Q B :Q B - in PSII ( Ducruet, 2003 ; Zurita et al, 2005 ; Roncel et al, 2007 ). The intensity of the B band exhibited a typical four-oscillation period with maxima after the second and sixth flashes (inset of Figure 2 ).…”

The afterglow thermoluminescence band as an indicator of changes in the photorespiratory metabolism of the model legumeLotus japonicus

“…We also studied the levels of lipid peroxidation in WT and Ljgln 2‐2 mutant plants grown under both photorespiratory and non‐photorespiratory conditions. The level of lipid peroxidation in photosynthetic membranes can be measured by the high temperature TL technique (HTL; see section Materials and methods and Vavilin and Ducruet , Ducruet and Vavilin , Vavilin et al , Roncel et al ).…”

“…This emission is due to the recombination of S 2 /S 3 Q B − pairs, Q B being the secondary quinone acceptor and S 2 /S 3 being the states of the oxygen‐evolving complex (OEC) storing 2 and 3 positive charges (Rutherford et al ). Another luminescence emission is the so‐called afterglow (AG) band, peaking around 45°C, which is usually observed in intact photosynthetic materials after far‐red (FR > 700 nm) irradiation (Bertsch and Azzi , Miranda and Ducruet , Roncel and Ortega , Roncel et al , ).…”

“…This AG emission is often weaker or absent after white light (Palmqvist et al , Roncel and Ortega , Roncel et al , ) but occurs in some material (Miranda and Ducruet ). However, this band has been observed under some metabolic conditions that slow down the use of photosynthetic energy, such as lack of CO 2 or phosphorus (Mellvig and Tillberg ).…”