Mechanism of Interaction of Al3+ with the Proteins Composition of Photosystem II

Abstract

The inhibitory effect of Al3+on photosystem II (PSII) electron transport was investigated using several biophysical and biochemical techniques such as oxygen evolution, chlorophyll fluorescence induction and emission, SDS-polyacrylamide and native green gel electrophoresis, and FTIR spectroscopy. In order to understand the mechanism of its inhibitory action, we have analyzed the interaction of this toxic cation with proteins subunits of PSII submembrane fractions isolated from spinach. Our results show that Al 3+, especially above 3 mM, strongly inhibits oxygen evolution and affects the advancement of the S states of the Mn4O5Ca cluster. This inhibition was due to the release of the extrinsic polypeptides and the disorganization of the Mn4O5Ca cluster associated with the oxygen evolving complex (OEC) of PSII. This fact was accompanied by a significant decline of maximum quantum yield of PSII (Fv/Fm) together with a strong damping of the chlorophyll a fluorescence induction. The energy transfer from light harvesting antenna to reaction centers of PSII was impaired following the alteration of the light harvesting complex of photosystem II (LHCII). The latter result was revealed by the drop of chlorophyll fluorescence emission spectra at low temperature (77 K), increase of F0 and confirmed by the native green gel electrophoresis. FTIR measurements indicated that the interaction of Al 3+ with the intrinsic and extrinsic polypeptides of PSII induces major alterations of the protein secondary structure leading to conformational changes. This was reflected by a major reduction of α-helix with an increase of β-sheet and random coil structures in Al 3+-PSII complexes. These structural changes are closely related with the functional alteration of PSII activity revealed by the inhibition of the electron transport chain of PSII.

Characterization of the structural changes and photochemical activity of photosystem I under Al3+ effect

“…It has been reported in previous studies that Al 3+ exerts an inhibitory effect on the photochemical activity of PSII complex in isolated thylakoid membranes and in PSII submembrane fractions [32,34,37,38]. However, there is a lack of information about the site(s), and the mode(s) of the Al 3+ interaction with PSI complex.…”

“…However, the amplitude of the second phase of P700 photooxidation increased. Under higher Al 3+ concentrations, above 3 mM, PSII activity was inhibited [37,38] and therefore the inhibition of electrons generated by PSII to PSI led to a suppression of the biphasic patern. At the same range of Al 3+ concentration, the amplitude of P700 photooxidation phase increased markedly with increasing Al 3+ concentrations.…”

“…After that, the second slower phase of the oxidation of P700 was established with a stable steady state level. Even though 1 mM Al 3+ is known to alter a fraction of PSII complexes [37,38], addition of 1 mM Al 3+ keep the biphasic pattern of P700 photooxidation owing to the remaining functional PSII centers that still could donate electrons to reduce a proportion of P700 + . However, the amplitude of the second phase of P700 photooxidation increased.…”

“…Under its trivalent cationic form, Al 3+ acts as a highly toxic non-essential element for plants growth causing a number of adverse effects on physiological and biochemical processes, especially the inhibition of photosynthetic activity. At this level, it was shown that Al 3+ inhibits photosynthetic electron transport in photosystem II (PSII), affects the PSII RC, destabilizes the oxygen evolution complex (OEC), impairs light harvesting complex (LHCII) antenna of PSII and induces a conformational changes of the secondary structure polypeptides of PSII [31][32][33][34][35][36][37][38].…”

Aluminum resistance in wheat involves maintenance of leaf Ca2+ and Mg2+ content, decreased lipid peroxidation and Al accumulation, and low photosystem II excitation pressure

“…Wheat seedlings exposed to Al 3? Aluminum reduces accumulation of divalent cations (especially Ca and Mg), slows root growth, and causes impairment of photosystem II (PSII) activity (Rengel 1992;Doncheva et al 2005;Li et al 2012;Hasni et al 2015). This decreased nutrient uptake is accompanied by a decreased root and shoot growth (Moustakas et al 1995).…”