Thermo-optically Induced Reorganizations in the Main Light Harvesting Antenna of Plants. I. Non-Arrhenius Type of Temperature Dependence and Linear Light-intensity Dependencies

Abstract

Thermo-optically induced structural reorganizations have earlier been identified in isolated LHCII, the main chlorophyll a/b light harvesting complexes of Photosystem II, and in granal thylakoid membranes [Cseh et al. (2000) Biochemistry 39: 15250-15257; Garab et al. (2002) Biochemistry 41: 15121-15129]. According to the thermo-optic mechanism, structural changes can be induced by fast, local thermal transients due to the dissipation of excess excitation energy. In this paper, we analyze the temperature and light-intensity dependencies of thermo-optically induced reversible and irreversible reorganizations in the chiral macrodomains of lamellar aggregates of isolated LHCII and of granal thylakoid membranes. We show that these structural changes exhibit non-Arrhenius type of temperature dependencies, which originate from the 'combination' of the ambient temperature and the local thermal transient. The experimental data can satisfactorily be simulated with the aid of a simple mathematical model based on the thermo-optic effect. The model also predicts, in good accordance with experimental data published earlier and presented in this paper, that the reorganizations depend linearly on the intensity of the excess light, a unique property that is probably important in light adaptation and photoprotection of plants.

Increased Thermostability of Thylakoid Membranes in Isoprene-Emitting Leaves Probed with Three Biophysical Techniques

“…In general, heat-or light-induced reorganizations occur mostly at the supramolecular level of structural complexity, rather than at the level of the building blocks of macroassemblies. For example, the stability of the single constituents of pigment-protein complexes has been shown to be considerably higher than the stability of their macroassemblies (Cseh et al, 2000(Cseh et al, , 2005Dobrikova et al, 2003). The experiment using CD spectroscopy therefore confirms that a higher thermal stability is conferred by isoprene to thylakoid membranes, and suggests that this might be due to a sustained stability of the ordered arrays of supercomplexes in the thylakoid membranes, rather than to a specifically induced resistance in a single photosystem component.…”

Molecular Architecture of Plant Thylakoids under Physiological and Light Stress Conditions: A Study of Lipid-Light-Harvesting Complex II Model Membranes

“…An important role of light-induced LHCII reorganization in photoprotection against light-induced damage has emerged from several studies, both in vivo and in vitro (Barzda et al, 1996;Dobrikova et al, 2003;Cseh et al, 2005;Holm et al, 2005;Gruszecki et al, 2009b;Johnson et al, 2011). Most of these data suggest that the primary site of light-induced reorganizations is on the outer loop segments of LHCII, affecting the phosphorylation (Zer et al, 1999), the cation binding sites (Cseh et al, 2000;Garab and Mustardy, 2000), and the ability of stacking and lateral reorganizations (Dobrikova et al, 2003;Gruszecki et al, 2009b).…”

Structural Changes and Non-Photochemical Quenching of Chlorophyll a Fluorescence in Oxygenic Photosynthetic Organisms

“…It is also important to realize that structural changes are confi ned to the psi-type CD band, without noticeably affecting the excitonic bands, i.e., without affecting the molecular architecture of bulk pigment -protein complexes . This also holds true for irreversible, photoinhibitory treatments (Gussakovsky et al 1997 ;Cseh et al 2005 ). We note, however, that the sensitivity of excitonic CD, especially if the changes affect only a small fraction of the complexes, might not be suffi cient to detect minor alterations.…”

“…Direct experimental evidence for the capability of lipidenriched lamellar aggregates of LHCII to undergo light-induced reversible changes has been obtained via CD spectroscopy (Barzda et al 1996 ). Figure 16.6 shows this type of CD changes and their peculiar, nonArrhenius temperature dependence (Cseh et al 2005 ), the signifi cance of which will be discussed in a later section. The loosely stacked lamellar aggregates, isolated by the method of Krupa et al ( 1987 ) and Simidjiev et al ( 1997 ), exhibit psi-type features, although much weaker than displayed by microscrystalline LHCII ; see Fig.…”