• Publication type
• Journal Article MeSH

• Publication type
• Journal Article MeSH

It has been thoroughly documented, by using 31P-NMR spectroscopy, that plant thylakoid membranes (TMs), in addition to the bilayer (or lamellar, L) phase, contain at least two isotropic (I) lipid phases and an inverted hexagonal (HII) phase. However, our knowledge concerning the structural and functional roles of the non-bilayer phases is still rudimentary. The objective of the present study is to elucidate the origin of I phases which have been hypothesized to arise, in part, from the fusion of TMs (Garab et al. 2022 Progr Lipid Res 101,163). We take advantage of the selectivity of wheat germ lipase (WGL) in eliminating the I phases of TMs (Dlouhý et al. 2022 Cells 11: 2681), and the tendency of the so-called BBY particles, stacked photosystem II (PSII) enriched membrane pairs of 300-500 nm in diameter, to form large laterally fused sheets (Dunahay et al. 1984 BBA 764: 179). Our 31P-NMR spectroscopy data show that BBY membranes contain L and I phases. Similar to TMs, WGL selectively eliminated the I phases, which at the same time exerted no effect on the molecular organization and functional activity of PSII membranes. As revealed by sucrose-density centrifugation, magnetic linear dichroism spectroscopy and scanning electron microscopy, WGL disassembled the large laterally fused sheets. These data provide direct experimental evidence on the involvement of I phase(s) in the fusion of stacked PSII membrane pairs, and strongly suggest the role of non-bilayer lipids in the self-assembly of the TM system.

• Keywords
• 31P-NMR spectroscopy; BBY membrane, Linear dichroism spectroscopy, Membrane fusion; non-bilayer lipids, Wheat germ lipase,
• MeSH
• Photosystem II Protein Complex * metabolism   MeSH
• Membrane Fusion physiology   MeSH
• Lipids chemistry   MeSH
• Magnetic Resonance Spectroscopy MeSH
• Thylakoids * metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Photosystem II Protein Complex * MeSH
• Lipids MeSH

• Publication type
• Journal Article MeSH

The present paper aims to open discussion on the information content, physical mechanism(s), and measuring protocols to determine the partitioning of the absorbed light energy in oxygenic photosynthetic organisms. Revisiting these questions is incited by recent findings discovering that PSII, in addition to its open and closed state, assumes a light-adapted charge-separated state and that chlorophyll a fluorescence induction (ChlF), besides the photochemical activity of PSII, reflects the structural dynamics of its reaction center complex. Thus, the photochemical quantum yield of PSII cannot be determined from the conventional ChlF-based protocol. Consequently, the codependent quantity - the quantum yield of the so-called nonregulatory constitutive nonphotochemical quenching (npq) - loses its physical meaning. Processes beyond photochemistry and regulatory npq should be identified and characterized by multifaceted studies, including ChlF. Such investigations may shed light on the putative roles of dissipation and other energy-consuming events in the stress physiology of photosynthetic machinery.

• Keywords
• Fv/Fm, chlorophyll a fluorescence, constitutive nonregulatory dissipation, nonphotochemical quenching, quantum yield, structural dynamics,
• Publication type
• Journal Article MeSH

In our earlier works, we have shown that the rate-limiting steps, associated with the dark-to-light transition of Photosystem II (PSII), reflecting the photochemical activity and structural dynamics of the reaction center complex, depend largely on the lipidic environment of the protein matrix. Using chlorophyll-a fluorescence transients (ChlF) elicited by single-turnover saturating flashes, it was shown that the half-waiting time (Δτ 1/2) between consecutive excitations, at which 50% of the fluorescence increment was reached, was considerably larger in isolated PSII complexes of Thermostichus (T.) vulcanus than in the native thylakoid membrane (TM). Further, it was shown that the addition of a TM lipid extract shortened Δτ 1/2 of isolated PSII, indicating that at least a fraction of the 'missing' lipid molecules, replaced by detergent molecules, caused the elongation of Δτ 1/2. Here, we performed systematic experiments to obtain information on the nature of TM lipids that are capable of decreasing Δτ 1/2. Our data show that while all lipid species shorten Δτ 1/2, the negatively charged lipid phosphatidylglycerol appears to be the most efficient species - suggesting its prominent role in determining the structural dynamics of PSII reaction center.

• Keywords
• chlorophyll-a fluorescence, core complex of photosystem II, rate-limiting step, structural dynamics, thylakoid lipids, waiting time,
• Publication type
• Journal Article MeSH

• Publication type
• Editorial MeSH

Haematococcus lacustris is an important species of green algae because it produces the high-value carotenoid astaxanthin. Astaxanthin production is enhanced by various stress conditions causing the transformation of green vegetative cells to red cells with high amounts of astaxanthin, which plays various photoprotective and antioxidant roles. Although intensive research has been conducted to reveal the regulation of astaxanthin production, the photosynthetic capacity of the various cell forms is unresolved at the single-cell level. In this work, we characterized the photosynthetic and morphological changes of Haematococcus cells, using a combination of microfluidic tools and microscopic chlorophyll fluorescence imaging. We found marked but reversible changes in the variable chlorophyll fluorescence signatures upon the transformation of green cells to red cells, and we propose that the photosynthetic activity as revealed by single-cell chlorophyll fluorescence kinetics serves as a useful phenotypic marker of the different cell forms of Haematococcus.

• Keywords
• Haematococcus lacustris, chlorophyll fluorescence, photoprotection, photosynthesis, photosystem II,
• Publication type
• Journal Article MeSH

To express my appreciation of Győző Garab, I describe below our association over the years, followed by a brief description of his fundamental research in the area of biophysics of photosynthesis.

• Keywords
• Hartmut Lichtenthaler, Hartmut Michel, Jan Anderson, Paul Mathis, Rajni Govindjee, Reto Strasser, Wolfgang Junge,
• Publication type
• Journal Article MeSH

Rate-limiting steps in the dark-to-light transition of Photosystem II (PSII) were discovered by measuring the variable chlorophyll-a fluorescence transients elicited by single-turnover saturating flashes (STSFs). It was shown that in diuron-treated samples: (i) the first STSF, despite fully reducing the QA quinone acceptor molecule, generated only an F1(

• Keywords
• chlorophyll-a fluorescence, conformational changes, dielectric relaxation, light-adapted charge-separated state of PSII, rate-limitation, temperature-dependence, waiting time,
• MeSH
• Chlorophyll A MeSH
• Chlorophyll MeSH
• Diuron * pharmacology   MeSH
• Photosystem II Protein Complex * MeSH
• Waiting Lists MeSH
• Light MeSH
• Temperature MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Chlorophyll A MeSH
• Chlorophyll MeSH
• Diuron * MeSH
• Photosystem II Protein Complex * MeSH