Papers by Flavio Garlaschi
The isolated reaction centre (RC) complex of photosystem II (PSII) known as D1/D2/cytb559 complex... more The isolated reaction centre (RC) complex of photosystem II (PSII) known as D1/D2/cytb559 complex which binds six chl a and two pheophytin molecules, is extremely crowded spectroscopically in the Qy absorption region. Seven main gaussian sub-bands are required between 660–684 nm (1) in order to provide a reasonable description of its thermal broadening characteristics. The longest wavelength electronic transition is generally thought to occur near 683–684 nm (2,3) and there is considerable discussion as to whether this is associated with the primary electron donor pigment or not (2–5). A recent photobleaching analysis of this transition at 80 K suggests that its electron-phonon coupling properties are those of a “normal” antenna type chlorophyll (5). If this interpretation is correct then it is apparent that absorption intensity in the long wavelength tail at room temperature (RT) cannot be due to this electron transition alone. Here we analyse the red absorption tail of the PSII RC...
Science Access, 2001
Plants exposed to high photon fluence are susceptible to photooxidative damage (photoinhibition).... more Plants exposed to high photon fluence are susceptible to photooxidative damage (photoinhibition). As photoinhibition is linear with the number of absorbed photons (reciprocity rule) it is generally thought that the antenna-based, non-photochemical quenching (qNP) represents an important protective strategy by lowering the excited singlet state levels in PSII antenna. We have investigated the relation between the lowering of the singlet excited state levels (quenching) and photoinhibition in thylakoids isolated from a variety of species (spinach, barley, Arabidopsis) and intact cells of the unicellular alga Chlamydomonas reinhardii. The results show that antenna quenching affords only a minimal protection against photoinhibition which is, at the most no more than 35% of that expected based on the reciprocity rule. Moreover the light-induced degradation of the reaction centre protein D1, generally considered to constitute an initial phase of the photoinhibition repair mechanism, is de...
The structure of P680, the primary donor of the PS2 reaction centre, is still a matter of debate.... more The structure of P680, the primary donor of the PS2 reaction centre, is still a matter of debate. Data obtained by different experimental approaches, as well as polypeptide primary structural homology with the bacterial RCs (1), suggest that P680 structure is that of a Chla dimer. However, other authors have shown that P680 is different from its bacterial counterparts: the special pair (if it exists) has a much weaker exciton interaction, its triplet state is located on a Chl monomer and (mutual) orientations of Chl molecules appear very different (1). Tetenkin et al. (2) and Durrant et al. (3) suggested that all or most of the D1/D2/cytb-559 pigments may be excitonically coupled, i.e. P680 should be structured as a multimer. In an attempt to gain further information on the PS2 RC structure, we have studied temperature and photobleaching effects on D1/D2/cytb-559 circular dichroism spectra by gaussian decomposition analysis, in which thermal broadening due to linear electron-phonon ...
Science Access, 2001
The strongly red shifted chlorophyll antenna forms associated with photosystem I are intriguing b... more The strongly red shifted chlorophyll antenna forms associated with photosystem I are intriguing both from the standpoint of their biological function and the physicochemical interactions which give rise to them. Due to their uncommonly strong electron/phonon coupling and charge transfer characteristics it is often suggested that they are brought about by strong Coulombic interactions with other chlorophylls leading to the formation of excitonic dimers. The accompanying excitonic splitting would then give rise to a low energy, red shifted, absorption band. In the present study direct evidence for this suggestion is presented. Selective destruction of the strongly dichroic red shifted chlorophyll state (CD) and absorption maxima at 709nm and extinguishing near 725nm) in photosystem I trimers from Spirulina by either high intensity illumination (photobleaching) or incubation with low concentrations of Triton X-100 is accompanied by changes in the circular dichroism spectrum of the same...
Photosynthesis: Mechanisms and Effects, 1998
The antenna system of photosystem I (PSI) is characterised by the presence of a number of very re... more The antenna system of photosystem I (PSI) is characterised by the presence of a number of very red absorbing chlorophyll spectral forms, which are energetically lower than the primary trap, P700 and are the main components of the “red edge” of chloroplast and leaf absorption. In maize PSI-200 at least three, and possibly four, emission forms have been identified (1). Limited evidence exists that these red forms have unusual electron-phonon coupling leading to very high values for the optical reorganisation energy, responsible for broad absorption bands and large Stokes shifts (2). While the biological function of these forms has been much discussed in recent decades, their physiological importance is still rather obscure. In this communication we present evidence from time resolved fluorescence measurements that these low energy forms lead to slow spectral equilibration within PSI-200, which in turn leads to a pronounced diffusion limitation to the overall photochemical rate. A thermal broadening analysis of the red absorption tail for isolated LHCI provides direct evidence that the optical reorganisation energy is in fact many times greater than that for “normal” antenna chlorophylls. We furthermore demonstrate from model calculations in which leaf absorption is described in terms of a linear combination of the in vitro spectra of PSI, PSI! and LHCII, corrected for multiple internal leaf scattering, that the red forms greatly increase light absorption in leaves exposed to a “shade light” regime and have a pronounced effect on the PSII/PSI absorption cross section ratio.
Photosynthesis: from Light to Biosphere, 1995
Photosynthesis: Mechanisms and Effects, 1998
Singlet exciton migration in the energetically heterogeneous chlorophyll (chi) arrays of plant ph... more Singlet exciton migration in the energetically heterogeneous chlorophyll (chi) arrays of plant photosystems depends, in the Forster theory framework (1), on such parameters as interchromophore separation and orientation, radiative lifetime and the integral between the fluorescence (F) and the absorption (A) spectra of the Donor-Acceptor (D-A) couple involved. For the F/A overlap integral, knowledge of the absorption bandshape for chis in a protein matrix is of a fundamental importance. Chlorophyll molecules in a host protein matrix are subject to interactions that modify their spectral properties both modulating the 0-0 transition energies as well as the absorption bandshape characteristics (e.g. 2). Hole-burning studies on different chi-protein complexes of plant photosystems indicate that a weak coupling (coupling strength S=0.4-1) of the chi electronic transition to a phonon “bath” with mean frequency vm=20cm−1, giving a reorganisation energy Svm=16cm−1, plays an important role in determining the homogeneous absorption bandshape and its temperature dependence (e.g. 3). However the presence of chi forms with higher reorganisation energy has been suggested in the red tail of PSI absorption (4,5). These red forms absorb at energies lower than the primary photochemical trap (P700) and contribute up to 85% to the room temperature (RT) fluorescence (6). As this fluorescence emission is from substantially thermal equilibrated excited states (6), the red forms clearly have a great importance in the energy transfer dynamics in PSI antenna. The role of the overlap integral in energy transfer has been highlighted in a pioneering study by Shipman fuwei Housman (7).
Physiologia Plantarum, 1972
Respiratory activity, RNA contents and protein synthesis capacity of isolated ribosomes of tubers... more Respiratory activity, RNA contents and protein synthesis capacity of isolated ribosomes of tubers of Solanum tuberosum, cv. Tonda di Berlino, at progressive stages of development have been determined. In the immature, still growing tubers, respiration steadily decreases with the increase of fresh weight. The entering into dormancy of the tubers collected when immature corresponds to a rapid drop of respiration to the values characteristic of mature tubers. The RNA contents per tuber increase progressively during maturation. A decrease of the RNA contents per tuber (ca. 50 %) is observed in the period between the moment of harvesting and the end of dormancy. The endogenous capacity of isolated ribosomes to carry on amino acid polymerization strongly decreases during tuber development, while the activity supported by polyuridilic acid remains almost unchanged when measured at optimum Mg2+ concentrations, and becomes larger for the more mature tubers at superoptimum Mg2+ concentrations...
FEBS Letters, 2005
The selectively red excited emission spectrum, at room temperature, of the in vitro reconstituted... more The selectively red excited emission spectrum, at room temperature, of the in vitro reconstituted Lhca4, has a pronounced non-equilibrium distribution, leading to enhanced emission from the directly excited low-energy pigments. Two different emitting forms (or states), with maximal emission at 713 and 735 nm (F713 and F735) and unusual spectral properties, have been identified. Both high-energy states are populated when selective excitation is into the F735 state and the fluorescence anisotropy spectrum attains the value of 0.3 in the wavelength region where both emission states are present. This indicates that the two states are on the same Lhca4 complex and have transition dipoles with similar orientation.
FEBS Letters, 2001
Selective destruction of the strongly dichroic red‐shifted chlorophyll form (C709 nm) in photosys... more Selective destruction of the strongly dichroic red‐shifted chlorophyll form (C709 nm) in photosystem I (PSI) trimers from Spirulina, by either non‐selective high intensity illumination (photobleaching) or incubation with low concentrations of Triton X‐100 is accompanied by changes in the circular dichroism spectrum of the same amplitude and of opposite sign at 677 nm. The data are interpreted in terms of a dimeric chlorophyll structure with excitonic bands at these two wavelengths. Similar photobleaching experiments with PSI‐200 from maize also suggest the presence of bulk antenna/red form excitonic interactions.
Journal of bioenergetics and biomembranes, 1977
The dependence of thylakoid osmotic volume on NH4Cl uncoupling and on phosphorylation substrates ... more The dependence of thylakoid osmotic volume on NH4Cl uncoupling and on phosphorylation substrates is determined by the centrifuge filtration method. The values obtained are used to evaluate the transmembrane proton gradient in conjunction with either the 9-aminoacridine fluorescence quenching method or the [14C]methylamine uptake method. The DeltapH values obtained with the two methods are compared and a linear relationship is demonstrated in the DeltapH range from 1.4 to 2.7 ([14C]methylamine values). Different linear relationships are obtained depending on the presence or absence of electron acceptor. We conclude that the 9-aminoacridine method can be used for DeltapH determination after calibration with other methods.
Plant Science Letters, 1978
ABSTRACT Trypsin digestion of chloroplast membranes for periods of time which eliminate the catio... more ABSTRACT Trypsin digestion of chloroplast membranes for periods of time which eliminate the cation effect on fluorescence, do not influence the cation stimulation of photosystem 2 activity. Cation titration curve of fluorescence stimulation and the increased photosystem 2 photochemical efficiency do not coincide. Typsin digestion for periods of time which eliminate the cation effect on photosystem 1 do not influence the stimulation of fluorescence. It is concluded that these cation effects do not seem to be explainable on the basis of a cation induced spillover interruption.
Ion Interactions in Energy Transfer Biomembranes, 1986
Photosynthesis: Mechanisms and Effects, 1998
PLANT PHYSIOLOGY, 1981
A mild typtic digestion of chloroplast membranes eliminates the effects of saturatng concentratio... more A mild typtic digestion of chloroplast membranes eliminates the effects of saturatng concentrations of cations (3 to 5 milhimolar MgCI2) on chlorophyll fluorescence yield, membrane stacking, and photosystem II photochemical efficiency in spinach. At the same time, the negative surface potential of the membranes i increased (by trypsin) as revealed by studies
PLANT PHYSIOLOGY, 1978
Trypsin digestion of photosynthetic membranes isolated from spinach (Spinacia oleraces L.) leaves... more Trypsin digestion of photosynthetic membranes isolated from spinach (Spinacia oleraces L.) leaves eliminates the cation stimulation of chlorophyil fluorescence. High concentrations of cations protect the fluorescence yield against trypsin digestion, and the cation specificity for this protection closely resembles that required for the stimulation of fluorescence by cations. Trypsin digestion reverses cation-induced thylakoid stackng, and the time course of this effect seems to parallel that of the reversal of cation fluorescence. High concentrations of cations protect thylakoid stacking and cation-stimulated fluorescence alike. The cation stimulation of photosytem II photochemistry remains intact after trypsinization has reversed both cation-induced thylakoid stacking and fluorescence yield It is concluded that cation-stimulated fluorescence yield, and not the cation stimulation of photosystem II photochemistry, is associated with thylakoid membrane stacking.
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Papers by Flavio Garlaschi