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Studies on cation induced thylakoid membrane stacking, fluorescence yield and photochemical efficiency
No full textTrypsin digestion of photosynthetic membranes isolated from spinach (Spinacia oleracea L.) leaves eliminates the cation stimulation of chlorophyll 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 stacking, 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
A study on the lateral distribution of the plastoquinone pool with respect to photosystem II in stacked and unstacked spinach chloroplasts.
No full textThe quenching of Photosystem II (PS II) chlorophyll fluorescence by oxidised plastoquinone has been used in an attempt to determine their relative distribution in the partition zone and stroma-exposed thylakoid membranes. Thus, the PS II-plastoquinone interaction was determined in stacked (2.5 mM MgCl2) and largely unstacked (0.25 mM MgCl2) membranes. A method to correct for spillover or other quenching changes at the different MgCl2 concentrations, which would compete with the plastoquinone-induced quenching, was devised utilising the quinone dibromothymoquinone. This compound is demonstrated to behave as an ideal (theoretically) PS II quencher at both high and low MgCl2 concentrations, which indicates that it distributes itself homogeneously between partition zone and stroma-exposed membrane regions. In passing from the stacked to the unstacked configuration, the PS II-plastoquinone interaction decreases less than the PS II-dibromothymoquinone interaction. This is interpreted to mean that plastoquinone is present in both the partition zone and stroma-exposed membranes, with somewhat higher concentrations in the stroma-exposed membranes. Thus, plastoquinone is well placed to transport reducing equivalents from the partition zones to the stroma-exposed membranes
A comparison of the light-induced, non-reversible fluorescence quenching in Photosystem II with quenching due to open reaction centres in terms of the chlorophyll emission spectral forms
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Photosystem ii fluorescence quenching phenomena in terms of the chlorophyll emission spectral forms
No full textThe Low Energy Emitting States of the Lhca4 Subunit of Higher Plant Photosystem I
No full textThe 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 735nm (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
Effects of cations on the adhesion between membrane vesicles obtained by digitonin fractionation of spinach chloroplasts.
No full textThe heavy fraction obtained by digitonin treatment of stacked spinach chloroplasts, suspended in media with different ionic composition, was examined by electron microscopy. In the presence of 5 mM MgCl2 the thylakoid fragments adhere to one another in a ‘stacked configuration,’ while, in the presence of 10 mM NaCl, mainly only single ‘unstacked’ vesicles are present, which, upon addition of 5 mM MgCl2, completely revert to the stacked configuration. As previously reported (Chow, W.S. and Barber, J. (1980) Biochim. Biophys. Acta 593, 149–157), no difference in fractionation of chlorophyll between light and heavy fractions was seen after a second digitonin treatment of this fraction suspended in media containing different cation concentrations. From these results it was concluded: (1) that for the unstacking process the movement of proteins or complexes from the stromal to the granal lamellae is not required. Upon lowering the screening by cations of the surface negative charges, the membranes separate from one another; (2) that, under these conditions, as in others (Jennings, R.C., Gerola, P.D., Garlaschi, F.M. and Forti, G. (1980) FEBS Lett. 115, 39–42), digitonin fractionation is not a tool to investigate the degree of membrane stacking
Partition zone penetration by chymotrypsin and the localization of the chloroplast flavoprotein and photosystem II
No full text1.
1. Chymotrypsin treatment of chloroplast membranes inactivates Photosystem II. The inactivation is higher when the activity is measured under low intensity actinic light, suggesting that primary photochemistry is preferentially inactivated.
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2. Membrane stacking induced by Mg2+ protects Photosystem II against chymotrypsin inactivation. When the membranes are irreversibly unstacked by brief treatment with trypsin, Mg2+ protection against chymotrypsin inactivation of Photosystem II is abolished.
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3. The kinetics of inactivation by chymotrypsin of Photosystem II indicates that membrane stacking slows down, but does not prevent, the access of chymotrypsin to Photosystem II, which is mostly located within the partition zones.
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4. It is concluded that a partition gap exists between stacked membranes of about 45 Å, the size of the chymotrypsin molecule.
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5. The kinetics of inhibition of the chloroplast flavoprotein, ferredoxin-NADP reductase, by its specific antibody is not affected by membrane stacking. This indicates that this enzyme is located outside the partition zones
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