Magnetic interaction of manganese with pheophytin anion-radical and chlorophyll cation-radical in reaction centers of the photosystem II

The influence of Mn on saturation curves of ESR spectra of Ph(-) and P(+)(680) at 1-200K in samples with different content of Mn has been studied. An analysis of these data and those on photoinduced changes of fluorescence yield of chlorophyll leads to the conclusion that the Mn-containing centre in Photosystem 2 is a cluster of 4 Mn atoms, two of which can be replaced by Mg(2+) or any other divalent metal. The distances between Mn Na Ph as well as between Mn and P(680) have been estimated.     

Composition and function of cytochrome b559 in reaction centers of photosystem II of green plants

A review of a recent study of the spectral and thermodynamic properties of cytochrome b559 as well as of the electron transfer between b559 and photosystem II reaction center cofactors in isolated D1/D2/cytochrome b559 complex RC-2 is presented. Attention is paid to the existence of intermediary-potential (IP, +150 mV) and extra-low-potential (XLP, –45 mV) hemes located close to the acceptor (quinone) and donor (P680) sides of the reaction center cofactors, respectively. These hemes found in isolated RC-2 probably correspond to the high-potential and low-potential hemes in chloroplasts, respectively. The above location of the hemes is believed to allow the photoreduction of the XLP heme and photooxidation of the IP heme. The electron transfer between the two hemes is discussed in terms of the cyclic electron flow and possible involvement in water splitting.     

Dynamics of the excited state of the primary electron donor in reaction centers of Rhodopseudomonas viridis as revealed by hole burning at 1.7K. Different conformational states

The spectra of absorbance changes (delta A) due to the formation of P+Q- (P, primary electron donor, Q, primary quinone acceptor) at 1.7K in Rhodopseudomonas viridis reaction centers (RCs) excited at 1014 nm has been shown to include, besides a progression of broad (170-190 cm-1) Gaussian vibronic bands separated by 150 cm-1, a 'narrow' structure near 1014 nm which can be simulated by a Lorentian zero-phonon hole (ZPH) and Lorentian one-mode (26.8 cm-1) phonon wings. The widths of ZPH of approximately 17 cm-1 for delta A reflecting the formation of P+Q- decaying in the ms time domain and of 6.8 +/- 0.4 cm-1 for P+Q- decaying in the min time domain at 1.7K, seems to correspond to different conformations of RCs with a relaxation time of P* of approximately 0.6 ps (in agreement with measurements in this time domain) and 1.6 +/- 0.1 ps, respectively. The comparison of the spectra of delta A in the region of the BL band for slow (min) and fast (ms) decaying components suggests a different mutual arrangement of P and BL for different conformations of RCs. It is assumed that the broad and narrow structures of the P band reflect the transitions to two configurations with different P-protein interactions. 'Narrow' structure of delta A spectrum with essentially the same phonon wings and ZPH (width of 3.8 +/- 0.4 cm-1) was observed within the P band when HL was photoreduced at 1.7K.     

Effect of Lincocin Treatment on the Greening Process in Bean (Phaseolus vulgaris) Leaves

The effect of lincocin (a plastid protein synthesis inhibitor) treatment on the greening process of bean (Phaseolus vulgaris L.) leaves have been studied. In comparison with control leaves treated ones had a decreased rate of chloroplast development. They had a marked chlorophyll deficiency and a decreased chlorophyll a/b ratio. Some long and short wavelength forms of chlorophyll a were lacking as evidenced from the absorption spectra at 25°C and the fluorescence spectra at 77°K. The –¹⁴CO₂ fixation was inhibited by 80–90% in treated leaves. The fluorescence induced by the measuring light was greater in the treated leaves than in the control ones, and the kinetics of the decline of the relative fluorescence intensity were also different. Electron microscopic studies showed macrogranum-like structures and incomplete membrane vesicles in the treated plastids. After longer treatment a destruction of membranes was observed. The results indicate some structural and functional membrane deficiencies and instability of the membranes.     

The primary photoreactions in the complex cytochrome-P-890 · P-760 (bacteriopheophytin760) of Chromatium minutissimum at low redox potentials

Experimental evidence for electron transfer, photosensitized by bacteriochlorophyll, from cytochrome c to a pigment complex P-760 (involving bacteriopheophytin-760 and also bacteriochlorophyll-800) in the reaction centers of Chromatium minutissimum has been described. This photoreaction occurs between 77 and 293 °K at a redox potential of the medium between ?250 and ?530 mV. Photoreduction of P-760 is accompanied by development of a wide absorption band at 650 nm and of an EPR signal with g = 2.0025±0.0005 and linewidth of 12.5±0.5 G, which are characteristic of the pigment radical anion.It is suggested that the photoreduction of P-760 occurs under the interaction of reduced cytochrome c with the reaction center state P⁺-890 · P^?-760 which is induced by light. The existence of short-lived state P⁺-890 · P^?-760 is indicated by the recombination luminescence with activation energy of 0.12 eV and $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{< 6}\text{ns}$. This luminescence is excited and emitted by bacteriochlorophyll and disappears when P-760 is reduced.At low redox potentials, the flash-induced absorbance changes related to the formation of the carotenoid triplet state with $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 6 μ}\text{s}$ at 20 °C are observed. This state is not formed when P-760 is reduced at 293 and 160 °K. It is assumed that this state is formed from the reaction center state P⁺-890 · P^?-760, which appears to be a primary product of light reaction in the bacterial reaction centers and which is probably identical with the state P^F described in recent works.     

Lecithotrophic development and metamorphosis in the Indo-West Pacific brittle star Ophiomastix venosa (Echinodermata: Ophiuroidea)

Summary

The larval development of the ophiocomid ophiuroid Ophiomastix venosais described using SEM. The gastrula transforms into a uniformly ciliated early larva which progressively changes into a lecithotrophic late premetamorphic larva with a continuous bilateral ciliated band. This stage is short-lived and equivalent to a highly reduced ophiopluteus. Comparisons between O. venosa and other ophiuroid species whose development has been investigated suggest that, whatever the developmental mode (lecithotrophic or planktotrophic), a pluteus stage always occurs in ophiuroids with planktonic development. Two metamorphic stages were identified, the late metamorphic larva differing from the early one by the closure of the larval mouth. The appearance of the permanent mouth marks the end of the metamorphosis. The postlarva still possesses remnants of larval features. The transformation of the reduced ophiopluteus into a barrel-shaped metamorphic larva with transverse ciliated bands, a vitellaria larva, is followed. The possible occurrence of a unique type of metamorphic larva in non-brooding ophiuroids is discussed. Verification of this, however, needs further SEM investigations on metamorphic larva from species having “regular” planktotrophic development.