Masculinization in a hermaphroditic female of the mosquitofishHeterandria formosa

A masculinized female ofHeterandria formosa is described for the first time. In size it ranges with 28 mm total length between adult males (17–20mm) and adult females (35–40mm). A masculinized anal fin of about 5 mm length is clearly evident. Rays I and II are reduced as in normal males. Rays III to V are elongated and show features of a developing gonopodium. The remaining rays VI to VIII show the expected shape of a “normal fin.” The genus-specific hook which normally originates in the anterior ramus of ray IV and the proximal serrae which derive from the posterior ramus of ray IV are absent in the masculinized analis. The gravid spots of pregnant normal females are absent. The causes for the formation of a masculinized anal fin in a female ofH. formosa are still unknown. In the masculinized female a hermaphroditic gonad is found in which female and male sections are readily distinguishable. The female regions are dominant. The oocytes of the hermaphroditic gonad are in the stage of vitellogenesis showing a thin zona radiata. The male regions with spermatozoa and Sertoli cells are distributed throughout the ovarian tissue. This mode of hermaphroditism, in which both mature oocytes and mature spermatozoa simultaneously occur in the gonad, is unique among fishes.     

Biological control of Meloidogyne incognita and Fusarium solani in dry common bean in the field

Meloidoyne incognita (root-knot nematode) and Fusarium solani (root-rot pathogen) were the common soil-borne pathogens and cause severe damage to bean plants in newly reclaimed sandy soil in Nubaryia district, Behera Governorate, Egypt. The antagonistic effects of Trichoderma album and Trichoderma viride as well as three commercial products namely Rhizo-N^® (Bacillus subtilis), Bio-Arc^® 6% (Bacillus megaterium) and Bio-Zeid^® 2.5% (T. album) were tested against M. incognita and F. solani under naturally infected field conditions. T. album and T. viride highly reduced the frequency (%) population of pathogenic fungi such as Fusarium spp., F. solani and Rhizoctonia spp., than the commercial products. Results indicated that all the tested bio-control agents reduced, significantly, the nematode criteria as evidenced by the number of juvenile (J₂) in soil and number of galls and egg masses on roots of common bean and Fusarium root-rot incidence (%). Rhizo-N^® highly reduced the number of J₂ in soil, while T. album was the best in reducing the number of galls and egg masses in roots. The bio-control agents also increased the plant growth parameters of common bean plants i.e. plant height, plant weight, branch no./plant, pods no./plant, pod weight/plant, pod weight, seeds no./plant, fresh seeds weight/pod, dry seeds weight/pod and dry weight of 100 seeds.     

Loss of rRNA genes during a phenotypic, masculinizing mutation in Allomyces arbuscla

Summary Saturation hybridization of ³H rRNA from Allomyces arbuscula Bali wild-type to homologous DNA and to DNA preparations from Allomyces arbuscula Bali X-ray induced male mutant and an interspecific male hybrid (Allomyces arbusculaxAllomyces macrogynus Emerson and Wilson) has shown approximately 50–60% reduction in the cistrons coding for rRNA in the masculinized strains.     

ADPribosylation reaction by free ADPribose in Sulfolobus solfataricus,a thermophilic archaeon

In the archaeon Sulfolobus solfataricus, protein ADPribosylation by free ADPribose was demonstrated by testing both [adenine-¹⁴C(U)]ADPR and [adenine- ¹⁴C(U)]NAD as substrates. The occurrence of this process was shown by using specific experimental conditions. Increasing the incubation time and lowering the pH of the reaction mixture enhanced the protein glycation by free ADPribose. At pH 7.5 and 10 min incubation, the incorporation of free ADPribose into proteins was highly reduced. Under these conditions, the autoradiographic pattern showed that, among the targets of ADPribose electrophoresed after incubation with ³²P-NAD, the proteins modified by free ³²P-ADPribose mostly corresponded to high molecular mass components. Among the compounds known to inhibit the eukaryotic poly-ADPribose polymerase, only ZnCl₂ highly reduced the ADPribose incorporation from NAD into the ammonium sulphate precipitate. A 20% inhibition was measured in the presence of nicotinamide or 3-aminobenzamide. No inhibition was observed replacing NAD with ADPR as substrate. J. Cell. Biochem. 66: 37–42, 1997. © 1997 Wiley-Liss, Inc.     

Rational Design of Hierarchically Open‐Porous Spherical Hybrid Architectures for Lithium‐Ion Batteries

Controlling the internal microstructure and overall morphology of building blocks used to form hybrid materials is crucial for the realization of deterministically designed architectures with desirable properties. Here, integrative spray‐frozen (SF) assembly is demonstrated for forming hierarchically structured open‐porous microspheres (hpMSs) composed of Fe₃O₄ and reduced graphene oxide (rGO). The SF process drives the formation of a radially aligned microstructure within the sprayed colloidal droplets and also controls the overall microsphere morphology. The spherical Fe₃O₄/rGO hpMSs contain interconnected open pores, which, when used as a lithium‐ion battery anode, enables them to provide gravimetric and volumetric capacities of 1069.7 mAh g^?1 and 686.7 mAh cm^?3, much greater than those of samples with similar composition and different morphologies. The hpMSs have good rate and cycling performance, retaining 78.5% capacity from 100 to 1000 mA g^?1 and 74.6% capacity over 300 cycles. Using in situ synchrotron X‐ray absorption spectroscopy, the reaction pathway and phase evolution of the hpMSs are monitored enabling observation of the very small domain size and highly disordered nature of Fe_xO_y. The reduced capacity fade relative to other conversion systems is due to the good electrical contact between the pulverized Fe_xO_y particles and rGO, the overall structural integrity of the hpMSs, and the interconnected open porosity.     

Expression of gibberellin mutations in fruits of Pisum sativum L.

The gibberellin (GA) economy of young pea (Pisum sativum L.) fruits was investigated using a range of mutants with altered GA biosynthesis or deactivation. The synthesis mutation lh-2 substantially reduced the content of both GA₄ and GA₁ in young seeds. Among the other synthesis mutations, ls-1, le-1 and le-3, the largest reduction in seed GA₁ content was only 1.7-fold (le-1), while GA₄ was not reduced in these mutants, and in fact accumulated in some experiments (compared with the wild type). Mutation sln appeared to block the step GA₂₀ to GA₂₉ in young pods and seeds, but not as strongly as in older seeds. Mutations ls-1, le-1 and le-3 markedly reduced pod GA₁ levels, but pod elongation was not affected. After feeds of [¹³C,³H]GA₂₀ to leaves, the pods contained ¹³C,³H-labelled GA₂₀, GA₁, GA₂₉ and GA₈₁, and the seeds, [¹³C,³H]GA₂₀ and [¹³C,³H]GA₂₉. These findings are discussed in relation to recent suggestions regarding the role and origin of GA₁ in pea fruits. Received: 6 June 1997 / Accepted: 15 July 1997     

A laboratory assessment of the relative susceptibility of Molinia caerulea (L.) Moench and Calluna vulgaris (L.) Hull to a range of herbicides

There is a concern that Molinia caerulea (L.) Moench may be increasing in upland moorland communities at the expense of Calluna vulgaris (L.) Hull and other ericaceous species. In order to develop a strategy for the control of Molinia, laboratory studies were carried out to determine the dose-response relationships of seven graminicides and glyphosate on both Molinia caerulea and Calluna vulgaris. Plants were grown under laboratory conditions and sprayed with increasing doses of herbicide using a precision sprayer. Results were highly variable, indicating the great morphological plasticity of these two species, making determination of the ED₅₀ difficult. Glyphosate, quizalofop-ethyl and sethoxydim successfully reduced various measures of Molinia growth to 50% of control levels (ED₅₀ estimates ranged from 0.41–0.67 kg a.i. ha^-1, 0.18–1.20 kg a.i. ha^-1and 0.37–0.49 kg a.i. ha^-1respectively). In contrast, only glyphosate reduced Calluna growth significantly (ED₅₀s ranged from 0.025–0.45 kg a.i. ha^-1), whilst selective herbicides left it undamaged. A comparison of the results for Molinia and Calluna suggests that there is no application rate of glyphosate which will reduce Molinia effectively whilst leaving Calluna undamaged. Recommendations for field testing of selective herbicides are discussed.     

Effects of Cationic Substitutions on Delayed Rectifier Current in Type I Vestibular Hair Cells

The resting potassium current (I _KI ) in gerbil dissociated type I vestibular hair cells has been characterized under various ionic conditions in whole cell voltage-clamp. When all K⁺ in the patch electrode solution was replaced with Na⁺, (Na⁺) _in or Cs⁺, (Cs⁺) _in , large inward currents were evoked in response to voltage steps between −90 and −50 mV. Activation of these currents could be described by a Hodgkin-Huxley-type kinetic scheme, the order of best fit increasing with depolarization. Above ∼−40 mV currents became outward and inactivated with a monoexponential time course. Membrane resistance was inversely correlated with external K⁺ concentration. With (Na⁺) _in , currents were eliminated when K⁺ was removed from the external solution or following extracellular perfusion of 4-aminopyridine, indicating that currents flowed through I _KI channels. Also, reduction of K⁺ entry through manipulation of membrane potential reduced the magnitude of the outward current. Under symmetrical Cs⁺, 0 K⁺ conditions I _KI is highly permeable to Cs⁺. However, inward currents were reduced when small amounts of external K⁺ were added. Higher concentrations of K⁺ resulted in larger currents indicating an anomalous mole fraction effect in mixtures of external Cs⁺ and K⁺. Received: 23 June 1999/Revised: 27 September 1999     

Chromate reduction by <Emphasis Type="Italic">Bacillus megaterium</Emphasis> TKW3 isolated from marine sediments

Summary Bacillus megaterium strain TKW3 was isolated from multiple-metal-contaminated marine sediments of Tokwawan, Hong Kong SAR. This facultative aerobe utilized arabinose, mannitol, N-acetylglucosamine, maltose, caprate, citrate, butyrate or lactate as the sole source of carbon and energy for growth.B. megaterium TKW3 reduced highly toxic and soluble Cr⁶⁺ (as CrO₄²⁻) into almost non-toxic and insoluble Cr³⁺ under aerobic conditions. Complete reduction of 0.20 mM Cr⁶⁺ by B. megaterium TKW3 was achieved within 360 h. Initial Cr⁶⁺ concentration below 0.90 mM or inoculum less than 10⁷ cells ml⁻¹ did not have significant effect on ⁶⁺ reduction, while the residue Cr⁶⁺ concentration was the lowest at 10⁷ cells ml⁻¹. Cr⁶⁺ reduction by this strain was inhibited by high levels of NaCl (55%). B. megaterium TKW3 was also resistant to other oxyanions including 0.34 mM Cr₂O₇²⁻ 0.32 mM AsO₄³⁻, 0.58 mM SeO₃²⁻ and 0.53 mM SeO₄²⁻, and reduced soluble Se⁴⁺ (as SeO₃²⁻) to insoluble red amorphous Se⁰. B. megaterium TKW3 might have potential application in bioremediation of Cr-laden sediments associated with other oxyanions.     

Epigenetic silencing of Na,K-ATPase β1 subunit gene ATP1B1 by methylation in clear cell renal cell carcinoma

The Na,K-ATPase or sodium pump carries out the coupled extrusion of Na⁺ and uptake of K⁺ across the plasma membranes of cells of most higher eukaryotes. We have shown earlier that Na,K-ATPase-β₁ (NaK-β) protein levels are highly reduced in poorly differentiated kidney carcinoma cells in culture and in patients' tumor samples. The mechanism(s) regulating the expression of NaK-β in tumor tissues has yet to be explored. We hypothesized that DNA methylation plays a role in silencing the NaK-β gene (ATP1B1) expression in kidney cancers. In this study, to the best of our knowledge we provide the first evidence that ATP1B1 is epigenetically silenced by promoter methylation in both renal cell carcinoma (RCC) patients’ tissues and cell lines. We also show that knockdown of the von Hippel-Lindau (VHL) tumor suppressor gene in RCC cell lines results in enhanced ATP1B1 promoter AT hypermethylation, which is accompanied by reduced expression of NaK-β. Furthermore, treatment with 5-Aza-2′-deoxycytidine rescued the expression of ATP1B1 mRNA as well as NaK-β protein in these cells. These data demonstrate that promoter hypermethylation is associated with reduced NaK-β expression, which might contribute to RCC initiation and/or disease progression.     

Molecular‐Level Design of Pyrrhotite Electrocatalyst Decorated Hierarchical Porous Carbon Spheres as Nanoreactors for Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) are a class of new‐generation rechargeable high‐energy‐density batteries. However, the persisting issue of lithium polysulfides (LiPs) dissolution and the shuttling effect that impedes the efficiency of LSBs are challenging to resolve. Herein a general synthesis of highly dispersed pyrrhotite Fe_1?xS nanoparticles embedded in hierarchically porous nitrogen‐doped carbon spheres (Fe_1?xS‐NC) is proposed. Fe_1?xS‐NC has a high specific surface area (627 m² g^?1), large pore volume (0.41 cm³ g^?1), and enhanced adsorption and electrocatalytic transition toward LiPs. Furthermore, in situ generated large mesoporous pores within carbon spheres can accommodate high sulfur loading of up to 75%, and sustain volume variations during charge/discharge cycles as well as improve ionic/mass transfer. The exceptional adsorption properties of Fe_1?xS‐NC for LiPs are predicted theoretically and confirmed experimentally. Subsequently, the electrocatalytic activity of Fe_1?xS‐NC is thoroughly verified. The results confirm Fe_1?xS‐NC is a highly efficient nanoreactor for sulfur loading. Consequently, the Fe_1?xS‐NC nanoreactor performs extremely well as a cathodic material for LSBs, exhibiting a high initial capacity of 1070 mAh g^?1 with nearly no capacity loss after 200 cycles at 0.5 C. Furthermore, the resulting LSBs display remarkably enhanced rate capability and cyclability even at a high sulfur loading of 8.14 mg cm^?2.     

Paramagnetic 1H NMR spectroscopy of the reduced, unbound Photosystem I subunit PsaC: sequence-specific assignment of contact-shifted resonances and identification of mixed-and equal-valence Fe-Fe pairs in [4Fe-4S] centers FA − and FB −

A and F_B. The g-tensor orientation of F_A ⁻ and F_B ⁻ is believed to be correlated to the preferential localization of the mixed-valence and equal-valence (ferrous) iron pairs in each [4Fe-4S]⁺ cluster. The preferential position of the mixed-valence and equal-valence pairs, in turn, can be inferred from the study of the temperature dependence of contact-shifted resonances by ¹H NMR spectroscopy. For this, a sequence-specific assignment of these signals is required. The ¹H NMR spectrum of reduced, unbound PsaC from Synechococcus sp. PCC 7002 at 280.4 K in 99% D₂O solution shows 18 hyperfine-shifted resonances. The non-solvent-exchangeable, hyperfine-shifted resonances of reduced PsaC are clearly identified as belonging to the cysteines coordinating the clusters F_A ⁻ and F_B ⁻ by their downfield chemical shifts, by their temperature dependencies, and by their short T ₁ relaxation times. The usual fast method of assigning the ¹H NMR spectra of reduced [4Fe-4S] proteins through magnetization transfer from the oxidized to the reduced state was not feasible in the case of reduced PsaC. Therefore, a de novo self-consistent sequence-specific assignment of the hyperfine-shifted resonances was obtained based on dipolar connectivities from 1D NOE difference spectra and on longitudinal relaxation times using the X-ray structure of Clostridium acidi urici 2[4Fe-4S] cluster ferredoxin at 0.94 Å resolution as a model. The results clearly show the same sequence-specific distribution of Curie and anti-Curie cysteines for unbound, reduced PsaC as established for other [4Fe-4S]-containing proteins; therefore, the mixed-valence and equal-valence (ferrous) Fe-Fe pairs in F_A ⁻ and F_B ⁻ have the same preferential positions relative to the protein. The analysis reveals that the magnetic properties of the two [4Fe-4S] clusters are essentially indistinguishable in unbound PsaC, in contrast to the PsaC that is bound as a component of the PS I complex. Received: 1 February 2000 / Accepted: 20 March 2000     

Ammonia excretion in the seawater blue crab (Callinectes sapidus) occurs by diffusion, and not Na+/NH4+ exchange

Summary A series of experiments was conducted to investigate whether ammonia is excreted across the seawater-acclimated blue crab's gills as ionized NH ₄ ⁺ or as the free base, NH₃. The net excretion rate of ammonia was not changed by transfer of the crabs to reduced (150 mM) Na⁺ solutions, by transfer to Na⁺- and K⁺-free artificial sea water, or by the sodium transport inhibitor amiloride. Ammonia excretion, therefore, does not appear to be linked to Na⁺ uptake in these animals, and appears to take place by passive diffusion. Since ammonia could diffuse either as NH ₄ ⁺ or NH₃, we examined two other kinds of evidence. The trans-epithelial potential was measured in sea water and the various artificial media. In spite of a 10 mV more negative potential in Na⁺-, K⁺-free medium, the ammonia excretion was not reduced. Also, in alkalinized seawater in which the partial pressure gradient of NH₃ was reduced, but the concentration gradient of NH ₄ ⁺ increased, ammonia excretion was reduced by about 70%. These results are consistent with the conclusion that ammonia excretion takes place by diffusion of the free base, NH₃.Abbreviations SW sea water - ASW artificial sea water - t.e.p. transepithelial potential The University of Texas Marine Science Institute Contribution No. 461Supported by NSF Grant PCM77-24358     

Blockade of potassium channels in the plasmalemma ofChara corallina by tetraethylammonium,Ba2+, Na+ and Cs+

Summary The outer membranes of plant cells contain channels which are highly selective for K⁺. In the giant-celled green algaChara corallina, K⁺ currents in the plasmalemma were measured during the action potential and when the cell was depolarized to the K⁺ equilibrium potential in high external K⁺ concentrations. Currents in both conditions were reduced by externally added tetraethylammonium (TEA⁺), Ba²⁺, Na⁺ and Cs⁺. In contrast to inhibition by TEA⁺, the latter three ions inhibited inward K⁺ current in a voltage-dependent manner, and reduced inward current more than outward. Ba²⁺ and Na⁺ also appeared to inhibit outward current in a strongly voltage-dependent manner. The blockade by Cs⁺ is studied in more detail in the following paper. TEA⁺ inhibited both inward and outward currents in a largely voltage-independent manner, with an apparentK _D of about 0.7 to 1.1mm, increasing with increasing external K⁺. All inhibitors reduced current towards a similar linear leak, suggesting an insensitivity of the background leak inChara to these various K⁺ channel inhibitors. The selectivity of the channel to various monovalent cations varied depending on the method of measurement, suggesting that ion movement through the K⁺-selective channel may not be independent.     

The effects of induced masculinization on reproductive and aggressive behaviors of the female mosquitofish,Gambusia affinis affinis

Synopsis FemaleGambusia affinis affinis were masculinized with the degraded products of 65% stigmastanol-30% B-sitosterol, a phytosterol. The masculinized females were paired with non-treated males, non-treated females, and other masculinized females. The pairs were analyzed for reproductive and aggressive behaviors exhibited. The behavioral patterns of these pairs were compared statistically to the behavior patterns of the following non-treated pairs: male with male, female with female, and male with female. The masculinized females behaved like males in that they followed, swung, and thrust their gonopodia at non-treated females and larger masculinized females. However, the male-like behavior of the masculinized females was not as intense as that of normal males. Also, the effect of masculinization on the behavior of the treated female was context-dependent as seen when placed with a male or a smaller masculinized female. Under these conditions the masculinized females behaved like typical females and exhibited no masculinized behaviors. The effects of anal spots and size differences are discussed as possible explanations for the variability in behaviors exhibited. The masculinized females displayed no change in aggressive behaviors.     

Effect of illumination on the redox state of cytochrome c oxidase in wheat leaves in vivo

The redox states of cytochrome a ₃ in wheat leaves (Triticum aestivum L.), in light and in the dark were monitored by its reaction with CO, which resulted in the stimulation of the in vivo reduction of nitrate to nitrite by nitrate reductase under aerobic conditions. Illumination of the leaves for 10 min markedly stimulated the steady state reduction of cytochrome a ₃, probably associated with a decreased energization of the mitochondria in light. In the dark, during steady state respiration of the tightly coupled mitochondria, cytochrome oxidase was in a more oxidised state than in the light, as judged by its reaction with CO. It is also likely that in light, intra mitochondrial NAD⁺ will be highly reduced on account of a high phosphate potential.     

Some Effects of Triazines on Growth, Photosynthesis and Translocation of Photosjuthate in Pinus Species

The effects of triazines on growth, ¹⁴CO₂-fixation and translocation of ¹⁴C-assimilates by young Pinus seedlings were investigated. Post-emergenceroot application of moderate and high concentrations of simazine and atrazine resulted in severe toxicity to the seedlings of Pinus nigra and P. coniorta as depicted by reduction in dry weight, chlorosis, wilting and mortality. Atrazine was more toxic than simazine and P. nigra was more susceptible than P. contorta to both the triazines. Simazine treatment to the roots of P. nigra seedlings, not only caused inhibition of ¹⁴CO₂-fixation but also reduced the short-term downward transloca-tion of ^l4 C-assimilates. Various possible mechanisms whereby simazine reduced the downward movement of ^I4C-assimilates in Pinus seedlings are discussed.     

A Single Genetic Determinant that Prevents Sex Reversal in C57BL-YPOS Congenic Mice

Sex determination in the mammalian embryo begins with the activation of a gene on the Y chromosome which triggers a cascade of events that lead to male development. The mechanism by which this gene, designated SRY in humans and Sry in mice (sex determining region of the Y chromosome), is activated remains unknown. Likewise, the downstream target genes for Sry remain unidentified at present. C57BL mice carrying a Y chromosome from Mus musculus musculus or molossinus develop normally as males. In contrast, C57BL/6 mice with the Y chromosome from M. m. domesticus often show sex reversal, i.e., develop as XY females. It has been documented that C57BL mice with the Y chromosome from Poschiavinus (Y^POS), a domesticus subtype, always develop as females or hermaphrodites. This suggests that a C57BL gene either up- or downstream of Sry is ineffective in interacting with Sry, which then compromises the processes that lead to normal male sex development. Nonetheless, by selective breeding, we have been able to generate a sex reversal-resistant C57BL/6-congenic strain of mice in which the XY^POS individuals consistently develop as normal males with bilateral testes. Because the resistance to sex reversal was transferred from strain 129S1/Sv (nonalbino) by simple selection over 13 backcross generations, it is inferred that a single autosomal gene or chromosomal region confers resistance to the sex reversal that would otherwise result. XY^POS normal males generated in these crosses were compared to XY^POS abnormal individuals and to C57BL/6 controls for sexual phenotype, gonadal weight, serum testosterone, and major urinary protein (MUP) level. A clear correlation was found among phenotypic sex, MUP level, and testis weight in the males and in the incompletely masculinized XY^POS mice. The fully masculinized males of the congenic strain resemble C57BL/6 males in the tested parameters. DNA analysis confirmed that these males, in fact, carry the Y^POS Sry gene.     

EPR and optical spectroscopic properites of the electron carrier intermediate between the reaction center bacteriochlorophylls and the primary acceptor in Chromatium vinosum

1. A reaction center-cytochrome c complex has been isolated from Chromatium vinosum which is capable of normal photochemistry and light-activated rapid cytochrome c₅₅₃ and c₅₅₅ oxidation, but which has no antenna bacteriochlorophyll. As is found in whole cells, ferrocytochrome c₅₅₃ is oxidized irreversibly in milliseconds by light at 7 K.2. Room temperature redox potentiometry in combination with EPR analysis at 7 K, of cytochrome c₅₅₃ and the reaction center bacteriochlorophyll dimer (BChl)₂ absorbing at 883 nm yields identical results to those previously reported using optical analytical techniques at 77 K. It shows directly that two cytochrome c₅₅₃ hemes are are equivalent with respect to the light induced (BChl)₂ At 7 K, only one heme can be rapidly oxidized in the light, commensurate with the electron capacity of the primary acceptor (quinone-iron) being unity.3. Prior chemical reduction of the quinone-iron followed by illumination at 200K, however, leads to the slow ( ) oxidation of one cytochrome c₅₅₃ heme, with what appears to be concommitant reduction of one of the two bacteriophytins (BPh) of the reaction center as shown by bleaching of the 760 nm band, a broad absorbance increase at approx. 650 nm and a bleaching at 543 nm. The 800 nm absorbing bacteriochlorophyll is also involved since there is also bleaching at 595 and 800 nm; at the latter wave-length the remaining unbleached band appears to shift significantly to the blue. No redox changes in the 883 absorbing bacteriochlorophyll dimer are seen during or after illumination under these conditions. The reduced part of the state represents what is considered to be the reduced form of the electron carrier (I) which acts as an intermediate between the bacteriochlorophyll dimer and quinoneiron. The state (oxidized ) relaxes in the dark at 200 K in approx. 20 min but below 77 K it is trapped on a days time scale.4. EPR analysis of the state trapped as described above reveals that one heme equivalent of cytochrome becomes oxidized for the generation of the state, a result in agreement with the optical data. Two prominent signals are associated with the trapped state in the g = 2 region, which can be easily resolved with temperature and microwave power saturation: one has a line width of 15 g and is centered at g = 2.003; the other, which is the major signal, is also a radical centered at g = 2.003 but is split by 60 G and behaves as though it were an organic free-radical spin-coupled with another paramagnetic center absorbing at higher magnetic field values; this high field partner could be the iron-quinone of the primary acceptor. The identity of two signals associated with I is consistent with the idea that the reduced intermediary carrier is not simply BPh but also involves a second radical, perhaps the 800 nm bacteriochlorophylls in the reduced state. As such, the single electron would be shared in some way, and it is probable that one of these centers will be very close to the paramagnetism of the iron-quinone. Alternatively, it is possible that the electron only occupies BPh (the optical changes associated with the 800 nm bacteriochlorophyll occurring on a secondary basis) and that some of the BPh population of the trapped state is not close enough to interact with the quinone-iron.5. Light-induced triplet state formation is dramatically diminished in material in which I as well as the quinone-iron is reduced before illumination. This supports the idea that with quinone-iron alone reduced before illumination, triplet formation requires light activated electron transfer from the bacteriochlorophyll dimer to I (not possible if I is already reduced) and that the triplet is formed by the return of the electron from I to (BChl)₂.6. Results indicate that although the two cytochrome c₅₅₃ hemes may be equivalent at the point of activation, once one has become oxidized the other becomes less competent for oxidation by the (BChl)₂.