Low pH-Induced Dissociation of Three Extrinsic Proteins from O2-Evolving Photosystem II

Three extrinsic proteins involved in oxygen evolution reversiblydissociated from Photo-system II (PS II) membranes at acidicpHs showing distinctly different pH dependencies. The pHs forhalf dissociation of 17, 23 and 33 kDa extrinsic proteins weredetermined to be 5.0, 4.1 and 3.6, respectively. The half dissociationpHs of 17 and 23 kDa proteins were much lower than their respectiveisoelectric points, while that for 33 kDa protein was closeto its isoelectric point. It was suggested that protonationof the negatively charged binding domain on membrane proteinscauses dissociation of the former two extrinsic proteins, whereasprotonation of the extrinsic protein itself is responsible forthe dissociation of 33 kDa protein. Based on these, featuresof low pH-induced dissociation of extrinsic proteins and Mnfrom PS II were discussed. (Received September 25, 1990; Accepted February 13, 1991)     

Multiple flash activation of the water-photolysis system in intermittently illuminated wheat leaves

The chloroplasts from wheat leaves greened under intermittentillumination at long intervals (1-msec light$5-min dark) arecapable of photoreducing DPIP (2,6- dichlorophenolindophenol)with DPC (diphenylcarbazide) as the electron donor but incapableof photoreducing this Hill oxidant with water as the donor.Exposure of such leaves to flashes at short intervals of theorder of a second rapidly induced the water-photolysis activityto reduce DPIP. The activation by single flashes at uniformintervals greatly depended on the interval, and the activitywas maximal at an interval of a few seconds. A pair of two flashesgiven successively at an interval of a few seconds was strikinglymore effective than a pair of two flashes given simultaneously.This suggested that at least two sequential photoevents areinvolved in the activation of the latent water-photolysis system.Double, triple and multiple flashes at the short intervals gaveprogressively higher yields of activation per flash. The mechanismof activation is discussed based on these activity data obtainedwith multiple flashes at various dark intervals. ¹ On leave for thesis from Kitazato University of Hygienic Sciences,Sagamihara-shi, Kanagawa, Japan. (Received November 21, 1974; )     

Light-dependent inhibitory action of p-nitrothiophenol on Photosystem II in relation to the redox state of electron carriers

The photosystem-II activity of chloroplasts was inhibited by the treatment with p-nitrothiophenol (NphSH) in the light, and the inhibition was accompanied by a change of the fluorescence spectrum. Aromatic mercaptans examined were active in causing this inhibition and fluorescence change. These effects of p-nitrothiophenol were highly accelerated by blocking the electron transport on the oxidation side of photosystem II by carbonyl cyanide-m-chlorophenylhydrazone (CCCP) or Tris · HCl or heat pre-treatment, whereas these were suppressed by blocking the transport on the reduction side by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). It was deduced that the site of NphSH action in the electron transport chain is closer to the reaction center of photosystem II that the blocking site of CCCP or Tris · HCl or heat, and that such a site in photosystem II is exposed to be modified with NphSH when electron carriers on the oxidation side of photosystem II are oxidized by illumination.     

A Short Lived Intermediate in the Photoconversion of Protochlorophyllide to Chlorophyllide a

The transient absorption change for the photoreduction of protochlorophyllide(PChlide) was studied with a solution of extracted PChlide holochromeand with etiolated leaves. The following results were obtained:(1) A short-lived intermediate with an absorption maximum at690 nm was found before formation of chlorophyllide a (Chlide).(2) The intermediate appeared instantly at the onset of theactinic laser, and it decayed very fast with a rate constantof 3.4 x 10⁵ sec^–1. (3) This decay constant for the intermediateagreed well with the rate constants for Chlide formation, 3.1x 10⁵ sec^–1 for the extract and 4.6 x 10⁵ sec^–1for the etiolated leaves. ¹Present address: Department of Botany, Faculty of Science,Kyoto University, Kitashirakawa, Kyoto 606, Japan. (Received September 24, 1980; Accepted December 6, 1980)     

Dark Reduction of P700+ in Photosystem I Particles by Illuminated Chlorophyllide

Illumination of chlorophyllide dissolved in a wet organic solventgenerates an unknown species of chlorophyllide which is capableof reducing P700⁺ in darkness ata considerably high rate inthe absence of ascorbate and redox mediators. The formationof this derivative species is accompanied by bleaching of boththe red and blue absorption bands of chlorophyllide concomitantwith the appearance of a new peak at around 500 nm. The generationof reducing capability is stimulated by the presence of basesbut does not require reducing agents. Some of the propertiesof this reaction are discussed in comparison with the Krasnovskiireaction. ¹Present address: Department of Environmental Biology, ResearchSchool of Biological Science, The Australian National University,Canberra City, ACT 2601, Australia. ³Present address: Department of Biology, Indiana University,Bloomington, IN 47405, U.S.A. (Received June 6, 1985; Accepted November 20, 1985)     

Genetic mapping in pea. 2. Identification of RAPD and SCAR markers linked to genes affecting plant architecture

 Random amplified polymorphic DNA (RAPD) markers linked to two morphological markers ( fa and det), three ramosus genes (rms2, rms3 and rms4) and two genes conferring flowering response to photoperiod in pea (sn, dne) were selected by bulk segregant analysis on F₂ populations. Two RAPD fragments were cloned and sequenced to generate the two SCAR markers V20 and S2 which are linked to rms3 and dne, respectively. All these genes, except rms2, were previously located on the pea classical linkage map. Rms2 mapped to linkage group IB which contains the afila gene. Precise genetic maps of the regions containing the genes were obtained and compared to the RAPD map generated from the recombinant inbred-lines population of the cross Térèse×K586. This cross was chosen because several mutants were obtained from cultivars Térèse and Torsdag (K586 was derived from Torsdag). This collection of isogenic lines was used for the construction of F₂ mapping populations in which polymorphic RAPD markers were already known and mapped. Moreover, the well-known problem in pea of variability in the linkage associations between crosses was avoided. This work contributes to the precise integration between the classical map and the molecular maps existing in pea. Received: 13 March 1998 / Accepted: 29 April 1998     

Sites of electron donation by alkylhydroquinones in the electron transport chain of spinach chloroplasts

Alkyl derivatives of p-hydroquinones were examined as electrondonors for the electron transport chain in spinach chloroplasts.Hydrophobic hydroquinones with long side chains donate relativelymore electrons to photosystem 1, while hydrophilic hydroquinoneand methylhydroquinone donate electrons specifically to photosystem2. ¹On leave; Research Laboratories, Fuji Photo Film Co., Ltd.,Asaka, Saitama. (Received March 2, 1973; )     

Comparative Photosynthetic Properties of Palisade Tissue Chloroplasts and Spongy Tissue Chloroplasts of Camellia japonica L.: Functional Adjustment of the Photosynthetic Apparatus to Light Environment within a Leaf

The photochemical properties of chloroplasts isolated separatelyfrom palisade and spongy tissues of Camellia leaves, were compared,and the following results were obtained: (1) The content ofthe light-harvesting Chi a/b-protein complex was higher in spongytissue chloroplasts (S-Chlts) than in palisade tissue chloroplasts(P-Chlts), while the contents of P700 and PS IT polypeptideswere higher in P-Chlts. (2) Fluorescence induction was slowerin P-Chlts, indicating that they had a larger plastoquinonepool than S-Chlts. (3) The quantum yield of PS II electron transportin S-Chlts was appreciably higher, while that of PS I electrontransport was higher in P-Chlts. (4) The maximal rates of bothPS I and PS IT electron transport under saturating light werehigher in P-Chlts than in S-Chlts. From these results, we concluded that the photochemical propertiesin P-Chlts are adjusted to high light intensity and those ofS-Chlts to low intensity enriched in green and far-red; bothare adjusted to their respective in situ light environments. (Received December 24, 1983; Accepted March 6, 1984)     

Requirement of divalent cations for photoactivation of the laten water-oxidation system in intact chloroplasts from flashed leaves

The effects of divalent cations on photoactivation of the latent water-oxidation system in intact chloroplasts isolated from wheat (Triticum aestivum L.) leaves grown under intermittent flash illumination were investigated by using A23187, an ionophore for divalent cations, and the following results were obtained. (a) Photoactivation in the intact chloroplasts was inhibited by A23187, but was restored on addition of a low concentration of Mn²⁺ (10 μM). (b) A high concentration of Mn²⁺ (70 μM) was inhibitory, in contrast, for photoactivation, but the inhibition was restored by the coexistence of a suitable concentration of Ca²⁺ (5 mM). (c) The Ca²⁺-dependent restoration was inhibited by a high concentration of Mg²⁺ or Sr²⁺, but the inhibition was restored by the coexistence of Ca²⁺. (d) Kinetic analyses of these competitive effects between divalent cations revealed that: (i) High concentration of Ca²⁺ inhibits photoactivation in competition with Mn²⁺. (ii) High concentration of Mn²⁺ inhibits photoactivation in competition with Ca²⁺. (iii) High concentration of Mg²⁺ affects photoactivation by inhibiting Ca²⁺-dependent restoration in competition with Ca²⁺. Based on these results, we propose that the latent water-oxidation center has two binding sites, each specific for Mn²⁺ and Ca²⁺, and that photoactivation takes place in the center having both Mn²⁺ and Ca²⁺ on their respective binding sites.     

Molecular interactions of the redox-active accessory chlorophyll on the electron-donor side of photosystem II as studied by Fourier transform infrared spectroscopy

A Fourier transform infrared (FTIR) difference spectrum upon photooxidation of the accessory chlorophyll (Chl_z) of photosystem II (PS II) was obtained at 210 K with Mn-depleted PS II membranes in the presence of fericyanide and silicomolybdate. The observed Chl_z⁺/Chl_z spectrum showed two differential bands at 1747/1736 and 1714/1684 cm⁻. The former was assigned to the free carbomethoxy C = 0 and the latter to the keto C = 0 that is hydrogen-bonded or in a highly polar environment. Also, the negative 1614 cm⁻ band assignable to the macrocycle mode indicated 5-coordination of the central Mg. The negative 1660 cm⁻¹ band, possibly due to the strongly hydrogen-bonded keto C = 0, may suggest oxidation of one more Chl_z, although an alternative assignment, the amide I mode of proteins perturbed by Chl_z oxidation, is also possible.