A highly active oxygen-evolving photosystem II (PSII) complex was purified from the HT-3 strain of the widely used cyanobacterium Synechocystis sp. PCC 6803, in which the CP47 polypeptide has been genetically engineered to contain a polyhistidine tag at its carboxyl terminus [Bricker, T. M., Morvant, J., Masri, N., Sutton, H. M., and Frankel, L. K. (1998) Biochim. Biophys. Acta 1409, 50-57]. These purified PSII centers had four manganese atoms, one calcium atom, and two cytochrome b(559) hemes each. Optical absorption and fluorescence emission spectroscopy as well as western immunoblot analysis demonstrated that the purified PSII preparation was devoid of any contamination with photosystem I and phycobiliproteins. A comprehensive proteomic analysis using a system designed to enhance resolution of low-molecular-weight polypeptides, followed by MALDI mass spectrometry and N-terminal amino acid sequencing, identified 31 distinct polypeptides in this PSII preparation. We propose a new nomenclature for the polypeptide components of PSII identified after PsbZ, which proceeds sequentially from Psb27. During this study, the polypeptides PsbJ, PsbM, PsbX, PsbY, PsbZ, Psb27, and Psb28 proteins were detected for the first time in a purified PSII complex from Synechocystis 6803. Five novel polypeptides were also identified in this preparation. They included the Sll1638 protein, which shares significant sequence similarity to PsbQ, a peripheral protein of PSII that was previously thought to be present only in chloroplasts. This work describes newly identified proteins in a highly purified cyanobacterial PSII preparation that is being widely used to investigate the structure, function, and biogenesis of this photosystem.

Winter wheat (Triticum aestivum L. cv Norin No. 61) was grown at 25°C until the third leaves reached about 10 cm in length and then at 15°C, 25°C, or 35°C until full development of the third leaves (about 1 week at 25°C, but 2-3 weeks at 15°C or 35°C). In the leaves developed at 15°C, 25°C, and 35°C, the optimum temperature for CO 2 -saturated photosynthesis was 15°C to 20°C, 25°C to 30°C, and 35°C, respectively. The photosystem II (PS II) electron transport, determined either polarographically with isolated thylakoids or by measuring the modulated chlorophyll a fluorescence in leaves, also showed the maximum rate near the temperature at which the leaves had developed. Maximum rates of CO 2 -saturated photosynthesis and PS II electron transport determined at respective optimum temperatures were the highest in the leaves developed at 25°C and lowest in the leaves developed at 35°C. So were the levels of chlorophyll, photosystem I and PS II, whereas the level of Rubisco decreased with increasing temperature at which the leaves had developed. Kinetic analyses of chlorophyll a fluorescence changes and P700 reduction showed that the temperature dependence of electron transport at the plastoquinone and water-oxidation sites was modulated by the temperature at which the leaves had developed. These results indicate that the major factor that contributes to thermal acclimation of photosynthesis in winter wheat is the plastic response of PS II electron transport to environmental temperature.Photosynthesis in plants native to areas with large seasonal variations in temperature during their growth exhibits an ability to acclimate to growth temperature (Berry and Bjö rkman, 1980). Plants that are grown at cold temperature regimes show maximum rates of photosynthesis at lower temperatures than do plants grown under warm temperature regimes, and an increase in growth temperature results in an increase in optimal temperature for photosynthesis. This enables plants to perform a high rate of photosynthesis at the growth temperature, provided that a shift in optimum temperature is not accompanied with counteracting changes in the photosynthetic capacity. The acclimation potential of photosynthesis to temperature greatly varies with the plant species and ecotypes. Although a shift in the optimum temperature for photosynthesis is generally less than one-half that in the growth temperature (Berry and Bjö rkman, 1980), several plants show dramatic changes in the temperature-response curve of photosynthesis. The optimum temperature for photosynthesis in winter wheat (Triticum aestivum L. cv Norin No. 61) grown at different seasons of the year increased with increase in the mean air temperature at a rate of about 3°C increase for each 4°C increase in the growth temperature (Sawada, 1970). A 15°C increase in the growth temperature resulted in a 15°C increase in optimum temperature for photosynthesis in Pinus taeda (Strain et al., 1976) and acclimation of Saxifraga cernua to a 10°C higher temperature was accompanied with about a 10°C upw...

The anatomy of the masticatory apparatus, the direction in which masticatory muscles act during mastication, and jaw muscle forces as estimated by muscle dry weight are compared between two murid rodents, the Japanese field mouse (Apodemus speciosus, subfamily Murinae) and the gray red-backed vole (Clethrionomys rufocanus; subfamily Arvicolinae). The occlusal forces exerted by the deep masseter and the anterior temporalis are large in C. rufocanus. Furthermore, in this species, the angle between the sagittal plane and the occlusal plane of the cheek teeth is larger than in A. speciosus. Therefore, a relatively large occlusal force can be generated in C. rufocanus. The estimated line of action of the anterior temporalis differs markedly between these two species. The functional significance of this difference is discussed relative to the adaptive dental characteristics for food processing, the forces required to masticate different types of food, and the forces that control mandibular forward movement.

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Membrane protein complexes such as the reaction center complexes of oxygenic photosynthesis or the complex I of mitochondira are composed of many subunit polypeptides. To analyze their polypeptide compositions by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), a wide range of molecular sizes has to be resolved, especially in the low molecular mass range. We have improved the traditional Tris/HCI buffer systems adopting a Tris/2-(N-morpholino)ethanesulfonic acid (MES) buffer system containing 6 M urea. This gel system was used with an 18-24% acrylamide gradient for the separation of polypeptides with molecular masses from below 5 kDa to over 100 kDa. This buffer system can also be applied to the usual uniform concentration of acrylamide gel and also to minislab gels.

Time courses of state I‐state II transitions were measured in the thermophilic blue‐green alga (Cyanobacterium), Synechococcus lividus, that was grown at 55°C. The rate of the state I–II transition using light II illumination was the same as that in the dark, and the dark state was identified to be state II. Therefore, light regulation attained by state transitions is produced by the state II–I transition induced by system I light. The redox level of plastoquinone did not affect this dark state II. Arrhenius plots of the state transitions showed a break point around 43°C that corresponded to the phase transition temperature of this alga. Since both the state I–II and II–I transitions were very much temperature‐independent, we could keep the alga in either state for a long time at a “low” temperature such as room temperature. Activities of both photosystems I and II in states I and II were also measured. After a state II–I transition, the system II activity increased about 16% and at the same time, svstem I activity decreased about 30%.

Diatoms occupy a key position as a primary producer in the global aquatic ecosystem. We developed methods to isolate highly intact thylakoid membranes and the photosystem I (PS I) complex from a marine centric diatom, Chaetoceros gracilis. The PS I reaction center (RC) was purified as a super complex with light-harvesting fucoxanthin-chlorophyll (Chl)-binding proteins (FCP). The super complex contained 224 Chl a, 22 Chl c, and 55 fucoxanthin molecules per RC. The apparent molecular mass of the purified FCP-PS I super complex (approximately 1000 kDa) indicated that the super complex was composed of a monomer of the PS I RC complex and about 25 copies of FCP. The complex contained menaquinone-4 as the secondary electron acceptor A1 instead of phylloquinone. Time-resolved fluorescence emission spectra at 77 K indicated that fast (16 ps) energy transfer from a Chl a band at 685 nm on FCP to Chls on the PS I RC complex occurs. The ratio of fucoxanthin to Chl a on the PS I-bound FCP was lower than that of weakly bound FCP, suggesting that PS I-bound FCP specifically functions as the mediator of energy transfer between weakly bound FCPs and the PS I RC.

Recovery processes of photosynthetic systems during rewetting were studied in detail in a terrestrial, highly drought-tolerant cyanobacterium, Nostoc commune. With absorption of water, the weight of N. commune colony increased in three phases with half-increase times of about 1 min, 2 h and 9 h. Fluorescence intensities of phycobiliproteins and photosystem (PS) I complexes were recovered almost completely within 1 min, suggesting that their functional forms were restored very quickly. Energy transfer from allophycocyanin to the core-membrane linker peptide (L(CM)) was recovered within 1 min, but not that from L(CM) to PSII. PSI activity and cyclic electron flow around PSI recovered within 2 min, while the PSII activity recovered in two phases after a time lag of about 5 min, with half times of about 20 min and 2 h. Photosynthetic CO(2) fixation was restored almost in parallel with the first recovery phase of the PSII reaction center activity. Although the amount of absorbed water became more than 20 times the initial dry weight of the N. commune colony in the presence of sufficient water, about twice the initial dry weight was enough for recovery and maintenance of the PSII activity.