Intermediate states between P* and Pf in bacterial reaction centers,as detected by the fluorescence kinetics

The fluorescence lifetimes of the reaction centers isolated from the wild-type Rhodopseudomonas sphaeroides purple bacterium and those from the R26 mutant strain, lacking the carotenoid, were measured at low redox potential. In addition to the prompt fluorescence occurring directly from P* and the long delayed emission related to the radical pair state Pf, two other components are present. We suggest that they may come from intermediate states between P* and Pf, or reflect the stabilization of Pf itself.     

The absorbance spectrum of the brown holo-membrane and the comparison of pI values of bacteriorhodopsin solubilized from purple membrane and from brown holo-membrane

Brown holo-membrane was prepared by the addition of all-trans-retinal to brown apo-membrane which was isolated from Halobacterium halobium grown in the presence of nicotine. The effects of pH and NaCI concentration on the absorbance spectrum of the brown holo-membrane were investigated in comparison with those of the purple membrane. The λ_max of the dark-adapted brown holo-membrane shifted from 560 to 600 nm by lowering pH. The pK value which was determined as the mid-point pH for the spectral red-shift was 5.8 in the absence of NaCl. It was lowered to 4.5 and 3.4 in 0.1 and 1 M NaCl solutions, respectively. The pK value for the brown holo-membrane was larger than the corresponding value for the purple membrane in the NaCl solution. Bacteriorhodopsins present in the purple membrane and in the brown holo-membrane were solubilized in the nonionic detergent, lauryl ester of sucrose. For both solubilized bacteriorhodopsins, the pK value of spectral red-shift was about 3.1 in water, and the pI value, determined by chromatofocusing, was about 4.6 at 22°C.     

云南紫稻细胞质雄性不育系花药发育过程中Ca2+的分布特点

运用焦锑酸钾沉淀法研究了云南紫稻细胞质雄性不育系和保持系花药在发育过程中Ca^2 的分布特点。结果表明,保持系的花粉母细胞和小孢子的胞质内部基本无Ca^2 的沉淀,后期花粉外壁出现Ca^2 的沉淀;保持系早期的绒毡层细胞形态正常,胞内有少量Ca^2 沉淀,后期绒毡层细胞开始凋亡,胞质凝集,胞内出现大量Ca^2 的颗粒。不育系花粉母细胞在减数分裂时期败育,胞质液泡化,内部出现大量Ca^2 的沉淀;不育系绒毡层细胞形态正常,胞内无Ca^2 的沉淀。绒毡层与花粉母细胞、小孢子之间出现大量Ca^2 颗粒。探讨了不育系花药花粉母细胞中以及与绒毡层细胞之间Ca^2 的异常积累与雄性不育的关系。     

Evidence for a shift in life-history strategy during the secondary phase of a plant invasion

We investigated the correlated response of several key traits of Lythrum salicaria L. to water availability gradients in introduced (Iowa, USA) and native (Switzerland, Europe) populations. This was done to investigate whether plants exhibit a shift in life-history strategy during expansion into more stressful habitats during the secondary phase of invasion, as has recently been hypothesized by Dietz and Edwards (Ecology 87(6):1359, 2006). Plants in invaded habitats exhibited a correlated increase in longevity and decrease in overall size in the transition into more stressful mesic habitats. In contrast, plants in the native range only exhibited a decrease in height. Our findings are consistent with the hypothesis that secondary invasion is taking place in L. salicaria, allowing it to be more successful under the more stressful mesic conditions in the invaded range. If this trend continues, L. salicaria may become a more problematic species in the future.     

Reproductive biology of the isopod Excirolana braziliensis at the southern edge of its geographical range

A full analysis of the reproductive biology of the isopod Excirolana braziliensis Richardson 1912 was conducted in a sandy beach of Uruguay, located at the southernmost edge of its distributional range in the Atlantic Ocean. Reproductive and recruitment periods of E. braziliensis were concentrated in austral summer. Females with oostegites appeared in November, whereas total biomass, individual sizes and fecundity of ovigerous females peaked between December and January. These concurrent traits were responsible for the significant peak of juveniles in January. The size at maturity was 9.88 mm. Four embryonic developmental stages were described and identified: mean length linearly increased from stages I to III, whereas dry weight exponentially decreased from stages I to IV. The high reproductive output (0.41–0.58), reported for the first time in this isopod, exceeds the rates documented for other isopods. Reproduction of E. braziliensis at the southern edge of its range is semelparous: females produce one brood during the reproductive season, exhaust their energy reserves during incubation, and probably die at the end of the reproductive season. A macroscale comparison suggests that E. braziliensis at the southern edge of its range counteracts its narrow reproductive period by a short incubation period with larger individual mature female and embryo sizes, higher fecundity and a higher percentage of ovigerous females than in subtropical and tropical populations. These extreme reproductive indicators could be attributed to the internal retention of embryos that assures offspring survival, coupled with a high adaptation capability to environmental variations across its range.     

CHAPS对M_(412)的动力学和共振拉曼光谱的影响

研究了表面活性剂CHAPS对紫膜中菌紫质在光循环过程中M_(412)的衰减速率及质子泵功能的影响.光循环中间体M_(412)快、慢衰减组分的衰减速率及质子衰减速率均受到CHAPS的影响,综合激光拉曼光谱对M_(412)和其它光循环中间体相对含量的测定,表明CHAPS对紫膜的影响是通过影响其膜脂完整的液晶结构,而使紫膜光循环动力学过程及质子泵功能发生变化的.     

表面活性剂TritonX－100对菌紫质蛋白紫外荧光性质的影响

用荧光光谱方法研究了ＴｒｉｔｏｎＸ－１００（以下缩写为ＴＸ－１００）对菌紫质蛋白（Ｂａｃｔｅｒｉｏｒｈｏｄｏｐｓｉｎ,ＢＲ）及视黄醛生色团漂白后的紫膜（Ｂａｔｅｒｉｏｐｓｉｎ,ＢＯ）紫外荧光性质的影响．结果表明：表面活性剂ＴＸ－１００使ＢＲ中色氨酸在３２６ｎｍ处的荧光发射强度增加。随着ＴＸ－１００对ＢＲ的增溶,改变了生色团的构象环境,破坏了ＢＲ中色氨酸与生色团之间的能量转移。增溶后的ＢＲ中,Ｔｒｐ趋向于更疏水性的环境。     

Bacteriorhodopsin (BR570) bathochromic band shift in an external electric field

In dry films of bacteriorhodopsin-containing purple membranes from Halobacterium halobium the external electric field (10⁴–10⁵ V · cm^?1) induces the appearance of a product spectrally close to the initial intermediate of bacteriorhodopsin (BR) photochromic cycle (batho form, K). This result and also preliminary data of the electret-thermal analysis of the preparations suggest that the dielectric polarization in chromophore-protein-lipid complexes might be an essential step of the primary stabilization of light energy in photo-bioenergetic processes.     

Photoreactions of bacteriorhodopsin

Bacteriorhodopsin is a membrane-bound light energy transducer which generates an electrochemical proton gradient. It undergoes a cyclic photoreaction in which five intermediates have been identified. During the cycle it releases a proton from one surface of the membrane and takes up a proton on the opposite surface. The active chromophore consists of retinal bound through a Schiff base to the protein. The Schiff base is deprotonized during the photoreaction cycle and appears to be involved in the transport of protons through the membrane. The retinal may also undergo an isomerization.Presented at the EMBO-Workshop on Transduction Mechanism of Photoreceptors, Jülich, Germany, October 4–8, 1976This work was supported by NASA Grant NSG-7151 and NHLI Grant HL-06285