Hole burning study of excited state structure and energy transfer dynamics of bacteriochlorophyll c in chlorosomes of green sulphur photosynthetic bacteria

Results of low temperature fluorescence and spectral hole burning experiments with whole cells and isolated chlorosomes of the green sulfur bacterium Chlorobium limicola containing BChl c are reported. At least two spectral forms of BChl c (short-wavelength and long-wavelength absorbing BChl c) were identified in the second derivative fluorescence spectra. The widths of persistent holes burned in the fluorescence spectrum of BChl c are determined by excited state lifetimes due to fast energy transfer. Different excited state lifetimes for both BChl c forms were observed. A site distribution function of the lowest excited state of chlorosomal BChl c was revealed. The excited state lifetimes are strongly influenced by redox conditions of the solution. At anaerobic conditions the lifetime of 5.3 ps corresponds to the rate of energy transfer between BChl c clusters. This time shortens to 2.6 ps at aerobic conditions. The shortening may be caused by introducing a quencher. Spectral bands observed in the fluorescence of isolated chlorosomes were attributed to monomeric and lower state aggregates of BChl c. These forms are not functionally connected with the chlorosome.Abbreviations BChl bacteriochlorophyll - EET electronic energy transfer - FWHM full width at half maximum - SDF site distribution function - RC reaction centre     

Strongly exciton-coupled BChle chromophore system in the chlorosomal antenna of intact cells of the green bacteriumChlorobium phaeovibrioides: A spectral hole burning study

Spectral hole burning studies of intact cells of the green bacteriumChlorobium phaeovibrioides have proven that the Q_y-absorption system of antenna bacteriochlorophylle (BChle) should be interpreted in terms of the delocalized exciton level structure of an aggregate. For the first time the 0-0 band of the lowest exciton state of BChle aggregates has been directly detected as the lowest energy inhomogeneously broadened band (FWHM 100 cm^–1; position of maximum, at 739 nm) of the near-infrared BChle band in the 1.8 K excitation spectrum (FWHM=750 cm^–1; position of maximum, at 715 nm). The comparative analysis of the hole spectra, measured for the three species of BChlc- ande-containing green bacteria, has shown that the 0-0 transition bands of the lowest exciton state of BChlc ande aggregates display fundamentally similar spectral features: (1) the magnitude of inhomogeneous broadening of these bands is about 100 cm^–1; (2) at the wavelength of the maximum of each band, the amplitude of the preburnt excitation spectrum makes up 20% of the maximum amplitude of the spectrum; (3) the spectral position of each band coincides with the spectral position of the longest wavelength band of the circular dichroism spectrum; (4) the width of these bands is 2.3-times less than that of monomeric BChl in vitro.     

The effects of detergents DDM and β-OG on the singlet excited state lifetime of the chlorophyll a in cytochrome b6f complex from spinach chloroplasts

The singlet excited state lifetime of the chlorophyll a (Chi a) in cytochrome b6f (Cyt b6f) complex was reported to be shorter than that of free Chl a in methanol, but the value was different for Cyt b6f complexes from different sources (～200 and ～600 ps are the two measured results). The present study demonstrated that the singiet excited state lifetime is associated with the detergents n-dodecyl-β-D-maltoside (DDM) and n-octyl-β-D-glucopyranoside (β-OG), but has nothing to do with the different sources of Cyt b6f complexes. Compared with the Cyt b6f dissolved in β-OG, the Cyt b6f in DDM had a lower fluorescence yield, a lower photodegradation rate of Chl a, and a shorter lifetime of Chl a excited state. In short, the singlet excited state lifetime, ～200 ps, of the Chl a in Cyt b6f complex in DDM is closer to the true in vivo.     

High pressure studies of energy transfer and strongly coupled bacteriochlorophyll dimers in photosynthetic protein complexes

High pressure is used with hole burning and absorption spectroscopies at low temperatures to study the pressure dependence of the B800B850 energy transfer rate in the LH2 complex of Rhodobacter sphaeroides and to assess the extent to which pressure can be used to identify and characterize states associated with strongly coupled chlorophyll molecules. Pressure tuning of the B800–B850 gap from 750 cm^\s-1 at 0.1 MPa to 900 cm^-1 at 680 MPa has no measurable effect on the 2 ps energy transfer rate of the B800–850 complex at 4.2 K. An explanation for this resilience against pressure, which is supported by earlier hole burning studies, is provided. It is based on weak coupling nonadiabatic transfer theory and takes into account the inhomogeneous width of the B800–B850 energy gap, the large homogeneous width of the B850 band from exciton level structure and the Franck-Condon factors of acceptor protein phonons and intramolecular BChl a modes. The model yields reasonable agreement with the 4.2 K energy transfer rate and is consistent with its weak temperature dependence. It is assumed that it is the C₉-ring exciton levels which lie within the B850 band that are the key acceptor levels, meaning that BChl a modes are essential to the energy transfer process. These ring exciton levels derive from the strongly allowed lowest energy component of the basic B850 dimer. However, the analysis of B850s linear pressure shift suggests that another Förster pathway may also be important. It is one that involves the ring exciton levels derived from the weakly allowed upper component of the B850 dimer which we estimate to be quasi-degenerate with B800. In the second part of the paper, which is concerned with strong BChl monomer-monomer interactions of dimers, we report that the pressure shifts of B875 (LH2), the primary donor absorption bands of bacterial RC (P870 of Rb. sphaeroides and P960 of Rhodopseudomonas viridis) and B1015 (LH complex of Rps. viridis) are equal and large in value (-0.4 cm⁰¹/MPa at 4.2 K) relative to those of isolated monomers in polymers and proteins (< -0.1 cm⁰¹/MPa). The shift rate for B850 at 4.2 K is-0.28 cm^–1/MPa. A model is presented which appears to be capable of providing a unified explanation for the pressure shifts.Abbreviations B800 BChl antenna band absorbing (at room temperature) at 800 nm (B850, B875, B1015 are defined similarly) - CD circular dichroism - FC factor Franck-Condon factor - FMO comple Fenna-Matthews-Olson complex - L-S theory Laird-Skinner theory - LH1 core light-harvesting complex of the BChl antenna complexes - LH2 peripheral light-harvesting complex of the BChl antenna complexes - NPHB non-photochemical hole burning - P960 absorption band of special pair of Rhodopseudomonas viridis absorbing at 960 nm (room temperature). P870 of Rhodobacter sphaeroides is defined similarly - QM/MM results quantum mechanical/molecular mechanical results - RC reaction center - ZPH zero phonon hole     

三种整地措施下尾巨桉人工林碳储量及其分配格局

以不炼山＋人工穴垦、不炼山＋机械带垦和炼山＋机械全垦3种不同整地组合下的2.5年生尾巨桉人工林为对象,对其碳储量及其分配格局进行研究。结果表明：(1)3种整地组合下尾巨桉各器官碳含量平均值为44.37％~57.42％,大小顺序为叶>干>枝>根>皮,带垦最大(51.21％),炼山全垦最小(49.95％);不同整地组合尾巨桉人工林林下地被物层的碳含量均无显著差异(P>0.05);土壤层(0~100 cm)碳含量均随土层深度的增大而减小,各层土壤平均碳含量总体趋势表现为带垦>炼山全垦>穴垦。(2)穴垦、带垦、炼山全垦措施下乔木层总碳储量依次为18.01、30.49和23.56 t.hm-2,各器官碳储量大小顺序为干>根>叶>枝>皮;除皮外,其余器官碳储量排序均为带垦>炼山全垦>穴垦。(3)尾巨桉人工林生态系统的总碳储量表现为带垦(197.03 t.hm-2)>炼山全垦(161.16t.hm-2)>穴垦(144.77 t.hm-2);不同整地措施碳储量分配格局均为土壤层>植被层>枯落物层。土壤层和乔木层碳储量均是带垦最大,在整个生态系统碳储量中处于主导地位,占整个系统碳储量在93％以上;不同整地组合措施对枯落物层的碳储量无显著影响。因此,从提高尾巨桉林分系统碳储量方面考虑,在雷州半岛及相似立地条件地区进行尾巨桉人工林造林时宜采取不炼山＋机械带垦的整地组合方式。     

Temperature dependence of energy transfer from the long wavelength antenna BChl-896 to the reaction center in Rhodospirillum rubrum,Rhodobacter sphaeroides (w.t. and M21 mutant) from 77 to 177K,studied by picosecond absorption spectroscopy

Decay of the bacteriochlorophyll excited state was measured in membranes of the purple bacteria Rhodospirillum (R.) rubrum, Rhodobacter (Rb.) sphaeroides wild type and Rb. sphaeroides mutant M21 using low intensity picosecond absorption spectroscopy. The excitation and probing pulses were chosen in the far red wing of the long wavelength absorption band, such that predominantly the minor antenna species B896 was excited. The decay of B896 was studied between 77 and 177K under conditions that the traps were active. In all species the B896 excited state decay is almost temperature independent between 100 and 177K, and probably between 100 and 300 K. In this temperature range the decay rates for the various species are very similar and close to 40 ps. Below 100 K this rate remains temperature independent in Rb. sphaeroides w. t. and M21, while in R. rubrum a steep decrease sets in. An analysis of this data with the theory of nuclear tunneling indicates an activation energy for the final transfer step from B896 to the special pair of 70cm^-1 for R. rubrum and 30cm^-1 or less for Rb. sphaeroides.Abbreviations B880 and B896 the main and long wavelength bacteriochlorophyll's of the LH-1 antenna - RC reaction centre - P special pair in the RC     

Analogies and surprising differences between recombinant nitric oxide synthase-like proteins from Staphylococcus aureus and Bacillus anthracis in their interactions with l-arginine analogs and iron ligands

Genome sequencing has recently shown the presence of genes coding for NO-synthase (NOS)-like proteins in bacteria. The roles of these proteins remain unclear. The interactions of a series of l-arginine (l-arg) analogs and iron ligands with two recombinant NOS-like proteins from Staphylococcus aureus (saNOS) and Bacillus anthracis (baNOS) have been studied by UV–visible spectroscopy. SaNOS and baNOS in their ferric native state, as well as their complexes with l-arg analogs and with various ligands, exhibit spectral characteristics highly similar to the corresponding complexes of heme-thiolate proteins such as cytochromes P450 and NOSs. However, saNOS greatly differs from baNOS at the level of three main properties: (i) native saNOS mainly exists under an hexacoordinated low-spin ferric state whereas native baNOS is mainly high-spin, (ii) the addition of tetrahydrobiopterin (H4B) or H4B analogs leads to an increase of the affinity of l-arg for saNOS but not for baNOS, and (iii) saNOS Fe^II, contrary to baNOS, binds relatively bulky ligands such as nitrosoalkanes and tert-butylisocyanide. Thus, saNOS exhibits properties very similar to those of the oxygenase domain of inducible NOS (iNOS_oxy) not containing H4B, as expected for a NOSoxy-like protein that does not contain H4B. By contrast, the properties of baNOS which look like those of H4B-containing iNOS_oxy are unexpected for a NOS-like protein not containing H4B. The origin of these surprising properties of baNOS remains to be determined.     

Effects of prescribed burning on plant available nutrients in dry heathland ecosystems

Heathland management is an important tool with which to modify ecosystem impacts caused by atmospheric nutrient deposition. Since changes in nutrient availability as a result of management measures affect the outcomes of heathland succession and species competition, studies on this issue are important from both a nature conservation and management point of view. This study reports the effects of prescribed burning on nutrient availability in dry heathland soils and the nutrient content of the two competing heathland species Calluna vulgaris and Deschampsia flexuosa, with particular reference to N and P. We hypothesise that winter prescribed burning leads to additional N availability, which enhances the importance of P in the context of nutrient limitation in heathland ecosystems. In the nature reserve “Lueneburg Heath” (NW Germany) we examined the availability of nutrients in the humus horizons and in the leachate as well as the relevant C:element ratios in Calluna and Deschampsia before and after a burning experiment. Our results show that prescribed burning resulted in drastically increased NH₄⁺ availability in the O-horizon. We observed only short-term effects (for NO₃⁻, PO₄³⁻, Mg) and insignificant effects on the availability of other nutrients (K, Ca). As a consequence of an increased nutrient availability in the humus horizons and a limited nutrient uptake by plants after burning, leaching increased significantly for N, Ca, K, and Mg after burning treatment. No significant changes were found in the foliar C:N ratios for either species after prescribed burning, although Deschampsia showed an increased deficiency for all the other nutrients, particularly for P, as expressed by increased foliar C:P and N:P ratios. By contrast, the nutrient content of Calluna did not change significantly, suggesting that prescribed burning favours the competitive capacity of Calluna as against Deschampsia. We assume that water shortage as a result of changes in the microclimate was mainly responsible for the deterioration of the nutrient content of Deschampsia. This gives Calluna a competitive advantage, enabling it to out-compete Deschampsia on burned heathlands, with respect to the key factor P-limitation.     

FTIR Emission Spectra of Bacteriorhodopsin in a Vibrational Excited-State

Vibrational IR-emission spectra of bacteriorhodopsin (bR) were recorded under continuous illumination with visible light at room temperature. They contain selective information about the chromophore, Schiff base, and opsin. The spectral bands were identified by comparing the data with resonance Raman and IR absorption data. The IR-emission spectra were shown to contain a set of bands characteristic for both all-trans (bR₅₆₈) and 13-cis conformations (K₆₁₀-like intermediate) simultaneously. Variation of spectral composition and the intensity of visible light illumination influenced the spectral traces and intensity distribution between them. Greater intensity of deformational vibrations suggests distorted retinal structure in the vibrationally excited ground electronic state. The origin of the emitting species of bR is discussed.     

Spectral sensitivity of the compound eyes in two day-active fireflies (Coleoptera: Lampyridae: Lucidota)

Summary The electroretinographic visual spectral sensitivity functions in day-active fireflies Lucidota luteicollis and Lucidota atra show a broad green sensitivity and a shoulder in the near-ultraviolet region of the spectrum (Figs. 1, 2) as is commonly found among day-active insects. The nomogram for P530 visual pigment matches the spectral sensitivity curves in the green. The adult L. luteicollis retains its larval bioluminescent light organ which has a peak emission at 562 nm. The _max of the ERG spectral sensitivity does not match the bioluminescent peak (Fig. 1B) as it does in twilight- and dark-active fireflies. Some relevant behavioural observations with respect to mating are presented.     

Excitation energy transfer in chlorosomes of Chlorobium phaeobacteroides strain CL1401: the role of carotenoids

The role of carotenoids in chlorosomes of the green sulfur bacterium Chlorobium phaeobacteroides, containing bacteriochlorophyll (BChl) e and the carotenoid (Car) isorenieratene as main pigments, was studied by steady-state fluorescence excitation, picosecond single-photon timing and femtosecond transient absorption (TA) spectroscopy. In order to obtain information about energy transfer from Cars in this photosynthetic light-harvesting antenna with high spectral overlap between Cars and BChls, Car-depleted chlorosomes, obtained by inhibition of Car biosynthesis by 2-hydroxybiphenyl, were employed in a comparative study with control chlorosomes. Excitation spectra measured at room temperature give an efficiency of 60–70% for the excitation energy transfer from Cars to BChls in control chlorosomes. Femtosecond TA measurements enabled an identification of the excited state absorption band of Cars and the lifetime of their S₁ state was determined to be 10 ps. Based on this lifetime, we concluded that the involvement of this state in energy transfer is unlikely. Furthermore, evidence was obtained for the presence of an ultrafast (>100 fs) energy transfer process from the S₂ state of Cars to BChls in control chlorosomes. Using two time-resolved techniques, we further found that the absence of Cars leads to overall slower decay kinetics probed within the Q_y band of BChl e aggregates, and that two time constants are generally required to describe energy transfer from aggregated BChl e to baseplate BChl a.This revised version was published online in October 2005 with corrections to the Cover Date.     

Theoretical studies on the mechanism of primary electron transfer in the photosynthetic reaction center of Rhodobacter sphaeroides

The mechanism of the primary electron transfer (ET) process in the photosynthetic reaction center (PRC) of Rhodobacter sphaeroides has been studied with quantum chemistry method of ab initio density functional theory (DFT) (B3LYP/6-31G) based on the optimized X-ray crystallographic structure. The calculation was carried out on different structural levels. The electronic structure of pigment molecules was first studied, and then the influence of the neighboring protein was taken into account at three approximation levels: (a) the surrounding proteins were treated as a homogeneous medium with a uniform dielectric constant (SCRF); (b) both the influence of axial coordination of His to the special pair P and ABChl as, and the hydrogen bonds between related residues and P and also BPhas were included; and (c) the influence of the electronic structure of the protein subunit chains as a whole was studied. The results suggest that: (1) according to the composition of the HOMO and LUMO of P, there might be a charge-separated state of (BChl_L ⁺BChl_M ⁻) for the excited state of P; (2) to treat the protein surroundings as a homogeneous medium is not sufficient. Different interactions between pigment molecules and related residues play different roles in the ET process; (3) the axial coordination of His to P raises the E _LUMO of P greatly, and it is very important for the ET process to occur in the PRC of wild-type bacterium; the axial coordination of His to ABChl as also raises their E _LUMO significantly; (4) the hydrogen-bonds between amino acid residues and P and also BPh as depress the E _LUMO of the pigment molecules to some extent, which makes the E _LUMO of P lower than those of ABChlas, and the E _LUMO of BPh a _L lower than that of BPh a _M. Consequently, the ET process from P to BPh a _L does not, according to our calculation model, occur via ABChl a _L. The possibility of the ET pathway from P to BPh a _L via ABChl a _L was discussed; (5) the frontier orbitals of protein subunit chains L and M are localized at the random coil area and the α–helix areas, respectively. Results mentioned above support the fact that the ET process proceeds in favourable circumstances along the branch L. This revised version was published online in June 2006 with corrections to the Cover Date.     

Expression of the mosquitocidal cryIVB gene under the control of different promoters in Bacillus sphaericus 2362 and acrystalliferous Bacillus thuringiensis subsp. israelensis c4Q2-72

The 3.7 kb XbaI fragment harbouring the cryIVB gene which encoded a 130 kDa mosquitocidal toxin protein from Bacillus thuringiensis subsp. israelensis (B.t.i.) was placed downstream to the cat-86 gene promoter (P _cat-86, spore stage specific expression) or bgaB gene promoter (P _bgaB , vegetative stage specific expression). The constructs were subcloned into pBC16 to obtain pBTC3 and pBTC6, respectively. Both plasmids and the other construct, pBTC1 were successfully transferred into B. thuringiensis subsp. israelensis c4Q2-72 and B. sphaericus 2362. Western blot analysis showed that P _bgaB in front of P _cryIVB could enable cells to produce a 130 kDa protein from the vegetative stage (4 h) whereas those with P _cat-86 could not. The positive detection of 130 kDa crystal protein during the vegetative stage (4 h) by Western blot analysis indicated the vegetative-stage-specific expression of P _bgaB , while the 130 kDa crystal protein produced from cryIVB gene under control of P _cat-86 was detected only at 48 h. The strong activity of P _bgaB , together with P _cryIVB within pBTC6 in both bacterial hosts was also shown by the toxicity assay against Aedes aegypti larvae (B.t.i. c4Q2-72, 5.6 ± 3.6 × 10² c.f.u./ml; B. sphaericus 2362, 5.4 ± 2.5 × 10² c.f.u./ml) which were 100-fold and 10-fold more toxic to such larvae when compared with pBTC3 (P _cat-86 together with P _cryIVB ) and pBTC1 (contained only its self promoter) in the same bacterial host strains, respectively. The plasmid pBTC6 is not stable in either Bacillus host.     

Differences in the Activation State of Ribulose-1,5-bisphosphate Carboxylase/Oxygenase in Barley,Pea, and Wheat at Two Altitudes

Activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) is an important parameter determining the rate of net photosynthesis (P _N) in situ for which no information is available with reference to altitude. We analyzed activation state along with P _N in three plant species and their cultivars grown at low (LA, 1 300 m) and high (HA, 4 200 m) altitudes. No significant change in P _N and the initial activity of RuBPCO was obtained with reference to altitude. However, activation state of RuBPCO was reduced significantly in the HA plants as compared to the LA ones. Hence low partial pressure of CO₂ prevailing at HA might be responsible for the lower activation state of RuBPCO.     

不同林分白蜡树云斑白条天牛种群空间格局地统计学分析

云斑白条天牛是我国重要林业害虫,在黄河三角洲地区对白蜡树造成严重危害。利用地统计学方法,通过调查城市行道绿化林、庭院绿化林、公路林和片林4种不同林分类型的白蜡树林地,以产卵刻槽、排粪孔和羽化孔为调查指标,对危害白蜡云斑白条天牛种群卵、幼虫、成虫(蛹)的空间格局进行了研究。结果表明:除片林样点成虫(蛹)的半变异函数模型为指数模型外,危害白蜡云斑白条天牛种群卵、幼虫、成虫(蛹)在不同林分类型下的半变异函数模型均为球形模型,其指明空间分布均为聚集分布,种群的聚集分布习性与林分类型相关性不强。但不同林分类型云斑白条天牛种群的空间相关性地统计学参数存在差异,片林调查样点的卵、幼虫和成虫(蛹)的变程a、块金值C0和基台值C0+C均小于其他3种林分类型的统计值,片林样点成虫(蛹)的半变异函数模型不同于其他林分类型为指数模型。     

Energy trapping and detrapping by wild type and mutant reaction centers of purple non-sulfur bacteria

Time-correlated single photon counting was used to study energy trapping and detrapping kinetics at 295 K in Rhodobacter sphaeroides chromatophore membranes containing mutant reaction centers. The mutant reaction centers were expressed in a background strain of Rb. sphaeroides which contained only B880 antenna complexes and no B800-850 antenna complexes. The excited state decay times in the isolated reaction centers from these strains were previously shown to vary by roughly 15-fold, from 3.4 to 52 ps, due to differences in the charge separation rates in the different mutants (Allen and Williams (1995) J Bioenerg Biomembr 27: 275–283). In this study, measurements were also performed on wild type Rhodospirillum rubrum and Rb. sphaeroides B880 antenna-only mutant chromatophores for comparison. The emission kinetics in membranes containing mutant reaction centers was complex. The experimental data were analyzed in terms of a kinetic model that involved fast excitation migration between antenna complexes followed by reversible energy transfer to the reaction center and charge separation. Three emission time constants were identified by fitting the data to a sum of exponential decay components. They were assigned to trapping/quenching of antenna excitations by the reaction center, recombination of the P⁺H^– charge-separated state of the reaction center reforming an emitting state, and emission from uncoupled antenna pigment-protein complexes. The first varied from 60 to 160 ps, depending on the reaction center mutation; the second was 200–300 ps, and the third was about 700 ps. The observed weak linear dependence of the trapping time on the primary charge separation time, together with the known sub-picosecond exciton migration time within the antenna, supports the concept that it is energy transfer from the antenna to the reaction center, rather than charge separation, that limits the overall energy trapping time in wild type chromatophores. The component due to charge recombination reforming the excited state is minor in wild type membranes, but increases substantially in mutants due to the decreasing free energy gap between the states P^* and P⁺H^–.Abbreviations PSU photosynthetic unit - Bchl bacteriochlorophyll - Bphe bacteriopheophytin - P reaction center primary electron donor - RC reaction center - Rb. Rhodobacter - Rs. Rhodospirillum - EDTA (ethylenediamine)tetraacetic acid - Tris tris(hydroxymethyl)aminomethane Author for correspondence     

Characterization of chlorophyll–protein complexes isolated from a Siphonous green alga, Bryopsis corticulans

Six chlorophyll–protein complexes are isolated from thylakoid membranes of Bryopsis corticulans by dodecyl-β-d-maltoside polyacrylamide gel electrophoresis. Unlike that of higher plants, the 77 K fluorescence emission spectrum of the CP1 band, the PSI core complexes of B. corticulans, presents two peaks, one at 675 nm and the other at 715–717 nm. The emission peak at 715–717 nm is slightly higher than that at 675 nm in the CP1 band when excited at 438 or 540 nm. However, the peak at 715 nm is obviously lower than that at 675 nm when excited at 480 nm. The excitation spectra of CP1 demonstrate that the peak at 675 nm is mainly attributed to energy from Chl b while it is the energy from Chl a that plays an important role in exciting the peak at 715–717 nm. Siphonaxanthin is found to contribute to both the 675 nm and 715–717 nm peaks. We propose from the above results that chlorophyll a and siphonaxanthin are mainly responsible for the transfer of energy to the far-red region of PSI while it is Chl b that contributes most of the transfer of energy to the red region of PSI. The analysis of chlorophyll composition and spectral characteristics of LHCP¹ and LHCP³ also indicate that higher content of Chl b and siphonaxanthin, mainly presented in LHCP¹, the trimeric form of LHCII, are evolved by B. corticulans to absorb an appropriate amount of light energy so as to adapt to their natural habitats.     

Male sterility caused by cytoplasm of Brassica oxyrrhina in B. campestris and B. juncea

Summary Synthetic alloploid Brassica oxyrrhina (2n = 18, OO) x B. campestris (2n = 20, AA) was repeatedly backcrossed with B. campestris to place B. campestris nucleus in the cytoplasm of B. oxyrrhina. Alloplasmic plants, obtained in BC₅ generation, were stably male sterile but mildly chlorotic during initial development. Synthetic alloploid B. oxyrrhina-campestris was also hybridized with B. juncea to transfer B. oxyrrhina cytoplasm. Segregation for green and chlorotic plants was observed in BC₁ and BC₂ generations. By selection, however, normal green male sterile B. juncea was obtained in BC₃. Pollen abortion in both B. campestris and B. juncea is post-meiotic.     

Microsatellite variation and differentiation among local populations of Castanopsis species in Japan

Microsatellite variations in Castanopsis species in Japan were examined to clarify the genetic relationships among 25 local populations according to the difference in the number of layers of adaxial epidermis in the leaves. Six microsatellite loci were assayed for 629 seedlings from the populations, and these seedlings were classified into five types according to the state of the leaf epidermis. Remarkable differences in the allele frequency of the six microsatellite loci were observed among these local populations. The coefficients of genetic differentiation, R_ST, of each locus ranged from 0.209 to 0.388. An unweighted pair-group method (UPGMA) phenogram constructed on the population pairwise R_ST over the loci revealed three clusters (A–C), and six sub-clusters. These clusters reflected the differences in the occurrence frequency of seedlings in each epidermis type within a population. Our findings suggest that clusters A and C are the local populations dominated by Castanopsis sieboldii and Castanopsis cuspidata, respectively, while local populations of cluster B are composed of the two Castanopsis species and/or include many individuals derived by hybridization. The six sub-clusters were found to reflect the geographic relationship among the populations, suggesting a different process for geographic population dynamics during the postglacial period.     

Short-term effects of fire frequency on vegetation composition and biomass in mixed prairie in south-western Manitoba

The net effects of one, two, and three spring burns in consecutive yearson the aboveground biomass, species composition, and soil variables wereassessed in two different mixed-grass prairie sites in south-western Manitoba.Precipitation in the first year was greater than the 30-year average but lowerduring the next three years. The first site (Area 6) was characterized byBouteloua gracilis, Stipa spartea,Selaginella densa and lichens, while the second, somewhatdrier site (Area 10) was dominated by B. gracilis andCarex spp. Each burn treatment was applied to 15 plots inarandom block design. Vegetation and soil data collected following the thirdburnare presented. In general, the effects of repeated burning were more pronouncedin the drier Area 10, where litter was significantly reduced with eachadditional burn. In Area 6, litter was significantly reduced only after threeyears of burning. In both sites, the cumulative effect of fire had nosignificant effect on total standing crop, even after three consecutive yearsofburning. In the drier Area 10, however, the biomass of several componentsshifted such that B. gracilis biomass increasedsignificantly and forb biomass decreased significantly after three burns. Plantcover was also affected more in the drier Area 10. The cover of B.gracilis, the dominant C₄ grass, significantly increasedand Carex spp. cover decreased after two burns in thedriersite. In Area 6, the most significant effect of fire was a reduction inSelaginella and lichen cover. Bare ground increased inbothsites as the number of burns increased. There was little change in soilnutrients with burning, but soil moisture somewhat decreased and surfacetemperature significantly increased after three burns.