低温弱光处理及恢复期间黄瓜叶片的光抑制与类囊体膜中脂肪酸组成的变化

低温导致黄瓜叶片严重的光抑制,同时类囊体膜不饱和脂肪酸含量下降.低温弱光处理后恢复期间,Vv/Fm和多聚不饱和脂肪酸含量都迅速恢复,暗示两者之间可能有一定的联系.     

Isolation of Plasma and Thylakoid Membranes from the Heterocystous Cyanobacterium Anabaena sp. PCC 7120

具异型胞蓝细菌 Anabaena sp.PCC 7120质膜和类囊体膜的分离纯化 李斌 徐冬一 赵进东*     

Photoinhibition of photosynthesis in intact kiwifruit (Actinidia deliciosa) leaves: Recovery and its dependence on temperature

Recovery of photoinhibition in intact leaves of shade-grown kiwifruit was followed at temperatures between 10° and 35° C. Photoinhibition was initially induced by exposing the leaves for 240 min to a photon flux density (PFD) of 1 500 mol·m^-2·s^-1 at 20° C. In additional experiments to determine the effect of extent of photoinhibition on recovery, this period of exposure was varied between 90 and 400 min. The kinetics of recovery were followed by chlorophyll fluorescence at 77K. Recovery was rapid at temperatures of 25–35° and slow or negligible below 20° C. The results reinforce those from earlier studies that indicate chilling-sensitive species are particularly susceptible to photoinhibition at low temperatures because of the low rates of recovery. At all temperatures above 15° C, recovery followed pseudo first-order kinetics. The extent of photoinhibition affected the rate constant for recovery which declined in a linear fashion at all temperatures with increased photoinhibition. However, the extent of photoinhibition had little effect on the temperature-dependency of recovery. An analysis of the fluorescence characteristics indicated that a reduction in non-radiative energy dissipation and repair of damaged reaction centres contributed about equally to the apparent recovery though biochemical studies are needed to confirm this. From an interpretation of the kinetics of photoinhibition, we suggest that recovery occurring during photoinhibition is limited by factors different from those that affect post-photoinhibition recovery.Abbreviations and symbols F _o, F _m, F _v instantaneous, maximum, variable fluorescence - K _D, K _F, K _P, K _T rate constants for non-radiative energy dissipation, fluorescence, photochemistry, transfer to photosystem I - K(PI), k(R) rate constants for photoinhibition and recovery - PFD photon flux density - PSI, II photosystem I, II - _i photon yield of photosynthesis (incident light)     

Photoinhibition of photosynthesis in intact bean leaves: role of light and temperature,and requirement for chloroplast-protein synthesis during recovery

Photoinhibition of photosynthesis was induced in intact leaves of Phaseolus vulgaris L. grown at a photon flux density (PFD; photon fluence rate) of 300 mol·m^-2·s^-1, by exposure to a PFD of 1400 mol·m^-2·s^-1. Subsequent recovery from photoinhibition was followed at temperatures ranging from 5 to 35°C and at a PFD of either 20 or 140 mol·m^-2·s^-1 or in complete darkness. Photoinhibition and recovery were monitored mainly by chlorophyll fluorescence emission at 77K but also by photosynthetic O₂ evolution. The effects of the protein-synthesis inhibitors, cycloheximide and chloramphenicol, on photoinhibition and recovery were also determined. The results demonstrate that recovery was temperature-dependent with rates slow below 15°C and optimal at 30°C. Light was required for maximum recovery but the process was light-saturated at a PFD of 20 mol·m^-2·s^-1. Chloramphenicol, but not cycloheximide, inactivated the repair process, indicating that recovery involved the synthesis of one or more chloroplast-encoded proteins. With chloramphenicol, it was shown that photoinhibition and recovery occurred concomitantly. The temperature-dependency of the photoinhibition process was, therefore, in part determined by the effect of temperature on the recovery process. Consequently, photoinhibition is the net difference between the rate of damage and the rate of repair. The susceptibility of chilling-sensitive plant species to photoinhibition at low temperatures is proposed to result from the low rates of recovery in this temperature range.Abbreviations and symbols Da Dalton - Fo, Fm, Fv instantaneous, maximum, variable fluorescence emission - PFD photon flux density - PSII photosystem II - photon yield C.I.W.-D.P.B. Publication No. 871     

Associating particulate essential fatty acids of the ω3 family with phytoplankton species composition in a Siberian reservoir

1. We studied variation in the composition of fatty acids in the seston of a small freshwater reservoir with changes in phytoplankton composition during four growth seasons. We focused on the dynamics of the ω3 fatty acids because of their potential importance for zooplankton nutrition. 2. Total diatoms were related to the 20:5ω3 fatty acid (eicosapentaenoic, EPA) content in seston. Among two dominant diatom genera, Cyclotella was not associated with EPA content. In contrast, there was a significant correlation between Stephanodiscus and the percentage contribution and content of EPA throughout the study. Hence, freshwater diatoms can differ strongly in content of the essential EPA. 3. We considered abundant cyanobacteria as a potential source of 18:3ω3 fatty acid (linolenic, ALA) to aquatic food webs. Among four dominant cyanobacteria species, two (Anabaena flos‐aquae and Planktothrix agardhii) showed significant correlation with the ALA content of the seston, while the other two (Aphanizomenon flos‐aquae and Microcystis aeruginosa) did not. 4. Dinophyta had a relatively high level of 22:6ω3 (docosahexaenoic, DHA) for freshwater species and can be also a source of EPA to aquatic food webs. 5. Our results show that various species of diatoms as well as cyanobacteria can be of contrasting nutritional value for zooplankton because of their different content of the essential PUFAs. Diatoms, which are low in EPA, could not be considered as a valuable food, while some field populations of cyanobacteria might be valuable sources of essential ALA.     

Photoinhibition of Photosynthetic Oxygen Production and its Recovery in the Subtidal Red Alga Polyneura hilliae

In the marine red alga Polyneura hilliae photoinhibition of photosynthesis was investigated by measuring the photosynthetic oxygen production. The extent of photoinhibition in this alga depends on the fluence rate as well as on the time of exposure. Strongly photoinhibited algae recover slowly. Full recovery is reached only in weak light after 3 days. Two phases of recovery can be distinguished: a first relatively fast phase of recovery that is independent of light, and a second slow phase which begins after about 6 hours and requires weak light. Consequently, even in complete darkness partial recovery is observed. An action spectrum of photoinhibition and its comparison with the in vivo absorption spectrum of Polyneura demonstrates that photoinhibition is mainly caused by light which is absorbed by phycobiliproteins, chlorophyll a and carotenoids. This fact and the ineffectiveness of light above 686 nm clearly indicate that the main photoinhibition site in this alga is PS II. No photosynthetic oxygen production is detectable after 3 h irradiation at 402 nm, 150 μmol quanta m^?2s^?1. As photosynthetic activity recovers slowly and to a limited extent, the suppression of oxygen production is apparently only in part the result of photoinhibition sensu strictu and in part due to permanent photodamage.     

菜豆叶片衰老过程中叶绿体被膜的相变特征

用示差扫描量热计测定了菜豆第一片真叶在衰老过程中叶绿体被膜相变温度与叶绿体总脂熔融温度的变化。15日龄成长叶片叶绿体被膜相变温度为-6.7～-3.6℃,当转向衰老后,在22,29和35日龄时的相变温度分别为3.2～8.8℃、18.7～24.1℃和27.3～37.8℃。叶绿体总脂的熔融温度在15至35日龄期间也逐渐升高,但升高幅度小于被膜相变温度的升高幅度。可是,叶绿体总脂熔融温度范围却大于相应时期被膜相变温度范围。蛋白质含量下降趋势发生在叶片15日龄前,而叶绿素含量下降趋势开始于叶片21日龄之后。     

UV-B Induced Alterations in Composition of Thylakoid Membrane and Amino Acids in Leaves of Rhizophora Apiculata Blume

Seedlings of Rhizophora apiculata were exposed to UV-B radiation at four doses equivalent to 10, 20, 30, and 40 % ozone depletion. The seedlings irradiated with high doses of UV-B had characteristic decline in contents of specific proteins with molecular masses of 33, 23, and 17 kDa. On the contrary, proteins of 55, 33, 25, 23, and 17 kDa were accumulated in the seedlings exposed to low doses of UV-B. The UV-B, in general, enhanced formation of saturated fatty acids and reduced unsaturated fatty acids, to a maximum extent of 88 and 26 %, respectively. The low dose of UV-B increased content of oleic acid by 9 %, and the high dose reduced it by 34 %. The high dose of UV-B enhanced the lipid peroxidation by 48 %, whereas the low dose of UV-B did not show any significant effect. The contents of amino acids such as aspartate, glutamate, asparagine, serine, glutamine, threonine, and histidine were increased in low UV-B doses by 53, 86, 142, 72, 3, 119, and 32 %, respectively; while in high doses they were reduced significantly.     

Photoinhibition of photosynthesis in intact kiwifruit (Actinidia deliciosa) leaves: effect of growth temperature on photoinhibition and recovery

Intact leaves of kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson) from plants grown in a range of controlled temperatures from 15/10 to 30/25°C were exposed to a photon flux density (PFD) of 1500 μmol·m⁻²·s⁻¹ at leaf temperatures between 10 and 25°C. Photoinhibition and recovery were followed at the same temperatures and at a PFD of 20 μmol·m⁻²·s⁻¹, by measuring chlorophyll fluorescence at 77 K and 692 nm, by measuring the photon yield of photosynthetic O₂ evolution and light-saturated net photosynthetic CO₂ uptake. The growth of plants at low temperatures resulted in chronic photoinhibition as evident from reduced fluorescence and photon yields. However, low-temperature-grown plants apparently had a higher capacity to dissipate excess excitation energy than leaves from plants grown at high temperatures. Induced photoinhibition, from exposure to a PFD above that during growth, was less severe in low-temperature-grown plants, particularly at high exposure temperatures. Net changes in the instantaneous fluorescence,F ₀, indicated that little or no photoinhibition occurred when low-temperature-grown plants were exposed to high-light at high temperatures. In contrast, high-temperature-grown plants were highly susceptible to photoinhibitory damage at all exposure temperatures. These data indicate acclimation in photosynthesis and changes in the capacity to dissipate excess excitation energy occurred in kiwifruit leaves with changes in growth temperature. Both processes contributed to changes in susceptibility to photoinhibition at the different growth temperatures. However, growth temperature also affected the capacity for recovery, with leaves from plants grown at low temperatures having moderate rates of recovery at low temperatures compared with leaves from plants grown at high temperatures which had negligible recovery. This also contributed to the reduced susceptibility to photoinhibition in low-temperature-grown plants. However, extreme photoinhibition resulted in severe reductions in the efficiency and capacity for photosynthesis.     

Photoinhibition of photosynthesis in intact kiwifruit (Actinidia deliciosa) leaves: Effect of light during growth on photoinhibition and recovery

Photoinhibition of photosynthesis was induced in intact kiwifruit (Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson) leaves grown at two photon flux densities (PFDs) of 700 and 1300 mol·m^-2·s^-1 in a controlled environment, by exposing the leaves to PFD between 1000 and 2000 mol·m^-2·s^-1 at temperatures between 10 and 25°C; recovery from photoinhibition was followed at the same range of temperatures and at a PFD between 0 and 500 mol·m^-2·s^-1. In either case the time-courses of photoinhibition and recovery were followed by measuring chlorophyll fluorescence at 692 nm and 77K and by measuring the photon yield of photosynthetic O₂ evolution. The initial rate of photoinhibition was lower in the high-light-grown plants but the long-term extent of photoinhibition was not different from that in low-light-grown plants. The rate constants for recovery after photoinhibition for the plants grown at 700 and 1300 mol·m^-2·s^-1 or for those grown in shade were similar, indicating that differences between sun and shade leaves in their susceptibility to photoinhibition could not be accounted for by differences in capacity for recovery during photoinhibition. Recovery following photoinhibition was increasingly suppressed by an increasing PFD above 20 mol·m^-2·s^-1, indicating that recovery in photoinhibitory conditions would, in any case, be very slow. Differences in photosynthetic capacity and in the capacity for dissipation of non-radiative energy seemed more likely to contribute to differences in susceptibility to photoinhibition between sun and shade leaves of kiwifruit.Abbreviations and symbols F _o , F _m , F _v instantaneous, maximum, variable fluorescence - F _v /F _m fluorescence ratio - F _i =F _v at t=0 - F F _v at t= - K _D rate constant for photochemistry - k(F _p ) first-order rate constant for photoinhibition - k(F _r ) first-order rate constant for recovery - PFD photon flux density - PSII photosystem II - _i photon yield of O₂ evolution (incident light)     

Involvement of DnaK3, One of the Three DnaK Proteins of Cyanobacterium Synechococcus sp. PCC7942, in Translational Process on the Surface of the Thylakoid Membrane

The Synechococcus sp. PCC7942 strain carrying a missense mutation in the peptide-binding domain of DnaK3, one of the essential dnaK gene products, revealed temperature-sensitive growth. We also isolated suppressor mutants of this strain. One of the suppressors was mapped in the ribosomal protein gene rpl24 (syc1876), which encodes the 50S ribosomal protein L24. Subcellular localization of three DnaK proteins was determined, and the results indicated that a quantity of DnaK3 was dislocated from membrane-bound polysomes when dnaK3 temperature-sensitive mutant was incubated at non-permissive temperatures. Furthermore, we examined the photosystem II reaction center protein D1 and detected a translational intermediate polypeptide in membrane-bound polysome fractions prepared from dnaK3 temperature-sensitive cells grown at high temperature. These characteristic features of DnaK3 localizations and detection of D1 protein intermediate were not observed in the suppressor mutant even at high temperatures.     

Photoinhibition in the Antarctic moss Grimmia antarctici Card when exposed to cycles of freezing and thawing

Freezing and thawing of the endemic moss species Grimmia antarctici Card, caused photoinhibition. When snow cover was removed from moss in the field, resulting in exposure to fluctuating temperatures and light conditions, photoinhibition, measured as a reduction in the ratio of variable to maximum chlorophyll a fluorescence (F_v/F_m), was observed. The extent of photoinhibition was highly variable and appeared to be reversible during periods of warmer temperatures. A series of controlled laboratory studies found that the light conditions that prevail between freezing and thawing events influenced the recovery from photoinhibition observed during freezing and thawing, with low light conditions facilitating the greatest rates of recovery. After four cycles of freezing and thawing, recovery from photoinhibition in hydrated moss was achieved within 12 h of transfer to 5°C and 15 μmol quanta m^?2 s^?1. These results favour the hypothesis that photoinhibition observed during freezing represents a protective process involving the down-regulation of photo-system II when photosynthetic carbon assimilation is limited by low temperatures.     

发菜类囊体膜色素蛋白复合物分离及其谱性质的研究

Nostoc flagelliforme Born. et Flah is highly adapted to drought stress, cold and light stresses, and suitable for growing in the unfavorable areas. This paper presents the results of the analysis of the membrane (mainly thylakoid membrane) lipids from N. flagelliforme in order to investigate the relationship between membrane lipid composition and stress resistance to this cyanobacteria. The membrane lipids are composed of monogalactosyl diacylglycerol (MGDG), digalactosyl diacylglycerol (DGDG), sulfoquinovosyl diacylglycerol (SQDG) and phosphatidylglycerol (PG). The major fatty acids in these lipids are palmitic (16∶0), palmitoleic (16∶1), stearic (18∶0), oleic (18∶1), linoleic (18∶2) and linolenic (18∶3) acids. In N. flagelliforme, polyunsaturated fatty acids account for 73% of the total fatty acids, much higher than that of the other cyanobacteria reported so far. Among which 16∶1 and 18∶3 are as high as 28.9% and 34.3% respectively. The high resistance of N. flagelliforme to abnormal conditions may be associated with the extent of unsaturation of fatty acids. In addition, the wild N. flagelliforme treated with water for 30 min and cultured for 24 h and the lipid and fatty acid composition were found to be not affected by water-absorption.     

The potential use of n-alkanes, long-chain alcohols and long-chain fatty acids as diet composition markers: indoor validation with sheep and herbage species from the rangeland of Inner Mongolia of China

To investigate the potential use of n-alkanes (alkanes), long-chain alcohols (alcohols) and long-chain fatty acids (acids) for estimating the diet composition of sheep, in a feeding trial. A total of 18 sheep were assigned randomly to three different diets (diet A, diet B and diet C) containing up to eight herbage species (Leymus chinensis, Leymus dasystachys, Elymus sibiricum, Chenopodium album, Puccinellia chinampoensis, Medicago sativa, Saussurea sinuata and Bromus inermis). Faecal recoveries of alkanes, alcohols and acids were determined, and diet compositions were estimated using different combinations of alkanes, alcohols and acids. The faecal concentrations of individual alkanes, alcohols and acids were corrected using the mean recovery of the dietary treatment that the respective animal belonged to (diet recovery), or the mean recovery across all dietary treatments (general recovery). In general, diets did not affect the faecal recovery values for alkanes, alcohols and acids, and no difference in accuracy was found between diet composition estimates based on dietary recovery and general recovery. The accuracy of diet composition estimates declined as the number of dietary components increased from four to eight herbage species (P < 0.001). Better (P < 0.05) estimates of diet composition were obtained with the combinations of two or three marker types instead of alkanes alone. Moreover, results showed that excluding minor diet components from the calculations decreased (P < 0.05) the accuracy of diet composition estimates, whereas including extra non-grazed herbage species did not reduce (P > 0.05) the quality of diet composition estimates. These results confirmed the usefulness of alkanes, alcohols and acids as markers for determining complex diet composition of sheep. However, a negative impact on the accuracy of diet composition estimates, caused by missing minor diet components from the calculation of diet composition, could happen when plant wax markers are used to estimate the diet composition of free-ranging animals.     

The value of lipid composition in the taxonomy of the Schizosaccharomycetales

In this study, the lipid fractions i.e. neutral (NL), phospho-(PL) and glycolipids (GL) with associated fatty acids (FAs) of 54 strains, representing the Schizosaccharomycetales, were analyzed during stationary growth phase and compared. Trace amounts of linoleic acid (18:2) were present in most of the strains representing Schizosaccharomyces. An increased percentage 18:2 was observed in the PL fraction when compared to the NL fraction. This is possibly related to membranes requiring polyunsaturated FAs for fluidity. On the basis of the percentage oleic acid (18:1) and 18:2 FAs in the different lipid fractions, the Schizosaccharomycetales can clearly be divided into two groups i.e. Group 1 (represented by the genus Hasegawaea) comprising strains producing relatively large amounts of 18:2 and relatively low amounts of 18:1 when compared to Group 2 (represented by the genus Schizosaccharomyces comprising Schizosaccharomyces octosporus and Schizosaccharomyces pombe). These results are in accordance with 18S and 26S rRNA base sequence analyses and emphasize the difference between the genera Hasegawaea and Schizosaccharomyces. Utilizing gas chromatography-mass spectrometry analyses, it was found that these strains were all capable of producing gamma-linolenic acid. This further emphasizes the uniqueness of this order in the Dikaryomycota.     

Photoinhibition of photosynthesis and growth responses at different light levels in psbA gene mutants of the cyanobacterium Synechococcus

Photoinhibition of photosynthesis and growth responses at diffrent light levels (10, 120 and 250 μmol m⁻² s⁻¹) were studied in psbA gene mutants R2S2C3 ( psbAI gene present) and R2K1 ( psbAIIIpsbAIII genes present) of the cyanobacterium Synechococcus sp . PCC 7942 ( Anacystis nidulans R2). Mutant R2K1 (possessing form II of the D1 protein of photosystem II) was much more resistant to photoinhibition than the mutant R2S2C3 (possessing form I of the D1 protein). At moderate inhibitory light levels (100 to 300 μmol m⁻² s⁻¹) this was largely ascribed to an increased rsistance of the photosystem II reaction cetres possessing form II of the D1 protein. However, at higher light levels the higher resistance mutant R2K1 was assigned to a higher rate of photosystem II repair, i.e. turnover of the D1 protein. Moreover, our results support the hypothesis that photoinhibition of photosystem II and photoinhibitory induced quenching are due to separate processes. Results from growth experiments show that the R2K1 mutant has a slower growth rate than the R2S2C3 mutant but shows an increased survival under high light stress conditions. It is hypothesized that high resistance to photoinhibition, though allowing a better survival under high light, is not advantageous for optimal growth.     

The potential use of long-chain alcohols and fatty acids as diet composition markers: factors influencing faecal recovery rates and diet composition estimates in sheep

The limitations of the alkane technique in estimating the diet components of herbivores call for the introduction of new diet composition markers. Recently, long-chain alcohols (alcohols) and long-chain fatty acids (acids) have received the most attention and show great potential, when combined with alkanes, to estimate composition of complex diets. In the current study, faecal recoveries of alcohols and acids were determined in sheep in four different live weight groups fed three herbage species, either Leymus chinensis, L. dasystachys or Elymus sibiricum. Analysis of variance (ANOVA) was used to examine the effects of herbage species and live weight of sheep on faecal recoveries of individual alcohols and acids. Further, an indoor experiment with six sheep fed a diet of equal proportions, on dry matter (DM) basis, of three herbages was performed, allowing to assess the accuracy of alcohols and/or acids in combination with alkanes, to estimate diet composition. A one-sample t-test was carried out to test the accuracy of these estimates. Results of the first experiment indicated that the faecal recoveries of alcohols and acids were significantly affected by herbage species (P < 0.05). While the effects were significant or near significant for the faecal recoveries of some alcohols (C24-ol, C30-ol and C26-ol) (P 0.05), no effect of live weight on faecal recoveries of acids was observed (P > 0.05). Therefore, adjustments based on diet-specific faecal recoveries might improve diet composition estimates. This was illustrated by the results of the second experiment. The diet composition estimated from alcohols or all combinations of alcohols with other marker types, after diet-specific correction of faecal recoveries, did not significantly differ from the actual composition (P > 0.05). However, using acids as additional markers resulted in poorer diet composition estimates. This study confirmed the utility of alcohols, combined with alkanes, as markers to estimate composition of complex diets. Although corrections based on mean faecal recoveries, average over animals and diets, resulted in some accuracy loss, results were still satisfactory and better than without recovery correction.     

Photoinhibition of photosynthesis in intact kiwifruit (Actinidia deliciosa) leaves: Changes in susceptibility to photoinhibition and recovery during the growth season

Kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson) plants grown in an outdoor enclosure were exposed to the natural conditions of temperature and photon flux density (PFD) over the growing season (October to May). Temperatures ranged from 14 to 21° C while the mean monthly maximum PFD varied from 1000 to 1700 mol · m^–2 · s^–1, although the peak PFDs exceeded 2100 mol · m^–2 · s^–1. At intervals, the daily variation in chlorophyll fluorescence at 692 nm and 77K and the photon yield of O₂ evolution in attached leaves was monitored. Similarly, the susceptibility of intact leaves to a standard photoinhibitory treatment of 20° C and a PFD of 2000 mol · m^–2 · s^–1 and the ability to recover at 25° C and 20 mol · m^–2 · s^–2 was followed through the season. On a few occasions, plants were transferred either to or from a shade enclosure to assess the suceptibility to natural photoinhibition and the capacity for recovery. There were minor though significant changes in early-morning fluorescence emission and photon yield throughout the growing season. The initial fluorescence, F_o, and the maximum fluorescence, F_m, were, however, significantly and persistently different from that in shade-grown kiwifruit leaves, indicative of chronic photoinhibition occurring in the sun leaves. In spring and autumn, kiwifruit leaves were photoinhibited through the day whereas in summer, when the PFDs were highest, no photoinhibition occurred. However, there was apparently no non-radiative energy dissipation occurring then also, indicating that the kiwifruit leaves appeared to fully utilize the available excitation energy. Nevertheless, the propensity for kiwifruit leaves to be susceptible to photoinhibition remained high throughout the season. The cause of a discrepancy between the severe photoinhibition under controlled conditions and the lack of photoinhibition under comparable, natural conditions remains uncertain. Recovery from photoinhibition, by contrast, varied over the season and was maximal in summer and declined markedly in autumn. Transfer of shade-grown plants to full sun had a catastrophic effect on the fluorescence characteristics of the leaf and photon yield. Within 3 d the variable fluorescence, F_v, and the photon yield were reduced by 80 and 40%, respectively, and this effect persisted for at least 20 d. The restoration of fluorescence characteristics on transfer of sun leaves to shade, however, was very slow and not complete within 15 d.Abbreviations and Symbols F_o, F_m, F_v initial, maximum, variable fluorescence - F_i F_v at t = 0 - F F_v at t = - PFD photon flux density - PSII photosystem II - leaf absorptance ratio - (_a photon yield of O₂ evolution (absorbed basis) - _{i a} at t = 0 - _a at t = We thank Miss Linda Muir and Amanda Yeates for their technical assistance in this study.     

The modulating influence of the fluidity of cell membrane on excision repair of DNA in UV-irradiated Escherichia coli

When the extent of liquid holding recovery (LHR) was measured as a function of the temperature at the time of liquid holding and the Arrhenius plot was made, two distinctive phases for the LHR were demonstrated in UV-irradiated RecA- derivative of E. coli ole28E1, which are unable to synthesize and degrade unsaturated fatty acids. The inflection temperatures were 17-18 degrees C, 23-24 degrees C and 28-30 degrees C for linoleate-, oleate- and elaidate-grown cells, respectively. These temperatures well corresponded to the phase transition temperatures of the cell membrane supplemented with the fatty acid. It is therefore concluded that at least a component involved in in vivo excision repair in E. coli is associated with cell membrane.     

Inhibition of FASN reduces the synthesis of medium-chain fatty acids in goat mammary gland

Fatty acid synthase (FASN) is known as a crucial enzyme of cellular de novo fatty acid synthesis in mammary gland which has been proved as the main source of short and medium-chain fatty acids of milk. However, the regulatory role of FASN in goat-specific milk fatty acids composition remains unclear. We cloned and analyzed the full-length of FASN gene from the mammary gland of Capra hircus (Xinong Saanen dairy goat) (DQ 915966). Comparative gene expression analysis suggested that FASN is predominantly expressed in fat, small intestine and mammary gland tissues, and expresses higher level at lactation period. Inhibition of FASN activity by different concentrations (0, 5, 15, 25 and 35 μM) of orlistat, a natural inhibitor of FASN, resulted in decreased expression of acetyl-CoA carboxylase α (ACCα), lipoprotein lipase and heart-type fatty acid binding protein (H-FABP) in a concentration-dependent manner in goat mammary gland epithelial cells (GMEC). Similar results were also obtained by silencing of FASN. Additionally, reduction of FASN expression also led to apparent decline of the relative content of decanoic acid (C10:0) and lauric acid (C12:0) in GMEC. Our study provides a direct evidence for inhibition of FASN reduces cellular medium-chain fatty acids synthesis in GMEC.