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51.
Two types of iron-sulfur clusters, [3 Fe–3 S] and [4 Fe–4 S], were identified by 1H-NMR in ferredoxins from Thermus thermophilus, Mycobacterium smegmatis and Pseudomonas ovalis. The [4 Fe–4 S] clusters always showed the redox couples which had potentials lower than that of the [3 Fe–3 S] clusters. 相似文献
52.
53.
The accumulation of transported materials in cut axons is demonstrated by the light and electron microscopic immunocytochemical localization of substance P and enkephalin in the caudal medulla and cervical spinal cord of adult rat. Two days following unilateral knife-cuts in the caudal medulla or spinal (C2-C3) levels, substance P and enkephalin-like immunoreactivity (SPLI and ELI) are detected in lesioned axons located rostral and caudal to the transection. Rostrally, SPLI and ELI are detected in the lateral reticular region and ventrolateral fasciculus corresponding to the location of previously identified bulbospinal pathways. Caudally, previously unidentified, propriospinal pathways showing SPLI are detected in the dorsal columns and in the dorsolateral fasciculus. In contrast, ELI is found caudal to the transection only in the reticular region of the medulla. For both peptides, immunoreactivity is present throughout axons containing numerous large, dense core, and small clear vesicles. These results support the concept of both particulate and soluble modes of transport for substance P and enkephalin within axons of the central nervous system. 相似文献
54.
An in vitro procedure for large scale multiplication of Sterculia urens Roxb. (Gum Kadaya Tree) has been developed using cotyledonary node segments. An average of 4.0 shoots per node were obtained on Murashige and Skoog's (MS) medium containing 2.0 mgl–1 6-benzyl amino-purine (BAP) within 21 days of initial culture. Upon subsequent subculture 16 shoots/node could be harvested every three weeks and upto three times. Sixty per cent of the shoots were successfully rooted. Rooted plantlets were transferred to plastic pots containing soil under mist house conditions before they were finally exposed to an external environment. Fifty seven per cent of the plantlets survived in nursery sheds. 相似文献
55.
Structural characterization of sulfated and sialyl Lewis (Le)-type glycosphingolipids performed by fast atom bombardment (FAB) and electrospray ionization (ESI) mass spectrometry is described. Both FAB and ESI collision-induced dissociation tandem mass spectrometry (CID-MS/MS) of acidic glycosphingolipids allowed identification of the sulfated or sialyl sugar, and provided information on the saccharide chain sequence. The negative-ion tandem FABMS of sulfated Le-type glycosphingolipids having the non-reducing end trisaccharide ion as the precursor can be used to differentiate the Lea- and LeX-type oligosaccharides. The ESI CID-MS/MS of multiple-charged ions provided even more detailed structural information, and some of the useful daughter ions appeared with higherm/z values than the precusor because of a lower charge-state. These methodologies can be applied to the structural analyses of glycoconjugates with much larger molecular masses and higher polarity, such as the poly-sulfated and sialyl analogues.Abbreviations CID
collision-induced dissociation
- ESI
electrospray ionization
- FABMS
fast atom bombardment mass spectrometry
- Fuc
fucose
- Gal
galactose
- GlcNAc
N-acetylglucosamine
- Le
Lewis
- Lea
Lewisa
- LeX
LewisX
- MS/MS
mass spectrometry/mass spectrometry
- NeuAc
N-acetylneuraminic acid
- 3-SO4-Lea
3-sulfated Lea pentaosyl ceramide
- 3-SO4-LeX
3-sulfated LeX pentaosyl ceramide
- 2,3-SO4-LeX
2,3-disulfated LeX pentaosyl ceramide
- 3-S-Lea
3-sialyl Lea pentaosyl ceramide
- 3-S-Lex
3-sialyl LeX heptaosyl ceramide
- 3-S-LeX-LeX
3-sialyl-Lex-Lex octaosyl ceramide. 相似文献
56.
Peter Fritsch 《American journal of botany》1996,83(3):342-355
Various hypotheses have been put forward to explain the presence of sclerophyllous plant disjuncts between western North America and the Mediterranean region. The Madrean–Tethyan hypothesis postulates that the two regions were floristically connected in the Early to Middle Tertiary by way of a low-latitude migration route. Others deny the possibility of such a route, and instead postulate convergence to xerophytic conditions from more widespread mesophytic ancestors, or suggest long-distance dispersal scenarios. One example of a “Madrean–Tethyan link” between the two regions is composed of four species within the genus Styrax: S. officinalis subsp. officinalis from the Mediterranean region, S. officinalis subsp. redivivus and subsp. fulvescens from California, and three closely related species in Texas and northeastern Mexico (S. texanus, S. platanifolius, and S. youngiae). This group was examined with isozymes to assess whether patterns of genetic variation are consistent with those predicted by the Madrean–Tethyan hypothesis. Ten populations from California, six from the Mediterranean region, and three from Texas were sampled. Pairwise comparisons revealed mean genetic identity (I) estimates of 0.581 between Mediterranean and California populations, 0.470 between Mediterranean and Texas populations, and 0.640 between California and Texas populations. Two populations of a species thought by many to be the closest relative of S. officinalis on morphological grounds (S. jaliscanus) exhibited low I (0.299–0.321) relative to all other group comparisons. Intercontinentally disjunct populations of S. officinalis possessed an I value that warrants species status for the Californian and Mediterranean groups. Divergence time estimates between Madrean and Tethyan Styrax range from 5.0 to 13.8 Mya, too recent to be consistent with the Madrean–Tethyan hypothesis. However, alternative explanations for this disjunction are suboptimal in that they require the invocation of either long-distance dispersal, which appears unlikely in this group, or extinction. Nonetheless, the evidence presented here and in other recent studies casts substantial doubt on the Madrean–Tethyan hypothesis as a general explanation for the presence of Madrean and Tethyan taxa similar in overall appearance. More plants with Madrean–Tethyan distributions must be sampled before definitive conclusions regarding this aspect of Madrean and Tethyan vegetation can be reached. 相似文献
57.
Tree growth varies closely with high–frequency climate variability. Since the 1930s detrending climate data prior to comparing them with tree growth data has been shown to better capture tree growth sensitivity to climate. However, in a context of increasingly pronounced trends in climate, this practice remains surprisingly rare in dendroecology. In a review of Dendrochronologia over the 2018–2021 period, we found that less than 20 % of dendroecological studies detrended climate data prior to climate-growth analyses. With an illustrative study, we want to remind the dendroecology community that such a procedure is still, if not more than ever, rational and relevant. We investigated the effects of detrending climate data on climate–growth relationships across North America over the 1951–2000 period. We used a network of 2536 tree individual ring-width series from the Canadian and Western US forest inventories. We compared correlations between tree growth and seasonal climate data (Tmin, Tmax, Prec) both raw and detrended. Detrending approaches included a linear regression, 30-yr and 100-yr cubic smoothing splines. Our results indicate that on average the detrending of climate data increased climate–growth correlations. In addition, we observed that strong trends in climate data translated to higher variability in inferred correlations based on raw vs. detrended climate data. We provide further evidence that our results hold true for the entire spectrum of dendroecological studies using either mean site chronologies and correlations coefficients, or individual tree time series within a mixed-effects model framework where regression coefficients are used more commonly. We show that even without a change in correlation, regression coefficients can change a lot and we tend to underestimate the true climate impact on growth in case of climate variables containing trends. This study demonstrates that treating climate and tree-ring time series “like-for-like” is a necessary procedure to reduce false negatives and positives in dendroecological studies. Concluding, we recommend using the same detrending for climate and tree growth data when tree-ring time series are detrended with splines or similar frequency-based filters. 相似文献
58.
Jan Tumajer Krešimir Begović Vojtěch Čada Michal Jenicek Jelena Lange Jiří Mašek Ryszard J. Kaczka Miloš Rydval Miroslav Svoboda Lukáš Vlček Václav Treml 《Global Change Biology》2023,29(2):462-476
Radial tree growth is sensitive to environmental conditions, making observed growth increments an important indicator of climate change effects on forest growth. However, unprecedented climate variability could lead to non-stationarity, that is, a decoupling of tree growth responses from climate over time, potentially inducing biases in climate reconstructions and forest growth projections. Little is known about whether and to what extent environmental conditions, species, and model type and resolution affect the occurrence and magnitude of non-stationarity. To systematically assess potential drivers of non-stationarity, we compiled tree-ring width chronologies of two conifer species, Picea abies and Pinus sylvestris, distributed across cold, dry, and mixed climates. We analyzed 147 sites across the Europe including the distribution margins of these species as well as moderate sites. We calibrated four numerical models (linear vs. non-linear, daily vs. monthly resolution) to simulate growth chronologies based on temperature and soil moisture data. Climate–growth models were tested in independent verification periods to quantify their non-stationarity, which was assessed based on bootstrapped transfer function stability tests. The degree of non-stationarity varied between species, site climatic conditions, and models. Chronologies of P. sylvestris showed stronger non-stationarity compared with Picea abies stands with a high degree of stationarity. Sites with mixed climatic signals were most affected by non-stationarity compared with sites sampled at cold and dry species distribution margins. Moreover, linear models with daily resolution exhibited greater non-stationarity compared with monthly-resolved non-linear models. We conclude that non-stationarity in climate–growth responses is a multifactorial phenomenon driven by the interaction of site climatic conditions, tree species, and methodological features of the modeling approach. Given the existence of multiple drivers and the frequent occurrence of non-stationarity, we recommend that temporal non-stationarity rather than stationarity should be considered as the baseline model of climate–growth response for temperate forests. 相似文献
59.
Dianye Zhang Lu Wang Shuqi Qin Dan Kou Siyu Wang Zhihu Zheng Josep Peñuelas Yuanhe Yang 《Global Change Biology》2023,29(14):3910-3923
The status of plant and microbial nutrient limitation have profound impacts on ecosystem carbon cycle in permafrost areas, which store large amounts of carbon and experience pronounced climatic warming. Despite the long-term standing paradigm assumes that cold ecosystems primarily have nitrogen deficiency, large-scale empirical tests of microbial nutrient limitation are lacking. Here we assessed the potential microbial nutrient limitation across the Tibetan alpine permafrost region, using the combination of enzymatic and elemental stoichiometry, genes abundance and fertilization method. In contrast with the traditional view, the four independent approaches congruently detected widespread microbial nitrogen and phosphorus co-limitation in both the surface soil and deep permafrost deposits, with stronger limitation in the topsoil. Further analysis revealed that soil resources stoichiometry and microbial community composition were the two best predictors of the magnitude of microbial nutrient limitation. High ratio of available soil carbon to nutrient and low fungal/bacterial ratio corresponded to strong microbial nutrient limitation. These findings suggest that warming-induced enhancement in soil nutrient availability could stimulate microbial activity, and probably amplify soil carbon losses from permafrost areas. 相似文献
60.
Kang Wang Hui Lin Conghui Peng Lin Sun Yahui Gao Baohong Chen 《Global Change Biology》2023,29(17):5099-5113
Noctiluca scintillans is one of the most common harmful algal species and widely known due to its bioluminescence. In this study, the spatial distribution, seasonal variations, and long-term trends of N. scintillans blooms in China and the related drivers were analyzed and discussed. From 1933 to 2020, a total of 265 events of N. scintillans blooms were recorded in Chinese coastal waters, with a total duration of 1052 days. The first N. scintillans bloom occurred in Zhejiang in 1933, and only three events were recorded before 1980. From 1981 to 2020, N. scintillans caused harmful algal blooms (HABs) almost every year, both the average duration and the proportion of multiphase HABs showed an increasing trend. 1986–1992, 2002–2004, and 2009–2016 were the three peak periods with a frequency of no less than five events of N. scintillans blooms per year. In terms of spatial distribution, N. scintillans blooms spread from the Southeast China Sea to the Bohai Sea after 2000, Guangdong, Fujian, and Hebei were the three provinces with the highest numbers of recorded events of N. scintillans blooms. Moreover, 86.8% of the events of N. scintillans blooms occurred in spring (March, April, and May) and summer (June, July, and August). Among environmental factors, the dissolved inorganic phosphate, dissolved silicate and chemical oxygen demand were significantly correlated with the cell density of N. scintillans during N. scintillans blooms, and most of N. scintillans blooms were recorded in the temperature range of 18.0–25.0°C. Precipitation, hydrodynamics, water temperature, and food availability might be the main factors affecting the spatial–temporal distribution of N. scintillans blooms along the Chinese coast. 相似文献