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排序方式: 共有208条查询结果,搜索用时 46 毫秒
81.
Kumar Manish Maharaj K. Pandit Yasmeen Telwala Dinesh C. Nautiyal Lian Pin Koh Sudha Tiwari 《Journal of plant research》2017,130(5):829-844
Despite decades of research, ecologists continue to debate how spatial patterns of species richness arise across elevational gradients on the Earth. The equivocal results of these studies could emanate from variations in study design, sampling effort and data analysis. In this study, we demonstrate that the richness patterns of 2,781 (2,197 non-endemic and 584 endemic) angiosperm species along an elevational gradient of 300–5,300 m in the Eastern Himalaya are hump-shaped, spatial scale of extent (the proportion of elevational gradient studied) dependent and growth form specific. Endemics peaked at higher elevations than non-endemics across all growth forms (trees, shrubs, climbers, and herbs). Richness patterns were influenced by the proportional representation of the largest physiognomic group (herbs). We show that with increasing spatial scale of extent, the richness patterns change from a monotonic to a hump-shaped pattern and richness maxima shift toward higher elevations across all growth forms. Our investigations revealed that the combination of ambient energy (air temperature, solar radiation, and potential evapo-transpiration) and water availability (soil water content and precipitation) were the main drivers of elevational plant species richness patterns in the Himalaya. This study highlights the importance of factoring in endemism, growth forms, and spatial scale when investigating elevational gradients of plant species distributions and advances our understanding of how macroecological patterns arise. 相似文献
82.
83.
Further Evidence for the Relationship between Light-Induced Changes of Plasmalemma Transport and Transthylakoid Proton Uptake 总被引:1,自引:0,他引:1
VANSELOW KLAUS HEINRICH; KOLBOWSKI J?RG; HANSEN ULF-PETER 《Journal of experimental botany》1989,40(2):239-245
The simultaneous measurement of the induction curves of chlorophyllfluorescence, its responses to saturating flashes, light-scatteringat 532 nm, and plasmalemma voltage supports previous findings(Hansen, Kolbowski, and Dau, 1987), that light-induced uptakeof protons into the inner thylakoid space causes the rapid (5to 20 s) light-induced depolarization at the plasmalemma viasubstrate depletion of the electrogenic H+-pump. These conclusionsare based on kinetic studies which enable the separation ofindividual components in complex signals by means of their assignmentto different time-constants. In contrast to the previous investigation,binary noise was used for modulation of the actinic light. Thenew input signal not only increased the reliability of the previousresults obtained by sine-waves, but also led to the detectionof three additional time-constants. One of these is probablyrelated to the action of light on the potassium channel of theplasmalemma. The others are assigned to the quencher Q and toa still unknown process. Key words: Chlorophyll fluorescence, plasmalemma potential, proton fluxes, noise, scattering, spinach, state-transitions, thylakoid membrane 相似文献
84.
JÜRG FUHRER 《Plant, cell & environment》1982,5(4):263-270
Abstract. Seedlings of Phaseolus vulgaris were exposed to solutions containing Cd2+ in the range 0 to 1 molm−3 . Ethylene formation started following 3 h of exposure to 10−2 , 10−1 and 1 mol m−3 Cd2+ , peaked at 18 h and returned to a relatively low rate after 24 h. Cadmium-induced ethylene formation depended on the formation of 1-aminocyclopropane-1-carboxylic acid (ACC). Aminoethoxyvinylglycine (AVG, 0.1 mol m−3 ) inhibited ACC accumulation and ethylene production during exposure to 0.2 mol m−3 Cd2+ .
Activity of soluble and ionically-bound peroxidase increased after 18 h of exposure to Cd2+ concentrations above 10−3 mol m−3 due to an increase in activity of cathodic isoperoxidases. Stimulation of soluble and ionically-bound peroxidase by 0.2 mol m−3 Cd2+ was reduced in the presence of 0.1 mol m−3 AVG.
Accumulation of soluble and insoluble ('ligninlike') phenolics was found in plants exposed to Cd2+ (10−2 mol m−3 or above) in the presence or absence of AVG. Deposition of insoluble (autofluorescing) material occurred in cell walls around vessels and was associated with reduced expansion and water content of leaves. 相似文献
Activity of soluble and ionically-bound peroxidase increased after 18 h of exposure to Cd
Accumulation of soluble and insoluble ('ligninlike') phenolics was found in plants exposed to Cd
85.
Dissociation constants for dihydrofolic acid and dihydrobiopterin and implications for mechanistic models for dihydrofolate reductase 总被引:1,自引:0,他引:1
G Maharaj B S Selinsky J R Appleman M Perlman R E London R L Blakley 《Biochemistry》1990,29(19):4554-4560
The dissociation constants (pKa) for the pteridine ring system of dihydrofolate (H2folate) have been redetermined, and those for dihydrobiopterin (H2biopterin) have been determined. Determination of the pKa for N5 of H2folate is complicated by the low solubility and instability of H2folate at pH 2-4, and other complicating factors. The initial rate of absorbance change due to degradation is a maximum at pH 2.5, and the products depend on the oxygen concentration: under aerobic conditions, (p-aminobenzoyl)glutamic acid and 7,8-dihydropterin-6-carboxaldehyde are major products. H2Biopterin is much more soluble and more stable at low pH. For protonation of N5, the pKa is 2.56 +/- 0.01 for H2biopterin and 2.59 +/- 0.03 for H2folic acid. Spectrophotometric determination of the pKa for the N3-O4 amide group of H2folate is subject to serious errors when a wavelength between 220 and 235 nm is used. These errors arise from the pH-dependent absorbance of mercaptoethanol often present in the preparation. The amide group has a pKa of 10.41 +/- 0.04 in H2biopterin and 10.85 +/- 0.04 in H2folate. The redetermined value for the pKa of N5 of H2folate has implications for mechanistic models for dihydrofolate reductase, and revised kinetic constants have been calculated for one model. 相似文献
86.
Germination and seedling growth of pea (Pisum sativum L. cv. Rachna) was studied in salts and PEG-6000 solution having osmotic potentials −0.1, −0.2, −0.3, −0.4 and −0.5 MPa.
At equivalent level of stress, NaCl proved more harmful to germination, seedling growth, vigour index, as well as initial
mobilizing efficiency of food material from seed to the growing seedling, while PEG-6000 was more harmful to imbibition rate
and mobilization efficiency in further days. 相似文献
87.
Effects of iso-osmotic levels of salts (NaCl, CaCl2, Na2So2) and PEG-6000 on saccharides, free proline and nitrogen contents were studied in cotyledons of pea. Saccharide (total, reducing
andnon-reducing) and nitrogen contents decreased with increasing the salt and water stress as compared to control at all the stages of seedling
growth. PEG-induced stress had more deleterious effect on total saccharide content and non-reducing saccharide (NRS) content,
while salt stress was more harmful to reducing saccharide (RS) and nitrogen content. Free proline content of cotyledons increased
with increasing the salt and especially PEG-induced stress at all the stages of seedling growth. 相似文献
88.
Effect of high- and low-protein diets on the regulation of rat liver tyrosine aminotransferase and tryptophan oxygenase activities by l-tyrosine and l-tryptophan
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Hasan Mukhtar Maharaj K. Sahib Coimbatore R. Krishna Murti 《The Biochemical journal》1973,135(1):225-229
Induction of rat liver tyrosine aminotransferase by l-tyrosine and tryptophan oxygenase by l-tryptophan was studied in groups of rats fed on diets containing 18 or 5% protein. The basal activity of hepatic tyrosine aminotransferase of rats receiving 5% protein gradually increased with the age of the animals but that of rats receiving 18% protein did not. l-Tyrosine induced hepatic tyrosine aminotransferase in rats receiving 18% protein when tested at ages from 4 to 20 weeks. When induction by l-tyrosine was carried out in rats receiving the 5% protein diet, significant induction of tyrosine aminotransferase occurred only in 4- or 6-week-old rats. Induction by l-tryptophan of tryptophan oxygenase in liver or the basal activity of this enzyme in liver did not differ between the groups fed on 5 and 18% protein. On changing the diet from 0 to 18% protein, the above-mentioned effects on the induction of hepatic tyrosine aminotransferase were reversed. 相似文献
89.
90.
Chen W Wu H Hernandez RJ Mehta AK Ticku MK France CP Coop A 《Bioorganic & medicinal chemistry letters》2005,15(13):3201-3202
Gamma-hydroxybutyric acid (GHB) is a drug of abuse, a therapeutic, and purportedly a neurotransmitter with a complex mechanism of action in vivo due to direct actions at GABA(B) as well as GHB receptors and because of its metabolism to GABA. Herein, we describe 3-ethers of 3-hydroxyphenylacetic acid, which have relatively high affinity at GHB sites, no significant affinity at GABA receptors, and would not be expected to be rapidly metabolized to GABAergic ligands. The selectivity of these compounds (UMB108, UMB109, and UMB119) could prove to be useful for studying the biology of GHB receptors, free from GABAergic effects. 相似文献