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121.
C. Jordan W. Caskey G. Escalante R. Herrera F. Montagnini R. Todd C. Uhl 《Plant and Soil》1982,67(1-3):325-332
Standing stocks and fluxes of nitrogen, including nitrogen fixation and denitrification, were measured in a tropical rainforest on Oxisol in the Amazon Territory of Venezuela. The standing stock of nitrogen was comparable to that of temperate forests, but was higher than that in an adjacent forest on Spodosol. Fluxes were higher than in forests in the temperate zone, but lower than in another tropical forest on more fertile soil. Even though nitrogen was abundant, this does not mean that nitrogen could not be limiting to agriculture if the forest is cleared and the land cultivated. The nitrogen fixing and nitrogen conserving mechanisms are dependent upon the structure of the undisturbed forest, and destruction of the forest would eventually decrease the input of nitrogen to the soil. 相似文献
122.
Effect of Steric and Nuclear Changes in Steroids and Triterpenoids on Sexual Reproduction in Phytophthora cactorum 总被引:3,自引:0,他引:3 下载免费PDF全文
The comparative biological activity of 21 naturally occurring or synthetically derived steroids, 7 tetracyclic and pentacylic triterpenoids, and antheridiol incubated with cultures of Phytophthora cactorum has been examined. There was greater dependence on precise steric features of the sterol side chain than on the extent of nuclear unsaturation in inducing oospore formation. There was no significant effect on oospore formation by changing nuclear unsaturation in ring B from Δ5 to Δ7 or to Δ5,7. Converting the unsaturated sterol to its corresponding stanol resulted in a significant reduction in the number of oospores produced. The effectiveness of sterols bearing different side chains in inducing oospores was found to be in the following relative order: 24α-ethyl = trans-Δ22-24α-ethyl > trans-Δ22-24β-ethyl = 24α-E-ethylidene = 24α-methyl > 24β-methyl = trans-Δ22-24β-methyl = 26-methyl = saturated C7 side chain and C-20 R (17-αH, 20-αH, right-handed conformer) = cis-Δ22-C7 side chain and C-20 R > saturated C7 side chain and C-20 S (17-αH, 20-βH, right-handed conformer) > no sterol = 29-hydroxyporiferasterol = 20α-hydroxycholesterol = 24ξ-hydroxy-24-vinylcholesterol. Of the sterols examined the most significant stereochemical criterion for the induction of oospore formation was absence of bulk on the front face of C-20. This follows from the observation that 20-isocholesterol and 20α-hydroxycholesterol, in which a methyl and hydroxy group, respectively, project to the front in the right handed conformation, were inactive in stimulating production of oospores. None of the triterpenoids studied induced oospore formation to any significant degree. Oospore formation was not induced by antheridiol nor 29-hydroxyporiferasterol in combination or added separately to growing cultures of P. cactorum in the concentration range 0.01 - 10.0 milligrams per liter. 相似文献
123.
An unusual new purine-requiring mutant, Ade?PAB, of Chinese hamster ovary cells (CHO-K1) is described. Ade?PAB will grow in medium supplemented with hypoxanthine, adenine, or aminoimidazole carboxamide. Ade?PAB fails to show genetic complementation with either Ade?A, defective in amidophosphoribosyltransferase (E.C. 2.4.2.14), or Ade?B, defective in phosphoribosylformylglycinamidine FGAM) synthetase (E.C. 6.3.5.3.), but will complement all five of our other hypoxanthine-requiring Ade? complementation groups. Analysis of purine synthesis in wild-type, mutant, and revertant cells and analysis of relevant enzyme activities in cell-free extracts prepared from these cells demonstrates that Ade?PAB is similar to Ade?B in that it has lost FGAM synthetase activity, and is similar to Ade?A in that it has lost glutamine-dependent amidophosphoribosyltransferase activity. Unlike Ade?A, however, Ade?PAB retains the ability to synthesize phosphoribosylamine (PRA), the product of the amidophosphoribosyltransferase reaction, if NH4Cl is substituted for glutamine as the nitrogen donor. Moreover, partial revertants of Ade?PAB can apparently synthesize sufficient purines for growth using the NH4Cl-dependent reaction. The available evidence indicates that neither a double mutation nor a deletion is probable in Ade?PAB. We discuss the relevance of these observations for our understanding of both the regulation of purine biosynthesis in mammalian cells and the structural organization of the enzymes defective in Ade?PAB and the genes coding for these enzymes. 相似文献
124.
Effects of Controlled Atmospheres on Production of Sesquiterpenoid Stress Metabolites by White Potato Tuber: Possible Involvement of Cyanide-resistant Respiration 下载免费PDF全文
Levels of katahdinone (solavetivone), lubimin, rishitin, and phytuberin, sesquiterpenoid stress metabolites of white potato (Solanum tuberosum), were monitored in tuber slices which were challenged with an extract of Phytophthora infestans and incubated under controlled atmospheres. A mixture of ethylene in air enhanced stress metabolite production. This enhancement was amplified by higher partial pressures of oxygen. Stress metabolite production was inhibited by salicylhydroxamic acid. These results suggest the involvement of cyanide-resistant respiration in the production of potato stress metabolites, compounds which may serve as phytoalexins. 相似文献
125.
Movement of Kinetin and Gibberellic Acid in Leaf Petioles during Water Stress-induced Abscission in Cotton 下载免费PDF全文
Movement of [14C]kinetin and [14C]gibberellic acid was examined in cotton (Gossypium hirsutum L.) cotyledonary petiole sections independent of label uptake or exit from the tissue. Sections 20 millimeters in length were taken from well watered, stressed, and poststressed plants. Transport capacity was determined using a pulse-chase technique. Movement of both kinetin and gibberellic acid was found to be nonpolar with a velocity of 1 millimeter per hour or less, suggesting passive diffusion. Neither water stress nor anaerobic conditions during transport of labeled material affected the transport capacity of the petioles. 相似文献
126.
Thomas Patterson 《Primates; journal of primatology》1979,20(3):341-354
A group of captive pygmy chimpanzees (Pan paniscus) was studied in the San Diego Zoological Gardens. The behavior patterns that these animals exhibit are described. Each of
these behavior patterns is compared to those described for wild and captive common chimpanzees (P. troglodytes). Differences in behavior between these two species are attributed to specialization of the pygmy chimpanzee to a rain forest
habitat and to a monogamous social system. 相似文献
127.
Control of porphyrin biosynthesis in Rhodopseudomonas spheroides and Propionibacterium shermanii. A direct 13C nuclear-magnetic-resonance spectroscopy study. 下载免费PDF全文
G Burton P M Jordan N E MacKenzie P E Fagerness A I Scott 《The Biochemical journal》1981,194(2):627-631
The facultative anaerobes Rhodopseudomonas spheroides and Propionibacterium shermanii were grown under anaerobic and aerobic conditions. The effect of light was studied with the photosynthetic R. spheroides, and the adaptation of both species to dark anaerobic life was monitored by direct observation of 5-amino[5-13C]laevulinic acid metabolism by using 13C nuclear-magnetic-resonance spectroscopy. 相似文献
128.
A comparative study was carried out in order to determine which of the most commonly used alkalies for protein hydrolysis in tryptophan determination gave the best results. Hydrolyses were performed with 2.5 and 4 n Ba (OH)2, 4 and 10 n NaOH, 5 n NaOH containing 5% SnCl2, and with 4 n LiOH, not previously reported for use. The effect of temperature and hydrolysis time on the measured tryptophan content was also determined. Based on results obtained with lysozyme and with seven high protein preparations 4 n LiOH gave the best results. A temperature of 145°C was selected as the most convenient temperature since maximum tryptophan values were obtained with 4–8 h. The hydrolysis time required was inversely related to the protein content of the preparation. Lysozyme, casein, bovine plasma protein, and dehydrated whole egg gave maximum tryptophan content after 4 h hydrolysis while skimmed milk powder, rice flour, wheat flour, and wild legume flour required 8 h hydrolysis. 相似文献
129.
On integrating experimental data published previously, the following picture of the mitochondrial adenine nucleotide (AdN) translocation system is being presented: 1. The AdN translocation system serves not only to transport ATP synthesized within mitochondria into the cytosol but also to transport cytosolic ATP into the mitochondria when oxidative phosphorylation is not functioning. 2. The AdN translocator is coded for by nuclear genes and the mitochondrial protein synthesis is not involved in its formation. 3. The AdN translocation system must be preserved and functioning even in cells which could dispense with oxidative phosphorylation. It assures appropriate concentrations of intramitochondrial ATP. 4. The intramitochondrial ATP is required for normal replication of mitochondrial DNA. Tis supports the view that the mitochondrion is a self-replicating semi-autonomous organelle. 5. The appropriate concentration of ATP must be present in mitochondria to make possible cell growth or multiplication. This points to a direct or indirect role of mitochondria in the control of cell proliferation. 相似文献
130.