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71.
Immature seeds of apricot (Prunus armeniaca L.) were fed the native gibberellin A5 (GA5) as 1- and 1,2-[3H]GA5 (5.3 Curies per millimole to 16 milliCuries per millimole) at doses (42 nanograms to 10.6 micrograms per seed) 2 to 530 times the expected endogenous level. After 4 days of incubation, seeds were extracted and free [3H]GA-like metabolites were separated from the highly H2O-soluble [3H]metabolites. For high specific activity feeds the retention times (Rts) of radioactive peaks were compared with Rts of authentic GAs on sequential gradient-eluted → isocratic eluted reversed-phase C18 high performance liquid chromatography (HPLC) -radiocounting (RC). From high substrate feeds (530 and 230 × expected endogenous levels) HPLC-RC peak groupings were subjected to capillary gas chromatography-selected ion monitoring (GC-SIM), usually six characteristic ions. The major free GA metabolites of [3H] GA5 were identified as GA1, GA3, and GA6 by GC-SIM. The major highly water soluble metabolite of [3H]GA5 at all levels of substrate GA5 had chromatographic characteristics similar to authentic GA1-glucosyl ester. Expressed as a percentage of recovered radioactivity, low substrate [3H]GA5 feeds (2 × expected endogenous level) yielded a broad spectrum of metabolites eluting at the Rts where GA1, GA3, GA5 methyl ester, GA6, GA22, GA29 (17, 14, 1.6, 7, 1.1, 0.5%, respectively) and GA glucosyl conjugates of GA1, GA3, GA5, and GA8 (33, 11, 1, 0.1%, respectively) elute. Metabolites were also present at Rts where GA glucosyl conjugates of GA6 and GA29 would be expected to elute (8 and 0.1%, respectively). Only 5% of the radioactivity remained as GA5. Increasing substrate GA5 levels increased the proportion of metabolites with HPLC Rts similar to GA1, GA6, and especially GA1 glucosyl ester, primarily at the expense of metabolites with HPLC Rts similar to GA3, GA3-glucosyl ester, and a postulated conjugate of GA6. There was evidence that high doses of substrate GA5 induced new metabolites which often, but not always, differed from GA1, GA3, and GA6 in HPLC Rt. These same metabolites, when analyzed by GC-SIM yielded m/e ions the same as the M+ and other characteristic m/e ions of the above GAs, albeit at differing GC Rt and relative intensities. 相似文献
72.
Protein Synthesis in Bromegrass (Bromus inermis Leyss) Cultured Cells during the Induction of Frost Tolerance by Abscisic Acid or Low Temperature 总被引:10,自引:9,他引:1 下载免费PDF全文
Bromus inermis Leyss cell cultures treated with 75 micromolar abscisic acid (ABA) at both 23 and 3°C developed more freezing resistance than cells cultured at 3°C. Protein synthesis in cells induced to become freezing tolerant by ABA and low temperature was monitored by [14C]leucine incorporation. Protein synthesis continued at 3°C, but net cell growth was stopped. Most of the major proteins detected at 23°C were synthesized at 3°C. However, some proteins were synthesized only at low temperatures, whereas others were inhibited. ABA showed similar effects on protein synthesis at both 23 and 3°C. Comparative electrophoretic analysis of [14C]leucine labeled protein detected the synthesis of 19, 21 and 47 kilodalton proteins in less than 8 hours after exposure to exogenous ABA. Proteins in the 20 kilodalton range were also synthesized at 3°C. In addition, a 31 kilodalton protein band showed increased expression in freezing resistant ABA treated cultures after 36 hours growth at both 3 and 23°C. Quantitative analysis of [14C]leucine labeled polypeptides in two-dimensional gels confirmed the increased expression of the 31 kilodalton protein. Two-dimensional analysis also resolved a 72 kilodalton protein enriched in ABA treated cultures and identified three proteins (24.5, 47, and 48 kilodaltons) induced by low temperature growth. 相似文献
73.
Construction of an Obligate Photoheterotrophic Mutant of the Cyanobacterium Synechocystis 6803 : Inactivation of the psbA Gene Family 总被引:14,自引:0,他引:14 下载免费PDF全文
psbA in Synechocystis 6803 was found to belong to a small multigene family with three copies. The psbA gene family was inactivated in vitro by insertation of bacterial drug resistance markers. Inactivation of all three genes resulted in a transformant that is unable to grow photosynthetically but can be cultured photoheterotrophically. This mutant lacks oxygen evolving capacity but retains photosystem I activity. Room temperature measurements of chlorophyll a fluorescence induction demonstrated that the transformant exhibits a high fluorescence yield with little or no variable fluorescence. Immunoblot analyses showed complete loss of the psbA gene product (the DI polypeptide) from thylakoid membranes in the transformant. However, the extrinsic 33 kilodalton polypeptide of the water-splitting complex of photosystem II, is still present. The results indicate that assembly of a partial photosystem II complex may occur even in the absence of the intrinsic D1 polypeptide, a protein implicated as a crucial component of the photosystem II reaction center. 相似文献
74.
All measurements of photorespiration and gross photosynthesis in leaves, whether using isotopes or not, are underestimated because of the recycling of O2 or CO2. On the basis of a simple diffusion model, we propose a method for the calculation of the recycling and the corresponding underestimation of the measurements. This procedure can be applied when the stomatal resistance is known, and allows for a correction of certain results in the literature. It is found that measurements of the photorespiratory CO2 release are usually underestimated by 20 to 100%, which sets the estimated rate of CO2 photorespired at 30 to 50% of the net photosynthesis in C3 plants under normal conditions. In water stress studies, the correction of the photorespiration is still more important (1.5-3.3) because the stomata are closed more. Analysis of the diffusion of O2 shows that its recycling is low and that the underestimation of photorespiration with 18O2 is negligible. 相似文献
75.
Phosphorylation of Thylakoid Proteins of Oryza sativa: In Vitro Characterization and Effects of Chilling Temperatures 下载免费PDF全文
The phosphorylation of thylakoid proteins of rice (Oryza sativa L.) was studied in vitro using [γ-32P]ATP. Several thylakoid proteins are labeled, including the light-harvesting complex of photosystem II. Protein phosphorylation is sensitive to temperature, pH, and ADP, ATP, and divalent cation concentrations. In the range pH 7 to 8.2, phosphorylation of the light-harvesting polypeptides declines above pH 7.5, whereas labeling of several other thylakoid polypeptides increases. Increasing divalent cation concentration from 3 to 20 millimolar results in a decrease in phosphorylation of the 26 kilodalton light-harvesting complex polypeptide and increased phosphorylation of several other polypeptides. ADP has an inhibitory effect on the phosphorylation of the light-harvesting complex polypeptides. Phosphorylation of the 26 kilodalton light-harvesting polypeptide requires 0.45 millimolar ATP for half-maximal phosphorylation, compared to 0.3 millimolar for the 32 kilodalton phosphoprotein. Low temperature inhibits the phosphorylation of thylakoid proteins in chilling-sensitive rice. However, phosphorylation of histones by thylakoid-bound kinase(s) is independent of temperature in the range of 25 to 5°C, suggesting that the effect of low temperature is on accessibility of the substrate, rather than on the activity of the kinase. 相似文献
76.
The chloroplast genes coding for the 16S ribosomal RNA from several spectinomycin-resistant Nicotiana mutants were analyzed. Two classes of mutants were identified. In one class, a G to A base transition is found at position 1140 of the tobacco-chloroplast 16S rRNA gene, which eliminates an AatII restriction endonuclease site. This base transition is proximal to a mutation previously described for spectinomycin resistance in Escherichia coli. In the other class, a novel G to A transition is found at position 1012 of the 16S rRNA gene. Although the mutations in the two classes are 128 nucleotides apart, the secondary structure model for 16S rRNA suggests that the two mutated nucleotides are in spatial proximity on opposite sides of a conserved stem structure in the 3' region of the molecule. Phylogenetic evidence is presented linking this conserved stem with spectinomycin resistance in chloroplasts. Perturbation of the stem is proposed to be the molecular-genetic basis for rRNA-dependent spectinomycin resistance. 相似文献
77.
Structural transition in inactive Balbiani ring chromatin of Chironomus during micrococcus nuclease digestion 总被引:4,自引:2,他引:2 下载免费PDF全文
We have analysed by micrococcus nuclease digestion the chromatin structure of genes in the Balbiani ring (BR) regions of a Chironomus cell line. Gel electrophoresis of the DNA fragments reveals a repeating structure which consists of two repeat sizes, a long repeat seen in the large fragments and a small repeat seen in the small fragments. The two repeats hardly overlap, except in a narrow transition zone which is at a different fragment size in the BR 2.2 and the BR 2.1 gene. The sizes of the large repeats fit the repeat of the underlying DNA sequence. The short repeats are between 170 and 180 bp, and after H1 depletion the short repeat in the BR 2.2 gene is 160 bp. Our most favoured interpretation of these data is that in intact chromatin the nucleosomes in the BR genes are phased with respect to the repeating DNA sequence, whereas micrococcus nuclease digestion leads to loss of a nucleosome-positioning constraint and hence to rearrangement of the nucleosomes. Our results imply a possible artefact of nuclease digestion of chromatin, which has to be taken into account in mapping nucleosome positions. 相似文献
78.
Most oil producing countries have extensive reserves of heavy oil and bitumen. As easily accessible sources of conventional crudes decline, these reserves will become more important in supplementing the energy requirements. Heavy oil and bitumen are highly viscous and contain 3 to 6% sulphur. These objectionable quantities of sulphur must be removed before being acceptable as refinery feedstock. This paper addresses the potential of biological desulphurization of heavy oil and bitumen. The aerobic and anaerobic processes to remove organic as well as inorganic sulphur have been reviewed. To date, most studies were performed with model substrates, particularly dibenzothiophene (DBT) in a synthetic medium. Early work concerned with the isolation of microorganisms, identification and characterization of intermediate metabolites, and the development of growth media. No commercially viable process has emerged since the engineering details of the process have not been addressed conclusively. Due to high utility and catalyst cost conventional hydrodesulphurization processes are reported to be uneconomic in case of high sulphur oils. Microbial desulphurization, on the other hand, appears to be promising due to the inherent low energy requirement. This process may become more attractive by the application of genetically modified bacteria and improvements in bioreactor design. 相似文献
79.