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71.
An immobilized lipase suitable for fat interesterification has been prepared by precipitation with acetone of a commercial lipase from Rhizopus arrhizus onto diatomaceous earth. As observed previously with a less active enzyme from Aspergillus sp., the interesterification activity was enhanced by addition of purified lipase or by high loadings of commercial enzyme. The interesterification activities reached maximum values in both cases. For immobilized preparations with purified enzyme, interesterification activity was also enhanced by the presence of a precoat of glutaraldehyde cross-linked commercial lipase. A 2.9-L column of immobilized lipase was used to interesterify batches of shea oleine (67 kg) and shea oil (40 kg). Little activity was lost processing shea oleine, but slow poisoning of the bed occurred when shea oil was fed to the column. 相似文献
72.
73.
Anecdotal, historical and critical commentaries on genetics twenty years of illegitimate recombination 总被引:6,自引:0,他引:6
Anderson P 《Genetics》1987,115(4):581-583
74.
75.
Regulation of Vacuolar pH of Plant Cells: I. Isolation and Properties of Vacuoles Suitable for P NMR Studies 下载免费PDF全文
Mathieu Y Guern J Kurkdjian A Manigault P Manigault J Zielinska T Gillet B Beloeil JC Lallemand JY 《Plant physiology》1989,89(1):19-26
For the first time, the 31P nuclear magnetic resonance technique has been used to study the properties of isolated vacuoles of plant cells, namely the vacuolar pH and the inorganic phosphate content. Catharanthus roseus cells incubated for 15 hours on a culture medium enriched with 10 millimolar inorganic phosphate accumulated large amounts of inorganic phosphate in their vacuoles. Vacuolar phosphate ions were largely retained in the vacuoles when protoplasts were prepared from the cells and vacuoles isolated from the protoplasts. Vacuolar inorganic phosphate concentrations up to 150 millimolar were routinely obtained. Suspensions prepared with 2 to 3 × 106 vacuoles per milliliter from the enriched C. roseus cells have an internal pH value of 5.50 ± 0.06 and a mean trans-tonoplast ΔpH of 1.56 ± 0.07. Reliable determinations of vacuolar and external pH could be made by using accumulation times as low as 2 minutes. These conditions are suitable to follow the kinetics of H+ exchanges at the tonoplast. The 31P nuclear magnetic resonance technique also offered the possibility of monitoring simultaneously the stability of the trans-tonoplast pH and phosphate gradients. Both appeared to be reasonably stable over several hours. The buffering capacity of the vacuolar sap around pH 5.5 has been estimated by several procedures to be 36 ± 2 microequivalents per milliliter per pH unit. The increase of the buffering capacity due to the accumulation of phosphate in the vacuoles is, in large part, compensated by a decrease of the intravacuolar malate content. 相似文献
76.
Light Quality and Irradiance Level Interaction in the Control of Expression of Light-Harvesting Complex of Photosystem II: Pigments, Pigment-Proteins, and mRNA Accumulation 下载免费PDF全文
Effects of red and blue light at irradiances from 1.6 to 28.3 micromolar per square meter per second on chloroplast pigments, light-harvesting pigment-proteins associated with photosystem II, and the corresponding mRNA were evaluated in maize (Zea mays L.) plants (OP Golden Bantum) grown for 14 days under 14 hours light/10 hours dark cycles. Accumulation of pigments, pigment-proteins, and mRNA was less in blue than in red light of equal irradiance. The difference between blue and red light, however, varied as a function of irradiance level, and the pattern of this variation suggests irradiance-controlled activation/deactivation (switching) of blue-light receptor. The maximum reduction in blue light of mRNA and proteins associated with light-harvesting complex occurs at lower irradiance levels than the maximum reduction of chlorophylls a and b. 相似文献
77.
Distribution of the major light-harvesting chlorophyll a/b-protein (LHCII) and its mRNA within bundle sheath and mesophyll cells of maize (Zea mays L.) was studied using in situ immunolocalization and hybridization, respectively. In situ hybridization with specific LHCII RNA probes from maize and Lemna gibba definitively shows the presence of high levels of mRNA for LHCII in both bundle sheath cells and mesophyll cells. In situ immuno-localization studies, using an LHCII monoclonal antibody, demonstrate the presence of LHCII polypeptides in chloroplasts of both cell types. The polypeptide composition of LHCII and the amount of LHCII in bundle sheath cells are different from those in mesophyll cells. Both mesophyll and bundle sheath chloroplasts can take up, import and process the in vitro transcribed and translated LHCII precursor protein from L. gibba. Although bundle sheath chloroplasts incorporate LHCII into the pigmented light-harvesting complex, the efficiency is lower than that in mesophyll chloroplasts. 相似文献
78.
The photorespiratory activity of mesophyll protoplasts of Nicotiana plumbaginifolia has been clearly demonstrated by the presence of a Warburg-effect, the occurrence of an important CO2-sensitive O2 uptake and the effect of some photorespiratory inhibitors on photosynthetic activity. At a nonsaturating dissolved inorganic carbon (DIC) concentration (0.1 millimolar), we observed that the rate of CO2 fixation was 60% lower at 50% O2 compared to that measured at 2% O2. Using 18O2 and mass spectrometry, we measured O2 exchange as a function of light intensity and of DIC concentration. Oxygen uptake measured at the CO2 compensation point (47.4 micromoles O2 per hour per milligram chlorophyll) was three-fold higher than that measured at a saturating CO2 concentration. Cyanide or iodoacetamide, inhibitors of the Calvin cycle, were found to reduce the O2 uptake to the same extent as CO2 saturation. We conclude from these results that the major part of the CO2-sensitive O2 uptake is due to photorespiration. Further, we investigated the effect on net photosynthesis of some inhibitors of the glycolate pathway. At CO2 saturation (10 millimolar DIC), 5 millimolar aminoacetonitrile (AAN), and 1 millimolar aminooxyacetate (AOA) did not cause any significant decrease in net photosynthesis. However, when these two inhibitors were added under a period of active photorespiration (10 minutes at the CO2 compensation point at 20% O2), we observed a decrease in the rate of net photosynthesis at 10 millimolar DIC measured afterward (respectively, 18 and 29%). This inhibition did not appear at 2% O2, but was stronger at 50% O2 (40% for AAN and 47% for AOA). With 0.05 millimolar butyl 2-hydroxy-3-butynoate (BHB) or 0.5 millimolar l-methionine-dl-sulfoximine (l-MSO), rates of net photosynthesis at 10 millimolar DIC were decreased by 10 to 15%. Additional decreases were observed after a period at the CO2 compensation point at 20% O2 (30% for BHB and 20% for l-MSO). From the sites of action of the four inhibitors tested, we suggest the inhibition of photosynthesis occurring after a period of active photorespiration to be due to the toxic accumulation of nonmetabolized phosphoglycolate. 相似文献
79.
Gibberellins in Embryo-Suspensor of Phaseolus coccineus Seeds at the Heart Stage of Embryo Development 总被引:2,自引:1,他引:1 下载免费PDF全文
Gibberellins (GAs) in suspensors and embryos of Phaseolus coccineus seeds at the heart stage of embryo development were analyzed by combined gas chromatography-mass spectrometry (GC-MS). From the suspensor four C19-GAs, GA1, GA4, GA5, GA6, and one C20 GA, GA44, were identified. From the embryo, five C19-GAs GA1, GA4, GA5, GA6, GA60 and two C20 GAs, GA19 and GA44 were identified. The data, in relation to previous results, suggest a dependence of the embryo on the suspensor during early stages of development. 相似文献
80.
Mode of Action Studies on Nitrodiphenyl Ether Herbicides : II. The Role of Photosynthetic Electron Transport in Scenedesmus obliquus 总被引:1,自引:1,他引:0
The nitrodiphenyl ether herbicide 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitroacetophenone oxime-o-(acetic acid, methyl ester) (DPEI) induces light- and O2-dependent lipid peroxidation and chlorophyll (Chl) bleaching in the green alga Scenedesmus obliquus. Under conditions of O2-limitation, these effects are diminished by prometyne and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), both inhibitors of photosynthetic electron transport. Mutants in which photosynthetic electron transport is blocked are also resistant to DPEI under conditions of O2-limitation. Light- and O2-dependent lipid peroxidation and Chl bleaching are also induced by 5-[2-chloro-4-(trifluoromethyl)phenoxy]-3-methoxyphthalide (DPEII), a diphenyl ether whose redox properties preclude reduction by photosystem I. However, these effects of DPEII are also inhibited by DCMU. Under conditions of high aeration, DCMU does not protect Scenedesmus cells from Chl bleaching induced by DPEI, but does protect against paraquat. DPEI, but not paraquat, induces tetrapyrrole formation in treated cells in the dark. This is also observed in a mutant lacking photosystem I but is suppressed under conditions likely to lead to O2 limitation. Our results indicate that, in contrast to paraquat, the role of photosynthetic electron transport in diphenyl ether toxicity in Scenedesmus is not to reduce the herbicide to a radical species which initiates lipid peroxidation. Its role is probably to maintain a sufficiently high O2 concentration, through water-splitting, in the algal suspension. 相似文献