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101.
102.
The hypothesis has been proposed that in Anabaena variabilis the phototactic reaction sign is regulated by an unknown reaction sign reversal generator which is controlled by the intracellular level of singlet molecular oxygen (1O2). This hypothesis is supported by the following findings presented in this paper: Gassing with N2 and Ar shifts the phototactic transition point at which the positive reaction becomes negative to higher fluence rates. Surprisingly this is true also for gassing with molecular oxygen 3O2. Since 1O2 is produced in photosynthesis, the availability of external molecular oxygen seems not to be important. Apparently, a stream of any gas which is fast enough to remove 1O2 from the surface of the Anabaena trichomes decreases the internal 1O2 concentration and this way acts on the reaction sign reversal generator. Moreover, several carotenoids such as the water-soluble crocetin and preparations of solubilized -carotene, canthaxanthine and the C30-ester ethyl--apo-8-carotenoate shift the transition point of phototaxis to higher fluence rates by about one order of magnitude. Several tested furan derivatives, such as dimethylfuran, diphenylisobenzofuran, and furfuryl ethanol, are either cytotoxic or not water-soluble at the concentrations necessary for an effective 1O2 quenching. Based one these results a model of the phototactic reaction chain of A. variabilis is proposed.Abbreviations DABCO
1,4-diazabicyclo(2.2.2)octane
- DMF
dimethylfuran
- DPBF
diphenylisobenzofuran
Dedicated to Prof. Dr. Gerhart Drews on the occasion of his 60th birthday 相似文献
103.
104.
105.
Stimulation of Symbiotic N2 Fixation in Trifolium repens L. under Elevated Atmospheric pCO2 in a Grassland Ecosystem 下载免费PDF全文
Zanetti S Hartwig UA Luscher A Hebeisen T Frehner M Fischer BU Hendrey GR Blum H Nosberger J 《Plant physiology》1996,112(2):575-583
Symbiotic N2 fixation is one of the main processes that introduces N into terrestrial ecosystems. As such, it may be crucial for the sequestration of the extra C available in a world of continuously increasing atmospheric CO2 partial pressure (pCO2). The effect of elevated pCO2 (60 Pa) on symbiotic N2 fixation (15N-isotope dilution method) was investigated using Free-Air-CO2-Enrichment technology over a period of 3 years. Trifolium repens was cultivated either alone or together with Lolium perenne (a nonfixing reference crop) in mixed swards. Two different N fertilization levels and defoliation frequencies were applied. The total N yield increased consistently and the percentage of plant N derived from symbiotic N2 fixation increased significantly in T. repens under elevated pCO2. All additionally assimilated N was derived from symbiotic N2 fixation, not from the soil. In the mixtures exposed to elevated pCO2, an increased amount of symbiotically fixed N (+7.8, 8.2, and 6.2 g m-2 a-1 in 1993, 1994, and 1995, respectively) was introduced into the system. Increased N2 fixation is a competitive advantage for T. repens in mixed swards with pasture grasses and may be a crucial factor in maintaining the C:N ratio in the ecosystem as a whole. 相似文献
106.
Porcine VEG Proteins and Tear Prealbumins 总被引:3,自引:1,他引:2
Garibotti Marina; Christiansen Heidje; Schmale Hartwig; Pelosi Paolo 《Chemical senses》1995,20(1):69-76
Small soluble proteins, belonging to the lipocalin family aresecreted in large amounts by tongue von Ebner's glands and lachrymalglands. In humans, the lingual protein, called VEG, and thelachrymal protein, called tear prealbumin, have shown identicalcDNA sequences. In the pig, we have purified homodimeric proteinswith subunits of 17 kDa, both from von Ebner's glands and fromlachrymal glands. In both cases, the proteins can be resolvedinto two isoforms on a chromatofocusing column. Partial aminoacidsequences and full cDNA sequences have been obtained for themore abundant forms purified from both tissues. The two proteinsappear to be identical, as in humans. The reason why the sameprotein is expressed in different tissues, as well as its physiologicalfunction, still remain to be clarified. 相似文献
107.
Does nitrogen nutrition restrict the CO2 response of fertile grassland lacking legumes? 总被引:7,自引:0,他引:7
S. Zanetti U. A. Hartwig C. van Kessel A. Lüscher T. Hebeisen M. Frehner B. U. Fischer G. R. Hendrey H. Blum J. Nösberger 《Oecologia》1997,112(1):17-25
The extent of the response of plant growth to atmospheric CO2 enrichment depends on the availability of resources other than CO2. An important growth-limiting resource under field conditions is nitrogen (N). N may, therefore, influence the CO2 response of plants. The effect of elevated CO2 (60 Pa) partial pressure (pCO2) on the N nutrition of field-grown Lolium perenne swards, cultivated alone or in association with Trifolium repens, was investigated using free air carbon dioxide enrichment (FACE) technology over 3 years. The established grassland ecosystems
were treated with two N fertilization levels and were defoliated at two frequencies. Under elevated pCO2, the above-ground plant material of the L. perenne monoculture showed a consistent and significant decline in N concentration which, in general, led to a lower total annual
N yield. Despite the decline in the critical N concentration (minimum N concentration required for non-N-limited biomass production)
under elevated pCO2, the index of N nutrition (ratio of actual N concentration and critical N concentration) was lower under elevated pCO2 than under ambient pCO2 in frequently defoliated L. perenne monocultures. Thus, we suggest that reduced N yield under elevated pCO2 was evoked indirectly by a reduction of plant-available N. For L. perenne grown in association with T. repens and exposed to elevated pCO2, there was an increase in the contribution of symbiotically fixed N to the total N yield of the grass. This can be explained
by an increased apparent transfer of N from the associated N2-fixing legume species to the non-fixing grass. The total annual N yield of the mixed grass/legume swards increased under
elevated pCO2. All the additional N yielded was due to symbiotically fixed N. Through the presence of an N2-fixing plant species more symbiotically fixed N was introduced into the system and consequently helped to overcome N limitation
under elevated pCO2.
Received: 11 November 1996 / Accepted: 20 May 1997 相似文献
108.
Phosphorus deficiency increases the argon-induced decline of nodule nitrogenase activity in soybean and alfalfa 总被引:1,自引:0,他引:1
Open-flow assays of H2 evolution in Ar:O2 (80:20, v/v) by nodulated roots were performed in situ with soybean [Glycine max (L.) Merr.] and alfalfa [Medicago sativa L.) grown in sand with orthophosphate (Pi) nutrition either limiting (low-P) or non-limiting (control) for plant growth.
Nodule growth was more limited than shoot growth by P deficiency. Phosphorus concentration was less affected in nodules than
in other parts of the low-P plants. During assays, nitrogenase activity declined a few minutes after exposure of the nodulated
roots to Ar. The magnitude of this argon-induced decline (Ar-ID) was less in alfalfa than in soybean. In both symbioses the
magnitude of the Ar-ID was larger in low-P than control plants. Moreover, the minimum H2 evolution after the Ar-ID, was reached earlier in low-P plants. The Ar-ID was partly reversed by raising the external partial
pressure of O2 in the rhizosphere. The magnitude of the Ar-ID in soybean was correlated negatively to nodule and shoot mass per plant, individual
nodule mass, H2 evolution in air prior to the assay, and nodule N and P concentrations. Possible reasons, including nodule size and nodule
O2 permeability, for the increase in Ar-ID in P-deficient plants are discussed and an interpretation of the P effect on nodule
respiration and energetic metabolism is proposed.
Received: 17 May 1996 / Accepted: 16 September 1996 相似文献
109.
Net soil carbon input under ambient and elevated CO2 concentrations: isotopic evidence after 4 years
Chris Van Kessel William R. Horwath Ueli Hartwig David Harris Andreas LÜscher 《Global Change Biology》2000,6(4):435-444
Elevation of atmospheric CO2 concentration is predicted to increase net primary production, which could lead to additional C sequestration in terrestrial ecosystems. Soil C input was determined under ambient and Free Atmospheric Carbon dioxide Enrichment (FACE) conditions for Lolium perenne L. and Trifolium repens L. grown for four years in a sandy‐loam soil. The 13C content of the soil organic matter C had been increased by 5‰ compared to the native soil by prior cropping to corn (Zea mays) for > 20 years. Both species received low or high amounts of N fertilizer in separate plots. The total accumulated above‐ground biomass produced by L. perenne during the 4‐year period was strongly dependent on the amount of N fertilizer applied but did not respond to increased CO2. In contrast, the total accumulated above‐ground biomass of T. repens doubled under elevated CO2 but remained independent of N fertilizer rate. The C:N ratio of above‐ground biomass for both species increased under elevated CO2 whereas only the C:N ratio of L. perenne roots increased under elevated CO2. Root biomass of L. perenne doubled under elevated CO2 and again under high N fertilization. Total soil C was unaffected by CO2 treatment but dependent on species. After 4 years and for both crops, the fraction of new C (F‐value) under ambient conditions was higher (P= 0.076) than under FACE conditions: 0.43 vs. 0.38. Soil under L. perenne showed an increase in total soil organic matter whereas N fertilization or elevated CO2 had no effect on total soil organic matter content for both systems. The net amount of C sequestered in 4 years was unaffected by the CO2 concentration (overall average of 8.5 g C kg?1 soil). There was a significant species effect and more new C was sequestered under highly fertilized L. perenne. The amount of new C sequestered in the soil was primarily dependent on plant species and the response of root biomass to CO2 and N fertilization. Therefore, in this FACE study net soil C sequestration was largely depended on how the species responded to N rather than to elevated CO2. 相似文献
110.