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1.
2.
Summary Characteristics of inorganic carbon assimilation by photosynthesis in seawater were investigated in six species of the Fucales (five Fucaceae, one Cystoseiraceae) and four species of the Laminariales (three Laminariaceae, one Alariaceae) from Arbroath, Scotland. All of the algae tested could photosynthesise faster at high external pH values than the uncatalysed conversion of HCO
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to CO2 can occur, i.e. can use external HCO
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. They all had detectable extracellular carbonic anhydrase activity, suggesting that HCO
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use could involve catalysis of external CO2 production, a view supported to some extent by experiments with an inhibitor of carbonic anhydrase. All of the algae tested had CO2 compensation concentrations at pH 8 which were lower than would be expected from diffusive entry of CO2 supplying RUBISCO as the initial carboxylase, consistent with the operation of energized entry of HCO
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and / or CO2 acting as a CO2 concentrating mechanism. Quantitative differences among the algae examined were noted with respect to characteristics of inorganic C assimilation. The most obvious distinction was between the eulittoral Fucaceae, which are emersed for part of, or most of, the tidal cycle, and the other three families (Cystoseiraceae, Laminariaceae, Alariaceae) whose representatives are essentially continually submersed. The Fucaceae examined are able to photosynthesise at high pH values, and have lower CO2 compensation concentrations, and lower K1/2 values for inorganic C use in photosynthesis, at pH 8, than the other algae tested. Furthermore, the Fucaceae are essentially saturated with inorganic C for photosynthesis at the normal seawater concentration at pH 8 and 10°C. These characteristics are consistent with the dominant role of a CO2 concentrating mechanism in CO2 acquisition by these plants. Other species tested have characteristcs which suggest a less effective HCO
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use and CO2 concentrating mechanism, with the Laminariaceae being the least effective; unlike the Fucaceae, photosynthesis by these algae is not saturated with inorganic C in normal seawater. Taxonomic and ecological implications of these results are considered in relation to related data in the literature. 相似文献
3.
Stenosiphon linifolius is a monotypic genus of the tribe Onagreae of the Onagraceae. The species is widespread in, but restricted to, the Great Plains of the United States. Three flavonol glycosides, kaempferol 3-O-rhamnoside, quercetin 3-O-rhamnoside and myricetin 3-O-rhamnoside, were found to occur in methanolic extracts of Stenosiphon leaves. Similar compounds are found in the leaves of such related genera as Oenothera and Gaura, but in the latter genera, additional flavonols exhibiting greater substitutional variation also are found. 相似文献
4.
J. A. Raven 《The Journal of membrane biology》1971,6(2):89-107
Summary The effects of various inhibitors on photosynthesis, respiration, and active influx of K and Cl in light and dark inHydrodictyon africanum is reported. The inhibitors used were arsenate (uncouples electron-transport phosphorylations), dicyclohexylcarbodiimide (energy-transfer inhibitor in electron-transport phosphorylation), quinacrine (uncouples photophosphorylation and inhibits oxidative phosphorylation), and ethionine (traps adenylates as S-adenosyl ethionine). The action of these inhibitors, and of those previously used onHydrodictyon africanum, suggests that K influx requires ATP, while Cl influx requires some earlier manifestation of the ATP synthesizing process. Possible reasons for the greater sensitivity of K influx than of CO2 fixation to treatments which interfere with photophosphorylation are discussed. 相似文献
5.
P. B. Raven B. L. Drinkwater S. M. Horvath R. O. Ruhling J. A. Gliner J. C. Sutton N. W. Bolduan 《International journal of biometeorology》1974,18(3):222-232
Metabolic, body temperature, and cardiorespiratory responses of 16 healthy middle-aged (40–57 years) men, 9 nonsmokers and 7 smokers, were obtained during tests of maximal aerobic power at ambient environmental temperatures of 25 ± 0.5 and 35 ± 0.5°C and 20% relative humidity under four conditions: (a) filtered air, FA; (b) 50 ppm carbon monoxide in filtered air, CO; (c) 0.27 ppm peroxyacetylnitrate in filtered air, PAN; and (d) a combination of all three mixtures, PANCO. There was no significant change in maximum aerobic power \(\left( {\dot VO2max} \right)\) related to the presence of air pollutants, although total working time was lowered in the 25°C environment while breathing CO. Older nonsmokers did have a decrement in \(\left( {\dot VO2max} \right)\) while breathing 50 ppm CO, while older smokers failed to show any change. This difference was related to the initial COHb levels of the smokers, who, when breathing this level of ambient CO, had only a 14% increase in COHb over their initial levels in contrast to the 200% increase in the nonsmokers. Smoking habits were the most influential factor affecting the cardiorespiratory responses of these older men to maximal exercise. Regardless of ambient conditions, smokers had a significantly lower (27%) aerobic power than nonsmokers, were breathing closer to their maximal breathing capacities throughout the walk, and had a higher respiratory exchange ratio. While the \(\left( {\dot VO2max} \right)\) of nonsmokers was only 6% less than that of younger nonsmoking males ( \(\bar x\) age = 25 years) working under similar conditions, the aerobic power of the older smokers was 26% lower than that of young smokers ( \(\bar x\) age = 24 years). 相似文献
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7.
Otto T. Solbrig Loran C. Anderson Donald W. Kyhos Peter H. Raven Lily Rüdenberg 《American journal of botany》1964,51(5):513-519
Reports of 100 new chromosome counts are made for the tribe Astereae of Compositae, mostly based on determinations of meiotic material, including first counts for 9 genera and 53 species. Counts are now available for 58 of the approximately 100–120 genera and 431 of the approximately 2000 species in the tribe. Comparisons are made between chromosome number and habit and also between chromosome number and geographical distribution. Species and genera with a basic number of x = 9 are the most abundant. Within different phyletic lines x = 9 is also the most abundant number. On the other hand, many species with x = 4 and 5, belonging to a number of small, largely annual genera, are concentrated in southwestern North America. The low chromosome number in these plants is probably correlated with the dry habitat they occupy, and is most likely a specialized condition. 相似文献
8.
The effects of the trichothecene mycotoxins (acetyl T-2 toxin, T-2 toxin, HT-2 toxin, palmityl T-2 toxin, diacetoxyscirpenol (DAS), deoxynivalenol (DON), and T-2 tetraol) on bovine platelet function were examined in homologous plasma stimulated with platelet activating factor (PAF). The mycotoxins inhibited platelet function with the following order of potency: acetyl T-2 toxin > palmityl T-2 toxin = DAS > HT-2 toxin = T-2 toxin. While T-2 tetraol was completely ineffective as an inhibitor, DON exhibited minimal inhibitory activity at concentrations above 10×10?4M. The stability of the platelet aggregates formed was significantly reduced in all mycotoxin treated platelets compared to that of the untreated PAF controls. It is suggested that the increased sensitivity of PAF stimulated bovine platelets to the more lipophilic mycotoxins may be related to their more efficient partitioning into the platelet membrane compared to the more hydrophilic compounds. 相似文献
9.
The prokaryotic endosymbionts that became plastids and mitochondria contained genes destined for one of three fates. Genes
required for free-living existence were lost. Most genes useful to the symbiosis were transferred to the nucleus of the host.
Some genes, a small minority, were retained within the organelle. Here we suggest that a selective advantage of movement of
genes to the nucleus is decreased mutation: plastids and mitochondria have high volume-specific rates of redox reactions,
producing oxygen free radicals that chemically modify DNA. These mutations lead to synthesis of modified electron carriers
that in turn generate more mutagenic free radicals—the “vicious circle” theory of aging. Transfer of genes to the nucleus
is also advantageous in facilitating sexual recombination and DNA repair. For genes encoding certain key components of photosynthesis
and respiration, direct control of gene expression by redox state of electron carriers may be required to minimize free radical
production, providing a selective advantage of organelle location which outweighs that of location in the nucleus. A previous
proposal for transfer of genes to the nucleus is an economy of resources in having a single genome and a single apparatus
for gene expression, but this argument fails if any organellar gene is retained. A previous proposal for the retention of
genes within organelles is that certain proteins are organelle-encoded because they cannot be imported, but there is now evidence
against this view. Decreased free radical mutagenesis and increased sexual recombination upon transfer to the nucleus together
with redox control of gene expression in organelles may now account for the slightly different gene distributions among nuclei,
plastids, and mitochondria found in major eukaryote taxa. This analysis suggests a novel reason for uniparental inheritance
of organelles and the evolution of anisogametic sex, and may also account for the occurrence of nitrogen fixation in symbionts
rather than in nitrogen-fixing organelles.
Correspondence to: J.F. Allen 相似文献
10.
To identify processes that might account for differences in growth rates of rhodophytes under constant and dynamic light supply, we examined nonequilibrium gas exchange by measuring time courses of photoinduction, loss of photoinduction, and respiration rates immediately after the light–dark transition. Using the rhodophyte species Palmaria palmata (Huds.) Lamour and Lomentaria articulata (Huds.) Lyngb., we compared the effects of growth-saturating constant photon flux density (PFD) (95 μmol photons · m?2· s?1) to those of a dynamic light supply modeled on canopy movements in the intertidal zone (25 μmol photons · m?2· s?1 background PFD plus light flecks of 350 μmol photons · m?2· s?1, 0.1 Hz). The time required for P. palmata and L. articulata to be fully photoinduced was not affected by the dynamics of light supply. L. articulata required only 6 min of illumination with either fluctuating or constant light to be completely induced compared to 20 min for P. palmata. The latter species also lost photoinduction more rapidly than did L. articulata in the dark. There was no significant decline in photoinduction state for either species at the background PFD. The time courses of respiration after illumination with constant and fluctuating light were significantly different for P. palmata but not for L. articulata when the total photon dose was equal. In general, gas exchange of P. palmata appeared to be particularly sensitive to the temporal distribution of light supply whereas that of L. articulata was sensitive to the amplitude of variations, being photoinhibited at high PFD. These results are discussed in terms of the different mechanisms of inorganic carbon acquisition in the two species. 相似文献