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61.
HAEMOGLOBIN Hopkins-2 (Ho-2) was discovered in a family in which haemoglobin S was also present1. Independent segregation of the two abnormal haemoglobins provided the first convincing evidence that two genetic loci are concerned with synthesis of the haemoglobin molecule1,2. Subsequently, evidence was obtained that the abnormality in haemoglobin Ho-2 is in the alpha chain3, whereas the lesion in haemoglobin S is in the beta chain of globin. We have reported the structural abnormality in Ho-2 and we now present a revised pedigree and the clinical status of carriers; we attempt to relate these findings to functional abnormalities exhibited by the haemoglobin. 相似文献
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63.
IRMGARD VON TEICHMAN F.L.S. ABRAHAM E. VAN WYK F.L.S. 《Botanical journal of the Linnean Society. Linnean Society of London》1991,105(3):211-237
VON TEICHMAN, I. & VAN WYK, A. E., 1991. Trends in the evolution of dicotyledonous seeds based on character associations, with special reference to pachychalazy and recalcitrance. The possible evolutionary status of the endothelium, hypostase, pachychalaza and the recalcitrant viability behaviour of seeds is considered in relation to bitegmy/unitegmy, crassinucellate/tenuinucellate ovules, nuclear/cellular endosperm development, large/small seed size, woody/herbaceous habit and tropical/temperate habitat. The presence of the endothelium, hypostase, pachychalaza and recalcitrance in dicotyledonous families is plotted against Dahlgren's system of classification. Results are compared with Sporne's advancement index for the various families. An endothelium is considered derived since it occurs more often in highly evolved superorders and is significantly associated with derived ovule and endosperm character states as well as with smaller seed size. A hypostase appears to be relatively ancestral and is significantly associated with pachychalazy and recalcitrance. The endothelium and hypostase have developed independently in many taxa and could be interpreted as being structurally and functionally analogous. Pachychalazy and recalcitrance are significantly associated with ancestral ovule character states and, at the species level, with large seed size (overgrown seed), woody habit and tropical habitat. The presence of pachychalazy, recalcitrance and associated large seed size are therefore regarded as ancestral character states of the dicotyledons. Consideration of currently accepted dicta on seed character state polarity, suggests a reversal in the evolutionary status of pachychalazy and large seed size. 相似文献
64.
65.
Alterations in Endogenous Levels of Gibberellin-like Substances during Germination of Phaseolus vulgaris Seeds 总被引:1,自引:0,他引:1
The endogenous gibberellin-like substances were determined in mature dry and germinating bean seeds, Phaseolus vulgaris L. cv. Alabaster. Methanol extracts were partitioned against ethyl acetate and butanol at neutral and acid pH. Each phase was individually chromatographed on a silica gel column. The gibberellin activity was measured with the Tan-ginbozu dwarf rice micro-drop bioassay. Each extract was tested in two dilutions. Extracts from dry seeds showed the highest gibberellin activity, largely attributable to ethyl acetate-soluble substances. The activity was considerably reduced in extracts from seeds imbibed for 1 day. Gibberellin-like substances soluble in butanol appeared in extracts from seeds soaked for 1 or more days. 相似文献
66.
To investigate the diurnal variation of stomatal sensitivity to CO2 , stomatal response to a 30 min pulse of low CO2 was measured four times during a 24 h time-course in two Crassulacean acid metabolism (CAM) species Kalanchoe daigremontiana and Kalanchoe pinnata , which vary in the degree of succulence, and hence, expression and commitment to CAM. In both species, stomata opened in response to a reduction in p CO2 in the dark and in the latter half of the light period, and thus in CAM species, chloroplast photosynthesis is not required for the stomatal response to low p CO2 . Stomata did not respond to a decreased p CO2 in K. daigremontiana in the light when stomata were closed, even when the supply of internal CO2 was experimentally reduced. We conclude that stomatal closure during phase III is not solely mediated by high internal p CO2 , and suggest that in CAM species the diurnal variability in the responsiveness of stomata to p CO2 could be explained by hypothesizing the existence of a single CO2 sensor which interacts with other signalling pathways. When not perturbed by low p CO2 , CO2 assimilation rate and stomatal conductance were correlated both in the light and in the dark in both species. 相似文献
67.
Stream acidification increases nitrogen uptake by leaf biofilms: implications at the ecosystem scale
1. While anthropogenic stream acidification is known to lower species diversity and impair decomposition, its effects on nutrient cycling remain unclear. The influence of acid‐stress on microbial physiology can have implications for carbon (C) and nitrogen (N) cycles, linking environmental conditions to ecosystem processes. 2. We collected leaf biofilms from streams spanning a gradient of pH (5.1–6.7), related to chronic acidification, to investigate the relationship between qCO2 (biomass‐specific respiration; mg CO2‐C g?1 fungal C h?1), a known indicator of stress, and biomass‐specific N uptake (μg NH4‐N mg?1 fungal biomass h?1) at two levels of N availability (25 and 100 μg NH4‐N L?1) in experimental microcosms. 3. Strong patterns of increasing qCO2 (i.e. increasing stress) and increasing microbial N uptake were observed with a decrease in ambient (i.e. chronic) stream pH at both levels of N availability. However, fungal biomass was lower on leaves from more acidic streams, resulting in lower overall respiration and N uptake when rates were standardized by leaf biomass. 4. Results suggest that chronic acidification decreases fungal metabolic efficiency because, under acid conditions, these organisms allocate more resources to maintenance and survival and increase their removal of N, possibly via increased exoenzyme production. At the same time, greater N availability enhanced N uptake without influencing CO2 production, implying increased growth efficiency. 5. At the ecosystem level, reductions in growth because of chronic acidification reduce microbial biomass and may impair decomposition and N uptake; however, in systems where N is initially scarce, increased N availability may alleviate these effects. Ecosystem response to chronic stressors may be better understood by a greater focus on microbial physiology, coupled elemental cycling, and responses across several scales of investigation. 相似文献
68.
Effects of growth light intensity on the temperature dependence of CO2 assimilation rate were studied in tobacco (Nicotiana tabacum) because growth light intensity alters nitrogen allocation between photosynthetic components. Leaf nitrogen, ribulose 1·5‐bisphosphate carboxylase/oxygenase (Rubisco) and cytochrome f (cyt f) contents increased with increasing growth light intensity, but the cyt f/Rubisco ratio was unaltered. Mesophyll conductance to CO2 diffusion (gm) measured with carbon isotope discrimination increased with growth light intensity but not with measuring light intensity. The responses of CO2 assimilation rate to chloroplast CO2 concentration (Cc) at different light intensities and temperatures were used to estimate the maximum carboxylation rate of Rubisco (Vcmax) and the chloroplast electron transport rate (J). Maximum electron transport rates were linearly related to cyt f content at any given temperature (e.g. 115 and 179 µmol electrons mol?1 cyt f s?1 at 25 and 40 °C, respectively). The chloroplast CO2 concentration (Ctrans) at which the transition from RuBP carboxylation to RuBP regeneration limitation occurred increased with leaf temperature and was independent of growth light intensity, consistent with the constant ratio of cyt f/Rubisco. In tobacco, CO2 assimilation rate at 380 µmol mol?1 CO2 concentration and high light was limited by RuBP carboxylation above 32 °C and by RuBP regeneration below 32 °C. 相似文献
69.
Effects of nutrients and light on periphyton biomass and nitrogen uptake in Mediterranean streams with contrasting land uses 总被引:3,自引:0,他引:3
DANIEL VON SCHILLER EUGÈNIA MARTÍ JOAN LLUÍS RIERA FRANCESC SABATER 《Freshwater Biology》2007,52(5):891-906
1. Nutrient diffusing substrata (NDS) were used to determine the relative importance of nutrients and light as potential limiting factors of periphyton biomass and nitrogen (N) uptake in Mediterranean streams subjected to different human impacts. The nutrients examined were phosphorus (P) and N, and we also further differentiated between the response of periphyton communities to N species (i.e. NO3‐N and NH4‐N). To examine the effect of light and nutrients on periphyton biomass, chlorophyll a accrual rates on NDS located at open and closed canopy sites were compared. The effect of nutrient availability on periphyton uptake was measured by 15N changes on the NDS after NO3‐15N short‐term nutrient additions. 2. Results show that light was the main factor affecting algal biomass in the study streams. Algal biomass was in general higher at open than at closed canopy sites. Nutrient availability, as simulated with the NDS experiments, did not enhance algal biomass accrual in either of the 2 light conditions. 3. In the control treatments (i.e. ambient concentrations), periphyton NO3‐N uptake rates increased and C : N molar ratios decreased consistently with increases in N availability across streams. NO3‐N uptake rates were altered when ambient N concentrations were increased artificially in the N amended NDS. Periphyton assemblages growing on N enriched substrata seemed to preferentially take up N diffusing from the substratum rather than N from the water column. This response differed among streams, and depended on ambient N availability. 4. Periphyton biomass was not significantly different between substrata exposed to the two forms of available N sources. Nonetheless, we found differences in the effects of both N sources on the uptake of N from the water column. NH4‐N seemed to be the preferred source of N for periphyton growing on NDS. 5. Results suggest that the effect of riparian zones on light availability, although seldom considered by water managers, may be more important than nutrients in controlling eutrophication effects derived from human activities. Finally, our results confirm that not only increases in concentration, but also stoichiometric imbalances should be considered when examining N retention in human altered streams. 相似文献
70.
Field and laboratory experiments on net uptake of nitrate and ammonium by the roots of spruce (Picea abies) and beech (Fagus sylvatica) trees 总被引:4,自引:0,他引:4