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921.
M. N. B. NAIR H. Y. MOHAN RAM 《Botanical journal of the Linnean Society. Linnean Society of London》1989,100(4):323-336
NAIR, M. N. B. AND MOHAN RAM, H. Y., 1989. Vestured pits and vestured vessel member walls in some Indian dicotyledonous woods. The woods of 144 taxa belonging to 38 families of angiosperms were examined for vestured pits and vestured vessel member walls using scanning electron microscopy. Vestured pits are present in 66 taxa (belonging to ten families) and vestured vessel member walls occur in only six taxa (belonging to three families). In Ehretiaceae and Euphorbiaceae vestures are present only in certain vessel members. In Wrighlia tinctoria , perforation plates containing vestures have been observed in addition to the presence of vestured pits. A classification of vestured pits based on their morphology and distribution is proposed by us. In all the types of vestured pits, vestures are present on the margin of the outer pit aperture or on the pit chamber wall. Occasionally, they are present in the pit canal, on the margin and in the vicinity of the inner pit aperture and rarely over the inner walls of the vessel members. The functions of vestured pits are not clear, although several suggestions are made. Whether or not these structures affect wood processing is not presently understood. It appears that vestured pits and vestured vessel member walls have diagnostic rather than phylogenetic value. 相似文献
922.
斜胸叶蝉属一新种(同翅目:叶蝉总科:耳叶蝉科) 总被引:1,自引:0,他引:1
本文记述耳叶蝉科斜胸叶蝉属一新种:黄缘斜胸叶蝉Epiclinata flavomarinata sp.nov.。标本采自我国西藏。文中描述了新种的外部形态及雄性外生殖器构造特征,并与近似种进行比较,附有主要特征图。模式标本保存于中国科学院动物研究所。 相似文献
923.
报道我国首次发现的三叠纪多板纲(Polyplacophora)鳞肋目(Lepidopleurina)鳞肋科(Lepidopleuridae)的—新属——中国石鳖(Sinochiton).新属保存较完整,贝体中等大,椭圆形,长宽比为1.44∶1;中间板宽远大于壳长,长方形,半圆形拱凸,壳顶不突出,后缘近直,中心区十分宽大,侧区很窄,或不明显,缝合片及嵌插板不发育;贝体具圆形环带.新属与菊石 Balatonites 共生,时代属 Anisian 期.新属与北美下二叠统的 Ochmazochiton Hoare, 1984 及宾夕法尼亚系的 Pedanochiton Debrock, Hoare et al 近似,它们之间可能存在着亲缘关系. 相似文献
924.
925.
Using data for 27 Texas counties from 1978-1987, it is shown that the incidence rates of suicide, homicide, and rape are significantly higher in counties whose drinking water supplies contain little or no lithium than in counties with water lithium levels ranging from 70-170 micrograms/L; the differences remain statistically significant (p less than 0.01) after corrections for population density. The corresponding associations with the incidence rates of robbery, burglary, and theft were statistically significant with p less than 0.05. These results suggest that lithium has moderating effects on suicidal and violent criminal behavior at levels that may be encountered in municipal water supplies. Comparisons of drinking water lithium levels, in the respective Texas counties, with the incidences of arrests for possession of opium, cocaine, and their derivatives (morphine, heroin, and codeine) from 1981-1986 also produced statistically significant inverse associations, whereas no significant or consistent associations were observed with the reported arrest rates for possession of marijuana, driving under the influence of alcohol, and drunkenness. These results suggest that lithium at low dosage levels has a generally beneficial effect on human behavior, which may be associated with the functions of lithium as a nutritionally-essential trace element. Subject to confirmation by controlled experiments with high-risk populations, increasing the human lithium intakes by supplementation, or the lithiation of drinking water is suggested as a possible means of crime, suicide, and drug-dependency reduction at the individual and community level. 相似文献
926.
Gerhard Sandmann M. Luisa Peleato Maria F. Fillat M. Carmen Lázaro Carlos Gómez-Moreno 《Photosynthesis research》1990,26(2):119-125
Iron-dependent formation of ferredoxin and flavodoxin was determined in Anabaena ATCC 29413 and ATCC 29211 by a FPLC procedure. In the first species ferredoxin is replaced by flavodoxin at low iron levels in the vegetative cells only. In the heterocysts from Anabaena ATCC 29151, however, flavodoxin is constitutively formed regardless of the iron supply.Replacement of ferredoxin by flavodoxin had no effect on photosynthetic electron transport, whereas nitrogen fixation was decreased under low iron conditions. As ferredoxin and flavodoxin exhibited the same Km values as electron donors to nitrogenase, an iron-limited synthesis of active nitrogenase was assumed as the reason for inhibited nitrogen fixation. Anabaena ATCC 29211 generally lacks the potential to synthesize flavodoxin. Under iron-starvation conditions, ferredoxin synthesis is limited, with a negative effect on photosynthetic oxygen evolution. 相似文献
927.
High light treatments were given to attached leaves of pumpkin (Cucurbita pepo L.) at room temperature and at 1°C where the diffusion- and enzyme-dependent repair processes of Photosystem II are at a minimum. After treatments, electron transfer activities and fluorescence induction were measured from thylakoids isolated from the treated leaves. When the photoinhibition treatment was given at 1°C, the Photosystem II electron transfer assays that were designed to require electron transfer to the plastoquinone pool showed greater inhibition than electron transfer from H2O to paraphenyl-benzoquinone, which measures all PS II centers. When the light treatment was given at room temperature, electron transfer from H2O to paraphenyl-benzoquinone was inhibited more than whole-chain electron transfer. Variable fluorescence measured in the presence of ferricyanide decreased only during room-temperature treatments. These results suggest that reaction centers of one pool of Photosystem II, non-QB-PS II, replace photoinhibited reaction centers at room temperature, while no replacement occurs at 1°C. A simulation of photoinhibition at 1°C supports this conclusion.Abbreviations BSA
bovine serum albumin
- Chl
chlorophyll
- DCMU
3-(3,4,-dichlorophenyl)-1,1,-dimethylurea
- DCPIP
dichlorophenol-indophenol (2,6-dichloro-4((4-hydroxyphenyl)imino)-2,5-cyclohexadien-1-one)
- DPC
diphenyl carbazide (2,2-diphenylcarbonic dihydrazide)
- FeCN
ferricyanide (hexacyanoferrate(III))
- app
apparent quantum yield of photosynthetic oxygen evolution
- MV
methyl viologen (1,1-dimethyl-4,4-bipyridinium dichloride)
- PPBQ
phenyl-p-benzoquinone
- PPFD
photosynthetic photon flux density
- PQ
pool plastoquinone
- QB
secondary quinone acceptor of PS II
- RT
room temperature
- WC
whole chain electron transfer 相似文献
928.
The major developments in the field of nuclear activation analysis, from 1936 to 1989, are discussed. The developments are
grouped into five consecutive time periods. The impact of various scientists on the development of the field in the first
35 years is also discussed. 相似文献
929.
Putzer V. M. de Zwaan A. Wieser W. 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1990,159(6):707-715
Summary Anoxia tolerance, glycogen degradation, free amino acid pool, adenylate energy charge and the accumulation and excretion of end products were monitored inLumbriculus variegatus Müller throughout 48 h of anoxia. A transition period lasting about 4 h could be distinguished from subsequent events during which malate, present in high amounts in the resting animals, is utilized, probably by conversion to succinate. Up to the 12th hour of anoxia there is an increase in concentration of free amino acids, except aspartate. Glutamate increases rapidly during the first half hour but decreases thereafter. Beginning with the second hour of anoxia the alanine concentration increases at the same rate glutamate concentration decreases, but the source of nitrogen during the first hour is unknown. It is argued that the nitrogen required for the synthesis of some of the amino acids is ultimately derived from proteolysis. After about 3 h of anoxia propionate and acetate are synthesized. At first these acids accumulate in the tissues, but after 4–6 h they are excreted into the surrounding medium. Acetate is excreted over the whole experimental period at a constant rate, whereas the excretion rate of propionate decreases slowly with time. The propionate/acetate ratio is in excess of 2. Classic malate dismutation is by far the most important mechanism in the maintenance of redox balance. Depletion of glycogen stores appears to play an important role in determining anoxic survival time. Due to extremely low activity of PEPCK the ratio of the specific activities of PK and PEPCK is very high. Further, the kinetic properties of pyruvate kinase do not support the assumption of a shift of the glycolytic carbon flow at the PEP level.Abbreviations
PK
Pyruvate kinase
-
PEPCK
phosphoenolpyruvate carboxykinase
-
PEP
phospho(enol)pyruvate
-
FBP
fructose-1,6-bisphosphate
-
AEC
adenylate energy charge
-
EMP-scheme
Embden-Meyerhof-Parnas scheme of glycolysis
-
f
w
fresh body weight
-
dw
dry body weight 相似文献
930.
James R. Griesemer 《Biology & philosophy》1990,5(1):3-36
Accounts of the relation between theories and models in biology concentrate on mathematical models. In this paper I consider
the dual role of models as representations of natural systems and as a material basis for theorizing. In order to explicate
the dual role, I develop the concept of a remnant model, a material entity made from parts of the natural system(s) under
study. I present a case study of an important but neglected naturalist, Joseph Grinnell, to illustrate the extent to which
mundane practices in a museum setting constitute theorizing. I speculate that historical and sociological analyses of institutions
can play a specific role in the philosophical analysis of model-building strategies. 相似文献