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YONG-JIANG ZHANG FREDERICK C. MEINZER GUANG-YOU HAO FABIAN G. SCHOLZ SANDRA J. BUCCI FREDERICO S. C. TAKAHASHI RANDOL VILLALOBOS-VEGA JUAN P. GIRALDO KUN-FANG CAO WILLIAM A. HOFFMANN & GUILLERMO GOLDSTEIN 《Plant, cell & environment》2009,32(10):1456-1466
Size-related changes in hydraulic architecture, carbon allocation and gas exchange of Sclerolobium paniculatum (Leguminosae), a dominant tree species in Neotropical savannas of central Brazil (Cerrado), were investigated to assess their potential role in the dieback of tall individuals. Trees greater than ∼6-m-tall exhibited more branch damage, larger numbers of dead individuals, higher wood density, greater leaf mass per area, lower leaf area to sapwood area ratio (LA/SA), lower stomatal conductance and lower net CO2 assimilation than small trees. Stem-specific hydraulic conductivity decreased, while leaf-specific hydraulic conductivity remained nearly constant, with increasing tree size because of lower LA/SA in larger trees. Leaves were substantially more vulnerable to embolism than stems. Large trees had lower maximum leaf hydraulic conductance ( K leaf ) than small trees and all tree sizes exhibited lower K leaf at midday than at dawn. These size-related adjustments in hydraulic architecture and carbon allocation apparently incurred a large physiological cost: large trees received a lower return in carbon gain from their investment in stem and leaf biomass compared with small trees. Additionally, large trees may experience more severe water deficits in dry years due to lower capacity for buffering the effects of hydraulic path-length and soil water deficits. 相似文献
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P de Taxis du Po?t Y Arcand R Bernier J N Barbotin D Thomas 《Applied and environmental microbiology》1987,53(7):1548-1555
Stability of the plasmid pKK223-200 in Escherichia coli JM105 was studied for both free and immobilized cells during continuous culture. The relationship between plasmid copy number, xylanase activity, which was coded for by the plasmid, and growth rate and culture conditions involved complex interactions which determined the plasmid stability. Generally, the plasmid stability was enhanced in cultured immobilized cells compared with free-cell cultures. This stability was associated with modified plasmid copy number, depending on the media used. Hypotheses are presented concerning the different plasmid instability kinetics observed in free-cell cultures which involve the antagonistic effects of plasmid copy number and plasmid presence on the plasmid-bearing/plasmid-free cell growth rate ratio. Both diffusional limitation in carrageenan gel beads, which is described in Theoretical Analysis of Immobilized-Cell Growth, and compartmentalized growth of immobilized cells are proposed to explain plasmid stability in immobilized cells. 相似文献
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Identification of dexamethasone-binding sites on male-rat liver plasma membranes by affinity labelling. 总被引:2,自引:0,他引:2
Binding studies with [3H]dexamethasone identified two binding sites on plasma membranes prepared from the male rat liver, a low-capacity site with a KD of 7.0 nM and a higher-capacity site with a KD of 90.1 nM. Both sites exhibited glucocorticoid responsiveness and specificity for glucocorticoids and progestins. Triamcinolone acetonide, which competes well for the binding of dexamethasone to the cytosolic glucocorticoid receptor, did not compete well for the binding of [3H]dexamethasone to the plasma-membrane binding sites. The binding sites were sensitive to protease and neuraminidase treatment, and resistant to extraction with NaCl, but were extracted with the detergent Triton X-100. As these experiments indicated the presence of plasma-membrane protein components which bind glucocorticoids at physiological concentrations, affinity-labelling experiments with dexamethasone mesylate were conducted. Two peptides were specifically labelled, one at approx. Mr 66,000 and one at Mr 45,000. The Mr-66,000 peptide was not sensitive to glucocorticoids, and was extracted by NaCl, and so did not correspond to either of the sites identified in the dexamethasone-binding studies. The Mr-45,000 entity, on the other hand, resembled the dexamethasone-binding sites in its response to glucocorticoid manipulation of the animal and in its resistance to salt extraction. This peptide was not present in rat serum. Thus we have identified a plasma-membrane peptide which binds dexamethasone. Whether this peptide is involved in transport of the glucocorticoid across the plasma membrane remains to be determined. 相似文献
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小麦芽经过匀浆、沉淀、高速及超速离心、透析以及DE_(52)离子交换层析等步骤,纯化小麦芽依赖于DNA的RNA聚合酶。用α-鹅膏蕈碱抑制试验,证明得到RNA聚合酶Ⅱ。用此聚合酶Ⅱ组建的体外转录体系的研究结果表明,绒毛烟斑驳病毒的拟病毒和卫星RNA(黄瓜花叶病毒相关RNA_3)都不能利用该体系进行转录,类病毒PSTV可进行转录,但转录效率明显低于小牛胸腺DNA;α-鹅膏簟碱可抑制类病毒的转录。绒毛烟斑驳病毒拟病毒和卫星RNA都不能被转录,表明他们的复制方法与类病毒不同。 相似文献
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华东植物区系成分与日本植物间的联系 总被引:15,自引:2,他引:13
华东和日本两地为东亚地区重组成部分,同属于中国-日本森林植物亚区。两地植区物系成具有较高的相似性。两地共有连香树科(Crcidiphyllaceae)、三尖杉科(Cephalotaceae)、领春木科(Eupteleaceae)、旌节花科ǎ樱簦幔悖瑁酰颍幔悖澹幔澹┑榷翘赜锌啤;腿毡玖降毓灿惺粼迹叮福岸嗍簟H缌迹ǎ茫颍穑簦铮恚澹颍椋幔⑺荆ǎ模椋螅幔睿簦瑁酰螅⑿」炊ǎ拢澹颍悖瑁 相似文献
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星花绣线菊中的一个新二萜——绣线菊内酯B 总被引:4,自引:1,他引:3
从星花绣线菊(Spiraeajaponicavar.stellaris)根中得到1个新的Atisine型二萜,命名为绣线菊内酯B(1)。通过光谱分析测定了其结构,此外还得到了9个已知化合物,包括1个atisine型二萜-spiraminol(2)和8个二萜生物碱,spiramineA,B,C,D,F,H,P,Q。 相似文献
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强噪声暴露后听觉脑干电反应及皮层电反应的变化 总被引:5,自引:2,他引:3
为了观察噪声作用豚鼠后,在暂时性或移和永久性阈移期间,听觉末梢和听觉各级中枢电反庆的变化规律,我们进行了62d的测定。听神经电反应振幅减小29%(P<0.05),耳蜗核电反应振幅减小28%(P<0.05),上橄榄核电反应反而增加21%(P<0.05),中脑下丘的电反应振幅进而增大37%(P<0.05),听觉皮层电反应振幅却意外地增加131%(P<0.001)。这说明强噪声(125dB 150min 相似文献
10.
本研究首次发现了毛鹃花芽分化过程中的一个特殊现象──秋季侧花芽伸长生长现象。并认为充足的光照,适宜的气温(25°─26℃)及充沛的降水伴随较高的空气相对湿度是导致这种花芽伸长生长的主要环境因子。也进一步证实了毛鹃是一类较喜阳生生境的灌木花卉。 相似文献