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81.
祁连山地区植被特征及其分布规律   总被引:22,自引:0,他引:22  
分析和讨论了祁连山地区主要植被类型及其分布特征。祁连山地区随着青藏高原的强烈隆升表现为整体抬升,植被具有明显的生态地理边缘效应特征和高原地带性规律。该区植被虽然受到四周的较大影响,但各类高寒植被占有绝对优势,表现出与青藏高原植被整体明显的相似性和广泛的一致性。另一方面,本区植被也有其特殊性及与高原面存在一些差异。因此,建议把祁连山地区做为青藏高原植被区的次一级独立单元  相似文献   
82.
光系统Ⅱ反应中心D1/D2/Cytb559 在分离纯化过程中失去了电子受体QA 和QB,人工合成的质体醌可以与D1/D2/Cytb559 复合物发生重组。癸基质体醌(DPQ)与D1/D2/Cytb599 复合物的重组导致该复合物的荧光强度下降及发射光谱蓝移,同时两个与光化学活性相关的长寿命(24 ns和73 ns)荧光衰减组分占整个荧光的百分数下降,这些结果表明DPQ作为Pheo- 的电子受体,限制了P680+ ·Pheo- 的电荷重组。DPQ 的加入对D1/D2/Cytb559复合物中Chla 分子的光破坏敏感性影响不大,但β-胡萝卜素在加入DPQ 之后可以被光照破坏,这个过程可能与β-胡萝卜素的生理功能相关。  相似文献   
83.
84.
采用RNA斑点杂交分析,对21例人脑原发性胶质瘤和11例人脑膜瘤中p53,Rb和c-myc基因转录水平的表达进行研究.发现48.4%的肿瘤中p53基因表达减弱,21.9%的肿瘤中Rb基因表达减弱;71.9%的肿瘤中c-myc基因表达增强.在p53基因表达减弱的15例病例中有13例(80%)c-myc基因表达增强.结果表明,p53基因表达减弱和c-myc基因表达增强与人脑原发性肿瘤的发生有关.  相似文献   
85.
在大肠杆菌中表达了人肾液泡型H ̄+-ATPase58kD亚基的基因,利用聚合酶链式反应(PCR)得到了58kD亚基的编码片段.直接将PCR产物连接到PET载体上表达.SDS聚丙烯酰胺凝胶电泳和蛋白质印迹分析表明58kD亚基的基因得到高效表达.表达产物可达细菌细胞质蛋白的50%.  相似文献   
86.
Ethylene production in rice bronzing leaves induced by ferrous iron   总被引:4,自引:0,他引:4  
Bronzing, a nutritional disorder of rice plants which is widely distributed in tropical lowlands, was induced by dipping the cut end of rice leaves into FeSO4 solution (pH 3.5). Ethylene production; the activities of peroxidase, polyphenol oxidase, and phenylalanine ammonia-lyase; and the effects of Co2+, aminoethoxyvinylglycine, Ag+, cycloheximide, and 1-aminocyclopropane-1-carboxylate, were investigated in the course of bronzing development. It was found that ethylene production could be stimulated up to about 20 times that of the control by Fe2+, and a peak could be reached at about 24 h after incubation. The Fe2+-treated leaves also had 10-fold higher peroxidase activity than the control, whereas in vitro enzyme activity was inhibited by Fe2+. Cycloheximide retarded in vivo stimulation of peroxidase, indicating that in vivo stimulation resulted from inducing de novo synthesis of the enzyme. No changes in the activities of phenylalanine ammonia-lyase and polyphenol oxidase were observed. The results, obtained from the incubation of leaves with Co2+, aminoethoxyvinylglycine, Ag+, cycloheximide, or 1-aminocyclopropane-1-carboxylate, showed that ethylene production was the effect of Fe2+ stress and that it was not involved in the process of bronzing development, which is probably an acclimation process to enable plants to cope with stress. The accelerated peroxidase activity may be associated with bronzing development.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine - EFE ethylene forming enzyme - PAL phenylalanine ammonia-lyase - POD peroxidase - PPO polyphenol oxidase - SE standard error  相似文献   
87.
尹长民  彭贤锦 《蛛形学报》1994,3(2):104-112
报道了我国园蛛科7新种,即:云南园蛛Araneus yunnanensis、景洪金蛛Argiopejing hongensis、长垂驼蛛Cyphalonolus elongalus、石门壮头蛛Chorizopes shimenensis、勐海曲腹蛛Cyrlarachne menghaiensis 、文山肥蛛Larinia wenshanensis 和十字亮腹蛛Singa cruciformis。  相似文献   
88.
Cell cycle regulation of the p34cdc2 inhibitory kinases.   总被引:15,自引:4,他引:11       下载免费PDF全文
In cells of higher eukaryotic organisms the activity of the p34cdc2/cyclin B complex is inhibited by phosphorylation of p34cdc2 at two sites within its amino-terminus (threonine 14 and tyrosine 15). In this study, the cell cycle regulation of the kinases responsible for phosphorylating p34cdc2 on Thr14 and Tyr15 was examined in extracts prepared from both HeLa cells and Xenopus eggs. Both Thr14- and Tyr15- specific kinase activities were regulated in a cell cycle-dependent manner. The kinase activities were high throughout interphase and diminished coincident with entry of cells into mitosis. In HeLa cells delayed in G2 by the DNA-binding dye Hoechst 33342, Thr14- and Tyr15-specific kinase activities remained high, suggesting that a decrease in Thr14- and Tyr15- kinase activities may be required for entry of cells into mitosis. Similar cell cycle regulation was observed for the Thr14/Tyr15 kinase(s) in Xenopus egg extracts. These results indicate that activation of CDC2 and entry of cells into mitosis is not triggered solely by activation of the Cdc25 phosphatase but by the balance between Thr14/Tyr15 kinase and phosphatase activities. Finally, we have detected two activities capable of phosphorylating p34cdc2 on Thr14 and/or Tyr15 in interphase extracts prepared from Xenopus eggs. An activity capable of phosphorylating Tyr15 remained soluble after ultracentrifugation of interphase extracts whereas a second activity capable of phosphorylating both Thr14 and Tyr15 pelleted. The pelleted fraction contained activities that were detergent extractable and that phosphorylated p34cdc2 on both Thr14 and Tyr15. The Thr14- and Tyr15-specific kinase activities co-purified through three successive chromatographic steps indicating the presence of a dual-specificity protein kinase capable of acting on p34cdc2.  相似文献   
89.
Addition of polyamines or their analogs to newly confluent LLC-PK1 cells resulted in down-regulation of Na+-glucose transport (symport) activity. Polyamines prevented the induction of this symporter by the differentiation inducer hexamethylene bisacetamide (HMBA) but did not influence induction by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). Partial depletion of endogenous polyamines after addition of α -difluoromethylornithine (DFMO) resulted in a 4 to 5-fold increase in symporter expression. Symporter induction by either HMBA or DFMO was inhibited by the protein kinase inhibitor H-7 but H-7 did not affect symporter induction by IBMX. Changes in symporter activity were accompanied by changes in levels of the 75 kD symporter subunit detected by Western blot. Cultures exposed to HMBA exhibited reduced levels of ornithine decarboxylase activity. Our results suggest that induction of symporter expression by HMBA may be mediated in part by its effects on polymine metabolism, and point to parallel roles of polyamines and cyclic AMP in regulating the expression of this physiologically important renal transport system. © 1993 Wiley-Liss, Inc.  相似文献   
90.
A significant increase in reactive nitrogen (N) added to terrestrial ecosystems through agricultural fertilization or atmospheric deposition is considered to be one of the most widespread drivers of global change. Modifying biomass allocation is one primary strategy for maximizing plant growth rate, survival, and adaptability to various biotic and abiotic stresses. However, there is much uncertainty as to whether and how plant biomass allocation strategies change in response to increased N inputs in terrestrial ecosystems. Here, we synthesized 3516 paired observations of plant biomass and their components related to N additions across terrestrial ecosystems worldwide. Our meta-analysis reveals that N addition (ranging from 1.08 to 113.81 g m−2 year−1) increased terrestrial plant biomass by 55.6% on average. N addition has increased plant stem mass fraction, shoot mass fraction, and leaf mass fraction by 13.8%, 12.9%, and 13.4%, respectively, but with an associated decrease in plant reproductive mass (including flower and fruit biomass) fraction by 3.4%. We further documented a reduction in plant root-shoot ratio and root mass fraction by 27% (21.8%–32.1%) and 14.7% (11.6%–17.8%), respectively, in response to N addition. Meta-regression results showed that N addition effects on plant biomass were positively correlated with mean annual temperature, soil available phosphorus, soil total potassium, specific leaf area, and leaf area per plant. Nevertheless, they were negatively correlated with soil total N, leaf carbon/N ratio, leaf carbon and N content per leaf area, as well as the amount and duration of N addition. In summary, our meta-analysis suggests that N addition may alter terrestrial plant biomass allocation strategies, leading to more biomass being allocated to aboveground organs than belowground organs and growth versus reproductive trade-offs. At the global scale, leaf functional traits may dictate how plant species change their biomass allocation pattern in response to N addition.  相似文献   
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