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21.
Summary Two alternative estimators of individual tree leaf area (A1) area are used to derive estimates of leaf-area index (L) for 40 plots in Pinus contorta Dougl. stands. One estimator of A1 is based on the common assumption of a constant ratio between A1 and sapwood cross-sectional area at breast height (As). The second estimator of A1 accounts for tree-to-tree variation in the relation between A1 and As. The apparent relationship between stand growth and leaf-area index is strongly dependent on the way leaf area is estimated. When L is derived from a constant A1As ratio, stand growth appears to be strongly correlated with L. However, when L is based on estmates of A1 that account for tree-to-tree variation in the A1 — As relation, stand growth is seen to be only weakly related to L. Stand structure, quantified as percent live-crown, accounts for a great deal of the observed variation in leaf-area efficiency. These contrasting relationships illustrate the importance of unbiased estimates of L in interpreting the link between stand-level processes and leaf area.Utah Aggriculural Experiment Station Journal Paper No. 3333 相似文献
22.
We investigated the effect of phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator on insulin receptors and insulin action in freshly isolated and primary cultures of rat hepatocytes. PMA (1 x 10–7 M) did not alter insulin receptor numbers or affinity either acutely or chronically but within 60 minute inactivated insulin stimulated tyrosine kinase of the insulin receptor. PKC activation inhibitied insulin (1 x 10–7M) stimulation of glycogen and lipid synthesis with a decrease or no change in basal glycogenesis and lipogenesis respectively. However, PKC activation did not alter insulin stimulated or basal amino acid transport even though PCK activation inhibited insulin stimulation of the insulin. receptor tyrosine kinase. Thus, within one tissue, PKC activation has differential effect on insulin action depending on which pathway is examined. Furthermore, insulin stimulation of the insulin receptor tyrosine kinase may not be a necessary step for all insulin signaling pathways. 相似文献
23.
Application of automated DNA sizing technology for genotyping microsatellite loci. 总被引:21,自引:0,他引:21
J S Ziegle Y Su K P Corcoran L Nie P E Mayrand L B Hoff L J McBride M N Kronick S R Diehl 《Genomics》1992,14(4):1026-1031
Highly polymorphic microsatellite loci offer great promise for gene mapping studies, but fulfillment of this potential will require substantial improvements in methods for accurate and efficient genotyping. Here, we report a genotyping method based on fluorescently labeled PCR primers and size characterization of PCR products using an automated DNA fragment analyzer. We capitalize on the availability of three distinct fluorescent dyes to label uniquely loci that overlap in size, and this innovation increases by threefold the number of loci that can be analyzed simultaneously. We label size standards with a fourth dye and combine these with the microsatellite PCR products in each gel lane. Computer programs provide very rapid and accurate sizing of microsatellite alleles and efficient data management. In addition, fluorescence signals are linear over a much greater range of intensity than conventional autoradiography. This facilitates multiplexing of loci (since signal intensities often vary greatly) and helps distinguish major peaks from artifacts, thereby improving genotyping accuracy. 相似文献
24.
p140trk mRNA marks NGF-responsive forebrain neurons: evidence that trk gene expression is induced by NGF. 总被引:18,自引:0,他引:18
D M Holtzman Y Li L F Parada S Kinsman C K Chen J S Valletta J Zhou J B Long W C Mobley 《Neuron》1992,9(3):465-478
Nerve growth factor (NGF) appears to act as a neurotrophic factor for basal forebrain and caudate-putamen cholinergic neurons. The mechanism by which NGF transduces its signal in these neurons is yet to be defined. Recent data indicate that the product of the trk gene, p140trk, is a critical component of the NGF receptor. Herein, we show that p140trk mRNA is highly restricted in its distribution in the adult rat forebrain, that it is present in cholinergic neurons, and that most if not all cholinergic neurons contain p140trk mRNA. Furthermore, induction of trk expression by NGF suggests that neurotrophin-mediated up-regulation of their receptor tyrosine kinases is an important feature of their actions and that neurotrophins may regulate the activity of responsive neurons through increasing the level of their receptors. 相似文献
25.
The distribution of holly ( Ilex aquifolium ) and its habitat preferences indicate a sensitivity to low temperature, particularly when exposed to high light. Experiments were conducted to determine whether photoinhibition of photosynthesis occurs in holly leaves in the field in United Kingdom during the winter. Photosynthetic efficiency was assessed in holly leaves that were exposed to or shaded from direct sunlight using measurements of photosynthetic oxygen evolution and chlorophyll fluorescence. Field measurements were conducted over 3 weeks during January and February. Correlation of the measurements of photosynthetic efficiency with weather conditions indicated that holly was suffering photoinhibition, particularly in leaves exposed to direct sunlight. Controlled environment studies demonstrated that exposure of leaves to low temperature and high light resulted in reductions in photosynthetic efficiency; however, leaves recovered rapidly when exposed to a higher temperature and reduced light level. 相似文献
26.
The Sequence of Change within the Photosynthetic Apparatus of Wheat following Short-Term Exposure to Ozone 总被引:30,自引:1,他引:29
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The basis of inhibition of photosynthesis by single acute O3 exposures was investigated in vivo using analyses based on leaf gas exchange measurements. The fully expanded second leaves of wheat plants (Triticum aestivum L. cv Avalon) were fumigated with either 200 or 400 nanomoles per mole O3 for between 4 and 16 hours. This reduced significantly the light-saturated rate of CO2 uptake and was accompanied by a parallel decrease in stomatal conductance. However, the stomatal limitation, estimated from the relationship between CO2 uptake and the internal CO2 concentration, only increased significantly during the first 8 hours of exposure to 400 nanomoles per mole O3; no significant increase occurred for any of the other treatments. Analysis of the response of CO2 uptake to the internal CO2 concentration implied that the predominant factor responsible for the reduction in light-saturated CO2 uptake was a decrease in the efficiency of carboxylation. This was 58 and 21% of the control value after 16 hours at 200 and 400 nanomoles per mole O3, respectively. At saturating concentrations of CO2, photosynthesis was inhibited by no more than 22% after 16 hours, indicating that the capacity for regeneration of ribulose bisphosphate was less susceptible to O3. Ozone fumigations also had a less pronounced effect on light-limited photosynthesis. The maximum quantum yield of CO2 uptake and the quantum yield of oxygen evolution showed no significant decline after 16 hours with 200 nanomoles per mole O3, requiring 8 hours at 400 nanomoles per mole O3 before a significant reduction occurred. The photochemical efficiency of photosystem II estimated from the ratio of variable to maximum chlorophyll fluorescence and the atrazine-binding capacity of isolated thylakoids demonstrated that photochemical reactions were not responsible for the initial inhibition of CO2 uptake. The results suggest that the apparent carboxylation efficiency appears to be the initial cause of decline in photosynthesis in vivo following acute O3 fumigation. 相似文献
27.
Effect of light/dark cycles on expression of nitrate assimilatory genes in maize shoots and roots 总被引:8,自引:2,他引:6
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The level of nitrate reductase (NR) and nitrite reductase (NiR) varied in both shoot and root tissue from nitrate-fed Zea mays L. grown under a 16-hour light/8-hour dark regime over a 10-day period postgermination, with peak activity occurring in days 5 to 6. To study the effect of different light regimes on NR and NiR enzyme activity and mRNA levels, 6-day-old plants were grown in the presence of continuous KNO3 (10 millimolar). Both shoot NRA and mRNA varied considerably, peaking 4 to 8 hours into the light period. Upon transferring plants to continuous light, the amplitude of the peaks increased, and the peaks moved closer together. In continuous darkness, no NR mRNA or NR enzyme activity could be detected by 8 hours and 12 hours, respectively. In either a light/dark or continuous light regime, root NRA and mRNA did not vary substantially. However, when plants were placed in continuous darkness, both declined steadily in the roots, although some remained after 48 hours. Although there was no obvious cycling of NiR enzyme activity in shoot tissue, changes in mRNA mimicked those seen for NR mRNA. The expression of NR and NiR genes is affected by the light regime adopted, but light does not have a direct effect on the expression of these genes. 相似文献
28.
Daina H. Simmonds Nancy E. Long Wilfred A. Keller 《Plant Cell, Tissue and Organ Culture》1991,27(3):231-241
Protoplasts were isolated from an embryogenic cell suspension culture derived from microspores of Brassica napus cv. Jet Neuf. Protoplast yield varied with the cell suspension growth medium. Optimization of protoplast plating density, manipulation of culture medium, carbon source and medium matrix, and inclusion of Ficoll resulted in protoplast plating efficiencies close to 30%. Placement of the protoplasts close to the gas interface contributed greatly to the elevated plating efficiency. Low density cultures could be induced to regenerate calli at optimum plating efficiencies if grown in the presence of nurse culture. This is of great advantage for manipulation of individual protoplasts or for microinjection. Plants were regenerated directly from the cell suspension or from the protoplast cultures.Abbreviations BA
N6-benzyladenine
- 2,4-D
2,4-dichlorophenoxyacetic acid
- IAA
indole-3-acetic acid
- NAA
naphthaleneacetic acid 相似文献
29.
用频率为2450MHz功率密度为10mW/Cm~2(WBASAR约11.4W/kg)的微波(连续波)对置于微波暗室内的昆明种雄性小鼠急性全身照射1小时后,立即按常规方法断头,取脑,制成样品,然后用放射免疫测定法测量小鼠脑内乙酰胆碱(ACh)含量及胆碱乙酰转移酶(ChAT)活性。结果表明:照射组的ACh含量为11.6±1.4pmol/mg(脑鲜重),ChAT活性为45.4±8.7pmolACh/min.mg(脑鲜重);而对照组的分别为16.0±2.1pmol/mg和61.0±13.8pmolACh/min.mg。证明微波照射后可引起动物脑内ACh水平和ChAT活性下降,提示微波辐射对中枢胆碱能系统确有不利影响。 相似文献
30.
In the radioreceptor assay for growth hormone (RRA-GH) using [125I]iodo-hGH, hGH and human liver membrane particulate fractions as tracer, hormone standard and receptors, respectively, ovine placental lactogen (oPL) is capable of inhibiting the binding of [125I]iodo-hGH in a parallel manner with hGH and in equipotency. Similarly, in the RRA-GH by employing [125I]iodo-oPL, oPL and human liver membrane particulate fractions as tracer, hormone standard and receptors, respectively, hGH is also equipotent as oPL in inhibiting the binding of [125I]iodo-oPL in a parallel fashion. The addition of monoclonal antibodies against oPL in the assay was effective in inhibiting the binding of [125I] iodo-oPL to human liver, but could not, however, inhibit the binding of [125I]iodo-hGH to human liver. Furthermore, the addition of the monoclonal antibodies in the RRA-GH did not affect the parallelism of the oPL standard but lowered the total binding of oPL. Our studies indicate that the structure of the binding sequence in oPL which binds to the GH receptor of human liver is not identical to the equivalent sequence of hGH and that the monoclonal antibodies compete with GH receptors in human liver for the binding of oPL. 相似文献