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1.
Copper is an essential yet toxic metal ion. To satisfy cellular requirements, while, at the same time, minimizing toxicity,
complex systems of copper trafficking have evolved in all cell types. The best conserved and most widely distributed of these
involve Atx1-like chaperones and P1B-type ATPase transporters. Here, we discuss current understanding of how these chaperones bind Cu(I) and transfer it to the
Atx1-like N-terminal domains of their cognate transporter. 相似文献
2.
T Brun 《Journal of biosocial science》1992,24(3):325-333
The paper reviews methods, and their difficulties, in the measurement of the daily energy expenditure of rural women under field conditions in developing countries. Since all methods need to be validated against a reference method which is usually based on indirect calorimetry, examples of the use of this technique are given. The energy costs of most agricultural and daily tasks of rural women in developing countries have been measured. Large intra- and inter-individual variations in the cost of a single activity occur, so repeated measurements are needed to obtain a valid mean energy cost for a specific activity for a homogeneous group of individuals. Much work remains to be done on the assessment of the duration and the intensity of the physical activity of the rural adolescent and adult female population. Studies indicate that the workload of most rural women in developing countries is excessive and frequently associated with acute poverty. 相似文献
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4.
Résumé La CoccinelleSerangium parcesetosum Sicard originaire de l'Inde a été importée en France en 1985 de Géorgie soviétique où elle avait été introduite pour lutter
contre l'Aleurode des CitrusDialeurodes citri Ashmead. Les premiers lachers ont été effectués sur la C?te d'Azur et en Corse où elle semble désormais bien acclimatée.
相似文献
5.
Relationship of endogenous abscisic Acid to sucrose level and seed growth rate of soybeans 总被引:15,自引:1,他引:14 下载免费PDF全文
It has been proposed that abscisic acid (ABA) may stimulate sucrose transport into filling seeds of legumes, potentially regulating seed growth rate. The objective of this study was to determine whether the rate of dry matter accumulation in seeds of soybeans (Glycine max L.) is correlated with the endogenous levels of ABA and sucrose in those sinks. The levels of ABA and sucrose in seed tissues were compared in nine diverse Plant Introduction lines having seed growth rates ranging from 2.5 to 10.0 milligrams dry weight per seed per day. At 14 days after anthesis (DAA), seeds of all genotypes contained less than 2 micrograms of ABA per gram fresh weight. Levels of ABA increased rapidly, however, reaching maxima at 20 to 30 DAA, depending upon tissue type and genotype. ABA accumulated first in seed coats and then in embryos, and ABA maxima were higher in seed coats (8 to 20 micrograms per gram fresh weight) than in embryos (4 to 9 micrograms per gram fresh weight. From 30 to 50 DAA, ABA levels in both tissues decreased to less than 2 micrograms per gram fresh weight. Levels of sucrose were also low early in development, less than 10 milligrams per gram fresh weight at 14 DAA. However, by 30 DAA, sucrose levels in seed coats had increased to 20 milligrams per gram fresh weight and remained fairly constant for the remainder of the filling period. In contrast, sucrose accumulated in embryos throughout the filling period, reaching levels greater than 40 milligrams per gram fresh weight by 50 DAA. Correlation analyses indicated that the level of ABA in seed coats and embryos was not directly correlated to the level of sucrose measured in those tissues or to the rate of seed dry matter accumulation during the linear filling period. Rather, the ubiquitous pattern of ABA accumulation early in development appeared to coincide with water uptake and the rapid expansion of cotyledons occurring at that time. Whole tissue sucrose levels in embryos and seed coats, as well as sucrose levels in the embryo apoplast, were generally not correlated with the rate of dry matter accumulation. Thus, it appears that, in this set of diverse soybean genotypes, seed growth rate was not limited by endogenous concentrations of ABA or sucrose in reproductive tissues. 相似文献
6.
The initial (F0), maximal (FM) and steady-state (FS) levels of chlorophyll fluorescence emitted by intact pea leaves exposed to various light intensities and environmental conditions, were measured with a modulated fluorescence technique and were analysed in the context of a theory for the energy fluxes within the photochemical apparatus of photosynthesis. The theoretically derived expressions of the fluorescence signals contain only three terms, X=J2p2F/(1–G), Y=T/(1–G) and V, where V is the relative variable fluorescence, J2 is the light absorption flux in PS II, p2F is the probability of fluorescence from PS II, G and T are, respectively, the probabilities for energy transfer between PS II units and for energy cycling between the reaction center and the chlorophyll pool: F0=X, FM=X/(1–Y) and FS=X(1+(YV/(1–Y))). It is demonstrated that the amplitudes of the previously defined coefficients of chlorophyll fluorescence quenching, qP and qN, reflect, not just photochemical (qP) or nonphotochemical (qN) events as implied in the definitions, but both photochemical and nonphotochemical processes of PS II deactivation. The coefficient qP is a measure of the ratio between the actual macroscopic quantum yield of photochemistry in PS II (41-1) in a given light state and its maximal value measured when all PS II traps are open (41-2) in that state, with 41-3 and 41-4. When the partial connection between PS II units is taken into consideration, 1-qP is nonlinearily related to the fraction of closed reaction centers and is dependent on the rate constants of all (photochemical as well as nonphotochemical) exciton-consuming processes in PS II. On the other hand, 1-qN equals the (normalized) ratio of the rate constant of photochemistry (k2b) to the combined rate constant (kN) of all the nonphotochemical deactivation processes excluding the rate constant k22 of energy transfer between PS II units. It is demonstrated that additional (qualitative) information on the individual rate constants, kN-k22 and k2b, is provided by the fluorescence ratios 1/FM and (1/F0)–(1/FM), respectively. Although, in theory, 41-5 is determined by the value of both k2b and kN-k22, experimental results presented in this paper show that, under various environmental conditions, 41-6 is modulated largely through changes in k
N, confirming the idea that PS II quantum efficiency is dynamically regulated in vivo by nonphotochemical energy dissipation.Abbreviations Chl
chlorophyll
- F0, FM and FS
initial, maximal and steady-state levels of modulated Chl fluorescence emitted by light-adapted leaves
- PS I and II
photosystem I and II
- qP and qN
(previously defined) photochemical and nonphotochemical components of Chl fluorescence quenching 相似文献
7.
Pregnant sows were injected subcutaneously (s.c.) or intramuscularly (i.m.) with a barium selenate suspension (0.5–1.0 mg Se/kg body weight (b.w.)) and together with control animals fed a commercial diet. No response to the injection was seen either in blood selenium levels or in glutathione peroxidase (GSH-Px) activity in the sows. There was, however, a significant difference in these parameters between piglets born from treated dams and control animals. This status was maintained during the nursing period. In another experiment pigs (20 kg b.w.) on a Se-deficient diet were injected s.c. and i.m. with barium selenate (2.5 mg Se/kg b.w.). The treated groups maintained their blood levels of selenium and GSH-Px activity, although the selenium values in the group treated intramuscularly started to decline after 4 weeks. Organ samples from both groups were equal with regard to selenium at the time of slaughter while the control group showed a rapid decline both in blood selenium levels and GHS-Px activity. 相似文献
8.
Nucleotide sequence of a Xenopus laevis mitochondrial DNA fragment containing the D-loop, flanking tRNA genes and the apocytochrome b gene 总被引:8,自引:0,他引:8
Extensive corrections of the nucleotide sequence of the Xenopus laevis mitochondrial (mt) displacement (D) loop and surrounding genes [Wong et al., Nucl. Acids Res. 11 (1983) 4977-4995] are reported, including addition of two stretches of nucleotides and 60 scattered modifications. The additional sequences presented here correspond to the apocytochrome b gene, the tRNAGlu gene and part of URF6. This allows us to propose a conformational model for the X. laevis apocytochrome b protein and also permits comparisons with mammalian mtDNA. The D-loop sequence is poorly conserved except for sequences involved in the regulation of the mt genome (conserved sequence blocks and the DNA polymerase stop sequences). On the other hand, all genes show marked conservation both of their nucleotide sequence and their respective location on the mt genome. Organization of the genetic information described for mammalian mtDNA also holds for the X. laevis mtDNA. This result strongly suggests that all animal vertebrate mtDNAs have followed the same evolutionary pathway. 相似文献
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