不同氮效率水稻全生育期内对增硝营养的响应及其生理机制

通过添加硝化抑制剂（二氰胺,DCD）来控制硝化作用的水培试验方法,研究了氮高效水稻品种南光和氮低效水稻品种ELIO的籽粒产量对增硝营养（NH4＋∶NO3-比例为100∶0和75∶25）的响应,同时从产量构成、不同生育时期水稻生长、氮素吸收和同化4个方面研究了造成其产量差异的生理机制。结果表明：增NO3-营养可以显著促进氮高效水稻品种南光的生长,从而使其籽粒产量水平提高21%,而对氮低效水稻品种ELIO的籽粒产量没有显著影响。进一步分析表明：在增NO3-营养条件下,南光的穗粒数增加了25%,结实率增加了16%,而氮低效水稻品种ELIO的结实率和穗粒数在两种营养条件下没有显著变化;增NO3-营养可以促进南光对氮素的吸收,使其在苗期、分蘖盛期、齐穗期和成熟期对氮素的吸收量平均增加了36%,进而促进了其生长,干物质积累量在四个生育时期平均增加了30%;南光叶片硝酸还原酶和根系谷氨酰胺合成酶的活力在增硝营养条件下分别增加了100%和95%,说明增硝营养促进了南光对NH4＋和NO3-的同化利用。与氮低效水稻品种（ELIO）相比,氮高效水稻品种（南光）对增硝营养表现出较强的生理响应。     

Simplified Velocity Equations for Characterizing the Partial Inhibition or Nonessential Activation of Bireactant Enzymes

The steady state velocity equation for a bireactant enzyme in the presence of a partial inhibitor or nonessential activator, M, contains squared substrate concentration and higher-ordered M concentration terms. The equation is too complex to be useful in kinetic analyses. Simplification by the method of Cha (J. Biol. Chem. 243, 820–825 (1968)) eliminates squared substrate concentration terms, but retains higher-ordered terms in [M]. It is shown that if strict equilibrium is assumed between free E, M, and EM and for all but one other M-binding reaction, a velocity equation is obtained for an ordered bireactant enzyme that is first degree in all ligands in the absence of products. The equation is an approximation (because it was derived assuming only one M-binding reaction in the steady state), but it contains five inhibition (or activation) constants associated with M, all of which can be obtained by diagnostic replots and/or curve-fitting procedures. The equation also provides a framework for obtaining limiting constants (V¹_max, K¹_ia, K¹_mA,K¹_mB) that characterize the enzyme at saturating M. The same approach is applicable to an enzyme that catalyzes a steady state ping pong reaction.     

GROUP FORMATION AND THE EVOLUTION OF SOCIALITY

In spite of its intrinsic evolutionary instability, altruistic behavior in social groups is widespread in nature, spanning from organisms endowed with complex cognitive abilities to microbial populations. In this study, we show that if social individuals have an enhanced tendency to form groups and fitness increases with group cohesion, sociality can evolve and be maintained in the absence of actively assortative mechanisms such as kin recognition or nepotism toward other carriers of the social gene. When explicitly taken into account in a game‐theoretical framework, the process of group formation qualitatively changes the evolutionary dynamics with respect to games played in groups of constant size and equal grouping tendencies. The evolutionary consequences of the rules underpinning the group size distribution are discussed for a simple model of microbial aggregation by differential attachment, indicating a way to the evolution of sociality bereft of peer recognition.     

Accurate prediction of human drug toxicity: a major challenge in drug development

Over the past decades, a number of drugs have been withdrawn or have required special labeling due to adverse effects observed post-marketing. Species differences in drug toxicity in preclinical safety tests and the lack of sensitive biomarkers and nonrepresentative patient population in clinical trials are probable reasons for the failures in predicting human drug toxicity. It is proposed that toxicology should evolve from an empirical practice to an investigative discipline. Accurate prediction of human drug toxicity requires resources and time to be spent in clearly defining key toxic pathways and corresponding risk factors, which hopefully, will be compensated by the benefits of a lower percentage of clinical failure due to toxicity and a decreased frequency of market withdrawal due to unacceptable adverse drug effects.     

THE SELECTION BARRIER BETWEEN POPULATIONS SUBJECT TO STABILIZING SELECTION

The introgression of genes carried by a small group of immigrants is studied. The recipient and the donor populations differ at several autosomal loci subject to weak selection, and two allelic forms of each gene are considered. Fitness variation is determined by additive allelic effects, by dominance effects, and by two-locus additive-by-additive epistatic interaction of the effects of the alleles. The fate of the group of immigrants is quantified by the selection barrier that describes the cumulative mean fitness of the hybrids and hybrid descendants relative to the fitness of the resident population. The monomorphic and the polymorphic loci of the recipient population contribute differently to the selection barrier. If the genetic difference between recipient and donor population is small, then the contribution of the monomorphic loci is dominated by a positive term dependent on the difference in gene frequencies. The contribution of the polymorphic loci depends only on the difference of the leading order in the pairwise linkage disequilibria between the two populations. This contribution may be positive or negative; and, thus, polymorphic loci may either contribute to the barrier or inflate the introgression.     

Binding of vitellogenin to membranes isolated from mosquito ovaries

The presence of specific receptors for vitellogenin (Vg) in ovary membranes of the mosquito, Aedes aegypti, was demonstrated by an in vitro binding assay. The binding reaction, which is dependent on pH and Ca2+, uses 4 micrograms membrane protein, 35S-Vg labeled metabolically by fat body culture in vitro, and unlabeled vitellin (Vn) for competition. At pH 7.0 and in the presence of 5 mM Ca2+, the binding of Vg to its receptor reaches equilibrium within 60-90 min at both 4 and 25 degrees C. The binding is specific to membranes prepared only from ovaries. While mosquito Vg and Vn bind with equal affinity to Vg receptors on ovary membranes, neither locust Vg nor mouse IgG has any measurable affinity towards these sites. Nonlinear least square analysis of the saturation isotherms is consistent with the presence of a single class of Vg receptors on ovary membranes with a dissociation constant (Kd) of 0.18 microM.     

An Appraisal of Tidal Activity Rhythms

Organisms of the marine littoral zone experience a much wider range of periodicities in their environment than do their terrestrial counterparts. Tidal cycles of semidiurnal, diurnal, lunar, and semilunar frequencies may all recur at the same locality, in addition to the diel cycle of light and darkness. The relationship of endogenous activity patterns to the prevailing geophysical variables thus poses problems for the temporal organization of the organism. The way in which intertidal animals synchronize their behaviour and physiology to such a diversely fluctuating environment, and the efficacy of different environmental factors as entraining agents is considered. Evidence pertaining to the endogenous control mechanisms, both physiological and behavioural, is reviewed, and the organization of the endogenous time-keeping system discussed in terms of identifiable oscillators of different frequencies.     

Branches in the lines of descent: Charles Darwin and the evolution of the species concept

Charles Darwin introduced a novel idea into the concept of species, namely that species are branches in the lines of descent (segments of population lineages). In addition to this novel evolutionary component, Darwin's species concept also retained an older taxonomic component, namely the view that the species category is a taxonomic rank; moreover, he adopted amount of difference as a criterion for ranking lineages as species. Subsequent biologists retained both components of Darwin's species concept, although they replaced Darwin's ranking criterion with ranking criteria that either are more objectively defined or relate more directly to the biological bases of lineage separation and divergence. Numerous alternative ranking criteria were proposed, resulting in a proliferation of species definitions and a controversy concerning the concept of species. That controversy can be resolved by distinguishing more explicitly between the theoretical concept of species and the operational criteria that are used to apply the concept in practice. By viewing the various alternative ranking criteria as operational indicators of lineage separation rather than necessary properties of species, the conflicts among competing species concepts are eliminated, resulting in a unified concept of species. A brief examination of the history of biology reveals that an important shift related to the unified species concept has been emerging ever since Darwin reformulated the concept of species with an evolutionary basis. The species category is effectively being decoupled from the hierarchy of taxonomic ranks and transferred to the hierarchy of biological organization. Published 2011. This article is a US Government work and is in the public domain in the USA. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 19–35.     

Open-ITC: an alternate computational approach to analyze the isothermal titration calorimetry data of complex binding mechanisms

Isothermal titration calorimetry (ITC) is an important technique used in quantitatively analyzing the global mechanism of protein-protein or protein-ligand interactions through thermodynamic measurements. Among different binding mechanisms, the parallel and ligand induced protein oligomerization mechanisms are technically difficult to analyze compared with a sequential binding mechanism. Here, we present a methodology implemented as a program "Open-ITC" that eliminates the need for exact analytical expressions for free ligand concentrations [L] and mole fractions of bound ligand θ that are required for the thermogram analysis. Adopting a genetic algorithm-based optimization, the thermodynamic parameters are determined, and its standard error is evaluated at the global minimum by calculating the Jacobian matrix. This approach yielded a statistically consistent result for a single-site and a two-site binding protein-ligand system. Further, a comparative simulation of a two-step sequential, a parallel, and a ligand induced oligomerization model revealed that their mechanistic differences are discernable in ITC thermograms, only if the first binding step is weaker compared with the second binding step (K(1) 相似文献