黄土高原子午岭油松林的种子雨和土壤种子库动态

对黄土高原区子午岭不同林龄(18a、29a、40a、54a)油松(Pinus tabulaeformis carr.)人工林及天然林(约75a)的种子雨和土壤种子库进行了研究.结果表明,该区油松种子雨一般从每年9月初开始,一直到11月底结束,种子雨降落历程与林龄大小有关,种子雨发生时间和降落高峰期有所不同.不同林龄的油松种子雨强度不同,种子雨总量大小顺序为:40a人工林((489 9±8.64)粒· m-2)＞29a人工林((346.8±7.45)粒· m-2)＞54a人工林((327.1±8.13)粒· m-2)＞天然林((146.9±5.25)粒· m-2)＞18a人工林((78.1±2.72)粒· m-2).种子雨总量随林龄的增加而增加,约40a时达到高峰,种子雨活力也以40a时最高.不同林龄油松林土壤种子库存在显著差异,其中18a人工林种子库最小,40a人工林种子库最大.从种子雨降落到次年4月,5种林分土壤种子库总量下降了42.34%～53.59%,空粒种子增加了26.72%～48.69%;从4月到8月份种子腐烂率由10.28%～13 62%增加到57.25%～63.28%.动物的搬运、取食和种子腐烂死亡是种子库损耗的主要因素.土壤种子库中的油松种子主要集中在枯枝落叶层,其次为0～2cm层,2～10cm层种子最少.到8月中旬,土壤中98.26%的油松种子都已丧失活性.不同林分下油松幼苗的密度差异较大,40a人工林下幼苗最多,其余依次为29a人工林、54a人工林和天然林,18a人工林下的实生苗极少,幼苗死亡率极高.在一定龄级范围内,人工林结实能力和更新潜力随林龄增加而增加,40a时更新潜力最大.虽然有大量种子下落,但由于种子大量损耗和幼苗死亡,通过环境筛作用而最终可以成熟的个体数量十分有限.     

洪湖生态环境的化学结构

本文探讨了化学元素在洪湖水、植物、沉积物中的分布,在此基础上分析了水生植物对元素的吸收特征及元素在生态系统中的贮存和迁移规律。指出湖水中Ｃａ￣（２＋）和是主要的阳离子和阴离子,湖水酸容纳能力在１．２×１０￣（－３）－２．０×１０￣（－３）ｍｏｌ／ｌＨ￣＋之间,水化学的稳定性受到碳酸盐地球化学平衡过程的控制;湖中水生植物具有富集Ｃ、Ｎ、Ｋ、Ｃａ和Ｃｄ的性质,并导致这些元素在沉积物表层集累;系统中Ｃ多存在于植物体中,Ｎ、Ｐ、Ｋ、Ｃａ和Ｍｇ多存在于沉积物中,沉积物分室是营养元素主要的贮存库。     

Abscisic acid and 14-3-3 proteins control K channel activity in barley embryonic root

Germination of seeds proceeds in general in two phases, an initial imbibition phase and a subsequent growth phase. In grasses like barley, the latter phase is evident as the emergence of the embryonic root (radicle). The hormone abscisic acid (ABA) inhibits germination because it prevents the embryo from entering and completing the growth phase. Genetic and physiological studies have identified many steps in the ABA signal transduction cascade, but how it prevents radicle elongation is still not clear. For elongation growth to proceed, uptake of osmotically active substances (mainly K(+)) is essential. Therefore, we have addressed the question of how the activity of K(+) permeable ion channels in the plasma membrane of radicle cells is regulated under conditions of slow (+ABA) and rapid germination (+fusicoccin). We found that ABA arrests radicle growth, inhibits net K(+) uptake and reduces the activity of K(+) (in) channels as measured with the patch-clamp technique. In contrast, fusicoccin (FC), a well-known stimulator of germination, stimulates radicle growth, net K(+) uptake and reduces the activity of K(+) (out) channels. Both types of channels are under the control of 14-3-3 proteins, known as integral components of signal transduction pathways and instrumental in FC action. Intriguingly, 14-3-3 affected both channels in an opposite fashion: whereas K(+) (in) channel activity was fully dependent upon 14-3-3 proteins, K(+) (out) channel activity was reduced by 14-3-3 proteins by 60%. Together with previous data showing that 14-3-3 proteins control the activity of the plasma membrane H(+)-ATPase, this makes 14-3-3 a prime candidate for molecular master regulator of the cellular osmo-pump. Regulation of the osmo-pump activity by ABA and FC is an important mechanism in controlling the growth of the embryonic root during seed germination.     

Engineering proteins with enhanced mechanical stability by force-specific sequence motifs

Use of atomic force microscopy (AFM) has recently led to a better understanding of the molecular mechanisms of the unfolding process by mechanical forces; however, the rational design of novel proteins with specific mechanical strength remains challenging. We have approached this problem from a new perspective that generates linear physical–chemical properties (PCP) motifs from a limited AFM data set. Guided by our linear sequence analysis, we designed and analyzed four new mutants of the titin I1 domain with the goal of increasing the domain's mechanical strength. All four mutants could be cloned and expressed as soluble proteins. AFM data indicate that at least two of the mutants have increased molecular mechanical strength. This observation suggests that the PCP method is useful to graft sequences specific for high mechanical stability to weak proteins to increase their mechanical stability, and represents an additional tool in the design of novel proteins besides steered molecular dynamics calculations, coarse grained simulations, and ?‐value analysis of the transition state. Proteins 2012; © 2011 Wiley Periodicals, Inc.     

Solution structure of the c-terminal dimerization domain of SARS coronavirus nucleocapsid protein solved by the SAIL-NMR method

The C-terminal domain (CTD) of the severe acute respiratory syndrome coronavirus (SARS-CoV) nucleocapsid protein (NP) contains a potential RNA-binding region in its N-terminal portion and also serves as a dimerization domain by forming a homodimer with a molecular mass of 28 kDa. So far, the structure determination of the SARS-CoV NP CTD in solution has been impeded by the poor quality of NMR spectra, especially for aromatic resonances. We have recently developed the stereo-array isotope labeling (SAIL) method to overcome the size problem of NMR structure determination by utilizing a protein exclusively composed of stereo- and regio-specifically isotope-labeled amino acids. Here, we employed the SAIL method to determine the high-quality solution structure of the SARS-CoV NP CTD by NMR. The SAIL protein yielded less crowded and better resolved spectra than uniform ¹³C and ¹⁵N labeling, and enabled the homodimeric solution structure of this protein to be determined. The NMR structure is almost identical with the previously solved crystal structure, except for a disordered putative RNA-binding domain at the N-terminus. Studies of the chemical shift perturbations caused by the binding of single-stranded DNA and mutational analyses have identified the disordered region at the N-termini as the prime site for nucleic acid binding. In addition, residues in the β-sheet region also showed significant perturbations. Mapping of the locations of these residues onto the helical model observed in the crystal revealed that these two regions are parts of the interior lining of the positively charged helical groove, supporting the hypothesis that the helical oligomer may form in solution.     

Competing phytoplankton undermines allelopathy of a bloom-forming dinoflagellate

Biotic interactions in the plankton can be both complex and dynamic. Competition among phytoplankton is often chemically mediated, but no studies have considered whether allelopathic compounds are modified by biotic interactions. Here, we show that compounds exuded during Karenia brevis blooms were allelopathic to the cosmopolitan diatom Skeletonema costatum, but that bloom allelopathy varied dramatically among collections and years. We investigated several possible causes of this variability and found that neither bloom density nor concentrations of water-borne brevetoxins correlated with allelopathic potency. However, when we directly tested whether the presence of competing phytoplankton influenced bloom allelopathy, we found that S. costatum reduced the growth-inhibiting effects of bloom exudates, suggesting that S. costatum has a mechanism for undermining K. brevis allelopathy. Additional laboratory experiments indicated that inducible changes to K. brevis allelopathy were restricted to two diatoms among five sensitive phytoplankton species, whereas five other species were constitutively resistant to K. brevis allelopathy. Our results suggest that competitors differ in their responses to phytoplankton allelopathy, with S. costatum exhibiting a previously undescribed method of resistance that may influence community structure and alter bloom dynamics.     

Direct action of endocrine disrupting chemicals on human sperm

Synthetic endocrine disrupting chemicals (EDCs), omnipresent in food, household, and personal care products, have been implicated in adverse trends in human reproduction, including infertility and increasing demand for assisted reproduction. Here, we study the action of 96 ubiquitous EDCs on human sperm. We show that structurally diverse EDCs activate the sperm‐specific CatSper channel and, thereby, evoke an intracellular Ca²⁺ increase, a motility response, and acrosomal exocytosis. Moreover, EDCs desensitize sperm for physiological CatSper ligands and cooperate in low‐dose mixtures to elevate Ca²⁺ levels in sperm. We conclude that EDCs interfere with various sperm functions and, thereby, might impair human fertilization.     

Random coil chemical shifts in acidic 8 M urea: Implementation of random coil shift data in NMRView

Studies of proteins unfolded in acid or chemical denaturant can help in unraveling events during the earliest phases of protein folding. In order for meaningful comparisons to be made of residual structure in unfolded states, it is necessary to use random coil chemical shifts that are valid for the experimental system under study. We present a set of random coil chemical shifts obtained for model peptides under experimental conditions used in studies of denatured proteins. This new set, together with previously published data sets, has been incorporated into a software interface for NMRView, allowing selection of the random coil data set that fits the experimental conditions best.     

Halting Regime Shifts in Floristically Intact Tropical Forests Deprived of Their Frugivores

Ecological restoration typically focuses on promoting vegetation recovery in degraded habitat or reintroducing endangered animals to enhance their regional or global persistence. Here, we argue that attention should also be devoted to vertebrate reintroductions in overhunted but floristically intact tropical forests in order to prevent insidious regime shifts in these systems. Growing evidence suggests that tropical forests deprived of seed‐dispersing animals exhibit replacement of fleshy fruiting trees by species with abiotic seed dispersal. Left unchecked, this process could eventually render the forest uninhabitable by frugivores through reduced density and diversity of their food plants. In tropical areas where hunting can be controlled, we contend that frugivore reintroduction, regulation of wild fruit harvest by humans, and outplanting of native fruiting trees should be deployed as management tools long before the systems are in need of traditional habitat restoration.     

Mapping of quantitative trait loci for clinical–chemical traits in swine

Clinical–chemical traits are diagnostic parameters essential for characterization of health and disease in veterinary practice. The traits show significant variability and are under genetic control, but little is known about the fundamental genetic architecture of this variability, especially in swine. We have identified QTL for alkaline phosphatase (ALP), lactate (LAC), bilirubin (BIL), creatinine (CRE) and ionized sodium (Na⁺), potassium (K⁺) and calcium (Ca⁺⁺) from the serum of 139 F₂ pigs from a Meishan/Pietrain family before and after challenge with Sarcocystis miescheriana , a protozoan parasite of muscle. After infection, the pigs passed through three stages representing acute disease, subclinical disease and chronic disease. Forty-two QTL influencing clinical–chemical traits during these different stages were identified on 15 chromosomes. Eleven of the QTL were significant on a genome-wide level; 31 QTL were chromosome-wide significant. QTL showed specific health/disease patterns with respect to the baseline values of the traits as well as the values obtained through the different stages of disease. QTL influencing different traits at different times were found primarily on chromosomes 1, 3, 7 and 14. The most prominent QTL for the investigated clinical–chemical traits mapped to SSC3 and 7. Baseline traits of ALP, LAC, BIL, Ca⁺⁺ and K⁺ were influenced by QTL regions on SSC3, 6, 7, 8 and 13. Single QTL explained up to 21.7% of F₂ phenotypic variance. Our analysis confirms that variation of clinical–chemical traits is associated with multiple chromosomal regions.