遮荫对青桐幼苗生长性状与化学计量特征的影响

营养元素含量及化学计量比可反映植物器官营养元素的分配及互作关系,亦可反映其营养利用效率及生长环境的养分限制状况.以青桐(Firmiana platanifolia)幼苗为材料,分析4种不同光强(全光照,50％、75％和95％遮荫)对青桐幼苗生长,C、N、P、K含量及其化学计量特征的影响.结果 表明:遮荫对青桐幼苗的生长...     

双链RNA和植物对病毒的抗性

双链RNA能诱导转录后的基因沉默,是生物抵御病毒入侵、维持自身基因稳定的一种自我保护机制.把源自病毒的基因构建成反向重复结构转入植物体内,其转录出的RNA会通过分子内序列互补形成双链,将入侵病毒的同源序列降解,使转基因植株获得对病毒的高抗性.RNA干扰型抗病毒转基因植株中,转病毒基因的mRNA不存在或存在量很少,也不会翻译成有功能的病毒蛋白,因此不存在病毒RNA重组、异源包装及协生作用的潜在风险,具有较高的生物安全性.双链RNA抗病毒转基因正在成为一种高效、安全的植物抗病毒策略.     

Trade-off between number and length of remote videos for rapid assessments of reef fish assemblages

Remote underwater videos are widely employed to assess the structure and composition of reef fish assemblages but the sampling effort employed on each survey differs considerably, indicating that both the number of assessments and video length could be optimized. We searched for this optimal sampling effort in remote video samples to conduct rapid assessments of community composition and discussed the relation between number of replicates and video length, and how it impacts the method's efficiency to characterize species assemblages. Remote video recordings from tropical reefs in northeastern Brazil were used to investigate how fish species richness and composition builds across time and number of assays. Videos as short as 5 min successfully recorded species richness, requiring about five repetitions to record most species that compose 80% of the total biomass. Recording species composition required even less time in these reefs, setting a minimum of 3 min with the same five videos. By comparing the detected richness per analysed time unit, we found several shorter videos recorded for more species than a few longer videos, indicating that increasing the sampling coverage in the reef area might be better than just extending the video length for rapid assessments.     

Sexual selection on spontaneous mutations strengthens the between‐sex genetic correlation for fitness

A proposed benefit to sexual selection is that it promotes purging of deleterious mutations from populations. For this benefit to be realized, sexual selection, which is usually stronger on males, must purge mutations deleterious to both sexes. Here, we experimentally test the hypothesis that sexual selection on males purges deleterious mutations that affect both male and female fitness. We measured male and female fitness in two panels of spontaneous mutation‐accumulation lines of the fly, Drosophila serrata, each established from a common ancestor. One panel of mutation accumulation lines limited both natural and sexual selection (LS lines), whereas the other panel limited natural selection, but allowed sexual selection to operate (SS lines). Although mutation accumulation caused a significant reduction in male and female fitness in both the LS and SS lines, sexual selection had no detectable effect on the extent of the fitness reduction. Similarly, despite evidence of mutational variance for fitness in males and females of both treatments, sexual selection had no significant impact on the amount of mutational genetic variance for fitness. However, sexual selection did reshape the between‐sex correlation for fitness: significantly strengthening it in the SS lines. After 25 generations, the between‐sex correlation for fitness was positive but considerably less than one in the LS lines, suggesting that, although most mutations had sexually concordant fitness effects, sex‐limited, and/or sex‐biased mutations contributed substantially to the mutational variance. In the SS lines this correlation was strong and could not be distinguished from unity. Individual‐based simulations that mimick the experimental setup reveal two conditions that may drive our results: (1) a modest‐to‐large fraction of mutations have sex‐limited (or highly sex‐biased) fitness effects, and (2) the average fitness effect of sex‐limited mutations is larger than the average fitness effect of mutations that affect both sexes similarly.     

The pleiotropic nature of <Emphasis Type="Italic">rib80, hit1</Emphasis>, and <Emphasis Type="Italic">red6</Emphasis> mutations affecting riboflavin biosynthesis in the yeast <Emphasis Type="Italic">Pichia guilliermondii</Emphasis>

The yeast Pichia guilliermondii is capable of riboflavin overproduction under iron deficiency. The rib80, hit1, and red6 mutants of this species, which exhibit impaired riboflavin regulation, are also distinguished by increased iron concentrations in the cells and mitochondria, morphological changes in the mitochondria, as well as decreased growth rates (except for red6) and respiratory activity. With sufficient iron supply, the rib80 and red6 mutations cause a 1.5–1.8-fold decrease in the activity of such Fe-S cluster proteins as aconitase and flavocytochrome b ₂, whereas the hit1 mutation causes a six-fold decrease. Under iron deficiency, the activity of these enzymes was equally low in all of the studied strains.     

Modeling the mechanisms of acute hepatitis B virus infection

Mathematical models have been used to understand the factors that govern infectious disease progression in viral infections. Here we focus on hepatitis B virus (HBV) dynamics during the acute stages of the infection and analyze the immune mechanisms responsible for viral clearance. We start by presenting the basic model used to interpret HBV therapy studies conducted in chronically infected patients. We then introduce additional models to study acute infection where immune responses presumably play an important role in determining whether the infection will be cleared or become chronic. We add complexity incrementally and explain each step of the modeling process. Finally, we validate the model against experimental data to determine how well it represents the biological system and, consequently, how useful are its predictions. In particular, we find that a cell-mediated immune response plays an important role in controlling the virus after the peak in viral load.     

斜纹夜幼虫对食物中重金属Ni2+的积累与排泄

为明确食物中重金属离子在昆虫体内的分布和转移情况,本文采用等离子体原子发射光谱仪检测了植食性昆虫斜纹夜蛾Spodoptera litura Fabricius连续3个世代6龄幼虫对食物中过量Ni²⁺的排泄和积累情况。结果表明：大部分Ni²⁺可通过粪便排出体外;沉积在体内的Ni²⁺主要积累在中肠,部分Ni²⁺可通过中肠上皮细胞基底膜进入血淋巴,经由血淋巴的转运作用积累在脂肪体和表皮等组织中。6龄幼虫不同组织中所积累Ni²⁺的含量为中肠>脂肪体>表皮,且不同组织和粪便中的Ni²⁺都随饲料中Ni²⁺浓度的增加而增加,并存在显著的剂量-反应关系。研究结果可为进一步研究过量Ni²⁺对斜纹夜蛾幼虫的生长发育和繁殖的影响,以及斜纹夜蛾幼虫不同组织对Ni²⁺的解毒能力等提供一定依据。     

A novel anti-plant viral protein from coelomic fluid of the earthworm Eisenia foetida: purification, characterization and its identification as a serine protease

A novel protein showing strong antiviral activities against cucumber mosaic virus (CMV) and tomato mosaic virus (TMV) was purified from the coelomic fluid of the earthworm Eisenia foetida. The protein was characterized as a cold-adapted serine protease. Its molecular weight was estimated to be 27,000 by SDS-PAGE. The enzyme was most active at pH 9.5 and 40–50 °C. The protease activity at 4 °C was 60% of that obtained at the optimal temperature. The activity was suppressed by various serine protease inhibitors. Partial N-terminal amino acid sequence of the enzyme showed homology with serine proteases of earthworms, E. foetida and Lumbricus rubellus previously studied. Our results suggest that the enzyme can be applicable as a potential antiviral factor against CMV, TMV, and other plant viruses.     

Role of Some Hormones in Protein Sparing Action of Dietary Fat

Feeding rats with a fat meal caused marked reduction in the level of plasma urea and urinary output of urea and total nitrogen. Experiments were carried out to examine the possible intervention of some hormones in these phenomena. Protein sparing action of fat was exerted even in the alloxan-diabetic, adrenalectomized, hypophysectomized and thyroidectomized rats. Feeding rats with a fat meal caused no appreciable change in the level of cyclic AMP in liver and gastrocnemius muscle. The overall results obtained here are through! to suggest that the action of fat may be exerted independently of any hormones examined; insulin, glucocorticoids, cyclic AMP and other hormones excreted from adrenal, hypophysis and thyroid gland.     

An intracellular antibody can suppress tumorigenicity in Hepatitis B virus X-expressing cells

Although the hepatitis B virus X protein (HBx) is thought to play a causative role in the development of hepatocellular carcinoma, it is not yet known whether interfering with HBx function may affect the cellular transformation of HBx-expressing tumor cells. To address this question, we adopted an intracellular antibody fragment expression approach to block the function of HBx. Expression of a single-chain variable fragment (scFv) specific to HBx (designated as H7scFv) inhibited HBx-dependent cellular transactivation. Furthermore, H7scFv suppressed the growth of HBx-expressing tumor cells in both soft agar and nude mice. The suppressive effect of H7scFv on tumorigenicity appeared not to be mediated by inhibition of HBx-induced growth stimulation since the growth rate of these cells was not affected significantly by H7scFv expression. In conclusion, these data suggest that the HBx-dependent transformed phenotype is reversible and that HBx may be a good molecular target for the treatment of HBV-related tumors.This study was supported by a grant of the Korea Health 21 R&D Project, Ministry of Health& Welfare, Republic of Korea (03-PJ1-PG3-20200–0023)