Experimental adaptation to high and low quality environments under different scales of temporal variation

We investigated the role of the scale of temporal variation in the evolution of generalism in populations of the bacterium Pseudomonas fluorescens. Replicate populations were propagated as batch cultures for approximately 1400 generations (192 days), in either high quality media only, low quality media only, or were alternated between the two at a range of temporal scales (between 1 and 48 days). Populations evolved in alternating media showed fitness increases in both media and the rate of alternation during selection had no effect on average fitness in either media. Moreover, the fitness of these populations in high quality media was the same as for populations evolved only in high quality media and likewise for low quality media. Populations evolved only in high or low quality media did not show fitness improvements in their nonselective media. These results indicate that cost-free generalists can evolve under a wide range of temporal variation.     

Post-transcriptional regulation of ribosome accumulation during myoblast differentiation

The synthesis, accumulation and stability of rRNA were examined in embryonic quail myoblasts differentiating in cell culture. Quail myoblasts initially divide rapidly in culture, and accumulate 28S and 18S rRNA and ribosomes at a rate which maintains a constant ribosome content during cell division. After these myoblasts fuse, cell division ceases and ribosomes accumulate in fibers, but at a reduced rate which is only one fourth that in dividing myoblasts. Measurements of rRNA stability by 3H-methyl-methionine pulse-chase analysis show that 28S and 18S rRNA formed by fibers turn over with half-lives of 45 hr, and rRNA formed by myoblasts remains stable until fusion and then also turns over in fibers. Turnover of rRNA in fibers accounts for only half the reduction in ribosome accumulation following myoblast fusion. Measurements of the incorporation of 3H-adenosine into rRNA and ATP pools show that the rates of synthesis of rRNA precursor do not decrease after myoblast fuse, but half the rRNA molecules synthesized by fibers are degraded during processing. Degradation of rRNA during processing reduces the rate of formation of 28S and 18S rRNA, and together with rRNA turnover quantitatively accounts for the reduced rate of ribosome accumulation in fibers.     

Post-transcriptional control of gene expression: bacterial mRNA degradation

Many biological processes cannot be fully understood without detailed knowledge of RNA metabolism. The continuous breakdown and resynthesis of prokaryotic mRNA permit rapid production of new kinds of proteins. In this way, mRNA levels can regulate protein synthesis and cellular growth. Analysing mRNA degradation in prokaryotes has been particularly difficult because most mRNA undergo rapid exponential decay. Prokaryotic mRNAs differ in their susceptibility to degradation by endonucleases and exonucleases, possibly because of variation in their sequencing and structure. In spite of numerous studies, details of mRNA degradation are still largely unknown. This review highlights those aspects of mRNA metabolism which seem most influential in the regulation of gene expression.     

不同光环境下烟草光合特性及同化产物的积累与分配机制

为了解烟草光合特性与光合作用同化产物的积累与分配对不同光环境的适应,以盆栽烟草为试验对象,于人工气候室中设置3种光照强度[遮阴(400±15)～(500±15) μmol·m^-2·s^-1;自然光强:(800±15)～(1000±15) μmol·m^-2·s^-1;高光强:(1500±15)～(1800±15) μmol·m^-2·s^-1]系统研究光照条件对烟草光合特性及光合作用同化产物在烟株-土壤系统分配的影响.结果表明: 随着光照强度的降低,烟草各组分生物量逐渐减小,根冠比降低.净光合速率(P_n)、气孔导度(g_s)、蒸腾速率(T_r)均随光照强度的减弱呈下降趋势,胞间CO₂浓度(C_i)升高;在强光条件下烟草最大净光合速率(A_max)、光饱和点(LSP)、光补偿点(LCP)、暗呼吸速率(R_d)均达到最大值,弱光条件则具有较大的表观量子效率.光照强度影响烟草对¹³C的吸收、积累与分配,弱光条件下,烟草富集的¹³C进入到根部的比例明显较少,更多的分配到地上部.由此可知,外界光环境的变化不仅显著影响烟草叶片的光合特性与生物量积累,也使光合碳在烟株-土壤系统的分配格局发生变化.     

城市不同遮阴环境下光强和光质特征

城市的发展伴随着大量高层建筑的出现,城市建筑作为人工构筑物,形成了与自然环境不同的人工遮阴环境,这种人工环境可能会对其下生长的植物产生一定的影响。为了研究人工建筑遮阴与自然遮阴环境之间的差异,北京市典型高层建筑遮阴和冠层遮阴光环境进行了测量,发现建筑和冠层显著改变其遮阴微环境的光强和光质。两种遮阴下光合有效辐射分别为天空自然辐射的9.09%和5.50%,遮阴处的光合有效辐射均小于200μmol m~(-2)s~(-1),低于多数城市植物的光饱和点。与天空自然辐射相比,建筑遮阴处蓝光在光合有效辐射中所占比例(B/P)、蓝光与红光的比例(B/R)以及蓝光与远红光的比例(B/FR)升高,且高于冠层遮阴,红光与远红光的比例(R/FR)没有显著变化,而冠层遮阴下R/FR则低于天空自然辐射。建筑遮阴下光质的改变可能会对植物的光合产生积极作用,并可能影响到植物的形态及生理反应。窄波段和宽波段两种不同积分方法对R/FR没有显著影响,采用宽波段积分得到的B/R低于窄波段,但降低幅度很小,在植物光合生理研究方面两种积分方法可以通用。     

Photosynthetic plasticity of Phalaenopsis in response to different light environments

The ability of a plant to dynamically acclimate to different light environments is, in general, genetically determined. Phalaenopsis amabilis is a CAM orchid with heavy self-shading. The aim of this study was to find out how the photosynthetic capacity of its mature lower leaves acclimates to the low light environment, and whether it possessed a potential for reacclimation following transfer of lower leaves to higher irradiance. We found that the photosynthetic performance of the leaves of Phalaenopsis was flexibly and reversibly adjusted to growth irradiance, making it possible to improve the light environment of the plant by increasing light exposure of lower leaves and bring about a higher photosynthetic production. We have tested the effectiveness of a simple setup using mirrors to augment light from the side and thus enhanced the irradiance in the shaded area of the plant. Both photosynthesis and starch contents of leaves as well as the number of flowers per plant increased greatly.     

The evolution of sex is favoured during adaptation to new environments

Both theory and experiments have demonstrated that sex can facilitate adaptation, potentially yielding a group-level advantage to sex. However, it is unclear whether this process can help solve the more difficult problem of the maintenance of sex within populations. Using experimental populations of the facultatively sexual rotifer Brachionus calyciflorus, we show that rates of sex evolve to higher levels during adaptation but then decline as fitness plateaus. To assess the fitness consequences of genetic mixing, we directly compare the fitnesses of sexually and asexually derived genotypes that naturally occur in our experimental populations. Sexually derived genotypes are more fit than asexually derived genotypes when adaptive pressures are strong, but this pattern reverses as the pace of adaptation slows, matching the pattern of evolutionary change in the rate of sex. These fitness assays test the net effect of sex but cannot be used to disentangle whether selection on sex arises because highly sexual lineages become associated with different allele combinations or with different allele frequencies than less sexual lineages (i.e., "short-" or "long-term" effects, respectively). We infer which of these mechanisms provides an advantage to sex by performing additional manipulations to obtain fitness distributions of sexual and asexual progeny arrays from unbiased parents (rather than from naturally occurring, and thereby evolutionarily biased, parents). We find evidence that sex breaks down adaptive gene combinations, resulting in lower average fitness of sexual progeny (i.e., a short-term disadvantage to sex). As predicted by theory, the advantage to sex arises because sexually derived progeny are more variable in fitness, allowing for faster adaptation. This "long-term advantage" builds over multiple generations, eventually resulting in higher fitness of sexual types.     

金花茶叶片性状对不同光环境梯度的响应

金花茶叶片对光环境变化的响应包括质量性状和数量性状的变异。对广西南部金花茶的5个自然种群的光环境及其叶片数量性状等进行观测研究。结果显示:光照强度影响金花茶叶长和叶宽生长间的相关性,当相对光强20‰时,叶片长宽增长具有显著相关性,相关系数≥0.85;在相对光强≥20‰的环境中,相关系数明显变小,相关性不显著;低光照强度下金花茶倾向于形成短窄型叶片,高光照强度则使其倾向于形成长阔型叶片。并对该研究揭示的这种叶片数量性状变异规律在金花茶保护中的应用前景进行了探讨。     

Dual targeting of plastid division protein FtsZ to chloroplasts and the cytoplasm

FtsZ is a filament-forming protein that assembles into a ring at the division site of prokaryotic cells. As FtsZ and tubulin share several biochemical and structural similarities, FtsZ is regarded as the ancestor of tubulin. Chloroplasts--the descendants of endosymbiotic bacteria within plant cells--also harbour FtsZ. In contrast to eubacteria, plants have several different FtsZ isoforms. So far, these isoforms have only been implicated with filamentous structures, rings and networks, inside chloroplasts. Here, we demonstrate that a novel FtsZ isoform in the moss Physcomitrella patens is located not only in chloroplasts but also in the cytoplasm, assembling into rings in both cell compartments. These findings comprise the first report on cytosolic localization of a eukaryotic FtsZ isoform, and indicate that this protein might connect cell and organelle division at least in moss.     

Phytochrome control of plastid mRNA in mustard (Sinapis alba L.)

The steady-state levels of plastid RNA sequences in dark-grown and light-grown mustard (Sinapis alba L.) seedlings have been compared. Total cellular RNAs were labeled in vitro with ³²P and hybridized to separated restriction fragments of plastid DNA. Cloned DNA fragments which encode the large subunit (LS) of ribulose-1,5-bisphosphate carboxylase [3-phospho-D-glycerate carboxylase (dimerizing), EC 4.1.1.39] and a 35,000 plastid polypeptide were used as probes to assess the levels of these two plastid mRNAs. The 1.22-kilobase-pair mRNA for the 35,000 polypeptide is almost undetectable in dark-grown seedlings, but is a major plastid mRNA in light-grown seedlings. The hybridization analysis of RNA from seedlings which were irradiated with red and far-red light indicates that the level of this mRNA, but not of LS mRNA, is controlled by phytochrome.Abbreviations LS large subunit - RuBP ribulose-1,5-bisphosphate - ptDNA plastid DNA     

Stress‐responsive accumulation of plastid chaperonin 60 during seedling development

Plastid chaperonin 60 (cpn60) is a chloroplast protein, presumed to assist in assembly and folding of plastid proteins. Although molecular chaperones often accumulate significantly in response to stress, this has never been demonstrated for cpn60. In this study, the accumulation of cpn60 in Nicotiana seedlings during their development was followed under different stress conditions. It was found that cpn60 accumulates markedly in developing seedlings in response to tentoxin and several other (but not all) stresses. Cpn60 accumulates only during a narrow period of seedling development. It is proposed that cpn60 accumulation under stress is developmentally regulated.