The Oil Bodies of Liverworts: Unique and Important Organelles in Land Plants

Oil bodies of liverworts are intracellular organelles bounded by a single unit membrane containing lipophilic globules suspended in a proteinaceous matrix. They are a prominent and highly distinctive organelle uniquely found in liverworts. Although they have been widely used in taxonomy and chemosystematics, and many of their secondary metabolites are known to be bioactive and are considered as potential sources of medicines, their origin, development and function still remain poorly understood. Recently, biochemical studies have indicated that the isoprenoid biosynthetic pathways in liverworts are similar to those of the seed plants and that oil bodies of Marchantia polymorpha contain a protein complex immunologically related to plastid and cytosolic enzymes of isoprenoid synthesis. Cytoplasmic lipid droplets lacking a bounding membrane have recently been recognized as important dynamic organelles playing active roles in cell physiology. Structural proteins, covering the surface of the lipid droplets and preventing them coalescing during desiccation, have been found in seed plants and also in the moss Physcomitrella patens. However, whether liverwort oil bodies play a dynamic role in cell metabolism, in addition to their role as sites of essential oil accumulation and sequestration, has not been formally tested. In this review, we present current knowledge on the oil bodies of liverworts on their origin and development, their role in taxonomy, chemosystematics and potential pharmaceutical applications leading to their functional significance, and we also identify avenues for future studies on this important but long-overlooked organelle.     

Hot air and the Colonialist 'Other': the 'German-English-Dutch Airship Expedition' to New Guinea

Il est largement admis en anthropologie que les images de «l'Autre>> exotique font partie de la «technologie intellectuelle>> grâce à laquelle le colonialisme a étendu et maintenu son contrôle sur les frontières impériales. Faute d'analyse, toutefois, un autre type d'Autre se languit encore en anthropologie : le Colon à demeure. Dans les narrations analytiques standard, cette figure et le milieu dans lequel elle agit sont encore dépeints en termes radicalement uniformisés. En réalité, le colonialiste maison était un agent complexe, obligé de naviguer et de négocier entre plusieurs conjonctures culturelles et sociales dans le cadre du développement de projets coloniaux appelés àêtre exportés au loin. Dans le présent article, les auteurs cherchent à mettre en lumière l'Autre colonisateur et sa place dans le colonialisme en s'intéressant à la destinée de l' oberleutnant Paul Graztz, «héros>> colonial allemand de la fin du XIX^e siècle, et à sa tentative (vouée à l'échec) d'expédition topographique en Nouvelle-Guinée dans un aéronef «à air chaud>>.     

Land Transitions in Northwest Vietnam: An Integrated Analysis of Biophysical and Socio-Cultural Factors

This paper discusses transitions in land use evidenced by the case of the Suoi Muoi catchment area in NW mountain of Vietnam. Land use transitions were detected from LANDSAT and SPOT satellite images taken over the last 40 years. The maps showing changes in land use were linked with biophysical properties of the land such as slope gradient, elevation and soil type, and cultural characteristic of various ethnic groups by means of logistic regression model. The combination of research methods and instruments from several disciplines, including statistical spatial analysis such as the multiple logistic regression (MLR) models and the multiple correspondence analysis (MCA) on household interview data, and key informant interviews allowed us to identify and validate a number of factors that drive land cover and land use changes in Northwest Vietnam.     

揭示植物在黑暗中变绿之谜

<正>东京大学生命科学院、立命馆大学生物科学与应用生物学、名古屋大学生物科学研究院以及大阪大学蛋白质研究所的研究人员共同合作,阐述了光独立的原叶绿素酸脂还原酶(Pchlide)X射线晶体结构,揭示了植物在黑暗中变绿之谜。该文章4月18日发表于《Nature》网络版,5月6日刊登在《Nature》杂志上。     

Evolution of Reproductive Organs in Land Plants

LEAFY gene is the positive regulator of the MADS-box genes in flower primordia. The number of MADS-box genes presumably increased by gene duplications before the divergence of ferns and seed plants. Most MADS-box genes in ferns are expressed similarly in both vegetative and reproductive organs, while in gymnosperms, some MADS-box genes are specifically expressed in reproductive organs. This suggests that (1) the increase in the number of MADS-box genes and (2) the subsequent recruitment of some MADS-box genes as homeotic selector genes were important for the evolution of complex reproductive organs. The phylogenetic tree including both angiosperm and gymnosperm MADS-box genes indicates the loss of the A-function genes in the gymnosperm lineage, which is presumably related to the absence of perianths in extant gymnosperms. Comparison of expression patterns of orthologous MADS-box genes in angiosperms, Gnetales, and conifers supports the sister relationship of Gnetales and conifers over that of Gnetales and angiosperms predicted by phylogenetic trees based on amino acid and nucleotide sequences. Received 30 July 1999/ Accepted in revised form 9 September 1999     

Functional Rearrangement of the Light-Harvesting Antenna upon State Transitions in a Green Alga

State transitions in the green alga Chlamydomonas reinhardtii serve to balance excitation energy transfer to photosystem I (PSI) and to photosystem II (PSII) and possibly play a role as a photoprotective mechanism. Thus, light-harvesting complex II (LHCII) can switch between the photosystems consequently transferring more excitation energy to PSII (state 1) or to PSI (state 2) or can end up in LHCII-only domains. In this study, low-temperature (77 K) steady-state and time-resolved fluorescence measured on intact cells of Chlamydomonas reinhardtii shows that independently of the state excitation energy transfer from LHCII to PSI or to PSII occurs on two main timescales of <15 ps and ∼100 ps. Moreover, in state 1 almost all LHCIIs are functionally connected to PSII, whereas the transition from state 1 to a state 2 chemically locked by 0.1 M sodium fluoride leads to an almost complete functional release of LHCIIs from PSII. About 2/3 of the released LHCIIs transfer energy to PSI and ∼1/3 of the released LHCIIs form a component designated X-685 peaking at 685 nm that decays with time constants of 0.28 and 5.8 ns and does not transfer energy to PSI or to PSII. A less complete state 2 was obtained in cells incubated under anaerobic conditions without chemical locking. In this state about half of all LHCIIs remained functionally connected to PSII, whereas the remaining half became functionally connected to PSI or formed X-685 in similar amounts as with chemical locking. We demonstrate that X-685 originates from LHCII domains not connected to a photosystem and that its presence introduces a change in the interpretation of 77 K steady-state fluorescence emission measured upon state transitions in Chalamydomonas reinhardtii.     

On the Distribution of Gentisic Acid in Green Plants

Gentisic acid has been shown to be one of the most commenlyoccurring aromatic acids of green plants. The systematic distributionof the compound is described and its possible relationship lignificationis discussed. Methods for its separation from other phenolicconstituents of plants and for the identification of the compoundare described.     

Green Plants in the Red: A Baseline Global Assessment for the IUCN Sampled Red List Index for Plants

Plants provide fundamental support systems for life on Earth and are the basis for all terrestrial ecosystems; a decline in plant diversity will be detrimental to all other groups of organisms including humans. Decline in plant diversity has been hard to quantify, due to the huge numbers of known and yet to be discovered species and the lack of an adequate baseline assessment of extinction risk against which to track changes. The biodiversity of many remote parts of the world remains poorly known, and the rate of new assessments of extinction risk for individual plant species approximates the rate at which new plant species are described. Thus the question ‘How threatened are plants?’ is still very difficult to answer accurately. While completing assessments for each species of plant remains a distant prospect, by assessing a randomly selected sample of species the Sampled Red List Index for Plants gives, for the first time, an accurate view of how threatened plants are across the world. It represents the first key phase of ongoing efforts to monitor the status of the world’s plants. More than 20% of plant species assessed are threatened with extinction, and the habitat with the most threatened species is overwhelmingly tropical rain forest, where the greatest threat to plants is anthropogenic habitat conversion, for arable and livestock agriculture, and harvesting of natural resources. Gymnosperms (e.g. conifers and cycads) are the most threatened group, while a third of plant species included in this study have yet to receive an assessment or are so poorly known that we cannot yet ascertain whether they are threatened or not. This study provides a baseline assessment from which trends in the status of plant biodiversity can be measured and periodically reassessed.     

A Multistep Process Gave Rise to RNA Polymerase IV of Land Plants

Since their discovery in Metazoa, the three nuclear RNA polymerases (RNAPs) have been found in fungi, plants, and diverse protists. In all eukaryotes studied to date, RNAPs I, II, and III collectively transcribe all major RNAs made in the nucleus. We have found genes for the largest subunit (RPD1/RPE1) of a new DNA-dependent RNAP, RNAP IV, in all major land plant taxa and in closely related green algae. Genes for the second-largest subunit (RPD2) of this enzyme were found in all land plants. Phylogenetic study indicates that RNAP IV genes are sister to the corresponding RNAP II genes. Our results show the genesis of RNAP IV to be a multistep process in which the largest and second-largest subunit genes evolved by independent duplication events in the ancestors of Charales and land plants. These findings provide insights into evolutionary mechanisms that can explain the origin of multiple RNAPs in the eukaryotic nucleus. Electronic Supplementary Material Electronic Supplementary material is available for this article at and accessible for authorised users. [Reviewing Editor: Dr. Patrick Keeling]     

MIR166基因家族在陆生植物中的进化模式分析

MicroRNA（miRNA）是一类广泛存在于真核生物中的具有转录后水平调控功能的内源非编码小分子RNA。在植物中．miRNA通过对靶基因的剪切或沉默来实现对植物生命活动的调控,它是基因表达调控网络的重要组成部分。miR165／166（miR166）是陆生植物中最为古老的MIRNA家族之一,它通过对3型同源异域型-亮氨酸拉链（1id—ZIPⅢ）等靶标的调控,在植物的众多发育时期起着关键的调控作用。本文分析了MIR166基因在陆生植物中的进化关系,并对MIR166在基部陆生植物小立碗藓（Physcomitrella patens）中的复制及进化进行了研究。此外,HD—ZIPⅢ蛋白是植物中重要的一类转录因子,miR166对HD-ZIP Ⅲ基因的调控作用在陆地植物保守的存在,本文对HD—ZIP Ⅲ基因和miR166在进化中的相互作用进行了初步的探讨。     

The Interrelationships of Land Plants and the Nature of the Ancestral Embryophyte

1. Download high-res image (194KB)
2. Download full-size image

     

Experimental Addition of Green Plants to the Nest Increases Testosterone Levels in Female Spotless Starlings

Multiple male traits and displays may act in signalling sexually selected processes during courtship. Spotless starling males (Sturnus unicolor) carry green plants into their nests before egg laying, and recent studies have shown that this behaviour is related to female breeding decisions and the production of male‐biased broods. Although the functional implications of this effect on females are not yet clear, data suggest that it could be mediated by female circulating hormones. Additionally, females may show higher androgen levels as a consequence of the increased female–female competition generated by the increase in male attractiveness. We tested this hypothesis using the same manipulation of green nesting material that has been previously shown to result in an increase of male attractiveness in male spotless starlings. We found that females in experimental nests increased their circulating testosterone levels during the laying period. In addition, there was an increase of social interferences in the experimental nests because of the addition of green plants. We hypothesise that testosterone may allow females to maintain their mating status when competing with other females for the preferred males. Addition of green plants also increased the variance in the levels of circulating testosterone, suggesting plasticity between females in their response to the manipulation. We propose that there is a functional link between high testosterone levels, male‐biased sex ratios and female resource‐holding potential in intra‐sexual competition in this species.     

Homocysteine Biosynthesis in Green Plants: Physiological Importance of the Transsulfuration Pathway in Lemna paucicostata

To permit an assessment of the relative contributions of the transsulfuration and the direct sulfhydration pathways for homocysteine biosynthesis, the time course of incorporation of ³⁵S from ³⁵SO₄²⁻ into various sulfur-containing compounds in Lemna paucicostata has been determined. Plants were grown with either low (4.5 micromolar) or ample (1,000 micromolar) sulfate in the medium. At the shortest labeling times, ³⁵S-cystathionine was the predominant ³⁵S-containing organic sulfur compound. The flux of sulfur into cystathionine was sufficient to sustain the known rate of methionine biosynthesis. It was calculated that transsulfuration accounted for at least 90 and 85% of the total homocysteine synthesis in low and ample sulfate-grown plants, respectively (and may have accounted for 100%). No marked rise in the ³⁵S-soluble cysteine:³⁵S-homocysteine ratio was observed even at the shortest labeling times, but it is argued that this may be due to (a) the observed compartmentation of soluble cysteine, and (b) the impracticality of using labeling times shorter than 17 seconds. Additional evidence supporting the importance of transsulfuration in Lemna is briefly described.     

Transitions and transversions in evolutionary descent: An approach to understanding

Summary In this paper I lay a quantitative theoretical groundwork for understanding the proportions of the possible types of base substitutions observed between 12 genes sharing a common ancestor and isolated from extant species. The experimentally observed types of base substitution between two sequenced genes do not give a direct measure of the types of base substitutions that occur during evolutionary descent. However, by use of a statistical assemblage of these observations, we can recover, without the assumption of parsimony, the conditional base substitution probabilities that determine this descent. Three methods—direct count, regression, and informational entropy maximization—are described by which these probabilities can be estimated from experimental data. The methods are complementary in that each is most useful for somewhat different types of experimental data. These methods are used to study the ratio of transversions to transitions during gene divergence. Though this ratio is not constant during divergence, it does approach a stable limiting value that in principle can vary from zero, corresponding to 100% transition differences, to infinity, corresponding to 0% transition differences. In practice the limiting ratio tends to hover around a value of two, which is expected on a random basis. However, base substitution pathways that are very nonrandom also may lead to a limiting ratio of exactly two, so that such a value is not diagnostic for random pathways. The limiting ratio can be directly calculated from a knowledge of the twelve conditional probabilities for each type of base substitution, or from a knowledge of the equilibrium base composition of the DNAs compared. An expression is given for this calculation. Fifteen years ago Jean Derancourt, Andrew Lebor and Emile Zuckerkandl (1967), analyzing the amino acid sequence of globin chains coded by nuclear genes, made the original observation that the proportion of transition differences decreases with increasing evolutionary time. Recently Brown et al. (1982) and Brown and Simpson (1982) have reported a decrease in the observed proportion of transition differences in mitochondrial DNA with increasing evolutionary divergence. The conditions that must be satisfied for this type of behavior to occur at stable base composition and with stable base substitution probabilities are defined. Multiple substitutionsper se do not lead to a decrease in transition differences with increasing evolutionary divergence.