VARIATION AND LOCALIZATION OF FLAVONOID AGLYCONES IN HELIANTHUS ANNUUS (COMPOSITAE)

Flavonoid aglycone variation within Helianthus annuus, a species widely distributed throughout North America, was analyzed. Flavonoid aglycones of H. annuus consist of two types, flavones and chalcones. The flavone aglycones are sequestered in glandular trichomes that occur on both leaf surfaces, whereas the chalcone aglycones appear to be incorporated in the waxy leaf cuticle. Considerable variation in flavonoid profile was observed with some plants exhibiting as few as one, and others as many as seven of the eight aglycones detected. No definable phytogeographic patterns were observed for this flavonoid variation. Flavonoid aglycone variation also did not differentiate the infraspecific taxa within H. annuus.     

Phylogenetic distribution and evolution of mycorrhizas in land plants

A survey of 659 papers mostly published since 1987 was conducted to compile a checklist of mycorrhizal occurrence among 3,617 species (263 families) of land plants. A plant phylogeny was then used to map the mycorrhizal information to examine evolutionary patterns. Several findings from this survey enhance our understanding of the roles of mycorrhizas in the origin and subsequent diversification of land plants. First, 80 and 92% of surveyed land plant species and families are mycorrhizal. Second, arbuscular mycorrhiza (AM) is the predominant and ancestral type of mycorrhiza in land plants. Its occurrence in a vast majority of land plants and early-diverging lineages of liverworts suggests that the origin of AM probably coincided with the origin of land plants. Third, ectomycorrhiza (ECM) and its derived types independently evolved from AM many times through parallel evolution. Coevolution between plant and fungal partners in ECM and its derived types has probably contributed to diversification of both plant hosts and fungal symbionts. Fourth, mycoheterotrophy and loss of the mycorrhizal condition also evolved many times independently in land plants through parallel evolution.     

Modulation of flavonoid and tannin production of Carpobrotus rossii by environmental conditions

Dietary supplementation with plant-derived polyphenolic compounds such as the flavonoids epigallocatechin-3-gallate (EGCG), quercetin and resveratrol can result in a beneficial effect on degenerative disease processes through both radical scavenging and activation of cellular ion channels. Preliminary investigations have shown that extracts from the halophyte species Carpobrotus rossii have high in vitro antioxidant and in vivo low-density-lipoprotein-lowering activities. In this study, we have investigated the environmental conditions responsible for inducing flavonoid production in C. rossii in an attempt to maximise production of these compounds. Both field surveys and controlled glasshouse experiments were conducted. Flavonoid production appears to be related to conditions known to cause oxidative stress in plants such as exposure to excessive light, reduced water availability, and low soil potassium levels. Flavonoid production was minimal under salinity levels optimal for C. rossi growth (around 50 mM NaCl) and increased dramatically at sub- and supra-optimal salinities. Flavonoids were clearly concentrated in metabolically active palisade mesophyll tissue rather than the spongy parenchyma. Non-optimal (outside 50–100 mM range) NaCl levels significantly increased flavonoid concentration on a per leaf basis. However, the reduction in biomass production at sub and supra optimal salinities diminished absolute flavonoid production per plant. As a result, saline conditions favouring optimal plant growth appear to be most suitable for maximising production of flavonoids in C. rossii.     

Variation in the quality and quantity of flavonoids in the leaves of coastal and inland Campanula punctata

Ultraviolet-B radiation is known as a noxious factor that destroys every life form. Plants that occupy the coastal area are assumed to be adaptive to UV-B as well as the other major stresses. The objective of this study was to clarify and compare (1) the flavonoid compositions of coastal and inland populations of Campanula punctata, and (2) UV-B effects on flavonoid content in plants originating from different habitats under uniform (i.e. experimental) and natural conditions. Flavonoid compositions of coastal and inland populations were shown to be identical. The UV-B exclusion experiment revealed two tendencies that were commonly observed in both coastal and inland populations: (1) the flavonoid accumulation decreased with an increase in degree of UV-B exclusion, and (2) the quantity of phenolic acids conversely became maximum under complete UV-B exclusion. Under the natural habitat conditions, significantly high accumulation of flavonoids were detected in two coastal populations even though no significant difference was found between the two other coastal populations and two inland populations. Weak correlations between UV-B intensity and flavonoid accumulation under the natural habitat conditions suggest that various micro-environmental factors may influence the production of flavonoids, and that the plants may acquire adaptive traits other than increasing flavonoids in order to inhabit the coastal environment.     

Flavonoid sequestration by the common blue butterfly Polyommatus icarus: quantitative intraspecific variation in relation to larval hostplant,sex and body size

Common blue butterflies (Polyommatus icarus) sequester flavonoids from their larval food and store these pigments as part of their adult wing colouration. Insects were reared on 10 different diets to assess effects of host plants on variation in flavonoid sequestration in this moderately polyphagous butterfly. Rearing experiments revealed an unexpectedly large gradient in flavonoid richness, ranging from individuals with high flavonoid loads (reared on inflorescences of Medicago sativa, Trifolium repens, T. pratense) to butterflies which contained almost no such pigments (fed with foliage of M. sativa or Robinia pseudoacacia). Flavonoid sequestration was much more effective from natural hostplants than from experimentally offered diets which would not be accepted in the field. Female butterflies on average sequestered almost 60% more flavonoids than males. This sex difference was more pronounced on natural than on experimental diets. Flavonoid load was significantly and positively related to dry mass and forewing length as two important fitness correlates of butterflies. This correlation was particularly strong on experimental diets (i.e. under constraining conditions for development). On natural hostplants, in contrast, when butterflies generally were flavonoid-rich, no clear relationship between flavonoid load and size or mass emerged. Our analytical data are consistent with field results according to which females rich in UV-absorbing flavonoid wing pigments are more attractive to mate-searching males. In P. icarus, flavonoid richness might therefore increase visibility (by more effective sensory stimulation of the visual system), but could also confer information about the feeding history, and thus ontogenetically determined ‘quality’ of a potential mate.     

Studies of Physcomitrella patens reveal that ethylene‐mediated submergence responses arose relatively early in land‐plant evolution

Colonization of the land by multicellular green plants was a fundamental step in the evolution of life on earth. Land plants evolved from fresh‐water aquatic algae, and the transition to a terrestrial environment required the acquisition of developmental plasticity appropriate to the conditions of water availability, ranging from drought to flood. Here we show that extant bryophytes exhibit submergence‐induced developmental plasticity, suggesting that submergence responses evolved relatively early in the evolution of land plants. We also show that a major component of the bryophyte submergence response is controlled by the phytohormone ethylene, using a perception mechanism that has subsequently been conserved throughout the evolution of land plants. Thus a plant environmental response mechanism with major ecological and agricultural importance probably had its origins in the very earliest stages of the colonization of the land.     

Major transitions in the evolution of early land plants: a bryological perspective

Background Molecular phylogeny has resolved the liverworts as the earliest-divergent clade of land plants and mosses as the sister group to hornworts plus tracheophytes, with alternative topologies resolving the hornworts as sister to mosses plus tracheophytes less well supported. The tracheophytes plus fossil plants putatively lacking lignified vascular tissue form the polysporangiophyte clade. Scope This paper reviews phylogenetic, developmental, anatomical, genetic and paleontological data with the aim of reconstructing the succession of events that shaped major land plant lineages. Conclusions Fundamental land plant characters primarily evolved in the bryophyte grade, and hence the key to a better understanding of the early evolution of land plants is in bryophytes. The last common ancestor of land plants was probably a leafless axial gametophyte bearing simple unisporangiate sporophytes. Water-conducting tissue, if present, was restricted to the gametophyte and presumably consisted of perforate cells similar to those in the early-divergent bryophytes Haplomitrium and Takakia. Stomata were a sporophyte innovation with the possible ancestral functions of producing a transpiration-driven flow of water and solutes from the parental gametophyte and facilitating spore separation before release. Stomata in mosses, hornworts and polysporangiophytes are viewed as homologous, and hence these three lineages are collectively referred to as the 'stomatophytes'. An indeterminate sporophyte body (the sporophyte shoot) developing from an apical meristem was the key innovation in polysporangiophytes. Poikilohydry is the ancestral condition in land plants; homoiohydry evolved in the sporophyte of polysporangiophytes. Fungal symbiotic associations ancestral to modern arbuscular mycorrhizas evolved in the gametophytic generation before the separation of major present-living lineages. Hydroids are imperforate water-conducting cells specific to advanced mosses. Xylem vascular cells in polysporangiophytes arose either from perforate cells or de novo. Food-conducting cells were a very early innovation in land plant evolution. The inferences presented here await testing by molecular genetics.     

Flavonoid chemistry and angiosperm evolution

A consideration of the distribution of flavonoid compounds in angiosperms indicates that exceptions exist to current thought on the presence of particular structural types occurring in primitive versus advanced flowering plants. As additional thorough survey work is done, the exceptions become increasingly common and the generalizations are weakened. A methodological problem in flavonoid surveys concerns documenting the “absence” of particular compounds and the question of quantitative versus qualitative variation of certain constituents. Consideration of flavonoid biosynthesis suggests that simple genetic differences likely control the classes of compounds present and this in turn indicates that caution be used in placing phylogenetic significance on such differences. Features of floral morphology used in studying angiosperm phylogeny have a complex genetic-developmental basis as compared to the genetic factors governing the presence of various flavonoid classes. This ostensibly is an important factor in explaining why reversals in certain trends of floral morphology are rarely noted and why these features are usually constant at higher taxonomic levels. By contrast, variation of flavonoid classes (by virtue of the small genetic differences controlling the presence of different classes) occurs at lower taxonomic levels. Genetic and enzymological studies of flavonoid biosynthesis also indicate that a single compound may be synthesized via different pathways, and this has significant implications for the use of flavonoid distribution in a phylogenetic sense. Given similar selection pressures, the same compounds may arise independently in distantly related plants. Clearly, this has occurred with floral anthocyanidins, where the distribution of particular compounds is related to pollinators. Flavonoid compounds will continue to be useful systematically at the generic level or lower, and possibly at the familial level in some instances. However, studies of the genetics and enzymology of flavonoid compounds in different groups of plants are needed if flavonoids are to be employed in a phylogenetic or evolutionary sense at higher taxonomic levels in the angiosperms. Much additional work in the difficult area of flavonoid functions is to be desired. Many more investigations of comparative flavonoid chemistry of fossil and extant members of what are considered the same genus must be carried out if any appreciation of flavonoid change through evolutionary time is to be achieved.     

Flavonoids are differentially taken up and transported long distances in Arabidopsis

Flavonoids are synthesized in response to developmental and environmental signals and perform many functions in plants. Arabidopsis (Arabidopsis thaliana) roots grown in complete darkness do not accumulate flavonoids since the expression of genes encoding enzymes of flavonoid biosynthesis is light dependent. Yet, flavonoids accumulate in root tips of plants with light-grown shoots and light-shielded roots, consistent with shoot-to-root flavonoid movement. Using fluorescence microscopy, a selective flavonoid stain, and localized aglycone application to transparent testa mutants, we showed that flavonoids accumulated in tissues distal to the application site, indicating uptake and movement systems. This was confirmed by time-course fluorescence experiments and high-performance liquid chromatography. Flavonoid applications to root tips resulted in basipetal movement in epidermal layers, with subsequent fluorescence detected 1 cm from application sites after 1 h. Flavonoid application to midroot or cotyledons showed movement of flavonoids toward the root tip mainly in vascular tissue. Naringenin, dihydrokaempferol, and dihydroquercetin were taken up at the root tip, midroot, or cotyledons and traveled long distances via cell-to-cell movement to distal tissues, followed by conversion to quercetin and kaempferol. In contrast, kaempferol and quercetin were only taken up at the root tip. Using ATP-binding cassette (ABC) transporter and H(+)-ATPase inhibitors suggested that a multidrug resistance-associated protein ABCC transporter facilitated flavonoid movement away from the application site.     

The sequenced genomes of nonflowering land plants reveal the innovative evolutionary history of peptide signaling

An understanding of land plant evolution is a prerequisite for in-depth knowledge of plant biology. Here we extract and explore information hidden in the increasing number of sequenced plant genomes, from bryophytes to angiosperms, to elucidate a specific biological question—how peptide signaling evolved. To conquer land and cope with changing environmental conditions, plants have gone through transformations that must have required innovations in cell-to-cell communication. We discuss peptides mediating endogenous and exogenous changes by interaction with receptors activating intracellular molecular signaling. Signaling peptides were discovered in angiosperms and operate in tissues and organs such as flowers, seeds, vasculature, and 3D meristems that are not universally conserved across land plants. Nevertheless, orthologs of angiosperm peptides and receptors have been identified in nonangiosperms. These discoveries provoke questions regarding coevolution of ligands and their receptors, and whether de novo interactions in peptide signaling pathways may have contributed to generate novel traits in land plants. The answers to such questions will have profound implications for the understanding of the evolution of cell-to-cell communication and the wealth of diversified terrestrial plants. Under this perspective, we have generated, analyzed, and reviewed phylogenetic, genomic, structural, and functional data to elucidate the evolution of peptide signaling.

The identification of orthologs of Arabidopsis signaling peptides and their receptors in nonflowering plants suggest their importance in cell-to-cell communication in all land plants.     

The evolution of vegetative desiccation tolerance in land plants

Vegetative desiccation tolerance is a widespread but uncommon occurrence in the plant kingdom generally. The majority of vegetative desiccation-tolerant plants are found in the less complex clades that constitute the algae, lichens and bryophytes. However, within the larger and more complex groups of vascular land plants there are some 60 to 70 species of ferns and fern allies, and approximately 60 species of angiosperms that exhibit some degree of vegetative desiccation tolerance. In this report we analyze the evidence for the differing mechanisms of desiccation tolerance in different plants, including differences in cellular protection and cellular repair, and couple this evidence with a phylogenetic framework to generate a working hypothesis as to the evolution of desiccation tolerance in land plants. We hypothesize that the initial evolution of vegetative desiccation tolerance was a crucial step in the colonization of the land by primitive plants from an origin in fresh water. The primitive mechanism of tolerance probably involved constitutive cellular protection coupled with active cellular repair, similar to that described for modern-day desiccation-tolerant bryophytes. As plant species evolved, vegetative desiccation tolerance was lost as increased growth rates, structural and morphological complexity, and mechanisms that conserve water within the plant and maintain efficient carbon fixation were selected for. Genes that had evolved for cellular protection and repair were, in all likelihood, recruited for different but related processes such as response to water stress and the desiccation tolerance of reproductive propagules. We thus hypothesize that the mechanism of desiccation tolerance exhibited in seeds, a developmentally induced cellular protection system, evolved from the primitive form of vegetative desiccation tolerance. Once established in seeds, this system became available for induction in vegetative tissues by environmental cues related to drying. The more recent, modified vegetative desiccation tolerance mechanism in angiosperms evolved from that programmed into seed development as species spread into very arid environments. Most recently, certain desiccation-tolerant monocots evolved the strategy of poikilochlorophylly to survive and compete in marginal habitats with variability in water availability.     

A fundamental plant evolutionary problem: the origin of land-plant sporophyte; is a new hypothesis possible?

The origin of the sporophyte in land plants represents a fundamental phase in the plant evolution. Today this subject is controversial and, in my opinion, scarcely considered in our textbooks and journals of botany, in spite of its importance. There are two conflicting theories concerning the origin of the alternating generations in land plants: the "antithetic" and the "homologous" theory. These have never been fully resolved. The antithetic theory maintains that the sporophyte and gametophyte generations are fundamentally dissimilar and that the sporophyte originated in an ancestor organism with haplontic cycle by the zygote dividing mitotically rather than meiotically, and with a developmental pattern not copying the developmental events of the gametophyte. The sporophyte generation was an innovation of critical significance for the land-plant evolution. By contrast, the homologous theory simply stated that a mass of cells forming mitotically from the zygote adopted the same developmental plan of the gametophyte, but giving origin to a diploid sporophyte. In this context, a very important question concerns the possible ancestor or ancestors of the land plants. Considerable evidences at morphological, cytological, ultrastructural, biochemical and, especially, molecular level, strongly suggest that the land plants or Embryophyta (both vascular and non-vascular) evolved from green algal ancestor(s), similar to those belonging to the genus Coleochaete, Chara and Nitella, living today. Their organism is haploid for most of their life cycle, and diploid only in the zygote phase (haplontic cycle). On the contrary, the land plants are characterized by a diplo-haplontic life cycle. Several questions are implied in these theories, and numerous problems remain to be solved, such as, for example, the morphological difference between gametophyte and sporophyte (heteromorphism, already present in the first land plants, the bryophytes), and the strong gap existing between these last with a sporophyte dependent on the gametophyte, and the pteridophytes having the gametophyte and sporophyte generations independent. On the ground of all of the evidences on the ancestors of the land plants, the antithetic theory is considered more plausible than the homologous theory. Unfortunately, no phylogenetic relationship exists between some green algae with diplontic life cycle and the land plants. Otherwise, perhaps, it should be possible to hypothesize another scenario in which to place the origin of the alternating generations of the land plants. In this case, could the gametophyte be formed by gametes produced from the sporophyte, through their mitoses or a delayed fertilization process?     

The transparent testa4 mutation prevents flavonoid synthesis and alters auxin transport and the response of Arabidopsis roots to gravity and light

We examined whether flavonoids act as endogenous auxin transport regulators during gravity vector and light intensity changes in Arabidopsis thaliana roots. Flavonoid deficient transparent testa4 [tt4(2YY6)] seedlings had elevated root basipetal auxin transport compared with the wild type, consistent with the absence of a negative auxin transport regulator. The tt4(2YY6) roots had delayed gravitropism that was chemically complemented with a flavonoid intermediate. Flavonoid accumulation was found in wild-type columella cells, the site of gravity perception, and in epidermal and cortical cells, the site of differential growth, but flavonoid accumulation was absent in tt4(2YY6) roots. Flavonoid accumulation was higher in gravity-stimulated root tips as compared with vertical controls, with maximum differences coinciding with the timing of gravitropic bending, and was located in epidermal cells. Exogenous indole-3-acetic acid (IAA) also elevated flavonoid accumulation, suggesting that flavonoid changes in response to gravity might be partly as a result of changing IAA distribution. Acropetal IAA transport was also elevated in roots of tt4(2YY6). Flavonoid synthesis was repressed in the dark, as were differences in root acropetal transport in tt4(2YY6). These results are consistent with light- and gravity-induced flavonoid stimulation that alters auxin transport in roots and dependent physiological processes, including gravitropic bending and root development.     

Evolution and function of red pigmentation in land plants

BackgroundLand plants commonly produce red pigmentation as a response to environmental stressors, both abiotic and biotic. The type of pigment produced varies among different land plant lineages. In the majority of species they are flavonoids, a large branch of the phenylpropanoid pathway. Flavonoids that can confer red colours include 3-hydroxyanthocyanins, 3-deoxyanthocyanins, sphagnorubins and auronidins, which are the predominant red pigments in flowering plants, ferns, mosses and liverworts, respectively. However, some flowering plants have lost the capacity for anthocyanin biosynthesis and produce nitrogen-containing betalain pigments instead. Some terrestrial algal species also produce red pigmentation as an abiotic stress response, and these include both carotenoid and phenolic pigments.ScopeIn this review, we examine: which environmental triggers induce red pigmentation in non-reproductive tissues; theories on the functions of stress-induced pigmentation; the evolution of the biosynthetic pathways; and structure–function aspects of different pigment types. We also compare data on stress-induced pigmentation in land plants with those for terrestrial algae, and discuss possible explanations for the lack of red pigmentation in the hornwort lineage of land plants.ConclusionsThe evidence suggests that pigment biosynthetic pathways have evolved numerous times in land plants to provide compounds that have red colour to screen damaging photosynthetically active radiation but that also have secondary functions that provide specific benefits to the particular land plant lineage.     

Chromosome number and flavonoid synthesis in Briza L. (Gramineae)

Following a recent reidentification of the apigenin C-glycosides in diploid Briza media, the luteolin C-glycosides were reexamined and three acylated derivatives of a luteolin C-glycoside were found. In an attempt to identify the chromosome or group of chromosomes responsible for the change in flavonoid synthesis from 4'-hydroxy- in diploid plants to 3',4'-dihydroxyflavone C-glycosides in autotetraploid plants, leaf flavonoids of artificially produced aneuploids of B. media were examined. Among these plants three different leaf flavonoid profiles were recognized: diploid, tetraploid, and a "modified" tetraploid pattern. All the aneuploids with the normal or "modified" tetraploid pattern were trisomic for one of the small acrocentric chromosomes. Induced polyploids of other Briza species were usually found to have similar flavonoid patterns in the two chromosome races. Flavonoid sulfates were found in three South American species but are absent from all the European species.     

微生物合成黄酮糖苷类天然产物研究进展

黄酮糖苷类天然产物是植物中黄酮类化合物的主要存在形式,通过糖基化修饰,可以改变其水溶性、稳定性等,赋予其新的生物活性和功能。黄酮类化合物的糖基化修饰通常由植物源或微生物源的糖基转移酶催化,根据糖基的位置、类型和数量的不同,可形成多种类型的黄酮糖苷类产物。随着合成生物学和代谢工程的快速发展,在微生物中合成植物源黄酮糖苷类天然产物取得了重要进展。综述了糖基转移酶的聚类分析及糖基供体的途径改造,并对代谢工程优化黄酮糖苷类天然产物的微生物合成进行了分析讨论,并对其发展前景进行了展望。     

The evolution of chloroplast RNA editing

RNA editing alters the nucleotide sequence of an RNA molecule so that it deviates from the sequence of its DNA template. Different RNA-editing systems are found in the major eukaryotic lineages, and these systems are thought to have evolved independently. In this study, we provide a detailed analysis of data on C-to-U editing sites in land plant chloroplasts and propose a model for the evolution of RNA editing in land plants. First, our data suggest that the limited RNA-editing system of seed plants and the much more extensive systems found in hornworts and ferns are of monophyletic origin. Further, although some eukaryotic editing systems appear to have evolved to regulate gene expression, or at least are now involved in gene regulation, there is no evidence that RNA editing plays a role in gene regulation in land plant chloroplasts. Instead, our results suggest that land plant chloroplast C-to-U RNA editing originated as a mechanism to generate variation at the RNA level, which could complement variation at the DNA level. Under this model, many of the original sites, particularly in seed plants, have been subsequently lost due to mutation at the DNA level, and the function of extant sites is merely to conserve certain codons. This is the first comprehensive model for the evolution of the chloroplast RNA-editing system of land plants and may also be applicable to the evolution of RNA editing in plant mitochondria.     

Molecular and Biochemical Characterization of Three Anthocyanin Synthetic Enzymes from Gentiana triflora

Full length cDNA clones of flavonoid 3',5'-hydroxylase, dihydroflavonol4-reductase and flavonoid 3-glucosyltransferase were clonedfrom petals of Gentiana triflora. Their sequences were homologousto counterparts from other plants. Flavonoid 3',5'-hydroxylaseand flavonoid 3-glucosyltransferase were enzymatically characterizedby expressing cDNAs in heterologous expression systems. (Received May 21, 1996; Accepted June 4, 1996)