Herbaceous Dicots Research Articles

Preliminary Report on Diet Estimation of Taruka (Hippocamelus antisensis d'Orbigny, 1834) in an Agricultural Area of the Andean Foothills of the Tarapacá Region, Chile.

The success of conservation programs for the taruka (Hippocamelus antisensis d'Orbigny), an endemic and endangered deer, depends on many factors, highlighting anthropogenic and ecological effects. Among the latter, how this herbivore interacts with forage resources is important. The objective of the study was to describe the main attributes of the diet of this deer in rangelands adjacent to agricultural areas of the foothills of the Tarapacá Region, Chile. The botanical composition of the diet (BCD) was determined by microhistology of feces and fecal nitrogen (NF, %) was measured in two contrasting seasons (rainy summer and dry winter). From the BCD and FN, their relative diversity (J) and crude protein percentage were estimated. In the BCD, Medicago sativa dominated (27.6 ± 8.2% vs. 53.9 ± 9.2%, in rainy summer and dry end winter, respectively), followed by herbaceous dicots (46.2 ± 9.4% vs. 19.4 ± 8.7%) and shrubby species (21.5 ± 7.8% vs. 23.4 ± 7.0%), from rangelands. The contribution of grasses and graminoid species was low, not exceeding 3% and 0.4% of the diet, respectively, with no differences between seasons of the year. Intake of horticultural crop species was marginal (1.3 ± 1.3%), being detected only in the wet season. Diet relative diversity was higher during the wet period (0.75 ± 0.07) compared to the dry period (0.58 ± 0.06), since in the first period it was possible to find a greater number of palatable species. There were no significant differences in the FN attributed to the time of the year (average of 1.8 ± 0.19%), which indicates that the diet of this deer would be stable in terms of its protein quality. These FN levels estimate sufficient dietary protein content to satisfy maintenance and early pregnancy, but these could be limiting during late gestation and lactation.

Fiber Artifacts from the Paisley Caves: 14,000 Years of Plant Selection in the Northern Great Basin

AbstractPaleoethnobotanical remains from basketry and cordage from the Paisley Caves offer an opportunity to explore how people engaged with plant communities over time. Fiber identification of textiles, together with radiocarbon dating, contributes new information about landscape use within the Summer Lake Basin. Expanded marshlands during the terminal Pleistocene / Early Holocene created suitable plant communities ideal for fiber technology, specifically wetland monocots and herbaceous dicots—including dogbane and stinging nettle—by 11,000 years ago. This technology is key to subsistence activities and craft production throughout the Holocene. Despite climatic events during the Middle Holocene, in which people transitioned from caves to sites centered on lakeshores and wetlands, the suite of fiber plants and their technological application remains constant. During the Late Holocene, bast fiber material diversified with the addition of flax and milkweed. The presence of flax in particular, a high-elevation plant, may reflect the increased use of upland root collection areas as populations increased. This research provides long-term data on culturally significant native plants used in the manufacture of fiber-based textiles over the last 14,000 years.

Time-resolved systems analysis of the induction of high photosynthetic capacity in Arabidopsis during acclimation to high light.

Induction of high photosynthetic capacity is a key acclimation response to high light (HL) for many herbaceous dicot plants; however, the signaling pathways that control this response remain largely unknown. Here, a systems biology approach was utilized to characterize the induction of high photosynthetic capacity in strongly and weakly acclimating Arabidopsis thaliana accessions. Plants were grown for 5 wk in a low light (LL) regime, and time-resolved photosynthetic physiological, metabolomic, and transcriptomic responses were measured during subsequent exposure to HL. The induction of high nitrogen (N) assimilation rates early in the HL shift was strongly predictive of the induction of photosynthetic capacity later in the HL shift. Accelerated N assimilation rates depended on the mobilization of existing organic acid (OA) reserves and increased de novo OA synthesis during the induction of high photosynthetic capacity. Enhanced sucrose biosynthesis capacity increased in tandem with the induction of high photosynthetic capacity, and increased starch biosynthetic capacity was balanced by increased starch catabolism. This systems analysis supports a model in which the efficient induction of N assimilation early in the HL shift begins the cascade of events necessary for the induction of high photosynthetic capacity acclimation in HL.

The most polyphagous insect herbivore? Host plant associations of the Meadow spittlebug, Philaenus spumarius (L.).

A comprehensive list of all known host plant species utilised by the Meadow Spittlebug (Philaenus spumarius (L.)) is presented, compiled from published and unpublished sources. P. spumarius feeds on 1311 host plants in 631 genera and 117 families. This appears, by a large margin, to be the greatest number of host species exploited by any herbivorous insect. The Asteraceae (222 species) and Rosaceae (110) together account for 25% of all host species. The Fabaceae (76) and Poaceae (73), are nearly tied for third and fourth place and these four families, combined with the Lamiaceae (62), Apiaceae (50), Brassicaceae (43) and Caprifoliaceae (34), comprise about half of all host species. Hosts are concentrated among herbaceous dicots but range from ferns and grasses to shrubs and trees. Philaenus spumarius is an "extreme polyphage", which appears to have evolved from a monophage ancestor in the past 3.7 to 7.9 million years. It is also the primary European vector of the emerging plant pathogen Xylella fastidiosa. Its vast host range suggests that it has the potential to spread X. fastidiosa among multiple hosts in any environment in which both the spittlebug and bacterium are present. Fully 47.9% of all known hosts were recorded in the Xylella-inspired BRIGIT citizen science P. spumarius host survey, including 358 hosts new to the documentary record, 27.3% of the 1311 total. This is a strong demonstration of the power of organized amateur observers to contribute to scientific knowledge.

Larval host plants of two lizard beetles in the genus Tetraphala (Coleoptera, Erotylidae, Languriinae, Languriini) from Taiwan, with a host plant list of Languriini

AbstractLizard beetles (Erotylidae, Languriinae, Languriini) are known as stem borers of plants and contain agricultural pests and endangered species, but their species–host plant associations have been poorly documented. Here we investigated the larval host plants of two species of the genus Tetraphala Strum, T. collaris (Crotch) and Tetraphala sp. occurring in Taiwan. Females of T. collaris excavated living leafstalks and stems of the herbaceous dicot, Sambucus chinensis (Adoxaceae) using their mandibles for oviposition. We observed the eggs and early‐instar larvae inside and nearby oviposition holes and late‐instar larvae inside stems, suggesting that T. collaris uses living leafstalks and stems of S. chinensis as oviposition substrate and the larvae tunnel into stems with feeding on the tissues. Similarly, females of Tetraphala sp. excavated living leafstalks of the fern, Pteris wallichiana (Pteridaceae) using their mandibles for oviposition. We observed the eggs and early‐instar larvae inside and nearby oviposition holes. When reared in laboratory, a larva reached adulthood inside the leafstalk. These results indicated that Tetraphala sp. uses living leafstalks of Pt. wallichiana as oviposition substrate and the larvae complete their development within. This study revealed that the genus Tetraphala contains both fern‐ and dicot‐users during larval period. Further study is needed to clarify the evolutionary process of host plant use of languriines. Additionally, the host plant list of Languriini is provided.

Vegetation in rural roadsides of the Pampa region (Argentina): an opportunity for grassland conservation?

ABSTRACTIn many areas of the agriculturalized Pampas of Argentina, rural roadsides (RRS) are the only relics of the grassland biome that originally dominated the region. Nowadays, no policies regulate the use and preservation of these environments. We assessed plant species diversity in 28 RRS in a representative area of the Southern Pampean region, and investigated the degree to which some RRS variables (width, slope, type, and density of RRS in a circular area of 2000 m in diameter) explain their floristic assemblages and species richness. We listed 107 species belonging to 25 families. The most species-rich families were Poaceae (33 species) and Asteraceae (22 species). Fifty percent of the species were native to the region and 58% perennial. There was a predominance of herbaceous dicots (68%), and 12 species (11%) were endemic to the region. A canonical correspondence analysis showed that the density of neighboring RRS significantly explained plant species assemblages. Exotic species richness decreased with the width of the RRS. We expect that this information and proper management will promote the potential of RRS for nature conservation as we consider RRS important refuge for grassland plants.

Disentangling evolutionary, environmental and morphological drivers of plant anatomical adaptations to drought and cold in Himalayan graminoids

Understanding what determine plants ability to survive drought and cold is crucial for predicting how plants may respond to ongoing climate change. Plant survival strategies are usually characterized by morphological and physiological adaptations, while their underlying anatomical settings are largely unknown. Woody angiosperms and herbaceous dicots have repeatedly evolved small water transporting conduits and large storage parenchyma tissues at colder or drier places to cope with freezing‐ and drought‐induced damages. However, whether these adaptations are also valid for graminoids remains unclear. Here we show that stem anatomical variations in grasses, sedges and rushes dominating in western Himalayan grasslands are driven by elevation and soil moisture via control over aboveground plant stature and belowground clonal growth, while phylogenetic constraints have only a weak effect. Phylogenetic comparative analyses controlling for confounding factors showed that the elevation‐related cooling controls the conductive system through reduced vessel diameter and extended assimilatory and storage tissues with more chlorenchyma and less sclerenchyma around vessels. The soil moisture deficit, on the other hand, determines stabilization structures by promoting short‐rhizomatous turf graminoids with hollow stems, thicker epidermis and deep adventitious roots in dry steppes and semi‐deserts. Saline wetlands and moist alpine pastures promote long‐rhizomatous short‐stature plants with lower need for mechanical support (absence of hollow stem) and exposure to high evaporative forcing (thinner epidermis). Observed trends of decreasing vessel sizes and lignification rate with elevation supports the existing knowledge that narrower vessels and extensive parenchyma assist plants to grow in cold environments by avoiding freezing‐induced cavitation. Our results bring novel information on ecological drivers influencing the evolution of anatomical adaptations in high mountain graminoids. Distinct grassland types, covering elevations from 2650 to 6150 m, harbor unrelated species with different evolutionary histories that have converged towards similar anatomical structures.

Stature of dependent forbs is more related to the direct and indirect above‐ and below‐ground effects of a subalpine shrub than are foliage traits

AbstractQuestionGraminoid/shrubland communities include groups of forbs (herbaceous dicots) that differ in their traits, and in their direct and indirect responses to dominant neighbours. Although we have a growing knowledge of which traits might influence species’ direct responses to dominant neighbours, and in particular the crucial importance of plant stature over foliage traits, less is known about the relationship between species’ traits and direct responses to dominant neighbours.LocationAn alpine graminoid/shrubland co‐dominated by the shrub Dasiphora fruticosa and graminoids such as the sedge Kobresia capillifolia on the Tibetan plateau (China).MethodsThe above‐ and below‐ground effects of the shrub in the absence or presence of graminoids were manipulated to quantify direct and indirect responses of forb species, which were grouped with a PCA. For the forbs, six traits characterizing both plant stature and foliage properties were measured and a redundancy analysis was used to assess their patterns of direct and indirect responses to the dominant neighbours.ResultsWe found contrasting direct and indirect responses of forb species to the graminoids, and the above‐ and below‐ground effects of the shrubs, separating the forbs into four species‐groups. A significant positive indirect net effect of the shrubs was observed at the community‐level. Traits of forb species were more tightly related to direct than indirect responses to dominant neighbours, while plant stature had a primary influence over foliage traits, which was only very weakly related to indirect responses.ConclusionsAlthough plant traits, in particular plant stature, have strong influences on species’ direct responses to dominant neighbours, relationships to indirect interactions are more subtle and variable. This inhibits our prediction of the influence of species’ traits on species composition of the community through indirect interactions.

The genome of the medicinal plant Andrographis paniculata provides insight into the biosynthesis of the bioactive diterpenoid neoandrographolide.

Andrographis paniculata is a herbaceous dicot plant widely used for its anti-inflammatory and anti-viral properties across its distribution in China, India and other Southeast Asian countries. A.paniculata was used as a crucial therapeutic treatment during the influenza epidemic of 1919 in India, and is still used for the treatment of infectious disease in China. A.paniculata produces large quantities of the anti-inflammatory diterpenoid lactones andrographolide and neoandrographolide, and their analogs, which are touted to be the next generation of natural anti-inflammatory medicines for lung diseases, hepatitis, neurodegenerative disorders, autoimmune disorders and inflammatory skin diseases. Here, we report a chromosome-scale A.paniculata genome sequence of 269Mb that was assembled by Illumina short reads, PacBio long reads and high-confidence (Hi-C) data. Gene annotation predicted 25428 protein-coding genes. In order to decipher the genetic underpinning of diterpenoid biosynthesis, transcriptome data from seedlings elicited with methyl jasmonate were also obtained, which enabled the identification of genes encoding diterpenoid synthases, cytochrome P450 monooxygenases, 2-oxoglutarate-dependent dioxygenases and UDP-dependent glycosyltransferases potentially involved in diterpenoid lactone biosynthesis. We further carried out functional characterization of pairs of class-I and -II diterpene synthases, revealing the ability to produce diversified labdane-related diterpene scaffolds. In addition, a glycosyltransferase able to catalyze O-linked glucosylation of andrograpanin, yielding the major active product neoandrographolide, was also identified. Thus, our results demonstrate the utility of the combined genomic and transcriptomic data set generated here for the investigation of the production of the bioactive diterpenoid lactone constituents of the important medicinal herb A.paniculata.

Plant Species Richness and Developmental Morphology Stage Influence Mycorrhizal Patagonia Plants Root Colonization

The objectives of this study were to determine the percentage of root colonization by arbuscular mycorrhizal (AM) fungi at various levels of plant species richness and developmental morphology stages in various perennial grass, and herbaceous and woody dicots species using experimental plots during 2013 and 2014. An auger was used to obtain six replicate root + soil samples at each sampling time on each of the study parameters. Roots were washed free of soil, and percentage AM was determined. The shrub Larrea divaricata was the species which showed the lowest percentage of colonization by AM at the vegetative developmental morphology stage at the monocultures and six-species-mixtures on the experimental plots. Dicots, but not grass, species showed a greater percentage colonization by AM fungi at the greatest (i.e., six-species-mixtures) than lowest (i.e., monocultures) species richness. Although at different degrees of species richness and developmental morphology stages, the perennial grasses Nassella longiglumis and N. tenuis, the herbaceous dicot Atriplex semibaccata, and the shrubs L. divaricata and Schinus fasciculatus showed a greater (p < 0.050) percentage colonization by AM fungi during the second than the first study year. Even though it was species- and sampling time-dependent, percentage colonization by AM fungi increased as species richness also increased most of the times. Our results demonstrated that the plant species differences in percentage colonization by AM fungi in the experimental plots were species richness-, developmental morphology stage-, and sampling-time dependents.

Linking hard and soft traits: Physiology, morphology and anatomy interact to determine habitat affinities to soil water availability in herbaceous dicots.

Background and aimsSpecies’ habitat affinities along environmental gradients should be determined by a combination of physiological (hard) and morpho-anatomical (soft) traits. Using a gradient of soil water availability, we address three questions: How well can we predict habitat affinities from hard traits, from soft traits, and from a combination of the two? How well can we predict species' physiological responses to drought (hard traits) from their soft traits? Can we model a causal sequence as soft traits → hard traits → species distributions?MethodsWe chose 25 species of herbaceous dicots whose affinities for soil moisture have already been linked to 5 physiological traits (stomatal conductance and net photosynthesis measured at soil field capacity, water use efficiency, stomatal conductance and soil water potential measured when leaves begin to wilt). Under controlled conditions in soils at field capacity, we measured five soft traits (leaf dry matter content, specific leaf area, leaf nitrogen content, stomatal area, specific root length).Key resultsSoft traits alone were poor predictors (R2 = 0.129) while hard traits explained 48% of species habitat affinities. Moreover, hard traits were significantly related to combinations of soft traits. From a priori biological knowledge and hypothesized ecological links we built a path model showing a sequential pattern soft traits → hard traits → species distributions and accounting for 59.6% (p = 0.782) of habitat wetness.ConclusionsBoth direct and indirect causal relationships existed between soft traits, hard traits and species’ habitat preferences. The poor predictive abilities of soft traits alone were due to the existence of antagonistic and synergistic direct and indirect effects of soft traits on habitat preferences mediated by the hard traits. To obtain a more realistic model applicable to a population level, it has to be tested in an experiment including species competition for water supply.

Predicting habitat affinities of herbaceous dicots to soil wetness based on physiological traits of drought tolerance.

Soil water availability is an important mechanism filtering plant species but the functional basis of this filtering in herbaceous dicots is poorly studied. The authors address three questions: Which physiological traits best predict different levels of drought tolerance or avoidance in herbaceous dicots? To what degree can species' habitat preferences along the gradient of soil moisture availability be predicted by their physiological responses to drought? What are the direct and indirect relationships between the physiological traits and how do they interact to determine the species' habitat preferences? Twenty-five species of herbaceous dicots whose field distributions span a gradient of soil moisture from continually moist to dry were chosen. Under controlled conditions, watering was stopped in a treatment group, the plants were monitored until death of the above-ground tissues and compared with a control group watered at field capacity. Fourteen traits related to plant water economy were measured, including stomatal conductance, net photosynthesis and the visual wilting of leaves. Traits were then analysed using a cumulative link model and path analysis. Five physiological traits (stomatal conductance and net photosynthesis measured at soil field capacity, water use efficiency, stomatal conductance and soil water potential measured when leaves begin to wilt) related to the ability to acquire resources (when water is not limiting) or conserve water (when it is limiting) best predicted different levels of drought tolerance or avoidance in herbaceous dicots. Species' habitat preferences can be fairly predicted by their physiological responses to drought ( R 2 = 0·48). Strong direct and indirect relationships between the five identified traits (plus net photosynthesis at wilting and the time until death) led to synergistic and antagonistic relationship in a path analysis model. To allow better prediction of species distributions along a wetness gradient, the next step would be to link these physiological traits to more accessible functional traits.

Mountain wetland restoration: The role of hydrologic regime and plant introductions after 15 years in the Colorado Rocky Mountains, U.S.A.

Twelve wetland complexes were buried and/or drained by golf course and ski area development in the Colorado Rocky Mountains in the 1980s and early 1990s. We restored all or portions of each wetland, including fens, wet meadows and riparian areas, during 1997–2002. Intensive pre- and post-construction monitoring was used to develop restoration plans and evaluate their success. We revisited the sites to analyze long-term restoration processes in 2013–2016. Prior to construction the depth to the water table was measured weekly in monitoring wells installed through the fill, and into the wetland surfaces during and following restoration. Reference sites for each wetland type were used to characterize water table depth and vegetation for each wetland type. Restoration included removal of fill material and drains to create land surfaces with water table depth and dynamics similar to the reference areas for each wetland type. We planted each site with nursery grown sedges, willows and herbaceous dicots. Post restoration monitoring of water table depth, vegetation composition, sedge shoot density and willow growth was analyzed.The water table depth and dynamics of each restored wetland was similar to suitable reference sites on short and long time scales, indicating a stable hydrologic regime. Carex utriculata reached its maximum shoot density 4–5 years after planting indicating rapid growth and high production. Willow stems were still increasing in height 15 years after planting and basal stem density was also increasing. Most planted herbaceous dicots disappeared, indicating the difficulty of establishing them from plantings. Exotic (non-native) plants have invaded all three wetland types, with their highest cover in riparian areas. Critical factors that led to success were careful hydrological analysis of reference and restoration sites prior to earthwork, creating appropriate land/ground water interactions, and establishing clonal rhizomatous sedges and native willows.

Comparative Genomic Analysis of the GRF Genes in Chinese Pear (Pyrus bretschneideri Rehd), Poplar (Populous), Grape (Vitis vinifera), Arabidopsis and Rice (Oryza sativa).

Growth-regulating factors (GRFs) are plant-specific transcription factors that have important functions in regulating plant growth and development. Previous studies on GRF family members focused either on a single or a small set of genes. Here, a comparative genomic analysis of the GRF gene family was performed in poplar (a model tree species), Arabidopsis (a model plant for annual herbaceous dicots), grape (one model plant for perennial dicots), rice (a model plant for monocots) and Chinese pear (one of the economical fruit crops). In total, 58 GRF genes were identified, 12 genes in rice (Oryza sativa), 8 genes in grape (Vitis vinifera), 9 genes in Arabidopsis thaliana, 19 genes in poplar (Populus trichocarpa) and 10 genes in Chinese pear (Pyrus bretschneideri). The GRF genes were divided into five subfamilies based on the phylogenetic analysis, which was supported by their structural analysis. Furthermore, microsynteny analysis indicated that highly conserved regions of microsynteny were identified in all of the five species tested. And Ka/Ks analysis revealed that purifying selection plays an important role in the maintenance of GRF genes. Our results provide basic information on GRF genes in five plant species and lay the foundation for future research on the functions of these genes.

Diversity and composition of plants, butterflies and odonates in an Imperata cylindrica grassland landscape in East Kalimantan, Indonesia

Abstract:In Indonesia and elsewhere, Imperata cylindrica grassland now covers millions of hectares of land previously covered by rain forest. In the present study, shrubs, trees and climbers were recorded in sixteen 10 × 20-m plots and herb cover (ferns, grasses and herbaceous dicots) estimated in nested 2 × 2-m subplots. Butterflies and odonates were netted along 300-m transects. All plots and transects were randomly allocated to a 450 ha, I. cylindrica-dominated landscape. A total of 43 shrub, tree and climber, 16 herb, 67 butterfly and 30 odonate species were recorded. Shrubs, trees and climbers were present throughout the study area, but basal area was very low and mainly consisted of invasive species. Imperata cylindrica covered an estimated 65% of the area with other plant species or bare soil covering the remainder. Butterfly and odonate communities mainly consisted of species with large geographic distributions, but some recorded species had more limited distributions. The latter were, however, species known to associate with perturbed forest environments. Variation in the composition of butterflies and odonates was also related to variation in habitat structure (e.g. altitude and slope) and plant composition. Plant composition in particular appeared to structure both butterfly and odonate communities.

Occurrence of different phytoplasma infections in wild herbaceous dicots growing in vineyards affected by bois noir in Tuscany (Italy)

1 , domenico RIZZO 2 Summary. Wild herbaceous dicotyledonous plants (dicots) showing symptoms ascribable to phytoplasma disor- ders were found to be widely distributed in organic vineyards in central Tuscany (Italy) affected by bois noir, a grapevine yellows disease caused by Candidatus Phytoplasma solani. In 2010 symptomatic dicots were tenta- tively identified to species level and the incidence of symptoms estimated in two selected vineyards in the prov- ince of Florence. Incidence ranged from 2 to 77%, and was not related to the relative abundance of hosts since very common species as well as relatively rare ones were consistently found to be symptomatic. PCR indexing and 16S rRNA sequence analyses indicated that two phytoplasmas co-existed in the vineyards: Ca. P. solani, infecting the root systems of 17 taxa, and a phytoplasma closely related to Ca. P. phoenicium, infecting 11 taxa, and occasion- ally co-infecting the same plant. Regardless of the high frequency of both pathogens in the vineyards, only Ca. P. solani could be detected in the grapevines. Population screening by means of tuf sequence analyses revealed the presence of only the tuf-b Ca. P. solani type both in dicot hosts and grapevine. This supports current notions of bois noir epidemiology, indicating that some infected dicots act as sources of Ca. P. solani inoculum whereas oth- ers are dead-end hosts. When the same specimens were screened by sequence analysis of the vmp1 gene, evidence was found that different phytoplasma genotypes may be predominant in grapevines and dicots.

Insights into epidemiology and control of diseases of annual plants caused by the Pseudomonas syringae species complex

The plant pathogenic Pseudomonas syringae species complex (Pssc) causes diseases of hundreds of species of monocots, herbaceous dicots and woody dicots worldwide. On annual plants, reports of disease caused by the Pssc have markedly increased in the last years. Hence, efforts are needed to mitigate the consequences of increasing disease outbreaks and to understand the underlying epidemiological factors. Here, we have reviewed the literature to highlight the salient features of the Pssc as pathogens of annual plant species and to underscore what remains unknown about the diseases they cause. The major points are as follows: (1) Since only the beginning of this century, 72 reports of disease outbreaks in 20 countries have been associated with the Pssc on over 40 annual plant species; (2) disease incidence caused by the Pssc on annual plants ranges from 50 to 100 % in epidemic years; (3) seed infestation is the main cause of long-distance pathogen dissemination; (4) foliar disease symptoms are very common on annual plants although the Pssc causes symptoms on fruits of bean, cantaloupe, cucumber, okra and tomato; (5) environmental factors such as rainfall and humidity have important roles in the Pssc disease epidemiology; (6) several new disease reports contradict the concept of the so-called pathovar, thereby raising the question of whether strains in the Pssc are mostly generalists rather than specialists as currently believed; and (7) disease control of annual plants is frequently based on approaches integrating biological, chemical and cultural measures with available plant resistance.

Insights into plant cell wall structure, architecture, and integrity using glycome profiling of native and AFEXTM-pre-treated biomass.

Cell walls, which constitute the bulk of plant biomass, vary considerably in their structure, composition, and architecture. Studies on plant cell walls can be conducted on both native and pre-treated plant biomass samples, allowing an enhanced understanding of these structural and compositional variations. Here glycome profiling was employed to determine the relative abundance of matrix polysaccharides in several phylogenetically distinct native and pre-treated plant biomasses. Eight distinct biomass types belonging to four different subgroups (i.e. monocot grasses, woody dicots, herbaceous dicots, and softwoods) were subjected to various regimes of AFEX™ (ammonia fiber expansion) pre-treatment [AFEX is a trademark of MBI, Lansing (http://www.mbi.org]. This approach allowed detailed analysis of close to 200 cell wall glycan epitopes and their relative extractability using a high-throughput platform. In general, irrespective of the phylogenetic origin, AFEX™ pre-treatment appeared to cause loosening and improved accessibility of various xylan epitope subclasses in most plant biomass materials studied. For most biomass types analysed, such loosening was also evident for other major non-cellulosic components including subclasses of pectin and xyloglucan epitopes. The studies also demonstrate that AFEX™ pre-treatment significantly reduced cell wall recalcitrance among diverse phylogenies (except softwoods) by inducing structural modifications to polysaccharides that were not detectable by conventional gross composition analyses. It was found that monitoring changes in cell wall glycan compositions and their relative extractability for untreated and pre-treated plant biomass can provide an improved understanding of variations in structure and composition of plant cell walls and delineate the role(s) of matrix polysaccharides in cell wall recalcitrance.

Deletion of a gene cluster encoding pectin degrading enzymes in Caldicellulosiruptor bescii reveals an important role for pectin in plant biomass recalcitrance.

BackgroundA major obstacle, and perhaps the most important economic barrier to the effective use of plant biomass for the production of fuels, chemicals, and bioproducts, is our current lack of knowledge of how to efficiently and effectively deconstruct wall polymers for their subsequent use as feedstocks. Plants represent the most desired source of renewable energy and hydrocarbons because they fix CO2, making their use carbon neutral. Their biomass structure, however, is a barrier to deconstruction, and this is often referred to as recalcitrance. Members of the bacterial genus Caldicellulosiruptor have the ability to grow on unpretreated plant biomass and thus provide an assay for plant deconstruction and biomass recalcitrance.ResultsUsing recently developed genetic tools for manipulation of these bacteria, a deletion of a gene cluster encoding enzymes for pectin degradation was constructed, and the resulting mutant was reduced in its ability to grow on both dicot and grass biomass, but not on soluble sugars. The plant biomass from three phylogenetically diverse plants, Arabidopsis (a herbaceous dicot), switchgrass (a monocot grass), and poplar (a woody dicot), was used in these analyses. These biomass types have cell walls that are significantly different from each other in both structure and composition. While pectin is a relatively minor component of the grass and woody dicot substrates, the reduced growth of the mutant on all three biomass types provides direct evidence that pectin plays an important role in biomass recalcitrance. Glycome profiling of the plant material remaining after growth of the mutant on Arabidopsis biomass compared to the wild-type revealed differences in the rhamnogalacturonan I, homogalacturonan, arabinogalactan, and xylan profiles. In contrast, only minor differences were observed in the glycome profiles of the switchgrass and poplar biomass.ConclusionsThe combination of microbial digestion and plant biomass analysis provides a new and important platform to identify plant wall structures whose presence reduces the ability of microbes to deconstruct plant walls and to identify enzymes that specifically deconstruct those structures.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-014-0147-1) contains supplementary material, which is available to authorized users.

The Optimization of Seed Yield across the Flowering Season of Gentiana leucomelaena (Gentianaceae), an Herbaceous Tibetan Annual

The seed yield of herbaceous annuals may be resource- or pollinator-limited. The extent to which either or both of these limitations negatively affect seed yield is hypothesized to vary with the timing of flowering because of seasonal changes in pollinator and resource availabilities. We tested this hypothesis by examining the relationship between seed yield and pollinator visitation rates, flowering phenology, aboveground plant biomass, and biomass allocation patterns, fruit set, and seed set, seed number per flower, and seed mass for Gentiana leucomelaena, an annual herbaceous dicot that produces four types of flowering shoots as a result of differences in flower color (blue and white) and dichogamy-type (protogyny and protandry). Bivariate plots of reproductive efficiency (total seed mass per shoot) versus vegetative mass were curvilinear and showed that early- and late-flowering shoots were more likely to be limited in seed yield than shoots flowering during the middle of the flowering season. Early-flowering shoots had greater biomass but had lower fruit set and seed set with fewer but larger seeds per fruit. These features were consistent with pollinator (visitation rate) limitations on seed yield. In contrast, late-flowering shoots had smaller biomass but had higher fruit set and seed set with many but smaller seeds per fruit. These features were consistent with resource (plant biomass) limitations on seed yield. Moreover, early-flowering shoots tended to produce white and protogynous flowers and allocated more to leaf growth, whereas late-flowering shoots tended to produce blue and protandrous flowers and allocated more to stem growth in height (perhaps to reduce shading by neighbors). In addition, the peak time of flowering shoot density coincided with the peak of reproductive efficiency. In conclusion, limitations on the seed yield of this species varied with the timing of flowering. G. leucomelaena appears to have evolved a system of changing flower color and dichogamy-type that optimizes seed yield in an alpine meadow habitat.