Growing duckweed for biofuel production: a review

Duckweed can be utilised to produce ethanol, butanol and biogas, which are promising alternative energy sources to minimise dependence on limited crude oil and natural gas. The advantages of this aquatic plant include high rate of nutrient (nitrogen and phosphorus) uptake, high biomass yield and great potential as an alternative feedstock for the production of fuel ethanol, butanol and biogas. The objective of this article is to review the published research on growing duckweed for the production of the biofuels, especially starch enrichment in duckweed plants. There are mainly two processes affecting the accumulation of starch in duckweed biomass: photosynthesis for starch generation and metabolism-related starch consumption. The cost of stimulating photosynthesis is relatively high based on current technologies. Considerable research efforts have been made to inhibit starch degradation. Future research need in this area includes duckweed selection, optimisation of duckweed biomass production, enhancement of starch accumulation in duckweeds and use of duckweeds for production of various biofuels.

A protocol for conducting 7-day daily renewal tests with Lemna gibba

Lemna gibba (a duckweed) is a freshwater macrophyte commonly used in toxicity testing, and Lemna spp are currently the only aquatic higher plants required for evaluation of pesticides under the pesticide registration guidelines of the EPA. The methods currently available for toxicity testing by various organizations and agencies, including ASTM, OECD, EPA and Environment Canada, are largely static or semistatic tests with unspecified renewal intervals (OECD) and may not provide a consistent means of exposure owing to short toxicant half-life in aquatic media, uptake of chemical by plants and evaporation of nutrient media. The procedure outlined here details a simple and efficient 7-day daily static renewal procedure for conducting toxicity tests with L. gibba, the appropriate end points to assess, the statistical criteria necessary for analyzing the toxicity data, as well as the steps required to culture and maintain L. gibba. This protocol is based on a modified version of a widely accepted static method.

Relationships within the Araceae: comparison of morphological patterns with molecular phylogenies

PREMISE OF THE STUDY

The first family-wide molecular phylogeny of the Araceae, a family of about 3800 published species in 120 genera, became available in 1995, followed by a cladistic analysis of morpho-anatomical data in 1997. The most recent and comprehensive family-wide molecular phylogeny was published in 2008 and included species from 102 genera. We reanalyzed the molecular data with a more complete genus sampling and compared the resulting phylogeny with morphological and anatomical data, with a view to contributing to a new formal classification of the Araceae.

METHODS

We analyzed 113 aroid genera and 4494 aligned nucleotides that resulted from adding 11 genera to the 2008 molecular matrix. We also analyzed 81 morphological characters in the context of the molecular phylogeny, using an extended version of the 1997 morpho-anatomical data set.

KEY RESULTS

The resulting maximum-likelihood phylogeny is well resolved and supported, and most of the 44 larger clades also have morphological or anatomical synapomorphies as well as ecological or geographic cohesion. Of the 44 clades, 16 are here newly circumscribed and informally named. However, some relationships remain poorly supported within the Aroideae subfamily. The most problematic placement is Calla within Aroideae, which conflicts with the distribution of morphological, anatomical, and palynological character states.

CONCLUSIONS

The comparison of the molecular analysis with morphological and anatomical data presented here represents an important basis for a new formal classification for the Araceae and for the understanding of the evolution of this ancient family, a monocot group known in the fossil record from the early Cretaceous.

Phytotoxicity of cobalt ions on the duckweed Lemna minor - Morphology, ion uptake, and starch accumulation

Cobalt (Co2+) inhibits vegetative growth of Lemna minor gradually from 1 μM to 100 μM. Fronds accumulated up to 21 mg Co2+ g(-1) dry weight at 10 μM external Co2+ indicating hyperaccumulation. Interestingly, accumulation of Co2+ did not decrease the iron (Fe) content in fronds, highlighting L. minor as a suitable system for studying effects of Co2+ undisturbed by Fe deficiency symptoms unlike most other plants. Digital image analysis revealed the size distribution of fronds after Co2+ treatment and also a reduction in pigmentation of newly formed daughter fronds unlike the mother fronds during the 7-day treatment. Neither chlorophyll nor photosystem II fluorescence changed significantly during the initial 4d, indicating effective photosynthesis. During the later phase of the 7-day treatment, however, chlorophyll content and photosynthetic efficiency decreased in the Co2+-treated daughter fronds, indicating that Co2+ inhibits the biosynthesis of chlorophyll rather than leading to the destruction of pre-existing pigment molecules. In addition, during the first 4d of Co2+ treatment starch accumulated in the fronds and led to the transition of chloroplasts to chloro-amyloplasts and amylo-chloroplasts, while starch levels strongly decreased thereafter.

Toxic effects of Pb on Spirodela polyrhiza (L.): Subcellular distribution, chemical forms, morphological and physiological disorders

The impact of lead (Pb) on Spirodela polyrhiza was studied to determine the subcellular distribution, chemical forms, and resulting morphophysiological modifications after treatments with 20 or 80 μM Pb(NO₃)₂ for 10 days. At the subcellular level, the Pb uptake by S. polyrhiza was mainly compartmentalized in the cell walls (70%), and the majority of Pb (approximately 70%) was extracted using 1 M NaCl and 2% acetic acid (HAc). Visual symptoms of phytotoxcity, surface roughness and closure of stomata, were observed in Pb-treated fronds. Electron-dense precipitates were present in cell walls, and changes to the ultrastructure were most noticeably exhibited in organelle shape, internal organization, and size of the plastoglobules of chloroplasts. Toxic concentrations of Pb induced oxidative stress in fronds, characterized by an accumulation of malondialdehyde (MDA) and decreased chlorophyll and unsaturated fatty acid contents. Pb exposure increased ABS/RC, TRo/RC, DIo/RC, Vj, and φDo (Fv/Fm), indicating that reaction centers were transformed to dissipation sinks, leading to a decrease in the efficiency of photosystem II, which was evident from the decreased values of F_v/F_o, F_v/F_m, ψEo, φEo, RC/ABS, and PI_abs. These results indicated that decreased photosynthesis in Pb-treated fronds was partially ascribed to the lower pigment content, inhibition of electron transport, inactivation of the reaction centers, damage to the chloroplast ultrastructure, and stomatal closure. The physiological implications of subcellular distribution and chemical forms are discussed in relation to Pb accumulation and detoxification. However, Pb accumulation significantly impaired photosynthesis and membrane integrity in the fronds of S. polyrhiza.

Reconstructing the origin and elaboration of insect-trapping inflorescences in the Araceae

PREMISE OF THE STUDY

Floral traps are among the most sophisticated devices that have evolved in angiosperms in the context of pollination, but the evolution of trap pollination has not yet been studied in a phylogenetic context. We aim to determine the evolutionary history of morphological traits that facilitate trap pollination and to elucidate the impact of pollinators on the evolution of inflorescence traps in the family Araceae. •

METHODS

Inflorescence morphology was investigated to determine the presence of trapping devices and to classify functional types of traps. We inferred phylogenetic relationships in the family using maximum likelihood and Bayesian methods. Character evolution of trapping devices, trap types, and pollinator types was then assessed with maximum parsimony and Bayesian methods. We also tested for an association of trap pollination with specific pollinator types. •

KEY RESULTS

Inflorescence traps have evolved independently at least 10 times within the Araceae. Trapping devices were found in 27 genera. On the basis of different combinations of trapping devices, six functional types of traps were identified. Trap pollination in Araceae is correlated with pollination by flies. •

CONCLUSIONS

Trap pollination in the Araceae is more common than was previously thought. Preadaptations such as papillate cells or elongated sterile flowers facilitated the evolution of inflorescence traps. In some clades, imperfect traps served as a precursor for the evolution of more elaborate traps. Traps that evolved in association with fly pollination were most probably derived from mutualistic ancestors, offering a brood-site to their pollinators.

Response of Pistia stratiotes to heavy metals (Cr, Ni, and Zn) and phosphorous

The effects of Cr, Ni, Zn, and P exposure on the root anatomic structure, growth, and chlorophyll a concentration of Pistia stratiotes L. were studied. Plastic aquaria containing 50 g of wet plants and 5 L of pond water added with the contaminant(s) were disposed. The treatments were: (1) Cr, (2) Ni, (3) Zn, (4) P, (5) Cr + Ni + Zn, (6) Cr + Ni + Zn + P, and (7) control. Contaminant additions were done seven times. In each addition, concentrations of 1 mg of metals or 5 mg of P per liter of water were added. Chlorophyll a was an indicator more sensitive to Zn and Cr toxicity than the relative growth rate. Ni and Cr + Ni + Zn treatments were the most toxic ones, in which biomass and the root anatomical parameters (root length, cross-sectional areas [CSAs] of root, stele, and metaxylem vessels) decreased significantly. The addition of P to the treatment with combined metals attenuated the decrease in plant growth and root length, and caused a significant increase in CSAs of total metaxylem vessels, suggesting that P increased the tolerance of P. stratiotes to metals. This fact has important implications for the use of this macrophyte in constructed wetlands for industrial wastewater treatment.

Chromatin organisation in duckweed interphase nuclei in relation to the nuclear DNA content

The accessibility of DNA during fundamental processes, such as transcription, replication and DNA repair, is tightly modulated through a dynamic chromatin structure. Differences in large-scale chromatin structure at the microscopic level can be observed as euchromatic and heterochromatic domains in interphase nuclei. Here, key epigenetic marks, including histone H3 methylation and 5-methylcytosine (5-mC) as a DNA modification, were studied cytologically to describe the chromatin organisation of representative species of the five duckweed genera in the context of their nuclear DNA content, which ranged from 158 to 1881 Mbp. All studied duckweeds, including Spirodela polyrhiza with a genome size and repeat proportion similar to that of Arabidopsis thaliana, showed dispersed distribution of heterochromatin signatures (5mC, H3K9me2 and H3K27me1). This immunolabelling pattern resembles that of early developmental stages of Arabidopsis nuclei, with less pronounced heterochromatin chromocenters and heterochromatic marks weakly dispersed throughout the nucleus.

A novel feature of structural variegation in leaves of the tropical plant Schismatoglottis calyptrata

We report a novel feature of leaf variegation. As is often the case in tropical forest floor herbs, Schismatoglottis calyptrata leaves feature structural variegation. Examination of leaf anatomy in S. calyptrata revealed a novel feature of structural variegation, which was generated by variation in the spatial arrangement of the adaxial-most tip of the palisade cells. In fully green leaf parts, contact between the adaxial-most tip of the palisade cells and the cone-shaped base of the outer epidermis cells was tight, and palisade cells were arranged radially around each epidermal cell. In dull, grayish-green leaf parts, the contact was loose, and no particular spatial arrangement of palisade cells relative to epidermal cells was observed. This feature of structural variation could be disadvantageous for photosynthesis efficiency in view of the hypothesis that, for rainforest herbs, cone-shaped epidermal cells may function as lenses. However, the high frequency of leaf variegation of S. calyptrata in natural habits suggests that this structural variegation plays an unknown advantageous role.

Anodic asymmetry of leaves and flowers and its relationship to phyllotaxis

BACKGROUND AND AIMS

New approaches are needed to evaluate the various hypotheses of phyllotaxis, and an examination of anodic leaf asymmetry may be one such approach.

METHODS

Data were collected on the direction of midrib curvature and leaf coil in Syngonium podophyllum, the location of floral buds in Acalypha virginica, the position of secondary leaves of Croton variegatus 'Banana' and the relative size of half-lamina in Aglaonema crispum and Calathea ornata.

KEY RESULTS

All five features were exclusively anodic with respect to the direction of the genetic spiral regardless of whether the spiral was clockwise or counterclockwise.

CONCLUSIONS

Any phyllotactic mechanism must include some asymmetric component which cannot be explained by the prevalent hypotheses of contact parastichies, inhibitory fields, available space, pressure waves and auxin transport. The most favourable hypothesis is the primary vasculature explanation as it includes an asymmetric feature.

Influence of nitrogen and phosphorus concentrations and ratios on Lemna gibba growth responses to triclosan in laboratory and stream mesocosm experiments

The effects of co-occurring nutrient and contaminant stressors are very likely to interact in aquatic systems, particularly at the level of primary producers. Site-specific nitrogen (N) and phosphorus (P) concentrations are often much lower and differ in relative availability than those used in nutrient-saturated laboratory assays for aquatic plants, which can introduce uncertainty in prospective ecological hazard and risk assessments. Because triclosan, an antimicrobial agent included in personal care products, potentially presents high relative risk among antimicrobial agents to aquatic plants and algae, we performed laboratory experiments with the model aquatic macrophyte Lemna gibba across a gradient of environmentally relevant N:P levels with and without triclosan co-exposure. Frond numbers (7 d) were significantly higher in N:P treatments of 16 and 23 but were lower in N:P of 937 and 2,500 treatments relative to standardized control media (N:P=3). When triclosan co-exposure occurred at high nutrient concentrations, frond number median effective concentration values at N:P 0.75, 3, and 16 were more than twofold lower than triclosan median effective concentration values in low nutrient media N:P ratios. However, a triclosan median effective concentration for frond number was twofold lower at N:P of 2,500 than at other N:P ratios in low concentration media. Influences of P enrichment on triclosan toxicity to L. gibba were further explored during a 14-d outdoor experimental stream mesocosm study. Effects of 2.6 and 20.8 microg L(-1) triclosan on L. gibba growth rates were more pronounced with increasing P treatment levels, which was generally consistent with our laboratory observations. Findings from these laboratory and field studies indicate that site-specific nutrient concentrations and ratios should be considered during assessments of primary producer responses to chemical stressors.

Status of duckweed genomics and transcriptomics

Duckweeds belong to the smallest flowering plants that undergo fast vegetative growth in an aquatic environment. They are commonly used in wastewater treatment and animal feed. Whereas duckweeds have been studied at the biochemical level, their reduced morphology and wide environmental adaption had not been subjected to molecular analysis until recently. Here, we review the progress that has been made in using a DNA barcode system and the sequences of chloroplast and mitochondrial genomes to identify duckweed species at the species or population level. We also review analysis of the nuclear genome sequence of Spirodela that provides new insights into fundamental biological questions. Indeed, reduced gene families and missing genes are consistent with its compact morphogenesis, aquatic floating and suppression of juvenile-to-adult transition. Furthermore, deep RNA sequencing of Spirodela at the onset of dormancy and Landoltia in exposure of nutrient deficiency illustrate the molecular network for environmental adaption and stress response, constituting major progress towards a post-genome sequencing phase, where further functional genomic details can be explored. Rapid advances in sequencing technologies could continue to promote a proliferation of genome sequences for additional ecotypes as well as for other duckweed species.

Floral biology and reproductive isolation by floral scent in three sympatric aroid species in French Guiana

We studied the reproductive biology of three sympatric Araceae species, Anthurium sagittatum, A. thrinax and Spathiphyllum humboldtii in French Guiana. The plants flowered simultaneously and were visited by scent-collecting male euglossine bees, which were apparently their major pollinators. In total, each species was visited by 3-7 euglossine species, and 2-3 euglossine species accounted for at least 80% of all flower visits, with visits being plant species-specific. Floral scent consisted of 6-10 main compounds, which made up 76-94% of the total amount of volatiles and were specific in these high amounts to each plant species. We suggest that the different floral scents lead to clear separation of the main pollinating euglossine species, providing a directed and efficient intraspecific pollen flow that results in high reproductive success. Since the simple floral (inflorescence) morphology of the studied plants does not support any morphological mechanisms to exclude visitors, as for example in euglossine-pollinated perfume orchids, floral scent might be of major importance for the reproductive isolation and sympatric occurrence of these plants.

Flowering mechanisms, pollination strategies and floral scent analyses of syntopically co-flowering Homalomena spp. (Araceae) on Borneo

In this study, the flowering mechanisms and pollination strategies of seven species of the highly diverse genus Homalomena (Araceae) were investigated in native populations of West Sarawak, Borneo. The floral scent compositions were also recorded for six of these species. The selected taxa belong to three out of four complexes of the section Cyrtocladon (Hanneae, Giamensis and Borneensis). The species belonging to the Hanneae complex exhibited longer anthesis (53-62 h) than those of the Giamensis and Borneensis complexes (ca. 30 h). Species belonging to the Hanneae complex underwent two floral scent emission events in consecutive days, during the pistillate and staminate phases of anthesis. In species belonging to the Giamensis and Borneensis complexes, floral scent emission was only evident to the human nose during the pistillate phase. A total of 33 volatile organic compounds (VOCs) were detected in floral scent analyses of species belonging to the Hanneae complex, whereas 26 VOCs were found in samples of those belonging to the Giamensis complex. The floral scent blends contained uncommon compounds in high concentration, which could ensure pollinator discrimination. Our observations indicate that scarab beetles (Parastasia gestroi and P. nigripennis; Scarabaeidae, Rutelinae) are the pollinators of the investigated species of Homalomena, with Chaloenus schawalleri (Chrysomelidae, Galeuricinae) acting as a secondary pollinator. The pollinators utilise the inflorescence for food, mating opportunities and safe mating arena as rewards. Flower-breeding flies (Colocasiomyia nigricauda and C. aff. heterodonta; Diptera, Drosophilidae) and terrestrial hydrophilid beetles (Cycreon sp.; Coleoptera, Hydrophilidae) were also frequently recovered from inflorescences belonging to all studied species (except H. velutipedunculata), but they probably do not act as efficient pollinators. Future studies should investigate the post-mating isolating barriers among syntopically co-flowering Homalomena sharing the same visiting insects.

Morphological and structural characterization of the attachment system in aerial roots of Syngonium podophyllum

The attachment of aerial roots of Syngonium podophyllum involves a multi-step process adjusted by multi-scale structures. Helical-crack root hairs are first found in the attachment system, representing specialized structures for surface anchorage. The morphological variability of attachment organs reflects diverse climbing strategies. One such anchoring mode in clinging-climbers involves the time-dependent interaction between roots and the support: By naturally occurring adhesive roots with root hairs, the plant can ascend on supports of any shape and size. As a typical root-climber, Syngonium podophyllum develops elongate aerial roots at nodes. Here, we studied its attachment behavior from the external morphology to the internal structure in detail. Through SEM and LM observation on several root-substrate interfaces, we suggested that the attachment of aerial roots was mediated by a multi-step process, in which root hairs played significant roles in releasing mucilaginous substance and securing the durable anchorage. We summarized all the types of shape changes of root hairs with particular focus on the abnormal transition from a tube to a helical-crack ribbon. We demonstrated our understanding with respect to the formation of the helical-crack root hairs, based on the structural evidence of cellulose microfibrils orientation on the cell wall lamellae. The helical-crack root hairs serving as energy-dissipating units retard the failure of adhesion under high winds and loads.

Comparative profiling of microRNAs and their effects on abiotic stress in wild-type and dark green leaf color mutant plants of Anthurium andraeanum 'Sonate'

MicroRNAs (miRNAs) are a class of non-coding small RNAs that play important roles in the regulation of gene expression. Although plant miRNAs have been extensively studied in model systems, less is known in other plants with limited genome sequence data, including Anthurium andraeanum. To identify miRNAs and their target genes in A. andraeanum and study their responses to abiotic stresses, we conducted deep-sequencing of two small RNA (sRNA) libraries prepared from young leaves of wild-type (WT) and dark green (dg) leaf color mutant plants of A. andraeanum 'Sonate'. A total of 53 novel miRNAs were identified, 32 of which have been annotated to 18 miRNA families. 10 putative miRNAs were found to be differentially expressed in WT and dg, among which two miRNAs were significantly up-regulated and eight down-regulated in dg relative to WT. One differentially expressed miRNA, Aa-miR408, was dramatically up-regulated in dg. qRT-PCR analysis and heterologous expression of Aa-miR408 in Arabidopsis under different stress treatments suggest that Aa-miR408 is involved in abiotic stress responses in A. andraeanum. Our results provide a foundation for further dissecting the roles of miRNAs and their targets in regulating abiotic stress tolerance in A. andraeanum.

Floral diversity and pollination strategies of three rheophytic Schismatoglottideae (Araceae)

Homoplastic evolution of 'unique' morphological characteristics in the Schismatoglottideae - many previously used to define genera - prompted this study to compare morphology and function in connection with pollination biology for Aridarum nicolsonii, Phymatarum borneense and Schottarum sarikeense. Aridarum nicolsonii and P. borneense extrude pollen through a pair of horned thecae while S. sarikeense sheds pollen through a pair of pores on the thecae. Floral traits of spathe constriction, presence and movement of sterile structures on the spadix, the comparable role of horned thecae and thecae pores, the presence of stamen-associated calcium oxalate packages, and the timing of odour emission are discussed in the context of their roles in pollinator management. Pollinators for all investigated species were determined to be species of Colocasiomyia (Diptera: Drosophilidae).

Conventional and novel modes of exine patterning in members of the Araceae--the consequence of ecological paradigm shifts?

In the family Araceae, the members of all subfamilies except Aroideae follow the conventional mode of exine formation pattern, which conforms with the textbook view of sporoderm stratification and chemistry (sporopollenin ektexine formed before the endexine). Only members of the subfamily Aroideae show a quite uncommon mode of exine formation pattern, with an endexine formed prior to the nonsporopollenin, polysaccharidic outer exine layer. The intine is formed simultaneously with this non-sporopollenin layer. From the differing timetable and especially from the different origin it is concluded that this outer exine layer is not homologous to the angiosperm ektexine. The fundamental question, why members of the Aroideae lack an elaborated sporopollenin ektexine, is discussed in terms of functionality of the nonsporopollenin outer exine layer. It seems that a major change in aroid evolution took place at the point when the family phylogenetically and ecologically shifted from bisexual (most subfamilies) to unisexual flowers (Aroideae only). The hypothesis is that ephemeral spathes and the absence of sporopollenin are the consequence of an adaptive syndrome for a short pollination time window in many members of the Aroideae, with short-lived pollen, an energetically not costly pollen wall, rapid germination of pollen tube, and brief receptivity of stigma.

Adaptations for insect-trapping in brood-site pollinated Colocasia (Araceae)

The Araceae include both taxa with rewarding and deceptive trap pollination systems. Here we report on a genus in which rewarding and imprisonment of the pollinators co-occur. We studied the pollination of four species of Colocasia in Southwest China and investigated the morpho-anatomical adaptations of the spathe related to the attraction and capture of pollinators. All four species were pollinated by drosophilid flies of the genus Colocasiomyia. The flies are temporally arrested within the inflorescence and departure is only possible after pollen release. Trapping of the flies is accomplished by the closure of the spathe during anthesis. Moreover, in two species the spathe is covered with papillate epidermal cells known to form slippery surfaces in deceptive traps of Araceae. However, in Colocasia the papillae proved not slippery for the flies. The morpho-anatomical properties of the spathe epidermis indicate that it is an elaborate osmophore and serves for the emission of odours only. Despite its similarity to deceptive traps of other aroids, Colocasia and Colocasiomyia have a close symbiotic relationship, as the attracted flies use the inflorescence as a site for mating and breeding. The trap mechanism has presumably evolved independently in Colocasia and is supposed to facilitate more efficient pollen export.

[Comparative identification on Dai medicine "Pokou" and its processing product]

OBJECTIVE

To research identification methods of the Dai Medicine "Pokou" (the rhizome of Homalomena gigantea) and its processing product, and provide basis for identification of the drug in further research and application.

METHODS

Macroscopic, microscopic observation and TLC and FTIR techniques were used to authenticate this raw medicine and its processing product.

RESULTS

There were certain differences in the macroscopic features. The TLC result and infrared spectra of the samples had also obvious differences. The methods for identification of this raw medicine and its processing product were established, The detailed tissue and powder of this medicine were drawn.

CONCLUSION

The results provided the basis for identification of the medicine and establishment of its quality standard.

Morphological diversity of the velamen radicum in the genus Anthurium (Araceae)

Epiphytes develop anatomical features to improve efficiency of the uptake of water and nutrients, such as absorptive foliar scales or a velamen radicum. Despite substantial studies on the occurrence, morphology, development and phylogeny of the velamen, most of the available literature is focused on Orchidaceae, making current knowledge on velamen clearly biased. A recent publication firmly established that velamina are common in Anthurium species. Thus, this study provides further insights by describing velamen morphological characteristics of Anthurium species and classifying them into different velamen types. Furthermore, we investigate if the different velamen morphological traits are clade-specific and phylogenetically conserved within the genus. Using SEM, we performed a morphological study on 89 Anthurium species, describing six micromorphological traits of velamen and exodermis, following traits used to classify Orchidaceae velamen by Porembski & Barthlott (1988). We distinguished nine velamen types, including two that are unique to Anthurium and not similar to any type found in Orchidaceae. Comparing velamen morphology within the phylogenetic tree of Anthurium revealed clear phylogenetic signals. This study provides detailed morphological descriptions among 89 species of Anthurium from the Araceae, and substantially broadens our knowledge of this tissue. However, velamen function has been even less studied, with hardly anything known about functional significance of having secondary cell wall thickening and perforations on velamen cell walls. Therefore, a logical next step would be to connect these anatomical features to their functions.

The evolution of the duckweed ionome mirrors losses in structural complexity

BACKGROUND AND AIMS

The duckweeds (Lemnaceae) consist of 36 species exhibiting impressive phenotypic variation, including the progressive evolutionary loss of a fundamental plant organ, the root. Loss of roots and reduction of vascular tissues in recently derived taxa occur in concert with genome expansions of ≤14-fold. Given the paired loss of roots and reduction in structural complexity in derived taxa, we focus on the evolution of the ionome (whole-plant elemental contents) in the context of these fundamental changes in body plan. We expect that progressive vestigiality and eventual loss of roots might have both adaptive and maladaptive consequences that are hitherto unknown.

METHODS

We quantified the ionomes of 34 accessions in 21 species across all duckweed genera, spanning 70 Myr in this rapidly cycling plant (doubling times are as rapid as ~24 h). We related both micro- and macroevolutionary ionome contrasts to body plan remodelling and showed nimble microevolutionary shifts in elemental accumulation and exclusion in novel accessions.

KEY RESULTS

We observed a robust directional trend in calcium and magnesium levels, decreasing from the ancestral representative Spirodela genus towards the derived rootless Wolffia, with the latter also accumulating cadmium. We also identified abundant within-species variation and hyperaccumulators of specific elements, with this extensive variation at the fine (as opposed to broad) scale.

CONCLUSIONS

These data underscore the impact of root loss and reveal the very fine scale of microevolutionary variation in hyperaccumulation and exclusion of a wide range of elements. Broadly, they might point to trade-offs not well recognized in ionomes.

The left-right-handedness of the cylindrical spathe correlates with the phyllotactic spiral direction in Arisaema (Araceae)

A left-right asymmetry of plants has attracted attention in various study areas (e.g., developmental biology, ethology, and evolutionary biology); however, the underlying mechanisms remain unclear. In the genus Arisaema (Araceae), each plant possesses a cylindrical spathe that exhibits the left-right-handedness in the folding direction. As the spathe is a modified leaf, a phyllotactic spiral (clockwise or counter-clockwise directions) in vegetative organs may affect this dimorphism. In this study, we aimed to examine (1) interannual changes in the spathe folding direction in the same individuals, (2) the effect of phyllotactic spirals on the left-right-handedness of the spathe, (3) the abundance ratio of left- and right-folded spathes in several Arisaema species, and (4) the relationship between the coiling direction of young folded leaves and phyllotactic spirals in other aroid genera. The spathe folding direction changed annually and was significantly related to the phyllotactic spiral direction. The left-right-handedness prevailed among the 27 tested Arisaema species, and frequencies of left- and right-folded spathes were mostly similar. In the five aroid genera, the phyllotaxis was clearly correlated with the leaf coiling direction. These results imply that the phyllotactic spiral affects the spathe folding direction of Arisaema and the leaf coiling direction of aroids. Considering developmental studies on asymmetric leaves in other taxa, the left-right-handedness of the spathe in Arisaema is possibly a consequence of the phyllotactic pattern formation.

Specific turion yields of different clones of Spirodela polyrhiza depend on external phosphate thresholds

Turions play an important role in the survival strategy of the duckweed Spirodela polyrhiza. Therefore, factors influencing the formation of these survival organs were studied. Phosphate deficiency is the main natural factor inducing turion formation and the specific turion yield (SY), i.e. the number of turions formed per frond, varied widely for five different clones from different climate zones. The concentrations of phosphate and nitrate in the nutrient media were investigated at the onset of turion formation, with SY ranging from 0.22 to 5.9. Tissue P and N content was also investigated in vegetative fronds at the onset of turion formation and in newly formed turions. The clones were selected to test possible correlations between SY and threshold nutrient concentration for turion formation. Only one correlation, between SY and external phosphate concentration, was significant: clones with high SY started turion formation at higher external phosphate concentrations. Turion formation is thus mainly induced by the external phosphate concentration, below a defined, clone-dependent threshold. We propose the following mechanism: a switch of the developmental programme of frond primordia from vegetative frond to turion formation at a higher phosphate threshold saves more phosphate for turion formation instead of using it for a further vegetative growth. However, the period of growth preceding turion formation does not depend on this threshold value, but rather on the growth rate of the vegetative fronds, which actually produce the phosphate shortage by taking it up from the surrounding medium.

Fly ash pollution causes morpho-anatomical and biochemical changes in Eichhornia crassipes (Mart.) Solms and Pistia stratiotes L: demonstrating stress-tolerant activity

This study aims to explore the impact of fly ash (FA) on two types of free-floating aquatic plants, Eichhornia crassipes and Pistia stratiotes, growing in two different locations. The stress caused by FA has led to a significant biochemical alteration in several leaf properties, including ascorbic acid, relative water, and chlorophyll, as well as anatomical changes in leaf, petiole, and stolon in the growing plants at highly contaminated sites (HCS) relative to the low contaminated site (LCS). According to the study, HCS plants lose total chlorophyll overall, have shallower ascorbic acid levels, and have higher RWC than LCS plants. These findings imply that both species are highly resilient to pollution. The assessment of the shape and size of the epidermis, cortex, palisade cells, air space, bundle sheath, xylem cavity, phloem cells, vascular bundle, parenchyma, pith of the leaves, petioles, and stolon in the HCS is shorter than the LCS. The APTI values of E. crassipes (8.407%) and P. stratiotes (9.681%) are higher in HCS than the values of E. crassipes (7.729%) and P. stratiotes (9.077%) in LCS. These results suggest that both species exhibit greater APTI values in plants from HCS, indicating their tolerance to pollution. We target six water bodies in HCS and LCS to assess the FA-containing water quality. We calculated the water quality using WA-WQI and CCME-WQI. The higher WA-WQI scores indicate higher water pollution levels. The value of WA-WQI is higher in HCS sites included in the KTPP colony (93.94), Amalhanda (91.43), and Barunan Ghoshpara (89.07) than in LCS sites such as in Kashinathpur (88.59), but the CCME-WQI scores are 64.33, 76.09 and 75.71 respectively. The investigation highlights that both species are exceptionally suitable as stress-tolerant plants for fly ash and possess the potential to serve as an option for the restoration of water bodies impacted by fly ash. This study will enhance our comprehension of the potential advantages of these plants, particularly in the phytoremediation of polluted aquatic ecosystems.