Plant Tissue Type Research Articles

Endophytic bacterial community composition in wheat (Triticum aestivum) is determined by plant tissue type, developmental stage and soil nutrient availability

To understand effects of tissue type, growth stage and soil fertilisers on bacterial endophyte communities of winter wheat (Triticum aestivum cv. Hereward). Endophytes were isolated from wheat grown under six fertiliser conditions in the long term Broadbalk Experiment at Rothamsted Research, UK. Samples were taken in May and July from root and leaf tissues. Root and leaf communities differed in abundance and composition of endophytes. Endophytes were most abundant in roots and the Proteobacteria were most prevalent. In contrast, Firmicutes and Actinobacteria, the Gram positive phyla, were most prevalent in the leaves. Both fertiliser treatment and sample time influenced abundance and relative proportions of each phylum and genus in the endosphere. A higher density of endophytes was found in the Nil input treatment plants. Robust isolation techniques and stringent controls are critical for accurate recovery of endophytes. The plant tissue type, plant growth stage, and soil fertiliser treatment all contribute to the composition of the endophytic bacterial community in wheat. These results should help facilitate targeted development of endophytes for beneficial applications in agriculture.

Expression of heterologous xyloglucan xylosyltransferases in Arabidopsis to investigate their role in determining xyloglucan xylosylation substitution patterns.

Putative XyG xylosyltransferases from Tropaeolum majus (nasturtium) and Solanum lycopersicum (tomato) homologous to characterized Arabidopsis genes were identified and shown to functionally complement Arabidopsis mutants lacking xyloglucan demonstrating they represent xyloglucan xylosyltransferases. Xyloglucan is a major hemicellulose in the plant cell wall and is important for the structural organization of the wall. The fine structure of xyloglucan can vary dependent on plant species and tissue type. Most vascular seed-bearing plants including Arabidopsis thaliana and nasturtium (Tropaeolum majus) have a xyloglucan structure, in which three out of four backbone glucosyl-residues are substituted with xylosyl-residues. In contrast, the xyloglucan found in plants of the Solanaceae family, which includes tomato (Solanum lycopersicum), is typically less xylosylated with only two of the four backbone glucosyl-residues substituted with xylosyl-residues. To investigate the genetics of xyloglucan xylosylation, candidate xyloglucan xylosyltransferase genes (XXTs) homologous to known A. thaliana XXTs were cloned from nasturtium and tomato. These candidate XXTs were expressed in the A. thaliana xxt1/2 double and xxt1/2/5 triple mutant, whose walls lack detectable xyloglucan. Expression of the orthologs of XXT5 resulted in no detectable xyloglucan in the transgenic A. thaliana plants, consistent with a lack of xyloglucan in the A. thaliana xxt1/2 double mutant. However, transformation of both the tomato and nasturtium orthologs of AtXXT1 and AtXXT2 resulted in the production of xyloglucan with a xylosylation pattern similar to wild type A. thaliana indicating that both SlXXT2 and TmXXT2 likely have xylosyltransferase activity. As the expression of the SlXXT2 did not result in xyloglucan with a decreased xylosylation frequency found in tomato, this gene is not responsible for the unique xylosylation pattern found in the solanaceous plants.

Comparing lignocellulose physiochemistry after decomposition by brown rot fungi with distinct evolutionary origins.

Among wood-degrading fungi, lineages holding taxa that selectively metabolize carbohydrates without significant lignin removal (brown rot) are polyphyletic, having evolved multiple times from lignin-removing white rot fungi. Given the qualitative nature of the 'brown rot' classifier, we aimed to quantify and compare the temporal sequence of carbohydrate removal among brown rot clades. Lignocellulose deconstruction was compared among fungi using distinct plant substrates (angiosperm, conifer, grass). Specifically, aspen, pine and corn stalk were harvested over a 16-week time series from microcosms containing Gloeophyllum trabeum, Fomitopsis pinicola, Ossicaulis lignatilis, Fistulina hepatica, Serpula lacrymans, Wolfiporia cocos or Dacryopinax sp. After quantifying plant mass loss, a thorough compositional analysis was complemented by a saccharification test to determine wood cell wall accessibility. Mass loss and accessibility varied depending on fungal decomposer and substrate, and trajectories of loss for hemicellulosic components and cellulose differed among plant tissue types. At any given stage of decomposition, however, lignocellulose accessibility and the fraction remaining of carbohydrates and lignin within a plant tissue type were generally the same, regardless of fungal isolate. This suggests that the sequence of plant component removal at this typical scale of characterization is shared among these brown rot lineages, despite their diverse genomes and secretomes.

Embryo cell wall properties in relation to development and desiccation in the recalcitrant-seeded Encephalartos natalensis (Zamiaceae) Dyer and Verdoorn.

Plant cell walls are dynamic entities that may change with development, differ between plant species and tissue type and play an important role in responses to various stresses. In this regard, the present investigation employed immunocytochemistry to determine wall composition and possible changes during development of immature and mature embryos of the recalcitrant-seeded cycad Encephalartos natalensis. Fluorescent and gold markers, together with cryo-scanning and transmission electron microscopy (TEM) were also used to analyse potential changes in the cell walls of mature embryos upon desiccation. Immature cell walls were characterised by low- and high methyl-esterified epitopes of pectin, rhamnogalacturonan-associated arabinan, and the hemicellulose xyloglucan. Arabinogalactan protein recognised by the LM2 antibody, along with rhamnogalacturonan-associated galactan and the hemicellulose xylan, were not positively localised using immunological probes, suggesting that the cell walls of the embryo of E. natalensis do not possess these epitopes. Interestingly, mature embryos appeared to be identical to immature ones with respect to the cell wall components investigated, implying that these may not change during the protracted post-shedding embryogenesis of this species. Drying appeared to induce some degree of cell wall folding in mature embryos, although this was limited by the abundant amyloplasts, which filled the cytomatrical space. Folding, however, was correlated with relatively high levels of wall plasticisers typified by arabinose polymers. From the results of this study, it is proposed that the embryo cell walls of E. natalensis are constitutively prepared for the flexibility required during cell growth and expansion, which may also facilitate the moderate cell wall folding observed in mature embryos upon drying. This, together with the abundant occurrence of amyloplasts in the cytomatrix, may provide sufficient mechanical stabilisation if water is lost, even though the seeds of this species are highly desiccation-sensitive.

The Use of Latent Class Analysis to Estimate the Sensitivities and Specificities of Diagnostic Tests forSquash vein yellowing virusin Cucurbit Species When There Is No Gold Standard

Squash vein yellowing virus (SqVYV) is the causal agent of viral watermelon vine decline, one of the most serious diseases in watermelon (Citrullus lanatus L.) production in the southeastern United States. At present, there is not a gold standard diagnostic test for determining the true status of SqVYV infection in plants. Current diagnostic methods for identification of SqVYV-infected plants or tissues are based on the reverse-transcription polymerase chain reaction (RT-PCR), tissue blot nucleic acid hybridization assays (TB), and expression of visual symptoms. A quantitative assessment of the performance of these diagnostic tests is lacking, which may lead to an incorrect interpretation of results. In this study, latent class analysis (LCA) was used to estimate the sensitivities and specificities of RT-PCR, TB, and visual assessment of symptoms as diagnostic tests for SqVYV. The LCA model assumes that the observed diagnostic test responses are linked to an underlying latent (nonobserved) disease status of the population, and can be used to estimate sensitivity and specificity of the individual tests, as well as to derive an estimate of the incidence of disease when a gold standard test does not exist. LCA can also be expanded to evaluate the effect of factors and was done here to determine whether diagnostic test performances varied among the type of plant tissue being tested (crown versus vine tissue), where plant samples were taken relative to the position of the crown (i.e., distance from the crown), host (i.e., genus), and habitat (field-grown versus greenhouse-grown plants). Results showed that RT-PCR had the highest sensitivity (0.94) and specificity (0.98) of the three tests. TB had better sensitivity than symptoms for detection of SqVYV infection (0.70 versus 0.32), while the visual assessment of symptoms was more specific than TB and, thus, a better indicator of noninfection (0.98 versus 0.65). With respect to the grouping variables, RT-PCR and TB had better sensitivity but poorer specificity for diagnosing SqVYV infection in crown tissue than it did in vine tissue, whereas symptoms had very poor sensitivity but excellent specificity in both tissues for all cucurbits analyzed in this study. Test performance also varied with habitat and genus but not with distance from the crown. The results given here provide quantitative measurements of test performance for a range of conditions and provide the information needed to interpret test results when tests are used in parallel or serial combination for a diagnosis.

A study of platinum accumulation in radish (Raphanus sativus) and durum wheat (Triticum durum) plants

The aim of this study was to investigate the accumulation of platinum (Pt) in C3 plants. In this experiment, radish (Raphanus sativus) and durum wheat (Triticum durum) were chosen as test species and three uncontaminated soils from Simcoe, Elora, and Kettleby, Ontario were chosen to represent a range of soil characteristics. Soils were amended with 0 to 20 mg Pt kg-1, applied as a Pt solution, before plants were exposed to the contaminated soils for 14 days. Statistical analyses using a Linear Model Procedure and a Student-Newman Keuls Test at α=0.05 found a significant different between Pt accumulation and plant type, tissue type, and soil type. Overall, root tissue in all soil and plant types accumulated approximately eight times more Pt than the corresponding shoot tissue (p

Hemicellulose biosynthesis

One major component of plant cell walls is a diverse group of polysaccharides, the hemicelluloses. Hemicelluloses constitute roughly one-third of the wall biomass and encompass the heteromannans, xyloglucan, heteroxylans, and mixed-linkage glucan. The fine structure of these polysaccharides, particularly their substitution, varies depending on the plant species and tissue type. The hemicelluloses are used in numerous industrial applications such as food additives as well as in medicinal applications. Their abundance in lignocellulosic feedstocks should not be overlooked, if the utilization of this renewable resource for fuels and other commodity chemicals becomes a reality. Fortunately, our understanding of the biosynthesis of the various hemicelluloses in the plant has increased enormously in recent years mainly through genetic approaches. Taking advantage of this knowledge has led to plant mutants with altered hemicellulosic structures demonstrating the importance of the hemicelluloses in plant growth and development. However, while we are on a solid trajectory in identifying all necessary genes/proteins involved in hemicellulose biosynthesis, future research is required to combine these single components and assemble them to gain a holistic mechanistic understanding of the biosynthesis of this important class of plant cell wall polysaccharides.

The effect of atmospheric CO2 concentration on carbon isotope fractionation in C3 land plants

Because atmospheric carbon dioxide is the ultimate source of all land-plant carbon, workers have suggested that pCO2 level may exert control over the amount of 13C incorporated into plant tissues. However, experiments growing plants under elevated pCO2 in both chamber and field settings, as well as meta-analyses of ecological and agricultural data, have yielded a wide range of estimates for the effect of pCO2 on the net isotopic discrimination (Δδ13Cp) between plant tissue (δ13Cp) and atmospheric CO2 (δ13CCO2). Because plant stomata respond sensitively to plant water status and simultaneously alter the concentration of pCO2 inside the plant (ci) relative to outside the plant (ca), any experiment that lacks environmental control over water availability across treatments could result in additional isotopic variation sufficient to mask or cancel the direct influence of pCO2 on Δδ13Cp. We present new data from plant growth chambers featuring enhanced dynamic stabilization of moisture availability and relative humidity, in addition to providing constant light, nutrient, δ13CCO2, and pCO2 level for up to four weeks of plant growth. Within these chambers, we grew a total of 191 C3 plants (128 Raphanus sativus plants and 63 Arabidopsis thaliana) across fifteen levels of pCO2 ranging from 370 to 4200ppm. Three types of plant tissue were harvested and analyzed for carbon isotope value: above-ground tissues, below-ground tissues, and leaf-extracted nC31-alkanes. We observed strong hyperbolic correlations (R≥0.94) between the pCO2 level and Δδ13Cp for each type of plant tissue analyzed; furthermore the linear relationships previously suggested by experiments across small (10–350ppm) changes in pCO2 (e.g., 300–310ppm or 350–700ppm) closely agree with the amount of fractionation per ppm increase in pCO2 calculated from our hyperbolic relationship. In this way, our work is consistent with, and provides a unifying relationship for, previous work on carbon isotopes in C3 plants at elevated pCO2. The values for Δδ13Cp we determined in our ambient pCO2 chambers are consistent with the Δδ13Cp values measured in large modern datasets of plants growing within the Earth’s wettest environments, suggesting that it may be possible to reconstruct changes in paleo-pCO2 level from plants that grew in consistently wet environments, if δ13CCO2 value and initial pCO2 level can be independently quantified. Several implications arise for the reconstruction of water availability and water-use efficiency in both ancient and recent plant Δδ13Cp values across periods of changing pCO2 level. For example, the change in Δδ13Cp implied by our relationship for the rise in pCO2 concentration observed since 1980 is of the same magnitude (= ∼0.7‰) as the isotopic correction for changes in δ13CCO2 required by the input of 13C-depleted carbon to the atmosphere. For these reasons, only the portion of the terrestrial isotopic excursion that persists after accounting for changes in pCO2 concentration should be used for the interpretation of a change in paleo-environmental conditions.

Distinct Cell-Specific Expression of Homospermidine Synthase Involved in Pyrrolizidine Alkaloid Biosynthesis in Three Species of the Boraginales

Homospermidine synthase (HSS) is the first specific enzyme in pyrrolizidine alkaloid (PA) biosynthesis, a pathway involved in the plant's chemical defense. HSS has been shown to be recruited repeatedly by duplication of a gene involved in primary metabolism. Within the lineage of the Boraginales, only one gene duplication event gave rise to HSS. Here, we demonstrate that the tissue-specific expression of HSS in three boraginaceous species, Heliotropium indicum, Symphytum officinale, and Cynoglossum officinale, is unique with respect to plant organ, tissue, and cell type. Within H. indicum, HSS is expressed exclusively in nonspecialized cells of the lower epidermis of young leaves and shoots. In S. officinale, HSS expression has been detected in the cells of the root endodermis and in leaves directly underneath developing inflorescences. In young roots of C. officinale, HSS is detected only in cells of the endodermis, but in a later developmental stage, additionally in the pericycle. The individual expression patterns are compared with those within the Senecioneae lineage (Asteraceae), where HSS expression is reproducibly found in specific cells of the endodermis and the adjacent cortex parenchyma of the roots. The individual expression patterns within the Boraginales species are discussed as being a requirement for the successful recruitment of HSS after gene duplication. The diversity of HSS expression within this lineage adds a further facet to the already diverse patterns of expression that have been observed for HSS in other PA-producing plant lineages, making this PA-specific enzyme one of the most diverse expressed proteins described in the literature.

A meta‐analytical review of the effects of elevated CO2 on plant–arthropod interactions highlights the importance of interacting environmental and biological variables

We conducted the most extensive meta-analysis of plant and animal responses to elevated CO(2) to date. We analysed > 5000 data points extracted from 270 papers published between 1979 and 2009. We examined the changes in 19 animal response variables to the main effect of elevated CO(2). We found strong evidence for significant variation among arthropod orders and feeding guilds, including interactions in the direction of response. We also examined the main effects of elevated CO(2) on: six plant growth and allocation responses, seven primary metabolite responses, eight secondary metabolite responses, and four physical defence responses. We examined these response variable changes under two-way and three-way interactions between CO(2) and: soil nitrogen, ambient temperature, drought, light availability, photosynthetic pathway, reproductive system, plant growth rate, plant growth form, tissue type, and nitrogen fixation. In general we found smaller effect sizes for many response variables than have been previously reported. We also found that many of the oft-reported main effects of CO(2) obscure the presence of significant two- and three-way interactions, which may help better explain the relationships between the response variables and elevated CO(2).

A Cryohistological Protocol for Preparation of Large Plant Tissue Sections for Screening Intracellular Fluorescent Protein Expression

In this study, we have developed a robust cryohistological method that allows imaging of virtually any type of plant cell or tissue while preserving fluorescent protein signals and maintaining excellent cellular and subcellular morphology. This method involves modified fixation of plant tissues (i.e., leaves, stems, and petioles), infiltration in a sucrose gradient, freezing, and collection of cryosections directly onto a cryoadhesive tape. Using this method followed by microscopic analysis, we demonstrated a localized accumulation of green fluorescent protein (GFP) in Nicotiana benthamiana plants agroinfiltrated with the movement-incompetent tobacco mosaic virus-based vector and systemic accumulation of GFP in plants infiltrated with the movement-competent vector. Overall, this simple cryohistological procedure reduced sample preparation time and allowed processing of tissue sections for high-resolution imaging of targeted fluorescent proteins in all plant tissues.

Enhanced Virulence Gene Activity of Agrobacterium in Muskmelon (Cucumis melo L.) cv. ‘Birdie’

Muskmelon (Cucumis melo L.) cultivar ‘Birdie’, was evaluated for its response to the tumorigenic Agrobacterium tumefaciens and the oncogenic A. rhizogenes strains. Stem and petiole of three week-old in vitro-grown muskmelon plants were inoculated with five strains of A. tumefaciens and A. rhizogenes each and observed phenotypic expressions i.e. induction of crown galls and hairy roots. This phenotypic expression was efficaciously increased when virulence gene activity of different strains of two Agrobacterium species was enhanced. Intensive studies on enhancement of virulence gene activity of Agrobacterium found to be correlated to the appropriate light intensity (39.3 μmol m-2 s-1) with a specific concentration of monocyclic phenolic compound, acetosyringone (20 μM). The gene activity was also influenced by several other physical factors e.g. plant tissue type, Agrobacterium species and their strains, and plant tissue-Agrobacterium interaction. Among the different A. tumefaciens strains, LBA4404 showed the best virulence gene activity in both stem and petiole through the formation of higher rate of crown galls. On the other hand, strain 15834 of A. rhizogenes showed better gene activity in stem and 8196 in petiole through the formation of higher rate of hairy roots as well as higher average number of hairy roots. Among the two different types of explants, petiole was more susceptible to both Agrobacterium species. Thus it was concluded that future muskmelon transformation study can efficiently be carried out with LBA4404, 15834 and 8196 strains using petiole explants by adding 20 μM of acetosyringone in the medium.

Factors Enhancing Virulence Response of Agrobacteria in Cucumber (<i>Cucumis sativus</i> L.)

The virulence response of five wild type Agrobacterium tumefaciens (tumorigenic) strains and five wild type A. rhizogenes (oncogenic) strains was studied in cucumber (Cucumis sativus L.), cv. Spring Swallow. Several physical and chemical factors e.g. Agrobacterium strains, tissue type (stem and petiole tissues), light intensity, dark incubation, concentrations of acetosyringone (a phenolic compound) were tested. The virulent response of Agrobacteria was found to be depend on plant tissue type, Agrobacterium strain, tissue-Agrobacterium interaction and both chemical-physical factors. Specific light intensity, 2500-lux, as well as the acetosyringone concentration, 20-mM, played important role in virulence response. Among the different strains, LBA 4404 and 15834 were highly virulent to cucumber compared to the other strains tested. A. tumefaciens strains A348 and A281 were failed to initiate crown galls in both stem and petiole tissues, however, in the presence of acetosyringone they produced crown galls. Similarly, A. rhizogenes strain A4 initiated hairy roots in the presence of acetosyringone. All developed crown galls and hairy roots showed an autonomous growth on a hormone free medium containing cefatoxime. Thus, enhancement of virulence response was not only dependent on Agrobacterium strains, but also on particular physical and chemical factors also play vital role.

J. Cosmet. Sci., 59, 419–430 (September/October 2008) Anti‐inflammatory activity of Crinum asiaticum Linne var. japonicum extract and its application as a cosmeceutical ingredient

Synopsis Crinum asiaticum Linne var. japonicum has long been used as a rheumatic remedy, as an anti‐pyretic and as an anti‐ulcer treatment, and for the alleviation of local pain and fever in Korea and Malaysia. In order to investigate the possibility of Crinum asiaticum Linne var. japonicum extract as a cosmetic ingredient, we measured its anti‐inflammatory effect by its inhibition of iNOS (inducible nitric oxide synthase) and the release of PGE2, IL‐6, and IL‐8. We also measured its anti‐allergic effect by its inhibition of beta‐hexosamidase release. An HPLC experiment after extraction with 95% EtOH at pH 3.5 showed that Crinum asiaticum Linne var. japonicum was mainly composed of lycorine (up to 1%), a well‐known immunosuppressor. The content of lycorine varied, depending on the type of plant tissue analysed and the extraction method. In an anti‐inflammatory assay for inhibition of nitric oxide formation on lipopolysaccharide (LPS)‐activated mouse macrophage RAW 264.7 cells, the ethanol extract of Crinum asiaticum showed an inhibitory activity of NO production in a dose‐dependent manner (IC50 = 58.5 μg ml‐1). Additional study by RT‐PCR demonstrated that the extract of Crinum asiaticum significantly suppressed the expression of the iNOS gene. Moreover, the extract of Crinum asiaticum did not show any cytotoxicity, but did show a cell proliferation effect against LPS (a 10–60% increase in cell viability). In an assay to determine inhibition of the H2O2‐activated release of PGE2, IL‐6, and IL‐8 in human normal fibroblast cell lines, the release of PGE2 and IL‐6 was almost completely inhibited above concentrations of 0.05% and 1%, respectively. Moreover, the release of IL‐8 was completely inhibited over the entire range of concentration (> 0.0025%). In order to investigate the skin‐sensitizing potentials of the extract of Crinum asiaticum, a human clinical test was performed after repeated epicutaneous 48‐h applicaticons under an occlusive patch (RIPT). The repeated and single cutaneous applications of Crinum asiaticum Linne var. japonicum extract under the occlusive patch did not provoke any cumulative irritation and sensitization reactions. The result showed that the extract of Crinum asiaticum Linne var. japonicum has a sufficient anti‐inflammatory effect. Therefore, Crinum asiaticum Linne var. japonicum extract may be useful for development as an ingredient in cosmetic products.

The communities of endophytic diazotrophic bacteria in cultivated rice ( Oryza sativa L .)

Even though attempts have been made to use endophytic diazotrophic bacteria as biofertilizers for rice cultivation, their community structure and complexity in rice tissues is not well understood. In this study, the diversity and the community structure of endophytic diazotrophs as well as the nifH gene expression within each plant part and growth stage of rice under different soil conditions were investigated. The population of viable endophytic diazotrophic bacteria in cultivated rice ( Oryza sativa L. cultivar KDML-105) was investigated under different soil conditions and the N 2-fixing ability of selected consortia and single isolates was assessed. Single isolates from each diazotrophic consortium were shown to be capable of both the inhibition and promotion of N 2-fixation. Some isolates were closely related to Enterobacter dissolvens, Brevundimonas aurantiaca, Pantoea agglomerans, Pseudomonas spp., and Enterobacteriaceae. Carbon source utilization, and production of IAA, pectinase and cellulase indicated high diversity in the rice tissues. The presence of diazotrophic bacteria was detected in roots, stems and leaves on the basis of the GUS reporter gene. PCR-DGGE analysis conducted directly on rice tissue samples using 16S rDNA primers was used to elucidate the structure of the endophytic bacterial communities. Nested PCR-DGGE analysis with nifH primer demonstrated less diazotrophic bacterial diversity in the roots of rice cultivated in paddy soil amended with nitrogen fertilizer than in unfertilized and previously uncultivated soil. Plant tissue type was found to dictate the endophytic diazotrophic community structure rather than the type of soil or fertilizer amendment. In order to detect the nifH gene expression which implies the nitrogen fixing activities of the diazotrophic bacterial community, the RT-PCR approach was used. The results demonstrated that nifH gene expression could be differently detected in each part and growth stage of rice plants as well as being influenced by soil nitrogen status. The expression level of the nifH gene in all roots from plants grown in N-fertilized soil was the lowest among the treatments studied. The results confirm the complexity of the endophytic diazotrophic bacterial community, and indicate that the type of plant tissue seems to influence the community structure.

Nonnutrient anthropogenic chemicals in seagrass ecosystems: Fate and effects

Impacts of human-related chemicals, either alone or in combination with other stressors, are important to understand to prevent and reverse continuing worldwide seagrass declines. This review summarizes reported concentrations of anthropogenic chemicals in grass bed-associated surface waters, sediments, and plant tissues and phytotoxic concentrations. Fate information in seagrass-rooted sediments and overlying water is most available for trace metals. Toxicity results in aqueous exposures are available for at least 13 species and a variety of trace metals, pesticides, and petrochemicals. In contrast, results for chemical mixtures and chemicals in sediment matrices are uncommon. Contaminant bioaccumulation information is available for at least 23 species. The effects of plant age, tissue type, and time of collection have been commonly reported but not biological significance of the chemical residues. Experimental conditions have varied considerably in seagrass contaminant research and interspecific differences in chemical residues and chemical tolerances are common, which limits generalizations and extrapolations among species and chemicals. The few reported risk assessments have been usually local and limited to a few single chemicals and species representative of the south Australian and Mediterranean floras. Media-specific information describing exposure concentrations, toxic effect levels, and critical body burdens of common near-shore contaminants is needed for most species to support integrated risk assessments at multiple geographical scales and to evaluate the ability of numerical effects-based criteria to protect these marine angiosperms at risk.

Plant Host Effect on the Development of <I>Heliothis virescens</I> F. (Lepidoptera: Noctuidae)

Heliothis virescens F. is an important polyphagous pest that can develop on >100 plant species, including 20 economic crops. Populations of this insect are believed to be locally maintained on a few crops and weed hosts in Washington County, MS. To find the intrinsic value of these plants for the development of H. virescens populations, we fed different laboratory and wild colonies with fresh and lyophilized plant tissue under a constant temperature. Development time of this insect under laboratory conditions varied up to 10 d between plant hosts and was dependent on the type of plant tissue provided: fresh or lyophilized. Life table parameters such as net reproductive rate, finite rate of increase, and generation time indicated that Trifolium repens, a wild host growing around agricultural fields year round, could be one of the most suitable local plant hosts for the development of H. virescens. Two species of Geranium, previously reported as the source of the first H. virescens generation in the region, had lower intrinsic value as a food source than did T. repens. Gossyipium hirsutum, perhaps the most important crop source of H. virescens in the region, produced low net reproductive rate and finite rate of increase parameters. Sampling conducted in agricultural fields during 2006 and 2007 found no larvae on the above mentioned wild hosts as it was previously reported. Results indicated that H. virescens populations in this region were not supported by the wild plant species growing around agricultural fields during the time when the survey took place.

Lymantria dispar herbivory induces rapid changes in carbon transport and partitioning in Populus nigra

AbstractWe tested for rapid changes in photosynthate transport and partitioning in response to Lymantria dispar (L.) (Lepidoptera: Lymantriidae) (gypsy moth) herbivory in Populus nigra L. (Salicaceae). Transport and partitioning of [11C]‐photosynthate from young mature leaves were measured in vivo before and 18 h after leaf chewing by gypsy moth larvae, which were caged on three older leaves. Following herbivory, there was an increase in export speed of recently fixed carbon from younger mature leaves. The increased export speed was due to a quicker transit time of 11C through the leaf, rather than a change in transport speed through the phloem. Additionally, basipetal partitioning of [11C]‐photosynthate was increased following herbivory. Neither of these changes was observed in control plants. This enhancement of export occurs even though herbivores are well known to induce increases in carbon allocation to secondary metabolites within leaves. Our results demonstrate that the use of non‐destructive imaging of 11C tracer is a powerful tool for examining plant responses to herbivory. Although the mechanisms underlying the rapid increase in carbon flux to stems and roots remain to be elucidated, our results raise the possibility of a coordinated whole plant response to herbivory. Thus, even when the herbivore specializes on only one plant tissue type, a whole plant approach may be key to understanding how plants respond to herbivory.

Genotype, age, tissue, and environment regulate the structural outcome of glucosinolate activation.

Glucosinolates are the inert storage form of a two-part phytochemical defense system in which the enzyme myrosinase generates an unstable intermediate that rapidly rearranges into the biologically active product. This rearrangement step generates simple nitriles, epithionitriles, or isothiocyanates, depending on the structure of the parent glucosinolate and the presence of proteins that promote specific structural outcomes. Glucosinolate accumulation and myrosinase activity differ by plant age and tissue type and respond to environmental stimuli such as planting density and herbivory; however, the influence of these factors on the structural outcome of the rearrangement step remains unknown. We show that the structural outcome of glucosinolate activation is controlled by interactions among plant age, planting density, and natural genetic variation in Arabidopsis (Arabidopsis thaliana) rosette leaves using six well-studied accessions. We identified a similarly complex interaction between tissue type and the natural genetic variation present within these accessions. This raises questions about the relative importance of these novel levels of regulation in the evolution of plant defense. Using mutants in the structural specifier and glucosinolate activation genes identified previously in Arabidopsis rosette leaves, we demonstrate the requirement for additional myrosinases and structural specifiers controlling these processes in the roots and seedlings. Finally, we present evidence for a novel EPITHIOSPECIFIER PROTEIN-independent, simple nitrile-specifying activity that promotes the formation of simple nitriles but not epithionitriles from all glucosinolates tested.

Transporters in starch synthesis.

Starch is synthesised and stored in plastids. In autotrophic tissues, the carbon skeletons and energy required for starch synthesis are directly available from photosynthesis. However, plastids of heterotrophic tissues require the metabolites for starch synthesis to be imported. Depending on plant species and tissue type, import is facilitated by several different plastid inner envelope metabolite transporters. Commonly, glucose-6-phosphate/phosphate translocators and adenylate translocators are used, but in the cereal endosperm, the role is carried out by ADP glucose transporters (Brittle1, BT1). This review predominantly focuses on transporters of the plastid inner envelope membrane. Their roles are discussed within an overview of starch synthesis. We also examine additional functions of these transporters according to our current knowledge.