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PubMed2003

The poplar root transcriptome: analysis of 7000 expressed sequence tags.

To date, most poplar expressed sequence tags (ESTs) are from above-ground tissues such as wood, leaf and buds. Here, we present a large-scale production of ESTs from roots of the hybrid cottonwood, Populus trichocarpaxdeltoides. cDNA libraries were generated from the root system of 2-month-old rooted cuttings, and roots of 2.5-month-old cuttings water-stressed for 19 days. Partial sequences obtained from 7013 clones were assembled into 1347 clusters and 3527 singletons. This set of ESTs represents 4874 unique transcripts expressed in roots. Putative functions could be assigned to 3021 (62%) of the transcripts. A significant portion of the ESTs encode proteins of common metabolic pathways; energy and metabolism represented 5% and 8% of total transcripts, respectively. Of specific interest to root functions are the 6% of ESTs involved in signalling pathways and hormone metabolism, and 4% encoding transporters and channels. The current poplar root ESTs and the aspen root ESTs present in public databases represent 6700 unique transcripts. The Unigene set was selected from the ESTs and used to generate nylon microarrays. Changes in aquaporins and transporter transcripts were then studied during adventitious root development.

Aquaporins↗

PubMed2004

Lignin dehydrogenative polymerization mechanism: a poplar cell wall peroxidase directly oxidizes polymer lignin and produces in vitro dehydrogenative polymer rich in beta-O-4 linkage.

An investigation was performed to determine whether lignin dehydrogenative polymerization proceeds via radical mediation or direct oxidation by peroxidases. It was found that coniferyl alcohol radical transferred quickly to sinapyl alcohol. The transfer to syringaresinol was slower, however, the transfer to polymeric lignols occurred very slightly. This result suggests that the radical mediator theory does not sufficiently explain the mechanism for dehydrogenative polymerization of lignin. A cationic cell wall peroxidase (CWPO-C) from poplar (Populus alba L.) callus showed a strong substrate preference for sinapyl alcohol and the sinapyl alcohol dimer, syringaresinol. Moreover, CWPO-C was capable of oxidizing high-molecular-weight sinapyl alcohol polymers and ferrocytochrome c. Therefore, the CWPO-C characteristics are important to produce polymer lignin. The results suggest that CWPO-C may be a peroxidase isoenzyme responsible for the lignification of plant cell walls.

Alcohols↗

PubMed2003

Biochemical characterization of two differentially expressed polyphenol oxidases from hybrid poplar.

Two polyphenol oxidase isoforms with distinct expression patterns were identified in hybrid poplar (Populus trichocarpaxP. deltoides). PPO-1, corresponding to the previously cloned PtdPPO (Constabel et al., Plant Physiol. 124: 285-295) was primarily leaf tissue-specific and detected only after wounding. PPO-2 was expressed constitutively in all tissue types tested except mature leaves, with highest expression in very young leaves and conducting tissues such as roots, stems and petioles. These two PPO isoforms were partially purified from hybrid poplar by ammonium sulfate fractionation followed by hydrophobic interaction chromatography. They were found to differ in stability, pH optimum, and activation by SDS. Tests with common phenolic substrates showed that PPO-1 had a broader substrate specificity than PPO-2. The distinct enzymatic properties and expression patterns of these two PPO isoforms suggest that they may have different physiological functions in hybrid poplar.

Catechol Oxidase↗

PubMed2002

Degradation of trichloroethylene in wetland microcosms containing broad-leaved cattail and eastern cottonwood.

Remediation of aquifers containing trichloroethylene (TCE) relies primarily on physical extraction of contaminated groundwater and soil. Unfortunately, this is typically expensive and does not always attain the desired treatment goals. In situ bioremediation via natural attenuation is an alternative treatment process in which TCE is transformed by indigenous microorganisms and plants. In this study, TCE was observed in a surficial aquifer that discharges into a wetland. Experiments were undertaken to determine whether natural attenuation of TCE in the wetland was possible. Microcosms were constructed using sandy soil+/-eastern cottonwoods (Populus deltoides) from the wetland's edge and organic soil+broad-leaved cattails (Typha latifolia) from the wetland's interior. [14C] TCE was added to each microcosm (1.27 microCi). Overtime, 14C was recovered from four microcosm compartments: (1) as 14C bound to soil and water, (2) as volatilized [14C] TCE, (3) as [14C] CO2 produced by mineralization of [14C] TCE, and (4) as 14C incorporated into the plants. Total recoveries of the 14C-label ranged from 73.6% to 95.8%. Volatilized [14C] TCE accounted for the majority ( > 50%) of the recovered label. In microcosms without plants, [14C] CO2 represented 3.2% (organic soil) to 15.6% (sandy soil) of the recovered 14C, indicating that TCE was mineralized by indigenous microorganisms. The presence of the broad-leaved cattail resulted in increased production of [14C] CO2 to 5.3% in the organic soil. The data thus suggest that natural attenuation is a potential bioremediative strategy for TCE-contaminated wetlands.

Biodegradation, Environmental↗

PubMed2003

Experimental evidence against diffusion control of Hg evasion from soils.

Elemental Hg (Hg(0)) evolution from soils can be an important process and needs to be measured in more ecosystems. The diffusion model for soil gaseous efflux has been applied to modeling the fluxes of several gases in soils and deserves testing with regard to Hg(0). As an initial test of this model, we examined soil gaseous Hg(0) and CO(2) concentrations at two depths (20 and 40 cm) over the course of a controlled environment study conducted in the EcoCELLs at the Desert Research Institute in Reno, Nevada. We also compared small, spatially distributed gas wells against the more commonly used large gas wells. In this study, two EcoCELLs were first watered (June 2000) and then planted (July 2000) with trembling aspen (Populus tremuloides). Following that, trees were harvested (October 2000) and one EcoCELL (EcoCELL 2) was replanted with aspen (25 April 2001). During most of the experiment, there was a strong vertical gradient of CO(2) (increasing with depth, as is typical of a diffusion-driven process), but no vertical gradient of soil gaseous Hg(0). Strong diel variations in soil gas Hg(0) concentration were noted, whereas diel variations in CO(2) were small and not statistically significant. Initial watering and planting caused increases in both soil gas CO(2) and Hg(0). Replanting in EcoCELL 2 caused a statistically significant increase in soil gas CO(2) but not Hg(0). Calculated Hg(0) effluxes using the diffusion model produced values two orders of magnitude lower than those measured using field chambers placed directly on the soil or whole-cell fluxes. Neither soil gas Hg(0) concentrations nor calculated fluxes were correlated with measured Hg(0) efflux from soil or from whole EcoCELLs. We conclude that (1) soil gas Hg(0) flux is not diffusion-driven and thus soil gas Hg(0) concentrations cannot be used to calculated soil Hg(0) efflux; (2) soil gas Hg(0) concentrations are increased by watering dry soil, probably because of displacement/desorption processes; (3) soil gas Hg(0) concentrations were unaffected by plants, suggesting that roots and rhizosphere processes are unimportant in controlling Hg(0) evasion from the soil surface. We recommend the use of the small wells in all future studies because they are much easier to install and provide more resolution of spatial and temporal patterns in soil gaseous Hg(0).

Carbon Dioxide↗

PubMed2002

A new cellulose synthase gene (PtrCesA2) from aspen xylem is orthologous to Arabidopsis AtCesA7 (irx3) gene associated with secondary cell wall synthesis.

We report here the molecular cloning and characterization of a new full-length cellulose synthase (CesA) cDNA, PtrCesA2 from aspen (Populus tremuloides) trees. The predicted PtrCesA2 protein shows a high degree of identity/similarity (87%/91%) to the predicted gene product of Arabidopsis AtCesA7 gene that has been associated with secondary cell wall development. Previously, a mutation in AtCesA7 gene (irx3) was correlated with a significant decrease in the amount of cellulose synthesized (about 70%) and genetic complementation of irx3 mutant with a wild-type AtCesA7 gene restored the normal phenotype. This is the first report of a full-length AtCesA7 ortholog from any non-Arabidopsis species. Interestingly, PtrCesA2 shares only 64% identity with our earlier reported PtrCesA1 from aspen suggesting its structural distinctness from the only other known CesA member from the aspen genome. PtrCesA1 is a xylem-specific and tension stress responsive gene that is highly similar to another Arabidopsis gene, AtCesA8 which also has been associated with secondary wall development. Moreover, AtCesA7 and AtCesA8 are suggested to be part of the same cellulose synthase complex. Isolation of PtrCesA2 from a xylem library enriched in cells with active secondary wall synthesis, PtrCesA2 expression levels similar to PtrCesA1 and high similarity of PtrCesA1 and PtrCesA2 to AtCesA8 and AtCesA7, respectively, suggest that both these aspen genes might be involved in the secondary wall development in aspen woody tissues. Availability of two aspen CesA orthologs will now enable us to examine if PtrCesA1 and PtrCesA2 functionally interact during aspen wood development that has long-term implications on genetic improvement of forest trees.

Arabidopsis Proteins↗

PubMed2003

Characterization of PTM5 in aspen trees: a MADS-box gene expressed during woody vascular development.

The vascular component of trees possesses some of the most specialized processes active in the formation of roots, stems, and branches, and its wood component continues to be of primary importance to our daily lives. The molecular mechanisms of wood development, however, remain poorly understood with few well-characterized regulatory genes. We have identified a vascular tissue-specific MADS-box gene, Populus tremuloides MADS-box 5 (PTM5) that is expressed in differentiating primary and secondary xylem and phloem. Phylogenetic analysis has shown that PTM5 is a member of the SOC1/TM3 class of MADS-box genes. Temporal expression analysis of PTM5 in staged vascular cambium and other tissues indicated that PTM5 expression is seasonal and is limited to spring wood formation and rapidly expanding floral catkins. Spatial expression analysis using in situ hybridization revealed that PTM5 expression is localized within a few layers of differentiating vascular cambium and xylem tissues as well as the vascular bundles of expanding catkins. Since many MADS-box genes are known to act as transcription factors, these results suggest that the coordinated expression of PTM5 with other vascular developmental genes may be a hallmark of the complex events that lead to the formation of the woody plant body.

Amino Acid Sequence↗

PubMed2004

North American populations of Entoleuca mammata are genetically more variable than populations in Europe.

Entoleuca mammata (syn. Hypoxylon mammatum) is a damaging pathogen of Populus tremuloides and P. grandidentata in North America and P. tremula in Europe, where the fungus occurs only sporadically in alpine regions and Scandinavia. It has been hypothesized that E. mammata was introduced to Europe from North America. In this study, E. mammata isolates collected from Europe and North America were compared by a sequence analysis of two DNA markers derived from DNA fingerprints. The objective of the study was to elucidate the relationship between North American and European E. mammata populations by testing two hypotheses: (1) North American and European isolates are conspecific; and (2) the fungus was introduced between continents causing both a founder effect and a genetic bottleneck. North American populations were found to be more polymorphic, but no major phylogenetic differences between fungal isolates collected from different continents were found. This result combined with the historical observations of the disease in Europe implies that E. mammata was introduced to Europe several centuries ago.

Alleles↗

PubMed2005

Crystal structure and solution NMR dynamics of a D (type II) peroxiredoxin glutaredoxin and thioredoxin dependent: a new insight into the peroxiredoxin oligomerism.

Peroxiredoxins (Prxs) constitute a family of thiol peroxidases that reduce hydrogen peroxide, peroxinitrite, and hydroperoxides using a strictly conserved cysteine. Very abundant in all organisms, Prxs are produced as diverse isoforms characterized by different catalytic mechanisms and various thiol-containing reducing agents. The oligomeric state of Prxs and the link with their functionality is a subject of intensive research. We present here a combined X-ray and nuclear magnetic resonance (NMR) study of a plant Prx that belongs to the D-Prx (type II) subfamily. The Populus trichocarpa Prx is the first Prx shown to be regenerated in vitro by both the glutaredoxin and thioredoxin systems. The crystal structure and solution NMR provide evidence that the reduced protein is a specific noncovalent homodimer both in the crystal and in solution. The dimer interface is roughly perpendicular to the plane of the central beta sheet and differs from the interface of A- and B-Prx dimers, where proteins associate in the plane parallel to the beta sheet. The homodimer interface involves residues strongly conserved in the D (type II) Prxs, suggesting that all Prxs of this family can homodimerize. The study provides a new insight into the Prx oligomerism and the basis for protein-protein and enzyme-substrate interaction studies by NMR.

Amino Acid Sequence↗

PubMed2002

Evidence of perchlorate (ClO4-) reduction in plant tissues (poplar tree) using radio-labeled 36ClO4-.

Phytoremediation of perchlorate (ClO4) by poplar trees Populus deltoidex nigrawas investigated using small cuttings growing in hydroponic Hoagland solution and plant tissue cultures, consisting of spherical photosynthetic cell aggregates (i.e. nodules) developing in Murashige and Skoog culture medium. Both plants and nodules were grown under a 16 h/8 h photoperiod cycle and under sterile conditions. Degradation experiments, performed by the incubation of pregrown plants and nodules in the presence of 36Cl radio-labeled ClO4- (25 mg L(-1)), showed a reduction of the initial ClO4- concentration in the solution of about 50% after 30 d of incubation. Analysis of the distribution of radioactivity in different plant fractions indicated that 27.4% of the total was translocated to the leaves, while 66.9% remained in the solution. Very little radioactivity (less than 3.0%) was detected in the other parts of the plants. 32.0% of the radioactivity recovered in the solution was shown to consist of 36Cl- and 68.0% of nontransformed 36ClO4-. The radioactivity recovered in the leaf extracts was distributed as chloride (36Cl-) (1.6% of the total), chlorite (36ClO2-) (2.4%), chlorate (36ClO3-) (4.8%), nontransformed 36ClO4- (21.6%), and an unidentified organic compound (1.4%). The radioactivity recovered in the solution containing submerged nodules consisted of 36Cl- (6.4% of the total), 36ClO3- (1.3%), and nontransformed 36ClO4- (51.5%). Radioactivity detected in the nodule extracts was distributed as 36Cl- (2.0% of the total), 36ClO2- (5.2%), 36ClO3- (6.4%), 36ClO4- (22.7%), and an unidentified organic compound (0.5%). These results provide evidence of perchlorate reduction inside poplar tree tissues. 36ClO4- is partially reduced to 36ClO3-, 36ClO2-, and 36Cl-.

Biodegradation, Environmental↗

PubMed2002

Uptake and leaching of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine by hybrid poplar trees.

The feasibility of remediating a high explosive, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), using hybrid poplar trees (Populus deltoides x nigra, DN34) was investigated. The fate, transport, and toxicity were determined. HMX was taken up by poplar cuttings from hydroponic solutions in long-term experiments (65 days) without evidence of toxicity. HMX was not toxic to actively growing hybrid poplar cuttings, even under saturated conditions. The measured log Kow for HMX was 0.19, less than other explosives, TNT, and RDX. However, the calculated transpiration stream concentration factor (TSCF) and root concentration factor (RCF) for HMX from an uptake study using radiolabeled [U-14C]HMX were 0.21 +/- 0.07 and 5.55 +/- 1.78 mL/g, respectively, both of which were intermediate between the values for TNT and ROX in previous reports. A 70% uptake of [U-14C]HMX was translocated and accumulated in leaves, and no metabolites were observed during a 65-day exposure using radiochromatography of plant tissue extracts. Most of the accumulated HMX (57%) in dried (fallen) poplar leaves was leached by deionized water after 5 days. Bioaccumulation in poplar trees and resolublization of HMX from leaves would be of significant ecological concern, and phytoremediation may not be warranted as a treatment option unless other processes occur under field conditions that degrade HMX to innocuous end products (e.g., photolysis, hydrolysis, or microbial degradation).

Azocines↗

PubMed2004

Application of controlled mesocosms for understanding mercury air-soil-plant exchange.

Whole system elemental mercury (Hg0) flux was measured for approximately 1.5 years using two large gas exchange mesocosms containing approximately 100 two-year old aspen trees (Populus tremuloides) planted in soil with elevated mercury concentrations (12.3 microg/g). We hypothesized that during leafout, whole mesocosm Hg0 flux would increase due to movement of Hg0 in the transpiration stream from the soil to the air. This hypothesis was not supported; plants were found to assimilate Hg0 from the contaminated air, and whole system Hg0 emissions were reduced as plants leafed-out due to shading of the soil. Surface disturbance, watering, and increases in soil moisture, light, and temperature were all found to increase whole system Hg0 flux, with light being a more significant factor. Although surface soils were maintained at 15-20% moisture, daily watering caused pulses of Hg0 to be released from the soil throughout the experiment. Data developed in this experiment suggested that those processes acting on the soil surface are the primary influence on Hg emissions and that the presence of vegetation, which shields soil surfaces from incident light, reduces Hg emissions from enriched soils.

Diffusion↗

PubMed2005

Biodegradability of fractions of dissolved organic carbon leached from decomposing leaf litter.

Dissolved organic matter leached from decomposing organic matter is important in the leaching of nutrients from the root zone of ecosystems, eluviation of metals, and transport of hydrophobic pollutants. The objective of this study was to compare microbial mineralization rates in intact soil cores of various fractions of water-soluble dissolved organic matter. Uniformly 14C-labeled Populus fremontii leaf litter that had decomposed for 1 year was extracted in water and this extract was fractionated into phenolic, humic acid, fulvic acid, hydrophilic acid, and hydrophilic neutral fractions. Fulvic acid comprised 42.1% of C in dissolved organic carbon (DOC) extracted from the litter. These fractions were added to intact cores of soil or sand, and respired 14CO2 was collected. The percentage of labeled substrate C mineralized in soil at the end of 1 year was, in order from least to greatest, hydrophilic acid (30.5), fulvic acid (33.8), humic acid (39.0), whole, unfractionated DOC (43.5), unseparated hydrophilic acid and neutral (44.7), phenolic (63.3), glucose (66.4), and hydrophilic neutral (70.2). In acid-washed nutrient-amended sand that was inoculated with soil microbes, mineralization rates of fulvic acid and glucose were lower. The fractionation appeared to separate the DOC into components with widely different rates of mineralization. Results also supported the ideas that the dissolved humic substance and hydrophilic acid fractions are inherently difficult for microbes to mineralize, and this property can contribute to movement of refractory C in soil and into aquatic ecosystems.

Biodegradation, Environmental↗

PubMed2006

Uptake of N-nitrosodimethylamine (NDMA) from water by phreatophytes in the absence and presence of perchlorate as a co-contaminant.

The uptake and fate of the emerging contaminants N-nitrosodimethylamine (NDMA) and perchlorate in phreatophytes was studied in a hydroponics system under greenhouse conditions. NDMA is a potent carcinogen, and perchlorate disrupts the functioning ofthe human thyroid gland. The rate of removal of NDMA from solution by rooted cuttings of black willow (Salix nigra) and hybrid poplar (Populus deltoides x nigra, DN34) trees varied seasonally, with faster removal in summer months when transpiration rates were highest. A linear correlation between the volume of water transpired and mass of NDMA removed from the root zone was observed, especially at higher NDMA concentrations. In bioreactors dosed with both NDMA (0.7-1.0 mg L(-1)) and perchlorate (27 mg L(-1)), no competitive uptake of NDMA and perchlorate was observed. While NDMA was primarily removed from solution by plant uptake, perchlorate was predominantly removed by rhizodegradation. In the presence of NDMA, a slower rate of rhizodegradation of perchlorate was observed, but still significantly faster than the rate of NDMA uptake. For experiments conducted with radiolabeled NDMA, 46.4 +/- 1.1% of the total 14C-activity was recovered in the plant tissues and 47.5% was phytovolatilized. The 46.4 +/- 1.1% recovered in the plants was distributed as follows: 18.8 +/- 1.4% in leaves, 15.9 +/- 5.9% in stems, 7.6 +/- 3.2% in branches, and 3.5 +/- 3.3% in roots. The poor extractability of NDMA with methanol-water (1:1 v/v) from stem and leaf tissues suggested that some fraction of NDMA was assimilated. The calculated transpiration stream concentration factor (TSCF) of 0.28 +/- 0.06 suggests that NDMA is passively taken up by phreatophytes, and mainly phytovolatilized.

Biodegradation, Environmental↗

PubMed2005

Rates of cuticular penetration of chelated Fe(III): role of humidity, concentration, adjuvants, temperature, and type of chelate.

Time courses of cuticular penetration of FeCl3 and Fe(III) complexes of citric acid, EDTA, EDDHA (Sequestrene 138Fe), imidodisuccinic acid (IDHA), and ligninsulfonic acid (Natrel) were studied using astomatous cuticular membranes (CMs) isolated from Populus x canescens leaves. At 100% relative humidity, the Fe(III) chelates disappeared exponentially with time from the surface of the CMs; that is, penetration was a first-order process that can be described using rate constants or half-times of penetration (t(1/2)). Half-times ranged from 20 to 30 h. At 90% humidity, penetration rates were insignificant with the exception of Natrel, for which t(1/2) amounted to 58 h. Rate constants were independent of temperature (15, 25, and 35 degrees C). Permeability decreased with increasing Fe chelate concentration (IDHA and EDTA). At 100% humidity, half-times measured with FeIDHA were 11 h (2 mmol L(-1)), 17 h (10 mmol L(-1)) and 36 h (20 mmol L(-1)), respectively. In the presence of FeEDTA, penetration of CaCl2 was slowed greatly. Half-times for penetration of CaCl2, which were 1.9 h in the absence of FeEDTA, rose to 3.12 h in the presence of an equimolar concentration of EDTA and 13.3 h when the FeEDTA concentration was doubled. Hence, Fe chelates reduced permeability of CMs to CaCl2 and to the Fe chelates themselves. It is suggested that Fe chelates reduced the size of aqueous pores. This view is supported by the fact that rate constants for calcium salts were about 5 times higher than for Fe chelates with the same molecular weights. Adding Tween 20 (5 g L(-1)) as a humectant did not increase permeability to FeIDHA at 90% humidity and below, while addition of glycine betaine did. Penetration of FeCl3 applied at 5 g L(-1) (pH 1.5) was not a first order process as rate constants decreased rapidly with time. Only 2% of the dose penetrated during the first 2 h and less than that in the subsequent 8 h. Recovery was only 70%. This was attributed to the formation of insoluble Fe hydroxide precipitates on CMs. These results explain why in the past foliar application of Fe compounds had limited success. Inorganic Fe salts are instable and phytotoxic because of low pH, while Fe chelates penetrate slowly and 100% humidity is required for significant penetration rates. Concentrations as low as reasonably possible should be used. These physical facts are expected to apply to stomatous leaf surfaces as well, but absolute rates probably depend on leaf age and plant species. High humidity in stagnant air layers may favor penetration rates across stomatous leaf surfaces when humidity in bulk air is below 100%.

Calcium↗

PubMed2006

Organosolv ethanol lignin from hybrid poplar as a radical scavenger: relationship between lignin structure, extraction conditions, and antioxidant activity.

Twenty-one organosolv ethanol lignin samples were prepared from hybrid poplar (Populus nigra xP. maximowiczii) under varied conditions with an experimental matrix designed using response surface methodology (RSM). The lignin preparations were evaluated as potential antioxidants. Results indicated that the lignins with more phenolic hydroxyl groups, less aliphatic hydroxyl groups, low molecular weight, and narrow polydispersity showed high antioxidant activity. Processing conditions affected the functional groups and molecular weight of the extracted organosolv ethanol lignins, and consequently influenced the antioxidant activity of the lignins. In general, the lignins prepared at elevated temperature, longer reaction time, increased catalyst, and diluted ethanol showed high antioxidant activity. Regression models were developed to enable the quantitative prediction of lignin characteristics and antioxidant activity based on the processing conditions.

Acetylation↗

PubMed2003

Antioxidants in the midgut fluids of a tannin-tolerant and a tannin-sensitive caterpillar: effects of seasonal changes in tree leaves.

The seasonal decline in foliar nutritional quality in deciduous trees also effects the availability of essential micronutrients, such as ascorbate and alpha-tocopherol, to herbivorous insects. This study first examined whether there are consistent patterns of seasonal change in antioxidant concentrations in deciduous tree leaves. Alpha-tocopherol concentrations increased substantially through time in late summer in sugar maple (Acer saccharum), red oak (Quercus rubra), and trembling aspen (Populus tremuloides). However, seasonal change in the concentrations of other antioxidants differed between each species: P. tremuloides had higher levels of ascorbate and glutathione in the spring, Q. rubra had higher levels of glutathione but lower levels of ascorbate in the spring, and A. saccharum had lower levels of both ascorbate and glutathione in the spring. To test the hypothesis that tannin-tolerant caterpillars maintain higher concentrations of antioxidants in their midgut fluids than do tannin-sensitive species, we measured antioxidants in Orgyia leucostigma (a spring- and summer-feeding, tannin-tolerant species) and Malacosoma disstria (a spring-feeding, tannin-sensitive species) that were fed tree leaves in the spring and summer. The midgut fluids of O. leucostigma larvae generally had higher concentrations of antioxidants in the summer than did those of M. disstria, and were significantly higher overall. The results of this study are consistent with the hypothesis that higher concentrations of antioxidants form an important component of the defenses of herbivores that feed on mature, phenol-rich tree leaves. Some limitations of the interpretation of total antioxidant capacity are also discussed.

Acer↗

PubMed2003

Leaf ontogeny influences leaf phenolics and the efficacy of genetically expressed Bacillus thuringiensis cry1A(a) d-endotoxin in hybrid poplar against gypsy moth.

We tested the hypothesis that ontogenetic variation in leaf chemistry could affect the efficacy of genetically expressed Bacillus thuringiensis cry1A(a) d-endotoxin, and thus provide spatial variation in (1) foliage protection and (2) selective pressures that could delay the resistance of folivores. Our model consisted of clonal hybrid Populus plants (NC5339). Consumption of foliage and relative growth rates of gypsy moth, Lymantria dispar (L.) increased, and phenolic glycoside concentrations decreased, as leaves from transformed plants containing the cry1A(a) d-endotoxin and nontransformed plants matured from leaf plastochron index (LPI) 1-6. Feeding and growth rates were negatively correlated with phenolic glycosides in both transformed and nontransformed foliage. The presence of the B. thuringiensis d-endotoxin was at most, additive to the effect of the phenolic glycosides. Feeding and growth rates were positively correlated with condensed tannins in transformed foliage, but there was no relationship with condensed tannins in nontransformed foliage. The results indicate that the presence of foliar allelochemicals of poplar can enhance the effectiveness of genetically expressed B. thuringiensis d-endotoxin against gypsy moth larvae. However, the spatial variation in gypsy moth performance in response to the combination of foliar allelochemicals and d-endotoxin was not greater than the effect of ontogenetic variation in foliar allelochemicals alone. These results suggest that for this important pest, foliage protection may be obtained without genetically engineered defenses, and instead, by relying on ontogenetic and clonal variation in allelochemicals. The benefits of combining novel resistance mechanisms with natural ones will depend upon the specific folivore's adaptation to natural resistance mechanisms, such as allelochemicals. Moreover, some of the greatest benefits from transgenic resistance may arise from the need to protect trees from multiple pests, some of which may not be deterred by, or may even prefer, allelochemicals that confer protection from a few species.

Animals↗