Light signals generated by vegetation shade facilitate acclimation to low light in shade-avoider plants.

When growing in search for light, plants can experience continuous or occasional shading by other plants. Plant proximity causes a decrease in the ratio of R to far-red light (low R:FR) due to the preferential absorbance of R light and reflection of FR light by photosynthetic tissues of neighboring plants. This signal is often perceived before actual shading causes a reduction in photosynthetically active radiation (low PAR). Here, we investigated how several Brassicaceae species from different habitats respond to low R:FR and low PAR in terms of elongation, photosynthesis, and photoacclimation. Shade-tolerant plants such as hairy bittercress (Cardamine hirsuta) displayed a good adaptation to low PAR but a poor or null response to low R:FR exposure. In contrast, shade-avoider species, such as Arabidopsis (Arabidopsis thaliana), showed a weak photosynthetic performance under low PAR but they strongly elongated when exposed to low R:FR. These responses could be genetically uncoupled. Most interestingly, exposure to low R:FR of shade-avoider (but not shade-tolerant) plants improved their photoacclimation to low PAR by triggering changes in photosynthesis-related gene expression, pigment accumulation, and chloroplast ultrastructure. These results indicate that low R:FR signaling unleashes molecular, metabolic, and developmental responses that allow shade-avoider plants (including most crops) to adjust their photosynthetic capacity in anticipation of eventual shading by nearby plants.

Effects of Supplementary Blue and UV-A LED Lights on Morphology and Phytochemicals of Brassicaceae Baby-Leaves.

Brassicaceae baby-leaves are good source of functional phytochemicals. To investigate how Chinese kale and pak-choi baby-leaves in response to different wavebands of blue (430 nm and 465 nm) and UV-A (380 nm and 400 nm) LED, the plant growth, glucosinolates, antioxidants, and minerals were determined. Both agronomy traits and phytochemical contents were significantly affected. Blue and UV-A light played a predominant role in increasing the plant biomass and morphology, as well as the contents of antioxidant compounds (vitamin C, vitamin E, phenolics, and individual flavonols), the antioxidant activity (DPPH and FRAP), and the total glucosinolates accumulation. In particular, four light wavebands significantly decreased the content of progoitrin, while 400 nm UV-A light and 430 nm blue light were efficient in elevating the contents of sinigrin and glucobrassicin in Chinese kale. Meanwhile, 400 nm UV-A light was able to increase the contents of glucoraphanin, sinigrin, and glucobrassicin in pak-choi. From the global view of heatmap, blue lights were more efficient in increasing the yield and phytochemical levels of two baby-leaves.

The influence of light combination on the physicochemical characteristics and enzymatic activity of soil with multi-metal pollution in phytoremediation.

Light irradiation with suitable quality and intensity could influence the success of phytoremediation by improving the biomass yield of plants. However, mechanisms involved in this influence on the contaminant accumulation and translocation ability of plants have rarely been studied. Five light combinations with different red (R) and blue (B) ratios (0, 10, 50, 75 and 100 % blue) at the same intensity (220 µmol m-2 s-1) were used to assist phytoremediation using Noccaea caerulescens, and the change in physicochemical characteristics and enzymatic activities of soils after phytoremediation were evaluated. Compared with the control, the light combinations and monochromic blue light significantly increased the activities of soil ureases, invertases, and phosphatases, whereas monochromic red light strongly inhibited the activities of these enzymes, because different light irradiations altered the formation and excretion of carbohydrates from plants for soil microorganism consumption. Plants under B50R50 treatment accumulated the highest concentrations of metals, but their chlorophyll concentrations and lipid peroxidation were similar to those other species with lower metal concentrations. Hence, light with a proper blue/red ratio can simultaneously improve the physicochemical characteristics and enzymatic activities of soils, increase the metal uptake capacity and oxidation resistance of plants, and reduce the leaching risk during phytoremediation processes.

Enhanced NPQ affects long-term acclimation in the spring ephemeral Berteroa incana.

The spring ephemeral Berteroa incana is a familial relative of Arabidopsis thaliana and thrives in a diverse range of terrestrial ecosystems. Within this study, the novel chlorophyll fluorescence parameter of photochemical quenching in the dark (qPd) was used to measure the redox state of the primary quinone electron acceptor (QA) in order to estimate the openness of photosystem II (PSII) reaction centres (RC). From this, the early onset of photoinactivation can be sensitively quantified alongside the light tolerance of PSII and the photoprotective efficiency of nonphotochemical quenching (NPQ). This study shows that, with regards to A. thaliana, NPQ is enhanced in B. incana in both low-light (LL) and high-light (HL) acclimation states. Moreover, light tolerance is increased by up to 500%, the rate of photoinactivation is heavily diminished, and the ability to recover from light stress is enhanced in B. incana, relative to A. thaliana. This is due to faster synthesis of zeaxanthin and a larger xanthophyll cycle (XC) pool available for deepoxidation. Moreover, preferential energy transfer via CP47 around the RC further enhances efficient photoprotection. As a result, a high functional cross-section of photosystem II is maintained and is not downregulated when B. incana is acclimated to HL. A greater capacity for protective NPQ allows B. incana to maintain an enhanced light-harvesting capability when acclimated to a range of light conditions. This enhancement of flexible short-term protection saves the metabolic cost of long-term acclimatory changes.

Genome draft of the Arabidopsis relative Pachycladon cheesemanii reveals novel strategies to tolerate New Zealand's high ultraviolet B radiation environment.

BACKGROUND: Pachycladon cheesemanii is a close relative of Arabidopsis thaliana and is an allotetraploid perennial herb which is widespread in the South Island of New Zealand. It grows at altitudes of up to 1000 m where it is subject to relatively high levels of ultraviolet (UV)-B radiation. To gain first insights into how Pachycladon copes with UV-B stress, we sequenced its genome and compared the UV-B tolerance of two Pachycladon accessions with those of two A. thaliana accessions from different altitudes. RESULTS: A high-quality draft genome of P. cheesemanii was assembled with a high percentage of conserved single-copy plant orthologs. Synteny analysis with genomes from other species of the Brassicaceae family found a close phylogenetic relationship of P. cheesemanii with Boechera stricta from Brassicaceae lineage I. While UV-B radiation caused a greater growth reduction in the A. thaliana accessions than in the P. cheesemanii accessions, growth was not reduced in one P. cheesemanii accession. The homologues of A. thaliana UV-B radiation response genes were duplicated in P. cheesemanii, and an expression analysis of those genes indicated that the tolerance mechanism in P. cheesemanii appears to differ from that in A. thaliana. CONCLUSION: Although the P. cheesemanii genome shows close similarity with that of A. thaliana, it appears to have evolved novel strategies allowing the plant to tolerate relatively high UV-B radiation.

Life after Harvest: Circadian Regulation in Photosynthetic Pigments of Rocket Leaves during Supermarket Storage Affects the Nutritional Quality.

Vegetables, once harvested and stored on supermarket shelves, continue to perform biochemical adjustments due to their modular nature and their ability to retain physiological autonomy. They can live after being harvested. In particular, the content of some essential nutraceuticals, such as carotenoids, can be altered in response to environmental or internal stimuli. Therefore, in the present study, we wondered whether endogenous rhythms continue to operate in commercial vegetables and if so, whether vegetable nutritional quality could be altered by such cycles. Our experimental model consisted of rocket leaves entrained under light/darkness cycles of 12/12 h over 3 days, and then we examined free-run oscillations for 2 days under continuous light or continuous darkness, which led to chlorophyll and carotenoid oscillations in both constant conditions. Given the importance of preserving food quality, the existence of such internal rhythms during continuous conditions may open new research perspective in nutrition science. However, while chromatographic techniques employed to determine pigment composition are accurate, they are also time-consuming and expensive. Here we propose for the first time an alternative method to estimate pigment content and the nutritional quality by the use of non-destructive and in situ optical techniques. These results are promising for nutritional quality assessments.

Aethionema arabicum: a novel model plant to study the light control of seed germination.

The timing of seed germination is crucial for seed plants and is coordinated by internal and external cues, reflecting adaptations to different habitats. Physiological and molecular studies with lettuce and Arabidopsis thaliana have documented a strict requirement for light to initiate germination and identified many receptors, signaling cascades, and hormonal control elements. In contrast, seed germination in several other plants is inhibited by light, but the molecular basis of this alternative response is unknown. We describe Aethionema arabicum (Brassicaceae) as a suitable model plant to investigate the mechanism of germination inhibition by light, as this species has accessions with natural variation between light-sensitive and light-neutral responses. Inhibition of germination occurs in red, blue, or far-red light and increases with light intensity and duration. Gibberellins and abscisic acid are involved in the control of germination, as in Arabidopsis, but transcriptome comparisons of light- and dark-exposed A. arabicum seeds revealed that, upon light exposure, the expression of genes for key regulators undergo converse changes, resulting in antipodal hormone regulation. These findings illustrate that similar modular components of a pathway in light-inhibited, light-neutral, and light-requiring germination among the Brassicaceae have been assembled in the course of evolution to produce divergent pathways, likely as adaptive traits.

Genome-wide DNA methylation changes in two Brassicaceae species sampled alongside a radiation gradient in Chernobyl and Fukushima.

The long-term radiological impact to the environment of the nuclear accidents in Chernobyl and Fukushima is still under discussion. In the course of spring of 2016 we sampled two Brassicacea plants, Arabidopsis thaliana and Capsella bursa-pastoris native to Ukraine and Japan, respectively, alongside a gradient of radiation within the exclusion and difficult to return zones of Chernobyl (CEZ) and Fukushima (FEZ). Ambient dose rates were similar for both sampling gradients ranging from 0.5 to 80 µGy/h at plant height. The hypothesis was tested whether a history of several generations of plants growing in enhanced radiation exposure conditions would have led to changes in genome-wide DNA methylation. However, no differences were found in the global percentage of 5-methylated cytosines in Capsella bursa pastoris plants sampled in FEZ. On the other hand a significant decrease in whole genome methylation percentage in Arabidopsis thaliana plants was found in CEZ mainly governed by the highest exposed plants. These data support a link between exposure to changed environmental conditions and changes genome methylation. In addition to methylation the activity concentration of different radionuclides, 137Cs, 90Sr, 241Am and Pu-238,239,240 for CEZ and 137, 134Cs for FEZ, was analysed in both soil and plant samples. The ratio of 5.6 between 137Cs compared to 134Cs was as expected five years after the FEZ accident. For CEZ 137Cs is the most abundant polluting radionuclide in soil followed by 90Sr. Whereas 241Am and Pu-isotopes are only marginally present. In the plant tissue, however, higher levels of Sr than Cs were retrieved due to a high uptake of 90Sr in the plants. The 90Sr transfer factors ranged in CEZ from 5 to 20 (kg/kg) depending on the locality. Based on the activity concentrations of the different radionuclides the ERICA tool was used to estimate the total dose rates to the plants. It was found that for FEZ the doses was mainly contributable to the external Cs-isotopes and as such estimated total dose rates (0.13-38 µGy/h) were in the same range as the ambient measured dose rates. In strong contrast this was not true for CEZ where the total dose rate was mainly due to high uptake of the 90Sr leading to dose rates ranging from 1 to 370 µGy/h. Hence our data clearly indicate that not taking into account the internal contamination in CEZ will lead to considerable underestimation of the doses to the plants. Additionally they show that it is hard to compare the two nuclear accidental sites and one of the main reasons is the difference in contamination profile.

Growth of Arabidopsis thaliana and Eutrema salsugineum in a closed growing system designed for quantification of plant water use.

The identification of genetic determinants for water-use efficiency (WUE) and their incorporation into crop plants is critical as world water resources are predicted to become less stable over the coming decades. However, quantification of WUE in small model species such as Arabidopsis is difficult because of low plant water loss relative to root zone evaporation. Furthermore, measurements of long-term WUE are labor-intensive and time-consuming. A novel high-throughput closed-container growing system for measuring plant WUE is described. The system eliminates nearly all water loss from the media and does not require irrigation throughout the duration of a typical experiment. Using the model species Arabidopsis thaliana and Eutrema salsugineum, it was confirmed that under growth chamber conditions, this system: (1) eliminates the need for irrigation for as much as 30 days with media water content remaining above 80% full capacity; (2) allows for quantification of WUE in plants with a leaf area as small as ca. 20 cm(2); (3) does not inhibit plant growth; and (4) does not alter media conditions outside of an acceptable range for these species. The growing system provides an efficient high-throughput system for quantifying plant water loss and WUE.

Resolution of Brassicaceae Phylogeny Using Nuclear Genes Uncovers Nested Radiations and Supports Convergent Morphological Evolution.

Brassicaceae is one of the most diverse and economically valuable angiosperm families with widely cultivated vegetable crops and scientifically important model plants, such as Arabidopsis thaliana. The evolutionary history, ecological, morphological, and genetic diversity, and abundant resources and knowledge of Brassicaceae make it an excellent model family for evolutionary studies. Recent phylogenetic analyses of the family revealed three major lineages (I, II, and III), but relationships among and within these lineages remain largely unclear. Here, we present a highly supported phylogeny with six major clades using nuclear markers from newly sequenced transcriptomes of 32 Brassicaceae species and large data sets from additional taxa for a total of 55 species spanning 29 out of 51 tribes. Clade A consisting of Lineage I and Macropodium nivale is sister to combined Clade B (with Lineage II and others) and a new Clade C. The ABC clade is sister to Clade D with species previously weakly associated with Lineage II and Clade E (Lineage III) is sister to the ABCD clade. Clade F (the tribe Aethionemeae) is sister to the remainder of the entire family. Molecular clock estimation reveals an early radiation of major clades near or shortly after the Eocene-Oligocene boundary and subsequent nested divergences of several tribes of the previously polytomous Expanded Lineage II. Reconstruction of ancestral morphological states during the Brassicaceae evolution indicates prevalent parallel (convergent) evolution of several traits over deep times across the entire family. These results form a foundation for future evolutionary analyses of structures and functions across Brassicaceae.

Substantial reprogramming of the Eutrema salsugineum (Thellungiella salsuginea) transcriptome in response to UV and silver nitrate challenge.

BACKGROUND: Cruciferous plants synthesize a large variety of tryptophan-derived phytoalexins in response to pathogen infection, UV irradiation, or high dosages of heavy metals. The major phytoalexins of Eutrema salsugineum (Thellungiella salsuginea), which has recently been established as an extremophile model plant, are probably derivatives of indole glucosinolates, in contrast to Arabidopsis, which synthesizes characteristic camalexin from the glucosinolate precursor indole-3-acetaldoxime. RESULTS: The transcriptional response of E. salsugineum to UV irradiation and AgNO3 was monitored by RNAseq and microarray analysis. Most transcripts (respectively 70% and 78%) were significantly differentially regulated and a large overlap between the two treatments was observed (54% of total). While core genes of the biosynthesis of aliphatic glucosinolates were repressed, tryptophan and indole glucosinolate biosynthetic genes, as well as defence-related WRKY transcription factors, were consistently upregulated. The putative Eutrema WRKY33 ortholog was functionally tested and shown to complement camalexin deficiency in Atwrky33 mutant. CONCLUSIONS: In E. salsugineum, UV irradiation or heavy metal application resulted in substantial transcriptional reprogramming. Consistently induced genes of indole glucosinolate biosynthesis and modification will serve as candidate genes for the biosynthesis of Eutrema-specific phytoalexins.

Garlic Mustard (Alliaria petiolata) Glucosinolate Content Varies Across a Natural Light Gradient.

Garlic mustard is a well-known invader of deciduous forests of North America, yet the influence of environmental factors on garlic mustard allelochemical production is not well understood. Three experiments were conducted to detect interactions between one garlic mustard allelochemical (glucosinolate) production and light availability. First, to detect patterns of glucosinolate production across a natural light gradient, leaves and roots of mature plants and first-year rosettes were sampled in patches ranging from 100 to 2 % of full sun within an Indiana forest. Second, to determine whether genetic variation drives observed correlations between glucosinolate content and light, seed collected across light gradients within six sites was grown in a common garden and glucosinolate production was measured. Finally, to understand whether local adaptation occurred in garlic mustard's response to light, seed collected from defined light environments across six sites was grown under four light treatments. Results of the field sampling showed that mature plants' root glucosinolate content was elevated in high compared to low light. In the common garden experiment, however, there was no correlation between light availability at seed origin and constitutive glucosinolate content. Additionally, in the common light treatments, there was no evidence for local adaptation to light environment. Overall, the results indicate that plasticity in response to light, not genetic variation among plants growing in different light environments, generates correlations between glucosinolate content and light in the field. Since mature garlic mustard populations in high light may exhibit increased glucosinolate content, it makes them potential targets for management.

Acquisition of freezing tolerance in Arabidopsis and two contrasting ecotypes of the extremophile Eutrema salsugineum (Thellungiella salsuginea).

Eutrema salsugineum (Thellungiella salsuginea) is an extremophile, a close relative of Arabidopsis, but possessing much higher constitutive levels of tolerance to abiotic stress. This study aimed to characterize the freezing tolerance of Arabidopsis (Columbia ecotype) and two ecotypes of Eutrema (Yukon and Shandong) isolated from contrasting geographical locations. Under our growth conditions, maximal freezing tolerance was observed after two- and three-weeks of cold acclimation for Arabidopsis and Eutrema, respectively. The ecotypes of Eutrema and Arabidopsis do not differ in their constitutive level of freezing tolerance or short-term cold acclimation capacity. However Eutrema remarkably outperforms Arabidopsis in long-term acclimation capacity suggesting a wider phenotypic plasticity for the trait of freezing tolerance. The combination of drought treatment and one-week of cold acclimation was more effective than long-term cold acclimation in achieving maximum levels of freezing tolerance in Eutrema, but not Arabidopsis. Furthermore, it was demonstrated growth conditions, particularly irradiance, are determinates of the level of freezing tolerance attained during cold acclimation suggesting a role for photosynthetic processes in adaptive stress responses.

Ultrasound-assisted biodiesel production from Camelina sativa oil.

The main drawbacks of biodiesel production are high reaction temperatures, stirring and time. These could be alleviated by aiding transesterification with alternative energy sources, i.e. ultrasound (US). In this study, biodiesel was obtained from Camelina sativa oil, aided with an ultrasonic probe (20kHz, 70% duty cycle, 50% amplitude). Design of experiments included the combination of sonication and agitation cycles, w/wo heating (50°C). To gain knowledge about the implications of the proposed methodology, conventional transesterification was optimized, resulting in higher needs on catalyst concentration and reaction time, compared to the proposed reaction. Although FAME content met EN 14103 standard, FAME yields were lower than those provided by US-assisted transesterification. Energy consumption measurements showed that ultrasound assisted transesterification required lower energy, temperature, catalyst and reaction time.

The effects of LED illumination spectra and intensity on carotenoid content in Brassicaceae microgreens.

The objective of this study was to evaluate the effects of irradiance levels and spectra produced by solid-state light-emitting diodes (LEDs) on carotenoid content and composition changes in Brassicaceae microgreens. A system of five high-power, solid-state lighting modules with standard 447-, 638-, 665-, and 731-nm LEDs was used in the experiments. Two experiments were performed: (1) evaluation of LED irradiance levels of 545, 440, 330, 220, and 110 µmol m(-2) s(-1) photosynthetically active flux density (PPFD) and (2) evaluation of the effects of 520-, 595-, and 622-nm LEDs supplemental to the standard set of LEDs. Concentrations of various carotenoids in red pak choi and tatsoi were higher under illumination of 330-440 µmol m(-2) s(-1) and at 110-220 µmol m(-2) s(-1) in mustard. All supplemental wavelengths increased total carotenoid content in mustard but decreased it in red pak choi. Carotenoid content increased in tatsoi under supplemental yellow light.

Variation of glucosinolate accumulation and gene expression of transcription factors at different stages of Chinese cabbage seedlings under light and dark conditions.

Chinese cabbage is one of the most important leafy vegetables widely used in East Asian cuisines. The glucosinolate (GSL) accumulation and transcript levels of 7 transcription factors (Dof1.1, IQD1-1, MYB28, MYB29, MYB34, MYB51, and MYB122, and their isoforms) involved in the biosynthesis of aliphatic and indolic glucosinolates (GSLs) were analyzed at different stages of Chinese cabbage (Brassica rapa ssp. pekinensis) seedlings under light and dark conditions using high performance liquid chromatography and quantitative real time PCR. During seedling development, transcription of almost all transcription factors under light conditions was higher expressed than under dark conditions. Five aliphatic GSLs (progoitrin, sinigrin, glucoalyssin, gluconapin, and glucobrassicanapin) and four indolic GSLs (4-hydroxyglucobrassicin, glucobrassicin, 4-methoxyglucobrassicin, and neoglucobrasscin) were detected. Total GSL contents under light conditions 6, 8, and 10 days after sowing (DAS) were 3.2-, 3.9-, and 6.9-fold higher, respectively than those of dark conditions. Interestingly, total GSL contents 2 {85.4 micromol/g dry weight (DW)} to 10 (7.74 micromol/g DW) DAS under dark conditions were gradually decreased. In this study, our results suggest that light affects the levels of GSL in Chinese cabbage seedlings. These results could be useful for obtaining cabbage varieties rich in GSLs.

Gas exchange, growth, and defense responses of invasive Alliaria petiolata (Brassicaceae) and native Geum vernum (Rosaceae) to elevated atmospheric CO2 and warm spring temperatures.

PREMISE OF STUDY: Global increases in atmospheric CO2 and temperature may interact in complex ways to influence plant physiology and growth, particularly for species that grow in cool, early spring conditions in temperate forests. Plant species may also vary in their responses to environmental changes; fast-growing invasives may be more responsive to rising CO2 than natives and may increase production of allelopathic compounds under these conditions, altering species' competitive interactions. METHODS: We examined growth and physiological responses of Alliaria petiolata, an allelopathic, invasive herb, and Geum vernum, a co-occurring native herb, to ambient and elevated spring temperatures and atmospheric CO2 conditions in a factorial growth chamber experiment. KEY RESULTS: At 5 wk, leaves were larger at high temperature, and shoot biomass increased under elevated CO2 only at high temperature in both species. As temperatures gradually warmed to simulate seasonal progression, G. vernum became responsive to CO2 at both temperatures, whereas A. petiolata continued to respond to elevated CO2 only at high temperature. Elevated CO2 increased thickness and decreased nitrogen concentrations in leaves of both species. Alliaria petiolata showed photosynthetic downregulation at elevated CO2, whereas G. vernum photosynthesis increased at elevated temperature. Flavonoid and cyanide concentrations decreased significantly in A. petiolata leaves in the elevated CO2 and temperature treatment. Total glucosinolate concentrations and trypsin inhibitor activities did not vary among treatments. CONCLUSIONS: Future elevated spring temperatures and CO2 will interact to stimulate growth for A. petiolata and G. vernum, but there may be reduced allelochemical effects in A. petiolata.

Phytochemicals of Brassicaceae in plant protection and human health--influences of climate, environment and agronomic practice.

In this review, we provide an overview of the role of glucosinolates and other phytochemical compounds present in the Brassicaceae in relation to plant protection and human health. Current knowledge of the factors that influence phytochemical content and profile in the Brassicaceae is also summarized and multi-factorial approaches are briefly discussed. Variation in agronomic conditions (plant species, cultivar, developmental stage, plant organ, plant competition, fertilization, pH), season, climatic factors, water availability, light (intensity, quality, duration) and CO(2) are known to significantly affect content and profile of phytochemicals. Phytochemicals such as the glucosinolates and leaf surface waxes play an important role in interactions with pests and pathogens. Factors that affect production of phytochemicals are important when designing plant protection strategies that exploit these compounds to minimize crop damage caused by plant pests and pathogens. Brassicaceous plants are consumed increasingly for possible health benefits, for example, glucosinolate-derived effects on degenerative diseases such as cancer, cardiovascular and neurodegenerative diseases. Thus, factors influencing phytochemical content and profile in the production of brassicaceous plants are worth considering both for plant and human health. Even though it is known that factors that influence phytochemical content and profile may interact, studies of plant compounds were, until recently, restricted by methods allowing only a reductionistic approach. It is now possible to design multi-factorial experiments that simulate their combined effects. This will provide important information to ecologists, plant breeders and agronomists.

Unveiling the phytoalexin biosynthetic puzzle in salt cress: unprecedented incorporation of glucobrassicin into wasalexins A and B.

Salt cress (Thellungiella salsuginea also known as T. halophila) is a wild cruciferous extremophile highly resistant to salt, drought, and cold. The recent discovery that salt cress produces the phytoalexins wasalexins A and B, and the phytoanticipins 1-methoxyglucobrassicin and 4-methoxyglucobrassicin in relatively higher amounts than other cruciferous species, prompted investigation of their biosynthetic relationships. Toward this end, perdeuterated 1-methoxybrassinin, l-Trp, glucobrassicin, 1-methoxyindolyl-3-acetaldoxime, brassinin, and methionine, as well as the corresponding natural abundance compounds, were administered to salt cress plants previously irradiated with UV-light (λ(max) 254 nm). Remarkably, administration of hexadeuterated glucobrassicin led to incorporation of several deuterium atoms into wasalexins A and B, 1-methoxyglucobrassicin and 4-methoxyglucobrassicin. This unprecedented discovery suggests that glucobrassicin is a biosynthetic precursor of wasalexins and methoxylated glucosinolates in salt cress.

UV-B impact on aphid performance mediated by plant quality and plant changes induced by aphids.

Plants face various abiotic and biotic environmental factors and therefore need to adjust their phenotypic traits on several levels. UV-B radiation is believed to impact herbivorous insects via host plant changes. Plant responses to abiotic challenges (UV-B radiation) and their interaction with two aphid species were explored in a multifactor approach. Broccoli plants [Brassica oleracea L. convar. botrytis (L.), Brassicaceae] were grown in two differently covered greenhouses, transmitting either 80% (high UV-B) or 4% (low UV-B) of ambient UV-B. Three-week-old plants were infested with either specialist cabbage aphids [Brevicoryne brassicae (L.), Sternorrhyncha, Aphididae] or generalist green peach aphids [Myzus persicae (Sulzer), Sternorrhyncha, Aphididae]. Plants grown under high-UV-B intensities were smaller and had higher flavonoid concentrations. Furthermore, these plants had reduced cuticular wax coverage, whereas amino acid concentrations of the phloem sap were little influenced by different UV-B intensities. Cabbage aphids reproduced less on plants grown under high UV-B than on plants grown under low UV-B, whereas reproduction of green peach aphids in both plant light sources was equally poor. These results are likely related to the different specialisation-dependent sensitivities of the two species. The aphids also affected plant chemistry. High numbers of cabbage aphid progeny on low-UV-B plants led to decreased indolyl glucosinolate concentrations. The induced change in these glucosinolates may depend on an infestation threshold. UV-B radiation considerably impacts plant traits and subsequently affects specialist phloem-feeding aphids, whereas aphid growth forces broccoli to generate specific defence responses.