•We studied VOC emissions in Alnus glutinosa induced by abiotic and biotic interacting stresses.•Herbivores were more strongly attracted to well-watered plants than the plants under drought.•The ...study demonstrates an important priming effect of drought in VOC emissions.
Plant volatile organic compounds (VOCs) elicited in response to herbivory can serve as cues for parasitic and predatory insects, but the modification of VOC elicitation responses under interacting abiotic stresses is poorly known. We studied foliage VOC emissions in the deciduous tree Alnus glutinosa induced by feeding by the larvae of green alder sawfly (Monsoma pulveratum) under well-watered and drought-stressed conditions. Drought strongly curbed photosynthesis rate and stomatal conductance, but there were no effects of insect feeding on photosynthetic characteristics. Feeding induced emissions of volatile products of lipoxygenase pathway and monoterpenes, and emissions of stress marker compounds (E)-β-ocimene and homoterpene DMNT. The emissions were more strongly elicited and reached a maximum value earlier in drought-stressed plants. In addition, methyl salicylate emissions were elicited in herbivory-fed drought-stressed plants. Herbivores were more strongly attracted to well-watered plants and consumed more than a four-fold greater fraction of leaf area than they consumed from drought-treated plants. Overall, this study demonstrates an important priming effect of drought, suggesting that plants under combined drought/herbivory stress are more resistant to herbivores.
Biocontrol providing parasitoids can orientate according to volatile organic compounds (VOCs) of their host's plants, the emission of which is potentially dependent on the availability of soil ...nitrogen (N). This paper aimed at finding the optimal N fertilization rate for oilseed rape (Brassica napus L.) to favor parasitism of pollen beetles (Brassicogethes aeneus Fab. syn. Meligethes aeneus Fab.) in a controlled environment. Pollen beetles preferred to oviposit into buds of plants growing under higher N fertilization, whereas their parasitoids favored moderate N fertilization. As a part of induced defense, the proportion of volatile products of glucosinolate pathway in the total oilseed rape VOC emission blend was increased. Our results suggest that the natural biological control of pollen beetle herbivory is best supported by moderate N fertilization rates.
Ozone (O3) entry into plant leaves depends on atmospheric O3 concentration, exposure time and openness of stomata. O3 negatively impacts photosynthesis rate (A) and might induce the release of ...reactive volatile organic compounds (VOCs) that can quench O3, and thereby partly ameliorate O3 stress. Water stress reduces stomatal conductance (gs) and O3 uptake and can affect VOC release and O3 quenching by VOC, but the interactive effects of O3 exposure and water stress, as possibly mediated by VOC, are poorly understood. Well-watered (WW) and water-stressed (WS) Brassica nigra plants were exposed to 250 and 550 ppb O3 for 1 h, and O3 uptake rates, photosynthetic characteristics and VOC emissions were measured through 22 h recovery. The highest O3 uptake was observed in WW plants exposed to 550 ppb O3 with the greatest reduction and poorest recovery of gs and A, and elicitation of lipoxygenase (LOX) pathway volatiles 10 min–1.5 h after exposure indicating cellular damage. Ozone uptake was similar in 250 ppb WW and 550 ppb WS plants and, in both treatments, O3-dependent reduction in photosynthetic characteristics was moderate and fully reversible, and VOC emissions were little affected. Water stress alone did not affect the total amount and composition of VOC emissions. The results indicate that drought ameliorated O3 stress by reducing O3 uptake through stomatal closure and the two stresses operated in an antagonistic manner in B. nigra.
Plant volatile organic compounds (VOCs) elicited in response to herbivory serve as cues for parasitic and predatory insects. Knowledge about quantitative relationships between the extent of ...herbivore-induced damage and the quantities of VOCs released is scarce. We studied the kinetics of VOC-emissions from foliage of the deciduous tree Alnus glutinosa induced by feeding activity of larvae of the geometrid moth Cabera pusaria. Quantitative relationships between the intensity of stress and strength of plant response were determined. Intensity of biotic stress was characterized by herbivore numbers (0-8 larvae) and by the amount of leaf area eaten. The strength of plant response was characterized by monitoring (i) changes in photosynthesis, (ii) leaf ultrastructure, and (iii) plant volatiles. Net assimilation rate displayed compensatory responses in herbivore-damaged leaves compared with control leaves. This compensatory response was associated with an overall increase in chloroplast size. Feeding-induced emissions of products of the lipoxygenase pathway (LOX products; (E)-2-hexenal, (Z)-3-hexenol, 1-hexanol, and (Z)-3-hexenyl acetate) peaked at day 1 after larval feeding started, followed by an increase of emissions of ubiquitous monoterpenes peaking on days 2 and 3. The emission of the monoterpene (E)-β-ocimene and of the nerolidol-derived homoterpene 4,8-dimethyl-nona-1,3,7-triene (DMNT) peaked on day 3. Furthermore, the emission kinetics of the sesquiterpene (E,E)-α-farnesene tended to be biphasic with peaks on days 2 and 4 after start of larval feeding. Emission rates of the induced LOX products, of (E)-β-ocimene and (E,E)-α-farnesene were positively correlated with the number of larvae feeding. In contrast, the emission of DMNT was independent of the number of feeders. These data show quantitative relationships between the strength of herbivory and the emissions of LOX products and most of the terpenoids elicited in response to feeding. Thus, herbivory-elicited LOX products and terpenoid emissions may convey both quantitative and qualitative signals to antagonists of the herbivores. In contrast, our data suggest that the feeding-induced homoterpene DMNT conveys the information “presence of herbivores” rather than information about the quantities of herbivores to predators and parasitoids.
Recently, a feedback inhibition of the chloroplastic 1-deoxy-D-xylulose 5-phosphate (DXP)/2-C-methyl-D-erythritol 4-phosphate (MEP) pathway of isoprenoid synthesis by end products dimethylallyl ...diphosphate (DMADP) and isopentenyl diphosphate (IDP) was postulated, but the extent to which DMADP and IDP can build up is not known. We used bisphosphonate inhibitors, alendronate and zoledronate, that inhibit the consumption of DMADP and IDP by prenyltransferases to gain insight into the extent of end product accumulation and possible feedback inhibition in isoprene-emitting hybrid aspen (Populus tremula×Populus tremuloides). A kinetic method based on dark release of isoprene emission at the expense of substrate pools accumulated in light was used to estimate the in vivo pool sizes of DMADP and upstream metabolites. Feeding with fosmidomycin, an inhibitor of DXP reductoisomerase, alone or in combination with bisphosphonates was used to inhibit carbon input into DXP/MEP pathway or both input and output. We observed a major increase in pathway intermediates, 3- to 4-fold, upstream of DMADP in bisphosphonate-inhibited leaves, but the DMADP pool was enhanced much less, 1.3- to 1.5-fold. In combined fosmidomycin/bisphosphonate treatment, pathway intermediates accumulated, reflecting cytosolic flux of intermediates that can be important under strong metabolic pull in physiological conditions. The data suggested that metabolites accumulated upstream of DMADP consist of phosphorylated intermediates and IDP. Slow conversion of the huge pools of intermediates to DMADP was limited by reductive energy supply. These data indicate that the DXP/MEP pathway is extremely elastic, and the presence of a significant pool of phosphorylated intermediates provides an important valve for fine tuning the pathway flux.
The pathogen Erysiphe cruciferarum is an increasingly serious threat to cruciferous oilseed crops worldwide. In the present study, the severity of powdery mildew was evaluated on spring oilseed rape ...(Brassica napus) and five alternative oilseed crop species (B. juncea, B. nigra, Sinapis alba, Raphanus sativus, Eruca sativa). The main aim of the study was to identify plant species that are less susceptible to powdery mildew for possible application as cover crop, in trap cropping or seed production. Powdery mildew assessments were conducted in two growing seasons that were characterised by unusually warm and dry conditions for northern temperate climatic conditions. In both growing seasons, a heavy powdery mildew infection (over 80%) was recorded on B. napus and B. nigra plants, indicating that E. cruciferarum is an important pathogen for oilseed crops in northern Baltics. However, three other cruciferous species S. alba, E. sativa and R. sativus showed full resistance to powdery mildew, and thus, even under strong powdery mildew pressure, they can be cultivated without pesticide application in northern Baltic conditions. We suggest that in changing climatic conditions powdery mildew is expected to become a more serious problem in cruciferous oilseed crops in northern Europe, especially under intensive short-rotation farming practices.
Water is the key resource limiting world agricultural production. Although an impressive number of research reports have been published on plant drought tolerance enhancement via genetic ...modifications during the last few years, progress has been slower than expected. We suggest a feasible alternative strategy by application of rhizospheric bacteria coevolved with plant roots in harsh environments over millions of years, and harboring adaptive traits improving plant fitness under biotic and abiotic stresses. We show the effect of bacterial priming on wheat drought stress tolerance enhancement, resulting in up to 78% greater plant biomass and five-fold higher survivorship under severe drought. We monitored emissions of seven stress-related volatiles from bacterially-primed drought-stressed wheat seedlings, and demonstrated that three of these volatiles are likely promising candidates for a rapid non-invasive technique to assess crop drought stress and its mitigation in early phases of stress development. We conclude that gauging stress by elicited volatiles provides an effectual platform for rapid screening of potent bacterial strains and that priming with isolates of rhizospheric bacteria from harsh environments is a promising, novel way to improve plant water use efficiency. These new advancements importantly contribute towards solving food security issues in changing climates.
The increase in the cultivation area of cruciferous oilseed crops and the use of short crop rotation has resulted in the enhanced spread of several major pests in Northern latitudes. There is ...currently limited information about incidence and severity of Alternaria black spot disease (Alternaria brassicae) on the main oilseed crop, spring oilseed rape (Brassica napus), in the Northern Baltics. Thus, spring oilseed rape and five alternative cruciferous oilseed crops were selected and their resistance to black spot disease was evaluated in field conditions during two growing seasons. We hypothesized that spring oilseed rape is more susceptible to Alternaria black spot disease than other alternative cruciferous oilseed crops. Both growing seasons were warmer and drier compared to the long-term average, and were thus suitable for A. brassicae development and assessments. In both years, incidence of Alternaria black spot infection was recorded on all cruciferous species, yet the disease development differed considerably among the crops. During both growing seasons, black mustard (B. nigra) plants were the most infected. Based on our observations during warm growing seasons we conclude that alternative oilseed crops such as Sinapis alba, Eruca sativa and Raphanus sativus are more resistant to the Alternaria black spot infection than the traditional oilseed crops and thus, possess a great potential to grow with limited chemical disease control in Northern Baltic conditions.
In addition to climate warming, greater herbivore pressure is anticipated to enhance the emissions of climate-relevant biogenic volatile organic compounds (VOCs) from boreal and subarctic forests and ...promote the formation of secondary aerosols (SOA) in the atmosphere. We evaluated the effects of Epirrita autumnata, an outbreaking geometrid moth, feeding and larval density on herbivore-induced VOC emissions from mountain birch in laboratory experiments and assessed the impact of these emissions on SOA formation via ozonolysis in chamber experiments. The results show that herbivore-induced VOC emissions were strongly dependent on larval density. Compared to controls without larval feeding, clear new particle formation by nucleation in the reaction chamber was observed, and the SOA mass loadings in the insect-infested samples were significantly higher (up to 150-fold). To our knowledge, this study provides the first controlled documentation of SOA formation from direct VOC emission of deciduous trees damaged by known defoliating herbivores and suggests that chewing damage on mountain birch foliage could significantly increase reactive VOC emissions that can importantly contribute to SOA formation in subarctic forests. Additional feeding experiments on related silver birch confirmed the SOA results. Thus, herbivory-driven volatiles are likely to play a major role in future biosphere-vegetation feedbacks such as sun-screening under daily 24 h sunshine in the subarctic.
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