Metabolic costs of terpenoid accumulation in higher plants

Plant-to-plant defence induction in cotton is mediated by delayed release of volatiles upon herbivory

Caterpillar feeding immediately triggers the release of volatile compounds stored in the leaves of cotton plants. Additionally, after 1 d of herbivory, the leaves release other newly synthesised volatiles. We investigated whether these volatiles affect chemical defences in neighbouring plants and whether such temporal shifts in emissions matter for signalling between plants. Undamaged receiver plants were exposed to volatiles from plants infested with Spodoptera caterpillars. For receiver plants, we measured changes in defence-related traits such as volatile emissions, secondary metabolites, phytohormones, gene expression, and caterpillar feeding preference. Then, we compared the effects of volatiles emitted before and after 24 h of damage on neighbouring plant defences. Genes that were upregulated in receiver plants following exposure to volatiles from damaged plants were the same as those activated directly by herbivory on a plant. Only volatiles emitted after 24 h of damage, including newly produced volatiles, were found to increase phytohormone levels, upregulate defence genes, and enhance resistance to caterpillars. These results indicate that the defence induction by volatiles is a specific response to de novo synthesised volatiles, suggesting that these compounds are honest signals of herbivore attack. These findings point to an adaptive origin of airborne signalling between plants.

Local carbon reserves are insufficient for phloem terpene induction during drought in Pinus edulis in response to bark beetle-associated fungi

Stomatal closure during drought inhibits carbon uptake and may reduce a tree's defensive capacity. Limited carbon availability during drought may increase a tree's mortality risk, particularly if drought constrains trees' capacity to rapidly produce defenses during biotic attack. We parameterized a new model of conifer defense using physiological data on carbon reserves and chemical defenses before and after a simulated bark beetle attack in mature Pinus edulis under experimental drought. Attack was simulated using inoculations with a consistent bluestain fungus (Ophiostoma sp.) of Ips confusus, the main bark beetle colonizing this tree, to induce a defensive response. Trees with more carbon reserves produced more defenses but measured phloem carbon reserves only accounted for c. 23% of the induced defensive response. Our model predicted universal mortality if local reserves alone supported defense production, suggesting substantial remobilization and transport of stored resin or carbon reserves to the inoculation site. Our results show that de novo terpene synthesis represents only a fraction of the total measured phloem terpenes in P. edulis following fungal inoculation. Without direct attribution of phloem terpene concentrations to available carbon, many studies may be overestimating the scale and importance of de novo terpene synthesis in a tree's induced defense response.

The Legacy Effect of Mountain Pine Beetle Outbreaks on the Chemical and Anatomical Defences of Surviving Lodgepole Pine Trees

The recent mountain pine beetle outbreaks have caused widespread mortality among lodgepole pine trees in western North America, resulting in a reduced population of surviving trees. While previous studies have focused on the cascading impacts of these outbreaks on the physiology and growth of the surviving trees, there remains a need for a comprehensive study into the interactions among various physiological traits and the growth in post-outbreak stands. Specifically, the relationship between chemical (primarily terpenes) and anatomical (mainly resin ducts) defences, as well as the allocation of non-structural carbohydrates (NSCs) to support these defence modalities, is poorly understood. To address these gaps, we conducted a field survey of surviving lodgepole pine trees in post-mountain pine beetle outbreak stands in western Canada. Our retrospective analysis aimed at determining correlations between the post-outbreak concentrations of monoterpenes, diterpenes, and NSCs in the phloem and the historical resin duct characteristics and growth traits before and after the outbreak. We detected strong correlations between the post-outbreak concentrations of monoterpenes and historical resin duct characteristics, suggesting a possible link between these two defence modalities. Additionally, we found a positive relationship between the NSCs and the total concentrations of monoterpenes and diterpenes, suggesting that NSCs likely influence the production of these terpenes in lodgepole pine. Furthermore, historical tree growth patterns showed strong positive correlations with many individual monoterpenes and diterpenes. Interestingly, while surviving trees had enhanced anatomical defences after the outbreak, their growth patterns did not vary before and after the outbreak conditions. The complexity of these relationships emphasizes the dynamics of post-outbreak stand dynamics and resource allocations in lodgepole pine forests, highlighting the need for further research. These findings contribute to a broader understanding of conifer defences and their coordinated responses to forest insect outbreaks, with implications for forest management and conservation strategies.

Phytochemical Characterization and Biological Activities of Essential Oil from Satureja montana L., a Medicinal Plant Grown under the Influence of Fertilization and Planting Dates

The rising demand for safe plant compounds and herbal products that contribute positively to human health is in line with current market trends. Plants belonging to the Satureja genus, particularly the aromatic medicinal S. montana L. from the Lamiaceae family, are well suited to these trends as they serve as pharmaceutical raw materials. This research aimed to assess the influence of sowing date and fertilization doses, as well as their interaction, on the fresh weight, essential oil content, and composition of S. montana. Experimental cultivation involved varying nitrogen and phosphorus levels. The second cut had the highest fresh weight and oil production compared to the first cut. The highest total plant biomass was achieved with autumn sowing and fertilization at 55 kg N/ha and 37 kg P/ha, whereas Spring sowing exhibited higher essential oil production, with the maximum oil % with 74 kg P/ha and oil yield after applying 55 kg N/ha and 74 kg P/ha. The GC-MS analysis revealed that carvacrol was the predominant compound, with it being recommended to grow S. montana in Spring at doses of 55 kg N/ha and 74 kg P/ha for the superior oil yield. Additionally, S. montana essential oil demonstrated notable biological and antimicrobial activity, positioning it as a potential alternative to chemical food preservatives.

Resistance to Frankliniella occidentalis during Different Plant Life Stages and under Different Environmental Conditions in the Ornamental Gladiolus

The defense mechanisms of plants evolve as they develop. Previous research has identified chemical defenses against Western flower thrips (WFT) in Gladiolus (Gladiolus hybridus L.). Consequently, our study aimed to explore the consistency of these defense variations against WFT across the various developmental stages of Gladiolus grown under different conditions. Thrips bioassays were conducted on whole plants at three developmental stages, using the Charming Beauty and Robinetta varieties as examples of susceptible and resistant varieties, respectively. Metabolomic profiles of the leaves, buds and flowers before thrips infestation were analyzed. The thrips damage in Charming Beauty was more than 500-fold higher than the damage in Robinetta at all plant development stages. Relative concentrations of triterpenoid saponins and amino acids that were associated with resistance were higher in Robinetta at all plant stages. In Charming Beauty, the leaves exhibited greater damage compared to buds and flowers. The relative concentrations of alanine, valine and threonine were higher in buds and flowers than in leaves. The Metabolomic profiles of the leaves did not change significantly during plant development. In addition, we cultivated plants under different environmental conditions, ensuring consistency in the performance of the two varieties across different growing conditions. In conclusion, the chemical thrips resistance markers, based on the analysis of vegetative plants grown in climate rooms, were consistent over the plant's lifetime and for plants grown under field conditions.

Plant Variety, Mycorrhization, and Herbivory Influence Induced Volatile Emissions and Plant Growth Characteristics in Tomato

Plants produce a range of volatile organic compounds (VOCs) that mediate vital ecological interactions between herbivorous insects, their natural enemies, plants, and soil dwelling organisms including arbuscular mycorrhizal fungi (AMF). The composition, quantity, and quality of the emitted VOCs can vary and is influenced by numerous factors such as plant species, variety (cultivar), plant developmental stage, root colonization by soil microbes, as well as the insect developmental stage, and level of specialization of the attacking herbivore. Understanding factors shaping VOC emissions is important and can be leveraged to enhance plant health and pest resistance. In this greenhouse study, we evaluated the influence of plant variety, mycorrhizal colonization, herbivory, and their interactions on the composition of emitted volatiles in tomato plants (Solanum lycopersicum L.). Four tomato varieties from two breeding histories (two heirlooms and two hybrids), were used. Tomato plants were inoculated with a commercial inoculum blend consisting of four species of AMF. Plants were also subjected to herbivory by Manduca sexta (Lepidoptera: Sphingidae L.) five weeks after transplanting. Headspace volatiles were collected from inoculated and non-inoculated plants with and without herbivores using solid phase-microextraction. Volatile profiles consisted of 21 different volatiles in detectable quantities. These included monoterpenes, sesquiterpenes, and alkane hydrocarbons. We documented a strong plant variety effect on VOC emissions. AMF colonization and herbivory suppressed VOC emissions. Plant biomass was improved by colonization of AMF. Our results show that mycorrhization, herbivory and plant variety can alter tomato plant VOC emissions and further shape volatile-mediated insect and plant interactions.

Night and day: Contributions of diurnal and nocturnal visitors to pollen dispersal, paternity diversity, and fruit set in an early-blooming shrub, Daphne jezoensis

PREMISE

Under uncertain pollinator visit conditions, plants often exhibit long flowering periods and generalized pollination systems. Flowering of the gynodioecious shrub Daphne jezoensis occurs in early spring in cool temperate forests. Pollination by nocturnal moths is expected, given the species' tubular-shaped flowers with sweet fragrance and nectar. However, the effectiveness of nocturnal moths under cool conditions is unknown. We evaluated the relative importance of diurnal and nocturnal visitors as pollinators in early spring.

METHODS

We investigated flowering duration, flower visitors, and floral scents in a natural population. We experimentally exposed flowers to visitors only during daytime or nighttime using bagging treatments and evaluated the contributions of diurnal and nocturnal insects to fruit set, pollen dispersal distance, and paternity diversity using 16 microsatellite markers.

RESULTS

Female flowers lasted ~3 wk, which was ~8 d longer than the flowering period of hermaphrodites. Various insects, including Coleoptera, Diptera, Hymenoptera, and Lepidoptera, visited the flowers during both daytime and nighttime. Flowers emitted volatiles, such as lilac aldehyde isomers and β-ocimene, which are known to attract moths. Fruit-set rate in the night-open treatment was similar to or higher than that in the day-open treatment. However, pollen dispersal distance in the night-open treatment was shorter than that in the day-open treatment. Paternity diversity was similar in day-open and night-open treatments.

CONCLUSIONS

Early-blooming plants ensure pollen receipt and dispersal by having a long flowering period and using both diurnal and nocturnal flower visitors, suggesting the importance of a generalized pollination system under uncertain pollinator visit conditions.

Overlaps and trade-offs in the diversity and inducibility of volatile chemical profiles among diverse sympatric neotropical canopy trees

A central goal in ecology is to understand the mechanisms by which biological diversity is maintained. The diversity of plant chemical defences and the strategies by which they are deployed in nature may influence biological diversity. Trees in neotropical forests are subject to relatively high herbivore pressure. Such consistent pressure is thought to select for constitutive, non-flexible defence-related phytochemistry with limited capacity for inducible phytochemical responses. However, this has not been explored for volatile organic compounds (VOCs) that have a relatively low ratio of production costs to ecological benefits. To test this, I sampled VOCs emitted from canopy leaves of 10 phylogenetically diverse tree species (3 Magnoliids and 7 Rosids) in the Peruvian Amazon before and after induction with the phytohormone methyl jasmonate (MeJA). There was no phylogenetic signal in induction or magnitude of MeJA-induced VOC emissions from intact leaves: all trees induced VOC profiles dominated by β-ocimene, linalool, and α-farnesene of varying ratios. Moreover, overall inducibility of VOCs from intact leaves was unrelated to phytochemical diversity or richness. In contrast, experimentally wounded leaves showed considerable phylogeny-based and MeJA-independent variation the richness and diversity of constitutive wound-emitted VOCs. Moreover, VOC inducibility from wounded leaves correlated negatively with phytochemical richness and diversity, potentially indicating a tradeoff in constitutive and inducible defence strategies for non-volatile specialised metabolites but not for inducible VOCs. Importantly, there was no correlation between any chemical profile and either natural herbivory or leaf toughness. The coexistence of multiple phytochemical strategies in a hyper-diverse forest has broad implications for competitive and multitrophic interactions, and the evolutionary forces that maintain the exceptional plant biodiversity in neotropical forests.

Ecological interactions affect the bioactivity of medicinal plants

Essential oils produced by medicinal plants possess important bioactive properties (antibacterial, antioxidant) of high value for human society. Pollination and herbivory can modify the chemical defences of plants and therefore they may influence the bioactivity of essential oils. However, the effect of ecological interactions on plant bioactivity has not yet been evaluated. We tested the hypothesis that cross-pollination and simulated herbivory modify the chemical composition of essential oils, improving the bioactive properties of the medicinal plant Lepechinia floribunda (Lamiaceae). Through controlled experiments, we showed that essential oils from the outcrossed plant progeny had a higher relative abundance of oxygenated terpenes and it almost doubled the bacteriostatic effect on Staphylococcus aureus, compared to inbred progeny (i.e., progeny produced in absence of pollinators). Herbivory affected negatively and positively the production of rare compounds in inbred and outcrossed plants, respectively, but its effects on bioactivity still remain unknown. We show for the first time that by mediating cross-pollination (indirect ecosystem service), pollinators can improve ecosystem services linked to the biological activity of plant's essential oils. We stress the importance of the qualitative component of pollination (self, cross); an aspect usually neglected in studies of pollination services.

Phytotoxicity of microplastics to the floating plant Spirodela polyrhiza (L.): Plant functional traits and metabolomics

Freshwater ecosystems are gradually becoming sinks for terrestrial microplastics (MPs), posing a potential ecological risk. Although the effects of MPs on plankton and aquatic animals in freshwater ecosystems have been given increasing attention, the toxicity of MPs to the metabolism of aquatic plants remains unclear. Here, the model aquatic plant Spirodela polyrhiza (L.) Schleid. (S. polyrhiza) was exposed to polyvinyl chloride (PVC; 0, 10, 100 and 1000 mg/L) MPs, and changes in the plant functional traits and physiological metabolism were monitored. The results showed that the high dose of PVC MPs decreased the adventitious root elongation ratio by 41.68% and leaf multiplication ratio by 61.03% of S. polyrhiza, and resulted in the decrease in anthocyanin and nitrogen contents to 63.45% and 84.21% of the control group, respectively. Moreover, the widely targeted metabolomics analysis results showed 37 differential metabolites in the low-dose treatment and 119 differential metabolites in the high-dose treatment. PVC MPs interfered with organic matter accumulation by affecting carbon metabolism, nitrogen metabolism, amino acid metabolism and lipid metabolism, and S. polyrhiza resists PVC MP stress by regulating the synthesis and metabolism of secondary metabolites. PVC MPs had concentration-related toxicological effects on plant functional traits, inhibited plant growth and reproduction, affected plant nutrient metabolism, and exhibited profound effects on the nitrogen fate of aquatic plant habitats. Overall, we systematically summarized the metabolic response mechanisms of aquatic plants to PVC MP stress, providing a new perspective for studying the effects of MPs on plant trait function and ecological risks.

Essential oil variability in Eugenia dysenterica fruits

Essential oils (EOs) of Eugenia dysenterica fruits from seven populations were assessed using GC/MS and chemometric analysis. Variations in EOs between populations and three operational chemical units (OCUs), combined with foliar Mn²⁺ as an environmental variable, indicate that 86.8% of variation in oils was explained by these predictors. Variance partitioning shows that the largest pure contribution was attributed to foliar Mn²⁺ (13.1%), followed by OCU (11.4%). Populational origin contributed with lowest variance (6.6%).

Diterpenes of Coffea seeds show antifungal and anti-insect activities and are transferred from the endosperm to the seedling after germination

Species of the genus Coffea accumulate diterpenes of the ent-kaurane family in the endosperm of their seeds, of which cafestol and kahweol are the most abundant. The diterpenes are mainly stored in esterified form with fatty acids, mostly palmitate. In contrast to the numerous studies on their effects on human health and therapeutic applications, nothing was previously known about their biological and ecological role in planta. The antifungal and anti-insect activities of cafestol and cafestol palmitate were thus investigated in this study. Cafestol significantly affected the mycelial growth of five of the six phytopathogenic fungi tested. It also greatly reduced the percentage of pupation of larvae and the pupae and adult masses of one of the two fruit flies tested. By contrast, cafestol palmitate had no significant effect against any of the fungi and insects studied. Using confocal imaging and oil body isolation and analysis, we showed that diterpenes are localized in endosperm oil bodies, suggesting that esterification with fatty acids enables the accumulation of large amounts of diterpenes in a non-toxic form. Diterpene measurements in all organs of seedlings recovered from whole seed germination or embryos isolated from the endosperm showed that diterpenes are transferred from the endosperm to the cotyledons during seedling growth and then distributed to all organs, including the hypocotyl and the root. Collectively, our findings show that coffee diterpenes are broad-spectrum defence compounds that protect not only the seed on the mother plant and in the soil, but also the seedling after germination.

Diversity and divergence: evolution of secondary metabolism in the tropical tree genus Inga

Plants are widely recognized as chemical factories, with each species producing dozens to hundreds of unique secondary metabolites. These compounds shape the interactions between plants and their natural enemies. We explore the evolutionary patterns and processes by which plants generate chemical diversity, from evolving novel compounds to unique chemical profiles. We characterized the chemical profile of one-third of the species of tropical rainforest trees in the genus Inga (c. 100, Fabaceae) using ultraperformance liquid chromatography-mass spectrometry-based metabolomics and applied phylogenetic comparative methods to understand the mode of chemical evolution. We show: each Inga species contain structurally unrelated compounds and high levels of phytochemical diversity; closely related species have divergent chemical profiles, with individual compounds, compound classes, and chemical profiles showing little-to-no phylogenetic signal; at the evolutionary time scale, a species' chemical profile shows a signature of divergent adaptation. At the ecological time scale, sympatric species were the most divergent, implying it is also advantageous to maintain a unique chemical profile from community members; finally, we integrate these patterns with a model for how chemical diversity evolves. Taken together, these results show that phytochemical diversity and divergence are fundamental to the ecology and evolution of plants.

The rhizospheric bacterial diversity of Fritillaria taipaiensis under single planting pattern over five years

Rhizospheric microorganisms can profoundly influence the nutritional status of soil and the growth of plant. To reveal the change on the bacterial diversity in the rhizosphere of Fritillaria taipaiensis under long-term single planting, the bacterial community structure in the rhizospheric soils of F. taipaiensis with different cultivation years from 1 to 5 were analyzed. The result showed the Chao1 and the ACE indices of the bacterial community had no significant difference among samples while the Shannon and Simpson indices declined with the cutivation year; the intra group beta diversity of the rhizospheric bacteria increased after a initial decline with the cultivation year; in the sample with 1 year of cultivation, the dominant bacterial genera were mainly the species that can improve the soil nutrient status and promote plant growth while with the increase of cultivation year, the dominant genera in samples then gradually reflected the pathogen accumulation and soil nutrient status deterioration; pH was the most significant factor affected by the bacterial community composition. These results indicated long term continuous cropping changed the bacterial community structure and soil nutritional status in the F. taipaiensis rhizospheric soils, which could badly affect its growth.

Allelopathic potential in rice - a biochemical tool for plant defence against weeds

Rice is a key crop for meeting the global food demand and ensuring food security. However, the crop has been facing great problems to combat the weed problem. Synthetic herbicides pose a severe threat to the long-term viability of agricultural output, agroecosystems, and human health. Allelochemicals, secondary metabolites of allelopathic plants, are a powerful tool for biological and eco-friendly weed management. The dynamics of weed species in various situations are determined by crop allelopathy. Phenolics and momilactones are the most common allelochemicals responsible for herbicidal effects in rice. The dispersion of allelochemicals is influenced not only by crop variety but also by climatic conditions. The most volatile chemicals, such as terpenoids, are usually emitted by crop plants in drought-stricken areas whereas the plants in humid zones release phytotoxins that are hydrophilic in nature, including phenolics, flavonoids, and alkaloids. The allelochemicals can disrupt the biochemical and physiological processes in weeds causing them to die finally. This study insight into the concepts of allelopathy and allelochemicals, types of allelochemicals, techniques of investigating allelopathic potential in rice, modes of action of allelochemicals, pathways of allelochemical production in plants, biosynthesis of allelochemicals in rice, factors influencing the production of allelochemicals in plants, genetical manipulation through breeding to develop allelopathic traits in rice, the significance of rice allelopathy in sustainable agriculture, etc. Understanding these biological phenomena may thus aid in the development of new and novel weed-control tactics while allowing farmers to manage weeds in an environmentally friendly manner.

Among- and within-population variation in morphology, rewards, and scent in a hawkmoth-pollinated plant

PREMISE

Floral scent is a complex trait that mediates many plant-insect interactions, but our understanding of how floral scent variation evolves, either independently or in concert with other traits, remains limited. Assessing variation in floral scent at multiple levels of biological organization and comparing patterns of variation in scent to variation in other floral traits can contribute to our understanding of how scent variation evolves in nature.

METHODS

We used a greenhouse common garden experiment to investigate variation in floral scent at three scales-within plants, among plants, and among populations-and to determine whether scent, alone or in combination with morphology and rewards, contributes to population differentiation in Oenothera cespitosa subsp. marginata. Its range spans most of the biomes in the western United States, such that variation in both the abiotic and biotic environment could contribute to trait variation.

RESULTS

Multiple analytical approaches demonstrated substantial variation among and within populations in compound-specific and total floral scent measures. Overall, populations were differentiated in morphology and reward traits and in scent. Across populations, coupled patterns of variation in linalool, leucine-derived compounds, and hypanthium length are consistent with a long-tongued moth pollination syndrome.

CONCLUSIONS

The considerable variation in floral scent detected within populations suggests that, similar to other floral traits, variation in floral scent may have a heritable genetic component. Differences in patterns of population differentiation in floral scent and in morphology and rewards indicate that these traits may be shaped by different selective pressures.

The Changes of Microbial Communities and Key Metabolites after Early Bursaphelenchus xylophilus Invasion of Pinus massoniana

Pine wood nematode, Bursaphelenchus xylophilus, is a worldwide pest of pine trees, spreading at an alarming rate and with great ecological adaptability. In the process of causing disease, the nematode causes metabolic disorders and changes in the endophytic microbial community of the pine tree. However, the changes at the pine nidus during early nematode invasion have not been well studied, especially the differential metabolites, in Pinus massoniana, the main host of B. xylophilus in China. In this study, we analyzed the endophytic bacterial and fungal communities associated with healthy and B. xylophilus-caused wilted pine trees. The results show that 1333 bacterial OTUs and 502 fungal OTUs were annotated from P. massoniana stem samples. The abundance of bacterial communities in pine trees varies more following infection by B. xylophilus, but the abundance changes of fungal communities are less visible. There were significant differences in endophytic microbial diversity between wilted and healthy P. massoniana. In wilted pine trees, Actinobacteria and Bacteroidia were differential indicators of bacterial communities, whereas, in healthy pine trees, Rhizobiales in the Proteobacteria phylum were the major markers of bacterial communities. Meanwhile, the differential markers of fungal communities in healthy pines are Malasseziales, Tremellales, Sordariales, and Fusarium, whereas Pleosporaceae is the key marker of fungal communities in wilted pines. Our study examines the effect of changes in the endophytic microbial community on the health of pine trees that may be caused by B. xylophilus infection. In parallel, a non-targeted metabolomic study based on liquid mass spectrometry (LC-MS) technology was conducted on pine trees inoculated with pine nematodes and healthy pine trees with a view to identifying key compounds affecting early pine lesions. Ultimately, 307 distinctly different metabolites were identified. Among them, the riboflavin metabolic pathway in pine trees may play a key role in the early pathogenesis of pine wood nematode disease.

Alteration in Light Spectra Causes Opposite Responses in Volatile Phenylpropanoids and Terpenoids Compared with Phenolic Acids in Sweet Basil (Ocimum basilicum) Leaves

Basil (Ocimum basilicum, cv. Dolly) grew under three different light spectra (A, B, and C) created by light-emitting diode lamps. The proportions of UV-A, blue, and green-yellow wavelengths decreased linearly from A to C, and the proportions of red and far-red wavelengths increased from A to C. Photosynthetic photon flux density was 300 μmol m^-2 s^-1 in all spectra. The spectrum C plants had highest concentrations of phenolic acids (main compounds: rosmarinic acid and cichoric acid), lowest concentrations and emissions of phenylpropanoid eugenol and terpenoids (main compounds: linalool and 1,8-cineole), highest dry weight, and lowest water content. Conversely, spectra A and B caused higher terpenoid and eugenol concentrations and emissions and lower concentrations of phenolic acids. High density of peltate glandular trichomes explained high terpenoid and eugenol concentrations and emissions. Basil growth and secondary compounds affecting aroma and taste can be modified by altering light spectra; however, increasing terpenoids and phenylpropanoids decreases phenolic acids and growth and vice versa.

Exploring plant volatile-mediated interactions between native and introduced plants and insects

In invasion scenarios, native and introduced species co-occur creating new interactions and modifying existing ones. Many plant–plant and plant–insect interactions are mediated by volatile organic compounds (VOCs), however, these have seldom been studied in an invasion context. To fill this knowledge gap, we explored some interactions mediated by VOCs between native and introduced plants and insects in a New Zealand system. We investigated whether a native plant, Leptospermum scoparium (mānuka), changes its volatile profile when grown adjacent to two European introduced plants, Calluna vulgaris (heather) and Cytisus scoparius (Scotch broom), in a semi-field trial using potted plants without above- or below-ground physical contact. We also investigated the influence of plant cues on the host-searching behaviour of two beetles, the native Pyronota festiva (mānuka beetle), and the introduced biocontrol agent Lochmaea suturalis (heather beetle), by offering them their host-plant and non-host volatiles versus clean air, and their combination in a Y-tube olfactometer. As a follow-up, we performed preference/feeding tests in Petri dishes with fresh plant material. Results of the semi-field experiment show a significant reduction in green leaf volatiles, sesquiterpenes and total volatile emissions by mānuka plants neighbouring heather. In the Y-tube assays, the native beetle P. festiva performed poorly in discriminating between host and non-host plants based on plant volatile cues only. However, it performed relatively well in the Petri dish tests, where other cues (i.e., visual, gustatory or tactile) were present. In contrast, the introduced beetle L. suturalis showed high host-specificity in both Y-tube and Petri dish assays. This study illustrates the importance of VOCs in mediating interactions between introduced and native species, suggesting that invasive plants can disrupt native plants’ communication and affect the host-searching behaviour of native insects. It also reinforces the relevance of regular host testing on introduced weed biocontrol agents to avoid unwanted host shifts or host-range expansion.

Into a dilemma of plants: the antagonism between chemical defenses and growth

Chemical defenses are imperative for plant survival, but their production is often associated with growth restrictions. Here we review the most recent theories to explain this complex dilemma of plants. Plants are a nutritional source for a myriad of pests and pathogens that depend on green tissues to complete their life cycle. Rather than remaining passive victims, plants utilize an arsenal of chemical defenses to fend off biotic attack. While the deployment of such barriers is imperative for survival, the production of these chemical defenses is typically associated with negative impacts on plant growth. Here we discuss the most recent theories which explain this highly dynamic growth versus defense dilemma. Firstly, we discuss the hypothesis that the antagonism between the accumulation of chemical defenses and growth is rooted in the evolutionary history of plants and may be a consequence of terrestrialization. Then, we revise the different paradigms available to explain the growth versus chemical defense antagonism, including recent findings that update these into more comprehensive and plausible theories. Finally, we highlight state-of-the-art strategies that are now allowing the activation of growth and the concomitant production of chemical barriers in plants. Growth versus chemical defense antagonism imposes large ecological and economic costs, including increased crop susceptibility to pests and pathogens. In a world where these plant enemies are the main problem to increase food production, we believe that this review will summarize valuable information for future studies aiming to breed highly defensive plants without the typical accompanying penalties to growth.

Molecular Cloning and Analysis of an Acetyl-CoA C-acetyltransferase Gene (EkAACT) from Euphorbia kansui Liou

Terpenoids are the largest class of natural products and are essential for cell functions in plants and their interactions with the environment. Acetyl-CoA acetyltransferase (AACT, EC2.3.1.9) can catalyze a key initiation step of the mevalonate pathway (MVA) for terpenoid biosynthesis and is modulated by many endogenous and external stimuli. Here, the function and expression regulation activities of AACT in Euphorbia kansui Liou (EkAACT) were reported. Compared with wild-type Arabidopsis, the root length, whole seedling fresh weight and growth morphology of EkAACT-overexpressing plants were slightly improved. The transcription levels of AtAACT, AtMDC, AtMK, AtHMGR, and AtHMGS in the MVA pathway and total triterpenoid accumulation increased significantly in transgenic Arabidopsis. Under NaCl and PEG treatment, EkAACT-overexpressing Arabidopsis showed a higher accumulation of total triterpenoids, higher enzyme activity of peroxidase (POD) and superoxide dismutase (SOD), increased root length and whole seedling fresh weight, and a decrease in the proline content, which indicated that plant tolerance to abiotic stress was enhanced. Thus, AACT, as the first crucial enzyme, plays a major role in the overall regulation of the MVA pathway.

Transcriptomic changes during the establishment of long-term methyl jasmonate-induced resistance in Norway spruce

Norway spruce (Picea abies) is an economically and ecologically important tree species that grows across northern and central Europe. Treating Norway spruce with jasmonate has long-lasting beneficial effects on tree resistance to damaging pests, such as the European spruce bark beetle Ips typographus and its fungal associates. The (epi)genetic mechanisms involved in such long-lasting jasmonate induced resistance (IR) have gained much recent interest but remain largely unknown. In this study, we treated 2-year-old spruce seedlings with methyl jasmonate (MeJA) and challenged them with the I. typographus vectored necrotrophic fungus Grosmannia penicillata. MeJA treatment reduced the extent of necrotic lesions in the bark 8 weeks after infection and thus elicited long-term IR against the fungus. The transcriptional response of spruce bark to MeJA treatment was analysed over a 4-week time course using mRNA-seq. This analysis provided evidence that MeJA treatment induced a transient upregulation of jasmonic acid, salicylic acid and ethylene biosynthesis genes and downstream signalling genes. Our data also suggests that defence-related genes are induced while genes related to growth are repressed by methyl jasmonate treatment. These results provide new clues about the potential underpinning mechanisms and costs associated with long-term MeJA-IR in Norway spruce.

Light Intensity and Temperature Effect on Salvia yangii (B. T. Drew) Metabolic Profile in vitro

Plant in vitro culture is a feasible system for the testing influence of an environmental factor on the accumulation and chemodiversity of specialized metabolites, especially in medicinal plants. Light and temperature are among the most important factors affecting the physiology of plant organisms but their influence on specific metabolic pathways is not completely understood. Here, we examined the morphogenetic response, photosynthetic pigments content, lipid peroxidation level, DPPH radical scavenging activity, and the production of volatile and non-volatile constituents in Salvia yangii B. T. Drew (syn. Perovskia atriplicifolia Benth.) in vitro cultures kept under different light intensities (70, 130, and 220 μmol m^-2 s^-1) and at two selected temperatures (25 and 30°C). The experiment was continued for 7 months to monitor the changes in the treatment response in time. Phytochemical analysis was performed using chromatographic (GC-MS and UHLPC) and spectrophotometric techniques. The light intensity significantly influenced metabolic response in a non-linear manner, whereas temperature-induced adaptive modifications varied within the long cultivation. Significant differences were noted in the content of carnosic and rosmarinic acid, as well as in several sesquiterpenes (alloaromadendrene, β-caryophyllene, α-humulene). At elevated (30°C) temperature, a trend of differently modulated content of two major antioxidants-rosmarinic acid (RA, a phenylpropanoid pathway derived phenolic acid) and carnosic acid (CA, an abietane diterpenoid) was observed, where RA, but not CA, was depending on the light intensity. At 25°C, both compounds depended on light but in various ways. Among the volatile terpenoid compounds, the influence of light was pronounced, leading to modulation of proportions between individual mono- and sesquiterpenes as well as between hydrocarbon and oxygenated compounds. The study provided new information on the metabolic profile plasticity in S. yangii and added to the existing knowledge on the chemical adaptations in plant species from severe habitats.

Control of resource allocation between primary and specialized metabolism in glandular trichomes

Plant specialized metabolites are often synthesized and stored in dedicated morphological structures such as glandular trichomes, resin ducts, or laticifers where they accumulate in large concentrations. How this high productivity is achieved is still elusive, in particular, with respect to the interface between primary and specialized metabolism. Here, we focus on glandular trichomes to survey recent progress in understanding how plant metabolic cell factories manage to balance homeostasis of essential central metabolites while producing large quantities of compounds that constitute a metabolic sink. In particular, we review the role of gene duplications, transcription factors and photosynthesis.

A plant balancing act: Meshing new and existing metabolic pathways towards an optimized system

Specialized metabolic pathways evolve from existing pathways, creating new functionality potentially boosting fitness. However, how these pathways are integrated into a pre-existing working and well-balanced metabolic system is unclear. They could be integrated to the system as a functional appendage, or they could be fully embedded into primary metabolism by establishing new biochemical and regulatory connections. A full integration into the primary metabolic system requires substantial system re-wiring and because of this complexity, the latter is often not experimentally pursued. New studies provide evidence that some specialized metabolic pathways are fully embedded in primary metabolism with extensive new regulatory and biochemical connections. This suggests, that we should consider whether other specialized metabolic pathways could be fully integrated rather than being simple appendages. In this mini review, we survey compelling evidence supporting that some specialized metabolic pathways are fully integrated and ask if these metabolites now act as de-facto primary metabolites?

Evidence for tissue-specific defense-offense interactions between milkweed and its community of specialized herbivores

Coevolution between plants and herbivores often involves escalation of defense-offense strategies, but attack by multiple herbivores may obscure the match of plant defense to any one attacker. As herbivores often specialize on distinct plant parts, we hypothesized that defense-offense interactions in coevolved systems may become physiologically and evolutionarily compartmentalized between plant tissues. We report that roots, leaves, flower buds and seeds of the tropical milkweed (Asclepias curassavica) show increasing concentrations of cardenolide toxins acropetally, with latex showing the highest concentration. In vitro assays of the physiological target of cardenolides, the Na⁺ /K⁺ -ATPase (hereafter 'sodium pump'), of three specialized milkweed herbivores (root-feeding Tetraopes tetrophthalmus, leaf-feeding Danaus plexippus, and seed-feeding Oncopeltus fasciatus) show that they are proportionally tolerant to the cardenolide concentrations of the tissues they eat. Indeed, molecular substitutions in the insects' sodium pumps predicted their tolerance to toxins from their target tissues. Nonetheless, the relative inhibition of the sodium pumps of these specialists by the concentration vs. composition (inhibition controlled for concentration, what we term 'potency') of cardenolides from their target vs. non-target plant tissues revealed different degrees of insect adaptation to tissue-specific toxins. In addition, a trade-off between toxin concentration and potency emerged across plant tissues, potentially reflecting coevolutionary history or plant physiological constraints. Our findings suggest that tissue-specific coevolutionary dynamics may be proceeding between the plant and its specialized community of herbivores. This novel finding may be common in nature, contributing to ways in which coevolution proceeds in multi-species communities.

Plant Nutrition Influences Resistant Maize Defense Responses to the Fall Armyworm (Spodoptera frugiperda)

Plants are often confronted by different groups of herbivores, which threaten their growth and reproduction. However, they are capable of mounting defenses against would-be attackers which may be heightened upon attack. Resistance to insects often varies among plant species, with different genotypes exhibiting unique patterns of chemical and physical defenses. Within this framework, plant access to nutrients may be critical for maximal functioning of resistance mechanisms and are likely to differ among plant genotypes. In this study, we aimed to test the hypothesis that access to nutrition would alter the expression of plant resistance to insects and alter insect performance in a manner consistent with fertilization regime. We used two maize (Zea mays) genotypes possessing different levels of resistance and the fall armyworm (Spodoptera frugiperda) as model systems. Plants were subjected to three fertilization regimes prior to assessing insect-mediated responses. Upon reaching V4 stage, maize plants were separated into two groups, one of which was infested with fall armyworm larvae to induce plant defenses. Plant tissue was collected and used in insect bioassays and to measure the expression of defense-related genes and proteins. Insect performance differed between the two plant genotypes substantially. For each genotype, fertilization altered larval performance, where lower fertilization rates hindered larval growth. Induction of plant defenses by prior herbivory substantially reduced naïve fall armyworm growth in both genotypes. The effects between fertilization and induced defenses were complex, with low fertilization reducing induced defenses in the resistant maize. Gene and protein expression patterns differed between the genotypes, with herbivory often increasing expression, but differing between fertilization levels. The soluble protein concentrations did not change across fertilization levels but was higher in the susceptible maize genotype. These results demonstrate the malleability of plant defenses and the cascading effects of plant nutrition on insect herbivory.

Patterns and roles of lignan and terpenoid accumulation in the reaction zone compartmentalizing pathogen-infected heartwood of Norway spruce

Lignan impregnation of the reaction zone wood protects against oxidative degradation by fungi. Traumatic resin canals may play roles in the underlying signal transduction, synthesis, and translocation of defense compounds. Tree defense against xylem pathogens involves both constitutive and induced phenylpropanoids and terpenoids. The induced defenses include compartmentalization of compromised wood with a reaction zone (RZ) characterized by polyphenol deposition, whereas the role of terpenoids has remained poorly understood. To further elucidate the tree-pathogen interaction, we profiled spatial patterns in lignan (low-molecular-weight polyphenols) and terpenoid content in Norway spruce (Picea abies) trees showing heartwood colonization by the pathogenic white-rot fungus Heterobasidion parviporum. There was pronounced variation in the amount and composition of lignans between different xylem tissue zones of diseased and healthy trees. Intact RZ at basal stem regions, where colonization is the oldest, showed the highest level and diversity of these compounds. The antioxidant properties of lignans obviously hinder oxidative degradation of wood: RZ with lignans removed by extraction showed significantly higher mass loss than unextracted RZ when subjected to Fenton degradation. The reduced diversity and amount of lignans in pathogen-compromised RZ and decaying heartwood in comparison to intact RZ and healthy heartwood suggest that α-conindendrin isomer is an intermediate metabolite in lignan decomposition by H. parviporum. Diterpenes and diterpene alcohols constituted above 90% of the terpenes detected in sapwood of healthy and diseased trees. A significant finding was that traumatic resin canals, predominated by monoterpenes, were commonly associated with RZ. The findings clarify the roles and fate of lignan during wood decay and raise questions about the potential roles of terpenoids in signal transduction, synthesis, and translocation of defense compounds upon wood compartmentalization against decay fungi.

Analysis of the transcriptome of the needles and bark of Pinus radiata induced by bark stripping and methyl jasmonate

BACKGROUND

Plants are attacked by diverse insect and mammalian herbivores and respond with different physical and chemical defences. Transcriptional changes underlie these phenotypic changes. Simulated herbivory has been used to study the transcriptional and other early regulation events of these plant responses. In this study, constitutive and induced transcriptional responses to artificial bark stripping are compared in the needles and the bark of Pinus radiata to the responses from application of the plant stressor, methyl jasmonate. The time progression of the responses was assessed over a 4-week period.

RESULTS

Of the 6312 unique transcripts studied, 86.6% were differentially expressed between the needles and the bark prior to treatment. The most abundant constitutive transcripts were related to defence and photosynthesis and their expression did not differ between the needles and the bark. While no differential expression of transcripts were detected in the needles following bark stripping, in the bark this treatment caused an up-regulation and down-regulation of genes associated with primary and secondary metabolism. Methyl jasmonate treatment caused differential expression of transcripts in both the bark and the needles, with individual genes related to primary metabolism more responsive than those associated with secondary metabolism. The up-regulation of genes related to sugar break-down and the repression of genes related with photosynthesis, following both treatments was consistent with the strong down-regulation of sugars that has been observed in the same population. Relative to the control, the treatments caused a differential expression of genes involved in signalling, photosynthesis, carbohydrate and lipid metabolism as well as defence and water stress. However, non-overlapping transcripts were detected between the needles and the bark, between treatments and at different times of assessment. Methyl jasmonate induced more transcriptional responses in the bark than bark stripping, although the peak of expression following both treatments was detected 7 days post treatment application. The effects of bark stripping were localised, and no systemic changes were detected in the needles.

CONCLUSION

There are constitutive and induced differences in the needle and bark transcriptome of Pinus radiata. Some expression responses to bark stripping may differ from other biotic and abiotic stresses, which contributes to the understanding of plant molecular responses to diverse stresses. Whether the gene expression changes are heritable and how they differ between resistant and susceptible families identified in earlier studies needs further investigation.

Additive genetic variation in Pinus radiata bark chemistry and the chemical traits associated with variation in mammalian bark stripping

Secondary metabolites are suggested as a major mechanism explaining genetic variation in herbivory levels in Pinus radiata. The potential to incorporate these chemical traits into breeding/deployment programmes partly depends on the presence of additive genetic variation for the relevant chemical traits. In this study, near-infrared spectroscopy was used to quantify the constitutive and induced levels of 54 compounds in the bark of trees from 74 P. radiata full-sib families. The trees sampled for chemistry were protected from browsing and induced levels were obtained by subjecting half of the trees to artificial bark stripping. The treatment effect on bark chemistry was assessed along with narrow-sense heritability, the significance of non-additive genetic effects and the additive genetic correlations of compounds with bark stripping by mammalian herbivores that was observed in unprotected replicates of the field trial. The results indicated: (i) significant additive genetic variation, with low-moderate narrow-sense heritability estimates for most compounds; (ii) while significant induced effects were detected for some chemicals, no significant genetic variation in inducibility was detected; and (iii) sugars, fatty acids and a diterpenoid positively genetically correlated while a sesquiterpenoid negatively genetically correlated with bark stripping by the mammalian herbivore, the Bennett's wallaby (Macropus rufogriseus). At the onset of browsing, a trade-off with height was detected for selecting higher amounts of this sesquiterpenoid. However, overall, results showed potential to incorporate chemical traits into breeding/deployment programmes. The quantitative genetic analyses of the near infrared predicted chemical traits produced associations with mammalian bark stripping that mostly conform with those obtained using standard wet chemistry.

Chemical Traits that Predict Susceptibility of Pinus radiata to Marsupial Bark Stripping

Bark stripping by mammals is a major problem in managed conifer forests worldwide. In Australia, bark stripping in the exotic plantations of Pinus radiata is mainly caused by native marsupials and results in reduced survival, growth, and in extreme cases death of trees. Herbivory is influenced by a balance between primary metabolites that are sources of nutrition and secondary metabolites that act as defences. Identifying the compounds that influence herbivory may be a useful tool in the management of forest systems. This study aimed to detect and identify both constitutive and induced compounds that are associated with genetic differences in susceptibility of two-year-old P. radiata trees to bark stripping by marsupials. An untargeted profiling of 83 primary and secondary compounds of the needles and bark samples from 21 susceptible and 21 resistant families was undertaken. These were among the most and least damaged families, respectively, screened in a trial of 74 families that were exposed to natural field bark stripping by marsupials. Experimental plants were in the same field trial but protected from bark stripping and a subset were subjected to artificial bark stripping to examine induced and constitutive chemistry differences between resistant and susceptible families. Machine learning (random forest), partial least squares plus discriminant analysis (PLS-DA), and principal components analysis with discriminant analysis (PCA-DA), as well as univariate methods were used to identify the most important totals by compound group and individual compounds differentiating the resistant and susceptible families. In the bark, the constitutive amount of two sesquiterpenoids - bicyclogermacrene and an unknown sesquiterpenoid alcohol -were shown to be of higher levels in the resistant families, whereas the constitutive sugars, fructose, and glucose, as well individual phenolics, were higher in the more susceptible families. The chemistry of the needles was not useful in differentiating the resistant and susceptible families to marsupial bark stripping. After artificial bark stripping, the terpenes, sugars, and phenolics responded in both the resistant and susceptible families by increasing or reducing amounts, which leveled the differences in the amounts of the compounds between the different resistant and susceptible classes observed at the constitutive level. Overall, based on the families with extreme values for less and more susceptibility, differences in the amounts of secondary compounds were subtle and susceptibility due to sugars may outweigh defence as the cause of the genetic variation in bark stripping observed in this non-native tree herbivory system.

Silencing of Oleuropein β-Glucosidase Abolishes the Biosynthetic Capacity of Secoiridoids in Olives

Specialized metabolism is an evolutionary answer that fortifies plants against a wide spectrum of (a) biotic challenges. A plethora of diversified compounds can be found in the plant kingdom and often constitute the basis of human pharmacopeia. Olive trees (Olea europaea) produce an unusual type of secoiridoids known as oleosides with promising pharmaceutical activities. Here, we transiently silenced oleuropein β-glucosidase (OeGLU), an enzyme engaged in the biosynthetic pathway of secoiridoids in the olive trees. Reduction of OeGLU transcripts resulted in the absence of both upstream and downstream secoiridoids in planta, revealing a regulatory loop mechanism that bypasses the flux of precursor compounds toward the branch of secoiridoid biosynthesis. Our findings highlight that OeGLU could serve as a molecular target to regulate the bioactive secoiridoids in olive oils.

Catch-22 in specialized metabolism: balancing defense and growth

Plants are unsurpassed biochemists that synthesize a plethora of molecules in response to an ever-changing environment. The majority of these molecules, considered as specialized metabolites, effectively protect the plant against pathogens and herbivores. However, this defense most probably comes at a great expense, leading to reduction of growth (known as the 'growth-defense trade-off'). Plants employ several strategies to reduce the high metabolic costs associated with chemical defense. Production of specialized metabolites is tightly regulated by a network of transcription factors facilitating its fine-tuning in time and space. Multifunctionality of specialized metabolites-their effective recycling system by re-using carbon, nitrogen, and sulfur, thus re-introducing them back to the primary metabolite pool-allows further cost reduction. Spatial separation of biosynthetic enzymes and their substrates, and sequestration of potentially toxic substances and conversion to less toxic metabolite forms are the plant's solutions to avoid the detrimental effects of metabolites they produce as well as to reduce production costs. Constant fitness pressure from herbivores, pathogens, and abiotic stressors leads to honing of specialized metabolite biosynthesis reactions to be timely, efficient, and metabolically cost-effective. In this review, we assess the costs of production of specialized metabolites for chemical defense and the different plant mechanisms to reduce the cost of such metabolic activity in terms of self-toxicity and growth.

Intra-Individual and Intraspecific Terpenoid Diversity in Erodium cicutarium

The chemodiversity between and within individuals of several plant species is remarkable and shaped by the local habitat environment and the genetic background. The forb Erodium cicutarium (Geraniaceae) is globally distributed and partly invasive. This paper hypothesizes a high intra-specific and inter-individual chemical diversity in this species and investigates this by comparing the concentration and diversity of terpenoid compounds in different plant parts, i.e., leaves, blossoms and fruits. Plants were grown from seeds, originating from native range Bavaria (BY), Germany, and invaded range California (CA), USA, populations. In total, 20 different terpenoids were found, which occurred in distinct combinations and the patterns clustered into groups of distinct chemotypes for all plant parts. Several of the chemotypes were specific to plants of one region. The terpenoid compositions of different plant parts within individuals were highly correlated. Chemodiversity was higher in reproductive plant parts compared to the leaves, and higher in plants from BY compared to CA. This study highlights the intra-specific and inter-individual chemodiversity in E. cicutarium, linked to its geographical origin, which may facilitate its invasion success but also calls for further investigation of the role of chemodiversity in invasive plants on interactions with the environment.

Photosystem II heat tolerances characterize thermal generalists and the upper limit of carbon assimilation

The heat tolerance of photosystem II (PSII) may promote carbon assimilation at higher temperatures and help explain plant responses to climate change. Higher PSII heat tolerance could lead to (a) increases in the high-temperature compensation point (T_max ); (b) increases in the thermal breadth of photosynthesis (i.e. the photosynthetic parameter Ω) to promote a thermal generalist strategy of carbon assimilation; (c) increases in the optimum rate of carbon assimilation P_opt and faster carbon assimilation and/or (d) increases in the optimum temperature for photosynthesis (T_opt ). To address these hypotheses, we tested if the T_crit , T₅₀ and T₉₅ PSII heat tolerances were correlated with carbon assimilation parameters for 21 plant species. Our results did not support Hypothesis 1, but we observed that T₅₀ may be used to estimate the upper thermal limit for T_max at the species level, and that community mean T_crit may be useful for approximating T_max . The T₅₀ and T₉₅ heat tolerance metrics were positively correlated with Ω in support of Hypothesis 2. We found no support for Hypotheses 3 or 4. Our study shows that high PSII heat tolerance is unlikely to improve carbon assimilation at higher temperatures but may characterize thermal generalists with slow resource acquisition strategies.

Essential Oils of Seven Lamiaceae Plants and Their Antioxidant Capacity

Oxidative stress has been reported as a cause of many diseases like Parkinson's, Alzheimer's, cardiovascular disease, and diabetes. Oxidative stress can also lead to cancer formation by promoting tumor development and progression. Antioxidants derived from Lamiaceae plants play an important role in natural medicine, pharmacology, cosmetology, and aromatherapy. Herein, we examine the antioxidative capacity of essential oils from seven aromatic Lamiaceae plants against the synthetic radicals DPPH and ABTS. Among the essential oils analyzed, the most robust scavenging capacities were found in mixtures of volatile compounds from thyme and savory. The scavenging activity of tested EOs against the ABTS radical was clearly higher than activity towards DPPH. Analysis of essential oils with weaker antioxidant activity has shown that volatile compounds from marjoram, sage, and hyssop were more active than EOs from lavender and mint. It can be suggested that the potent antioxidant capacity of thyme (Thymus vulgaris) and savory (Satyreja hortensis) are related to a high level of phenolic constituents, such as thymol and carvacrol. On the other hand, the elevated antioxidative power of marjoram, sage, and hyssop essential oils may also be due to their terpinene, o-cymene, terpinolene, and terpinen-4-ol constituents. Although non-phenolic components are less active than thymol or carvacrol, they may affect antioxidant capacity synergistically.

An Ecological Perspective on Living with Fire in Ponderosa Pine Forests of Oregon and Washington: Resistance, Gone but not Forgotten

Wildland fires (WLF) have become more frequent, larger, and severe with greater impacts to society and ecosystems and dramatic increases in firefighting costs. Forests throughout the range of ponderosa pine in Oregon and Washington are jeopardized by the interaction of anomalously dense forest structure, a warming and drying climate, and an expanding human population. These forests evolved with frequent interacting disturbances including low-severity surface fires, droughts, and biological disturbance agents (BDAs). Chronic low-severity disturbances were, and still are, critical to maintaining disturbance resistance, the property of an ecosystem to withstand disturbance while maintaining its structure and ecological function. Restoration of that historical resistance offers multiple social and ecological benefits. Moving forward, we need a shared understanding of the ecology of ponderosa pine forests to appreciate how restoring resistance can reduce the impacts of disturbances. Given contemporary forest conditions, a warming climate, and growing human populations, we predict continued elevation of tree mortality from drought, BDAs, and the large high-severity WLFs that threaten lives and property as well as ecosystem functions and services. We recommend more comprehensive planning to promote greater use of prescribed fire and management of reported fires for ecological benefits, plus increased responsibility and preparedness of local agencies, communities and individual homeowners for WLF and smoke events. Ultimately, by more effectively preparing for fire in the wildland urban interface, and by increasing the resistance of ponderosa pine forests, we can greatly enhance our ability to live with fire and other disturbances.

Sex-specific differences in Juniperus communis: essential oil yield, growth-defence conflict and population sex ratio

In plants, biomass and nutrient allocation often generate trade-offs between the different biochemical pathways conflicting the utilization of the common source among growth, reproduction and chemical defence. However, in dioecious plant species, these trade-off patterns could appear as a more contrasted problem between males and females due to the dissimilar reproduction investment. Generally, the growth ratio is higher in males than females, while females have a stronger defence than males. To understand the possible role of the sex-specific dissimilarities within the growth-defence conflict framework, we investigated the possible causes of the high variance of the essential oil yield in a dioecious evergreen species, Juniperus communis. Specifically, we tested the correlations between the essential oil yield with other individual-specific traits (e.g. sex, age), the presence of the growth-defence trade-off, and the differential growth and survival patterns between males and females through an extensive field survey with sample collection in three natural populations (Kiskunság National Park, Hungary). The individual-specific essential oil yield was also measured and served as a proxy to describe the degree of chemical defence. We found that the essential oil yield showed strong and consistent sex-specific patterns decreasing with age in adults. Contrary to the predictions, the males showed a consistently higher yield than the females. We also observed a growth-defence trade-off in males but not in females. Consistently with the growth-defence conflict hypothesis, the populations' sex ratio was male-biased, and this pattern was more evident with ageing modifying the demographic structure due to the sexually dissimilar lifespan. Our juniper study revealed a contrasting and unique essential oil accumulation driven by the complex allocation trade-off mechanisms within individuals, which could be a flexible and adaptive defence response against the increasing biotic and abiotic environmental stresses exacerbated under global climate change.

Bleaching effect in Sarcophyton spp. soft corals-is there a correlation to their diterpene content?

Rising seawater temperature is one of the greatest threats to the persistence of coral reefs. While great efforts have been made to understand the metabolic costs of thermal acclimation, the exact roles of many secondary metabolites involved in the immediate response exhibited by soft corals remain largely unknown. Herein, an untargeted metabolomics approach using ultra-performance liquid chromatography coupled to high-resolution mass spectrometry (UPLC-MS) was employed to investigate thermal stress-induced modifications to the de novo synthesis of secondary metabolites in two soft coral species, Sarcophyton ehrenbergi and S. glaucum. Exposure to elevated temperature resulted in symbiont photoinhibition primarily via either damage to photosystem II (PSII) or the loss of algal symbionts during coral bleaching. This was suggested by a decrease in pulse amplitude modulated (PAM) measurements of corals incubated at different temperatures. Thermal stress was also found to impair the production of diterpenoid secondary metabolites in soft corals. Principally, reduction in the levels of a number of diterpenes, viz. sarcophytoxide and deoxysarcophytoxide, in heat stressed S. ehrenbergi and S. glaucum was observed indicative that thermal acclimation is energetically costly and will necessitate downstream changes in secondary metabolic pathways. Our data suggest that, while the host controls the production of ecologically important terpenes, when energetic contribution from the algal symbiont is reduced or absent as a result of a bleaching event, energy reserves may be insufficient to maintain the production of such energetically cost chemicals. This study provides for the first time a holistic assessment of secondary metabolite changes imposed in soft corals during exposure and acclimation to elevated temperatures.

Resource allocation strategies among vegetative growth, sexual reproduction, asexual reproduction and defense during growing season of Aconitum kusnezoffii Reichb

Natural plants must actively allocate their limited resources for survival and reproduction. Although vegetative growth, sexual reproduction, asexual reproduction and defense are all basic processes in the life cycle of plants, the strategies used to allocate resources between these processes are poorly understood. These processes are conspicuous in naturally grown Aconitum kusnezoffii Reichb., which makes it a suitable study subject. Here, the morphology, dry matter, total organic carbon, total nitrogen and aconitum alkaloid levels of shoot, principal root (PR) and lateral roots were measured throughout the growing season. Then, transcriptome and metabolite content analyses were performed. We found that vegetative growth began first. After vegetative growth ceased, sexual development began. Flower organ development was accompanied by increased photosynthesis and the PR consumed temporarily stored resources after flower formation. Asexual propagule development initiated earlier than sexual reproduction and kept accumulating resources after that. Development was slow before flower formation, mainly manifesting as increasing length; then, after flower formation it accelerated via enhanced material transport and accumulation. Defense compounds were maintained at low levels before flowering. In particular, the turnover of defense compounds was enhanced before and after flower bud emergence, providing resources for other processes. After flower formation, defense compounds were accumulated. The pattern found herein provides a vivid example for further studies on resource allocation strategies. The exciting finding that the PR, as a more direct storage site for photosynthate, is a buffer unit for resources, and that defense compounds can be reused for other processes, suggests a need to explore potential mechanisms.

Flower Production, Headspace Volatiles, Pollen Nutrients, and Florivory in Tanacetum vulgare Chemotypes

Floral volatiles and reward traits are major drivers for the behavior of mutualistic as well as antagonistic flower visitors, i.e., pollinators and florivores. These floral traits differ tremendously between species, but intraspecific differences and their consequences on organism interactions remain largely unknown. Floral volatile compounds, such as terpenoids, function as cues to advertise rewards to pollinators, but should at the same time also repel florivores. The reward composition, e.g., protein and lipid contents in pollen, differs between individuals of distinct plant families. Whether the nutritional value of rewards within the same plant species is linked to their chemotypes, which differ in their pattern of specialized metabolites, has yet not been investigated. In the present study, we compared Tanacetum vulgare plants of five terpenoid chemotypes with regard to flower production, floral headspace volatiles, pollen macronutrient and terpenoid content, and floral attractiveness to florivorous beetles. Our analyses revealed remarkable differences between the chemotypes in the amount and diameter of flower heads, duration of bloom period, and pollen nutritional quality. The floral headspace composition of pollen-producing mature flowers, but not of premature flowers, was correlated to that of pollen and leaves in the same plant individual. For two chemotypes, florivorous beetles discriminated between the scent of mature and premature flower heads and preferred the latter. In semi-field experiments, the abundance of florivorous beetles and flower tissue miners differed between T. vulgare chemotypes. Moreover, the scent environment affected the choice and beetles were more abundant in homogenous plots composed of one single chemotype than in plots with different neighboring chemotypes. In conclusion, flower production, floral metabolic composition and pollen quality varied to a remarkable extend within the species T. vulgare, and the attractiveness of floral scent differed also intra-individually with floral ontogeny. We found evidence for a trade-off between pollen lipid content and pollen amount on a per-plant-level. Our study highlights that chemotypes which are more susceptible to florivory are less attacked when they grow in the neighborhood of other chemotypes and thus gain a benefit from high overall chemodiversity.

Direct and correlated responses to artificial selection for growth and water-use efficiency in a Mediterranean pine

PREMISE

Persistence of tree populations in the face of global change relies on their capacity to respond to biotic and abiotic stressors through plastic or adaptive changes. Genetic adaptation will depend on the additive genetic variation within populations and the heritability of traits related to stress tolerance. Because traits can be genetically linked, selective pressure acting on one trait may lead to correlated responses in other traits.

METHODS

To test direct and correlated responses to selection for growth and drought tolerance in Pinus halepensis, we selected trees in a parental population for higher growth and greater water-use efficiency (WUE) and compared their offspring with the offspring of random trees from the parental population in two contrasting common gardens. We estimated direct responses to selection for growth and WUE and correlated responses for growth and tolerance to abiotic and biotic stressors.

RESULTS

We found a strong response to selection and high realized heritability for WUE, but no response to selection for growth. Correlated responses to selection in other life-history traits were not significant, except for concentration of some chemical defenses, which was greater in the offspring of mother trees selected for growth than in the offspring of unselected control trees.

CONCLUSIONS

The empirical evidence of direct responses to selection for high WUE suggests that P. halepensis has the potential to evolve in response to increasing drought stress. Contrary to expectations, the results are not conclusive of a potential negative impact of WUE and growth selection on other key life-history traits.

Insect defoliation is linked to a decrease in soil ectomycorrhizal biomass and shifts in needle endophytic communities

Insect outbreaks of increasing frequency and severity in forests are predicted due to climate change. Insect herbivory is known to promote physiological changes in forest trees. However, little is known about whether these plant phenotypic adjustments have cascading effects on tree microbial symbionts such as fungi in roots and foliage. We studied the impact of defoliation by the pine processionary moth in two infested Pinus nigra forests through a multilevel sampling of defoliated and non-defoliated trees. We measured tree growth, nutritional status and carbon allocation to chemical defenses. Simultaneously, we analysed the putative impact of defoliation on the needle endophytes and on the soil fungal communities. Higher concentrations of chemical defenses were found in defoliated trees, likely as a response to defoliation; however, no differences in non-structural carbohydrate reserves were found. In parallel to the reductions in tree growth and changes in chemical defenses, we observed shifts in the composition of needle endophytic and soil fungal communities in defoliated trees. Defoliated trees consistently corresponded with a lower biomass of ectomycorrhizal fungi in both sites, and a higher alpha diversity and greater relative abundance of belowground saprotrophs and pathogens. However, ectomycorrhizal alpha diversity was similar between non-defoliated and defoliated trees. Specific needle endophytes in old needles were strongly associated with non-defoliated trees. The potential role of these endophytic fungi in pine resistance should be further investigated. Our study suggests that lower biomass of ectomycorrhizal fungi in defoliated trees might slow down tree recovery since fungal shifts might affect tree-mycorrhizal feedbacks and can potentially influence carbon and nitrogen cycling in forest soils.

Herbivory and Attenuated UV Radiation Affect Volatile Emissions of the Invasive Weed Calluna vulgaris

Calluna vulgaris (heather) is an aggressive invasive weed on the Central Plateau, North Is., New Zealand (NZ), where it encounters different environmental factors compared to its native range in Europe, such as high ultraviolet radiation (UV) and a lack of specialist herbivores. The specialist herbivore Lochmaea suturalis (heather beetle) was introduced from the United Kingdom (UK) in 1996 as a biocontrol agent to manage this invasive weed. Like other plant invaders, a novel environment may be challenging for heather as it adjusts to its new conditions. This process of “adjustment” involves morphological and physiological changes often linked to phenotypic plasticity. The biochemical responses of exotic plants to environmental variables in their invaded range is poorly understood. The production and release of volatile organic compounds (VOCs) is essential to plant communication and highly susceptible to environmental change. This study therefore aimed to explore the VOC emissions of heather in response to different levels of UV exposure, and to feeding damage by L. suturalis. Using tunnel houses clad with UV-selective filters, we measured VOCs produced by heather under NZ ambient, 20% attenuated, and 95% attenuated solar UV treatments. We also compared VOC emissions in the field at adjacent sites where L. suturalis was present or absent. Volatiles produced by the same target heather plants were measured at four different times in the spring and summer of 2018–2019, reflecting variations in beetle’s abundance, feeding stage and plant phenology. Heather plants under 95% attenuated UV produced significantly higher amounts of (E)-β-farnesene, decanal, benzaldehyde, and benzeneacetaldehyde compared to 25% attenuated and ambient UV radiation. We also found significant differences in volatiles produced by heather plants in beetle-present versus beetle-absent sites on most sampling occasions. We also recorded a lower number of generalist herbivores on heather at sites where L. suturalis was present. Interactions between invasive plants, a novel environment, and the native communities they invade, are discussed.

Zingerone in the Flower of Passiflora Maliformis Attracts an Australian Fruit Fly, Bactrocera Jarvisi (Tryon)

Passiflora maliformis is an introduced plant in Australia but its flowers are known to attract the native Jarvis’s fruit fly, Bactrocera jarvisi (Tryon). The present study identifies and quantifies likely attractant(s) of male B. jarvisi in P. maliformis flowers. The chemical compositions of the inner and outer coronal filaments, anther, stigma, ovary, sepal, and petal of P. maliformis were separately extracted with ethanol and analyzed using gas chromatography-mass spectrometry (GC-MS). Polyisoprenoid lipid precursors, fatty acids and their derivatives, and phenylpropanoids were detected in P. maliformis flowers. Phenylpropanoids included raspberry ketone, cuelure, zingerone, and zingerol, although compositions varied markedly amongst the flower parts. P. maliformis flowers were open for less than one day, and the amounts of some of the compounds decreased throughout the day. The attraction of male B. jarvisi to P. maliformis flowers is most readily explained by the presence of zingerone in these flowers.

Interspecific variation and elevated CO2 influence the relationship between plant chemical resistance and regrowth tolerance

To understand how comprehensive plant defense phenotypes will respond to global change, we investigated the legacy effects of elevated CO2 on the relationships between chemical resistance (constitutive and induced via mechanical damage) and regrowth tolerance in four milkweed species (Asclepias). We quantified potential resistance and tolerance trade-offs at the physiological level following simulated mowing, which are relevant to milkweed ecology and conservation. We examined the legacy effects of elevated CO2 on four hypothesized trade-offs between the following: (a) plant growth rate and constitutive chemical resistance (foliar cardenolide concentrations), (b) plant growth rate and mechanically induced chemical resistance, (c) constitutive resistance and regrowth tolerance, and (d) regrowth tolerance and mechanically induced resistance. We observed support for one trade-off between plant regrowth tolerance and mechanically induced resistance traits that was, surprisingly, independent of CO2 exposure. Across milkweed species, mechanically induced resistance increased by 28% in those plants previously exposed to elevated CO2. In contrast, constitutive resistance and the diversity of mechanically induced chemical resistance traits declined in response to elevated CO2 in two out of four milkweed species. Finally, previous exposure to elevated CO2 uncoupled the positive relationship between plant growth rate and regrowth tolerance following damage. Our data highlight the complex and dynamic nature of plant defense phenotypes under environmental change and question the generality of physiologically based defense trade-offs.

Resin acids as inducible chemical defences of pine seedlings against chewing insects

Inducibility of defences in response to biotic stimuli is considered an important trait in plant resistance. In conifers, previous research has mostly focused on the inducibility of the volatile fraction of the oleoresin (mono- and sesquiterpenes), leaving the inducibility of the non-volatile resin acids largely unexplored, particularly in response to real herbivory. Here we investigated the differences in the inducibility of resin acids in two pine species, one native from Europe (Pinus pinaster Ait.) and another from North America (Pinus radiata D. Don), in response to wounding by two European insects: a bark chewer, the pine weevil (Hylobius abietis L.), and a defoliator, the pine processionary caterpillar (Thaumetopoea pityocampa Schiff.). We quantified the constitutive (control) and induced concentrations of resin acids in the stem and needles of both pine species by gas chromatography techniques. Both pine species strongly increased the concentration of resin acids in the stem after pine weevil feeding, although the response was greater in P. pinaster than in P. radiata. However, systemic defensive responses in the needles were negligible in both pine species after pine weevil feeding in the stem. On the other hand, P. radiata locally reduced the resin acid concentration in the needles after pine caterpillar feeding, whereas in P. pinaster resin acid concentration was apparently unaffected. Nevertheless, systemic induction of resin acids was only observed in the stem of P. pinaster in response to pine caterpillar feeding. In summary, pine induced responses were found highly compartmentalized, and specific to herbivore identity. Particularly, plant defence suppression mechanisms by the pine caterpillar, and ontogenetic factors might be potentially affecting the induced response of resin acids in both pine species.