Metabolic profiling and enhanced production of phytosterols by elicitation with methyl jasmonate and silver nitrate in whole plant cultures of Lemna paucicostata

Girdling behavior of the longhorn beetle modulates the host plant to enhance larval performance

BACKGROUND

Preingestive behavioral modulations of herbivorous insects on the host plant are abundant over insect taxa. Those behaviors are suspected to have functions such as deactivation of host plant defenses, nutrient accumulation, or modulating plant-mediated herbivore interactions. To understand the functional consequence of behavioral modulation of insect herbivore, we studied the girdling behavior of Phytoecia rufiventris Gautier (Lamiinae; Cerambycidae) on its host plant Erigeron annuus L. (Asteraceae) that is performed before endophytic oviposition in the stem.

RESULTS

The girdling behavior significantly increased the larval performance in both field monitoring and lab experiment. The upper part of the girdled stem exhibited lack of jasmonic acid induction upon larval attack, lowered protease inhibitor activity, and accumulated sugars and amino acids in compared to non-girdled stem. The girdling behavior had no effect on the larval performance of a non-girdling longhorn beetle Agapanthia amurensis, which also feeds on the stem of E. annuus during larval phase. However, the girdling behavior decreased the preference of A. amurensis females for oviposition, which enabled P. rufiventris larvae to avoid competition with A. amurensis larvae.

CONCLUSIONS

In conclusion, the girdling behavior modulates plant physiology and morphology to provide a modulated food source for larva and hide it from the competitor. Our study implies that the insect behavior modulations can have multiple functions, providing insights into adaptation of insect behavior in context of plant-herbivore interaction.

Melatonin Treatment Enhances the Growth and Productivity of Useful Metabolites in the In Vitro Culture of Spirodela polyrhiza

Spirodela polyrhiza (Araceae family) is a duckweed species that serves as a potential resource for feed, food, bioremediation, and pharmaceutical applications. In this study, we assessed the effects of different concentrations of melatonin (0, 0.1, 1, and 10 μM) on the growth of S. polyrhiza during in vitro culture and the metabolic profiles and productivities of useful metabolites using gas chromatography-mass spectrometry coupled with multivariable statistical analysis. We found that exogenous melatonin significantly improved the total dry weight and altered the metabolic profiles of S. polyrhiza cultures. Melatonin significantly enhanced the cellular production of useful metabolites, such as γ-aminobutyric acid, dopamine, threonine, valine, and phytosterols. The volumetric productivities (mg/L) of γ-aminobutyric acid, dopamine, campesterol, β-sitosterol, and stigmasterol were the highest in the presence of 10 μM melatonin on day 12. Moreover, the productivities of ascorbic acid and serotonin were the highest in the presence of 1 μM melatonin on day 12. Therefore, melatonin could be used to enhance the production of biomass and useful metabolites during large-scale S. polyrhiza cultivation in cosmetic, food/feed, and pharmaceutical industries.

Flavone-associated resistance of two Lemna species to duckweed weevil attack

Lemna perpusilla and Lemna minor are free-floating plants that often live in the same habitat. However, little is known about how they differ in response to herbivore attacks. In this study, we examined the species-specific resistance of two Lemna species to the duckweed weevil, Tanysphyrus lemnae. The female adults of T. lemnae preferred to lay eggs on L. perpusilla over L. minor. In addition, the larvae of T. lemnae performed better when fed on L. perpusilla than on L. minor. To understand the physiological basis of species-specific resistance in the two Lemna species, we measured the amounts of jasmonic acid (JA), phytosterols, and flavonoids. Attacks by duckweed weevils increased the levels of JA in the two Lemna species, but these levels did not differ significantly between the two species. Interestingly, the levels of flavones (isoorientin, vitexin, and isovitexin) in L. minor species were higher than those in L. perpusilla. The in vitro bioassay showed that three flavones significantly decreased the survival rate of duckweed weevil larvae. Although L. perpusilla was less resistant to duckweed weevil attack compared to L. minor, L. perpusilla grew faster than L. minor regardless of the duckweed weevil attack. These results suggest that these two Lemna species have different defense strategies against the duckweed weevil.

Ontogeny-dependent effects of elevated CO2 and watering frequency on interaction between Aristolochia contorta and its herbivores

Effects of environmental change on plants can differ due to sequential changes in their life-history strategies (i.e., ontogenetic variations). The fitness of herbivorous insects by physiological changes of the host plant could be affected depending on their diet breadth. However, little is known regarding the combinational effects of plant ontogeny and climate change on plant-herbivore interactions. This study examined the plant ontogeny-dependent effects of climate change on the interaction between a host plant (Aristolochia contorta), its specialist herbivore (Sericinus montela), and a generalist herbivore (Spodoptera exigua). Plants were grown under a factorial design of two distinct CO₂ concentrations (ambient, 400 ppm; elevated, 560 ppm) and two watering frequencies (control, once a week; increased, twice a week). Plant ontogeny ameliorated the effects of climate change by altering its defensive traits, where nutrient-related factors were cumulatively affected by climate change. Herbivore performance was assessed at three different plant ontogenetic stages (1st-year juvenile, 1st-year senescence, and 2nd-year juvenile). Elevated CO₂ levels reduced the growth and survival of the specialist herbivore, whereas increased watering frequency partially alleviated this reduced performance. Generalist herbivore performance slightly increased under elevated CO₂ levels with progressing ontogenetic stages. The effects of climate change, both elevated CO₂ and increased watering frequency were weaker in 2nd-year juveniles than in 1st-year juveniles. Elevated CO₂ levels detrimentally affected the nutritional quality of A. contorta leaves. The effects of climate change on both specialist and generalist herbivore performance differed as plant ontogenetic stage proceeded. Increased growth rates and survival of the generalist herbivore at the latter ontogenetic stage might negatively affect the population dynamics of a specialist herbivore. This study suggests that biases are possible when the plant-herbivore interaction under a changing environment is predicted from a singular plant ontogenetic stage.

Dose-dependent methyl jasmonate effects on photosynthetic traits and volatile emissions: biphasic kinetics and stomatal regulation

Exogenous application of methyl jasmonate (MeJA) has been extensively used to study jasmonate-dependent signaling events triggered by biotic stresses. MeJA application leads to complex jasmonate-dependent physiological responses, including changes in stomatal openness and induction of emissions of a multitude of volatile compounds. Whether the alterations in stomatal conductance and emissions of MeJA-induced volatiles are quantitatively associated with MeJA dose, and whether the induced volatile emissions are regulated by modifications in stomatal conductance had been poorly known until recently. Our latest studies highlighted a biphasic kinetics of jasmonate-dependent volatile emissions induced by MeJA treatment in the model species cucumber (Cucumis sativus), indicating induction of an immediate stress response and subsequent gene-expression level response. Both the immediate and delayed responses were MeJA dose-dependent. The studies further demonstrated that stomata modulated the kinetics of emissions of water-soluble volatiles in a MeJA dose-dependent manner. These studies contribute to understanding of plant short- and long-term responses to different biotic stress severities as simulated by treatments with a range of MeJA doses corresponding to mild to acute stress.

Impact of potential stimulants on asiaticoside and madecassoside levels and expression of triterpenoid-related genes in axenic shoot cultures of Centella asiatica (L.) Urb

The triterpenoid saponins, asiaticoside and madecassoside from Centella asiatica (L.) Urb. are known to have a wide range of applications in pharmaceutical and cosmetic industries. The effect of addition of Potential Metabolite Stimulants (PMSs) - casein acid hydrolysate, meat peptone, salicylic acid, copper sulphate, and silver nitrate, on the concentrations of these saponins and transcript levels of associated genes encoding important biosynthetic enzymes, was assessed in axenic shoot cultures of C. asiatica. Among the stimulants, silver nitrate induced asiaticoside content approximately 6-fold increase in madecassoside levels, after three weeks post-treatment with a decrease in biomass compared to its control. Gene expression analysis of essential genes involved in triterpenoid synthesis such as β-amyrin synthase showed an upregulation of approximately 50-fold at the third week of silver nitrate treatment compared to control. These findings suggest that silver nitrate can act as a metabolite stimulant, to enhance the formation of triterpenoids in axenic shoot culture of C. asiatica, which could be utilized in studying the regulation of terpenoid biosynthesis and biotechnological application for the increased production of these bioactive molecules.

Essential oil yield estimation by Gas chromatography-mass spectrometry (GC-MS) after Methyl jasmonate (MeJA) elicitation in in vitro cultivated tissues of Coriandrum sativum L

Coriandrum sativum is an important spice plant known for its unique fragrance. Coriander oil is also one of the major essential oils in world global market. The oil yield varies with different coriander varieties; and the content and quality of oil is governed by several factors. In recent times, a variety of technologies have been exploited to improve phyto-compounds including essential oils. In this present study, Methyl jasmonate (MeJA) was amended in medium and the yield of essential oil was measured and compared in different cultivating tissues. The cultured tissues were nonembryogenic callus and embryogenic tissues (induction, proliferation and maturation stages of embryos). MeJA acts as a signaling molecule in accumulating secondary metabolites. Four different MeJA treatments i.e. T1 = 50, T2 = 100, T3 = 150 and T4 = 200 μM, along with a control (T0) were used and the yield of coriander essential oil was estimated in different in vitro cultivating tissues by using Gas chromatography-mass spectrometry (GC-MS). The addition of MEJA enriched essential oil yield, maximum oil being in maturation stage of embryos at T3 (150 μM). Other added treatments also had varied stimulatory role. The addition of MeJA induced stress as the stress marker enzymes like superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) content were high compared to non treated tissue (T0). In T4, the CAT activity was maximum i.e. 5.83 and 6.28 mg-1 protein min-1 in Co-1 and RS respectively in matured somatic embryos. The SOD activity was also high at maturation stage of embryos at T4 (5.3 mg-1 protein min-1 in RS). The APX activity on the other, was high (3.32 mg-1 protein min-1) in induction stage of embryogenesis at T3. The comparative biochemical (sugar, protein and proline) analyses of tissues were performed and presented that had high and low essential oil. MeJA induced stress may help in accumulating essential oils in C. sativum.

Foliage inoculation by Burkholderia vietnamiensis CBMB40 antagonizes methyl jasmonate-mediated stress in Eucalyptus grandis

Methyl jasmonate (MeJA) is widely used as a model chemical to study hypersensitive responses to biotic stress impacts in plants. Elevated levels of methyl jasmonate induce jasmonate-dependent defense responses, associated with a decline in primary metabolism and enhancement of secondary metabolism of plants. However, there is no information of how stress resistance of plants, and accordingly the sensitivity to exogenous MeJA can be decreased by endophytic plant growth promoting rhizobacteria (PGPR) harboring ACC (1-aminocyclopropane-1-carboxylate) deaminase. In this study, we estimated stress alleviating potential of endophytic PGPR against MeJA-induced plant perturbations through assessing photosynthetic traits and stress volatile emissions. We used mild (5 mM) to severe (20 mM) MeJA and endophytic plant growth promoting rhizobacteria Burkholderia vietnamiensis CBMB40 and studied how MeJA and B. vietnamiensis treatments influenced temporal changes in photosynthetic characteristics and stress volatile emissions. Separate application of MeJA markedly decreased photosynthetic characteristics and increased lipoxygenase pathway (LOX) volatiles, volatile isoprenoids, saturated aldehydes, lightweight oxygenated compounds (LOC), geranyl-geranyl diphosphate pathway (GGDP) volatiles, and benzenoids. However, MeJA-treated leaves inoculated by endophytic bacteria B. vietnamiensis had substantially increased photosynthetic characteristics and decreased emissions of LOX, volatile isoprenoids and other stress volatiles compared with non-inoculated MeJA treatments, especially at later stages of recovery. In addition, analysis of leaf terpenoid contents demonstrated that several mono- and sesquiterpenes were de novo synthesized upon MeJA and B. vietnamiensis applications. This study demonstrates that foliar application of endophytic bacteria B. vietnamiensis can potentially enhance resistance to biotic stresses and contribute to the maintenance of the integrity of plant metabolic activity.

Effects of coronatine elicitation on growth and metabolic profiles of Lemna paucicostata culture

In this study, the effects of coronatine treatment on the growth, comprehensive metabolic profiles, and productivity of bioactive compounds, including phenolics and phytosterols, in whole plant cultures of Lemna paucicostata were investigated using gas chromatography-mass spectrometry (GC-MS) coupled with multivariate statistical analysis. To determine the optimal timing of coronatine elicitation, coronatine was added on days 0, 23, and 28 after inoculation. The total growth of L. paucicostata was not significantly different between the coronatine treated groups and the control. The coronatine treatment in L. paucicostata induced increases in the content of hydroxycinnamic acids, such as caffeic acid, isoferulic acid, ρ-coumaric acid, sinapic acid, and phytosterols, such as campesterol and β-sitosterol. The productivity of these useful metabolites was highest when coronatine was added on day 0 and harvested on day 32. These results suggest that coronatine treatment on day 0 activates the phenolic and phytosterol biosynthetic pathways in L. paucicostata to a greater extent than in the control. To the best of our knowledge, this is the first report to investigate the effects of coronatine on the alteration of metabolism in L. paucicostata based on GC-MS profiling. The results of this research provide a foundation for designing strategies for enhanced production of useful metabolites for pharmaceutical and nutraceutical industries by cultivation of L. paucicostata.

Methyl jasmonate-induced emission of biogenic volatiles is biphasic in cucumber: a high-resolution analysis of dose dependence

Methyl jasmonate (MeJA) is a key airborne elicitor activating jasmonate-dependent signaling pathways, including induction of stress-related volatile emissions, but how the magnitude and timing of these emissions scale with MeJA dose is not known. Treatments with exogenous MeJA concentrations ranging from mild (0.2 mM) to lethal (50 mM) were used to investigate quantitative relationships among MeJA dose and the kinetics and magnitude of volatile release in Cucumis sativus by combining high-resolution measurements with a proton-transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) and GC-MS. The results highlighted biphasic kinetics of elicitation of volatiles. The early phase, peaking in 0.1-1 h after the MeJA treatment, was characterized by emissions of lipoxygenase (LOX) pathway volatiles and methanol. In the subsequent phase, starting in 6-12 h and reaching a maximum in 15-25 h after the treatment, secondary emissions of LOX compounds as well as emissions of monoterpenes and sesquiterpenes were elicited. For both phases, the maximum emission rates and total integrated emissions increased with applied MeJA concentration. Furthermore, the rates of induction and decay, and the duration of emission bursts were positively, and the timing of emission maxima were negatively associated with MeJA dose for LOX compounds and terpenoids, except for the duration of the first LOX burst. These results demonstrate major effects of MeJA dose on the kinetics and magnitude of volatile response, underscoring the importance of biotic stress severity in deciphering the downstream events of biological impacts.

Bioactivity of Phytosterols and Their Production in Plant in Vitro Cultures

Phytosterols are a kind of plant metabolite belonging to the triterpene family. These compounds are essential biomolecules for human health, and so they must be taken from foods. β-Sitosterol, campesterol, and stigmasterol are the main phytosterols found in plants. Phytosterols have beneficial effects on human health since they are able to reduce plasma cholesterol levels and have antiinflammatory, antidiabetic, and anticancer activities. However, there are many difficulties in obtaining them, since the levels of these compounds produced from plant raw materials are low and their chemical synthesis is not economically profitable for commercial exploitation. A biotechnological alternative for their production is the use of plant cell and hairy root cultures. This review is focused on the biosynthesis of phytosterols and their function in both plants and humans as well as the different biotechnological strategies to increase phytosterol biosynthesis. Special attention is given to describing new methodologies based on the use of recombinant DNA technology to increase the levels of phytosterols.

Role of phytosterols in drought stress tolerance in rice

Phytosterols are integral components of the membrane lipid bilayer in plants. They regulate membrane fluidity to influence its properties, functions and structure. An increase in accumulation of phytosterols namely campesterol, stigmasterol and β-sitosterol was observed in rice as seedlings matured. The levels of the major phytosterol, β-sitosterol in N22 (drought tolerant) rice seedlings was found to increase proportionately with severity of drought stress. Its levels were 145, 216, 345 and 364 μg/g FW after subjecting to water stress for 3, 6, 9 and 12 days respectively, while for IR64 (drought susceptible), levels were 137, 198, 227 and 287 μg/g FW at the same stages. Phytosterols were also found to increase with maturity as observed at 30, 50 and 75 days after planting. The activity of HMG-CoA reductase (EC 1.1.1.34) which is considered to be a key limiting enzyme in the biosynthesis of phytosterols was 0.55, 0.56, 0.78 and 0.85 μmol/min/L at 3, 6, 9 and 12 days of water stress in N22 and 0.31, 0.50, 0.54 and 0.65 μmol/min/L in case of IR64 respectively. The elevation in the levels of phytosterols as well as the activity of HMG-CoA reductase during drought stress indicates the role of phytosterols in providing tolerance to stress.