Responses of Mikania micrantha, an Invasive Weed to Elevated CO2: Induction of β-Caryophyllene Synthase, Changes in Emission Capability and Allelopathic Potential of β-Caryophyllene

Abstract

To better understand the effect of predicted elevated levels of carbon dioxide (CO₂) on an invasive weed Mikania micrantha, we constructed a suppressive subtractive hybridization (SSH) library from the leaves of M. micrantha exposed to CO₂ at 350 and 750 ppm for 6 d, and isolated a novel gene named β-caryophyllene synthase. β-Caryophyllene synthase catalyses the conversion of farnesyl diphosphate to β-caryophyllene, a volatile sesquiterpene with allelopathic potential. Real-time PCR analysis revealed that gene expression of β-caryophyllene synthase in M. micrantha leaves was strongly induced in response to elevated CO₂. Gas chromatography-mass spectrometry (GC-MS) and gas chromatography (GC) analyses showed that emission levels of β-caryophyllene from leaves of M. micrantha increased when exposed to 750 ppm CO₂. Bioassays showed that phytotoxicity of β-caryophyllene against Raphanus sativus, Brassica campestris, Lactuca sativa, and M. micrantha was dose-dependent and varied with the receptor plants and concentrations of CO₂. β-Caryophyllene displayed higher phytotoxic effects at 750 ppm than those at 350 ppm CO₂, especially on R. sativus. These results suggest that elevated atmospheric CO₂ levels may enhance biosynthesis and phytotoxicity of allelochemicals in M. micrantha, one of the worst invasive weeds in the world, which in turn might enhance its potential allelopathic effect on neighboring native plants if released in bioactive concentrations. Further investigations are required to determine the adaptive responses of both invasive and native plants to a gradual increase of atmospheric CO₂ to 750 ppm predicted over a 100 year period.

Chemical composition and pharmacological properties of the essential oils obtained seasonally fromLippia thymoides

“…Considering that the sesquiterpene b-caryophyllene is the majority in all essential oils, studies have indicated that interrelationship of the plant with various organisms in their environment induce the synthesis this compound, since b-caryophyllene can attract natural enemies of herbivores, as entomopathogenic nematodes below ground and parasitic wasps (Köllner et al, 2008). Furthermore, gene expression of b-caryophyllene synthase, that catalyses the conversion of farnesyl diphosphate to b-caryophyllene, is induced in response to elevated CO 2 and may enhance biosynthesis and phytotoxicity of allelochemicals, as b-caryophyllene (Elakovich & Stevens, 1985;Wang et al, 2010). Pascual et al (2001) extensively revised the chemistry of Lippia and found that the components with the highest frequency in the essential oils of this genus are limonene, b-caryophyllene, p-cymene, camphor, linalool, a-pinene, and thymol.…”

Elevated temperature may accelerate invasive expansion of the liana plant Ipomoea cairica

“…Allelopathy has been regarded as a mechanism for successful exotic plant invasion (Callaway & Aschehoug, 2000; Chen et al. , 2009; Wang et al. , 2010).…”

“…Both biotic factors (insects, herbivores, pathogens) and abiotic factors (temperature, moisture, light and nutrients status) can affect the synthesis of allelochemicals (Lobón et al. , 2002; Wang et al. , 2010), the allelopathic potential of the donor plant, as well as the sensitivity of the receptor (Lobón et al.…”

“…Allelochemicals play an important role in mediating plant-plant interactions (Rice, 1984). Allelopathy has been regarded as a mechanism for successful exotic plant invasion (Callaway & Aschehoug, 2000;Chen et al, 2009;Wang et al, 2010). Ma et al (2009) isolated two allelochemicals: 3-3¢-5-trihydroxy-4¢-7-dimethoxyflavone-3-O-sulphate and 3-3¢-5-trihydroxy-4¢-7-dimethoxyflavone from I. cairica, which were shown to inhibit seed germination of Raphanus sativus L., Cucumis sativus L., Brassica pekinensis L. and Ligularia virgaurea L. Ipomoea cairicaÕs rampant growth, wide eco-physiological tolerance, strong reproduction and allelopathic inhibitory effect on neighbouring plants (Wu et al, 2006;Zhao & Peng, 2008;Ma et al, 2009) have now caused substantial damage to natural ecosystems and biodiversity in Guangdong province of China (Zhao & Peng, 2008).…”

Infraspecific variations in essential oil and glandular trichomes in Nepeta heliotropifolia

“…Moreover, thymol, carvacrol and carvone showed high inhibition even at low concentrations against weed seeds such as Amaranthus retroflexus, Centaurea solstitialis, Raphanus raphanistrum, Rumex nepalensis, Sinapis arvensis and Sonchus oleraceus (Azirak and Karaman 2008). Wang et al (2010) found that β-caryophyllene inhibited the germination of seed, growth of the root as well as shoot in various taxa such as Raphanus sativus, Mikania micrantha, Brassica campestris, Lactuca sativa. Moreover, δ-cadinene had phytotoxic activity on Isolepis nodosa (Ens et al 2009).…”