Dandelion Species Research Articles

Laticifer tissue-specific activation of the Hevea SRPP promoter in Taraxacum brevicorniculatum and its regulation by light, tapping and cold stress

Hevea brasiliensis is an important plant species currently cultivated for the commercial production of natural rubber. As the demand for rubber continues to increase, it is important to identify alternative sources of natural rubber and to increase plant rubber content using molecular approaches. Taraxacum kok-saghyz, a Russian dandelion, produces natural rubber that is of high quality. In this study, the SMALL RUBBER PARTICLE PROTEIN (SRPP) promoter from H. brasiliensis was characterized to determine its suitability for the expression of latex-specific genes in Taraxacum brevicorniculatum which is another Russian dandelion species of T. kok-saghyz from the similar geographical areas. Studies using transgenic Taraxacum plants carrying the SRPP promoter::β-glucuronidase (GUS) sequence indicate that the SRPP promoter does induce gene expression primarily in laticiferous tissues. Additionally, the promoter was regulated by various external conditions including light, tapping, and cold. These findings suggest that the SRPP promoter will be a useful molecular tool for the manipulation of gene expression in the laticiferous tissues of Taraxacum plant species.

Proteomic analysis of latex from the rubber‐producing plant Taraxacum brevicorniculatum

Many plants produce latex, a specialized, metabolically active cytoplasm. This is generally regarded as a defensive trait but latex may also possess additional functions. We investigated the role of latex in the dandelion species Taraxacum brevicorniculatum that contains considerable amounts of high-quality natural rubber by carrying out a comprehensive analysis of the latex proteome. We developed reliable protocols for the preparation of protein samples for one-dimensional gel electrophoresis, two-dimensional gel electrophoresis, and subsequent mass spectrometry analysis, which led to 278 unique identifications. A gene ontology classification system based on comparisons with known Arabidopsis thaliana root proteins showed that dandelion proteins involved in lipid metabolism and transport were enriched in the latex proteome, whereas those involved in stress responses were not. We also found that proteins involved in rubber biosynthesis were distributed among different fractions of the latex proteome.

Characterization of dandelion species using 1H NMR- and GC-MS-based metabolite profiling

Taraxacum, known as dandelion, is a large genus of plants in the family Asteraceae. Pharmacological studies have shown that these plants display a wide variety of medicinal properties because Taraxacum extracts contain many pharmacologically active metabolites that display anti-inflammatory, antinociceptive, antioxidant, and anticancer activity. Each plant species displays several different natural constituents, the majority of which have not been studied as no global metabolite screen of the diverse Taraxacum species has been performed. In this study, we investigated the metabolite difference in three species of Taraxacum (T. coreanum, T. officinale, and T. platycarpum) by (1)H NMR spectroscopy and gas chromatography-mass spectrometry (GC-MS) coupled with multivariate statistical analyses. The aim of this study was to identify the different chemical compositions of the polar and nonpolar extracts in these species. A partial least-squares discriminant analysis showed a significantly higher separation among nonpolar extracts (mainly fatty acids and sterols) compared to polar extracts (mainly amino acids, organic acids, and sugars) between these species. A one-way ANOVA was performed to statistically certify the metabolite differences of these nonpolar extracts. Taken together, these data suggest that a metabolomic approach using combined (1)H NMR and GC-MS analysis is an effective analytical method to differentiate biochemical compositions among different species in plants.

Polyphenoloxidase silencing affects latex coagulation in Taraxacum species.

Latex is the milky sap that is found in many different plants. It is produced by specialized cells known as laticifers and can comprise a mixture of proteins, carbohydrates, oils, secondary metabolites, and rubber that may help to prevent herbivory and protect wound sites against infection. The wound-induced browning of latex suggests that it contains one or more phenol-oxidizing enzymes. Here, we present a comprehensive analysis of the major latex proteins from two dandelion species, Taraxacum officinale and Taraxacum kok-saghyz, and enzymatic studies showing that polyphenoloxidase (PPO) is responsible for latex browning. Electrophoretic analysis and amino-terminal sequencing of the most abundant proteins in the aqueous latex fraction revealed the presence of three PPO-related proteins generated by the proteolytic cleavage of a single precursor (pre-PPO). The laticifer-specific pre-PPO protein contains a transit peptide that can target reporter proteins into chloroplasts when constitutively expressed in dandelion protoplasts, perhaps indicating the presence of structures similar to plastids in laticifers, which lack genuine chloroplasts. Silencing the PPO gene by constitutive RNA interference in transgenic plants reduced PPO activity compared with wild-type controls, allowing T. kok-saghyz RNA interference lines to expel four to five times more latex than controls. Latex fluidity analysis in silenced plants showed a strong correlation between residual PPO activity and the coagulation rate, indicating that laticifer-specific PPO plays a major role in latex coagulation and wound sealing in dandelions. In contrast, very little PPO activity is found in the latex of the rubber tree Hevea brasiliensis, suggesting functional divergence of latex proteins during plant evolution.

Population Dynamics of Broadleaf Weeds in Turfgrass as Influenced by Chemical and Biological Control Methods

A 3-yr field study was conducted to determine the effect of a biological control agent,Sclerotinia minorJagger, and a common herbicide, Killex, on the population dynamics of dandelion and other broadleaf species and on the dandelion seed bank. Treatments were applied as one spring, one early autumn, or a spring plus an early autumn treatment per year. The response of the dandelion population to a spring herbicide treatment was similar to two applications per year (spring and early autumn). Significantly less dandelion control occurred after the first early autumn application of the herbicide. Two weeks after application, spring or early autumn treatments withS. minorwere equally effective in suppressing dandelions. In the second year of the two applications per year ofS. minortreatment, weed control was equivalent to the herbicide. By the third year of the one spring application ofS. minor, weed control was equivalent to the herbicide. Generally over the study period, the early autumn application ofS. minorwas less effective than the spring or the spring and early autumn applications. TheS. minortreatments significantly reduced the dandelion seed bank, and this effect was not significantly different from the Killex herbicide treatment. The rate, frequency, and seasonal timing of application had no effect on the dandelion seed-bank size, but terminating the application would gradually replenish the seed bank. Populations of white clover, broadleaf plantain, birdsfoot trefoil, and common ragweed were similarly suppressed by either theS. minoror the herbicide treatments. Yellow woodsorrel significantly increased after 1 yr of herbicide treatment compared with theS. minorand untreated control treatments, indicating a possible weed species shift. Turf quality was improved because of the herbicide andS. minortreatments, but grass injury and smooth crabgrass invasion were recorded in 17% of herbicide-treated plots.

(221) Phenotypic Plasticity as an Indicator for Exotic Noxious Plants

Exotic noxious plants, including invasive plants and exotic weeds, have caused huge economic loss and ecological damage around the world. To prevent further introductions of such species as crops or ornamental plants, biological and ecological traits associated with invasiveness and weediness need to be identified so that prediction can be made on the potential of being noxious for proposed species. It was suggested that weeds were usually generalists that can survive and reproduce in a wide range of environments; i.e., they were quite “plastic” in response to different environments. In accordance to this idea, phenotypic plasticity has been recently proposed as an indicator and predictor for weeds and invasive plants. This hypothesis is tested using two exotic dandelion species: Taraxacum officinale (common dandelion), widespread weed, and T. laevigatum (red-seeded dandelion), which occurs in a much lower frequency in Ohio. A greenhouse experiment was conducted in which the two species were grown in two soil moisture levels (dry vs. wet) combined with two light exposure levels (full sun vs. shade). Various traits were measured to see whether T. officinale is more plastic than T. laevigatum in these four environments. The results show that, when using coefficient of variance (CV) as a measurement of plasticity, T. officinale has significantly larger CV than T. laevigatum in plant diameter (P = 0.02), shoot: root ratio (P = 0.04) and soil pH (P = 0.02). This indicates that T. officinale is more plastic in some of the resource-capture-related traits such as leaf morphology and biomass allocation, and presumably also in root exudates, which alter the soil pH.

A comparison of phenotypic plasticity in the native dandelionTaraxacum ceratophorumand its invasive congenerT. officinale

We compared plastic responses to variation in the light environment for sympatric populations of native and exotic dandelion species, Taraxacum ceratophorum and Taraxacum officinale. Plasticity in leaf size, inflorescence height, reproductive phenology and dispersal-related traits were measured under experimentally altered light quality (red : far-red light ratio, R : FR) and light intensity (photosynthetically active radiation, PAR). To test whether differences in means and reaction norms of dispersal-related traits between species affected colonization potential, we created seed-dispersal models based on seed-fall rate and release height. Differences in plasticity between species were not systematic, but varied in direction and magnitude among traits. Taraxacum officinale produced larger leaves that exhibited greater plasticity in size under variable light intensity than T. ceratophorum. Plasticity in scape length at flowering occurred in relation to R : FR ratio in both species, but tended to be greater in T. ceratophorum. Seed-bearing scapes of T. officinale were taller and more canalized in height across light regimes than scapes of T. ceratophorum. Seeds of T. officinale were smaller than seeds of T. ceratophorum. Models predict greater dispersal in T. officinale within open and vegetated habitats. In contrast to the idea that plasticity promotes invasiveness, results suggest that the lack of plasticity in dispersal-related traits enhances the colonization potential of T. officinale.