Invasive plants (species, toxicity, enemies)
Plant species may become particularly competitive and invasive in new environments, thus threatening local biodiversity (Garcia-Serrano et al. 2009). However, the invasion success of invasive plants is determined by their ability to deal with new environmental restrictions (Garcia-Serrano et al. 2009). ). Researchers believe that due to climate change and land use management some previously marginal plant species have became invasive and noxious, such as Jacobaea vulgaris, Senecio inaequidens.

Jacobaea vulgaris is a monocarpic biennial with long flowering period from June until November (Van der Meijden and Van der Waals-Kooi. 1979) native to the Netherlands and invasive elsewhere. (Van der Meiden 2005).
Senecio inaequidens is widespread throughout north and west of Europe and during the last 20 years is expanding towards the south and east of continental Europe continent (Garsia-Serrano et al. 2008).
It is an exotic perennial species (Bossdorf et al. 2008) native from South-Africa (van der Meiden 2005). Senecio erucifolious is a rare native from the Netherlands morphologically similar to Jacobaea vulgaris (Van der Meiden. 2005) and it is the control plant in this research.
They are not categorized in weed families which grow in agriculture fields that compete against crops, however, they grow in grasslands where herbivores graze, they are a treat to herbivore due to their toxic contents. Eating Senecio inaequidens may lead to chronic diseases and death of livestock, however, hepatotoxic and carcinogenic characteristics to human world-wide have been reported (Hartmann and Zimmer 1986) due to consumption of the contaminated herbivores’ meat by toxic weeds.
Because of those monitoring invasive plants frequently has been requested from many stakeholders.
The role of PA
Pyrrolizidine alkaloids (PA) are secondary metabolites which can only be found in the angiosperms. Angiosperms are plants whose seeds are contained in an ovary or fruit. PA is frequently found in some genera of genus Senecioneae, Eupatorieae, Asteraceae, many genera of the Boraginaceae and many more families (Pelser et al, 2005). About 100 different kinds of PAs are found in different plants of Senecionea or Asteraceae family (Hartmann and Witte 1995; Macel et al. 2004; Pelser et al. 2005) that have hepatotoxic characteristics (Macel et al. 2004). A plant is classified hepatotoxic when it is able to damage the liver of mammals.
Pyrrolizidine alkaloids are species-specific (Hartmann and Dierich 1998; Macel et al. 2004). which vary in type but all of them share some specific characteristics 

• i) double bond between C-atom 1 and C-atom 2
• ii) esterified allylic hydroxyl group at C-9 and
• iii) second esterified alcoholic hydroxyl at C-7.

Senecio Jacobaea can contain more than 10 senecionine related alkaloids; the two main chemotypes in Jacobaea vulgaris are the jacobine and the erucifoline (Macel et al 2004). While the main two PA type present in Senecio inaequidens are retrorsine and senecionine (Dimande et al. 2007).
Senecionin N-oxide has been identified as the primary product of biosynthesis (Toppel et al. 1987; Pelser et al. 2005) and can be considered as the back bone structure of most PAs. It is synthesized in the roots and transported to the shoots via the phloem-path where it is transformed in to the species specific PA profile (Pelser et al 2005).
Phloem is the living tissue that carries organic nutrients. Phloem is mainly concerned with the transport of soluble organic material made during photosynthesis.
Depending on the plant organ the concentration of the PAs varies and generally the flower heads have the highest amount of the PAs (Hartmann and Dierich 1998). A variation in pyrrolizidine alkaloids concentration seems to exist in these plants, not only between organs but also between plants, the total pyrrolizidine alkaloid concentrations found in some studies varied between 0.1 and 6 mg. g-1. dry weight (Hol et al. 2003; Macel et al. 2004).
These alkaloid concentration variations are believed to be influenced by nutrient availability and above- and belowground damaged tissue as found by Hol et al. (2003) in shoots of Jacobaea vulgaris. Nutrients have been found to indirectly affect the concentration of alkaloids. The results found, show that Jacobaea vulgaris grows bigger with higher nutrient conditions while maintains the productions of the alkaloids, which resulted in a dilution effect, i.e. in larger plants with the same alkaloid productions capacity results in a generalized lower concentration (Hol et al 2003).
Author: F. Eghbali Moghaddam