Pyrrolizidine alkaloid variation in Jacobaea plants : from plant organ to cell level

The aim of this thesis is to understand the diversity of pyrrolizidine alkaloids (PAs) in Jacobaea plants with respect to their spatial distribution and its consequences for generalist insects. Chapter 2 reports on the role of endophytes in the production of PAs in Jacobaea. Plants were treated with different systemic fungicides to eliminate endophytic fungi and the effect on PA concentration and composition was determined. Chapter 3, 4 and 5 deal with the variation of PA distribution at organ, tissue and cell levels. Chapter 3 describes the capacity of different plant organs to produce PAs, using different types of in-vitro organ cultures including roots, shoots and complete plants. Chapter 4 reports on the metabolomics of different leaf tissues, focusing on differences of PA distribution between epidermis and mesophyll. Chapter 5 deals with a metabolomic study on the different cell types of Jacobaea leaves resi stant to thrips. Laser micro dissection coupled with NMR was used in this study. Chapter 6 describes structure activity relationships for the effect of different PAs on S. exigua larvae and cell cultures. The results on the variation of PA distribution in Jacobaea plants and their consequence to generalist insects are summarised and discussed in Chapter 7UBL - phd migration 201

Toxicity of Pyrrolizidine Alkaloids to Spodoptera exigua Using Insect Cell Lines and Injection Bioassays

Pyrrolizidine alkaloids (PAs) are feeding deterrents and toxic compounds to generalist herbivores. Among the PAs of Jacobaea vulgaris Gaertn, jacobine and erucifoline are the most effective against insect herbivores as indicated by correlative studies. Because little is known about the effect of jacobine and erucifoline as individual PAs, we isolated these compounds from their respective Jacobaea chemotypes. These PAs and other commercially available senecionine-like PAs, including senecionine, seneciphylline, retrorsine, and senkirkine, were tested as free base and N-oxide forms at a range of 0–70 ppm. Feeding bioassays using live insects are closer to the natural pattern but require relatively large amounts of test compounds. We, therefore, compared the toxicity of PAs using both Spodoptera exigua cell line and larval injection bioassays. Both bioassays led to similar results in the order of PA toxicity, indicating that the cell lines are a valuable tool for a first toxicity screen. Testing individual PAs, jacobine and erucifoline were the most toxic PAs, suggesting their major role in plant defense against generalist herbivores. Senkirkine and seneciphylline were less toxic than jacobine and erucifoline but more toxic than retrorsine. Senecionine was not toxic at the tested concentrations. For all toxic PAs, the free base form was more toxic than the N-oxide form. Our results demonstrate that structural variation of PAs influences their effectiveness in plant defense

NMR metabolite profiling analysis of pigmented rice resistance to rice ear bug

Rice ear bugs or Leptocorisa oratorius F. are major rice pests reported to reduce the rice yields severely. The present study aimed to screen local pigmented cultivars for resistance to rice ear bugs and perform metabolomics analysis to identify the metabolites responsible for the resistance character. For screening, eight cultivars including both black and red varieties were used. Rice ear bugs used for bioassay were collected from the field. The assay results showed that two cultivars of black rice and one cultivar of red rice exhibited high resistance characters as per the Standard Evaluation System guidelines for rice. Metabolite profiling of rice seeds was performed at the milky stage using 500 Mhz NMR JEOL, followed by multivariate analysis with SIMCA ver 14. Metabolite profiling identified nine out of 15 metabolites, which were significantly different between the most resistant and susceptible cultivars. In the red rice, hydroxy-L-proline, threonine and formic acid and for black rice, valine, glutamate, α-glucose, β-glucose, galactinol and raffinose were identified as potential metabolites conferring the resistance character. This study identified the most resistant cultivars which can be used in the future to support the development of a novel line of cultivar resistant to rice ear bug. © 2021 World Research Association. All rights reserved