Abstract
BackgroundMatrix-assisted laser-desorption and ionisation time-of-flight mass spectroscopy (MALDI-TOF MS) is a powerful tool for the characterisation and/or identification of protein-containing samples. Several MALDI-TOF MS sample-preparation methods are currently available but few of these are well suited to the analysis of plant material. We have recently developed a simple, rapid, and relatively-cheap method for MALDI-TOF MS that is applicable to plant material (in addition to microbial and insect material), and our aim in this study was to distinguish between closely-related plant species and/or between regional biotypes within an invasive weed species using this method with a view to optimising the selection of biological control agents that can be used for weed management.ResultsWe have employed a combination of principal-component analysis and closest-relatedness diagrams derived from MALDI-TOF MS spectral-comparison data to discriminate between the closely-related Impatiens spp. Impatiens noli-tangere, Impatiens parviflora, Impatiens scabrida, Impatiens balsamina, and two regional biotypes of the invasive weed Impatiens glandulifera. We have also developed a method for sample discrimination based upon comparison between blind-test MALDI-TOF MS spectra and reference-sample spectra. Using this latter method, we have been able to discriminate on the basis of the acid-soluble-protein mass spectra generated between four regional biotypes of I. glandulifera that differ in their susceptibility to the biological control agent Himalayan balsam rust (Puccinia komarovii var. glanduliferae) using mature leaf material. Using younger leaves, discrimination was not possible between these four regional biotypes.ConclusionsMALDI-TOF MS analysis is able to discriminate between closely-related plant species within the genus Impatiens and between regional biotypes of I. glandulifera. Because of this, MALDI-TOF MS holds great promise for improving weed biological control, a management technique which uses highly-specific co-evolved natural enemies for the control of an invasive non-native plant species, through the optimal matching of biological control agents with susceptible target species/regional biotypes.
Highlights
Matrix-assisted laser-desorption and ionisation time-of-flight mass spectroscopy (MALDI-TOF MS) is a powerful tool for the characterisation and/or identification of protein-containing samples
Samples For discrimination between closely-related Impatiens spp. and regional biotypes of I. glandulifera using grouping based on principal-component analysis (PCA) and closest-relatedness diagrams (Experiment 1), samples were collected from glasshouse-grown: I. glandulifera originating from Harmondsworth Moor and Silwood Park, UK; I. noli-tangere; I. parviflora; I. scabrida; and I. balsamina
Whilst a number of excellent sample-preparation methods are currently available and detailed in the above references, as mentioned earlier, these methods are not convenient for the analysis of plant material and so, in order to overcome this, we developed a highly-simplified and inexpensive method for MALDI-TOF MS sample preparation that is applicable to plant material in which cells are lysed by maceration in aqueous acetonitrile containing trifluoroacetic acid (TFA), which selectively extracts acid-soluble proteins
Summary
Matrix-assisted laser-desorption and ionisation time-of-flight mass spectroscopy (MALDI-TOF MS) is a powerful tool for the characterisation and/or identification of protein-containing samples. Matrix-assisted laser-desorption and ionisation timeof-flight mass spectroscopy (MALDI-TOF MS) employs MALDI soft ionisation of biological samples [1] In this process, large proteins can be prepared intact in the gas phase with predominantly a single positive charge [2]. A key driver has been human clinical microbiology; a field that has been transformed by MALDI-TOF MSbased diagnostics, for bacterial and yeast infections [8] This area is extensively and comprehensively reviewed by Clark et al [5], along with the current art regarding methods for sample preparation that are commonly used within clinical settings for microbial diagnostics. Lagging behind slightly has been the development of methods for MALDI-TOF MS-based identification and/ or characterisation of filamentous fungi [4], though this area is catching up steadily, largely due to the development of robust methods commonly referred to as ‘fullextraction’ protocols after the seminal work of Cassagne et al [3]
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