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Multivariate analysis of MALDI imaging mass spectrometry data of mixtures of single pollen grains
(2018)
Mixtures of pollen grains of three different species (Corylus avellana, Alnus cordata, and Pinus sylvestris) were investigated by matrixassisted laser desorption/ionization time-of-flight imaging mass spectrometry (MALDI-TOF imaging MS). The amount of pollen grains was reduced stepwise from > 10 to single pollen grains. For sample pretreatment, we modified a previously applied approach, where any additional extraction steps were omitted.
Our results show that characteristic pollen MALDI mass spectra can be obtained from a single pollen grain, which is the prerequisite for a reliable pollen classification in practical applications. MALDI imaging of laterally resolved pollen grains provides additional information by reducing the complexity of the MS spectra of mixtures, where frequently peak discrimination is observed. Combined with multivariate statistical analyses, such as principal component analysis (PCA), our approach offers the chance for a fast and reliable identification of individual pollen grains by mass spectrometry.
The process of silicification in plants and the biochemical
effects of silica in plant tissues are largely unknown. To
study the molecular changes occurring in growing cells
that are exposed to higher than normal concentration of
silicic acid, Raman spectra of germinating pollen grains of
three species (Pinus nigra, Picea omorika, and Camellia
japonica) were analyzed in a multivariate classification
approach that takes into account the variation of biochemical
composition due to species, plant tissue structure,
and germination condition. The results of principal
component analyses of the Raman spectra indicate differences
in the utilization of stored lipids, a changed mobilization
of storage carbohydrates in the pollen grain bodies,
and altered composition and/or structure of cellulose of
the developing pollen tube cell walls. These biochemical
changes vary in the different species.
Matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) is a well-implemented analytical technique for the investigation of complex biological samples. In MS, the sample preparation strategy is decisive for the success of the measurements. Here, sample preparation processes and target materials for the investigation of different pollen grains are compared. A reduced and optimized sample preparation process prior to MALDI-TOF measurement is presented using conductive carbon tape as target. The application of conductive tape yields in enhanced absolute signal intensities and mass spectral pattern information, which leads to a clear separation in subsequent pattern analysis. The results will be used to improve the taxonomic differentiation and identification, and might be useful for the development of a simple routine method to identify pollen based on mass spectrometry.