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Raman signatures of the carotenoid component are studied in individual pollen grains from different species of trees. The information is obtained as differences in the strong pre-resonant Raman spectra measured before and after photodepletion of the carotenoid molecules. The results provide the first in situ evidence of interspecies differences in pollen carotenoid content, structure, and/or assembly between plant species without prior purification. The analysis of carotenoids in situ is confirmed by high-performance thin-layer chromatography (HPTLC)-supported resonance Raman data measured directly on the HPTLC plates after separation of carotenoids in pollen extracts. Utilization of the in situ, extraction-free procedure in carotenoid analysis will improve sensitivity and structural selectivity and provides insight into carotenoid structure and composition in single pollen grains.
We report on the in situ characterization of tree pollen molecular composition based on Raman spectroscopy. Different from purification-based analysis, the nondestructive approach allows (i) to analyze various classes of molecules simultaneously at microscopic resolution and (ii) to acquire fingerprint-like chemical information that was used for the classification of pollen from different species. Hierarchical cluster analysis of spectra from fresh pollen samples of 15 species partly related at the genus level and family level indicates separation of species based on the complete Raman spectral signature and yields classification in accord with biological systematics. The results have implications for the further elucidation of pollen biochemistry and also for the development of chemistry-based online pollen identification methods.
The processes associated with pollen germination were studied in vitro for two tree species, Salix caprea and Fraxinus excelsior under different nutrient conditions. The results provide evidence of changes in chemical composition of the pollen grains during germination. From the comparison of spectra of the pollen grain body and the growing pollen tube, it can be concluded that there are major chemical differences between these two morphological units. Comparison of germinated and ungerminated pollen grains reveals alterations in the metabolism. Composition of the germinating pollen grain and its morphological units depends on the plant species, but also on the nutrient conditions. The results suggest species-specific utilization of metabolite storage, and potential alterations of the pollen outer coat. Furthermore, discharge of molecules into the nutrient medium may depend on the nutrient conditions in the germination experiments. This has implications for further experiments on dynamic processes in pollen and related plant materials.
Silver nanoparticles were generated based on citrate reduction in the ultrastructure of the sporopollenin biopolymer of Ambrosia artemisiifolia (ragweed) and Secale cereale (rye). The nanoparticles enable the acquisition of SERS spectra and thereby a vibrational characterization of the local molecular structure of sporopollenin.