Molecular Plant Biophysics and Biochemistry

Lily Pollen Metabolome (Obermeyer et al. (2013) Plant Physiol, 162: 1822-1833)
Investigation of the metabolome and the transcriptome of pollen of Lilium longiflorum Thunb. gave a comprehensive overview of metabolic pathways active during pollen germination and tube growth. More than 100 different metabolites were determined simultaneously by gas chromatography coupled to mass spectrometry and expressed genes of selected metabolic pathways were identified by next generation sequencing of lily pollen transcripts. The time-dependent changes in metabolite abundances as well as the changes after inhibition of the mitochondrial electron transport chain (mitETC) revealed a fast and dynamic adaption of the metabolic pathways in the range of minutes. The metabolic state prior to pollen germination differed clearly from the metabolic state during pollen tube growth as indicated by principal component analysis of all detected metabolites and by detailed observation of individual metabolites. For instance, the amount of sucrose increased during the first 60 min of pollen culture but decreased during tube growth while glucose and fructose showed the opposite behavior. Glycolysis, tricarbonic acid (TCA) cycle, glyoxylate cycle, starch and fatty acid degradation were activated providing energy during pollen germination and tube growth. Inhibition of the mitETC by antimycin A resulted in an immediate production of ethanol and a fast re-arrangement of metabolic pathways which correlated with changes in the amounts of the majority of identified metabolites, e.g. a rapid increase in -aminobutyric acid (GABA) indicated the activation of a GABA shunt in the TCA cycle while ethanol fermentation compensated the reduced ATP production after inhibition of the oxidative phosphorylation.

All identified metabolites (blue) and enzymes (red) were marked in the general KEGG pathway scheme.