Pollen sporopollenin: degradation and structural elucidation

We report the isolation of purified sporopollenin from pollen grains of dif ferent species and its complete solubilization. Exine from Pinus pinaster, Betula alba, Ambrosia elatior and Capsicum annuum was extracted by treatmen t with hydrogen fluoride in pyridine. These exines were purified from their aromatic moieties and from fatty acids linked by ester bonds using acidoly sis and saponification treatments. The biopolymer obtained retains almost c ompletely the shape of the original pollen grain. Fourier-transform infrare d spectroscopy analysis of the isolated sporopollenin showed the absence of polysaccharide and phenolic material and the presence of carboxylic acid g roups joined to unsaturations and ether linkages. Sporopollenin samples wer e successfully degraded by exhaustive 24-h ozonolysis at room temperature. Gentle ozonolysis (3 h at 0 degrees C) did not completely degrade the biopo lymer. The compounds obtained after exhaustive ozonolysis were analysed by gas chromatography-mass spectrometry. Dicarboxylic acids with a low number of carbon atoms were identified as major components of sporopollenin from P . pinaster, A. elatior and C. annuum, representing 28.8%, 63.2% and 88.5%, respectively, of the total compounds obtained. Fatty acids and n-alkanes al so were identified in P. pinaster, A. elatior and B. alba sporopollenin. Fr om the data obtained, an hypothesis about the chemical nature and structura l arrangement of the sporopollenin is proposed.