| Abstract: | Investigations were carried out to clarify sporopollenin biosynthesis. Tracer experiments were focussed on the incorporation of specifically labeled 14C-phenylalanine into sporopollenin. In addition, the incorporation of further 14C-labeled substances, such as glucose, acetate, malonic acid, mevalonate and tyrosine, was investigated. The sporopollenin fraction was isolated and purified by a gentle method including extractions by different solvents, incubations with hydrolyzing enzymes and fractionated saponifications. During the purification procedure the whereabouts of the initially applied radioactivity was followed. After each step the remaining as well as the released radioactivity was determined. Saponification of samples labeled after application of phenylalanine yielded p-coumaric acid and p-coumaric acid methyl ester as labeled products. In comparison with the other substances applied, the highest incorporation rates were obtained with phenylalanine, regardless of the position of labeling. After degradation of the sporopollenin sample labeled with ring-14C-phenylalanine, p-hydroxybenzoic acid was detected as the main labeled product. These results unequivocally show that an integral incorporation of the aromatic ring system occurred. Tracer experiments were carried out at different stages of development. Their results show that, although the incorporation rates of 14C-phenylalanine into sporopollenin differ, the substantial incorporation of this substance is not bound to defined stages of development. |
