Studies on Sporopollenin Biosynthesis in Cucurbita maxima I: The Substantial Labeling of Sporopollenin from Cucurbita maxima after Application of [14C]Phenylalanine

Cucurbitaceae, Cucurbita maxima, Tracer Experiments, Potash Fusion, Sporopollenin The results of tracer experiments performed with anthers of Tulipa cv. Apeldoorn have already shown that a high level of incorporation into the sporopollenin fraction was achieved, when [14C]phenylalanine was applicated as a precursor. In order to investigate whether the substantial incorporation of [14C]phenylalanine is a unique phenomenon restricted to Tulipa, tracer experiments were carried out on anthers of Cucurbita maxima. The sporopollenin fraction was isolated and purified by a gentle method including extrac­ tions with various solvents, incubations with hydrolysing enzymes and fractionated saponifications. The remaining, as well as the released radioactivity, was determined after each purifi­ cation step. After the application of [U-14C]phenylalanine, a substantial incorporation into the sporopollenin fraction was determined. The values were clearly higher than those obtained with [ ll4C]glucose or those from corresponding experiments on Tulipa anthers. After potash fusion of sporopollenin fractions labeled via [U-14C]phenylalanine, /»-hydroxybenzoic acid was shown to be the main component among the ether soluble acids; moreover it showed the highest level of radioactivity. No radioactivity was detected in the degradation products oxalic acid, benzoic acid, phthalic acid and terephthalic acid or octanedioic acidand decanedioic acid-dimethylester.