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

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 extractions with various solvents, incubations with hydrolysing enzymes and fractionated saponifications. The remaining, as well as the released radioactivity, was determined after each purification 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 [1-¹⁴C]glucose or those from corresponding experiments on Tulipa anthers. After potash fusion of sporopollenin fractions labeled via [U-¹⁴C]phenylalanine, p-hydroxybenzoic acid was shown to be the main com ponent 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 acid- and decanedioic acid-dimethylester.