Synthesis of phenylpropanes during pollen development

Abstract

The synthesis and accumulation of several phenylpropanes in the anther content (pollen+tapetum fraction) during microsporogenesis has been investigated by chromatographic techniques in Narcissus pseudonarcissus, Lilium candidum, and in the Darwin tulip “Apeldoorn”. In these species, the pigmentation process is initiated by the synthesis of several cinnamic acid derivates (mainly derivates of ferulic acid) during meiosis II. In Narcissus, and intense synthesis of kaempferol glycosides takes place during the separation of the tetrad which follows immediately upon its formation. In Tulipa and Lilium, however, chalcones are synthesized in an intermediate phase before flavonols and anthocyanins (in Tulipa) are produced in significant amounts. In Tulipa, the investigations revealed the following sequence in the pigmentation process: cinnamic acid derivatives-chalcone-flavonols-anthocyanins. The sequence is discussed in relation to flavonoid biosynthesis. Because of biogenetic considerations a special emphasis is laid on the “chalcone stage”. Chromatographic and spectroscopic data show that the isomerization product of the chalcone is eriodictyol. Accordingly, this chalcone must be 2′,3,4,4′,6′-pentahydroxychalcone. Other chalcones could not be identified. During anthesis the following aglycones are accumulated in the pollen of Tulipa cv. “Apeldoorn”: ferulic acid, p-coumaric acid, kaempferol, quercetin, isorhamnetin, delphinidin, and small traces of the pentahydroxy-chalcone, which is the main pigment in the intermediate stages of microsporogenesis. On the basis of histochemical findings, it is suggested that at least the final steps of synthesis leading to flavonol and anthocyanidin glycosides take place on the pollen wall in the loculus of the anthers, that is, in the extracellular space.