The outerwallof pollen and spores,namely the exine,is composed of sporopollenin,which is highly resistantto chemicalreagents and enzymes.In this study,we demonstrated that phenylpropanoid pathway derivatives are essentialcomponents of sporopollenin in seed plants.Spectral analyses showed that the autofluorescence of Lilium and Arabidopsis sporopollenin is similar to that of lignin.Thioacidolysis and NMR analyses of pollen from Lilium and Cryptomeria further revealed that the sporopollenin of seed plants contains phenylpropanoid derivatives,including p-hydroxybenzoate(p-BA),p-coumarate(p-CA),ferulate(FA),and lignin guaiacyl(G)units.The phenylpropanoid pathway is expressed in the tapetum in Arabidopsis,consistent with the fact that the sporopollenin precursor originates from the tapetum.Further germination and comet assays showed that this pathway plays an important role in protection of pollen against UV radiation.In the pteridophyte plant species Ophioglossum vulgatum and Lycopodium clavata,phenylpropanoid derivatives including p-BA and p-CA were also detected,but G units were not.Taken together,our results indicate that phenylpropa-noid derivatives are essential for sporopollenin synthesis in vascular plants.In addition,sporopollenin auto-fluorescence spectra of bryophytes,such as Physcomitrella and Haplocladium,exhibit distinct characteristics compared with those of vascular plants,indicating the diversity of sporopollenin among land plants.