INVOLVEMENT OF PHENYLALANINE AMMONIA-LYASE IN THE DEVELOPMENT OF POLLEN IN BROCCOLI (BRASSICA-OLERACEA L)

To determine whether phenylalanine ammonia-lyase (EC 4.3.1.5) is invol ved in the maturation of microspores to fertile pollen, anthers of a f ertile strain of broccoli (Brassica oleracea L.) were studied in a com parison with anthers of a cytoplasmic male sterile strain. In the norm al fertile strain, immature anthers of about 2 mm in length exhibited higher phenylalanine ammonia-lyase activity than mature anthers or tho se shorter than 2 mm. The 2-mm-long anthers corresponded to the mononu cleate stage, just after release of the microspores during pollen deve lopment. Immunohistochemical localization of phenylalanine ammonia-lya se in the anthers indicated that the protein was present predominantly in the tapetal cells. The immature anthers of cytoplasmic male steril e broccoli had a lower phenylalanine ammonia-lyase activity than those of the normal fertile strain. The level of phenylalanine ammonia-lyas e activity in the immature anthers was positively correlated with the number of fertile pollen grains at the flowering stage in both strains . It seems possible, therefore, that phenylpropanoid metabolism, which involves phenylalanine ammonia-lyase, may play an important role in t he maturation of microspores in flowering plants.