Ultrastructural observations on the foliar secretory cavities of Porophyllum lanceolatum DC. (Asteraceae)

The ultrastructure of foliar secretory cavities of Porophyllum lanceolatum DC. was studied at three developmental phases, and shows to have the basic characteristics of terpene-secreting glands. The ability to secrete is alre ady present in young, differentiating cavities. In the epithelial cells, da rk osmiophilic material occurs in plastids, mitochondria, the nuclear envel ope, the endoplasmic reticulum (ER) and dictyosomes, indicating the partici pation, in some way, of such structures in the secretory process. The ER is seen to be associated with plastids (periplastidal ER), mitochondria and t he nuclear envelope, seeming to play a role in transporting the secretory m aterial from these organelles to the plasmalemma. The granulocrine mechanis m, involving portions of ER, and independently, vesicles derived from dicty osomes, is considered to be the main process for the elimination of secreto ry material from the protoplast. Multivesicular, multilamellar and mixed bo dies were also observed, as well as microbodies (associated with ER in some cases), in the epithelial cells. In the cells of the gland sheath the wall s are thicker than those of the epithelial cells; starch is often present i n their plastids.