Ultrastructure and development of sporoderm in Aristolochia clematitis (Aristolochiaceae)

Abstract

The purpose of this study was to investigate the sporoderm development of inaperturate pollen grains in Aristolochia clematitis (Aristolochiaceae). During successive microsporogenesis several types of tetrads are formed; no tetrahedral tetrads were observed. In the tetrad period, the primexine is observed around the perimeter of microspores. In the free microspore period, a thick lamellar endexine develops around the perimeter of the microspore; the thick tubular intine appears later in this period. At the maturation of pollen grains, the intine is stratified into two layers: an outer tubular ectintine and an inner homogeneous endintine. Finally, the intine forms an aperture thickening. The thickened intine deforms and displaces the endexine and tears the ectexine apart. This shows that pollen grains of A. clematitis are aperturate. The apertures are colpi.