Nature of the sporoderm in monocotyledons, with special reference to the pollen grains of canna and heliconia

Abstract

Cytochemical techniques, TEM and SEM were used to resolve the basic structure and nature of the pollen grain wall of Canna, Heliconia, Crocus, Gladiolus and Zea. The results of tests using 2-ethanolamine, alcoholic fuchsin and auramine O suggest that the acetolysis-resistant exine of these genera, and probably most monocotyledons, is ektexinous; the endexine, when present, is restricted to the apertural region. Stratified nexines, which characterize many dicotyledonous pollens, are the result of temporal separation of the ontogenetic development of the respective layers. The acid-degradable intine can be resolved into two basic layers: an outer presumably pectic polysaccharide (alcian blue positive) component, and an inner primarily cellulosic (PAS and calcofluor white positive) layer adjacent to the protoplast. The two intine components are here called the “exintine” and “endintine,” respectively. We suggest that the outer channeled intine layer of the inaperturate grains of Canna, Heliconia and Crocus is equivalent to the Zwischenkörper of aperturate pollen grains. Both the exintine and the endintine may be characterized by the presence of vesicles or tubules in the region of pollen tube emergence.