Ontogeny of the exine in pollen of Aristea (Iridaceae)

Abstract

The ontogeny of the pollen wall was studied in four species of Aristea , from the vacuolated stage of the microspores, to observe the possible formation of an endexine. At this stage, the ectexine is completely formed (tectum, columellae, and structurally homogeneous foot layer), but its maturation is incomplete and variable depending on the species. In all cases, there are one or several tripartite lamellae with a white line under the foot layer, in the apertural and extra-apertural regions. In A. major , and A. pauciflora , the exintine is not yet present, whereas in A. macrocarpa and A. glauca , it has started to initiate. In mature pollen of the four species, the tripartite endexine lamellae of the vacuolated stage disappear and there is no trace of endexine. The tripartite intine is completely formed. Maturation of exine is complete and it appears homogeneous and of medium electron density, except in A. glauca , which has particularly fragile exine, where it remains incomplete with a granular and highly electron dense appearance, which contrasts with the usually mature exine. Despite the very clear presence of endexine lamellae at the vacuolated stage, it is thus very difficult to conclude that endexine exists in pollen of the genus Aristea .